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92 UNIMOLECULAR FILM BALANCE RESEARCHES ON MQNQLAYERS PART 4.-A STUDY OF DYEING PROCESSES BY THE USE OP THE UNIMOLECULAR FILM BALANCE BY Mrss MARGARET M. ALLINGHAM, C. H. GILES AND E. L. NEUST~DTER Dept. of Technical Chemistry, Royal Technical College, Glasgow, C. 1 Received 29th June, 1953 Possible modes of dye-fibre combination have been studied by determination of the effect of dyes, or model compounds representing dyes or fibres, as solutes in the aqueous layer below monolayers of a variety of surface-active compounds, the interpretation of the interactions being based on measurements of molecular areas and compressibilities. Cetyl acetate, representing cellulose acetate, and dimethylterephthalate, representing Terylcne and used in a mixed monolayer, both gave evidence of the formation of inter- molecular CH .. . N and CH . . . 0 bonds and it is suggested that this type of bond may be responsible for the attachment of dyes to these fibres. The known facts con- cerning the sorption of dyes by cellulose from aqueous solutions are more consistent with a mechanism of van der Waals’ attraction between fibre and dye than with one involving hydrogen bonds. It is postulated that the carbohydrate molecules are too firmly attached to water for hydrogen bonds with dyes in aqueous solution to be formed. Surface-active planar and non-planar benzidinc disazo-dyes representative of a direct cotton dye and a non-substantive isomer have been used in experiments to determine whether van der Waals’ attraction alone operates between such dyes and solutcs repre- senting cellulose.It is found that the planar dye does associate with cellobiose molecules which, as anticipated, remain surrounded by a layer of water, and so are prcvcnted from forming hydrogen bonds with the dye. Regarding the dyeing of proteins and Nylon, some evidence of intermolecular hydrogen-bonding involving aniide groups is obtained, but it is pointed out that this does not always agree with data obtained from sorption experiments on the fibres them- selves, perhaps because the fibre molecules are not always able to form intermolecular bonds with solutes, owing to competing intramolecular forces. The extensivc studies which have been devoted to the chemistry of dycing and relatcd processes in the last two decades have produced clear evidence of the oper- ation of elcctrovalent bonds as one of the important forms of linkage binding dyes to two types of fibre, viz., proteins and Nylon.16 With this exception, however, the nature of the attractions providing the driving force of the dyeing mechanism in fibres has not been clearly elucidated, though the operation ofMARGARET M.ALLINGHAM, c . H. GILES AND E. L. NEUSTADTER 93 hydrogen bonding and van der Waals’ forces have been suggested and to some extent demonstrated as actually involved in some types of dyeing. It has therefore seemed desirable to bring to bear on this problem an in- vestigation of the mutual hydrogen-bonding reactivities of organic radicals typical of the principal groups occurring in fibres and dyes. Dyeing operations are virtually always carried out in an aqueous medium and it was thought particularly important therefore to study the appropriate reactivities in presence of water.The method used in this research is that employed in the preliminary experiments already described : 4 the examination of the intcraction of pairs of hydrogen-bonding compounds as monolayer and solute, respectively, by means of thc Langmuir-Adam unimolecular film balance. So far the work has been confincd simply to measurements of film area and compressibility, but nevertheless, the results seem to havc valid use in interpretation of some dyeing phenomena, as we hope to show in this paper. A parallel investigation has bccn procccding 1 s 5 into the possibility of detecting the molar ratio of hydrogen-bondcd complexes of solutes in binary solution in a variety of solvents, including water.Some of thc prcdictions made as a result of this investigation have been tested in the present work. In thc previous experiments,4 surface-active compounds containing, e.g., amide, azo-, hydroxy- or quinonc groups, were spread on aqueous solutions of solutes containing hydrogen-bonding groups, principally phenols, and the changes in film arca and compressibility noted. Monofunctional solutcs, e.g., monohydric phenols, appear usually to cause increased solvation of groups with which they can rcact in the monolayer ; this alters the tilt of unsymmetrical molecules, and usually increases the film area and compressibility. Bifunctional solutes, e.g., dihydric phenols, react in a more distinctive manner.If the two hydroxy-groups are suficicntly separated in the solute molecule, they appear to act as a cross-link betwcen two molecules of the surface film, and this leads to a considerable increase in both area and compressibility of the film. In the special cases where the film molecule happens to contain two proton-acceptor groups separated by a distance approximatcly equal to that between the two hydroxy-groups of the solute, the two molecules appear to join in parallel as a 1 : 1-complex, e.g., quinol as solute combines thus with a benzoquinone surface-active derivative. The effect on the film in these cases is to increase the area slightly while the compressibility is hardly affectcd. Solutes without groups capable of hydrogen-bonding with the mono- layer molecules appeared to have no significant effect on the film.There were some indications also that when more than two functional groups are present in a solutc molecule, those most widely separated determine the degrce of film expans ion. Thc pronounced effect of the cross-linking agents affords a ready means of examining the hydrogcn-bonding reactivity of groups in an aqueous medium. The gcneral procedure is as follows : suppose it is desired to determine if hydrogen- bonding is possible bctween two groups, A and B. Thc group A is introduced into the molecule of the surface-active compound, and a solute molecule is chosen having a pair of groups, B, B, placed some distance apart. If hydrogen-bonding takes place between monolayer and solute molecules we may envisage a film structure built up as shown in fig.1, where A, A, are the heads of the monolayer molecules and B-B those of the bifunctional solute. If A is small and comparable in dimensions with the width of the molecules BB when tightly packed, then the whole structure should be quite compact and the increase in film arca by introduction of the solute should be predictable from a knowledge94 UNIMOLECULAR FILM BALANCE of the dimensions of the molecule BIB. Further, if more than onc solute compound containing pairs of groups BB, at different separation distances in the molecule, can be used, then the film area should increase with this separation, and the observation of such an effect would be a confirmation both of the bonding pro- perties of the groups A and B, and of the validity of this hypothesis of cross- bonding in the film.This procedure, as well as thc use of monofunctional solutes, has bcen followed here. The following representative compounds have been employed :- Model compounds representing fibres cellulose : cellulose acetate : cetyl acetate. Nylon and protcins : Terylenc : dimcthylterephthalate. cellobiose, glucosc, mannitol, sucrosc. glycine, N-methyl stearamide, octadecyl acetamidc. Dyes and rcppr-eseiitative coinpounds Crystal Violet (Colour Indcx No. 681) L-/ f Acid Magenta (Colour Indcx No. 692) CH3 SO3- Orange I (Colour Index No. 150) 3 : 3’-diethylthiacyanine iodide 3 : 3’-diethylthiacarbocyaninc iodidc NMARGARET M . ALLINGHAM, c. H . GILLS AND E . L . NEUSTADTER 95 3 : 3’-diethylthiatricarbocyanine iodide S ~s>-CH=CH-CH=CH-CH=CH-C€€==C \” ”ii N + \ / -I C2K5 Alizarinc Cyaninc WRS (Colour Index No.1063) (1 : 2 : 4 : 5 : 6 : 8-hcxahydroxy- anthraquinone sodium 3 : 7-disulphonate). 1 : 4-Diaminoanthraquinone-2-sulphonic acid (sodium salt), 1 : 5-dihydroxynaphthalene. disazo dyes from 2 : 2’- and 3 : 3’-dimethylbenzidine, coupled respectivcly with p-octa- decylphenol, p-dodecy laniline --> j?-naphthol, 2-p’-dodccylphenyl-p-bcnzoquinone, p-hexa- decyloxyanilinc - > o-cresol, y-~nethoxystearylphenonc, phenol, quinol, stearylethyl ketone. EXPERIMENTAL APPARATUS AND MATERIALS, etc.-The film balance and general technique used have already been described.3 The reagents were all purified by recrystallization, or were of analytical reagent quality.Alizarine Cyanine WRS (Bayer) was a commercial sample (purity, 62 %, the remainder probably being sodium chloride). Catalin (Stuart-type) atom models were used for determination of molecular dimensions. Microanalyses were by Dr. A. C. Symc, Royal Technical College, Glasgow. Light absorption curves wcrc determined on a Unicam SP 500 photoelectric spectrophotometer. CEI’YL AcETATE.-Dry hydrogen chloride gas was bubbled through a mixture of cetyl alcohol (0.3 mole) and glacial acetic acid (0.6 mole) for 1 h ; the mixture was then warmed several hours on the water bath. The acetate was isolated by vacuum distillation ; imp. 22” c. disAZO-COMPOUNDS.-~ecrysta~~izcd samples of 0- and rn-tolidine sulphates were tetrazotiscd and coupled with p-octadecylphenol (prcpared as previously described 3), dissolved in aqueous alcoholic sodium hydroxide.The precipitated disazo-compounds were filtered off, washed, dried and (Soxhlet) extracted with toluene. The solutions were orangc-brown and showed absorption peaks at 3100 A (3 : 3’-isomer) (sharp) and 3500 A (2 : 2’-isomer). Thc solid substances, which did not crystallize, werc orange-brown and were obtained by evaporation of the solution. M.p., 3 : 3’-isomer, 93” C ; 2 : 2‘- isomer, 95” C (found : 16, 6.2, 6.4 %, respcctively ; C22H9402N4 requires N, 6.05 %). ~-oCTADECYLACETAMrDE.-Stearoy~ chloride (0.1 6 mole) was added carefully to excess of an ice-cold solution of ammonia (sp. gr. 0-SSO), the precipitated amide filtered off, washed, dried, and treated with thionyl chloride (0.3 mole) to yieId p-stearonitrile.This was reduced by refluxing several hours with excess sodium in cthanol. On addition of hydrochloric acid and cooling, the amine hydrochloride crystallized out. This was distilled over quicklime, the distillate warmed a few minutes with acetic anhydride, and the product crystallized from glacial acetic acid with the aid of charcoal ; m.p. 79” C. The preparation of the other surface-active compounds has already been dcscribed.3~ DISCUSSION ‘Tables 1 and 2 summarize the expcrimcntal rcsults, and comments Icgarding their relationship to dyeing phenomena now follow. (A few results of thc pre- liminary work4 have been includcd where necessary for comparison, and these arc suitably distinguished in the tables.) The tangent of the angle made by the uppcr part of the force-area curve with the y-axis is a convenient measure of film compressibility, and has been quoted here in this sense. The interpretation of the results should give decisive information about solute groups which cannot form specific chemical bonds with fibre substrates. Informa- tion regarding groups which might form such bonds is less decisive, because of the uncertain factor introduced by the presence of inter- and intra-chain bonds in thc substrate itself.Unless the affinity of the solute is suficient to enable it to replace such bonds, it may not be able to co-ordinate with the substrate.TABLE 1 ,-MOLECULAR AREAS AND COMPRESSIBILITES OF MONOLAYERS Molecular area (812) at zero compression and compressibility t of surface-active substances substrate I water 11* Acid Magenta 111" D-cellobiose IV* Crystal Violet V* 1 : 4-diaminoanthraquinone sodium VI$ 3 : 3'-diethylthiacyanine iodide 2-sulphonate VIl$ 3 : 3'-diethylthiacarbocyanine iodide VIII$ 3 : 3'-diethylthiatricarbocyanine iodide IX* 1 : 5-dihydroxynaphthalene X** dimethylterephthalate (1 : 2-ratio) XI* cc-D-glucose XII* glycine XIII* 1 : 2 : 4 : 5 : 6 : 8-hexahydroxyanthra- quinone sodium 3 : 7-disulphonate XIV* mannitol XV* phenol XVI* sucrose XVlI* sulphanilic acid 3 a-naphthol XVIII* quinol Data in brackets are from previous paper.4 a b c 24, 0.04 125, 0-25 255, 0.27 84, 1-15 250, 0.65 305, 0.51 41, 0.84 35, 0.32 65, 0.42 89, 0.29 127, 0.70 48, 0-60 75, 1-66 210, 0.60 28, 0.05 135 (?) 230 (?) 59, 1.73 d e f (43, 0.16) (26, 0.02) (37, 0.07) 30, 0.17 (54, 0.31) 100, 0-84 59, 0-40 54, 0.34 45, 0.40 49, 0.32 (102, 0.42) 8 h i j 36, 0.11 (21, 0.03) 22, 0.09 (48, 0.09) 34, 0.11 85, 0.32 (44, 0.36) 90, 0.58 48, 0.16 (23, 0.05) 50, 0.53 28, 0.11 22, 0.09 50, 0.09 40, 0.10 50, 0.06 72, 0.65 (29, 0.08) 42, 0.19 (55, 0.05) j- expressed as the tangent of the angle to the vertical of the upper portion of the lI-A curve (scales as in fig.2). * 0.1 M aqueous solution. u = cetyl acetate ; $ 0.00025 M aqueous solution. ** used in binary solution with surface-active compound. b, c = 3 : 3'- and 2 : 2'-dimethylbenzidine + (p-octadecylphenol)z, respectively ; d = p-dodecylaniline -+ /3-naphthol ; e = 2-p'- dodecylphenyl-p-benzo-quinone ; f = p-hexadecyloxyaniline --f o-cresol ; g = p-methoxystearylphenone ; h = N-methylstearamide ; i = N-octadecy- acetamide ; j = 1-stearamidoanthraquinone.MARGARET M.ALLINGHAM, c . H . GILES AND E. L. NEUSTADTER 97 Robinson and Ambrose,13 e.g., have drawn attention to evidence that polypeptide molecules in water have all their hydrogen bonds satisfied by inter- or intra-chain linkages and none is left to co-ordinate with the water. CELLULOSE ACETATE.-Marsden and Urquhart 8 as the result of a thorough investigation of the sorption of phenol and related compounds by cellulose acetate, concluded that sorption occurs by reason of the formation of a hydrogen bond between the phenolic hydroxy-group and carbonyl oxygen in the acetyl group, CH3 I giving O H ------ O=C I , and this suggestion has been extended by Vicker- c I staff 16 to cover the dyeing of cellulose acetate fibre with the commonly employed " disperse " dyes. These are anthraquinone or azo-derivatives devoid of powerful water-solubilizing groups, and are necessarily applied as dispersions in water.They are probably enabled to penetrate the fibre by virtue of their extremely slight water-solubility.17 Most of these dyes contain potential proton-donating groups, usually -OH and -NH2, which might well combine in the manner suggested for phenol. TABLE 2.-AREAS (A2) AT COMMENCEMENT OF DEVELOPMENT OF MEASURABLE SURFACE PRESSURE AND AT LOWEST POINT OF UPPER n-A CURVE monoIayer a b C d e f 6 h i i substrate I 25, 20 250, 90 320, 220 (32, 25) (38, 35) 44, 34 (23,21) 40,21 (54,48) I1 90, 80 111 350,190 380,250 35, 30 39,33 85, 85 IV 72, 31 VI 70, 61 VII 95, 85 VIII 134,120 IX X XI 64,56 90, 90 V 38, 33 48,45 XI1 56,39 53,47 XI11 75,75 XIV 350, 150 XV XVI 48,26 380 330 36,29 25, 18 57,48 XVII 70,51 41,40 52,49 XVIII 95,65 45,41 56, 53 59,46 There are, however, two facts which tend to throw doubt upon the exact characterization of the hydrogen-bonding mechanism in this substrate.These are : (i) certain dyes which have affinity for cellulose acetate, e.g., nitroazobenzene derivatives (for formulae, see mighty), have no hydrogen atom in their molecule available for bonding ; (ii) the carbonyl group in ketones is protected against intermolecular hydrogen- bonding in water by the solvent and this type of protection appears also to occur with the carbonyl oxygen in the acetyl group, though this evidence is not conclusive.1 It is now found 1 that proton-acceptors, e.g.azobenzene or benzoquinone, can form complexes with aliphatic acetates, presumably through a hydrogen atom of the methyl residue in the acetyl group, which is activated by the adjacent carbonyl oxygen atom. In the present work we have sought to confirm tbis by using a film-forming acetyl compound, cetyl acetate, and studying the influence of proton-accepting D98 UNIMOLECULAR FILM BALANCE solutes, particularly those with two functional groups, beneath it. The particular solute compounds chosen included a series of three cyanine dycs with increasing lengths of nicthin chain. It seems justifiable to assume that the two nitrogen atoms, because of rcsonancc, may bc considered equally able to form a hydrogen bond with a proton-donator group in the monolayer and these substances will therefore be bifunctional. For comparison, a few other solute compounds, of symmetrical and unsymmetrical types, but containing proton-donating groups were examined also (fig. 2).TabIe 3 shows the apparent molecular areas, predicted and observed, of cetyl acetate on the various substrates ; considering the difficulty of determining the exact orientation of the molccules in the film the agreement is thought to be reasonably good. (With the particular atom models used, the thiazole ring in Molecular area (A2). FIG. 2.-Force-area curves for cetyl acetates in various substrates- V : Cyanine dye (VIII). Left to right I : water. I1 : sucrose. I11 : Cyanine dye (VI).IV : Cyanine dyc (VII). VI-VIII is difficult to construct and data for these three compounds are con- sidered less reliable. The increasing departure of the area increases of these compounds from the predicted values may be an indication of the enhanced water-attraction of the longer conjugate chains.) In calculating the dimensions of each AB-BA complex (cp. fig. 1) it has been assumed that the following criteria must be satisfied. Each of these has been formulated from a consideration of the known properties of the groups concerned, especially as revealed in their behaviour in monolayers or in hydrogen bonding experiments (cf. 1 9 3 9 49 5). (i) Each sulphonic acid group is surrounded by a layer of water approximately one molecule deep. (ii) Each carbonyl group in the acetate radical is associated with one water molecule. (iii) The unsynlmetrical sulphonates (XVII and V) when associated with the film molecules, stand with their sulphonic acid groups deep in the water and their main molecular axis oriented at ca.30" to the vertical (cf. 3), since the molecules then appear to be better balanced relative to the water phase.MARGARET M. ALLINGHAM, c. H. GILES AND E. L . NEUSTADTER 99 (iv) Where the solute molecules contain bulky substituent groups, e.g., SO3-, or are non-planar and their close mutual association is thus hindered, it is assumed that the two associated cetyl acetate molecules are accommodated in the inter- molecular space at the side of the solute molecules. With compounds XIII, 11, XVII, V and 1V this does not require the solute molecules to be disturbed from a close-packed position; with VZ, VII and VlII they must be forced apart somewhat to offer the requircd accommodation.(v) The mutual association between thc molecules of IX, which are simple and planar, is assumed to be sufficient to prevent interpenetration by molecules of cetyl acetate ; these must, therefore, be accommodated at the ends of the solute molecules. TABLE 3.-EFI-’ECT OF SOLUTES ON FILMS OF CETYL ACETATE ditnensions of AB-BA complex in surface planc (est.) (A) film area (A21 pcr mol. cctyl acetate no. VI VII VIII XI11 I1 IX XVII V IV solute (water) 3 : 3’-diethylthiacyanine iodide 3 : 3’diethylthiacarbocyanine 3 : 3’-diethylthiatricarbocyanine Alizarine Cyanine WRS Acid Magenta 1 : 5-dihydroxynaphthalene Orange I 1 : 41diaminoanthraquinone- Crystal Violet iodide iodide sodium 2-sulphonate lcngth 5 CaPPr.) 14.0 16.5 21.5 17.0 15.0 18-0 10.0 8.5 16.0 breadth 5 (appr.) 9.5 9.5 9.5 10.0 11-5 5.0 10.0 10.0 5.0 predicted found - 24 66 65 78 89 105 127 85 75 86 84 45 48 50 59 43 35 40 41 (vi) Each solute molecule is specifically attached to two cetyl acetate molecules, thus the apparent cross-sectional area of the complex AB-BA in the plane of the water surface, estimated according to the above criteria, must be halved to determine the predicted area per molecule of cetyl acetate.The results are considered good evidence that the acetate group in cetyl acetate, and therefore also in cellulose acetate, can form intermolecular hydrogen bonds with dyes and the behaviour of compounds VI-VIII suggests that the acetate group can act as the hydrogen donor.Whether it behaves thus with all types of dye is not certain, but seems likely.1 The commercial product is partially hydrolyzcd (approximately to thc diacetate) and the hydroxy-groups may also operate, but the triacetate can be coloured with the same type of dyes as the diacetate, so these groups cannot be very important in determining dyeing effects. TERYLENE.-Dimethyl terephthalate, rcpresenting this fibre, was incorporated in the solution used for spreading the film, on account of its low water-solubility. The surface-active compound used, p-dodecylaniline --t p-naphthol, has no free hydrogen, owing to the internal chelate ring it contains, and the undoubted evidence of cross-bonding obtained (tables 1 and 4) must therefore represent bonding between an azo-nitrogen atom and a hydrogen of the methyl ester group.In binary solutions also, both this ester and ethylene glycol dibenzoate, which more nearly resembles the Terylene polymer, appear to form bonds by a similar mechanism.1 At the 2: 1 azo compound/ester ratio the film niust be rather compact and as more cster molccules are added they at first cause a slight expansion and then appcar to be forced into the water below. * Note added in prooJ-The data are not inconsistent with a parallel association of azo compound and ester [see comment (by C. H. G.) on paper by Schuler and Remington], but the hydrogen bonding mcchaiiism is considered more liltely.100 UNIMOLECULAR FILM BALANCE TABLE 4.-DATA FOR MIXED FILMS OF DIMETHYL TEREPHTHALATE AND 0-HYDROXYAZO COMPOUND ratio, ester/azo-componnd ii iii 0.25: 1 58 70 0.5: 1 100 0.84 125 1 : 1 I35 0.58 145 2: 1 132 1-43 145 i apparent mol.area at zero pressure (Az), ii tangent to vertical (cf. table 1). iii commencement of curve (A2) (cf. table 2). iv commencement of upper portion (A2) (cf. table 2). iv 80 125 115 In connection with both cellulose acetate and Terylene we have therefore some evidence in favour of -C-H . . . 0- or -C-H . . . N- bonds being operative in dye sorption. This type of hydrogen bond has not been suggested before in connection with dyeing phenomena, but though not common, several examples of it are known amongst organic compounds (cf. ref. (1 l), (18)).CELLuLosE.-It is well established that for dyes to manifest substantivity for ccllulose they must have a long planar molecule, which can approach close alongside and lie parallel to the cellulose chain.69 10916 It has previously bcen assumed that the binding force holding the dye to the fibre lies in hydrogen bonds formed between hydroxy- (or ether) groups of cellulose and suitable groups in the dye. There are, however, a number of objections to this belief, especially the following : (i) it is not clear why the shape and planarity of the dye molecule so critically determine substantivity, since potential hydrogen-bonding groups are so abundant along the cellulose chain; (ii) Marsden and Urquhart 8 obtained evidence of considerable sorption of phenol from water by cellulose acetate, almost certainly due to hydrogen bonding, yet they were unable to detect any sorption wf this compound by cellulose under similar conditions; (iii) there is no correlation between the number of hydrogen-bonding groups in dye mole- cules, even if they are planar, and their substantivity for cellulose.* HYDROGEN-BONDING OF CARBOHYDRATES It has now been found 1 that the hydroxy- and ether groups in the ring forms of soluble carbohydrates, e.g.glucose or cellobiose, are unable to form inter- molecular bonds with other solutes in water, because of protection by the solvent, and a similar effect may account for the non-absorption of phenol by cellulose. The conclusion may thus be drawn that dyes do not readily form hydrogen bonds with the fibre in water, and that van der Waals’ forces alone are operative in determining their substantivity.This conclusion conforms with the known facts of substantivity on this fibre and explains why the planarity and shape of the dye molecule is such a critical factor, since the van der Waals’ forces attenuate far more rapidly with distance than electrostatic forces and, to be sufficiently effective, they will therefore require the closest possible approach of the dye molecule to the fibre. It should be explained here that the aldehyde group, unlike the ether and hydroxy-groups, is not prevented from forming intermolecular bonds by water, and the aldehyde group in the open-chain tautomer of glucose and cellobiose does in fact seem to co-ordinate with other solutes in water.1 This disturbs the equilibrium between the pyranose ring carbohydrate molecules and their open-chain forms in favour of the latter, and a noticeable bonding affinity of the aldehyde group of these compounds for, e.g., amines, results.There is, however, no evidence that under normal circumstances in water any form of * cf., e.g., (a) Benzo Violet A (C.I. no. 388) and (6) Orange I. These can form 2 and 3 intermolecular hydrogen bonds, respectively, yet (a) dyes cellulose and (b) does not. The molecule of (a) is, however, about twice as long as that of (b).MARGARET M . ALLINGHAM, C. H . GlLES AND E. L . NEUSTADTER 101 bond other than this one is operative. In cellulose, of course, the proportion of aldehyde end-groups is too small to be of significance in dyeing operations.The keto group, unlike the aldehyde group, is rendered inoperative towards other solutes by water so that the ketose sugars are unable to form any sort of intermolecular bonds in aqueous solution, and no complexes are observed between, e.g., fructose or sucrose and amines in water.1 The hydroxy-groups in open-chain alcohols, e.g., mannitol, are rather more reactive in water than those in carbohydrate rings, towards other solutes. With these facts in mind, we may consider the significance of the present monolayer experiments using carbohydrate solutes. In the first instance, if any of the soluble carbohydrates discussed did actually, through their hydroxy-groups, form bonds with film molecules, we should expect them to act as cross-linking agents, considerably expanding the film.Moreover, the longer molecules, cello- biose and sucrose, should have about twice the ef&t of the shorter glucose molecule, because our experience with these films leads us to believc that polyfunctional solutes act as cross-linking agents by means of the most widely separated active groups in their molecules. Secondly, if the hydroxy-groups are quite inoperative, then sucrose should have no effect on the films, while glucose or cellobiose should behave very similarly to each other, acting as monofunctional solutes. They should thus cause increased water attraction of the monolayer, by co-ordination therewith, and, in fact, should have a somewhat similar effect to phenol in this respect. The results shown are consistent with the second set of conditions and incon- sistent with the first.Sucrose has no effect, or at most, a slight expansive action, far less than cross-linking would produce ; in one case (c) it decreases the area slightly. Probably the expansion represents a very weak affinity of keto-groups for monolayer molecules. On the other hand, glucose and cellobiose behave very similarly to each other and have considerably more expansive action. MODEL SURFACE-ACTIVE COTTON DYES In order to obtain further evidence having a possible bearing on this problem, experiments were next made with surface-active compounds structurally similar to the benzidine series of direct cotton dyes. It has been suggested 10 that planar dyes of this series are highly substantive to cellulose because the repeat interval (10.8 A) of potential bonding groups, e.g., -N2-, in their molecules corresponds with that (10.3 A) of the cellobiose unit of cellulose, and thus the best conditions are satisfied for groups taking part in mutual hydrogen bonding, to make close contact.3 : 3’-Disubstituted benzidine derivatives give planar, substantive dyes ; 2 : 2’-derivatives give non-planar, non-substantive dyes. Disazo-compounds were thereforc prepared by coupling tetrazotized u- and rn-tolidine, respectively, with p-octadecylphenol, to give the two disazo-compounds shown in fig. 3. c18H37 s - - - brN===yfc>-<>-.-<~ - - - s CH3 ‘**.. / HO I planar I1 non-planar FIG. 3 .102 UNIMOLECULAR FILM BALANCE Both compounds were found to form stabIc films, of large apparent moIecular area, and high compressibility, as might be expected (fig.4). A consideration of the symmetry of these molecules suggests that they must rest on the water very much as pictured in fig. 3, the water surface SS being normal to the plane of the paper. If the repeat distance at right-angles to the longest molecular axis is 6 & as it is for the monoazo surface-active compounds,3 where a water molecule appears to be interposed between each pair of azo-groups, then the cross-scctional area of the planar (3 : 3’-) molecule in the film should be about 140A? The actual value found is 125 A2, so that the basis of prediction of the mode of orientation RG. +Force-area curves for surface-active disazo-compounds on various substrates, (i) compound b (planar) on water alone.(ii) compound b on cellobiose solution. (iii) compound c (non-planar) on water alonc. (iv) compound c on cellobiose solution. and packing appears fairly well founded. It is more difficult to predict the cor- responding value for the non-planar isomer, because its irregular shape must allow some interlocking to occur, but it will certainly be larger than that of the planar compound. Actually it is found to be 255 A2. EFFECT OF SOLUTES ON PLANAR ISOMERS The effcct of some carbohydrate and polyhydric alcohol molecules, as solutes in the water, upon the monolayers of these two compounds was next examined. Mannitol was chosen as a suitable polyhydric straight-chain alcohol. As already stated, the hydroxy-groups in this type of compound appcar to be able to form intcrmolecular bonds in water more readily than do those of the carbohydrates and, indeed, apparcnt cross-linking effects observed with the Cz-compound, ethylcne glycol, have already been reported.5 If mannitol acts by cross-linking, considerable expansion of the film should occur.The mannitol molecule will be expected to assume a compact, crumpled form between the azo molccules. The most compact arrangement gives a separation of ca. 6-5w between outermost hydroxy-groups. If this form wcre interposed between the azo-groups in each pair of the planar disazo-molecules the repeat distance wouid be cu. 9A, and the apparent molccular area of the disazo conipound ca. 215A2. ActualIy, a value of 210 A2 is found. This seems to substantiate the view that cross-linking occurs.Thc results to be expected to follow from the use of carbohydrates as solutes will depend upon the extent to which their hydroxy-groups (and potential aldchyde groups) are capable of intcrmolecular bonding, and several possible modes of intcraction may occur. Consider, e.g., the planar isomer spread on a solutionMARGARET M. ALLINGI-IAM, c. H . GILES AND E . L. NEUSTADTEK 103 of cellobiose. This might form a complcx in which the carbohydrate functions as a straight-chain aldehyde, as in binary aqueous solutions. An aldehyde group would in this case combine with cach azo-group and the rest of the carbohydrate molecule would probably remain dissolved in the underlying water. A study of table 1 will show that cellobiose (or glucose) acting probably in this way, in- creases the film area by from 35 to 100 %, the increase rising with differcnt types of molecule in the order of decreasing closeness of packing on water (i.c.benzo- quinone compound, anthraquinone compound, azo-compound 4s 3). In the present case, therefore, we should anticipate an increase of ca. 35-40 %, i.e. an apparent molecular area of ca. 170 &. In view, however, of the undoubted fact that in cellulose the hexose rings of the carbohydrate chain have strong enough attraction for long planar benzidine disazo-dye molecules to hold them closely in parallel, we may suppose this type of union to occur in the film. If so, the hexose ring-forms of the carbohydrate will be favoured in the equilibrium between these forms and the open-chain aldehyde, as is normally the case in watcr.We should then expect to have a 1 : 1- complex between disazo-molecule and cellobiose, which may involve either of two modes of packing, depending on the nature of the attractive force between thc molecules. On the one hand, if hydrogen bond attraction holds the two molecules together they must be in close contact. This requires a repeat distance between azo-compound molecules corresponding to an apparent molecular area of ca. 170A2. (If we suppose that the hydroxy-groups on the side not attached to the azo-compound remain bonded each to a water molecule, this value rises to ca. 185 A2.) On the other hand, if the carbohydrate molecules firmly retain a completely protecting “ atmospherc ” of water molecules, which is suggested 1 as the cause of their inability to form intermolecular bonds in water, and if this covering is one molecule thick on both sides of the hexose rings, then the repeat area should be ca.270 A2. Actually it is found to be 250 A2. This value, there- fore, seems to favour the hypothesis that no bonds are formed between azo-groups and carbohydrate hydroxy-groups. EFFECT OF SOLUTES ON NON-PLANAR ISOMERS The non-planar isomer cannot form a close-packed arrangement with cellobiose molecules. If cross-linking through hydroxy-groups were, however, to take place, a large area increase would occur. The precise magnitude of this increase is difficult to predict from models, but it appears that a change of 150-300% in the apparent area per disazo-molecule is likely.If, however, such bonds do not occur, and the solute behaves monofunctionally through the aldehyde group, we may predict an area increase (see above) of ca. lO%, or perhaps a lower value, because of the greater possibility of adjustment of the non-planar film molecules by interlocking. The actual increase observed is about 20 %. CONCLUSIONS The general conclusions, which are admittedly speculative and based on only the limited amount of indirect evidence which it has been possible to obtain in the time available, are that the results are consistent with the view that dycs are held to cellulose fibres by van der Waals’ attraction rather than by hydrogen bonds. Glucose and cellobiose in water appear to act normally as monofunctional aldehydes towards monolayer molecules.In the special case, however, when the monolayer molecules are long and planar, the increased van dcr Waals’ attraction for the solute favours a 1 : 1-longitudinally arranged complcx, in which the mode of union resembles that of dyes with cellulose. ETHYL cELLuLosE.--It was hoped to obtain more information upon the re- actions of cellulose by a study of a film-forming derivative, ethyl cellulose, a commercial material, containing some residual hydroxy-groups. A suitable104 UNIMOLECULAR FILM BALANCE material of this type was spread and found to give an apparent molecular area of about 40A2 per hexose unit. Expansion of the film does occur with some hydrogen-bonding substances, but a full interpretation of the results has not yet been made. The material appears to resemble cellulose acetate in dyeing properties.This suggests it has available hydrogen-bonding groups. These might be either the ether groups, which other work1 has shown can act as proton-donors under some circumstances, or the residual hydroxy-groups, which may have different properties in this environment than they do in cellulose itself. Further work is in progress on this subject. PROTEIN FIBRES.-The maximum sorption of a variety of inorganic and organic acid anions on wool is closely equivalent to the content of free amino-groups in the fibre and there seem good grounds for the belief that combination of anions with charged amino-groups by electrovalencies is responsible for the sorption.14 As the size and complexity of the anions increascs, the titration curve of wool with organic acids moves towards the alkaline side, i.e., the maximum sorption is reached at lower acidities.There is no close relationship between affinity and dissociation constant of the acid,14 and this increase in affinity must be attributed either to an increasing tendency for the large anions to form hydrogen bonds with -CONH-, -NH2 or -COOH, etc., groups in the fibre, or to in- creased van der Waals’ attraction, or to both causes 9 s 14s 15. This uncertainty has not yct, as far as we are aware, been resolved, though the very high sorption by wool of unionized organic acids of small molecular size 15 would seem to be attributable to hydrogen-bonding. Thc groups named above can undoubtedly form intermolecular bonds with other groups typical of dye molecules, and even with dyes themselves.This is demonstrated by the present * and previous experiments 4 and by examination of binary solutions.1. 5 Yet there appears to be no very clear correlation between the information so obtained and the evidence of sorption experiments of simple organic compounds on wool.2 We must therefore recall Robinson and Ambrose’s comment 13 quoted above, and entertain some doubt as to whether many solutes can enter into hydrogen-bonding attachment with protein fibres unless they have high affinity and are able to break down bonds already present. Phenol is able to do this, and the results of actual sorption tests with this compound are in better agreement with experiments on model compounds in binary solution or mono- layers.2 NYLoN.-The comments upon protein fibres apply also to Nylon.Anions of acids and dyes appear to combine with charged amino-groups in the fibre, which are far fewer in number than those in wool, and at low pH values the greatly increased uptake of dye anions is attributed to attraction by the amide groups, which have then become positively charged.12 This type of elcctrovalent link has not been so clearly demonstrated in wool. In attempting to study hydrogen- bonding with Nylon, there is again found to be difficulty in correlating the present and related experiments with actual sorption tests? This investigation is being continued and further results of our work on proteins and Nylon will be reported later. The authors express their thanks to Prof. P. D. Ritchie for his interest and encouragement, to Mr. A. Clunie for the construction of the film balance, to Dr. J. D. Kendell and Dr. J. Whetstone for supplying pure samples of cyanine dyes, and an anthraquinone dye, respectively, and to Imperial Chemical Industries Ltd., Dyestuffs Division, who supplied several intermediates. One of us (E. L. N.) is indebted to Tmperial Chemical Industries Ltd., Dyestuffs Division, and another (M. M. A.) to the Wool Textile Research Council, for financial assistance. * cf., c g . , the increase in area of films of the amides when spread on Orange I solutions and of azo-compounds spread on glycine.MARGARET M. ALLINGHAM, c. H . GILES AND E . L. NEUSTXDTER 105 1 Arshid, Giles, McLure, Ogilvie and Rose, to be published. 2 Chipalkatti, private communication. 3 Giles and Neustadter, J. Chem. SOC., 1952, 918. 4 Giles and Neustadter, J . Chem. Soc., 1952, 3806. 5 Giles, Rose and Vallance, J. Chem. SOC., 1952, 3799. 6 Hodgson, J. SOC. Dyers Col., 1933, 49, 213. 7 Knight, J . SOC. Dyers Col., 1950, 66, 169. 8 Marsden and Urquhart, J. Text. Inst., 1942, 33, T105. 9 Meggy, J. SOC. Dyers Col., 1950, 66, 510. 10 Paine and Rose, quoted by Vickerstaff.*6 11 Pauling, The Nature of the Chemical Bond (Cornell Univ. Press, Ithica, N.Y. 194% 12 Peters, J. SOC. Dyers Col., 1945, 61, 95. 13 Robinson and Ambrosc, Trans. Faraclay SOC., 1952, 48, 854. 14 Steinhardt, Fuggitt and Harris, J. Res. Nat. Bur. Stand., 1941, 26, 293. 15 Steinhardt, Fuggitt and Marris, J. Res. Nat. Bur. Stand., 1943, 30, 123. 16 Vickerstaff, The Physical Chemistry of Dyeing (Olivcr and Boyd, Ltd., Edinburgh, 17 Vickerstaff and Waters, J. Soc. Dyers Col., 1942, 58, 1 1 6. 18 Watson, Modern Theories of Organic Cheniistry (Oxford Univ. Press, 1941), 2nd edn. 2nd edn. 1950).

ISSN:0366-9033    

DOI:10.1039/DF9541600092

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

MARGARET M. ALLINGHAM, c. H . GILES AND E . L. NEUSTXDTER 105 GENERAL DISCUSSION Dr. P. Larose (Nat. Res. Council, Ottawa) said: As supporting evidence for the view that the rate of diffusion measured was determined by diffusion through the fibres and not through a liquid layer surrounding the fibres, Dr. Hudson cites the more rapid rate of sorption which followed when the fabric was re- immersed in the solution after interrupting the sorption by removing the fabric from the solution for a few minutes and partially removing the excess liquid in a mangle. Since a higher diffusion rate would be expected under such circum- stances even for a liquid-controlled process, the evidence is not very conclusive. One could question also the use of a diffusion equation worked out by Wilson for linear absorption.Whether one favours the Gilbert and Rideal explanation for the sorption of acids by wool or the application of the Donnan equilibrium to such a system, the relation between acid sorbed and concentration is not linear. Dr. B. Olofsson (Swedish Inst. Text. Res.) said: I agree with Dr. Hudson that the a-value to be used should correspond to the radius of the single fibres, not of the yarn. When working with fabrics the same formulae are applicable, although the diffusion is appreciably slowed down, because of the structure of the material. However, if we use a neutralizing agent in equivalent amount for washing out acid, the bath being considered of infinite volume, we get the same magnitude of /3 as for free fibres, i.e. a should have the same value.But I am not sure that it is necessary to account for the low value of D, found by Hudson, by introducing the Donnan quotient k. The value in the absorption of HC1 in my paper is D == 2a2/60 N 14 x 10-8 cm2/sec and if the real absorption isotherm is used instead of the linear approximation, this value seems to increase appreciably. Also the k-values in table 1 are remarkably low at the small acid concentrations used and do not vary with concentration. Dr. R. F. Hudson (Queen Mary Coll., E.1) (communicated) : I appreciate that the application of the Wilson equation to the present system can only be regarded as an approximation, but the close similarity between theoretical and experimental rate curves is probably due to the following characteristics.Firstly, the form of the theoretical rate curve is not highIy dependent on the value of a, and secondly the changes in a near the fibre surface are not large during the absorption (table 4). It may well be therefore that the true form of the rate curve is similar to that106 GENERAL DISCUSSION assuming a linear isotherm, owing to the logarithmic form of the acid absorption curve. The actual values of D obtaincd in this way may be in considerablc error, but it seems unlilcely that the very low valucs (- 10-8 cm2/sec), which agree closely with values given by Lindberg 1 arc due entirely to the adoption of this approximate treatmcnt. The low values are morc likely attributed to the low mobility of Hi- within the fibre.2 The low mobility is due to the low concentration of free hydrogen ions within the swollen fibre, an estimation of which may be obtained by applying the Donnan membrane treatment.Prof. R. M. Barrer (Aberdeen) said : Interruption tests of the kind described by Dr. Hudson may bc intcrpreted in several ways. One may suppose first that the film mechanism is operative ; in this event the concentration gradients before interrupting the experiment will be of the form shown in fig. la. Upon interrupt- ing the experiment and then re-immersing the fibre in the dye-bath one will have 4 distance FIG. 1. condition (b), if all adhering solution was removed from the fibre of fig. l a when the experiment was interrupted. If, however, a film of water (or solution necessarily much depleted in dye) adhered to the fibre, on re-immersing the fibre the concentration-distance curve would initially have the character of fig.lc. Clearly, a distribution like that in fig. l b would give an initial acceleration after the interruption (as observed) while fig. l c would give an initially slower rate of uptake of dye. Alternatively it may be that fibre diffusion is rate-controlling. In this case the three concentration-distance curves corresponding to fig. la, b and c will be distancc (4 solution solution FIG. 2. ._ _..___- soh! tion respectively those seen in fig. 2a, b and c. Again initial acceleration will follow the interruption experiment for the distribution of fig. 2b, while a bricf slowing- down would result from the distribution of fig. 2c. Evidently therefore little con- 1 Lindberg, Textile Res.J., 1950, 22, 381. 2 Wright, Trans. Faraday SUC., 1953, 49, 95.GENERAL DISCUSSION 107 R - \ ..%> .*.> --\, - '>\ ><,,2,\ b; .o Sh 4.: '*, '\ ; 2 B 6 \ $11 B A! A I > , , ( ' , , 1 ' '\ , I :I .= 5 , 1 ' , , I I * , , I * I , I * 1 , \ ( I , \- - A &\ $,, -, 0: '5 \\ :: ; '\ :: ', ' 1 6 , ', \ :,$ ',,, '*\. a; , s+~:, - I t , . i ',\ 'tt y * *. ', ', , . ' I $ * . . \ . . (6 1 FIG. 1. solution, and has neglected the influence of the diffusion layer at the fibre surface. The rapid rate of penetration which Prof. Barrer deduced from fig. 1 (b), which refers to a film-controlling mechanism, is accompanied by a rapid change in the diffusion gradient within the layer represented in fig. 1 (6) above. The first effect on separating the two phases completely (if this is possible) will be an instantaneous decrease in concentration in solution due to thc equilibration of the concentration difference across AB.If the quantity of solute in the difusion layer is small in comparison with the quantity in solution (as in the present case), this decrease A B (6 1 FIG. 2. .A 0 is negligible. As the diffusion gradient changes from 1-4 (fig. 1 (b)) the rate of transport across the plane AA' is zero so that the concentration in solution (which is experimentally mcasured in the present case) will not change until the original diffusion gradicnt is set up. Thc rate of establishment of this gradient will be rapid compared with the original rate of diffusion, i.e., if the amount of solute within the diffusion layer is small the time-lag will be negligible. The rate of change of concentration in solution on re-immersion is therefore approximately equal to the rate immediately prior to interruption.If the rate is fibrc diffusion controlled, the diffusion gradient will be as in fig. 2(a), not as given by Prof. Barrer. For the sake of simplicity in constructing the108 GENERAL DISCUSSION diagram a distribution coefficient K of unity is assumed. In the present case, however, it should be remembered that the solubility in the fibre is very high and K is of the order of 102. On re-immersion the instantaneous rate across the plane AA’ will be zero, although the rate of penetration into the fibre is infinite. Again, the changes in the diffusion gradient 1-3 will be extremely rapid until a gradient across AB is established. As the solubility in the fibre is high, the concentration of solute at the fibre surface will be much lower than in 2 (a) so that the diffusion gradient across AB is now considerable (gradient 3 of 2 (b)).The rate of diffusion across AA’ therefore remains high until the diffusion gradient within the fibre is of the same order of magnitude as in (a). This will take a considerable time (as diffusion within thc fibre is rate determining) and the concentration in solution will therefore change considerably as shown in fig. 2 (b‘), at an increased rate. The case (c) discussed by Prof. Barrer is a very real one and is probably of more importance experimentally than case (b), owing to the difficulty of achieving a complete separation at BB‘.In either case 1 or 2, an instantaneous decrease in concentration due to mixing will occur if the aqueous film removed with the fibres (represented by CC’) is wider than the diffusion layer. This is followed by a very rapid reestablishment of the diffusion gradient across AB shown in l(c). When the original gradient (4) is set up, the rate is approxirnatcly equal to the rate prior to interruption, if the mixing effect does not change the concentration in solution appreciably. If it does, the subsequent rate will be slower. In case (2c) given by Prof. Barrer, a similar series of processes will occur, followed by the increased sorption rate given in 2(b’). In both cases, therefore, an immediate decrease in concentration will be observed followed in case 1 by il resumption of the original rate and in case 2 by an increased rate.In the experi- ment given in my paper, the volume of water adhering to the fibres was determined by weighing a mangled sample, after interruption. The decrease in concentration due to mixing on re-immersion was calculated, assuming the concentration in the liquid film to equal that in solution, and assuming that all the solute in this film is transferred to the fibre during the interruption. The calculated decreasc was subtracted from the observed concentration decreases on re-immersion in con- structing the graph in fig. 4 in the paper. In addition, it was established that no rate increase is caused by interruption under conditions of slow stirring (ca. 80 revlmin), when the mechanism is controlled by film diffusion.Similar observa- tions have been made by Kressman and Kitchener 1 on the rate of exchange on synthetic resins. Dr. K. H. Gustavsom (Sweden) (contributed) said : As a contribution to the problem of the forces involved in binding of polyvalent anions (colour acids) by proteins (keratin), which is touched upon in the first two papers, some unpublished results from investigations of the irreversible fixation of some polysulphonic aromatic acids, so-called synthetic tannins, by collagen will be mentioned. The collagen lattice is apparently able to accommodate large anions more easily than the keratin structure with its large crystalline regions inaccessible to heavy anions. Hence, the stereochemical complications are less conspicuous with collagen as the substrate.The governing effect of the affinity of the anions of polyacids for the cationic protein groups in such reactions is now generally realized. The continuous line of the curve in fig. 1 shows the irreversible uptake of a rnonosulphonic acid of a condensed phenol (Novolak) at final pH values 1-9. The dashed curve gives the percentage of the basic groups of collagen inactivated by the fixed sulpho-acid. The fixation of the Novolak is not very much influenced by the hydrogen ion concentration of the system. Particular attention should be given to the degree of inactivation of the cationic protein groups, which amounts to ca. 90 % in the pH range < 3. Furthermore, at the pH corresponding to the isoelectric point of collagen, or pH 5, not less than two-thirds of the total number 1 Kressman and Kitchener, Faraduy SOC.Discussions, 1949, 7, 90.109 of cationic protein groups have been inactivated. Even at pH values above the isoelectric point, up to pH 10, a large fixation of the Novolak occurs, more than a third of the basic groups of collagen entering into the reaction. This is a rather convincing proof of a direct interaction of the SO3--groups with the cationic sites of collagen, even at pH > 5, with subsequent discharge. Ovcr the whole PH range covered, the hydrogen bonding of the phenolic groups of the sulphonated GENERAL DISCUSSION FIG. 1.-Fixation of Novolak-sulphonic acid by collagen as a function of the final hydrogen ion concentration and the degree of inactivation of the cationic protein groups by the suipho-acid.Novolak on the protein chains (probably to the keto-imide groups) has been shown to occur. The rapid drop in fixation at pH > 10 is probably due to the smaller number of hydrogen bonding sites (OH groups) resulting from the ionization of the OH groups at the high pH values. A third type of binding may be due to electrostatic attraction of dipoles in the aromatic rings to the resonating keto-imide links. Particularly Otto 1 has emphasized the important I I FIG. 2.-Fixation of trinaphthalene-dimethane-disulphonic acid by collagen as a function of the final hydrogen ion concentration, and the degrees of inactivation of the cationic protein groups by the sulpho-acid. function of the >C-H group adjacent to the substituent in the aromatic nucleus as a dipole (mdectrons) in the reaction of dyestuffs and synthetic tannins with fibrous proteins.Some support for the suggestion of the participation of such auxiliary forces is given by data from the fixation of trinaphthalene-dimethane-disulphonic acid by collagen, represented graphically in fig. 2. The sole reactive groups of this compound are the terminal sulphonic acid groups. Accordingly, it would be 1 Otto, Leder, 1953, 4, 193.110 GENERAL DISCUSSION expected that collagen would not bind this fairly strong acid at final pH values above 5, the isoelectric point of ordinary limed hide powder. On the contrary, a marked fixation takes place in the pH range 5-10. Further, it is important to note from the curve showing the extent of inactivation of the cationic protein groups that the binding of the naphthalene compound at pH values above 7 does not result in any inactivation of the basic protein groups.Since no co- ordination centres are present in this compound, the only valency forces available for the binding are those associated with the resonating )CH group and the -CH2 link connecting the naphthalene rings. Whether the binding of the naphthalene sulphonate is connected with different electron density or due to other factors must be left open. In any case, these data form additional evidence that the polyvalent sulpho-acid anions are held in the protein structure by various forces, the relative importance of the various types of forces depending on the structure of the anions and the experimental conditions. Dr.G. A. Gilbert (Birmingham University) said : Perhaps the result most calling for comment in the paper by Peters and Lister is the value they find for the heat of reaction of wool with Orange 11, C.I. 151. This is ca. -0-8 kcal/mole in the temperature range 60-80" C and leads, when combined with the standard free energy of adsorption, to a calculatcd entropy of adsorption of + 10-20 cal/deg. mole more than the corresponding value for the adsorption of HCI. Lemin and Vickerstaff, on the other hand, in ref. (3) quoted by Peters and Lister, estimate the heat of reaction for the same dye (Orange G, C.I. 151) to be -7 kcal/mole, and the entropy change on adsorption compared with HCl to be - 8 cal/deg. mole. Since detailed arguments are put forward by Peters and Lister which depend upon the sign and magnitude of this entropy change, some inquiry seems necessary into the origin and meaning of the difference between these two sets of experi-- mental results.Can it be that in one or the other cases there has been lack of equilibrium, or can aggregation of the dye solution possibly be affecting the results of Peters and Lister more than those of Lemin and Vickerstaff, because their technique requires concentrations of dye much higher than those used by Lemin and Vickerstaff ? Is it not perhaps significant that the heat of dilution of Orange G is found by Derbyshire and Marshall (this Discussion) to be 6.0 kcal/mole, and that this figure corresponds almost exactly in sign and magnitude to the one required to reconcile the two results ? These differences in sign emphasize how desirable it is to avoid introducing confusion by making unnecessary changes of convention? and it is to be hoped that energies of adsorption and not desorption will continue to be used as hitherto.The question as to whether simple anionic dyes react preferentially with the positively charged groups of wool may receive its most direct answer from studies with dissolved proteins. There the hydrogen ion no longer plays such a domin- ating role and the independent adsorption of anions is possible. Some of the extensive evidence which already exists in this field was reviewed by Klotz and Ayers recently.1 Mr. G. King (Wool Industries Res. Assn., Leeds) (said) : I would like to apply Gurney's theory 2 of proton transfer to Dr.Peters' results. Gurney writes (1) where A and B are constants, and E is the dielectric constant of the solvent medium. The first term represents the free energy contribution due to quantum forces, and the second is the electrostatic contribution. The former is largely independent of temperature while the latter will vary in accordance with the dielectric constant against temperature relation. Assuming the solvent to be water, the above relation gives a good fit with AF" = - R T h K = A + B/E, 1 Klotz and Ayers, Faraday Soc. Discussions, 1953, 13, 189. 2 Gurney, J . Chem Physics, 1938, 6, 499.GENERAL DISCUSSION 111 Peters’ curve for the temperature dependence of pK for HCl, and values are ob- tained for A and B, viz., A = 2.9 kcal/mole, B/E = 2.9 kcal/mole (e = 80). Now relation (1) also gives the change in pK value with change in dielectric constant of the solvent and predicts that the afinity of HC1 for keratin should increase as the dielectric constant falls.This is in agreement with the results of Daniel 1 for HC1 absorption by gelatin from alcohol 4- water mixtures. Ac- cording to her results, the mid-point of thc titration curve increases in pH by about one unit on changing from water to a mixture containing 60 % ethyl alcohol. Assuming the values already determined for A and B to hold for the gelatin system, and taking E for the alcohol mixture to be 44, the pK in the alcohol solution turns out to be 6.0 as compared with 4.3 for water. This corresponds to a shift in pH of 0.85 unit which is near to the value measured.Prof. R. M. Barrer (Aberdeen) said : Dr. Peters and Dr. Lister make use of a quantity which they describe as the “ standard free energy ” of sorption as a measurc of the “ affinity ” of a solute for the fibre. The “ standard free energy ” obtained varies according to the amount of solute at equilibrium in fibre and in solution, and cannot therefore be the thermodynamic standard free energy. It is as well to recall how the true standard free energy is derived, and how it is related to the “ standard free energy ” of Peters and Lister. Consider the transfer of a solute from a solution where it has an arbitrarily chosen activity cis to the fibre where it has an arbitrarily chosen activity af. The free energy AG of the transfer is given by the van’t Hoff isotherm as (1) If each of the arbitrarily chosen activities af and as refers to the standard state of unit activity, then a f = a, = 1 and (2) where AGO is the true standard frce energy and (af/as)equ2e is the thermodynamic equilibrium constant.Whatever the individual concentration values (CJ)~~,,~. and (Cs)equil. in the quotient (C’/Cs)equil. the thermodynamic equilibrium con- stant (af/aJeqUi~~ will be the same, and so only one thermodynamic standard free energy is possible. Peters and Lister have used activities as given by the model in the Gilbert- Rideal theory to evaluate a so-called equilibrium constant and a so-called “ standard free energy ” AG’o such that AG = - RT In (aflaJequil. + RT In (ajlas).AG = AGO = - RTln (af/aJequil., If the Gilbert-Rideal theory is imperfect the expression in the brackets in the right hand side of eqn. (3) will not give (q/aS),,,il. correctly, and the left-hand side will thus not give the true thermodynamic standard free energy. In particular the right-hand side of eqn. (3), and therefore AG’o, will probably vary according to the absolute values of the concentrations and (CJequil. This is just what Peters and Lister have observed, and the observation thus amounts to a demonstration of quantitative imperfection in the Gilbert-Rideal theory. One should not in these circumstances use AG’o as a quantitative measure of the affinity of the solute for the fibre. When using mixtures of HC1 and H2SO4 a standard free energy term for the anions may be writtcn as Dr.B. Olofsson (Swedish Inst. Text. Res.) said: 1 Daniel, J. Gen. Physiology, 1933, 16, 457.112 GENERAL DISCUSSION If experimental values are substituted we get AGO < 0; and we get about the same AGO value if instcad of using " Gilbert-Rideal activities " we calculate internal activities as " Donnan concentrations " a,& and as&, where a is the amount absorbed and v the corresponding volume of the swelling water. How- ever, if v is calculated as the total swelled fibre volume, the absolute value of AGO decreases appreciably and is probably not significantly different from 0. Mr. D. M. G. Armstrong (Royal Veterinary COX, London) said : In connection with the controversy as to the applicability of the Donnan, Steinhardt and Harris, and Gilbert and Rideal theories, it seems to me that the theory chosen should be such that it applies equally well to the titration of keratin, collagen and ion- exchange resins since these form very similar systems.It would appear that neither the Steinhardt-Harris nor the Gilbert-Rideal theories apply to collagen when in contact with acid and salt solutions since a two-phase system consisting of swollen collagen and solution, of differing ionic molalities, is established. 1 Dr. C . H. Giles (Royal Tech. COIL, Glasgow) said : The straight-line isotherms for disperse dyes sorbed on cellulose acetate (and polyethylene terephthalate) 2 are not necessarily inconsistent with a mechanism of sorption at specific sites. The tangent of the angle, relative to they-axis, of any portion of an isotherm, represents the increment of equilibrium concentration of solute (or vapour) in the external phase, necessary to maintain a constant increment of concentration at equilibrium in the substrate.The complement of this angle, i.e. the slope of the isotherm, at any point may thus be regarded as a measure of the ease with which bombarding solute molecules can find vacant sites in the sorbate. At the origin of a normal sorption isotherm (B.E.T., type 1) the slope is high, all sites being vacant. At the saturation point the slope is nil, for no vacant sites remain. Between these points, the steadily diminishing slope represents the progressive filling up of the sites. A straight-line isotherm is therefore consistent with conditions in which the number of equal-energy sites does not diminish as sorption progresses.Such conditions might arise in one of two ways : (i) the solute, but not the solvent, is a swelling agent for the substrate. As each solute molecule becomes attached, it forces apart molecules of the substrate and exposes fresh sites. The fibres under discussion are hydrophobic, so that the use of water as the solvent medium, and dyes with specific attraction for the fibre, would satisfy the required conditions. (If the solvent can swell the fibre, maximum swelling will occur even in solutions of zero concentration, and the process of sorption of solute cannot then expose fresh sites. Thus, e.g., sorption isotherms of dyes on cellulose from aqueous solutions are normal (type l).) (ii) An alternative, but less likely, explanation is that the balance of affinities between solvent + solute, solute + solute, and solute + substrate is such that a multilayer of solute molecules can readily form on the substrate surface; i.e.a bombarding solute molecule will become attached to one of its own kind, pre- viously fixed, as readily as to a vacant site in the substrate. Thus the number of available sites does not diminish as the solute is progressively sorbed. To account for the abrupt change of slope of the isotherm at the satura- tion value it is necessary to suppose there is a sudden decrease in available sites, as e.g., might occur if sorbed molecules blocked access to intermolecular pores. A sorption process of type (i) above can still be considered as a form of solid solution, even though specific solute + substrate interactions are involved.The partition of a solute between two immiscible solvents is a special case of condition (i) above. Immiscible solvents can be considered as mutually non-swelling, and 1 Armstrong, The Nature and Structure of Collagen (Butterworths, London). 2 Schuler and Remington, this Discussion.GENERAL DISCUSSION 113 the solute can be considered to be a swelling agent for either. The interface is mobile and fresh sites are continually exposed. The general question of isotherm shape in relation to sorption mechanism, briefly discussed here, will be dealt with in more detail elsewhere. Dr. H. E. Schroeder (du Pont de Nemours Co., Delaware) said: Our work with synthetic polymers shows clearly that in cases where a specific concentration of ionic sites is introduced in the polymer, subsequent saturation and equilibrium dyeing studies point to an excellent agreement between the concentration of dye ions and number of sites.For example, in our paper on polyacrylonitrile containing pyridine cations or co-ordinated cuprous cations, the dye anion con- centration extrapolates very closely to the site concentration. With polyamides, the work of Remington and Gladding 1 shows that dyeing occurs on terminal amino groups as NH3+. The limiting concentration of dye anion is equivalent to the number of amino sites. Further application of dye at low pH leads to chain scission. This method is in fact sufficiently precise to permit measurement of the concentration of amino chain ends.There appears to be no reason for using the Donnan concept in these cases. Dr. J. L. Horner (Wool Industries Res. Assn., Leeds) said : With regard to the presence of a small excess of carboxyl groups over proton acceptor groups (i.e. imidazole, terminal and side-chain amino and guanidine groups), referred to in the paper of Lister and Peters, reference to the works of Steinhardt et al. shows that they purified their wool samples by low temperature solvent extraction, followed by repeated washing with distilled water. No occasion arises, there- fore, for hydrolysis of amide groups during preparation. I have obtained a theoretical titration curve for the combination of alkali with wool protein 2 which, when compared with the experimental curve for virgin root wool, gives definite indication of the presence of free carboxyl groups in the isoelectric protein.Thus, although the theoretical curve agrees precisely with experiment above pH 11, perfect agreement between the two at pH 6 to 11 can only be obtained if the presence of 0.05 mequiv. of excess carboxyl group per g of dry protein is postulated. Recent analyses of the amino-acid composition of wool protein by Corfield and Robson,3 who used partition chromatography coupled with a tracer technique, give a total for the basic side-chains of 0.835 mequiv./g, which, with terminal amino groups 4 yield the value of 0.852 mequiv./g for basic groups. This may be compared with approximately 0.90 mequiv./g for the total of carboxyl groups, leading to the conclusion that there is a small excess of carboxyl groups in the native protein.Dr. K. H. Gustavson (Stockholm) said : The technique described by Armstrong which enables continuous estimation of the rate of diffusion of vegetable tannins through skin, will likely be very useful for the study of the progress of tanning processes in situ. The selection of mimosa tannin for the main investigation was wise, and even fortunate, since the tanning mechanism is much simpler with this tannin than with tannic acid, a fact also stressed by the author. This observation is supported by results from an entirely different approach, i.e., by investigating the reactions of the two tannins with collagen and other substrates. In view of the fact that the paper under discussion is the only one bearing on the vegetable tannage, some data from unpublished work, directly related to the present subject, are deemed to be of sufficient importance for con- sideration on this occasion.In the experiments which form the basis of the results shown graphically in fig. 1 and 2, solutions of mimosa extract, a typical condensed tannin, and of 1 Remington and Gladding, J. Amer. Chem. SOC., 1950, 72, 2553. 2 Horner, to be published. 3 Corfield and Robson, private communication. 4 Middlebrook, Thesis (University of Leeds, 1949). Tibbs, Thesis (University of Leeds, 1951).114 GENERAL DISCUSSION tannic acid, a representative of the hydrolyzable class of tannins, were interacted with intact and modified specimens of hide powder, as well as with the modified polyamide, mentioned in my paper.Its main reactive sites are the -CO . NH links. A certain degree of irregularity is imposed upon the polyamide structure a I $ f T 6 7 4 2 /e ~ FIG, 1 .-Mimosa extract. 1: hide powdcr ; 11: hide powder + 3w/v % NaCl ; 111: methylated hidc powder ; IV: polyamide. FIG. 2.-Tannic acid. I: hide powder; 11: hide powder + 3w/v % NaCl; HI: mcthylated hide powder; IV: polyamide. by copolymerization (Nylon-66 with caprolactame), which enables the ac- commodation of molecules of the size of vegetable tannins in the interchain spaces and further makes free co-ordination sites (for hydrogen bonding) available on some of the keto-imide links (hydrated). The curves show the irreversible fixation of the two tannins by ordinary hide powder, esterified hide powder and the hydrated polyamide from solutions covering the pH range 2-9.Firstly, on examining the curves for the fixation of mimosaGENERAL DISCUSSION 115 tannin (fig. l), it is to be noted that its binding by the polyamide is independent of the Hf ion concentration of the solutions over the whole pH range, large quantities of tannin being fixed. This is an experimental proof of the ability of the keto-imide group to bind polyphenolic tannins, probably by a mechanism of hydrogen bonding. The reactivity of the peptide link would be expected to be independent of pH. The sharp drop of the fixation of tannins by the polyamide and coiiagen substrates at pH > 9 is most likely due to the ionization of the phenolic groups at pH > 9, denoting a smaller number of OH groups available for hydrogen bonding.The intact hide powder shows the typical pH function in binding of vegetable tannins, with a minimum in the isoelectric zone of collagen, a marked maximum at pH - 2 and a rapid decline of the curve in the range of high pH values. The general trend of the fixation curves reflects the number of available reactive protein groups, non-ionic as well as cationic ones, for the fixation of the tannins, which is a function of the degree of swelling of the substrate. If the swelling is eliminated by the addition of salt, the curve of the fixation of the mimosa tannin is independent of the pH of the system in the range 2-8. These data indicate the dominant role of the keto-hide group as the site for fixation of tannins of the condensed type.It will be evident from data to be presented in the following that their fixation by collagen also involves its ionic groups. The corresponding fixation of tannic acid, which contains strong acidic groups (carboxylic) besides numerous weakly acid groups (phenolic) is more complicated (fig. 2). The polyamide fixes very large amounts of tannic acid in a restricted, very acid range. A tremendous drop in fixation is already evident at pH 4-5. Augmented molecular weight of tannic acid by aggregation at low pH values, and participation of the -COOH group of the molecule of tannic acid in hydrogen bonding on the polyamide are factors which have to be considered in any attempt to explain the peculiar pH function of the fixation.The pH function of the intact hide powder resembles that of the mimosa tannin. However, it should be noticed that the swelling-depressing action of salt hardly effects the curve of the fixation of tannic acid, and further that the fixation curve of esterified collagen for tannic acid is entirely different from that of the mimosa tannin. The curve which represents the system tannic acid + polyamide proves that the keto-imide group plays a subordinate role compared to that in the mimosa + polyamide system. It is also seen that the participation of ionic protein groups in the fixation of tannic acid, and of hydrolyzable tannins generally by collagen has to be included in the tanning equation. Further information on the mode of fixation of the two tannins by collagen has been obtained by comparative studies of their fixation by hide powder (through ionic and non-ionic groups) and by modified hide powder, in which the ionic groups have been inactivated by irreversibly fixed condensed naphthalene di- sulphonic acid.The latter does not appreciably interfere with the reactivity of the non-ionic groups of collagen. Thc modified collagcn should mainly react by means of non-ionic valency forces (keto-imide groups). Some relative values obtained after 24 h tannage show the ratio of ionic to non-ionic binding of mimosa tannin to be about 1/1, whereas the corresponding value for tannic acid is of the order of 3/1. There are certain indications that the ionic protein groups are involved simul- taneously with the non-ionic (hydrogen bonding) groups in the fixation of a part of the mimosa tannins1 That would imply a multipoint fixation of the tannin molecule by means of the two principal types of valency forces.In the initial fixation of tannic acid, with ionic protein groups dominating, a considerable part of the tannins held in irreversible binding with collagen would be expected to have reacted with the cationic protein groups. The marked shift of the pH corresponding to the isoelectric point of collagen towards low pH values which 1 Page, J. SOC. Leather Trades Chent., 1953, 37, 183.116 GENERAL DISCUSSION is produced by the binding of tannic acid by collagen and the convincing experi- ment of the late F. C. Thompson 1 demonstrating complete displacement of hydrochloric acid held by gelatin by the addition of tannic acid, may be cited as proofs of this hypothesis.Finally, fig. 3 and 4 give an idea of the rate of fixation of tannic acid and mimosa tannin by the two types of protein groups involved in The initial, very rapid fixation which has been shown to impart their fixation, hydrothermal FIG. 3.-Fixation of tannic acid by ionic and non-ionic protein groups (sulpho-acid inactivated). FIG. 4.-Fixation of mimosa tannins by ionic and non-ionic protein groups (sulpho- acid inactivated). stability to the collagen lattice 2 appcars to be due mainly to the participation of ionic protein groups. The gradual uptake of tannin in the later stage of the pro- cess is shown to be hydrogen bonding on non-ionic protein groups. It is clcar from the data reviewed that mimosa tannin (condensed) and tannic acid (hydrolyzable) show cntirely different types of reaction with collagen.1 Thompson, J. Int. SOC. Leather Trades Cliem., 1934, 18, 175. 2 Gustavson and Nestvold, Leder, 1951, 2, 121.GENERAL DISCUSSION 117 Armstrong’s observation that the reactions of stages I1 and 111, in his designation, probably occur simultaneously in the tannic acid system may be due to the different types of reaction which have taken place on the fixation of tannic acid by collagen, while the tannins of mimosa show a more normal behaviour towards collagen. It is also clear from these investigations, and these facts are of sufficient importance to merit restatement, that the mechanism of the reaction of hydro- lyzable tannins with collagen involves ionic protein groups to a great extent besides non-ionic protein sites, and thus that it differs markedly from the re- action of the condensed type of vegetable tannins with hide protein, in which tannage the non-ionic groups of collagen are primarily concerned, but not, however, to the complete exclusion of other groups.Dr. B. Olofsson (Swedish Inst. Text. Res.) said: I would ask Dr. Armstrong if his moving boundary is really sharp. This is, however, a very general question as such boundaries are formed not only in tanning but also when dye or vapour penetrates fibres. Only if this boundary is sharp is the theory of Hill-Hennans strictly applicable; if not a theory involving the sorption isotherm as devised by Wilson-Crank and myself must be used. Mi.D. M. G. Armstrong (Royal Veterinary College, London) (communicated) : In reply to Dr. Olofsson’s query, Stather 1 observed that the boundary between the tanned and untanned region of skin was very sharp with the following tannin materials ; mimosa, quebracho, mangrove, myrobalans, sumac and pine bark. With sulphited quebracho, chestnut, algarobilla, valonia and gambier, the boundary was not very sharp. With mimosa, the sharpness of the boundary can be seen in sections, unstained with dichromate, over the whole of the first stage of tanning. With tannic acid, the boundary is difficult to see since the tanned region is almost the same colour as the untanned in unstained sections: in crudely stained sections it does not appear very sharp. Thus the use of the Hill-Hermans theory is justified in many systems.In those where it may not be strictly applicable, its simplicity and the unavailability of any valid sorption data justify its use for practical purposes where approximate estimates of rates and states of tanning are better than none at all. Prof. R. M. Barrer (Aberdeen) said : The term self-diffusion originally referred to the diffusion of a substance in itself, e.g. Pb in Pb ; Au in Au ; H20 in H20 ; H2 in H2, and so on. The use which has been made of the term self-diffusion in the paper by Wright is an extension of the term in a direction which cannot be wholly justifiable. The dyestuff tagged by radio-active atoms is not diffusing in a crystal of itself, but is surrounded by and is diffusing in the fabric of the polymer.The polymer, not the dye, is the diffusion medium. It seems desirable to limit the term self-diffusion to its original use, and to employ some other term for a description of the process discussed by Dr. Wright. Dr. Andre Parisot (Inst. Text. de France) said: I t would seem that in all the papers presented insufficient account has been taken of the architecture peculiar to the wool fibre. It has been proved that the actual surface of the fibre presents a physical structure differing from that of the layers situated immediately below. Whether one regards the epicuticle as being a distinct morphological membrane, or as being a superficial state of the cuticle, it remains none the less true that this epicuticle governs all the phenomena of diffusion in the wool fibre.Since its slight thickness makes it somewhat fragile, the treatments to which the fibre is subjected may destroy or considcrably modify the epicuticle. The result of this is that the subsequent behaviour of the reagents on passing from the sur- rounding solution into the fibre will depend on the treatments to which the fibre has been previously subjected. The diffusion of the reagent, in particular, is one of the phenomena most liable to be affected by this factor. 1 Stather, Collegium, 1933, 326.118 GENERAL DISCUSSION The morphology of the fibre is aIso a factor, especially its degree of crimping or curliness. Certain dyes are more readily absorbed in the concave areas; and we have found that the bubbles or blisters of the Allworden reaction, consisting of the action of bromine water or chlorine water on the wool, more readily appear on the convex portions of the crimps.Dr. L. Valentine (Leeds University) said: I should like to take this oppor- tunity to present some results on a diffusion-controlled reaction involving wool fibres, although neither dyeing nor tanning is actually involved. Lipson and Speakman 1 showed that considerable amounts of vinyl monomers, e.g. methacrylic acid, could be polymerized within wool fibres by first impregnating them with Fez-!- ions, and then immersing them in an acid aqueous solution of the monomer and H202. The H202 and monomer diffuse into the wool, whereupon the H202 reacts with the Fez+ to liberate OH radicals which initiate the polymerization ; it can be shown that the polymerization takes place within, not on the surface of, the fibres.A study of the polymerization of acrylonitrile within loose wool at 25", using a slightly modified version of Lipson and Speakman's technique, indicates that the percentage increase in weight Wof the wool due to polymerization is a linear r------' ' ' -I 1- 80 I FIG. 1. function of the square root of the time t up to a value of W e 4 0 %. The reaction mixture, which was not agitated, consisted of acrylonitrile 3.8 %, H202 0.003 %, H2SO4 0.01 N, liquor/wool ratio, lOS/l. As shown in the fig. 1, the weight increase reached a saturation value at W = 75 %. The W against t+ relationship is similar to that found for a diffusion process followed by rapid adsorption, and it scems probable that here the polymerization is rapid compared to the diffusion of reactants, which then becomes the rate-determining step. The apparent diffusion constant D has been calculated on this assumption by two slightly different methods which yicld concordant results : (i) Using Hill's 2 graph of the average degree of saturation as a function of D r p , where r is the radius of the fibre (24 p), the following values were obtained : av. degree of saturation 0.15 0.30 0.50 0.75 0.90 D (cm2/sec x 1011) 1.02 0.99 1.14 1-15 0.85 (ii) Using the initial lincar W against t t plot, D was calculatcd from Hill's equation for the amount Q diffused into a semi-infinite solid, viz., Q = 2 c ( D t / ~ ) 4 1 Lipson and Speakman, J.SOC. Dyers Col., 1949, 65, 390. 2 Hill, Proc. Roy. SUC.B, 1928, 104, 39.GENERAL DISCUSSION 119 where c is the concentration determining diffusion. There is some ambiguity as to the meaning to be assigned to c in this reaction, but reasonable values would seem to be either (a) the saturation concentration of monomer units in the wool + polymer system, taking the volume to be the total volume of the wool 4- polymer (0.58 Q cm-3), or (6) the concentration of monomer units in (i) poly- acrylonitrile, i.e. its density (1.14 g cm-3), or (ii) acrylonitrile monomer (0.80 g cm-3). These assumptions lead to values of D of 2.3, 0.6, and 1.2 X 10-11 cm2/sec, respectively, the last figure being in good agreement with that calculated from the saturation increase in weight. It is rather striking that the reaction can apparently be described adequately by a single diffusion constant up to a weight increase of 70 % at 25" ; preliminary experiments at 37" indicate that a similar position holds up to weight increases of 100 %.Compensatory processes are probably at work, since the increase in fibre diameter would counteract the expected diminution in D as polymer fills the fibre. The absolute value of D is perhaps somewhat lower than might have been expected for the diffusion of acrylonitrile into swollen fibres at pH 2 ; Hudson 1 finds values of ca. 10-9 cm2/sec for picric acid and C6HsS03H for well-agitated solutions. (Extrapolation to zero rate of stirring suggests values of ca. 3 x 10-10 cm2/sec.) The activation energy has been found to be 7.7 kcal/mole, compared with the value of 6.3 kcal/mole for C6H5S03H found by Hudson.However, both the absolute value of D and its activation energy are in harmony with the view that D is a true diffusion constant, probably that of acrylonitrile into the fibre, although it cannot be claimed that this has been proved. Mr. D. M. G. Armstrong (Royal Veterinary Coll., London) (communicated) : In the paper by Underwood and White, it is not clear whether any adsorption of sodium sulphate on hair takes place although there is no doubt that there is ab- sorption of the salt into the fibre. It is unlikely that there is any positive adsorp- tion of sodium sulphate by hair since with skin collagen Eilers and Labout 2 have shown, from analyses of solutions of sodium sulphate and other saIts in contact with skin powder, that negative adsorption takes place, part of the water inside the fibres (to the extent of 0.38 g/g collagen with 0.2 M sodium sulphate) being "non-solvent " water.In the absence of any clear evidence for positive adsorption there is no justification for the suggestion that there are bonding sites in the fibre to the presence of which absorption can be ascribed. Dr. P. Larose (Nat. Res. Council, Ottawa) said: Nowhere in the paper of Underwood and White is there any evidence that a correction was made for the acid or salt that would normally be taken up by the fibre due to the free water in it. If that has not been done then the evidence for the sorption of sodium sulphate is compIeteIy destroyed as the following figures show. For acid sorption, neglect of the correction does not give rise to such large errors.Uptake (mm/g) * tcxpt. calc. expt. calc. expt. calc. expt. calc. 0.0285 0.031 0.0419 0.071 0.0026 0*0008 0,0132 0.0033 0.00443 0.0033 0.0204 0.029 0.0204 0.031 0.080 0.156 0.058 0.207 0.079 0.240 0.083 0.42 0.099 0.43 0.003 15 0.00079 0.0380 0,074 *This is the uptake that one would expect if it is assumed that the hair contained Texpt. values from column 4, table 1, in the paper by Underwood and White. 0-30 ml of free water per gram before immersion in the salt solution. Dr. M. L. Wright (Wool Industries Res. Assn., Leeds), said : In connection with the paper of Underwood and White I would like to give an account of some 1 Hudson, this Discussion. 2 Eilers and Labout, Symp. Fibrous Proteins (Soc. Dyers Col.) (Bradford, 1946), p.30.120 GENERAL DISCUSSION work on the absorption of simple salts by horn keratin (at present in the press) 1 as it is related to the work of Underwood and White. Using horn membranes in radioactive NaBr solutions exposed to the air, measurements have been made of self-diffusion, membrane conductance, membrane potential and equilibrium sorption. It was found that the sodium and bromide ions are not picked up in equal amounts, the disparity being greatest in dilute solutions (fig. 1). Hydrogen ions maintain the electroneutrality ; these can be obtained from the solutions which can absorb atmospheric carbon dioxide to give a solution at about pH 5.7. It is suggested that when keratin and similar polymers are placed in dilute salt solutions, the net result is mainly the sorption of the acid of that salt.Evidence for this can be obtained by consideration of the work of Steinhardt on the acid titration of wool keratin in the presence of salts at various ionic strengths2 From their data, the amounts of hydrogen ion combined at pH 5.7 for various KC1 concentrations can be obtained ; these are in good agreement with the values obtained, by difference, from the amounts of bromide and sodium absorbed. FIG. 1.-Ionic sorption from NaBr solution by horn keratin at pH - 5.7. Any one, or any one combination of the equilibrium sorption theories can be applied to the sorption of these three ion species, viz., Na, Br and H, but un- fortunately it does not seem possible to use the results to distinguish critically between the theories. If we apply the Gilbert and Rideal3 theory to the NaBr results we get a value for ApNaBr approximately zero, indicating little specific affinity.Using the same results we can calculate A h e r at approximately 6-7 kcal/mole which compares well with results obtained from the HBr titration curve for wool keratin. When the simple Donnan theory is used, the ratio of the ionic activity product inside to outside should be unity. If we calculate the activity inside as a concentration in the imbibed water using Peters and Speakman’s4 value of 0.285, values about 6-7 are obtained, but if we regard the keratin as a total swollen phase then the values become nearer unity. 1 Wright, Trans. Faraday SOC. (in press). 2 Steinhardt and Harris, J. Res. Nat.Bur. Stand., 1940, 24, 335. 3 Gilbert and Rideal, Proc. Roy. SOC. A, 1944, 182, 335. 4 Peters and Speakman, J. SOC. Dyers Col., 1949, 65, 63.GENERAL DISCUSSION 121 Referring to Underwood and White’s results, I would like to suggest that the low value found for DNazso4 is in fact the measurement of the small diffusion coeficient for hydrogen ions at low concentrations in the polymer1 which is controlling the process. Secondly it is seen from analysis of fig. 1 in their paper that desorption and exchange can be distinguished. Possibly this slow desorption is the result of chemical diffusion of sulphuric acid out of the fibre, which will be controlled by the hydrogen ion diffusion coefficient. Exchange, on the other hand, would correspond to the relatively rapid value of the self-diffusion coefficient for sulphate ions.Dr. Howard J. White, Jr., and Mr. Donald A. Underwood (Text. Res. Inst., Princeton, N.J.) (communicated) : In answer to Dr. Armstrong, we wish to point out that three results-the shape of the curve of uptake against concentration, the inhibition of the absorption of Na+ by H-C, and the slow rate of absorption of salt-are cited in the paper as experimental evidence difficult to reconcile with a simple “ internal solution ” theory of absorption. These results are qualitatively explainable in terms of absorption on to sites, and, while they may not supply “clear evidence ”, they are at least suggestive. Hair could well give results similar to those cited for collagen in 0.2 M solution. Thus, if the amount of water absorbed by the fibre remains roughly constant regardless of the concentration of the treating solution for a 0.2 M solution, water would be preferentially absorbed from solution by dry hair, as can be deduced, for example, from Dr.Larose’s table. In answer to Dr. Larose, no correction of the type mentioned has been made. As Dr. Larose’s table shows, “ corrected ” values would be positive at low con- centrations of treating solution and negative at higher concentrations. The physical meaning of such a result is obscure and, since the correction rests on an assumption of “ free water in the fibre ”, we prefer to abandon the assumption. In fact, one of the main purposes of the experiments with Na2S04 was to examine the validity of this assumption. It was concluded that it was untenable in its simple form.In Dr. Wright’s discussion, reference is made to the low value of D(Na2S04). The diffusion experiments are discussed. The pH of the treating solution and the fact that Na22 and S3504 are absorbed in equivalent quantities as far as the equilibrium results are concerned make it unlikely that the rate of absorption can refer to anything but Na2S04. In desorption into slightly acid distilled water, hydrolysis of absorbed Na2S04 could very possibly account for the difference between the rate of desorption and of exchange. Dr. T. Vickerstaff (I.C.I. Dyestufi), said: With reference to the difficulty of measuring the very small time intervals involved in Mann and Morton’s work, we ourselves have studied the rate of dyeing of acid dyes on gelatin film preswollen in water. Using hand agitation, rate curves were measured down to times of 2 sec.Plotted against d t t h e data gave straight lines down to the smallest observed times although a scatter of the points due to experimental error occurred below 4 sec. No evidence of a two-stage process with an initial rapid absorption followed by a slower diffusion could be detected. Is it possible that the effect observed could be due to the use of an anionic surface-active agent in the dye- bath which might be adsorbed on the outer surface of the fibre more rapidly than dye ? This would then retard the initial adsorption of dye until it had been replaced by dye. Alternatively, if the effect is real, may it not be regarded as the initial setting up of an equilibrium distribution of dye between the fibre surface and the dye- bath ? In this case is the initial dye uptake the same as that which is generally termed “ strike ” and if so may “ strike ” be defined as the concentration of dye on the fibre surface which would be in equilibrium with the initial dye-bath? 1 Wright, Trans.Faradny SOC., 1953, 49, 95.122 GENERAL DISCUSSION Dr. T. H. Morton (Courtadds Ltd., Braintree) (partly communicated) : We would have no quarrel with Dr. Vickerstaff’s findings that the rate of uptake of acid dyes on pre-swollen gelatine fiIm is linear with the square root of time. Under these conditions, it is difficult to see how a two-stage process could be set up. The absorptions with which we have dealt in the paper are not linear with the square root of time, simply because the time required to wet out the film or fila- ment is finite and further, during wetting in the dye solution, a very concentrated layer of dye is laid down in the interface which further complicates the simple dye diffusion.We do not believe that our observation of an initial dye sorption is related to the dyer’s “ strike ”. The initial absorption is roughly the same for a variety of dyes, whereas the varying “ strike ” is related to the varying speed of initial diffusion of dye from bath to yarn, that is, to the second of the two stages of thc process. The point made above on the linearity of sorption with the square root of time is well shown by the data of fig. 1. With Azo Geranine 2G (C.I. 31) the sorption is linear within experimental error on pre-swollen shcet cellulose, whereas with initially dry shcet, thc absorption, though linear over most of its range, is not linear in the very early stages.Azo Geranine is a dye almost, but not quite, without substan- 0.1 tivity towards cellulose. With Sky Blue FF absorbed on to initially dry sheet-cellulose, the absorption departs greatly from the linear relation. It will be 46 noticed that the perturbation lasts much longer than the time for fully wetting the cellulose sheet and is more probably re- latcd to the time required for the dispersal by diffusion of the con- centration of dye at the cellulose surface. The experiments of fig. 1 FIG. 1 .-Dye absorbtion by regenerated sheet c e h - show clearly that a two-stage lose at 20” C: 1 % pure A20 Geranine 2G-A, sheet process occurs even with simple previously wetted; B, sheet immersed dry: 0.2% Sky non-substantive solutes and that Blue FF and 0.5% NaC1-C, shect immersed dry.the two-stage nature of the pro- cess is even more marked when dealing with substantive dyes of comparatively slow diffusion speed. Dr. H. Zollinger (Bade University) said : Bird, Manchester and Harris deter- mined the standard heat of dyeing. They think that the calculated value of - 10.5 kcal/mole indicates two hydrogen bonds. On the other hand they showed in an excellent way that dyeing of dispersed dyes takes place from a saturated solution. It may be assumed that the dye molecules are solvated by water molecules in solution. The measured heat of dyeing therefore does not correspond to the formation of dye-fibre hydrogen bonds, but to the difference between the heat of formation of these bonds and heat of breaking the dye-water molecules hydrogen bonds.I think, thcrefore, that the value found does not prove definitely the existence of two hydrogen bonds. A similar opinion is mentioned in Robinson’s paper.1 Dr. T. Vickerstaff (I.C.I. Dyestufi) said: I would like to support the views expressed in the paper of Bird et al. that Clavel’s theory of the dyeing of cellulose acetate is worthy of reconsideration. Several points in support of this view are : constant distribution ratio of dye between fibre and dyebath in desorption 1 this Discussion. -08 ‘04 .02GENERAL DISCUSSION 123 experiments, the effect of particle size on equilibrium absorption, and finally the fact that the rate of dyeing of cellulose acetate from an infinite dyebath does vary with the concentration of dispersed dye.The latter fact suggests that under these conditions the rate-determining step in the dyeing process is the rate of solution of the solid dye. I am still of the opinion that the dye used in Kartashoff's experiments was in the form of negatively charged particles and that the ac- cumulation of dye particles at the fibre surface arose from the mechanical limita- tions of his experimental arrangement but this must remain pure conjecture. Dr. H. E. Schroeder (du Pont de Nemours Co., Delaware) said : The data of Bird et al. extend only to about one-sixth of saturation. The methods described in Schuler and Remington's paper have been extended by them to the dyeing of cellulose acetate with non-ionic dyes.Isotherms have been determined for 1-amino-4-hydroxyanthraquinonc and N1 : N4-diphenyl-3-nitrosulphaniIamide. It was clearly shown that up to saturation each colour gives a linear plot of DF against Ds. The corresponding values at fibre saturation were for the anthraquinone DF = 10 mg/g ; Ds = 0.01 15 mg/d and for the sulphanilamide DF = 32.6 mg/g ; Ds = 0.0077 mg/ml. The same results were obtained with mixtures of the two dyes, For the saturated case, the total amount of dye on the fibre was the sum of the solubilities of the individual dyes, namely, 42.6mglg. In all cases the plots of Dr: against Ds were linear. This indicates clearly that in the sorption of non-ionic dyes by cellulose acetate there is no need for a concept of a limited number of sites, i.e.of Langmuir's absorption. A solution of dye in the fibre appears the best representation of the situation. Dr. H. Zollinger (Bask University) said : Dr. Giles discussed the question of hydrogen bonds of the benzidine dyestuffs. In this connection it seems to me to be worth while clarifying a spatial problem which is mentioned in most textbooks on dyeing, dyestuffs and textile chemistry. These books presuppose that direct dyestuffs have hydrogen bond-forming groups, spaced at a distance very closely approaching the length of the cellulose unit cell, which is 10-3A. Probably the most frequently mentioned example is Congo Red.1 This view is based on an unpublished investigation of Paine and Rose, who attribute a value of l0.8A to the distance between the respective hydrogen bonding atoms.In most papers (e.g. Vickerstaff 1) the amino hydrogen atoms are the species assumed to be the hydrogen bonding atoms. Working with scale models based on recent and accurate measurements of bond lengths, I found that the distance between the amino hydrogens is much larger (fig 1). Depending whether we assume the Congo Red ion to have a trans configuration (lower formula of fig. 1) or a " symmetric " configuration (upper formula), we got values of 16.2A and 15.3A respectively, these values do not at all correspond to the length of the cellulose unit. Some rough calculations based on the effect of these two dipoles of the sul- phonic groups shows that thc trails has a somewhat lower energy.The difference in energies of these two configurations is about 1/40 of the thermal energy at room temperature, therefore it is probable that the trans configuration is favoured slightly." Coming back to the spatial problem, it does not seem likely that the other two hydrogens are involved in the hydrogen-bonding with cellulose, because they belong to the rather strong hydrogen bridge to the azo nitrogen. Opening of 1 cp. fig. 56 in Vickerstaff, The Physical Chemistry of Dyeing (London and Edinburgh * Assuming a dipole moment of 4 D for the sulphonic group and neglecting all other 1950), p. 168. moments and the influence of the surrounding medium: trans-configuration 12.2 x 10-16 erg, symmetric configuration 23-5 x IO-l6erg, thermal energy (300" K) 414 x 10-16erg. (unpublished calculations of H. Labhart, Physics Laboratory, Ciba Ltd., Bask).1 24 GENERAL DISCUSSION this bridge would cause a remarkable shift in the wavelength of the absorption peak. This is, in fact, not the case. The only distance corresponding roughly to the cellulose unit is the distance between the nitrogens attached to the diphenyl nucleus, i.e. lO.1A. But these nitrogens can hardly be hydrogen-bonded to cellulose so long as their pair of unshared electrons is involved in a hydrogen bond with the amino group. It is a well-known fact that the nitrogen atoms of an azo group are able to form only one hydrogen bond (compare complex formation, etc.). Another example is Chrysophenin G, a stilbene dyestuff. Willis, Warwicker, Standing and Urquhart 1 think that this dye is hydrogen-bonded at the phenolic oxygens. These atoms are 24-8 8, apart. The distances between the azo nitrogens are 12-2 and 13.6A respectively. Therefore, this dyestuff is another example of the non-existence of a correlation with the cellulose unit length. As a result, I think that the hypothesis of the corresponding lengths of the cellulose unit and the reactive groups in direct dyes cannot be upheld any longer. This supports the view of Dr. Giles that hydrogen bonding is not a condition sine qua non for substantivity. Congo Red 0 1 2 3 4 5 --I-- FIG. l.--Scale models of Congo Red. I emphasize that my remark concerning the correlation between distances uf groups which are able to form hydrogen bonds with the cellulose unit cell, is intended to show that it is unlikely that such a correlation is important for sub- stantivity. I do not say that it proves the non-existence of hydrogen bonds between fibre and direct dyestuffs. The models of Dr. Robinson 2 show (i) that hydroxy groups are abundant along the cellulose chain and therefore almost every distance between potential hydrogen-bonding groups in a dyestuff molecule “ fits ” the hydroxyls of the cellulose, (ii) that in amorphous cellulose the chains are curved in such a way that dyestuff adsorption is still possible. Concerning the last point we think that dichroism of dyed cellulose fibres indicates that dyeing takes place on the surface of oriented (i.e. crystallized) regions of cellulose, as shown by Boulton and Morton,3 Frey-Wyssling and Walchli 4 and others. Dyestuff ions do not penetrate crystallized regions. This does not exclude the oriented adsorption which seems to be important, although my remark shows that the mentioned correlation between distances is improbable. 1 Willis, Warwicker, Standing and Urquhart, Trans. Faraday Soc., 1945, 41, 506. 2 this Discussion, compare fig. 2a, 2b and 3 of Robinson’s paper. 3 Boulton and Morton, J. Suc. Dyers Cul., 1940, 56, 145 ; 1946, 62, 272. 4 0. Walchli, Thesis (Federal Institute of Technology, Zurich, 1945). Frey-Wyssling, J. Polymer Sci., 1947, 2, 314.

ISSN:0366-9033    

DOI:10.1039/DF9541600105

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

ATOMIC MODELS PART 3.-SOME STEREOCHEMICAL PROBLEMS IN DYEING BY CONMAR ROBINSON Courtaulds Limited Research Laboratory Maidenhead Berks Received 22nd July 1953 Models of dye molecules and of cellulose and polypeptide chains have been built with the type of atomic model previously described by Hartley and Robinson. Their use in investigating stereochemical problems related to dyeing has been illustrated. The anisotropic flexibility of the cellulose chain has been demonstrated. The shape of a number of dye molecules in relation to the shape of the cellulose chain has been discussed and also the part played by intra- and intermolecular hydrogen bonds in both dyes and cellulose. The models suggest that contrary to the usual assumptions hydrogen bonding to cellulose can take place irrespective of the position of those groups in the dye molecule which are capable of forming such bonds.When an amide group links two aromatic rings together it appears unlikely that the group can be in the cis configuration when attached to cellulose as this configuration involves great steric hindrance. The possible part played by steric hindrance in the dyeing of a synthetic polypeptide is discussed. Although atomic models have frequently been used to investigate stereochemical problems in dyeing their usefulness has been limited by shortcomings in the designs of the models available. Recently Hartley and Robinson 1 have described a development of the Stuart type of model. In these the atoms are linked to- gether by a combination of link and collar which allows the valency bond to be distorted a few degrees from the normal when strained but which provides a restoring force which insures that the valency angle shall have its normal value when the model is not under strain.This linking mechanism not only allows molecules to be built in which the valency angles are known to deviate from the normal values but also allows an estimate of the distortion involved when a model of a configuration involving strain is built. Another advantage of the distortable link is that it allows the full value of the van der Waals radius to be used in designing the atoms while in the Stuart models 293 where the valency angles are fixed it is necessary to reduce this radius by an arbitrary percentage (e.g.15 %) for otherwise no structures could be built in which there was even a small deviation from the normal bond angles or van der Waals radii. The use of atomic models for quantitative work is analogous to that of a calculating machine. However mechanically perfect the models may be any result obtained (e.g. in determinink the relative positions of two atoms imposed by a certain configuration) can only have a degree of accuracy corresponding to that of the data used in their design. For this reason it is a great advantage to be able to use models for which the nearest approach cor- responds to the minimal energy conditions pertaining in crystals since then any distortion of the valency bonds which is found in a configuration will be a measure of the degree of strain involved and the probability of its occurrence can be judged accordingly.In this paper some results will be given which were obtained by building models of dye and fibre molecules and considering the steric factors which are involved when they are bound together in the dyeing process. Examples were chosen to illustrate the possibilities of using such models and to show that results are sometimes obtained which are contrary to what has been assumed as the result 125 126 carbon. benzene benzene ring (Ca) carbonyl graphite naphthalene ring (Clo) tetrahedral hydrogen , bonded nitrogcn amide ,# STEREOCHEMICAL PROBLEMS I N DYEING of neglecting to use models or using inadequate models. In some cases the facts observed could have been obtained from fairly simple scale drawings or calcula- tions but in other cases the number of degrees of freedom involved in manipulating the large molecules is so high as to make calculation of the required results tedious or even impracticable.Correctness of the results obtained will depend on the suitability of thc data used in the design of the atomic models employed in building the molecules which are under consideration. MODELS usED.-Table 1 summarizes the values for the radii and bond angles used in designing the models of all the atomic species which were here employed. Some of these have already been described in part 1 and 2,19 4 while others were designed since. The design of the later models will be understood from the principles given in part.1 and the following notes. TABLE 1 .-DESCRIPTION OF ATOMIC MODELS USED IN THE INVESTIGATION atomic species covalent radii van der colour bond arrangement b $ ~ ~ ~ ~ ~ Waals radii black , ,I , I 9 aluminium S blue , white s. , yellow 120.0 1 single 2 partial double {e:: 6 single 2 single 1 double 3 partial double - 124 124 112 120.0 - 8 singlc 4 single 1 single 1 single 120.0 2 single 1 partial double 1 single 1 doublc 1 double 2 single 1 partial double 2 single (4 single sockets) double bond 0.695 (partial) 0.665 0.715 (partial) azo oxygen carbonyl , ethcr , negatively charged sulphur di-univalent , tctrahedral , Benzene ring (C~).-This is a block of hexagonal cross-section based on the 1-38 Apartial double bond length for benzene and having a press-stud socket mounted on each of its six sides.The design is such that when univalent atoms are attached to these sockets their positions will be those demanded by the co- valent radius of single-bonded carbon (0-77A). The height of the block normal to the benzene ring corresponds to 3.6A at its centre but thc edges are chamfered so that the height at the edges is only 3.308,. Benzene carbon.-This is a prism of equilateral-triangle cross-section two sockets are mounted on one face and one on each of the others. The model is designed in such a way that if six of them are linked together by alternate double and single links the resulting model will correspond in outline to the c6 block described above.(Making the section of the model an equilateral triangle has not involved any inaccuracy in the single and partial-double bond lengths but the lines passing through the links forming the ring do not pass through the “ nuclei ” which are 0-058 nearer the centre of the ring.) The alternate single and double links not only give the required stability to the ring but they also allow the various canonical forms to be represented and the building of quinonoid structures. “ Graphite” carbon.-This is a prism the section of which is an equilateral triangle designed to give a covalent radius of 0-71 5 A while the height corresponds to a van der Waals radius of 1.70A-thc values found in graphite.5 The socket 105.0 124.0 - - 100.0 109.5 109.5 - - - 1 *o 0.30 - 1.0 and 0.30 0.5 1-50 1 a70 - 1 *oo (compromise value) (A) single bond - 0.77 centre 0.77 0.77 1.65 1.80 0.77 0.77 0.70 0.53 (partial) 0.60 0.55 0.70 0.66 - 1-50 1 -40 1 -40 - (partial) 0.50 - 1 *04 1 -40 1 *85 1.85 CONMAR ROBINSON 127 arrangement is the same as in benzene carbon.In building fused-ring systems this model is used to represent any carbon shared by two or three six-membered rings while the benzene carbon model is used for all unshared carbons. Con- sequently the three possible combinations of the two models give three bond lengths of 1.38 1.415 and 1.43 A.The use of the two atoms is well illustrated in the model of Coronene shown in fig. 5d. In this hydrocarbon six six-membered rings are symmetrically arranged about a central ring. Robertson and White 6 found that the bond lengths in the central rings and those radiating from it are 1.43A while those round the pcriphery are either 1.41 or 1.38 8 according to whether or not a shared carbon atom is involved. The model therefore gives all the bond lengths correct to + 0.005 A. In models of less symmetrical hydrocarbons such as anthracene or pyrene the bond lengths are7 still all within 0.02 In ovalene the discrepancy between the model and the observed bond lengths is higher but here the model is in better agreement with the calculated values. In this investigation these two atom models have been used for building the condensed ring systems (other than naphthalene) in dyes.Naphthalene block (Clo).-The observed bond lengths in naphthalene 8 are not in accordance with theoretical expectations,g the bond joining the two shared carbon atoms having the same value as the two bonds parallel to it. A naphthalene block (Clo) was therefore designed based on the X-ray data of Abrahams Robertson and White.8 The angles of the block were made equal to 120" which was within one degree of the observed vzlues. The plan of the resulting block was a hexagon with two opposite sides longer than the other four. A socket is mounted on each of the four short sides while two are mounted on each of the longer sides. The model has six sides instead of eight as a result of the cutting back of the van der Waals radius to an extent determined by the length of the links.An accurate design demanded a V-shaped cut in the centre of each long side which being less than 0.2A deep could be eliminated for practical purposes. Negatively charged oxygen.-This resembles the double-bonded carbonyl oxygen model but is provided with only one socket while the surface i s cut back so as to give a covalent radius of 0-50 A instead of 0.66 A. When attached to the carbonyl carbon model it gives the correct value of the C-0 bond in a carboxyl ion. Tetrahedra( sulphur.-This was designed as a compromise atom to allow the building of sulphates sulphones and sulphonates. It is a regular tetrahedron with one socket on each face each giving a covalent radius of 1.00h;.Only data for sulphones were available. Combined with the previous model and tetra- hedral carbon it gives C - S = 1.77A and S - 0 = 1-50 compared to the values 1.80 A and 1.43 A for diinethyl sulphone. In this investigation it was used combined with three negatively charged oxygens to represent a sulphonic group. Strained rings.-With the link and collar system described in part 1 the maximum deviation of any bond angle from the normal is only 6". In order to extend the usefulness of the model the design of the brass link was modified so as to allow a deviation of 15" from the normal if the usual collar which provides the restoring force was omitted. By using these links with a sponge rubber collar which gave reasonable stability to the ring though no longer providing a restoring force it was possible to represent even four-membered rings when using the tetra- hedral carbon atom models.The use of this device in building the %- I / C-N/ \C- ring is shown in fig. 5a. The model of such a ring is necessarily imperfect since the valency bond directions no longer pass through the atom centres and the distribution of the deviation from the normal bond angles in a given ring cannot be expected to give the exact values. The device however will often provide a satisfactory first approximation and illustrates the adaptability of the linking STEREOCHEMICAL PROBLEMS IN DYEING 128 mechanism. Where a more accurate representation of a ring is required and the data are available the bond angles could be fixed at the correct value by wedges while bond lengths could be modified by using links of several lengths differing CH3 I say by 0.02A.Choice of models.-The planar amide nitrogen model already described in part 2 4 was used to build the -CONH- groups. This is a prism of triangular cross-section with a single socket mounted on each face. One face is cut back to give a covalent radius of 0.50 A so that when it is joined to a single-bonded carbon atom it gives a partial double-bond distance of 1-30 A. This model was also used to build a planar aromatic amino group instead of the pyramidal amino nitrogen described in part 1. The cut-back hydrogen atom with a cylindrical surface of 0.5A radius described in part 2 was used for all hydrogen bonds.The formation of the bond was judged to be possible if this surface could be brought into contact with the van der Waals radius of the oxygen or nitrogen atom considered. If table 1 is consulted no difficulty should be found in seeing how the atomic models were used as the choice was in each case determined by the valencies shown in the ordinary chemical formula. The standard link and collar were used throughout except when building the five-membered ring shown in fig. 5a. CELLuLosE.-The cellulose chain contains only pure single bonds and one would therefore expect to find close agreement between the dimensions of the model and those found for the actual molecule. The repeat distance in the model was 10.2 to 10.3A.The model draws attention to several facts which would not at once be obvious without it. Cellulose is frequently referred to as a comparatively rigid polymer chain. The model shows that a greater degree of flexibility is to be expected normal to the plane of the ring than in the plane of the ring. Movement in the plane of the ring is restricted by the steric hindrance of the hydroxyl groups. In spite of this a ring could be formed without strain containing 20 glucose rings and 3514 in diameter. However as fig. 2a shows intramolecular hydrogen bonds can be formed by bonding each primary alcohol group to the nearest secondary alcohol group in the next ring. The nature of the environment will decide whether or not such bonds are formed as their formation will have to compete with a tendency to bond to solvent or other cellulose molecules.Under conditions where these intramolecular bonds are formed they would still further restrict the flexing of the chain in the plane of the rings since very little bending is possible without breaking them. NormaZ to the plane of the ring the model was found to be much more flexible and it could be arranged in a circle some 15 A in diameter and containing 9 or 10 glucose rings (fig. 3). Flexing in this direction is not re- stricted by the presence of intra-chain hydrogen bonds which do not tend to separate when the molecule is bent in this way. This anisotropy of flexibility would be an important factor in determining the arrangements assumed by cellulose chains when subjected to orienting forces.Hermans 10 has suggested that the rings in cellulose might be able to undergo a boat-chair transformation which would contribute to the flexibility of the chains. The transformation cannot be carried out in the model without breaking the ring. This suggests that even if it is possible it would require considerable energy to overcome the steric hindrance. SUBSTANTIVE DYES.-Benzopurpurine 4B Q T N = N \ - L - \ ‘f CH3 >- /-< N=N/\/\ SOjNa SO3Na w NH2 CONMAR ROBINSON 129 may be chosen to illustrate some of the steric factors arising in direct cotton dyeing since this dye has been the subject of so many researches. Fig. 4dshows a modcl of the dye. In this thc benzene and naphthalene rings are joined by links giving single bonds.Since these bonds actually have partial double bond character the length of the model is not strictly accurate. The data for trans- azobenzene 11 shows that in the model the C-N-N-C distance is 0.16 A too long while in diphenyl 12 the bond joining the ring is 1-48 A instead of the single bond length of 1.5481. Conscquently the model of the dye would seem to be 0.38A too long which should be taken into account in considering how the dye fits on to a cellulose chain. The dye is shown in the photograph in its coplanar configuration the ability to assume such a planar configuration being as is well known a general property of direct cotton dyes. There is a small amount of steric hindrance from the hydrogens attached to the diphenyl group in the 2 2’ positions which in the model has caused the C-H bonds to be slightly distorted to an extent that can be accommodated by the flexible links.This is probably a good reprcsentation of reality since electron diffraction analysis has shown the separation of the 2 2’ hydrogen in the coplanar diphenyl molecule to be only 1.8481 instead of 2.0A as would be expected if there was no distortion showing that energy is required to force the molecule into coplanarity.12 The well-known effect of substituents such as methyl groups in the 2 2‘ positions destroying the substantivity by making it impossible for the molecule to take up a planar configuration is illustrated by the model of 2 2’ dimethyldiphenyl in fig. 4a in which it will be seen the methyl groups force the benzene rings considerably out of the coplanar position.The diazo groups may be arrangcd in one of two trans configurations (in the cis configuration the rings are not coplanar) as shown in fig. 4b and 4c. In one of these positions a hydrogen bond can be formed it while in the other position the N-H . . . N distance is too great for this to between the diazo group and the amino group which is in the ortho position to be possible. The resulting chelate ring would contribute to the coplanarity of the dye molecule and is shown formed in fig. 46 and 4d. -NH2 or -OH groups that could bond in this way are frequently in this position in azo dyes. The benzene and naphthalene rings and the diazo and amino groups would be all parts of one resonating system with the 7~ electrons in one plane so that both diazo and amino groups would be planar and coplanar with aromatic rings.It follows that the height of the azo and amino nitrogen atoms normal to the plane of the valency bonds should be the same as that of the benzene ring and not less as in the models. The dye will then be coplanar and of uniform thickness except for the bulky -SO3- groups which in the model has a greater height than the benzene ring. If the SO3- group is rotated so that two of the oxygens are parallel to the plane of the naphthalene rings the whole molecule can lie undistorted on a plane surface. THE ATTACHMENT OF THE AZO DYE TO THE CELLULOSE.-Fig. 2b shows model of Benzopurpurine 4B placed on that of the cellulose chain.The remarkable flatness of the cellulose molecule which allows the dye atoms to make contact with cellulose atoms at many points is brought out in the photograph. Attempts have been made to correlate the length of the cellulose repeat unit or multiples of it with the distance between groups which are capable of bonding to cellulose. It is however unlikely that there is any significance in such a relationship since as the model shows if a group (on a dye molecule) capable of forming a hydrogen bond is made to travel parallel to the long axis of the cellulose chain it is never in a position in which it cannot bond with one or other of the OH groups of the cellulose. This can be shown for groups that are either donors or acceptors of protons.Iiefcrence may here be made to attempts to estimate the number of hydrogen bonds formed between the dye molecule and the cellulose from the heat of dyeing. Willis Warwicker Standing and Urquhart conclude that thc heat of dycing of E STEREOCHEMICAL PROBLEMS I N DYEING 130 - 14 kcal/mole which they found for Chrysophenine G and cellulose corresponds to the heat of formation of two hydrogen bonds for each molecule. It should however bc remembered that the heat of dyeing so calcuIated must correspond to the diference between the heat of formation of the bonds which are formed and of any bonds such as cellulose-water or dye-water bonds which must be broken before the dyeing can take place. It would seem therefore that Willis Warwicker Standing and Urquhart's results show that there are forces in addition to those arising from the two hydrogen bonds which can be formed with the diazo groups.Such additional forces seem to be connected with the r electron system which in dircct cotton dyes runs through the aromatic rings and the groups connecting them along the whole length of the molecule. This is borne out by the sub- stantivity of certain vegetable dycs which are characterized by a chain of con- jugated double bonds (bixin etc.14) and of the leuco compounds of anthroquinone vat dyes whcre hydrogen bonding through polar groups can make little or no contribution to the substantivity. Whatever the exact nature of the binding forces which seem to be associated with the resonating system it is of importance to notice that with typical direct dyes the models show that not only the group capable of hydrogen bonding but the entire surface of the dye molecules can comc in contact with the surface of thc cellulose chain.An intcresting exampic of a condensed ring system in a vat dye is given by Calcdon Jade Green 16.17 (dimcthoxydibenzanthrone). A model of the leuco derivative is shown in fig. 5c. The condensed ring system was built with the bcnzeiie and graphitc carbon atoms using graphite carbon for all atoms shared by two or three rings as already described for the coronene model. A drawing of the planar molecule 15 shows considerable overlapping of the van der Wads radii of the methoxy groups (only one methoxy group has been attached to the model as shown in fig.5c). The resonance energy tending to keep the molecule coplanar incrcases with the number of rings in the condensed ring system and therefore would be considerable in such a molecule and thcre would be a marked tendency for the coplanar configuration to be maintained by distortion of bond angles and the van der Waals radii of the inethoxy groups. However if the second methoxy group is attached and the model distorted out of the plane is laid along the cellulose chain it is found that all the carbon atoms can be arranged on an uiidulating surface in which the carbon atoms are little removed from a common plane and which can be followed by the cellulose chain without straining it. Actually since the model allows no distortion of the van der Waals radii and distortion of bond angles would probably be greatcr than the collar and link arrangement allows (6" from the normal) the dye molecule would probably be considcrably more planar than the modcl suggests.Fig. 5b shows a model of Chlorantine Fast Green BLL. This dye is cited by Venkataraman 15 as an example of one which is far from linear. In the model the dye is posed in a configuration which is considerably more linear than that shown by Venkataraman and it will be seen that four out of six of the aromatic nuclei lie on one line with a naphthalene and a benzene nucleus on either side of it (the latter is the only part of the molecule which does not lie in the common plane). There are four intramolecular hydrogen bonds which contribute to the coplanarity of the greater part of this configuration.is known to contribute to sub- AZOIC DYEs.-The amide group -CONH- stantivity in a dye molecule containing it and it is somctimes depicted in the cis configuration with both the -NH- and -CN- groups hydrogen bonded to cellulose.16 Vickerstaff accepts such an arrangement 17 for the method of attachment of azoic dyes to cellulose when referring to the sign of the dichroism observed by Morton 18 in ccllulose dyed with certain dyes showing it when writing the formula in the ordinary conventional manner (fig. 1). Fig. 4e shows a model of the corresponding configuration in which the steric hindrancc was found to be so great that it was impossible to attach the OH group FIG. 2a.-Cellulose straight chain. 2h.-Benzopurpurine 4B on cellulose chain FIG.3.-Cellulose curved in plane normal to rings. [To face p. 130 FIG. 4a.-2 :2”-dimethyl diphenyl. 4h.-trans-diazo group bonded to ortho-amino group. 4c.-trans-diazo group in position where bond is impossible. 4d.-Benzopurpurine 4B. 4e.-cis-configuration of amide group in azoic dye. 4f-trans-configuration of amide group in azoic dye. FIG. 5a.-Solophenyl Yellow FFL. Sb.-Chlordntine Fast Green BLL. 5c.-Caledon Jade Green. 5d.-Coronene. 5e.-Duranol Red 2B. FIG. 6a.-Copolymer of L-leucine and ~-fi-phenylalanine folded as a 3.7 residue Pauling helix. Benzopurpurine 4B shown for comparison in size. 66.-Copolymer of L-leucine and L-/3-phenylalanine in extended /3 configuration. CONMAR ROBINSON -!! P H- lose (Vickerstaff).o=ci3-N=Nu to the naphthalene ring and two of the hydrogen atoms on the benzene ring. The high degree of distortion that would be required by this configuration seems un- likely and suggests that the attachment may not be of this nature (similar steric hindrance will arise when forming the cis configuration in any molecule where any two aromatic rings are attached to an amide group). Fig. 4f shows the corresponding trans con- figuration. Here the NH group can hydrogen bond to the OH group which can also form a bond with the diazo group. It would then apparently be pos- sible for these three groups each to form a bond with an OH group of the cellulose chain. In this case the benzene and naphthalene rings would lie flat on the cellulose chain and parallel to its long axis an arrangement which would also be in agree- ment with the nature of the dichroism since the rest of the conjugated chain would be at right-angles to the cellulose chain as Morton postulated.Fig. 5e shows a model of Duranol Red 2B re- ferred to by Bamford Boulton Hanby and Ward.20 Hydrogen bonds are shown formed between the NH2 and OM groups and the quinonoid oxygens. 131 s o1 FIG. 1.-Azoic dye on cellu- THE DYEING OF SYNTHETIC POLYPEPTIDES.-when dealing with the polypeptide chain in either proteins or synthetic polypeptides we have to consider the dye molecule in relation to a polymer chain which may be folded in more than one way and in which the attached side chain may assume different configurations.The steric problems therefore become much more complicated and for this reason the models are all the more valuable since without them it may be extremely difficult to decide whether or not there is a configuration which will fulfil certain conditions. The use of the models in studying the polypeptide chain has already been described.4319 We shall here consider the dyeing of the 1 1 Copolymer of DL-P-phenylalanine and m-leucine which has been studied by Bamford Boulton Hanby and Ward20 It is of interest to see from models whether steric hindrance of the side chain could prevent a dye molecule from coming into contact with the backbone of the polypeptide chain. A model of the 1 1 copolymer was built in which the leucine and phenylalanine residues were arranged alternately along the chain (this was of course an arbitrary choice for the amino-acid arrangement).The model was built as an L instead of a DL configuration. In fig. 6b the polymer is shown in the p configuration. It will be seen that it would be possible for a dye molecule to lie parallel to the backbone and in contact with it (the model of Benzopurpurine 4B shown above it allows the spatial arrangement to be visualized). This of course does not necessarily mean that a dye molecule will reach the backbone since the penetration of the dye may be prevented by intermolecular forces. In fig. 6a the same copolymer is shown folded as 3.7 residue Pauling helix 21 a fold which may form the basis of the a fold in some polypeptides.The alternate leucine and phenylalanine side chains now appear as two helices as on a two-start screw. Even if a dye is chosen whose greatest width is no more than the diameter of a benzene ring the space between these side-chain helices would not allow it to lie flat on the backbone. This is so even if the side chains are pushed out of their symmetrical positions as much as the model allows. On the other hand the end of a dye molecule could be inserted between the side-chains. It will be noticed that the position of the side chains could not prevent water molecules reaching the backbone in either the a or the configurations of the polypeptides. For any method of attachment other than to end groups the model of the Pauling helix would not lead one to expect the close similarity in the dyeing properties of the a and ,8 fold found by Bamford Boulton Hanby and Ward.It is however 132 by no means certain that the Pauling helix is the fold involved in the dyeing of the cc helix. It should be remembered that the dyeing is probably largely confined to the isotropic regions where the polypeptide chains are not necessarily in the same configuration as in the crystal and further that its configuration may well be modified by contact with the dye. In the 27b fold,4 for instance the backbone would be exposed to the dye in much the same way as in the /? configuration. Thanks are due to Mr. J. E. Goodwin for the photography and his assistance in assembling the models. I am grateful to Mr. E. J. Ambrose for introducing the use of the more flexible link in strained rings and to Dr.G. S . Park for sugges- tions leading to the design of the negative oxygen and tetrahedral sulphur models. ADSORPTION OF DYES BY CRYSTALS 1 Hartley and Robinson Trans. Faruday SOC. 1952 48 847. 2 Stuart 2. physik. Chem. B 1934 27 350. 3 Briegleb Chem. Forschung. 1950 1 642. 4 Robinson and Ambrose Trans. Faraduy SOC. 1952 48 854. 5 Pauling The Nature of the Chemical Bond (Cornell University Press New York 1945). 6 Robertson and White J. Chem. SOC. 1945 607. 12 Karle and Brockway J. Amer. Chem. SOC. 1944 66 1974. 7Robertson Proc. Roy. SOC. A 1951 207 101. 8 Abrahams Robertson and White Acra Cryst. 1949,2,233. 9 Daudel and Daudel J. Chem. Physics 1948 16 630. 10 Hermans Physics and Chemistry of Cellulose Fibres (Elsevier Publishing Co.Inc. 11 Lange Robertson and Woodward Proc. Roy. SOC. A 1939,171 398. 1949). 13 Willis Warwicker Standing and Urquhart Trans. Furaduy SOC. 1945 41 506. 14 Shirm J. prakt. Chem. 1935 144 69. 15 Venkataraman The Chemistry of Synthetic Dyes vol. 2 (Academic Press Inc. New Y ork) . 16 Krzikalla and Eistert J. prakt. Chem. 1935 143 50. 17 Vickerstaff The Physical Chemistry of Dyeing (Oliver and Boyd London 1950). 18 Morton J. SOC. Dyers Col. 1946 62 272. 19 Robinson Nature 1953 172,27. 20 Bamford Boulton Hanby and Ward this Discussion 1953. 21 Pauling Corey and Branson Proc. Nat. Acad. Sci. 1951 37 205. ATOMIC MODELS PART 3.-SOME STEREOCHEMICAL PROBLEMS IN DYEING BY CONMAR ROBINSON Courtaulds Limited Research Laboratory Maidenhead Berks Received 22nd July 1953 Models of dye molecules and of cellulose and polypeptide chains have been built with the type of atomic model previously described by Hartley and Robinson.Their use in investigating stereochemical problems related to dyeing has been illustrated. The anisotropic flexibility of the cellulose chain has been demonstrated. The shape of a number of dye molecules in relation to the shape of the cellulose chain has been discussed and also the part played by intra- and intermolecular hydrogen bonds in both dyes and cellulose. The models suggest that contrary to the usual assumptions hydrogen bonding to cellulose can take place irrespective of the position of those groups in the dye molecule which are capable of forming such bonds.When an amide group links two aromatic rings together it appears unlikely that the group can be in the cis configuration when attached to cellulose as this configuration involves great steric hindrance. The possible part played by steric hindrance in the dyeing of a synthetic polypeptide is discussed. Although atomic models have frequently been used to investigate stereochemical problems in dyeing their usefulness has been limited by shortcomings in the designs of the models available. Recently Hartley and Robinson 1 have described a development of the Stuart type of model. In these the atoms are linked to-gether by a combination of link and collar which allows the valency bond to be distorted a few degrees from the normal when strained but which provides a restoring force which insures that the valency angle shall have its normal value when the model is not under strain.This linking mechanism not only allows molecules to be built in which the valency angles are known to deviate from the normal values but also allows an estimate of the distortion involved when a model of a configuration involving strain is built. Another advantage of the distortable link is that it allows the full value of the van der Waals radius to be used in designing the atoms while in the Stuart models 293 where the valency angles are fixed it is necessary to reduce this radius by an arbitrary percentage (e.g. 15 %) for otherwise no structures could be built in which there was even a small deviation from the normal bond angles or van der Waals radii.The use of atomic models for quantitative work is analogous to that of a calculating machine. However mechanically perfect the models may be any result obtained (e.g. in determinink the relative positions of two atoms imposed by a certain configuration) can only have a degree of accuracy corresponding to that of the data used in their design. For this reason it is a great advantage to be able to use models for which the nearest approach cor-responds to the minimal energy conditions pertaining in crystals since then any distortion of the valency bonds which is found in a configuration will be a measure of the degree of strain involved and the probability of its occurrence can be judged accordingly. In this paper some results will be given which were obtained by building models of dye and fibre molecules and considering the steric factors which are involved when they are bound together in the dyeing process.Examples were chosen to illustrate the possibilities of using such models and to show that results are sometimes obtained which are contrary to what has been assumed as the result 12 126 STEREOCHEMICAL PROBLEMS I N DYEING of neglecting to use models or using inadequate models. In some cases the facts observed could have been obtained from fairly simple scale drawings or calcula-tions but in other cases the number of degrees of freedom involved in manipulating the large molecules is so high as to make calculation of the required results tedious or even impracticable. Correctness of the results obtained will depend on the suitability of thc data used in the design of the atomic models employed in building the molecules which are under consideration.MODELS usED.-Table 1 summarizes the values for the radii and bond angles used in designing the models of all the atomic species which were here employed. Some of these have already been described in part 1 and 2,19 4 while others were designed since. The design of the later models will be understood from the principles given in part. 1 and the following notes. TABLE 1 .-DESCRIPTION OF ATOMIC MODELS USED IN THE INVESTIGATION atomic species carbon. benzene benzene ring (Ca) carbonyl graphite naphthalene ring (Clo) tetrahedral hydrogen , bonded nitrogcn amide ,# azo oxygen carbonyl , ethcr , negatively charged sulphur di-univalent , tctrahedral van der colour bond arrangement b $ ~ ~ ~ ~ ~ Waals radii (A) black 1 single 120.0 -2 partial double centre , 6 single - {e::: 1.65 ,I 2 single 124 124 112 1.80 1 double , 3 partial double 120.0 1 a70 I 8 singlc 9 4 single aluminium 1 single S 1 single blue 2 single, 1 partial double , 1 single 1 doublc white 1 double s.2 single , 1 partial double - -109.5 - - 1 *o - 1.0 and 0.5 120.0 1-50 124.0 1-50 - 1 -40 105.0 1 -40 - 1 -40 yellow 2 single 100.0 1 *85 , (4 single sockets) 109.5 1.85 covalent radii single bond 0.77 0.77 0.77 0.77 0.77 0.30 0.30 0.70 0.70 0.66 --1 *04 1 *oo double bond 0.695 (partial) 0.665 0.715 (partial) 0.53 (partial) 0.60 0.55 0.50 (partial) (compromise value) --Benzene ring (C~).-This is a block of hexagonal cross-section based on the 1-38 Apartial double bond length for benzene and having a press-stud socket mounted on each of its six sides.The design is such that when univalent atoms are attached to these sockets their positions will be those demanded by the co-valent radius of single-bonded carbon (0-77A). The height of the block normal to the benzene ring corresponds to 3.6A at its centre but thc edges are chamfered so that the height at the edges is only 3.308,. Benzene carbon.-This is a prism of equilateral-triangle cross-section two sockets are mounted on one face and one on each of the others. The model is designed in such a way that if six of them are linked together by alternate double and single links the resulting model will correspond in outline to the c6 block described above.(Making the section of the model an equilateral triangle has not involved any inaccuracy in the single and partial-double bond lengths but the lines passing through the links forming the ring do not pass through the “ nuclei ” which are 0-058 nearer the centre of the ring.) The alternate single and double links not only give the required stability to the ring but they also allow the various canonical forms to be represented and the building of quinonoid structures. “ Graphite” carbon.-This is a prism the section of which is an equilateral triangle designed to give a covalent radius of 0-71 5 A while the height corresponds to a van der Waals radius of 1.70A-thc values found in graphite.5 The socke CONMAR ROBINSON 127 arrangement is the same as in benzene carbon.In building fused-ring systems, this model is used to represent any carbon shared by two or three six-membered rings while the benzene carbon model is used for all unshared carbons. Con-sequently the three possible combinations of the two models give three bond lengths of 1.38 1.415 and 1.43 A. The use of the two atoms is well illustrated in the model of Coronene shown in fig. 5d. In this hydrocarbon six six-membered rings are symmetrically arranged about a central ring. Robertson and White 6 found that the bond lengths in the central rings and those radiating from it are 1.43A while those round the pcriphery are either 1.41 or 1.38 8 according to whether or not a shared carbon atom is involved.The model therefore gives all the bond lengths correct to + 0.005 A. In models of less symmetrical hydrocarbons, such as anthracene or pyrene the bond lengths are7 still all within 0.02 In ovalene the discrepancy between the model and the observed bond lengths is higher but here the model is in better agreement with the calculated values. In this investigation these two atom models have been used for building the condensed ring systems (other than naphthalene) in dyes. Naphthalene block (Clo).-The observed bond lengths in naphthalene 8 are not in accordance with theoretical expectations,g the bond joining the two shared carbon atoms having the same value as the two bonds parallel to it.A naphthalene block (Clo) was therefore designed based on the X-ray data of Abrahams Robertson and White.8 The angles of the block were made equal to 120" which was within one degree of the observed vzlues. The plan of the resulting block was a hexagon with two opposite sides longer than the other four. A socket is mounted on each of the four short sides while two are mounted on each of the longer sides. The model has six sides instead of eight as a result of the cutting back of the van der Waals radius to an extent determined by the length of the links. An accurate design demanded a V-shaped cut in the centre of each long side which being less than 0.2A deep could be eliminated for practical purposes. Negatively charged oxygen.-This resembles the double-bonded carbonyl oxygen model but is provided with only one socket while the surface i s cut back so as to give a covalent radius of 0-50 A instead of 0.66 A.When attached to the carbonyl carbon model it gives the correct value of the C-0 bond in a carboxyl ion. Tetrahedra( sulphur.-This was designed as a compromise atom to allow the building of sulphates sulphones and sulphonates. It is a regular tetrahedron, with one socket on each face each giving a covalent radius of 1.00h;. Only data for sulphones were available. Combined with the previous model and tetra-hedral carbon it gives C - S = 1.77A and S - 0 = 1-50 compared to the values 1.80 A and 1.43 A for diinethyl sulphone. In this investigation it was used combined with three negatively charged oxygens to represent a sulphonic group.Strained rings.-With the link and collar system described in part 1 the maximum deviation of any bond angle from the normal is only 6". In order to extend the usefulness of the model the design of the brass link was modified so as to allow a deviation of 15" from the normal if the usual collar which provides the restoring force was omitted. By using these links with a sponge rubber collar, which gave reasonable stability to the ring though no longer providing a restoring force it was possible to represent even four-membered rings when using the tetra-hedral carbon atom models. The use of this device in building the ring is shown in fig. 5a. The model of such a ring is necessarily imperfect since the valency bond directions no longer pass through the atom centres and the distribution of the deviation from the normal bond angles in a given ring cannot be expected to give the exact values.The device however will often provide a satisfactory first approximation and illustrates the adaptability of the linking %- \C-I / C-N 128 STEREOCHEMICAL PROBLEMS IN DYEING mechanism. Where a more accurate representation of a ring is required and the data are available the bond angles could be fixed at the correct value by wedges, while bond lengths could be modified by using links of several lengths differing, say by 0.02A. Choice of models.-The planar amide nitrogen model already described in part 2 4 was used to build the -CONH- groups. This is a prism of triangular cross-section with a single socket mounted on each face.One face is cut back to give a covalent radius of 0.50 A so that when it is joined to a single-bonded carbon atom it gives a partial double-bond distance of 1-30 A. This model was also used to build a planar aromatic amino group instead of the pyramidal amino nitrogen described in part 1. The cut-back hydrogen atom with a cylindrical surface of 0.5A radius described in part 2 was used for all hydrogen bonds. The formation of the bond was judged to be possible if this surface could be brought into contact with the van der Waals radius of the oxygen or nitrogen atom considered. If table 1 is consulted no difficulty should be found in seeing how the atomic models were used as the choice was in each case determined by the valencies shown in the ordinary chemical formula.The standard link and collar were used throughout except when building the five-membered ring shown in fig. 5a. CELLuLosE.-The cellulose chain contains only pure single bonds and one would therefore expect to find close agreement between the dimensions of the model and those found for the actual molecule. The repeat distance in the model was 10.2 to 10.3A. The model draws attention to several facts which would not at once be obvious without it. Cellulose is frequently referred to as a comparatively rigid polymer chain. The model shows that a greater degree of flexibility is to be expected normal to the plane of the ring than in the plane of the ring. Movement in the plane of the ring is restricted by the steric hindrance of the hydroxyl groups.In spite of this a ring could be formed without strain containing 20 glucose rings and 3514 in diameter. However as fig. 2a shows intramolecular hydrogen bonds can be formed by bonding each primary alcohol group to the nearest secondary alcohol group in the next ring. The nature of the environment will decide whether or not such bonds are formed as their formation will have to compete with a tendency to bond to solvent or other cellulose molecules. Under conditions where these intramolecular bonds are formed they would still further restrict the flexing of the chain in the plane of the rings since very little bending is possible without breaking them. NormaZ to the plane of the ring the model was found to be much more flexible and it could be arranged in a circle some 15 A in diameter and containing 9 or 10 glucose rings (fig.3). Flexing in this direction is not re-stricted by the presence of intra-chain hydrogen bonds which do not tend to separate when the molecule is bent in this way. This anisotropy of flexibility would be an important factor in determining the arrangements assumed by cellulose chains when subjected to orienting forces. Hermans 10 has suggested that the rings in cellulose might be able to undergo a boat-chair transformation which would contribute to the flexibility of the chains. The transformation cannot be carried out in the model without breaking the ring. This suggests that even if it is possible it would require considerable energy to overcome the steric hindrance. SUBSTANTIVE DYES.-Benzopurpurine 4B NH2 I CH3 CH3 >- /-< N=N/\/\ w Q T N = N \ - L - \ ‘f SO3Na SOjN CONMAR ROBINSON 129 may be chosen to illustrate some of the steric factors arising in direct cotton dyeing since this dye has been the subject of so many researches.Fig. 4dshows a modcl of the dye. In this thc benzene and naphthalene rings are joined by links giving single bonds. Since these bonds actually have partial double bond character the length of the model is not strictly accurate. The data for trans-azobenzene 11 shows that in the model the C-N-N-C distance is 0.16 A too long while in diphenyl 12 the bond joining the ring is 1-48 A instead of the single bond length of 1.5481. Conscquently the model of the dye would seem to be 0.38A too long which should be taken into account in considering how the dye fits on to a cellulose chain.The dye is shown in the photograph in its coplanar configuration the ability to assume such a planar configuration being as is well known a general property of direct cotton dyes. There is a small amount of steric hindrance from the hydrogens attached to the diphenyl group in the 2 2’ positions which in the model has caused the C-H bonds to be slightly distorted to an extent that can be accommodated by the flexible links. This is probably a good reprcsentation of reality since electron diffraction analysis has shown the separation of the 2 2’ hydrogen in the coplanar diphenyl molecule to be only 1.8481 instead of 2.0A as would be expected if there was no distortion showing that energy is required to force the molecule into coplanarity.12 The well-known effect of substituents such as methyl groups in the 2 2‘ positions destroying the substantivity by making it impossible for the molecule to take up a planar configuration is illustrated by the model of 2 2’ dimethyldiphenyl in fig.4a, in which it will be seen the methyl groups force the benzene rings considerably out of the coplanar position. The diazo groups may be arrangcd in one of two trans configurations (in the cis configuration the rings are not coplanar) as shown in fig. 4b and 4c. In one of these positions a hydrogen bond can be formed between the diazo group and the amino group which is in the ortho position to it while in the other position the N-H . . . N distance is too great for this to be possible.The resulting chelate ring would contribute to the coplanarity of the dye molecule and is shown formed in fig. 46 and 4d. -NH2 or -OH groups that could bond in this way are frequently in this position in azo dyes. The benzene and naphthalene rings and the diazo and amino groups would be all parts of one resonating system with the 7~ electrons in one plane so that both diazo and amino groups would be planar and coplanar with aromatic rings. It follows that the height of the azo and amino nitrogen atoms normal to the plane of the valency bonds should be the same as that of the benzene ring and not less as in the models. The dye will then be coplanar and of uniform thickness except for the bulky -SO3- groups which in the model has a greater height than the benzene ring.If the SO3- group is rotated so that two of the oxygens are parallel to the plane of the naphthalene rings the whole molecule can lie undistorted on a plane surface. of Benzopurpurine 4B placed on that of the cellulose chain. The remarkable flatness of the cellulose molecule which allows the dye atoms to make contact with cellulose atoms at many points is brought out in the photograph. Attempts have been made to correlate the length of the cellulose repeat unit or multiples of it with the distance between groups which are capable of bonding to cellulose. It is however unlikely that there is any significance in such a relationship since, as the model shows if a group (on a dye molecule) capable of forming a hydrogen bond is made to travel parallel to the long axis of the cellulose chain it is never in a position in which it cannot bond with one or other of the OH groups of the cellulose.This can be shown for groups that are either donors or acceptors of protons. Iiefcrence may here be made to attempts to estimate the number of hydrogen bonds formed between the dye molecule and the cellulose from the heat of dyeing. Willis Warwicker Standing and Urquhart conclude that thc heat of dycing of THE ATTACHMENT OF THE AZO DYE TO THE CELLULOSE.-Fig. 2b shows model 130 STEREOCHEMICAL PROBLEMS I N DYEING - 14 kcal/mole which they found for Chrysophenine G and cellulose corresponds to the heat of formation of two hydrogen bonds for each molecule. It should, however bc remembered that the heat of dyeing so calcuIated must correspond to the diference between the heat of formation of the bonds which are formed and of any bonds such as cellulose-water or dye-water bonds which must be broken before the dyeing can take place.It would seem therefore that Willis Warwicker, Standing and Urquhart's results show that there are forces in addition to those arising from the two hydrogen bonds which can be formed with the diazo groups. Such additional forces seem to be connected with the r electron system which in dircct cotton dyes runs through the aromatic rings and the groups connecting them along the whole length of the molecule. This is borne out by the sub-stantivity of certain vegetable dycs which are characterized by a chain of con-jugated double bonds (bixin etc.14) and of the leuco compounds of anthroquinone vat dyes whcre hydrogen bonding through polar groups can make little or no contribution to the substantivity.Whatever the exact nature of the binding forces which seem to be associated with the resonating system it is of importance to notice that with typical direct dyes the models show that not only the group capable of hydrogen bonding but the entire surface of the dye molecules can comc in contact with the surface of thc cellulose chain. An intcresting exampic of a condensed ring system in a vat dye is given by Calcdon Jade Green 16.17 (dimcthoxydibenzanthrone). A model of the leuco derivative is shown in fig. 5c. The condensed ring system was built with the bcnzeiie and graphitc carbon atoms using graphite carbon for all atoms shared by two or three rings as already described for the coronene model.A drawing of the planar molecule 15 shows considerable overlapping of the van der Wads radii of the methoxy groups (only one methoxy group has been attached to the model as shown in fig. 5c). The resonance energy tending to keep the molecule coplanar incrcases with the number of rings in the condensed ring system and therefore would be considerable in such a molecule and thcre would be a marked tendency for the coplanar configuration to be maintained by distortion of bond angles and the van der Waals radii of the inethoxy groups. However if the second methoxy group is attached and the model distorted out of the plane is laid along the cellulose chain it is found that all the carbon atoms can be arranged on an uiidulating surface in which the carbon atoms are little removed from a common plane and which can be followed by the cellulose chain without straining it.Actually since the model allows no distortion of the van der Waals radii and distortion of bond angles would probably be greatcr than the collar and link arrangement allows (6" from the normal) the dye molecule would probably be considcrably more planar than the modcl suggests. Fig. 5b shows a model of Chlorantine Fast Green BLL. This dye is cited by Venkataraman 15 as an example of one which is far from linear. In the model the dye is posed in a configuration which is considerably more linear than that shown by Venkataraman and it will be seen that four out of six of the aromatic nuclei lie on one line with a naphthalene and a benzene nucleus on either side of it (the latter is the only part of the molecule which does not lie in the common plane).There are four intramolecular hydrogen bonds which contribute to the coplanarity of the greater part of this configuration. AZOIC DYEs.-The amide group -CONH- is known to contribute to sub-stantivity in a dye molecule containing it and it is somctimes depicted in the cis configuration with both the -NH- and -CN- groups hydrogen bonded to cellulose.16 Vickerstaff accepts such an arrangement 17 for the method of attachment of azoic dyes to cellulose when referring to the sign of the dichroism observed by Morton 18 in ccllulose dyed with certain dyes showing it when writing the formula in the ordinary conventional manner (fig.1). Fig. 4e shows a model of the corresponding configuration in which the steric hindrancc was found to be so great that it was impossible to attach the OH grou FIG. 2a.-Cellulose straight chain. 2h.-Benzopurpurine 4B on cellulose chain FIG. 3.-Cellulose curved in plane normal to rings. [To face p. 13 FIG. 4a.-2 :2”-dimethyl diphenyl. 4h.-trans-diazo group bonded to ortho-amino group. 4c.-trans-diazo group in position where bond is impossible. 4d.-Benzopurpurine 4B. 4e.-cis-configuration of amide group in azoic dye. 4f-trans-configuration of amide group in azoic dye FIG. 5a.-Solophenyl Yellow FFL. Sb.-Chlordntine Fast Green BLL. 5c.-Caledon Jade Green. 5d.-Coronene. 5e.-Duranol Red 2B FIG. 6a.-Copolymer of L-leucine and ~-fi-phenylalanine folded as a 3.7 residue Pauling helix.Benzopurpurine 4B shown for comparison in size. 66.-Copolymer of L-leucine and L-/3-phenylalanine in extended /3 configuration CONMAR ROBINSON 131 to the naphthalene ring and two of the hydrogen atoms on the benzene ring. The high degree of distortion that would be required by this configuration seems un-likely and suggests that the attachment may not be of this nature (similar steric hindrance will arise when forming the cis configuration in any molecule where any two aromatic rings are attached to an amide group). Fig. 4f shows the corresponding trans con-figuration. Here the NH group can hydrogen bond to the OH group which can also form a bond with the diazo group. It would then apparently be pos-sible for these three groups each to form a bond with an OH group of the cellulose chain.In this case the benzene and naphthalene rings would lie flat on the cellulose chain and parallel to its long axis an arrangement which would also be in agree-ment with the nature of the dichroism since the rest of the conjugated chain would be at right-angles to the cellulose chain as Morton postulated. Fig. 5e shows a model of Duranol Red 2B re-ferred to by Bamford Boulton Hanby and Ward.20 Hydrogen bonds are shown formed between the NH2 and OM groups and the quinonoid oxygens. THE DYEING OF SYNTHETIC POLYPEPTIDES.-when dealing with the polypeptide chain in either proteins or synthetic polypeptides we have to consider the dye molecule in relation to a polymer chain which may be folded in more than one way and in which the attached side chain may assume different configurations.The steric problems therefore become much more complicated and for this reason the models are all the more valuable since without them it may be extremely difficult to decide whether or not there is a configuration which will fulfil certain conditions. The use of the models in studying the polypeptide chain has already been described.4319 We shall here consider the dyeing of the 1 1 Copolymer of DL-P-phenylalanine and m-leucine which has been studied by Bamford Boulton Hanby and Ward20 It is of interest to see from models whether steric hindrance of the side chain could prevent a dye molecule from coming into contact with the backbone of the polypeptide chain.A model of the 1 1 copolymer was built in which the leucine and phenylalanine residues were arranged alternately along the chain (this was, of course an arbitrary choice for the amino-acid arrangement). The model was built as an L instead of a DL configuration. In fig. 6b the polymer is shown in the p configuration. It will be seen that it would be possible for a dye molecule to lie parallel to the backbone and in contact with it (the model of Benzopurpurine 4B shown above it allows the spatial arrangement to be visualized). This of course does not necessarily mean that a dye molecule will reach the backbone since the penetration of the dye may be prevented by intermolecular forces. In fig. 6a the same copolymer is shown folded as 3.7 residue Pauling helix 21 a fold which may form the basis of the a fold in some polypeptides.The alternate leucine and phenylalanine side chains now appear as two helices as on a two-start screw. Even if a dye is chosen whose greatest width is no more than the diameter of a benzene ring the space between these side-chain helices would not allow it to lie flat on the backbone. This is so even if the side chains are pushed out of their symmetrical positions as much as the model allows. On the other hand the end of a dye molecule could be inserted between the side-chains. It will be noticed that the position of the side chains could not prevent water molecules reaching the backbone in either the a or the For any method of attachment other than to end groups the model of the Pauling helix would not lead one to expect the close similarity in the dyeing properties of the a and ,8 fold found by Bamford Boulton Hanby and Ward.It is however, P H-o=ci3-N=Nu lose (Vickerstaff). FIG. 1.-Azoic dye on cellu- s o1 -!! configurations of the polypeptides 132 ADSORPTION OF DYES BY CRYSTALS by no means certain that the Pauling helix is the fold involved in the dyeing of the cc helix. It should be remembered that the dyeing is probably largely confined to the isotropic regions where the polypeptide chains are not necessarily in the same configuration as in the crystal and further that its configuration may well be modified by contact with the dye. In the 27b fold,4 for instance the backbone would be exposed to the dye in much the same way as in the /? configuration. Thanks are due to Mr. J. E. Goodwin for the photography and his assistance in assembling the models. I am grateful to Mr. E. J. Ambrose for introducing the use of the more flexible link in strained rings and to Dr. G. S . Park for sugges-tions leading to the design of the negative oxygen and tetrahedral sulphur models. 1 Hartley and Robinson Trans. Faruday SOC. 1952 48 847. 2 Stuart 2. physik. Chem. B 1934 27 350. 3 Briegleb Chem. Forschung. 1950 1 642. 4 Robinson and Ambrose Trans. Faraduy SOC. 1952 48 854. 5 Pauling The Nature of the Chemical Bond (Cornell University Press New York, 6 Robertson and White J. Chem. SOC. 1945 607. 7Robertson Proc. Roy. SOC. A 1951 207 101. 8 Abrahams Robertson and White Acra Cryst. 1949,2,233. 9 Daudel and Daudel J. Chem. Physics 1948 16 630. 1945). 10 Hermans Physics and Chemistry of Cellulose Fibres (Elsevier Publishing Co. Inc., 11 Lange Robertson and Woodward Proc. Roy. SOC. A 1939,171 398. 12 Karle and Brockway J. Amer. Chem. SOC. 1944 66 1974. 13 Willis Warwicker Standing and Urquhart Trans. Furaduy SOC. 1945 41 506. 14 Shirm J. prakt. Chem. 1935 144 69. 15 Venkataraman The Chemistry of Synthetic Dyes vol. 2 (Academic Press Inc. New 16 Krzikalla and Eistert J. prakt. Chem. 1935 143 50. 17 Vickerstaff The Physical Chemistry of Dyeing (Oliver and Boyd London 1950). 18 Morton J. SOC. Dyers Col. 1946 62 272. 19 Robinson Nature 1953 172,27. 20 Bamford Boulton Hanby and Ward this Discussion 1953. 21 Pauling Corey and Branson Proc. Nat. Acad. Sci. 1951 37 205. 1949). Y ork)

ISSN:0366-9033    

DOI:10.1039/DF9541600125

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

132 ADSORPTION OF DYES BY CRYSTALS THE ADSORPTION OF DYES BY CRYSTALS BY J. WHETSTONE Imperial Chemical Industries, Ltd., Research Dept., Nobel Division, Stevenston, Ayrshire Received 18th June, 1953 Explanations of the crystal habit modifying powers of certain dyes have usually depended on the adsorption, by means specified or unspecified, of the dye molecules by the growing crystal. The present work has confirmed the importance of dye adsorption in crystal habit modification phenomena. Studies of modified crystals in which dye adsorptions, followed by overgrowth of the dye molecules, have occurred to give pleo- chroic dye inclusions have indicated, however, that adsorption is not necessarily on the habit modified plane. More frequently it is perpendicular to the modified face of the crystal, which is very reasonable if modern views on the layerwise growth processes of crystal faces are accepted.It was assumed that the polar groups of dye molecules were responsible for the ad- sorption of dyes by growing crystals, and a considerable weight of evidence has been ob- tained to support the view that adsorption is due to a close similarity in pattern between the polar groups in a dye molecule and the ions of a crystal plane. The type of crystalJ. WHETSTONE 133 plane involved depends on the nature of the dye molecule ; for instance planes containing anions and cations will be most favourabIe to the adsorption of an acid triphenyl methane dye with amino and sulphonate substituents in approximately equal numbers, whereas another plane containing anions only may be more favourable to the adsorption of an azo dye with a predominance of sulphonate substituents.The most obvious evidence of dye adsorption having occurred in a crystal grown from a saturated aqueous solution containing a suitable dye is sometimes the presence of coloured areas symmetrically disposed about the central region of the crystal. Often, however, by heating the crystal on the stage of a microscope, it can be seen that such coloured regions are not due to adsorption phenomena at all, but are due to inclusions of mother liquor, which etch the edges of their containing cavities as the temperature rises. However, in many cases it will be found that the coloured inclusions are genuinely due to the adsorption of dye in the growing crystal lattice.Usually, but not invariably, this dye adsorption is accompanied by alteration of the normal crystal habit of the substance grown from water. Many instances have been observed, however, in which crystallization from a dye-containing solution has yielded much-modified crystals without significant traces of dye adsorption having occurred, and it seems reasonable to suppose that the habit modification has been due to the adsorption of dye molecules which have been displaced by the subsequent growth processes of the crystal. When highly coloured dye inclusions are present, it might reasonably be suggested that the adsorbed dye molecules have been overgrown. Easy overgrowth of adsorbed dye molecules might be associated with a lessened obstructive effect by the dye molecules on the growth of crystal planes, so that the finding of habit modified crystals might be considered to be, on the whole, a more typical manifestation of the occurrence of dye adsorption than the production of highly coloured crystals.ADSORPTION MECHANISM.-AtfemptS to explain crystal habit modifications have always hinged on elucidating the interaction of the modifying agent and the planes of the crystallographic “form”, the growth of which is most affected. Solid solution formation of the modifier with the substrate, or compound forma- tion, or some type of physical adsorption have all been suggested. Thus Buckley suggested that adsorption was due to similarities between the oxygen triangles of the sulphonate groups of the modifying dye molecules and the oxygen triangles of the oxyacid anions such as sulphate, etc.1 This view could not be maintained when Frondel demonstrated that sulphonated dyes were capable of modifying the crystal habit of halides.2 Bunn thought that the adsorptions were due to the formation of surface solid solutions due to similarities between the primitive translations of the modifier and substrate,3 but this view could not be applied to dyes as their crystal structures were unknown, and probably in many cases non-existent owing to their colloidal properties.At the time when the author became interested in the problem of dye adsorption in growing crystals new ideas as to the nature of crystal growth phenomena were coming to the fore. Bunn and Emmett had demonstrated photographically that crystal growth in many substances was associated with the spreading from continuously renewed nuclei of “ growth layers ” over the crystal faces.4 Frank had postulated that sometimes these continuously renewed nuclei might consist of spiral dislocations of the crystal lattice,5 a view which was soon to receive practical support by the direct observation of surface irregularities on some crystal faces, sometimes taking the form of slight prominences showing evidence of spiral growth.The writer has described elsewhere the evidence which led him to suggest adsorption of foreign matter might occur on the edge-faces of the growing layers tending to build up a growing face 6 so that in fact the plane in which the adsorption has occurred may134 ADSORPTION OF DYES BY CRYSTALS be perpendicular to the plane the rate of growth of which has obviously been modified. Buckley had noted that the plane of dye adsorption sometimes appeared to be quite unrelated to the plane of habit modification.7 PLEOcmOIsM.-The simplest cases for investigation of the nature of the ad- sorption phenomena between dyes and growing crystals were those in which regular deposition of dye in broadening tracks as the crystal grew was indicated by coloured inclusions as “ hour-glass ” or ‘‘ Maltese Cross ” shapes.Photo- graphs of such crystals are included in many of Buckley’s publications.1 In certain specific examples of habit modifications these inclusions varied strongly in colour when the crystal was rotated in plane-polarized light on the microscope stage.Buckley had examined the dichroism of many such examples without coming to any definite conclusion as to the significance.7 Sometimes the colour variation is from full colour to virtually colourless, but often the effect is only the lightening and darkening of the colour, probably with some concurrent vari- ation of shade. The effect is evidently due to the change of position of the adsorbed dye molecules relative to the electric vector as the crystal is rotated, i.e. ultimately to the differences in polarizability of the dye molecules in different directions, and it was thought that observation of the colour changes should prove helpful in interpreting the adsorption behaviour of dyes on crystah. THE STUDY OF PLEOCHROIC MODIFIED CRYSTALS.- Considerable progress towards the understanding of the nature of the influences affecting the possibility of dye adsorption in crystals was achieved by the study of crystals modified with acid tri- phen ylmethane dyes, not ably Acid Magenta modified ammo- nium nitrate crystals. The tr,c normal habit of ammonium i n w m .nitrate IV consists of long prisms, elongated on (001). When the salt was very care- fully crystallized from a solu- tion containing 0.01 % Acid Magenta, large platy (010) crystals were obtained, in which the path of deposi- tion of the dye as the crystal grew was revealed by an ever-broadening track starting from the centre of the crystal, and being symmetrical about the a axis (fig. 1) forming an “hour glass ”type of inclusion. These inclusions were pleochroic, varying from colourless to pale magenta in colour as the crystals lying flat on the microscope stage were rotated in plane-polarized light.Now, the Acid Magenta dye molecule is of a very symmetrical type, and the very similar dye “ trisulphonated pararosaniline ” is completely symmetrical. It was con- firmed that exactly the same crystal habit modification of ammonium nitrate IV was given by the latter dye, and the pleochroism of the modified crystals was again similar, the maximum coloration being developed when the crystals were so positioned that the c crystallographic axis and the electric vector were parallel. The pleochroic properties of the modified crystals necessarily imply that the dye molecules in the crystal must be arranged all parallel with one another, so that the differential interaction with the polarized light ranges from a maximum to zero.In view of the symmetrical nature of the molecules, it further is necessary that the minimum of absorption must be when the electric vector is perpendicular to the plane of the molecules, and the maximum when the electric vector lies in their plane. Reference to the experimental observations of the pleochroism of the modified crystals (fig. 1) showed quite clearly that the dye molecules in the modified crystal must be standing perpendicular to the modified plane and per- pendicular to the axis of elongation of the modified crystals, i.e. they are adsorbed on or lying in (100). c PXIS FIG. 1.J . WHETSTONE 135 Trisulphonated pararosaniline Acid magenta N.D.(C.I. 676). prepared from new magenta (C.T. 678) STRUCTURAL COMPARISONS OF DYE AND CRYSTAL.-BY comparison of the ionic structure of the {loo} plane of ammonium nitrate IV and the Acid Magenta molecule drawn to scale it was apparent that a very strong similarity existed between the pattern of the polar groups of the dye molecule and the ions of the crystal plane, it being possible to superimpose the dye model on the map of the plane so that the SO3- groups coincided with NO3- ions and the NH2+ groups with NH4f ions (fig. 2). On the basis of this evidence and other similar observations it was suggested that the dye molecules were adsorbed into a growing crystal plane because of the Coulomb attractions of ions in situ for the polar groups of the dye molecules in solution, and that the strength of adsorption depended on the number of polar groups involved and their accuracy of fitting on to the crystal structure.FIG. 2.-Ammonium nitrate IV (100) and pararosaniline trisulphonate. Consecutive parallel layers of ions in a crystal structure alternate in their rela- tive dispositions of anions and cations. Where the van der Waals radii of the polar groups approximate to those of the ions in the crystal plane, which is usual with simple oxyacid salts, the dye molecules may be supposed to be held on the crystal plane by the mutual attraction of ions in the surface layer and polar groups of unlike charge (e.g. the NO3- ion for the NH2+ group and vice versa), followed by the growth of the next layer of ions, in which the polar groups will replace ions of a similar charge.It has been observed that the presence of adsorbed dye molecules does not make any perceptible difference to the crystal structure as indicated by X-ray powder photographs, which is consistent with the dye molecules being truly in136 ADSORPTION OF DYES BY CRYSTALS " solid solution ". The consistency of the deductions and predictions as to the possibility of dye adsorption according to the above scheme, derived in the course of the work, is strong support for the above statement. This explanation of dye adsorption is not unlike the theories to account for the formation of orientated overgrowths on crystals advanced by van der Merwe,g but since the repeating unit would be many times larger than the crystal unit cell, if the large dye molecules could form into a characteristic crystal structure, the cases cannot be regarded as strictly analogous.The formation of micellar ag- gregates would increase the disparity between the sizes of the structural units. In this connection it has been shown in a separate investigation that there are good grounds for supposing that in fact the single dye molecules aremore important than micelles in dye adsorption phenomena with crystals. The effect of dye adsorption on crystal growth may be related to the difficulty of completing the growth of layers of ions owing to the necessity of displacing adsorbed foreign matter, or to the lessening of the Coulomb forces between ions in situ and ions in solution owing to the interposition of the hydrocarbon matter of the dye molecules, probably with the dielectric effect also contributing, adsorption is dependent on sufficient similarity between the patterns of the polar groups of a dye molecule and the corresponding ions of a crystal plane (assuming that the dye is adequately soluble to allow of a sufficient concentration in the saline solution) and due to the Coulomb forces, normally associated with crystal growth, drawing in the polar groups of the dye molecules into ionic sites, clearly certain conditions must be satisfied for the adsorption to be really strong.The number of polar groups attached to a single dye molecule (or micelle possibly) must be a factor in determining the strength of the adsorption. The polar groups should fit snugly without overlap into the ionic sites, so that adjacent ions are not excluded and the Coulomb forces attracting the polar group are at a maximum.This latter factor is of importance. For instance, the differing effects of triphenyl- methane dyes such as Acid Magenta on the habits of sodium, potassium and ammonium nitrates seem to be connected with the differing atomic radii of the cations; it is noteworthy that alkylation of the amino groups (thus making them larger) notably decreases the habit modifying powers of the dyes. Further, the nature of the anion will exert a considerable influence on the nature of the crystal planes on which dye adsorption by sulphonated dyes is possible, For instance, an XO3- anion like nitrate or chlorate is usually of dimensions very similar to the SO3- group, and it is unlikely that the dye adsorption will be on a plane which involves that the planes of the oxygen triangles of the anion and sulphonate group will be mutually orthogonal; it is more probable that the crystal plane involved in the dye adsorption will be one perpendicular (or nearly so) to the planes of the oxygen triangles of the anions so that the oxygen triangles of the sulphonate groups correspond as nearly as possible.This viewpoint can be tested in respect of the habit modification of ammonium nitrate IV with Amaranth. The modified crystals are pleochroic, the maximum absorption occurring when the electric vector is parallel with the c axis, indicating that dye adsorption is on (100) if the molecules are adsorbed perpendicularly to the modified plane, which contains the nitrate ions.The model of the dye structure can in fact be fitted to (100) drawn to scale, with the sulphonate groups falling into anion positions. How- ever, the dye model can equally well be fitted to (OlO), the modified plane, but in this case the oxygen triangles of anion and sulphonate group are orthogonal. Even so, it may be that the observed pleochroism is due to the differential inter- action of the electric vector with the length and the breadth of the dye molecule adsorbed flat on the modified plane in this way. That this latter view cannot be maintained, however, is shown by the direction of the supposed adsorption of the dye molecules, maximum absorption would be when the electric vector is at about 45" to the c axis, not parallel with the c axis as observed.GENERAL CONSIDERATIONS AFFECTING DYE ADSORPTION IN CRYSTALS.-If dyeJ . WHETSTONE 137 When the anion is of the X04 type there are four sets of oxygen triangles and the directional effect on influencing adsorption observed with the XO3 anions is lost. Since dye adsorption is commonly perpendicular or nearly perpendicular to the plane of habit modification, this implies that many more opportunities for adsorption and a multiplicity of types of habit modification should be possible. This has in fact been observed by Buckley for potassium and ammonium per- chlorates, and to some extent for the sulphates, but here the pseudohexagonal symmetry is effective in reducing the number of crystal forms on which adsorption may take place.An interesting situation arises when dye adsorption is possible on more than one plane of a crystal lattice. In general there will be differences in the tendencies for the dye to be adsorbed on the differing planes, but owing to the reduction of the growth rate of the plane on which the dye is most strongly adsorbed at first, the opportunities for adsorption on a second more rapidly growing plane will become relatively greater, and it is often found that by increasing continuously the proportion of dye in a given solution the habit modification may be induced to change from one plane to another. Many examples of this are quoted in Buckley's work on potassium and ammonium perchlorates,lo and in an as yet unpublished study of the author's it is shown that it is possible to pre- dict with a fair degree of accuracy the habit modification changes from consider- ation of the possibilities of dye adsorption on alternative crystal planes of ammonium perchlorate. The effect of the oxygen triangles of X03 ions in conjunction with the sulphon- ate groups of the dye molecules is also lost in the alkali metal halides, which in many instances have been found to be susceptible to habit modification, although owing to their cubic symmetry the habit modifications have generally been in the direction (100) + (111).The adsorption of a dye by means of its polar groups into a single crystal plane necessitates that the dye molecule shall lie flat in the plane, i.e. the various aromatic nuclei carrying the important polar groups shall be coplanar, or very nearly so.The importance of this requirement may be very clearly demonstrated by quoting the observed results with mono- and dis-azo dyes as habit modifiers. The mono-azo dyes based on a-naphthylamine -+ /%naphthol or P-naphthylamine lose their modifying powers if a sulphonate substituent group is introduced into an 8-position, thereby destroying any possibility of coplanarity between the naph- thalene ring systems. NaOS-( ) __ S03Na \ Ponceau 6R S03Na \ Amaranth138 ADSORPTION OF DYES BY CRYSTALS Thus, while Amaranth (C.I. no. 184) is frequently a potent crystal habit modifier, the further 8-sulphonated dye Ponceau 6R (C.I. no. 186) is ineffective. bis-Azo TABLE 1 .-PREDICTIONS OF DYE ADSORPTIONS AND RESULTANT CRYSTAL HABIT MODIFICATIONS fitting of polar groups on ion sites plane anions cations of dye modification solu- bility observed dye substance Acid Magenta rnm‘m’’- (NH4)$04 (100) 2/3 good 2/3 good f.sol. *1/3 poor 1/3 sat. trisulphonated pp’p”- triamino triphenyl carbinol anhydride Violet mm’-disulphon- ated pp‘-diamino tri- phenyl carbinol an- hydride anthraquinone 2 sodium sulphonate sulphonated triphenyl pararosaniline disulplzonated Dobner’s (NH&S04 (100) 2/2 good 2/2 good sol. 1 : 4 : 5 : 8-tetramino- NaN03 (10i2) - 4/4 good sol. Ink blue pp’p”-tri- NaN03 (1120) 3/3 good - sol. or-naphthylamine 3 : 6- NH4N031V (100) 3/3 good - f. sol. disulphonate -> 8- NaN03 (1012) 3/3 good - sol. naphthol-4-sulphonate (NH&S04 (100) 3/3 good - sol. Solochrome Yellow YS (NH&S04 (100) 313 good 8-naphthylamine 6 : 8- disulphonate --f sali- cylic acid /3-naphthylamine 5 : 7- disulphonate -+ a- naphthylamine 7- NaN03 (1012) s u 1 p h o n a t e -+ p- n a p h t h o l 3 : 6-di- sulphonate /3-naphthylamine 5 : 7- d i s u l p h o n a t e - t or-naphthylamine -+ NaN03 (1012) /3:naphthol 3:6- disulphonate 3-sulphonate 4 2 mol.415 good i 11/5 sat. 314 good { 1/4 sat. Trypan Red benzidine KNO3 (010) 5/5 good j3-naphthylamine 3 : 6-disulphonate disulphonate --> a- naphthylamine 7- s u l p h o n a t e + j3- n a p h t h o l 3 : 6-di- suiphonate a-naphthylamine 3 : 6- NaN03 (1012) 515 good 1/1 sat. sol. V.S.S. (cold) V.S.S. (cold) - sol. - insol. (hot, cold) (010) tablets, plates (010) plates strong (0001) modification strong (0001 1 modification 010 (laths) f.strong (0001 modification) strong (001) modification strong (001) modification f. strong (0001) mod. (hot) no mod. (cold) f. strong (0001) mod. (hot) no mod. (cold) f. strong (001) modification no modificationJ . WHETSTONE 139 dyes containing 8-sulphonates may, however, be habit modifiers, apparently because the dye molecules can easily take up such a configuration that two aromatic ring systems are coplanar, even when the third is forced out of alignment. appears to be some kind of correlation between the type of dye molecule and the kind of crystal plane on which adsorption is likely to occur. If models of the space lattices of a few crystals are examined it can be seen that the prominent planes can be classified either as " close packed " or " stepped " types.In the former all the constituent ions (or atoms or molecules) are co-planar, but not so in the stepped planes ; the individual particles all differ somewhat in their parameters perpendicular to the plane, so that the plane might be supposed to pass through the mean of the positions of its constituent ions. These planes may consist entirely of the same types of ions or of both anions and cations. The ionic reticular density in the plane is obviously likely to be highest in the close packed planes and these are regarded as most suitable for dye adsorption; close packed planes consisting entirely of anions would appear to be most suitable for the adsorption of azo dyes, etc., with a large preponderance of sulphonate over cationic groups.Similarly close packed planes consisting entirely of cations would appear to favour the adsorption of dyes with a preponderance of amino groups over sulphonates, e.g. 1 : 4 : 5 : 8-tetraminoanthraquinone 2-sulphonate. Close packed planes with both anions and cations would appear to be very suitable for adsorption of dyes with approximately equal proportions of anionic and cationic groups. Stepped planes should be suitable for adsorption in a similar manner to the above, but owing to their much sparser packing at any one given level, they might be less frequently involved in adsorption phenomena. The available evidence appears to indicate that the above considerations are in fact important in influencing dye adsorption phenomena and it is possible successfully to predict the adsorption of dyes and the resultant crystal habit modifications on the basis of comparisons of the ionic patterns of the dye molecules and crystal planes selected according to the above guide.A number of examples of how predictions of habit modifying powers in dyes for various salts have been made by testing the possibility of the occurrence of dye adsorption on suitable planes of the crystal lattice are given in table 1. It will be seen that where habit modifications have been obtained the possibility of demonstrating a high proportion of coincidences between polar groups and appropriate ionic sites exists. The dye must also have an adequate solubility in the saturated saline solution-if the dye is not sufficiently soluble the expected habit modification cannot possibly be realized. In some cases where no habit modifications were obtainable in cold solutions, but the temperature coefficient of solubility of the dye was suitable, its solubility could be increased by crystallizing at higher temperatures, so that the expected habit modifications could be obtained. PREDICTION OF POSSIBILITY OF DYE ADSORPTION ON CRYSTAL PLANES.-There The coincidences are indicated by terms : (a) good-within 0.5 A, (c) poor-just outside 1 A, (b) satisfactory-within 1 A, and (d) no coincidence, and the number of coincidences of those possible is indicated by a fraction. In order to avoid the unpredictable effects due to shading additions and the use of unpurified dye intermediates such as might be encountered with com- mercial dye samples, the foregoing investigation was carried out using specially laboratory-prepared dyes made from purified dye intermediates. The author wishes to express his indebtedness to I.C.I. Ltd., Dyestuffs Division, Research Department, and especially to Dr. E. K. Pierpoint, for the supply of these pure dye samples.140 CALORIMETRIC STUDIES 1 Buckley, Crystal GrowtA (Wiley, New York), p. 370. 2 Frondel, Amer. Miner., 1940, 25, 91. 3 Bunn, Proc. Roy. SOC. A , 1933, 141, 567. 4 Bunn and Emmett, Faraday SOC. Discussion, 1949, 5, 119. 5 Frank, Faraday SOC. Discussion, 1949, 5, 48. 6 Whetstone, Nature, 1951, 168, 663. 7 Buckley, Faraday SOC. Discussion, 1949, 5, 243. 8 Buckley, Mem. Proc. Manchester, Lit. Phil. SOC., 1938-9, 83, 3 1. 9 van der Merwe, Faraday SOC. Discussion, 1949, 5, 201. 10 Buckley, Mem. Proc. Manchester, Lit. Phil. SOC., 1950-1, 92, 1.

ISSN:0366-9033    

DOI:10.1039/DF9541600132

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

140 CALORIMETRIC STUDIES CALORIMETRIC STUDIES OF THE REACTION OF NAPHTHA- LENE ORANGE G WITH AMINO ACIDS BY A. N. DERBYSHIRE AND W. J. MARSHALL Imperial Chemical Industries Ltd., Dyehouse Laboratories, Hexagon House, Manchester 9 Received 21st July, 1953 The heats of reaction AH of eight amino acids with hydrochloric acid and the free acid of Naphthalene Orange G, respectively have been measured. All were found to be less than 1 kcal/mole. AH was found to be the same for the reaction of any one amino acid with either hydrochloric acid or the dye acid in every case except that of 1-lysine for which AH differed by a few hundred calories for the two reactions. This was inter- preted as evidence that the heat of adsorption of Naphthalene Orange G by wool (-8 kcal/mole) is not due to direct interaction between the groupings in the amino acids and the dye.An extraordinarily high heat of dilution was found for this dye and it is suggested that this substantiates Meggy’s proposal that the heat of dyeing is due to the large hydrocarbon residue of the dye being withdrawn from the aqueous phase. It is now generally recognized that combination of strong acids with fibrous proteins 1 is due to the adsorption of hydrogen ions by the fibre to give unionized carboxyl groups, the anions of the acid serving to neutralize the positively charged basic groups. Gilbert and Rideal,2 and Peters and Speakman 3 independently have used this concept to explain quantitatively the adsorption of hydrochloric and sulphuric acids on wool. Their thermodynamic treatments differ in detail but both conclude that the anion acts as a gegen-ion of very low affinity to the strongly adsorbed hydrogen ion, the dissociation constant of the carboxyl groups being similar to those in the carboxyl amino acids. However, acid dye anions are adsorbed much more strongly.Many show “ neutral affinity ” whereas the chloride ion is not adsorbed at all under similar conditions. There is there- fore undoubted evidence that the anions of acid dyes combine with the protein molecule in some additional way, the magnitude of the binding force depending on the various structures of the dyes involved. Although Gilbert 5 and others 697 used this treatment to characterize in thermo- dynamic terms the adsorption of dye anions no real knowledge exists regarding the nature of these additional binding forces.The present authors considered that the calorimetric measurement of dye properties would provide a new approach and might give some interesting results. Since it has been shown from adsorption data that the heat of reaction between wool and hydrochloric acid is < - 1 kcal/mole 1 whereas that of the free acid of Naphthalene Orange G (C.T. 151) is - 7 to - 9 kcal/mole 8 , 9 under similar conditions, a comparison of the heats of reaction of these two acids with theA. N. DERBYSHIRE AND W. J . MARSHALL 141 various constituents of this fibre would show whether or not this comparatively large heat change could be assigned to particular groupings. Gilbert and Rideal2 postulated the basic groups as sites for anion adsorption and since these are present in wool as internal salts 10 a close analogy can be made with the reaction between acids and the amino acid constituents, these latter existing almost entirely as zwitterions in aqueous solutions.Other sites are possible. Vickerstaff 1 has suggested adsorption on the amide groups, while Meggy 11 has proposed that the adsorption may be due merely to the hydrocarbon residue being withdrawn from the aqueous phase. The only accurate measurements of the heats of reaction of strong acids with amino acids are those due to Sturtevant.12 For hydrochloric acid and glycine he found this to be - 0.93 kcal/mole which is of the right order of magnitude to agree with sorption data for hydrochloric acid and wool. A number of ap- proximate heats of reaction have been quoted 13 for various amino acids calculated from the temperature coefficient of the dissociation constant.These all being < 1 kcal/mole also agree with this analogy. No data exist for the heat of reaction of the free acid of dyes with amino acids. In the present paper the heats of reaction of a number of amino acids and two polypeptides with hydrochloric acid have been compared with the corresponding figures for Naphthalene Orange G ((2.1. 151). EXPERIMENTAL APPARATUS.-The thermal measurements were made in an isothermal calorimeter designed for reasonably fast reactions between solutions. The calorimeter vessel contains both the reactants, and is immersed in a large water thermostat whose temperature is constant to better than f 0*0005" C.The calorimeter vessel shown in half-section in fig. 1 consists of a silvered glass Dewar vessel A, contained in a water-tight brass case B, fully immersed in the thermostat tank. The Dewar is fitted with a double lid C of Tufnol which provides thermal insulation and contains the glass pipette D to hold one of the reactants. An aluminium cancpy E with an acid-resisting resin coating is suspended from the lid by 3 Tufnol rods. A rubber disc on top of the canopy and a rubber sleeve round the lid seal the gaps between these components and the inner wall of the Dewar vessel. The rod of the stirrer F, the heater tube G and the main thermometer element (not shown in fig. I) leave the calorimeter through close-fitting Tufnol tubes in the lid and are brought above the water level in the thermostat in brass tubes on the lid of the outer vessel.The calorimeter stirrer F is a horizontal ring of Perspex which is moved vertically through a stroke of 3 in. by a synchronous motor at 4 strokes per min. This provides adequate stirring with a very low heat of stirring (about 0.05 cal/min). A second manually operated stirrer H consisting of a horizontal plate of Tufnol is used to mix the contents of the pipette to a uniform temperature just before it is opened. The pipette has a maximum capacity of 80 ml of I FIG. 1. solution and is sealed by a rubber bung I at the bottom and by a rubber disc at the top. Correction is necessary for the temperature difference between the two reactants at the instant of mixing and this is measured by a subsidiary single-junction copper/constantan thermocouple J.The leads from this thermocouple pass up the central brass tube alongside the stirrer tube. The pipette is opened by pulling out the rubber bung with a wire through the stirrer tube. The calorimeter temperature is measured by the main thermometer element-a six- jiinction copper,konstantan thermocouple. Since the method of measuring the heat142 CALORIMETRIC STUDIES evolved consists of comparing the temperature rise produced by the reaction with that produced by a measured electrical energy input into the same system these teniperat ures need only be measured with respect to an arbitrary zero and an arbitrary but linear scale. The cold junction is therefore immersed in a small sealed Dewar vessel containing water which is kept in the thermostat liquid.This provides an adequate zero since the high heat capacity and low thermal conductivity of the arrangement smooths out the fluctua- tions of bath temperature to less than the detectable minimum (2 x 10-5” C) over the period of temperature measurement. r - - - - - - - - - - - 1 The temperature measuring circuit is shown in fig. 2. The e.ni.f. generated by the thermel TI is balanced by supplying voltage from the potentiometer P through the ratio resistances R1 and RZ until the galvanometer G shows zero deflection. Temperatures are measured in volts on the potentiometer, since only an arbitrary scale is required. For convenience the values of the ratio resistances are chosen to give 1 V approximately equal to 1” C, the actual value being 1 V = 0.990 f 0*002” C.The galvanometer is fitted with a split-cathode photocell amplifier which enables temperatures to be read to 2 x 10-5 “C, this being the limit set by short-term galvanometer fluctuations. Long- term drifts in the galvanometer are much larger : they are eliminated using a “neutral coil” Gmpruhre dgerence ( “C) (~?o~h-Cuhor/rneh) Heah ~ . c f . :y- 0.080 technique. With the switch in position 1 the thermel is in circuit. Immediately before each reading the copper wound resistance (the “neutral coil” R2), equal to the resistance of the thermel, is substituted for it (switch position 2). The galvanometer reading obtained is then used as the zero. Readings of the single- junction copper constantan thermocouple T2, required for the calorimeter-pipette temperature difference, are made with the same circuit by switching to position 3.The resistance of this thermo-couple plus the copper-wound coil R4 equals that of the thermel so the same zero setting will serve for either reading. It is necessary to make the effect of parasitic e.m.f.’s in the circuit less than the detectable minimum of thermocouple voltage. Such e.m.f.’s in the taken, the whole of the low resistance circuit including R1, R3 and R4 being of copper with the exception of the switch and the thermocouples. The method of operation is indicated by the graph of a typical experiment in fig. 3. The assembled calorimeter vessel is allowed to equilibrate overnight and the run is started with the calorimeter temperature below that of the bath.Temperature readings are made at 2-min intervals for a period of about 20 min. The calorimeter temperature changes linearly with time during this period due to heat of stirring and heat exchange with the bath. The reactants are then mixed by opening the mixing pipette. After a short non-equilibrium period a second period of linear temperature drift is obtained.A. N. DERBYSHIRE A N D W. J. MARSHALL 143 By extrapolation of these two straight lines to the instant of mixing the temperature change due to reaction may be determined. After the second period, a measured quan- tity of electrical energy is supplied to the calorimeter, a third linear temperature drift being subsequently established. A similar extrapolation of the second and third lines to the mid-time of the heating period gives the temperature change due to the electrical heat supplied.Then, if At1 is the temperature change due to reaction, At2 is the temperature change due to electrical heating, - q1 is the heat evolved by the reaction, q 2 is the electrical heat supplied, since the heat capacity of the system is the same for q1 and q2. The electrical energy is determined potentiometrically, the standards being a Weston type standard cell and a 1 ohm standard resistance. The energy is measured in inter- national joules but all results are expressed in calories (1 cal = 4-1833 int. J). In order to correct for the temperature difference between the two reactants, the read- ings of thc subsidiary thermocouple must be expressed on an absolute scale.This was done by a series of experiments in which water in the pipette was added to water in the calorimeter. The heat produced gave a satisfactory linear plot with temperature difference to within the reproducibility of a heat determination (about 0.05 cal). A similar check experiment at the end of the work showed no change in calibration. MATERTALS.-The 1 -tyrosine, l-glutamic acid, 1 -cysthe, 1 -1ysine monohydrochloride and l-arginine were B.D.H. laboratory reagents, the glycylglycine and glycyl-l-tyrosine were obtained from Roche Products Ltd., and the glycine was A.R. material. Other reagents used were of analytical quality apart from the Naphthalene Orange G. This was obtained as unstandardized batch material (sodium salt) and purified by recrystallizing from water followed by alcohol extraction.The free acid was prepared from the sodium salt by precipitation from aqueous solution with 2 N hydrochloric acid, washing the pre- cipitate with acid of the same strength and repeating the procedure five times, the product finally being dried in a desiccator over solid caustic soda. A solution of the free dye acid was made up and passed through an acid exchange column (Zeocarb 315) to remove the final traces of sodium ion. The purity of the sodium salt, estimated as 95 % by titanous chloride titration, and the optical density of a suitably diluted solution, measured at 485 mp on the Cary recording spectrophotometer, were used to calculate the extinction coefficient (23,000). Using this figure the dye anion concentration in the dye acid solution was measured optically (the extinction coefficient is insensitive to pH).The acid strength was then measured by direct electrometric titration with sodium hydroxide. As a final check the dye content of the solution was estimated by titanous chloride titration. All of these figures agreed to within the limits of accuracy of the methods (& 1 %). - 41 = 42AtltAt2 RESULTS THE REACTION OF GLYCINE WITH HYDROCHLORIC ACID AND NAPHTHALENE ORANGE G FREE ACID.-GlyCine is the simplest of the amino acids and the heat of reaction with hydrochloric acid (I) has already been measured by Sturtevant.12 In addition it has a high solubility and its properties have been extensively examined. It is therefore an ideal substance for this type of work.Since it is desired to compare the dyelglycine reaction (11) with that of HCl (I) it is clearly preferable to measure both rather than compare the experimental results for reaction I1 with the published data on reaction I. The agreement of the hydrochloric acid data gives an indication of the accuracy of the experimental techniques. The high solubility of glycine allows experimental runs to be carried out by adding glycine from the pipette to the more dilute acid as well as vice versa. Furthermore, the higher concentrations possible give temperature rises of the order of 2000 x 10-5" C so that these experiments could be carried out in an earlier and less sensitive form of the calorimeter. The method of calculating the heat of reaction from the observed heat evolved followed the method of Sturtevant.12 The strengths of the glycine solutions were measured by titration with acid in the presence of formaldehyde 14 while the hydro- chloric acid solutions were prepared by diluting N/1 acid and calculating the molalities from published density fig~res.15~ 16 The heats of dilution of the glycine and hydro- chloric acid are those given by Sturtevant 17s 18 while those of the dye have been measured in the present work over the required concentration ranges.Table 1 summarizes results of four typical runs and outlines the method of calculation.144 CALORIMETRIC STUDIES TABLE HEAT OF REACTION OF HYDROCHLORIC ACID AND NAPHTHALENE ORANGE G WITH GLYCINE Some typical sets of results hydrochloric acid run number - 1 final molality of acid (ml) final molality of glycine (m2) final weight of water (g) number of moles of acid number of moles of gly- bath temperature (“C) 25.8 initial temp.of reactants (“C) 25.1 temperature rise on inix- ing (At,) 0.0166 heat capacity of system ( q 2 1 W , cal/deg 1067.0 heat change on mixing (cal) 17-50 heat of dil. of glycine (cal) +0-37 heat of dil. of acid (cal) -0.56 heat change due to reaction no. of moles of product heat of reaction at 25” C 0.09053 0.01943 996.0 (Ml) 0.0901 8 cine (M2) 0.01 93 5 (- 4 = 42AtllAf2) (call - 17.31 0.01825 (AH) (cal/mol) - 0.953 I1 0.09053 0,01962 996.0 0.09068 0.01 954 25.8 25.1 0.01 63 1071-0 17.46 + 0.38 - 0.56 - 17.28 0.01 843 - 0.945 Napththalene Orange G free acid 111 0.0085 1 0.00871 995.0 0.00847 0.00867 25.7 25.35 0.0025 1095.0 2.74 + 0.08 + 0.85 - 3.67 0.00423 - 0.87 1v 0.01 659 0.0 1692 9920 0.01 645 0.01679 25.45 25.0 0-0074 10900 8.07 + 0.28 + 0.66 - 9.01 0.00993 - 0.91 In all, five runs with hydrochloric acid and six with the dye acid were carried out at different concentrations, each being accompanied by appropriate measurements of the heat of dilution of dye.These results are given in table 2. Sturtevant 12 gives AH = - (0.93 + 0.30 m) kcal/mole, where m is the molality of the hydrochloric acid and to give a comparison, figures based on his results (obtained by using his extrapolation from the higher concentration) are shown in parentheses. The estimated error is mostly calorimetric and is therefore greater for the more dilute solutions. Agreement with published results for reaction I is therefore good and within the experimental error.Since the solutions employed were too dilute to show concentra- tion dependence, the mean values were calculated by weighting according to the estimated error. From these mean values of - 0.956 f. 0.006 and - 0.92 & 0.03 cal/mole for reactions I and I1 respectively it can be concluded that the heat of reaction of glycine with TABLE 2.-A COMPARISON OF THE HEAT CHANGES ON REACTING GLYCINE WITH HYDROCHLORIC ACID ABD NAPHTHALENE ORANGE G FREE ACID, RESPECTIVELY (Bracketed figures are extrapolated from Sturtevant’s data) hydrochloric acid Naphthaline Orange G free acid molali ty AH, heat of reaction AH, heat of reaction molali ty of HCI (kcal/mole) (kcal/moIe) of dye acid 0.09086 - 0.957 & 0.008 (- 0.958) - 0.87 *0.07 0.00851 0.09053 -0.953 &0.021 (-0.957) - 0.87 f007 O.OO85 1.0.09053 - 0.945 & 0.021 (- 0,957) - 0.91 f 0.03 0.01 659 0.03662 - 0.977 k0.021 (- 0.941) - 0.95 k0.03 0.01659 0.03619 -0.950&0*021 (-0.941) -0.98f0.04 040866 -0*80+0.25 000 1 67 weighted mean values - 0.956 &.0.006 (- 0.957)) - 0.92 f0.03A . N. DERBYSHIRE A N D W. J . MARSHALL 145 the free acid of Naphthalene Orange G is the same as with hydrochloric acid, and, as this latter is almost entirely due to the heat of dissociation of the carboxyl group, there is no detectable interaction between this amino acid and the dye anion. THE REACTION OF VARIOUS AMINO ACIDS WITH HYDROCHLORIC ACID AND NAPHTHALENE ORANGE G.-Having studied the glycine reaction fairly fully it was decided that in further experiments the primary object would be to determine whether or not there is a consider- able difference between the heat of reaction of an amino acid with dye acid and with hydrochloric acid.Consequently it was merely necessary to react a given amount of hydrochloric and dye acid in turn with a fixed concentration of the amino acid and measure the heat changes. Corrections were applied for the known heat of dilution of the two acids but not for the heats of dilution of the amino acids. Since the latter were diluted by a factor of only 1-06, the hydrochloric and dye acid in this series always being added from the pipette, the error is considerably less than the calorimetric error and can therefore be neglected, In any case such a correction can have no bearing on the direct coinparison of the two acids as it applies equally to both.The concentrations used were such that the final molality of the amino acids was ca. 0.002 and the dye or hydro- chloric acid was in approximately 100 % excess. An exception was 1-cystine, the low solubility of which would allow a final molality of only 0.00038. The small heat change produced when concentrations as low as 0.002 mole per 1000 g water were used required considerably more calorimetric sensitivity and it was at this point that the calorimeter was improved to the form described in the section on experimental methods. This calori- meter was used for all subsequent work described here. TABLE 3.-HEAT CHANGE ON REACTING HCI AND DYE ACID WITH VARIOUS AMINO ACIDS (Molality of acid after dilution = 0.00422 mole/1000 g of water) amino acid (mole/1000 - molality of heat change on mixing due to reaction amino acid (950 ml of solution) g of water) HCl (cal) dye acid (cal) - 054 - 0.43 I &58} - 0'56 - 0.62 - 0.64 - 0.02 - 0.11 - 0.41 - 0.42 - 0.57) OS5O 1-tyrosine 0~00210 1-glutamic acid 0.00203 - 0.54} - 0.58 - o.62} - 0.63 1-cystine 0*00038 - o.08} - 0.05 - o.09} - 0.10 glycy IgI ycine 040348 - o.39}- 0.40 - 0.46) - - 0.041 glycy I- 1 - tyrosine 0*00098 + :::} + 0.03 I 0.01 J - 0.03 1-lysine monohydrochloride 0*00208 1 ::::} - 0.26 1 ::;;}, - 0-94 - 17'50 - 17.66* - 17-83) - 0.39 - 0.39 1-arginine monohydrochloride 0.0021 1 - 0-47 * accompanied by precipitation.The results are given in table 3, each experiment having been carried out in duplicate.It will be seen that apart from the last two amino acids there is no difference in the heats of reaction with hydrochloric and dye acids respectively. 1-Lysine monohydrochloride and 1-arginine monohydrochloride require further examination. In both cases the heat changes with dye acid are greater than those occurring with hydrochloric acid, In particular, the value for 1-arginine is misleadingly high since the complex formed was partially precipitated and it therefore includes the heat of solution for this complex. Attention was therefore turned to neutral conditions, the sodium salt of the dye and sodium chloride being added in turn to solutions of 1-lysine monohydrochloride, and 1-arginine monohydrochloride.No heat change could be detected on addition of sodium chloride, nor could interaction between lysine and the dye be detected but arginine monohydrochloride and Naphthalene Orange G give a definite and measurable heat change on mixing. This is small and amounts to a mere 200 cal/mole of arginine monohydrochloride originally present even when there is a 300 % excess of dye present. The heat AH of the reaction per mole of The results are given in table 4.146 CALORIMETRIC STUDIES TABLE 4.-HEAT CHANGE ON REACTING NAPHTHALENE ORANGE G SODIUM SALT WITH ~-LYSINE MONOHYDROCHLORIDE AND ~-ARGININE MONOHYDROCHLORIDE (corrected for heats of dilution) beat change due to reaction molality after dilution -___ measured (950 ml) per mole of (kcal/mole) dye of a solution amino acid in sol.amino acid (f 0.05 cal) 0.00208 0.00422 z ::::}- 0.05 - 0.03 rt 0-02 1-lysine monohydro- chloride 0.00106 0.00422 1 ::;;}- 0.25 - 0.23 f 0.03 0.00422 1 :I::} - 0.39 - 0.19 f 0.02 1-arginine monohydro- o.oo21 chloride I \0.00422 0.00422 1 :;} - 0.75 - 0.18 & 0.01 product cannot be calculated with certainty unless a large excess of one of the reagents is present. Measurement under such conditions was not possible because of the low solubility of the product and the minute amounts of heat evolved when the concentration is reduced. Arginine contains a guanidine side-chain and it was thought that if the latter were the cause of the specific interaction of this amino acid with dye, then reacting the sodium salt of the dye with guanidine hydrochloride would circumvent the difficulties associated with arginine.Unfortunately the complex formed was even more insoluble and though confirming the specific interaction of the dye with guanidine it did not over- come the difficulties of measurement. Returning to the results in table 3, published values of the ionization constants of the amino acids 13 can be used to obtain the concentrations of the various amino acid ions and hence calculate the heat of reaction per mole. As a check, the change in pH due to addition of acid was measured and good agreement with the calculated figures was obtained for all the amino acid hydrochloric acid solutions and for all the amino acid+ dye acid solutions with the exception of the last two. This is in agreement with the calori- metric data which shows that there is no interaction in the former cases with the dye anion.The heats of reaction calculated in this way are given in table 5. Lysine mono- hydrochloride solution gave a greater pH change on addition of dye acid than when hydro- chloric acid was added and the heat of the reaction with the dye was calculated using the observed pH change. It will be seen that this brings the two heats of reaction much closer than is apparent in table 3. Arginine monohydrochloride is rather inore complicated and is discussed separately. TABLE 5.-HEAT OF REACTION AH OF HYDROCHLORIC ACID AND NAPHTHALENE ORANGE G FREE ACID, RESPECTIVELY, WITH VARIOUS AMINO ACIDS amino acid glycine 1 -tyrosine 1-glutamic acid 1-cystine glycylgl ycine g 1 ycyl-1 -tyrosine 1-lysine monohydrochloride 1-arginine monohydrochloride (a) no.of moles of amino acid (b)no. of moles which have reacted - (a) 0.00199 (6) 0.00071} (a) 0.00192 (b) 0*0007s> (a) 0.00036 (6) 0*00011} (a) 0.00330 (b) 0.00232) (a) 0.00093 (b) 0-000'71) (a) 0.00197 (b) 0*00052} (a) 0*00200 (6) 0.00062) heat of reaction AH (kcal/mole) HCl - 0.95 - 0.79 - 0.74 < 10.51 - 0.17 < lO.11 - 0.50 - 0.68 dye - 0.92 - 0.72 -- 0.81 < (0.51 - 0.19 - 0.56"" * no. of moles reacted = 0*00106 ** see text for details of calculation.A. N. DERBYSHIRE AND W. J . MARSHALL 147 THE INTERACTION OF 1 -ARGIMNE MONOHYDROCHLORIDE AND NAPHTHALENE ORANGE G. -When dye acid is added to a solution of l-arginine monohydrochloride at the con- centrations described in table 3 a considerably greater heat change occurs than with hydro- chloric acid under identical conditions, namely, - 17-66 cal and - 0.42 cal respectively in 950 ml of solution.This, however, is accompanied by partial precipitation of an arginine-dye complex and, to make a comparison between the two reactions, proper allowance must be made for the heat change due to precipitation. Thus the heat of solution of dye and arginine monohydrochloride must be subtracted algebraically from the measured value of -17.66 cal. A comparison of this residual heat change with that produced by the arginine monohydrochloride + hydrochloric acid reaction will then indicate the magnitude of any additional bonding between the amino acid and the dye. The method of calculation is as follows.The dye remaining in solution was estimated colorimetrically and the amount pre- cipitated was calculated by difference. From the change in pH and the known concentra- tion of dye it was concluded that the complex contained two moles of dye for every mole of amino acid. The exact proportion of amino acid is not very critical, the correction due to it being a comparatively small proportion of the total. Thus: total dye in 950 ml dye in solution in 950 ml = 4.00 mmoles ; = 1-29 mmoles. :. dye in the precipitate from 950 ml = 2.71 mmoles. Heat of solution of the dye to the final concentration in solution (1.36 mmoles/l) = 5.87 kcal/moIe. :. Heat of solution of dye in the precipitate = 15.91 cal (qtS). The results in table 3 have already been corrected for the heat of dilution of the dye to a niolality of 0.00422 whereas in this case the dye left in solution is at a niolality cor- responding to 1.29 mmoles in 950 ml of solution so that further correction is heat of dilution of 1-29 mmoles = 1.29 X 0.99 ~ a l = 1.28 cal (q’dil).Zittle and Schmidt 19 give the heat of solution of arginine = 1.5 kcal/mole. The amount of arginine in the precipitate = 1.36 mmoles; :. the heat of solution of this arginine = 1-36 x 1-5cal = 2-04 cal (q”J. The heat of dilution of the arginine is small and has been neglected. then the measured heat change after correction for dilution as given in table 3 is If q R is the heat due to the reaction of the dye with the arginine monohydrochloride 4 q R - 4‘s 4’ dil- q”s q R - 15.91 + 1.28 - 2.04 = - 17-66 Cal thus qR = - 099 Cal.Comparison of this figure with the heat change of - 0.42cal for the corresponding reaction with hydrochloric acid shows that there is no great difference. The final com- parison in table 5 which gives a value of - 056 kcal/mole as against - 0.68 kcal/mole for hydrochloric acid is even closer. This is because as with lysine monohydrochloride more dye acid reacted with arginine than did hydrochloric acid. The agreement is much better than could be expected in view of the magnitude of the corrections which have been made and is therefore somewhat fortuitous. DISCUSSION From adsorption data, the heat of reaction of Naphthalene Orange G on wool can be calculated 8 ~ 9 as exceeding that of hydrochloric acid by 8.8 kcal/mole. A comparison of AH for the reaction dye acid 3- amino acid with that of hydro- chloric acid + amino acid shows that heat changes of this order do not take place in the interaction of Napthalene Orange G with glycine, l-tyrosine, glutamic acid, 1 -cystine, gl ycylglycine, glycyl-1 -tyrosine or l-lysine monohydrochloride.1- Arginine monohydrochloride alone shows a significant heat change on reacting.148 CALORIMETRIC STUDIES Thus there is no evidence to associate the heat of adsorption of acid dyes on wool with the bonding of the dye acid to the amine or the amido groups in the fibre. Arginine certainly shows a considerable heat of reaction with the dye but this is accompanied by precipitation. In the previous section, however, this large heat change on precipitation was shown to be due almost entirely to the measured or known heats of solution of dye and arginine contained in the complex.The residual heat of reaction, although it cannot be estimated accurately, is of similar magnitude to that with hydrochloric acid as in the case of the other amino acids. Meggy 11 has proposed that the destruction of the hydrocarbon/water inter- face is the origin of the free energy change when acid dyes are adsorbed by wool, and the behaviour found here shows that such a picture is also compatible with the magnitude of the heat of reaction. Lemin and Vickerstaff4 found wool containing 0.41 mole/kg of Naphthalene Orange G to be in equilibrium with a solution containing 0.001 8 mole dye/]. Peters and Speakman consider adsorbed anions to be in solution in an aqueous phase within the fibre which for wool is 0.30 g per g of wool so that the dye is at a concentration 750 timcs greater in the wool than in the external aqueous phase. The heat of dilution of Naphthalenc Orange G free acid was also found to be unusually high-diluting from 0.08 mole/l. to 0.00011 mole/l., gives a heat change of 6.5 kcal/mole and therefore the present authors believe that the heat of dyeing may be due either to the de- creased heat content of the highly concentrated dye in the fibre compared to that in the dilute solution with which it is in equilibrium, or to the more hydrophobic nature of the environment in fibrous proteins. However, further discussioii on this aspect is outside the scope of this paper. 1 Vickerstaff, PhysicaZ Chemistry of Dyeing (Oliver and Boyd, London, 1950), chap 2 Gilbert and Rideal, Proc. Roy. SOC. A, 1944, 182, 335. 3 Peters and Speakman, J. SOC. Dyers Col., 1949, 65, 63. 4 e.g. Lemin and Vickerstaff, J. SOC. Dyers Cof., 1947, 63, 405. 5 Gilbert, Proc. Roy. SOC. A, 1944, 183, 167. 6 Meggy, Trans. Faraday Soc., 1947, 43, 502. 7 Benson and Larose, Can. J. Res. F, 1949, 28, 238. 8 Lemin and Vickerstaff, Symp. Soc. Dyers Col. (1946), p. 136. 9 Fern (unpublished). 10, 11. 10 Speakman and Hirst, Trans. Faraday Soc., 1933,29, 148. 11 Meggy, J. SOC. Dyers CoZ., 1950, 66, 510. 12 Sturtevant, J, Amer. Chem. SOC., 1941, 63, 88 ; 1942, 64, 762. 13 Cohn and Edsall, Proteins, Amino Acids and Peptides (Reinhold Publishing Cor- 14 Sorenson, Biochem. Z., 1908, 7, 45. 15 Gucker, Ford and Moser, J. Physic. Chem., 1939, 43, 153. 16 Int. Crit. Tables, 3, 54. 17 Sturtevant, J. Amer. Chem. Soc., 1940, 62, 1879. 18 Sturtevant, J. Amer. Chem. Soc., 1940, 62, 3265. 19 Zittle and Schmidt, J. BioZ. Chem., 1935, 108, 161. poration, New York, 1943), chap. 4.

ISSN:0366-9033    

DOI:10.1039/DF9541600140

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

THE SOLUBILITY AND ACTIVITY OF ORANGE 11 IN SODIUM CHLORIDE AND SODIUM SULPHATE SOLUTIONS BY A. B. MEGGY Dept. of Textile Industries, The University, Leeds 2 Received 4th June, 1953 The solubility of Orange I1 in NaCl and Na2S04 solutions at 25" has been determined, and the activity factor k y has been calculated. The partition of Orange I1 between amyl alcohol and water, 0.05 N NaCl, and 0.2 N NaCl has been studied, but the data did not permit the determination of the constant k in the activity factor ky. The activity coefficient increases by a factor of 30-50 in 2 N NaCl or Na2SO4, and is sufficient to nullify the stripping and levelling effect which these electrolytes have at higher temperatures. The behaviour of certain cellulose acetate dyes towards salts can be ex- plained by assuming that they show the same type of behaviour at 80-100" as Orange I1 does at 25".The majority of dyes are organic sulphonic acids, and in their application inorganic electrolytes, chiefly NaCl and NazS04, are used to control their ab- sorption by the fibre. This control can be effected by two different mechanisms. Firstly, the electrolyte may supply an ion which accompanies dye ions on the fibre, SO that an increase in the concentration of electrolyte causes an increase in the absorption of dye. This is the case with "direct" dyes on cellulose.1 The electrolyte may supply an ion which competes with the dye ions, when an increase in electrolyte concentration causes a reduction in dye uptake. This occurs with " acid" dyes on wool, leather, and other protein materials.2.39 4 In dilute electrolytes at temperatures from 60-1 00" simple relationships exist between dye uptake and electrolyte concentration, but in more concentrated solutions these relationships break down.The second mechanism by which electrolytes could influence dye uptake is by their effect on the activity coefficient of the dye in solution. In general, electro- lytes increase the activity of organic substances in aqueous solutions, and there- fore this effect would tend to increase dye uptake, irrespective of the mechanism by which the dye was absorbed on the fibre. The combined effect of these two processes, when applied to acid dyes on wool, would lead one to expect that in dilute solutions electrolytes would have a de- sorbing effect, but in concentrated solutions this would be nullified, or even re- versed, by the increase in the activity coefficient of the dye.The change in the activity of a dye in the presence of electrolytes is most readily followed by the change in solubility. In the saturated solution, l/[(Na+)(D-)]& = ky. (1) The solubility of a number of dyes in the presence of NaCl and HCl has been studied by one investigator.5 The present paper deals with the solubility and activity of a typical monovalent acid dye, Orange I1 (sulphanilic acid -+ P-naphthol) in the presence of NaCl and Na2S04 at 25". At higher temperatures the solu- bility of the dye increases very rapidly. Approximate measurements show that at 60" the solubility is about 1.4 M in water, and about 0.35 M in N NaCl.The corresponding values for k y are 0.71 and 1.46, so that at this temperature the activity coefficient increases by a factor of about 2 in N NaCl. 1 49150 ACTIVITY OF ORANGE I1 EXPERIMENTAL Orange I1 was purified by crystallization three times from water and drying at 100". The anhydrous dye was scarlet, the hydrated form yellow. The solubility determinations were carried out in the usual way. In strong solutions of electrolytes the scarlet anhydrous form of the dye was converted rapidly to the hydrated form, and equilibrium was estab- lished quickly. In more dilute electrolytes, and especially in pure water, the dye dissolved as the anhydrous salt, and marked supersaturation occurred, amounting sometimes to as much as four times the equilibrium value.In such cases it was necessary to inoculate the solution with the hydrated salt, and even so, equilibrium was reached only slowly. The solid phase from water, and from 2 N NaCl was the pentahydrate,s and this appeared to be the only stable hydrate under the experimental conditions used. The anhydrous salt does not hydrate to the pentahydrate in 4 N NaCI, in which it appears to be totally insoluble at all temperatures. Samples were filtered through a small plug of cotton wool. The cotton wool absorbed a small amount of dye, which caused an appreciable error for those solutions in which the solubility of the dye was small. In such cases the solution was drawn through the filter once or twice, and then returned to the flask. After a few minutes a new sample was taken through the same filter, and used for the solubility determination.The results of the determinations are given in table 1. TABLE 1 sodium chloride N 2.0 1.0 0.5 0.25 0.1 0.05 0.02 0.0 Orange 11; M 4.01 x 10-5 9-58 x 10-5 3-20 x 10-4 2.70 x 10-3 5.00 x 10-2 1-65 X 10-1 2-13 X 10-1 2.90 X 10-1 1 10.0 2.0 102.0 1.0 79.1 0.5 38.3 0.2 11.5 0.1 5.3 0.05 4.5 sodium sulphate Orange 11; M 2.43 x 10-5 1.22 x 10-4 4-03 x 10-4 4.98 x 10-3 8.91 X 10-2 1-65 X 10-1 ky 143.0 90.5 70.3 31.2 7.7 5.3 The usual method for determining the activity coefficient from solubility data is to extrapolate k y to zero ionic strength, and to assume that under these conditions y = 1, so that the extrapolated value gives k directly. This is not possible in the present case, as the solubility of Orange I1 in the absence of electrolyte is far too great, 0.29 M.The dye is slightly soluble in amyl alcohol, and in table 2 are given the results of partition -_-I___ C (water) 1-41 x 10-5 1.80 x 10-4 2-91 x 10-3 7.51 X 10-4 1.22 x 10-2 4.98 x 10-2 1-71 X 10-1 2.90 X 10-1 water C (alcohol) 9-25 x 10-6 3-70 x 10-5 7.63 x 10-5 1.99 x 10-4 4.75 x 10-4 1.13 x 10-3 1-97 x 10-3 2-90 x 10-3 TABLE 2 - sodium chloride, 0.05 N -- C (water) C (alcohol) Cwlca 1.5 9-73 x 10-6 4-86 x 10-5 4.9 6-03 x 10-5 1-48 x 10-4, 9-8 3.64 X 10-4 4.08 X 10-1 15.0 1-85 x 10-3 6.25 X 10-4 26.0 7.41 x 10-3 8.92 x 10-4 44.0 3.43 x 10-2 1-28 x 10-3 87.0 1-21 x 10-1 1.81 x 100.0 1.65 x 10-1 2-00 x 10-3 sodium chloride, 0.2 N CwlCa 0.20 0.41 0.89 2.96 8.3 27.0 67.0 83.0 C (water) C (alcohol) CwlCa 5.10 X 10-6 5.33 x 10-5 0.095 1-44 x 10-5 1.15 x 10-4 0.125 5-76 x 10-5 3-56 x 10-4 0.16 3.75 x 10-4 9.72 x 10-4 0.39 4-17 x 10-3 1-85 x 10-3 2.25 6.3 x 10-3 1-90 x 10-3 3.3A.B . MEGGY 151 experiments between amyl alcohol and water, 0-05N NaCl and 0.2N NaCl. The partition coefficient does not approach a constant value for low concentrations of dye, and the concentration of dye in the amyl alcohol phase is greater when in equilibrium with the saturated solution in water than in 0.2N NaCI. Since the activity of the dye is the same in all saturated solutions, the concentration in the amyl alcohol is not pro- portional to the activity of the dye in the aqueous phase. DISCUSSION The activity of the dye is profoundly influenced by electrolytes. The normality of the electrolyte is the principal factor, though there are small differences in the effect of the C1- and SO:- ions.The rate of change of activity with ionic strength is greatest in the region from 0.1 N to 0.5 N ; over this range ky increases by a factor of about 7 in NaC1, and about 9 in Na2SQ4. For a monovalent dye and an electrolyte in equilibrium with a material, such as an insoluble protein in an acid solution, in which dye is absorbed on ionized sites, the following relationship holds : (2) aD, ai are the activities of the dye ions and the anions in the solution, z the valency of the anions, and K is a constant which depends on the proportion of dye ions and inorganic ions on the fibre, and the temperature. z loglo aD - loglo ar = K. Converting to molar concentrations, Z loglo D f Z loglo Y D - loglo i - loglo yi = K.(3) At temperatures from 60-loo", and electrolyte concentrations below about 0.1 M, the plot of loglo D against loglo i is a straight line, having approximately the slope TABLE 3 NaCl, M 2.0 1.0 0.5 0.25 0.10 0.05 0.02 Orange I1 (arbitrary units) Na~S04, M 1.77 - 0.95 1.0 0-64 0.5 070 0.25 1-00 0.10 1-15 0.05 0.57 0.025 Orange I1 (arbitrary units) - 0.47 0.60 0.62 1.00 3-12 3.44 1/z3 3- 4 Under these conditions the effect of the activity coefficients is small. At electrolyte concentrations greater than 0.1 M the slope of the curve diminishes, as in this region the activity coefficients differ appreciably from unity. Never- theless, there is an appreciable part of the curve in which the simple relationship implied in eqn.(2) applies in practice. At 25" this is no longer the case. In table 3 the variation of the dye con- centration with the electrolyte concentration is calculated from eqn. (3). The dye concentration is expressed in arbitrary units, the concentration in equilibrium with 0.1 M electrolyte, being taken as unity. Since log ky = log k -1- logy, the values of ky in table 1 may be used in place of y, this being equivalent to an alter- ation of the constant Kin eqn. (3). The simple relationship between dye and electrolyte in solution is completely obscured at 25" at electrolyte concentrations above 0.05 M. The addition of electrolyte causes a decrease in the amount of dye in the solution. It follows that the stripping and levelling effect which is shown at higher temperatures is absent at 25".Since protein fibres are dyed at 80-loo", this is not of any technical importance, except for leather, which has to be dyed at low temperatures. Certain dyes for cellullose acetate contain as a solubilizing unit the group -NH . CH2CH2.OS03Na. Usually only one such group is present. The152 ABSORPTION OF OPTICAL ANTIPODES absorption of these dyes by cellulose acetate is greatly assisted by the presence of NaCl or Na2S04. The dye can be salted out of aqueous solution into ethyl acetate in the same way as on to cellulose acetate. This seems to rule out any Donnan membrane or similar effects; it appears that the salt sensitivity of these dyes is due entirely to an increase in the activity coefficient in the presence of electrolytes, and that they show a behaviour at high temperatures which is shown by Orange I1 only at low temperatures. This impression is confirmed by the behaviour of these dyes on Nylon. Here, in contradiction to their behaviour on cellulose acetate, salts have little influence on dye absorption. Absorption is on ionic sites, so that an increase in the activity of sulphate ions, for instance, in the solution should cause an increase in the activity of dye ions in the solution. At the same time, however, the increase in the electrolyte concentration causes an increase in the activity coefKcient of the dye, which happens to just balance the increase in sulphate activity. In consequence the dye concentration in the solution does not alter. The behaviour is similar to that calculated for Orange I1 at 25" in table 3. The author is indebted to Messrs. Brotherton Ltd., of Leeds, for a Research Lectureship. 1 Neale, J. SOC. Dyers Col., 1936, 52, 252. 2 Speakman and Clegg, J. SOC. Dyers Col., 1934, 50, 348. 3 Lemin and Vickerstaff, Symp., SOC. Dyers Col. (Bradford, 1947), p. 41. 4 Gilbert, Proc. Roy. SOC. A, 1944, 183, 167. 5 Siseley, Bull. SOC. chim. France, 1901, 25, 862.

ISSN:0366-9033    

DOI:10.1039/DF9541600149

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

152 ABSORPTION OF OPTICAL ANTIPODES THE SELECTIVE ABSORPTION OF OPTICAL ANTXFODES BY WOOL BY W. BRADLEY, R. A. BRINDLEY AND G. C. EASTY The Clothworkers' Research Laboratory, University of Leeds Received 30th June, 1953 Immersed in aqueous (f)-mandelic acid at 31.3" 1 kg of wool absorbs 0.45 mole of the acid at pH 2.5. This value is closely similar to that reported for hydrochloric acid (0.4 mole). The mandelic acid is resolved into its optical antipodes by the wool, the (+)-forin being taken up more abundantly than the (-)-form. Mandelic acid is similarly resolved when it combines with L-arginine or L-lyshe to form salts. These facts, together with the knowledge that L-arginine and L-lysine are the principal basic amino-acids of wool, suggest that mandelic acid combines with wool to form a typical salt.A number of simple derivatives of mandelic acid are similarly resolved as also are certain related planar molecules of larger size and derivatives carrying long (C7-C10) alkyl chains. About 75 % of the mandelic acid bound at equilibrium combines within 4 min and resolu- tion occurs from the beginning of the process. Dry-chlorinated wool and solvent- scoured wool behaved similarly. p-Decoxy- and p-hexadecoxy-mandelic acid were ab- sorbed at a lower rate and the more complex acid was not resoIved at all. These acids and some of lower complexity, in contrast to mandelic acid, were retained by the wool after immersion in water. In this they showed in some degree the " affinity " characteristic of the acid dyes. In a recent communication 1 it was shown that both wool and casein selectively absorb (+)-mandelic acid from an aqueous solution of (-l-)-mandelic acid (I) at room temperature.Later2 the processes of absorption and resolution into optical antipodes were studied in greater detail. It was found that mandelicW. BRADLEY, R . A . BRINDLEY AND G . C . EASTY 153 acid resembled hydrochloric acid and chloracetic acid in that 0.45 mole of mandelic acid combined with 1 kg of wool at pH 2.5 and 31.3". Equilibrium was reached in 5-6 days and three-quarters of the acid ultimately bound combined within 4 min. The process of absorption did not bring about hydrolysis of the wool; a sample of wool which had taken up mandelic acid and had been subsequently treated with ammonia showed the same properties as the original.This applied equally to wool which had been in contact with mandelic acid for 5-6 days. Selective absorption of the (+)-form of the acid occurred from the beginning of the absorption and after the initial 4-min period the ratio, (excess of (+) over (-) acid absorbed)/(total acid absorbed) was constant. Within the initial period the value of the ratio was lower. It was also shown that many derivatives of mandelic acid were resolved on wool, in- cluding those containing o-nitro-, rn-nitro-, p-nitro-, p-methoxy-, p-hydroxy- and o-ethoxy-groups as nuclear substituents. Further it was found that when mandelic acid combined with L-arginine or L-lysine the resulting salts contained the (+)-acid in greater amount ; the occurrence of resolution coincided with the separation of the crystalline salts.L-Arginine and L-lysine are the principal basic amino acids of wool and for this reason it appeared probable that the form of the union between wool and mandelic acid at pH 2.5 is the same as between wool and hydrochloric acid or wool and chloracetic acid at the same pH, and that in each of these instances the chloride, chloroacetate or mandelate ions are as intimately associated with the positive centres of the fibre as they are with the cations in crystalline L-arginine (or L-lysine) mandelate. Olofsson 3 has formed the same opinion regarding the sulphate ion from a study of the com- bination of wool with sulphuric acid. It is now generally accepted that wool fibres consist of mainly crystalline and non-crystalline assemblages of polypeptide molecules and that the more open and less crystalline regions are the more easily reached by water and aqueous acids.Ultimately, carboxylic acids such as benzoic or naphthoic which are comparable in size with mandelic acid do penetrate even the mainly crystalline regions though certain azo-sulphonic acids do n0t.4 For this reason it is probable that the initial rapid absorption of mandelic acid occurs in the more accessible and less crystalline regions, and that thereafter slow penetration of a mainly crystalline region takes place. The second stage is characterized by constancy of the ratio, (acid resolved)/(acid absorbed), which would be expected if the acid is encountering a chemically and physically homogeneous region of the fibre.It suggests that resolution is occurring on a crystal lattice as in the resolution of mandelic acid on crystals of L-arginine. The argument does not exclude resolu- tion in the mainly non-crystalline regions but there the degree of resolution should be smaller and more variable.5 Our results show that resolution occurs from the beginning of the absorption process but that the degree of resolution is greater in the second stage. When wool combined with mandelic acid is placed in water, transfer of acid from wool to water occurs almost immediately, a new equilibrium being reached at a new value of pH. In this respect mandelic acid differs completely from the higher p-alkoxymandelic acids and the simplest acid dyes, e.g. p-sulphobenzeneazo- P-naphthol, which are retained on the fibre after immersion in water.When wool equilibrated with a solution of (-)-mandelic acid at pH 2.5 is immersed in (f)-mandelic acid at the same pH, replacement of (-)-mandelic acid on the wool by (+)-mandelic acid in solution occurs. The rate of change is low. This result is not unexpected since the (+) and (-)-forms of the mandelate ion are chemically identical and a difference in behaviowr of the (+) and (-) forms of the acid, which must in any event be small, depends solely on the structures of the two mandelate salts when combination with wool has taken place. When the anions concerned are chemically and physically different the process ofI54 ABSORPTION OF OPTICAL ANTIPODES replacing one by the other may proceed at a readily observable rate.Thus Elod 6 found that wool immersed in an aqueous solution of the disodium salt of 1- naphthalencazo-2-naphthol-3 : 6-disulphonic acid containing hydrochloric acid combined first with hydrogen and chloride ions, the latter being replaced sub- sequently by anions of the dye. The present experiment indicates that interchange of anions can take place independent o€ a difference in the composition of the anions. Earlier workers who studied the resolution of organic acids on wool generally obtained negative or variable results and this was probably because in almost every instance the acid molecule was very large. For example, Ingersoll and Adam7 reported the resolution of the azo dye obtained by coupling diazotized a-p-benzamidophenylacetic acid to dimethylaniline, but Brode and Adams 8 found that the rate of uptake of the two optical enantiomorphs was the same.Again, Porter and Ihringg stated that the azo-compound obtained by coupling diazotized m-aminomandelic acid to P-naphthol was resolved on wool but Brode and Adamslo could not confirm the claim. Later the same authors 11 found no evidence for the selective absorption of optical antipodes when the acid was the bis-azo-compound derived by coupling tetrazotized 2 : 2'-diamino-l : 1'- dinaphthyl to two molecules of phenyl-J-acid. We ourselves have found that the behaviour of mandelic acid is reproduced in its simple substitution products but not with m-(p-hydroxypheny1azo)mandelic acid (TI). (I) m H O H - C O 2 H (11) /-\-CHOH-CO~H HO<>N=N >-' It should be mentioned that the resolution of racemic mixtures has been ob- served on substrates other than wool, but the circumstances of the experiments were quite different from the uptake of acids by wool from an aqueous or aqueous alcoholic solution.Thus Henderson and Rule 12 prepared an '' activated " form of lactose and on it resolved an azo-compound and p-phenylene-bis-imino- camphor. In addition Kotake, Sakan, Nakamura and Senoh 13 resolved amino acids on cellulose, Tsuchida, Kobayashi and Nakamura 14 resolved chloro-bis- (dimethylg1yoxime)amminocobalt on quartz, and Kayagunis and Coumoulos 15 resolved Cr [(en)3] Cl3 on the same substrate. We have investigated the effect of size and configuration of acids on their absorption and resolution on wool in some detail.Three ring-homologues of mandelic acid having compact, planar structures were all readily absorbed and resolved. They were a-naphthylglycollic acid (III), p-naphthylglycollic acid (IV), and 9-arithrylglycollic acid (V). Evidently compact molecules of this size do reach the basic centres of wool quite readily. The 9 : 10-dihydro-derivative (VI) of the anthracene acid was absorbed but not resolved. It differs from the preceding acids in being non-planar but the failure to resolve it may have been due to low molecular rotation or low optical stability, both properties being characteristic of the aliphatic acids. CHOH-CO2H I CHON-C02H H CHOH-C02HW. BRADLEY, R. A. BRINDLEY AND G . C. EASTY 155 Apart from the binding of anions at the ammonium groups of wool there is another factor (" affinity 7 which increases the amount of acid absorbed at a given pH.16 In our experiments the existence of affinity would havc the effect of increasing the absorption of (4-) and (-) forms of mandelate ions equally and so reducing the observed degree of resolution.Steinhardt, Fugitt and Harris 17 have stated that affinity due to a benzene nucleus is not considerable, nor is it greatly increased by the introduction of simple substituents. This accords with our own experience that not only is mandelic acid resolved on wool but its 0-, m- and p-nitro and its p-hydroxy, p-methoxy and o-ethoxy derivatives are a11 readily absorbed and resolved. The resolution of the nitromandelic acids is particularly interesting because the highly polar character of the nitro group should favour non-specific absorption of both forms of nitromandelate ions.To test the efYect of unsaturated centres we have also investigated the two planar heterocyclic acids (WI) and (VIHI) which contain an ether oxygen atom and are respectively the furan and diphenyleneoxide analogues of mandelic acid. Both were resolved and there was no indication of any special effect due to the hetero- oxygen atom. 4-Diphenylglycollic acid (IX), a relatively large molecule which can adopt a non-planar form, was also absorbed and resolved. (IX) C m H O H - C O 2 H - (x) RO<>CHOH-CO~H - The non-resolution of rn-(p-hydroxypheny1azo)mandelic acid led us to in- vestigate the effect of including an unbranched aliphatic chain of increasing length in a series of p-alkoxy derivatives of mandelic acid (X).Thep-methoxy (R=CH3), p-ethoxy, (R= C2H5), p-pentoxy, (R= C~lHll), and p-heptoxy, (R= C7H15), sub- stituted acids were all readily absorbed and resolved. The p-decoxy, (R= C~OHZ~), acid was absorbed to a smaller extent than the lower acids in equal time. The observed rotation of the absorbed acid was also smaller. p-Hexadecoxymandelic acid (R=C&33), also was poorly absorbed and not resolved at all. Further, with increasing chain length the absorbed acid becomes increasingly difficult to desorb with aqueous ammonia. The results harmonize with the view that, for the Clo- and C16-alkyl acids, sorption by non-ionic forces plays a dominant role and diminishes or even eliminates the differences between the (+) and (-) forms of the anions arising from their spatial arrangement.Reference should be made in this connection to the observation of Preston18 who showed that certain sulphonated acid dyes containing long alkyl chains were absorbed by wool, from which the epicuticle had been removed, through sulphonic acid groups, when dyeing was done in sulphuric acid solution, and by means of the alkyl chain, when the dyebath was neutral. The non-resolution of m-(p-hydroxy- pheny1azo)mandelic acid is noteworthy. p-Heptoxymandelic acid is resolved quite readily, even though it is also difficult to remove from the fibre by treatment with cold ammonia. It appears that in this acid a marked affinity can be demon- strated whilst at the same time the anions of the acid do reach the ammonium groups of the fibre.The relationship of p-heptoxymandelic acid to the simplest of the levelling acid dyes such as Orange I1 must be close indeed. EXPERIMENTS WITH MODIFIED wooL.--rFhrough the kindness of Mr. C. 0. M. Steward we have been able also to compare the absorption and resolution of mandelic acid on slubbing from a dry-combed 64's top and a similarly treated 64's dry-chlorinated top. We could observe no difference whatever in the be- haviour of the two samples of wool. The dry-chlorination of wool has been stated to affect the surface structure of the fibre and to lead to an increased rate of dyeing with acid dyes without correspondingly increasing the basic properties of ~ 0 0 l . 1 9156 ABSORPTION OF OPTICAL ANTIPODES Also through the kindness of Mr.Steward we have been able to examine 60/64‘s Australian wool which has been scoured by the solvent scour procedure devised by Lindberg (Swedish Research Institute). This wool still retains the very thin outer membrane (“epicuticle”) of wool fibres. I n its reaction with mandelic acid it proved to be indistinguishable from the wool used in the main experiments. Tt appears certain, therefore, that the uptake of mandelic acid relates to the fibre as a whole without regard to its external morphological structure. EXPERIMENTAL Australian 64’s Merino wool in the form of dubbing, for which we are indebted to Mr. C . 0. M. Steward of Messrs. W. and J. Whitehead (Laisterdyke) Ltd., Bradford, was cleaned by extraction in a Soxhlet with ether, then with alcohol.It was then kept for 24 h in water acidified with acetic acid and finally it was washed in running water for not less than 24 h. GENERAL PROCEDURE.-WOOL (usually 50 g) was immersed for 18-24 h at room tem- perature in 1 1. of a mixture of water and alcohol having the composition stated in the following table and containing 0.025 mole of the acid under investigation, except in the cases noted. The wool was then filtered off, using a sintered-glass funnel, and squeezed as dry as possible. An amount of the mother liquor equal in weight to the dubbing remained mechanically held. The Jiltrate * was evaporated to small volume, hydrochloric acid was added and the organic acid extracted by means of ether. The extract, filtered when necessary, was evaporated to constant weight (vacuum desiccator) and the residue was dissolved in absolute alcohol or acetone and its optical rotation determined in a 20-cm tube, capacity 17.5 ml, in a Hilger type M413 polarimeter. The error arising from the retention of mother liquor by the wool was negligible. The wool containing absorbed and mechanically held mandelic acid was immersed for an hour in 1 1.of 0.1 N aqueous (or aqueous-alcoholic) ammonia, then filtered, washed with aqueous alcohol or water and squeezed. The filtrate was treated as filtrate * and the rotation due to the acid held by the wool was determined. With rnandelic and p-methoxymandelic acids one treat- ment with 0.1 N ammonia was sufficient to remove all the acid. With the acids con- taining longer alkyl chains two or more treatments were necessary.Details of the experi- ments are shown in the following table 1. TABLE 1 difference be- tween initial v ~ ’ * aD of acid solutions (”) wt. of wt. of FLd z;i total wt. andwt. oft%- period of acid sorbed not acid unabsorbed perl contact acid used and ab- reco- a c i ~ o l e 1. of- final (h) acid pH absorbed not absorbed reco- sorbed vered vered (6) (g) (s) (€9 (9) perkgt& wool mandelic p-CH30 99 (0) P-C~HSO 19 (b) P-CSHIIO ,Y P-C7H150 9, (a) (b) P-CIOHZIO 3, (0) (b) PC16H330 (0) (b) a-furylglycollic acid dip hen y I e n e o xi degl y - p-phenylmandelic acid fi-naphthylglycollic acid 9 : 10-dihydro-9-anthryl- collic acid 3.80 1.78 1.93 3.71 1.87 0.25 4.55 1.96 2.38 4.34 2.17 0.24 4.55 1.99 2.52 4.51 2.03 0.23 4.90 2.10 2.65 4-75 2.25 0.23 5.95 2.78 3.31 6-09 264 0422 6.65 3.93 2.88 6.81 3.77 0.28 6.65 3.60 2.78 6.38 3.87 0.29 6-69 0.84 5.75 6.59 0.94 0.06 5.49 2.89 2.05 4.94 3.44 0.22 9.80 0.69 7.14 7.93 2.66 0.13 9.80 1.07 6.09 7.16 3.71 0.19 6-10 2.9 2.8 5.7 3.3 0.27 7.10 3.7 - - - - 5.70 2.55 2.8 5.35 2.9 0.25 4.87 2.40 2.18 4.58 2.69 0.27 6.10 1.85 3.30 5.15 2.80 0.22 500 750 500 500 500 500 500 750 750 800 750 500 500 500 800 800 24 18 24 24 24 24 24 24 18 24 24 24 120 3.91 24 156 4.31 156 4.72 + 0.240 -1- 0.245 + 0.225 + 0.225 + 0.225 + 0.200 +0.145 + 0.04 +0*12* 0.0 - 0.04 +0*16 + 0.07 + O * l O t +0.425 8 0.0 -0.217 -0.215 -0.200 -0.175 -0.08 -0.11 - 0.22 -0.03 -0.07** 0.0 0-0 -0.19 -0.18 f: -0*215@ 0.0 I glycollic acid 9-anthrylglycollic acid (i) 2.63 1.30 0.62 1.92 2.01 0.20 750 120 4.72 +0.05 -0.13111] (ii) 5.58 3.63 1.61 524 3.97 0.21 750 120 5.04 +0-1011 -0.18 71 * for 2.45 g, ** for 1.8 g, 1) for 1.45 g, 1111 for 0.4 g.7 for 0.83 g, f for 1.3 g. § for 2.12 g, 3 for 1.2 g, fs for 1.92 g.W. BRADLEY, R . A . BRINDLEY A N D G . C. EASTY 157 NoTEs.--I. The amounts (moles) of the following acids used were : p-decoxymandelic (a), 0.021 7, (6) 0.01 77 ; a-furylglycollic 0.05 ; p-naphthylglycollic 0.024 ; 9-anthrylgly- collic (a), 0.01, (6) 0.022. 2. The volume (ml) of solvent employed in certain experiments was : p-decoxymandelic, 3. The amount (8) of wool used in certain experiments was: a-furylglycollic, 75; 4. In thep-hexadecoxymandelic expt. (a), the medium containing the wool was heated In expt. (b), the temperature 5. Two or more treatments with cold ammonia were required to desorb the acids (b), 600 ; 9-anthrylglycollic, (a), 500, (b), 600.9-anthrylglycollic (a), 39, (6) 75. under reflux for an hour before withdrawing the wool. was that of the refluxing solvent throughout the whole period. completely in the following instances (table 2). TABLE 2 amount and rotation of acid desorbed - acid wt (g) c(D ("1 p-pentoxymandelic stage 1 2.37 +Om14 p-heptoxymandelic (a) 97 1 3.01 + 0.075 7) 3 0.20 + 0.035 9 ) 2 0.56 + 0.065 9 9 2 0.85 -1- 0.085 9 7 2 0 72 -t 0.090 p-heptoxymandelic (6) 9 , 1 2.72 + 0.06 9 9 3 0.27 + 0.02 99 4 0.05 0.0 7 9 2 0.13 0.0 p-decoxymandelic (a) 79 1 0.52 + 0.025 Y 7 3 0-19 $0.015 6. When the amount of acid absorbed was about one-half of that used in the experi- ment the difference between the total amount of acid retained by the wool and the amount of acid combined with the wool was negligible.This was true of all the experiments excepting those with 9 : 10-dihydro-9-anthrylglycollic acid, p-decoxymandelic acid (a), and p-hexadecoxymandelic acid (a) and (6). In these instances the acid mechanically held formed a substantial part of the total retained. Even so this circumstance did not affect the degree of resolution of p-hexadecoxymandelic acid, for this was not resolved at all. With p-decoxymandelic acid (a) the degree of resolution would be higher than is conveyed by the recorded optical rotation. DRY CHLORINATED woo~.-Wool (30 g dry weight) was immersed for 5 days at 31.3" in a solution of 5 g (5)-mandelic acid in 600 ml of water. The amount of acid absorbed and its optical rotation were determined and the experiments was repeated several times.An identical and parallel series of experiments was carried out using chlorinated wool. The following results were obtained. acid absorbed acid unabsorbed _ _ _ wt (g) 'D(") wt (g) aD(") wool 2.418 + 0.26 2.447 - 0.26 chlorinated wool 2425 + 0.26 2.471 - 0.25 CoNcLusIoNs.--The molar amount of mandelic acid that combines with 1 kg of wool at pH 2.5 and 31.3" is almost identical with the corresponding amount of hydrochloric acid. At least a part of the acid present in the wool-mandelic acid complex is in the form of mandelate ions which are bound to the ammonium groups of the complex in the same manner as are the ion-pairs of a simple crystal- line salt. Similarly, typical ammonium salt links are formed between wool and the u-, m- and p-nitro, p-hydroxy, p-methoxy, 0- and p-ethoxy, p-pentoxy, p - heptoxy and p-decoxy derivatives of mandelic acid, and also between wool and several more complex derivatives of mandelic acid having larger, planar molecules.p-Hexadecoxymandelic acid is absorbed but not resolved. Probably, in this instance the acid is attached to the fibre by means of the alkyl chain. In the158 PROTEIN MONOLAYERS p-alltoxymandelic acids as the length of the alkyl chain increases the absorption rate decreases and it becomes increasingly difficult to remove the absorbed acid from the wool. No difference was found between soap-and-soda scoured wool, solvent scoured wool and dry chlorinated wool in their reaction with mandelic acid, which is not influenced therefore by the surface structure of the fibres.We desire to express our thanks to the International Wool Secretariat for the award of a Research Scholarship to one of us (R. A. B.), and to the University of Leeds for the award of a Brotherton Research Fellowship in Physical Chemistry to one of us (G. C . E.). 1 Bradley and Easty, J. Chem. SOC., 1951, 499. 2Bradley and Easty, J. Chem. SOC., 1953, 1519. 3 Olofsson, J. SOC. Dyers Col., 1952, 68, 506. 4 Astbury and Dawson, J. SOC. Dyers Col., 1938, 54, 6. 5 Ferreira, Nature, 1953 171, 39. 6 Elod, Trans. Faraday SOC., 1933, 29, 327, 7 Ingersoll and Adams, J. Amer. Chem. SOC., 1922, 44, 2930. 8 &ode and Adams, J. Amer. Chem. SOC., 1926, $8,2193, 2202. 9 Porter and Ihring, J. Amer. Chem. Soc., 1923, 45, 1990. 10 Brode and Adams (ref. 8). 11 Brode and Adarns, J. Amer. Chem. SOC., 1941, 63, 923. 12 Henderson and Rule, J. Chem. Soc., 1939, 1568. 13 Kotake, Sakan, Nakamura and Senoh, J. Amer. Chem. SOC., 1951, 73, 2973. 14 Tsuchida, Kobayashi and Nakamura, Bull. Chem. SOC. Japan, 1936, 11, 38. 15 Kayagunis and Coumoulos, Nature, 1938, 142, 162. 16 Steinhardt, Fuggitt and Harris, Bur. Stand. J. Res., 1941, 26, 293. 17 Steinhardt, Fuggitt and I-Iarris, Bur. Stand. J. Res., 1942, 28, 201. 18 Preston, Hexagon Digest, 1952, 11, 3 1 (Messrs. Imperial Chemical Industries Ltd.). 39 Lemin and Vickerstaff, Fibrous Proteins (The Society of Dyers and Colourists, Bradford, 1946), p. 129. Barritt and Elsworth, J. SOC. Dyers Col., 1948, 64, 19. Stevens, Whewell and R. M. Bradley, J. Suc. Dyers CoE., 1950, 66, 435.

ISSN:0366-9033    

DOI:10.1039/DF9541600152

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

158 PROTEIN MONOLAYERS TANNING S P PATTY ACID, AMNO ACID AND PROTEIN MONQLAYERS BY METAL IONS BY J. €3.. SCHULMAN AND M. 2. DOGAN Ernest Oppenheimer Laboratory, Dept. of Colloid Science, University of Cambridge Received 6th July, 1953 Fatty acid monolayers are made insoluble by metal ions only at the pH at which the basic metal ions are found. This interaction is accompanied by a large increase in the area per molecule of fatty acid and solidification of the monolayer. By a chemical analysis of these “ tanned” monolayers it was shown that in the case of chromium ions and straight chain fatty acids one ion is attached to one fatty acid molecule. If the area of fatty acid is made greater by branch chain substitution a further chromium atom can be anchored into the monolayer per fatty acid molecule.The structure of these two-dimensional solid lattices can be shown to be brought about by the interlinking between neighbouring molecules by hydrogen bonding between the hydroxyl groups attached to the basic metal ion and ketonic groups in the carboxyl group in the fatty acid. Steric conditions in the formation of these two-dimensional lattices vary with each metal ion, but the greatest possibilities are shown with chromium and copper. Long-chain hydrocarbon amino acid inonolayers behave similarly, but no tanning i s observed with long-chain amine monolayers. Protein monolayers in which there is aJ . H. SCHULMAN A N D M. Z. DOGAN 159 carboxyl group in the protein molecule such as serum albumin, but not gliadin, react in direct analogy to the fatty acids, with the basic metal ions other than copper.These monolayers expand and solidify with time effects showing that the steric factors involved in the cross-linking between the hydroxyl groups in the basic metal ions to neighbouring protein chains are important in the tanning of the protein monolayers. Copper, in direct contrast, does not react with the carboxyl group in the protein monolayer but with the imidazole group, thus tans gliadin and methaemoglobin monolayers readily but not serum albuinin. It has been shown by Wolstenholme and Schulman191a and Thomas and Schulman 2 that metal ions such as Fe, Al, Co, Cu, Zn, Pb, interact with fatty acid and long-chain sulphate monolayers over the pH stability of the basic metal ions. Ions such as U@+ and Ca2+ form insoluble soaps in the ionized and not in the basic ionic form owing to steric hindrance both from the shape and size of the long-chain ionic compounds and from the metal ions themselves.Thus various steric factors and pH of the solution play an important part in controlling the interaction between metal ions and ionic groups in orientated monolayers. The nature of the reaction is first an adsorption of the basic metal ion on to the carboxyl or sulphate ionic group in the monolayer and then a link between the adlineated hydroxyl groups by hydrogen bonding to build up a two- dimensional solid lattice. On this structure the long-chain hydrocarbon com- pounds are spaced. In contrast the simple metal soap monolayers are readily soluble. It has been further shown by Smith and Schulman 3 and Cuming and Schulman4 that adsorption of these long chain ionic compounds from solution on to the solid surfaces of the metals or minerals composed of the metals men- tioned above takes place under identical pH and stereochemical conditions as with the monolayer interactions.It is the purpose of this publication to test the analogy between the interactions of basic metal ions and monolayers of fatty acids, amino acids and different proteins with the tanning of collagen by chromium ion solutions. It has already been shown by Schulman and Rideal5 and Cock- bain and Schulman6 that there is a direct analogy between the interaction of large molecules or polymers containing spaced phenolic or silicic acid groups and long-chain amine and protein monolayers, and vegetable tanning.EXPERIMENTAL METHoD.-This consisted of measuring the solidification area and the forcelarea curves of monolayers of the various fatty acids (straight and branch chain), stearyl tyrosine and protein such as gliadin, bovine serum albumin, insulin and methaemoglobin with the metal ions in the underlying solution at a concentration, chiefly, of M/2000. Addition of salts such as Na~S04 and NaCl were added where necessary to enable a protein such as methaemoglobin to spread to a monolayer and also to discharge the amine ionic groups of the protein monolayer to overcome the positive potential barrier in order to permit the positive basic metal ions to adsorb and interact with the negative carboxyl groups. The pH was controlled by addition of N/10 NaOH or N/IO MCI to a COz solution containing the metal salt, or by sodium bicarbonate and sodium acetate.The mechanical properties of the interacted monolayers were qualitatively observed by blowing talc powder on the surface of the monolayer. on straight and branch chain fatty acid (myristic and 4 : 10-butyl decyl acetic acid) mono- layers spread on chrome alum solutions in order to find out the composition of the basic chromium ion fatty acid complexes. A Perspex trough of 100 x 17 x 1 cni was used and 12 monolayers were spread and removed. After spreading a monolayer the area of solidification was recorded and the film then compressed. 'The nionolayer was collected with a glass scoop and was dried with a filter paper before transferring it to a weighing crucible ; this eliminated the inclusion of the solution in the film.It was heated in an oven to 100" C and weighed to a constant weight in a microbalance. The crucible CHEMICAL ANALYSIS OF INTERACTED MONOLAYERS.-ChemiCd analysis Was carried out160 PROTEIN MONOLAYERS was then heated to redness before chromium determination in order to dispel the fatty acid. The following procedure was adopted for the chromium analysis. The sample was fused with Na202 to convert chromium into chromate. The latter in acid solution (H2SO4) gave a pink colour with the reagent diphenyl carbazide. The intensity of the colour was determined on a Spekker colorinieter. This method gave reproducible results. In parallel with fatty acid monolayers, hexadecyl alcohol monolayers spread on M/2000 chrome alum and were collected to find out the quantity of chromium ions held to the monolayer by physical adsorption.There is no interaction between metal ions and alcohol monolayers. Approximately 2 mg of monolayer were collected by these methods. A convenient method of determining the amount of fatty acid collected would be to hydrolyze the chromium soap in acid and then respread the fatty acid on the Langmuir trough and determine its area and hence its weight. This method was not used in the following determination with the chromium interactions, but was used by Thomas in his copper ion fatty acid interactions. A summary of Thomas' work will be given. He obtained a 65-70 % recovery of the amount of film spread, a result very similar to that found for the chromium experiments. The weight of the films collected was about 2 mg.RESULTS A N D DISCUSSION INTERACTION OF M/2000 CHROME ALUM ON LONG CHAIN FATTY ACID MONO- LAYERS.-It has been shown by Wolstenholme and Schulmaii 1 9 la that myristic FIG. 1. A. pH 1.971, 7.5" c 1. pH 3.25, 17.5" c 2. pH 3.72, 14" C 3. pH 4.39, 17.5" C 4. pH 4-80, 18" C 5. pH 5.40, 19" C 6. pH 5.65, 14.5" C 7. pH 5.87, 15.5" C acid or branch chain fatty acid monolayers readily proceed to go into solution at pH 3 or greater. They are made insoluble by the formation of the basic metal soaps, steric hindrance can prevent the hydrogen bonding between the hydroxyl groups in a decreasing order of magnitude, for the following ions, Ca2+, c02+, Fe3+, A13-'-, Cr3+, Cu3f and thus prevent the formation of the insoluble complex.1~ In fig.1 , 2 and 3 the interaction of M/2000 chrome alum solutions has been shown with myristic acid, a-methyl myristic acid and butyldecylacetic acid, by a study of their force area curves at different pH. The largest area of solidication of the monolayer occurs around pH 5.3 and is 42 A2, 53 A2 and 80 A2 respectively as the size of the fatty acid molecule increases, further the pH range of solidification diminishes as the cross-sectional 8. pH 6-20, 17' C 9. pH 6.42, 15.5" C 10. pH 6.73, 17" CJ. H. SCHULMAN AND M. Z . DOGAN 161 area of the fatty acid is increased. Without the chromium ions in solution the liquid fatty acid films would be very soluble at pH 5.3. This is summarized in fig. 4, showing also the variation of the area per molecule at solidification with changing pH for the different metal ions.Fig. 5 shows clearly that FIG. 2.--a-Methyl myristic acid and M/2000 chrome alum interaction. 4. pH 5-44, 15" C 5. pH 5-71, 15.2" C 6. pH 5.89, 13.8" C 1. pH 4.30, 14" C 2. pH 4.80, 14" C 3. pH 5.14, 14" C 7. pH 6.11, 14.3" C 8. pH 6-38, 16" C A. pH 294, 16" C at pH 5.3 for chromium ion solutions the maximum number of Cr(0H)zf ions (calculated from the data of Pourbaix 7 ) is available, this number diminishing rapidly on increasing pH. It thus could be supposed that at pH 5.3 for chromium solutions the fatty acid mono- layers are solidified by the formation of a chromium monosoap molecule interlinked with its neighbours either side by the hydrogen bonding of the two hydroxyl groups PU I FIG.3 . 4 : 10 acid and MI2000 chrome alum interaction. 1. pH 4.72, 13" C 2. pH 5.05, 14.6" C 3. pH 5.14, 14.5" C 4. pH 5-53, 15" C 5. pH 5.86, 16.5" C A. pH 2.05, 16" C (see fig. 6). As the cross-sectional area of the fatty acid molecule is increased by branch- chain substitution another basic chromium ion can bridge the gap in the chain polymer. A further cross-bridging can be envisaged by the C=O group in the carboxyl group of the fatty acid interlinking with one of the hydroxyl groups of the neighbouriog molecule. A close-packed solid network consisting of linear chain polymer bonded by these two F162 PROTEIN MONOLAYERS forms of hydrogen bonding and by the van der Waals forces of the hydrocarbon chains can be seen as the structure of the two-dimensional lattices (fig.6). This picture of the structure of the " tanned " two-dimensional solid chrome fatty acid lattice receives strong support from the chemical analysis of myristic and 4 : 10-acid monolayers spread on M/2000 2 4 6 8 FIG. 4. A. Effect of M/2000 chrome alum on 1. 4 : 10 fatty acid CloH21CHCOOH B. Effect of pH on area of solidification cross-sectional area 46 W2/mol. fatty acids. I C4H9 I CH5 2. 1 : 12 fatty acid Cl2H25CHCQQH cross-sectional area 30 Az/mol. 3. Myristic acid ClzH25CH2COOH cross-sectional area 20 A2/moI. chrome alum solution. It will be shown in the following section that one chrome atom is analyzed for one myristic acid molecule and two chrome atoms for one butyldecyl- acetic acid molecule in the solid monolayers at pH 5.3.CHEMICAL ANALYSIS OF THE FATTY ACID MONOLAYERS SPREAD IN M/200 CHROME ALUM. -The results of the experiment are shown in table 1. Octadecyl alcohol monolayers I FIG. 5.--Basic ions in M/lOQQ chromic solution. do not interact with metal ions. Therefore, Cr determined with these monolayers would be due to physical adsorption only. At pH 4.9 and 4.95 no Cr was found ; at pH 5.35. chromium hydroxyl started to precipitate, hence Cr was included in the alcohol monolayers This physically adsorbed Cr was taken into account with the evaluation of Cr content163 of the long chain fatty acid lnonolayers at pH 5.35. 72 % of the long-chain alcohol monolayers could be collected. The percentage recovery for myristic acid Or 4 : lo-acid monoIaYers could not be determined directly owing to presence of cr.Cr may be adsorbed as Cr(OH)2+, c ~ ( o H ) ~ 2 + or Cr(HC03)2+ and in addition may contain sulphate J . H . SCHULMAN AND M. Z . DOGAN 1 FIG. 6.-Two types of hydrogen bonding in the two dimensional ,mned lattices. TABLE 1 (a) myristic acid inonolayers on M/2000 chrome alum amount spread amount weighed Cr determined Crlmyristic acid Cr/myristic acid (m) (mg) recovery) (mg) in the sample (assume 60y0R) (assume 70% PH 5.0 1.39 1.6 0175 0.92 0.83 4.9 1.785 1.8 0-150 0.68 0.55 4.95 1 -79 2 1 0.220 0.90 0.8 1 5-35 1.885 2.4 0.400 1 *05 0.90 5.35 1-885 2.0 0.440 1.20 1.03 (b) 4 : 10-acid on M/2000 chrome alum amount spread amount weighed Cr determined Cr/4:lO acid Cy::J22d PH (mg) (mg) in t g g m p l e (assume 60% R) 70% R) 5.35 1.50 1.8 0.469 1.9 1.6 5-35 1.54 1.6 0.39 1.45 1-25 (c) octadecyl alcohol on M/2000 chrome alum 4.9 2-68 2-0 - 720 4.95 2-35 1.7 - 72.5 5.35 1.885 1.7 0.16 - 5.35 1-885 1.5 011 - ions from the sub-solution.Some of the fatty acid monolayers could not be recovered owing to the fact that with these systems the film tended to stick to the glass slides so high recovery could not be obtained. In working out Crlfatty acid ratio, two recovery figures were assumed 60 % and 70 %. Thomas2 has shown that by hydrolyzing the collected basic copper soap and respreading the fatty acid, that a 70 % recovery was obtained.164 PROTEIN MONOLAYERS From an analysis of known and equivalent quantities of chromium salts by this analytical method, the results of the collected chromium were about 15 %' too low.Corrections can l5e made for this, but it can be seen (table 1) that at the optimum pH for solidification 5.35 about one atom of chromium is collected for one myristic acid (area 42A2) molecule in the monolayer and 2 atoms of chromium for the branch chain fatty acid molecule (area 80 A2) where another chromium dihydroxide ion is required to bridge the gap in the solid lattice produced by the substituted branch chain. The fatty acid molecules in the monolayer are only partially dissociated at pH 5.3. By forma- tion of an insoluble basic metal soap with the available fatty acid ions the equilibrium would be changed and more fatty acid ions would become available until the whole mono- layer would be in the insoluble basic metal soap form.This gives strong support to the type of structure given for the tanned fatty acid monolayers in the previous section. INTERACTION OF STEARYL TYROSINE MONOLAYERS WITH M/2000 CHROME ALUM AND the stearyl tyrosine monolayer on M/100 Na2SO4 solution at different pH's. The presence of Na2S04 is necessary since the positive basic metal ions cannot approach the zwitter M/2000 COPPER SULPEIATE IN THE PRESENCE OF M/100 SODIUM suLPHATE.-Fig. 7 shows FIG. 7.-Stearyl tyrosine monoIayers on M/100 Na2S04 solution. ion monolayer in the presence of the positive amine group. The sulphate ion removes the positive potential barrier. This becomes very important in the case of the proteins. Fig. 8 and 9 show the effect of chromium ions and copper ions in the underlying solution.Here again the reaction is similar to those already seen for the fatty acid monolayers. The films become tanned and solid at very increased areas per amino acid molecule at the pH of the basic metal ion formation, 5.25 for chromium and 6.26 for copper. The striking interaction of the copper ions with the amino acid monolayers is interesting in view of the experiments in the following section. These show that the copper ions do not interact with the carboxyl groups in protein monolayers. The metal ions chromium and copper as acetate solutions show no interaction with long-chain amine monolayers. Complexes can only be formed with the amine group in its associated form, and the metal ions are not in solution but precipitated at the alkaline pH necessary.THE INTERACTION OF MONOLAYERS OF PROTEINS WITH METAL IONS Cr, Cu, Fe and Al. -Bovine Serum albumin manoZayers.-The serum albumin was dissolved in distilled water, 1 mg/inl, containing 1 % ethanol as a spreader. The protein monolayer spread quickly to consistent values on distilled water or buffers. They were spread on the chromiumJ . 13. SCHULMAN A N D M. Z . DOGAN 165 ion solutions at different pHs and it immediately became evident that whereas the inter- action and solidification were immediate on fatty acid and amine acid monolayers time effects were observed with the protein monolayers. The spreading values became con- sistent after 1 h. This time effect may be due to steric factors in the linking of the various carboxyl groups in the protein molecule chains orientated at the surface, similar to the tanning of the branch chain fatty acids, by the basic chromium ion bridges.I cji.43 FIG. 8. - Stearyl tyrosine monolayers on M/2000 chrome alum M/100 Na~S04. FIG. 9.-Stearyl tyrosine monolayers on M/2000 CuSO4, MI100 NazS04. FIG. 10.-Bovine albumin films. A. pH 3.8, M/lOONazS0410H20 18" C 1. pH 2.1, M/2000 chrome alum 18" C 2. pH 3-7, ,, 7, ,, 20" C 1 h. 3. pH 4.21, ,, 9 , ,, 17.5" C 1 h. 4. pH 4.76, ,, 3, ,, 18.5" C 1 h. 5. pH 5.26, ,, 9 ) ,, 185°C 1 h. 6. pH 5.71, ,, Y7 ,, 17~5°C 1 h. 7. pH 6.07 ,, 3, ,, 18.5"C 1 h. 40 ClTl 30 Fig. 10 shows quite clearly that the optimum expansion and solidification of the protein monolayer takes place at pH 5.26, which is identical with the tanning pH of fatty acid monolayers.Curve 5 shows a tanned serum albumin film without visco-elastic properties, rigid and incompressible standing very high pressures before collapsing.166 PROTEIN MONOLAYERS The surface potential against area (m2/mg) curve shows likewise that the structure is a solid in which no reorientation of the polar groups takes place on compression, the surface potential remains constant at 200 mV (curve 5). At pH 2 the surface potential changes from 150 mV to 350 mV on compression over curve 1 showing no tanning, and changes from 200 mV to 300 mV at pH 4-8 for curve 4, showing partial tanning. FIG. 11 .-Bovine albumin films. 1. pH 3.8 : M/100 Na2S04, 21" C. 2. pH 2.38: M/lOO ferric chloride, 3. pH 2.86: M/100 ferric chloride, M/10 Na2S04.10 H20. 21" C (2 h). 21" C (14 h); 4.pH 4.2: M/100 AIC13 . 6 H20, 5. pH 4.4: M/100 AlC13. 6 H20, 21" C (1 h). 20.5" C (1 h); M/10 Na2S04.10 H20. 6. pW 5-52 : M/100 hSo4.5 H20, 20" c. 7. pH 5.26: M/2000 chrome alum, 18-5" C (1 h). 8. pH 7.15 : phosphate buffer; tannic acid 80 mg/l. ; rigid unstable film after 19 h. Fig. 11 shows that again by analogy with the fatty acid tanning other metal ions such as Fe and A1 only tan the serum albumin protein monolayer at the pH at which the basic metal ions are formed, pH 2.8 and pH 4.2 respectively, enabling the hydroxyl cross- bridges to be built in the tanned two-dimensional lattice. It can be observed that tanning only takes place in the Na2S04 solution, which overcomes the positive potential barrier of the amine groups in the protein monolayer. FIG. 12.--Serum albumin mono- layers on M/2000 CuSO4.5 H20; M/100 Na2SO . 10 El204 after 1 h. x pM 3.81, sat. C02 A pH 5.42, sat. CO2 El pH 6.57, sat. C02 0 pH 7.24, sat. C02. In fig. 11 as comparison, both the tanning by chromium ions and that given by tannic acid are shown (curves 7, 8). The spaced phenolic groups in the tannic acid molecule, as described by Schulman and Cockbain,6 bridge scross the amine groups in the mono- layer and this expands and rigidifies the protein monolayer by analogy with the immobilizing of the carboxyl groups by the basic metal ionic lattices.J . H. SCHULMAN A N D M. Z . DOGAN 167 Fig. 12 also shows the astonishing result that copper ions have no effect on serum albumin monolayers. The reason for this is not clear since copper solutes at the basic metal ion pH of 6.3 tan fatty acid and amino acid monolayers very readily, expanding these films to large areas per molecule.It may be that the basic copper ion can only FIG. 13.-Gliadin on chrome alum. M/2000 chrome alum, M/100 Na2S04 ; (sat. C02, pH 5.5). x after 10 nin ; 0 after 30 min ; after 60 min. exist in the monohydroxide form, whereas all the metal ions which tan, such as Fe, Al, Cr, can exist in the dihydroxide form and can thus have other dimensions to form cross- linkages with the carboxyl groups in the serum albumin monolayer. This is much more evident when a protamine such as gliadin is used. Gliadin monolayem.-These monolayers were spread from 60 % ethanol solutions and it can be seen from fig. 13 that chromium ions have no effect on the gliadin monolayer ; it is known that there are very few carboxyl groups available in gliadin.On the other hand, there are allarge number of amine groups in gliadin with which chromium ions as FIG. 14.-Gliadin monolayers. A pH 5-79 M/100 Na2S04 10 H20 (1 h). 0 pH 6-6 (after 1 h) subsolution, M/200 CUSO~ 5 H20, M/100 Na2S04 10 H20. x on distilled water. seen from their inactivity on long-chain amine films are unreactive, but copper ions appear to be able to react with the positive groups as seen in fig. 14. This is even more strikingly shown with monolayers of methaemoglobin in which there are a considerable number of imidazole (histidine) 33 groups compared to 16 in serum albumin.168 PROTEIN MONOLAYERS Methaemoglobirz monoZayers.-Methaemoglobin does not spread on distilled water nor is it adsorbed from solution at the airlwater interface as shown by the non-frothing of haemoglobin solutions.But niethaemoglobin readily spreads on salt solutions. Copper, as can be seen from fig. 15, is very reactive on methaemoglobin but does not ex- pand the film as do the other basic metal ions. If the protein is spread on the copper sulphate solution at the active pH range 6.15-6.7 buffered with C02, prevention of the spreading takes place presumably by reaction and because the isoelectric point of methaemoglobin is near that of the pH of formation of the basic copper ion, where minimum spreading could be expected. These films are strongly rigidified. Some small expansion does take place with this type of tanning if the copper solution is injected under a spread methaemoglobin film.This is due primarily to the incompressibility of the reacted monolayer and not to the expansion and solidification as found with the fatty acids or chromium ion tanning. The question of the buffer salts in relation to the copper tanning is important since Cu(0H)z precipitates at pH 5.8 and basic copper carbonate at pH 6.4. The basic copper carbonate solutions have been found by Thomas 2 FIG. 15.-Methaemoglobin monolayers on x pH 4-9 [C02 sat.] A pH 6-15 [C02 sat.] 9 pH 6.71 [COZ sat.] M/2000 CuSO4.5 HzO ; M/100 Na~SO4.10 H20 (1 h). A pH 3.0 El pH 4-04 0 pH 4.9 [COZ sat.] + pH 7-23 [COz sat.] 3 pH 9.4 [COz sat.] to be much more reactive than solutions buffered with sodium acetate. This does not occur with the chromium salts.Very large expansions have been found with fatty-acid tanned monolayers with copper solution buffered by COz and NaOH whereas only small expansions occur when they are buffered with sodium acetate. Similar structures as shown in fig. 6 can be built up. The reaction of copper with the histidine groups in the protein monolayer apparentIy has an optimum again at the basic metal ion pH of 6.1-6-7. This is very surprising since a positive amine group is being attacked instead of the carboxyl. The neutralization of the imidazole group overlaps with this pH. The reaction of copper ions with methaemo- globin is strong (see fig. 15), a reduction of 40 % of the area of the monolayer is observed at the optimum pH whereas the reaction with chromium ions is smaller in comparison (see fig. 16).This could be due to the fact that the isoelectric point, pH 68, of methaemo- globin is above the basic metal ion pH for chromium. Insulin mono1ayers.-Insulin containing both imidazole and carboxyl groups is reacted upon by both copper ions and chromium ions at the basic metal ion pH (see fig. 17). The tanning is not so marked as with serum albumin by chromium ions.J . H . SCHULMAN AND M . Z . DOGAN I69 Table 3 summarizes the basic metal ion interactions with the various protein mono- layer according to the availability of carboxyl or imidazole groups in the proteins. This is compared to the bulk reaction with gelatin or colIagen. FIG. 0 3. X 16.-Methaeinoglobin mono- layers on chrome alum. M/2000 chrome aIum ; M/100 Na2S04 10 H20 pH 2-92 I3 pH 4.48 ; pH 5-47; A pH 6.12; pH 7-0.COMPARISON OF MONOLAYER REACTIONS WITH THE BULK TANNING.-ElOd and Schackowsky 8 have investigated the solubility of gelatin films with metal ions. The pH range of insolubility of the metal complexes with gelatin coincides closely with the pH range of interaction of the basic metal ions with fatty acid mono- layers and serum albumin monolayers. The metal ions investigated are Ca2+, FIG. 17.4nsulin monolayers. x pH 5.40 substrate M/lOO Na2S04 . 10 H20 (sat. C02). A pH 6.4 (1 h) substrate M/1000 CUSO4 5 H20 M/100 Na2S04 10 H20 (sat. C02) chrome alum (sat. C02) M/100 Na2S04. 0 pH 5.14 substrate M/2000 U@+, Fe3+, AP+, Cr3+. It has been shown by Thomas and Schulman3 that U20:+ does not interact with fatty acid monolayers at the basic metal ion pH owing to steric considerations but because of the size of the UzO$+ ion insoluble soaps can be formed, in contrast to the other metal soaps.The pH of interaction of gelatin with UO$+ and fatty acid monolayers is identical (see table 2). This table can be directly compared with fig. 4.170 COLLAGEN TABLE 2 pH of optimum insolubility of gelatin film 7.5-9.0 4.1-5.0 3.5-4.0 2.3-3.0 4'0-6.0 4.5-5.0 4.5-5.0 3.5-4.0 MONOLAYERS Further, there is direct evidence in bulk reactions that copper ions do not interact with the carboxyl groups but with the imidazoIe groups.9 There is much evidence that the carboxyl groups in collagen are responsible for the effect of chromium ions on its solubility, hydro- lysis by trypsin and its thermal properties and that this is due to the bridging of the carboxyl groups in the protein by the basic metal chromium ion lattices. TABLE 3 .-METAL ION PROTEIN MONOLAYER INTERACTION Fe A1 Cr c u long chain tyrosine +++ -I- + + gliadin 0 ++ ins u 1 in + 4- ++ methaemoglobin -I- +++ bovine serum albumin +++ +++ +++ 0 gelatin (bulk) 3. ++ + -k + + One of us, M. 2. Dogan, is indebted to the Mining Research Institute of 1 Wolstenholme and Schulman, Trans. Faraday Soc., 1950, 46,475. la Wolstenholme and Schulman, Trans. Faraday SOC., 1951,47,788. 2 Thomas and Schulman (unpublished), J. G. N. Thomas, Dim. (Cambridge, 1953). 3 Schulman and Smith, Kolloid-Z., 1952, 126,20. 4 Guming and Schulman, Symp. Mineral Dressing (Tnst. Min. Met., 1952). 5 Schulman and Rideal, Proc. Roy. SOC. B, 1937, 122,29. 6 Cockbain and Schulman, Trans. Faraday Soc., 1939,35, 1. 7 Pourbaix, Tlzermodyrzamics of Dilute Aqueous Solutiorzs (Edward Arnold and Co., 8 Elod and Schackowsky, Kolloid-Z., 1935, 72, 221 ; Kolloid-Z., Beih., 1939, 311, 1. 9Tanford, J. Amer. Chem. SOC., 1952,74,211. Turkey for a personal grant. London, 1949). 10 Gustavson, Advances in Protein Chemistry, 1949, 5, 354.

ISSN:0366-9033    

DOI:10.1039/DF9541600158

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

170 COLLAGEN MONOLAYERS THE INTERACTION QF TANNING MATERIALS WITH COLLAGEN MONOLAYERS BY S. C. ELLIS AND K. G. A. PANKHURST The British Leather Manufacturers’ Research Association, Milton Park, Egham, Surrey Received 1st July, 1953 The reactions between collagen monolayers and tanning materiak dissolved in the underlying liquid have been followed by changes in surface pressure, surface potential and surface viscosity. Tanning is characterized by the development of a highly viscous film. This is accompanied by changes in surface potential and/or surface pressure in a manner which enables a distinction to be made between different types of tanning materials, e.g. catechol tannins produce a marked condensation of the monolayer in- dicating ‘‘ multi-point ’’ association between the multi-functional tannin molecules and a number of protein chains, producing a compact cross-linked structure.The potential results indicate the neutralization of some of the positive charges in the protein molecule by anionic components present in the tannin above pH 3, although it is uncertain if this contributes to the tannin reaction. On the other hand, chromium sulphate produces aS. C. ELLIS AND K. G. A. PANKHURST 171 slight expansion of the film at all areas and an elevation of surface potential, which is attributed to an initially electrovalent bonding of cationic chromium to negatively charged carboxyl groups of the acidic side chains, producing an open net-work. The development of tanning properties during polymerization of certain non-tanning monomers, e.g.benzoquinone and catechin, has also been followed. The interaction of tannic acid and gliadin monolayers has been studied by Schulman and Rideall and by Cockbain and Schulman 2 who injected an aqueous solution of tannic acid under a pre-formed monolayer of gliadin. Gorter and Blokker3 have studied the same reaction by spreading a gliadin film on to the surface of a dilute solution of tannic acid. Both techniques have shown that the reaction that ensues results in a reduction of surface potential of ca. 100 mV, and the production of a less compressible and considerably more rigid film. In the present work the reaction of collagen monolayers, spread from an- hydrous formic acid solution, with tanning materials dissolved in the underlying liquid, has been followed by observing changes in surface pressure, surface potential and surface viscosity, the surface viscosity being determined with a modified two-dimensional Couette viscometer.EXPERIMENTAL Surface pressures and potentials were measured in the usual way 4 with a single-wire surface balance 5 and an ionizing air electrode-valve potentiometer circuit. Surface viscosities were measured with a separate apparatus, which allowed simultaneous measurement of surface pressure. The apparatus which is described in detail elsewhere,6 was developed from that of Chaminade, Dervichian and Joly.7 The film is confined within a floating framework of waxed mica, at one end of which is a circular compart- ment in the centre of which floats a waxed ring of 25 s.w.g. platinum wire ca.6 cm diam. The ring is connected to a rotating shaft through a 47 s.w.g. phosphor bronze torsion wire, 20 cm long, and the viscous drag imposed by the film which fills the annular space between the ring and the mica frame is measured in terms of the angular displacement between the ring and the rotating shaft. The shaft was driven by a synchronous motor through a multispeed pulley gear box, by which the rate of shear could be varied, although for the work described below a constant velocity gradient of 0918 sec-1 was used. The surface viscosity 77 of the film is defined as the change in the viscosity of the water surface produced by the insoluble film. The difference between the angular displacement of the ring in the presence and in the absence of the film is proportional to the surface viscosity of the film, the calculation of which is analogous to that for a Couette viscometer, i.e., tC R22 - R12 $ 7 ~ 2 R12R22 T = A - - in c.g.s.units (surface poise), where A = angular displacement of torsion wire due to the film (i.e. Afilm - Awater), t = time (sec) for one revolution of ring, C = total torsional constant of the wire, R2 = radius of circular compartment, Rl = radius of ring. The mean velocity gradient i in the annulus is given by Y = 2vRl/[t(R2 - RI)] sec-1. In this apparatus 112 = 5.03 cm, R1 = 3.04 cm, which with a 20 cm 47 s.w.g. phosphor bronze wire (C = 0.01805 dyne cm/deg.) gives 77 = t A 1.56 x 10-5 surface poise. The deflections could be read to f 2", and no permanent set was obtained up to 3000".Surface pressures, measured concurrently with surface viscosity, were made with a vertical torsion wire balance (Guastalla 8). All measurements were made at 20 & 2" C. The protein monolayers were formed by spreading from dilute solutions, using an Agla syringe with its glass tip just in contact with the surface, care being taken that the surface pressure did not rise above 0.2 dynelcm during spreading. Solutions of collagen were prepared from the middle layer of petrol degreased and acetone dehydrated cow hide, dissolved in anhydrous formic acid at 35°C. Monolayers of hide gelatin were spread from aqueous solutions immediately after preparation, before sufficient time had elapsed for micellar structure to occwr.9172 COLLAGEN MONOLAYERS Mimosa tannin was obtained from the bark of Acacia mollissirnu and purified by first adsorbing on pelt (tanning), washing with water to remove non-tanning materials and finally desorbing with acetone.A commercial sulphonated phenolic synthetic tannin consisting of a mixture of two types of polymer, of which the monomers are HoQ-so~-( ) Z ~ ~ s o ~ ~ a Ho-~-~Z(J~~2s03~a I CH3 was used without further treatment. Basic chromium sulphate was prepared by reduction of chromium trioxide solution with SO2 at room temperature, followed by basification with barium hydroxide. Catechin, obtained from the leaves of Uncaria gambir by ether extraction, was recrystallized nine times from water, including two treatments with charcoal (m.p. tetrahydrate 97" C). Benzoquinone was of A.R. quality and was resublimed immediately before use. Tn all cases the proteins were spread on to the surface of very dilute solutions of the tanning material.This was preferred to the injection technique since it overcame the difficulty of obtaining a uniform distribution in a reasonable time. A few trial experi- ments showed that identical surface pressures and potentials were obtainable by both techniques provided sufficient time was given for equilibrium to be established. RESULTS MIMOSA TANNIN.-Fig. 1 shows l7-A curves for collagen on mimosa solutions (6 ms/l.) at PH 3-15, 4.05, 5.04 and-6.05, together with the curves in the absence of tannin. All 2.0 0 /so 2.0 A W / m g ) FIG. 1.-Collagen on mimosa tannin, 20" C. Surface pressure (---@--). (controls without tannin - - - x - - -).substrates were buffered with 0.02 M sodium acetate and hydrochloric acid, and measure- ments were made 20 min after spreading, when equilibrium had been reached. In every case the tannin brings about considerable condensation of the film at surface areas greater than 0.8 mz/mg. At smaller areas the film becomes more incompressible than that for unreacted collagen, and collapses at 8-10 dynelcm. There is no evidence from the pressure curves that the reaction is pH dependent within the range 3-6. Surface potentials, however, do vary with pH. Above areas of 1-2 rnyrng, where 17 is approximately constant, large fluctuations in A V are found over the surface, but below this area these disappear and the AV-A curves run parallel to those found in the absence of tannin, but displaced below them if the pH is above 3, the displacement increasing as the pH is raised (fig.2). For surface viscosity measurements, films were spread in the usual way to ensure completeS. C. ELLIS AND K . G. A. PANKHURST 173 spreading and then compressed to the desired pressure, at which they were maintained throughout the experiment. Readings were made on the continuously rotating visco- meter, usually at intervals of a minute. Most of the measurements were made at 3 dyne/cm pressure, where the film undergoes little change in area on tanning. rl for un- reacted collagen at this pressure is less than 0003 surface poise and is practically inde- pendent of pH and age of the film. The influence of pH on the rate of rise of surface FIG.2.-Collagen on mimosa tannin, 20" C. Surface potential. viscosity is shown in fig. 3, where the time taken for the viscosity to rise to 0.15 surface poise is plotted against pH. In these experiments 2 mg of tannin per litre was used in the substrate, since 6 mg/l. produced very rapid reaction, particularly at the higher pH values. These curves, like the potential curves, show the dependence of the reaction on pH, the reaction going approximately twice as fast at pH 5 as at pH 4, or four times as fast as at pH 3. Fig. 4 shows viscosity-time curves for mimosa at pH 4, in concentrations from 1 to 6 mg/l. The time taken to reach a given viscosity is only roughly proportional to the concentration of tannin. The effect of surface pressure on the rate of increase of surface viscosity for collagen on 2 mg/l.mimosa at pH 4 is shown in fig. 5. In the absence of tannin there is little change in the viscosity of a collagen monolayer between 1 and 7-5 dynelcm. When tannin is present, however, the rise in viscosity becomes much more rapid as the pressure is raised, the time taken to reach a given viscosity at 7.5 dyne/cm being about one-tenth of that required at 1 dyne/cm. Furthermore, the reaction having been started at 1 dyne/cm, proceeds more rapidly if later compressed, as shown by the circles in fig. 5. Here the film after 8 min was compressed from 1 to 3 dynelcm pressure, whereupon the viscosity-time curve became almost coincident with the original 3 dyne/cm isobar. SYNTHETIC TANNlN.-The surface pressure, potential and viscosity curves for collagen re- acted with the sulphonated phenolic syntan at pH 4-0 (0.02 M acetate buffer) and at a con- < x FIG.3.-Collagen on mimosa tannin, 20" C. Surface viscosity. centration of 6 mg/l. are shown in fig. 6. Measurements of pressure and potential were made 20 min after spreading, as before. Unlike the mimosa results, there is no condensation at high areas, the curves for reacted and unreacted collagen being identical above about 1.5 m2/mg. When compressed below this area, the tanned film exerts a much greater pressure than the untanned. A reduction in surface potential of ca. 1OOmV is produced, and the rise in surface viscosity is similar to that obtained with mimosa.174 COLLAGEN MONOLAYERS BASIC CHROMIUM suLPHATE.-Gelatin monolayers spread from aqueous solution were used with chromium tanning materials to avoid the possible danger of the formic FIG.4.-Collagen on mimosa tannin, 20" C. Surface viscosity. 0 mg tannin/l. 1 ? 9 ?9 2 9 9 9? -0- - + - 4 9 , Y ? El - 6 Y Y 99 - - - _ - X - - acid solvent masking the chrome complex, it having been shown that collagen and gelatin monolayers are identical as regards surface pressure and potential.10 l7-A and A V-A curves for gelatin on two solutions of 50 % basic chromium sulphate at pH 4, containing Q FIG. 5.-Collagen on mimosa tannin, 20" C . Surface viscosity. - 8) - 1.0 dynelcm - x - 3 4 Y9 - 5.0 ,) A - 7.5 )) - 0- 1+3 ,, - -S. C. ELLIS AND K . G . A. PANKHURST 175 25.4 and 127 mg Cr203/I. are given in fig. 7. As with the other tanning materials, 20 lnin was allowed to elapse between spreading the monolayer and compressing it.After re- action the n-A curves are slightly expanded at all areas and the AV-A curves are dk- placed upwards by ca. 50 mV. The pressure and potential curves are identical for both i FIG. 6.--Collagen on sulphonated phenolic synthetic tannin, 20" C. Surface pressure, potential and viscosity, (controls without tannin - - - - -). FIG. 7.-Gelatin on basic chromium sulphate, 20" C. Surface pressure and potential - + - 127 ,> Y Y - - 0 - - 0 mg Cr2O3/l. - x - 25.4 ,, ), concentrations, indicating that reaction was complete. It was not possible to measure the viscosity of the chrome-tanned films, as they broke away from the ring before starting to flow in the annulus. This may be due to the formation of an excessively rigid film, or to poor adhesion between the tanned film and the waxed ring.The shear at which the film broke away from the ring could be determined within about 10 % and was ca.176 COLLAGEN MONOLAYERS 36 dyne cm compared with a couple of 0.18 dyne cm required to balance the viscous drag of an untanned film. THE DEVELOPMENT OF TANNING PROPERTIES WITH INCREASE IN MOLECULAR SIZE OF PHENOLIC AND RELATED COMPOUNDS. One of the CharacteriStics of vegetable tanning FIG. 8.-Collagen on benzoquinone, 20" C. Surface viscosity. solution 0 and 1 day old - +- ,? 4 days old 8- 9 ) 8 9s ¶S 0- Y Y 19 Y9 Y? - - FIG. 9.-Collagen on catechin, 20" C. Surface pressure, potential and viscosity. control without catechin -0-{ monomeric catechin - A - catechin boiled for 10 h.+- *> 9 9 99 20 h. X - Y Y ¶ I ¶ > 40 h. - -S . C. ELLIS AND K. G. A. PANKHURST 177 materials is their ability to react with a collagen monolayer to form a cross-linked film of high viscosity. Accordingly a study has been made of simpler phenolic compounds to discover what degree of complexity of structure is required for this property to appear. Phenol, resorcinol, catechol, pyrogallol, hydroquinone, gallic acid, benzoquinone and catechin, when pure, produce no increase in surface viscosity of a collagen monolayer at pH 4.0, even when present to the extent of 60 mg/l. in the underlying liquid. Ordinary " bench " samples of both benzoquinone and catechin, on the other hand, showed con- siderable tanning properties.The development of tanning power was therefore investi- gated and fig. 8 shows viscosity-time curves for collagen spread on solutions of benzo- quinone immediately after preparation and at periods up to 19 days. Similarly, fig. 9 shows the effect of boiling solutions of catechin in the presence of atmospheric oxygen, on U-A and AV-A curves and on the viscosity-time relationship. Before heating the catechin solutions, all the films were similar to those obtained on plain buffer, but after heating, tanning properties similar to those observed with mimosa tannin emerged. DISCUSSION Several mechanisms for the reaction of vegetable tannins with proteins have been suggested. Von Schroeder 11 suggested that the reaction consisted of electro- valent combination between cationic collagen and anionic tannins, while Freuden- berg 12 postulated binding by hydrogen bond formation.Recently Gustavson 13 bas concluded that both mechanisms are involved and quotes 14 electrophoretic measurements of Danielson showing mimosa tannin to be negatively charged. Recently we have found 15 by microelectrophoresis that although at pH 3 mimosa tannin is electrophoretically inert, it becomes increasingly negatively charged as the pH is raised. The origin of the negative charges is not clear. Phenolic hydroxyl groups would not be expected to dissociate at such a low pH value. They would, however, be capable of reacting with carboxyl and amino groups of the protein as well as with the keto-imide groups, by hydrogen bond formation, and at pH 3 where the tannin is electrophoretically neutral, and where tanning of the monolayer is not accompanied by any change in AV, it seems likely that such a mechanism is responsible for the tanning reaction.In this way a tannin molecule would react with several collagen molecules, binding them together into aggregates with a close-packed structure. The existence of tanned aggregates at areas above about 1.2 m2/mg, is indicated by the fluctuations in surface potential and by the reduction in surface pressure. On compression these island aggregates, which have a surface vapour pressure smaller than that of the free-moving un-tanned collagen molecules, themselves become close packed and at about 0.8 mZ/mg, there is considerable resistance to compression, the films collapsing above ca.8 dyne/cm pressure. At pH values above 3, where the tannin acquires a negative charge, reaction between these and the positively charged basic side chains might be expected, and surface potentials indicate that this does happen. Whether or not this subsidiary reaction contributes to the main tanning process is uncertain. The rise of surface viscosity with time is more rapid the higher the pH, but this may merely be due to a reduction in net positive charge on the protein molecules reducing their mutual repulsions and making easier the combination with tannins by hydrogen bond formation. Thus the changes in surface pressure and viscosity can be explained in terms of '' multipoint " association of the vegetable annin with the protein (most probably through the keto-imide groups), whereby the individual protein molecules are knit together into a close-packed continuum.The potentials provide evidence of combination of anionic components of the tannin which are present above pH 3 with the collagen, though there is no proof that they contribute to the tanning reaction. Implicit in this hypothesis is that the tannin molecule shall have at least more than one reactive group which shall be so spaced that they are able to combine inter-molecularly with the"protein. It is therefore not surprising to b d that such simple substances as mono-, di- and even tri-hydric phenols are not capable of tanning collagen monolayers.178 COLLAGEN MONOLAYERS Even monomeric catechin does not appear to fulfil the requiremsnts. The polymsr- ization of both benzoquinone and catechin has been known for some time and Stecker 16 has suggested that benzoquinone polymerizes and oxidizes to give a network structure thus : OH OH 0 0 0 Such a polymer has the requisite characteristics for multi-point attachment to the collagen monolayer through the hydroxyl groups around the periphery.The number and disposition of these will be critically dependent on the degree and manner of polymerization, and it can be shown that for a network made up of x rows of y monomer units per row, the number of hydroxyl groups is equal to x + y . The larger and more symmetrical the polymer, the smaller will be the percentage of hydroxyl groups, and the further apart will they be. It is most likely, therefore, that there will be an optimum size for tanning beyond which the functional groups, which according to Stecker's model are exclusively peripheral, will be too far apart for adequate tanning of the monolayer.This may account for the limiting value of the surface viscosity found with polymerized benzoquinone. With heated catechin no such limiting value was found. Here the monomeric catecliin has five hydroxyl groups disposed about three rings, and polymerization would lead to a molecule with functional groups distributed throughout, and not OW confined to the periphery as with benzoquinone. Thus the size limitation would not be so important, being governed entirely by the solubility of the polymer. Throughout the discussion of benzoquinone and catechin, the term polymer- ization has been used.The role of oxygen has yet to be investigated, but there is little doubt of its importance. Indeed the Stecker model of polymerized benzo- quinone implies oxidation. In contrast to the behaviour of vegetable tannins and their precursors, the sulphonated synthetic tan and the chromium salts do not produce any condensa- tion of the collagen film at low areas, indeed the basic chromium sulphate causes a slight expansion of the film. As the film on the syntan is compressed below about 1-5 m2/mg it becomes much more resistant to compression than the un- tanned film, and does not collapse until about 20 dynelcm. The chrome tanned film is only slightly expanded. This failure to condense the film indicates that close-packed aggregates are not formed and strongly suggests that reaction takes place between the polyfunctional tannin ions and oppositely charged polar side chains of the collagen.The strong binding of sulphonate groups to basic side chains of gelatin has been reported,l72 18 and there is good evidence that basic chromium salts are bound to the acidic side chains.19~20~21 The reduction ofS. C . ELLIS AND K . G . A . PANKHURST 179 surface potential by the anionic syntan, and its elevation by cationic chromium support this view. The necessity of the tanning material being multi-functional still applies as with the vegetable tannin-the syntan polymer providing anionic groups dispersed throughout the large molecule, and the basic chromium sulphate providing cationic groups throughout the polynuclear aggregates which are known to exist in solution.22 As with vegetable tannins, the surface viscosity increases as the tanning reaction proceeds, although with the chromium sulphate, it was not possible to measure this.To summarize, the reaction of collagen monolayers with condensed vegetable tannins appears to be predominantly by hydrogen bonding between the multi- functional tannin molecules and the keto-imide groups of the protein. At pH values above 3 there is evidence of a coulombic binding of anions present in the tannin, with the cationic groups of the protein, but there is no evidence that this coiitributes to the tanning reaction. One effect of the vegetable tannin “ clamps ” is to increase the cohesion of the film and to produce a very compact structure of high surface viscosity.Ionic tannins, e.g. syntans and chromium salts, however, appear to act initially by coulombic forces with the oppositely charged side chains of the protein, thereby building up a more open, but equally viscous, network. Our thanks are due to the Director and Council of the British Leather Manu- facturers’ Research Association for permission to publish this paper, to Dr. A. Cheshire who prepared the sample of mimosa tannin and to Mr. F. K. Quinn who prepared the collagen. 1 Schulman and Rideal, Proc. Roy. SOC. B, 1937, 122,29, 46. 2 Cockbain and Schulman, Trans. Faraday Soc., 1939,35, 1266. 3 Gorter and Blokker, Proc. K. Ned. Akad. Wetensch., 1942, 45, 228, 335. 4 Adam, The Physics and Chemistry of Surfaces (Oxford, 1941), 3rd ed., pp. 27-44. 5 Pankhurst, Trans. Faraday Soc., 1945, 41, 156. 6 Ellis, Lanham and Pankhurst, in press. 7 Chaminade, Dervichian and Joly, J. Chim. Phys., 1950, 47, 883. 8 Guastalla, Compt. rend., 1929,189,241. 9 Pouradier, J. Chim. Phys., 1949, 46, 626. 10 Ellis and Pankhurst, in press. 11 Von Schroeder, Kol1oidchem.-Beih., 1909, 1, 1. 12 Freudenberg, Collegium, 1921, 353. 13 Gustavson, Svensk Kern. Tidskr., 1941, 53, 324. 14 Gustavson, Advances in Protein Chemistry, 1949, 5, 395. 15 Czeczowiczka and Pankhurst, unpublished work. 16 Stecker, see McLaughlin and Theis, Chemistry of Leather Manufacture (Rheinhold, 17 Pankhurst, Furaday SOC. Discussions, 1949, 6, 52. 18 Smith, Nature, 1949, 164,447. 19 Bowes and Kenten, J. SOC. Leather Trades Chem., 1949,33, 368. 20 Kuntzel, Kolloid-Z., 1940, 91, 152. 21 Shuttleworth, J. SOC. Leather Trades Chem., 1948, 32, 116, 22 Riess and Barth, Collegium, 1935, 62. New York, 1945), p. 399.

ISSN:0366-9033    

DOI:10.1039/DF9541600170

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

VISCOSIMETRIC STUDY OF THE HARDENING OF GELATI" BY CHROME ALUM * BY J. POURAD~ER Research Laboratories, Kodak Path6 S.A.F., Vincennes, France Received 10th July, 1953 The reaction of gelatin with chrome alum is followed by the change in viscosity of solutions containing chrome alum and gelatin. The type of effect obtained depends on the concentration of gelatin and the pH. At relatively high gelatin concentrations there is an increase in viscosity which at highest chrome alum and gelatin concentrations may lead to the formation of a rigid gel. At low concentrations of gelatin and at the pH of the isoelectric point a fall in viscosity can take place. These effects are explained on the basis of variations in the relative amounts of inter- and intramolecular bonding. It is considered that intramolecular bonding is favoured by proximity to the isoelectric point when the gelatin molecule is most tightly coiled, and by low concentrations of gelatin.Although the reaction of chromium salts on gelatin has been somewhat neglected as a subject of research, it is less complex than the reaction of the same salts on hides or leather. In fact, as gelatin is soluble in water above a certain temperature, it can be tanned by chromium salts in the homogeneous phase, and there is no risk of the reaction being disturbed by difficulties in penetration, like those which often occur with hides. This solubility also has the advantage of allowing one to apply to the reaction products the semiquantitative relations which have recently been established between the physical properties of the dilute solutions and the molec- ular characteristics of the solute.It would seem, therefore, that research on the reaction of chromium salts and gelatin, in addition to the interest which it presents for its own sake, should be capable of providing information on the tanning of collagen. EXPERIMENTAL kfATERIALs.-Gelatin.-hReasurements were carried out on a de-ashed Eastman Kodak gelatin obtained from limed calf-skin. Its isoelectric point 1 was at pH 4.75 : its number average molecular weight 2 was 65,000 : and its average molecular weight determined viscometrically 3 was 102,000. Gelatin concentrations are expressed in dry weight of gelatin (dried for 48 h in thin layers at 310" C ) in 100 ml of solution. Chrome alum.-The chromium salt used in this study was pure crystallized potassium chrome alum.Solutions were prepared by dissolving a known weight of chrome alum in twice-distilled water, and checking by a chromium determination. Chrome alum concentrations are expressed in terms of K2S04, Cr2(SO&, 24 H20. PROCEDURE.-The gelatin solution adjusted to the required pH was kept in a thermostat to reach temperature equilibrium. The titrated solution of chromium salt was then added, and after thorough agitation the mixture was kept in the thermostat with re- adjustment of the pH when necessary. The viscosity of the solution was measured at regular intervals. The addition of a chromium salt to the gelatin solution generally gives rise to a change in viscosity, which, according to the experimental conditions, increases or decreases.If q is the viscosity of a solution at a temperature t and TO the viscosity of the solvent at the same temperature, then the specific viscosity is given by the ratio q SF r= (q - TO)/TO. In order to estimate the action of a chromium salt on a gelatin in solution we took the hardening $1 defined as the relative variation in the specific viscosity ; H = His positive if the chromium saIt has brought about an increase in viscosity and is negative in the contrary case. * Communication no. 1494V, from the Kodak Research Laboratories. 180J . POURADTER 181 RESULTS The reaction between chromium salts and gelatin is not instantaneous but sometimes proceeds for several days. It is therefore necessary to specify the duration of the reaction for each test.On comparing the results obtained by treating solutions of different concentrations, it is found that the concentration of gelatin in the solution during the reaction is one I 2 3 4 5 6 7 Hours FIG. 1.-Variation of hardening as a func- FIG. 2.Variation of hardening as a func- tion of the reaction time. tion of the reaction time. Concentration of gelatin solution 0.85 % ; Concentration of gelatin solution 1-70 % ; chrome alum concentrations are indicated chrome alum concentrations are indicated on the curves ; buffer : acetic acid + on the curves ; buffer : acetic acid + sodium acetate ; pH = 4.75, t = 38" C ; sodium acetate ; pH = 475, t = 38" C ; SO$- concentration 8 x 10-3 M. SO$- concentration 8 x 10-3 M. of the factors which determine the sign and the amplitude of the variations in viscosity.For example, fig. 1 and 2 show the results of two series of measurements carried out under identical conditions on solutions of gelatin with concentrations of 0-85 % and 1-70 %. Whatever the quantity of alum added, the effect of the reaction with chrome alum is to decrease the viscosity of the solution at 0.85 % and to increase it at 1-70 %. As a general rule there is a diminution in the viscosity when the chromium salt is added to a dilute solution, and an increase when it is added to a concentrated solution (fig. 3). 0.5 4-0 4, - 0.0. minutes ,25 ,50 75 Hardening [.25 I / / e'- FIG. 3.Variation of hardening as a func- FIG. 4.-Variation of hardening as a func- tion of the reaction time. tion of the chrome alum concentration.Gelatin concentrations are indicated on the Gelatin concentrations are indicated on the curves ; chrome alum concentration 1.5 % ; curves ; reaction time : 1 h ; pH = 4.75, pH = 4.75, t = 39.8" C. t = 39.8" C.182 HARDENING OF GELATIN The limits of concentration depend essentially on the experimental conditions (pH, con- centration and nature of the salts present, etc.). A complete series of measurements was made on isoelectric gelatin solutions (the pH of which had been readjusted regularly during the reaction) containing variable quan- tities of chrome alum. The hardening values obtained at the end of 1 h at 39.5" C are set out in fig. 4. Consideration of these curves leads to four cases : (i) gelatin concentrations equal to or greater than 4 % : the hardening increases with the concentration of chrome alum and above a certain value of this concentration the solution becomes rigid ; (ii) gelatin concentration of 2 % : the hardening increases with the chrome alum con- centration and tends towards a limiting value ; (iii) gelatin concentration of 1 %: the hardening increases with the concentration of chrome alum, passes through a maximum and then decreases ; (iv) gelatin concentrations equal to or lower than 0.5 %: the addition of chrome alum brings about a diminution in the viscosity of the solution.The strange behaviour of the tests in (iii) was found once more when, not the variations in viscosity, but the Harde niny FIG. 5.-Hardening as a function of the FIG. 6.-Hardening as a function of the PH.PH. Concentration of gelatin solution 4 %; Concentration of gelatin solution 4 %; chrome alum concentration 3 % ; reaction chrome alum concentration 1.5 % ; reaction times are indicated on the curves; t = times are indicated on the curves; t = 39.8" c. 39.8" C. variations in melting point of gelatin gels treated with different chromium salts were considered. The classification of (i), (ii), (iii) and (iv) is not absolute since measurements carried out under different experimental conditions have shown that if the nature of the phenomena is unchanged, the gelatin concentrations corresponding to the different kinds of behaviour vary with the experimental conditions. Among these the most important seem to be pH and the nature of any salts present.In order to study the influence of pH let us consider first the simple case of a gelatin solution of a concentration sufficient for the chromium salt always to bring about an in- crease in the viscosity, and containing only the hydrochloric acid or sodium hydroxide necessary to adjust the pH. Two series of measurements have been carried out on 4 % gelatin solutions maintained at 39.8" C and containing respectively 1.5 and 3.0 % chrome alum with respect to the weight of dry gelatin. The results corresponding to reaction times specified in regard to the curves are shown in fig. 5 and 6. Consideration of these curves leads to the three following observations. (i) Whatever the reaction time, the hardening, which is zero below a limiting pH of about 3, increases with pH to pass through a maximum, and then decreases again.J .POURADIER 183 These results are in agreement with those published earlier by different authors 4-6. It is very difficult to study the process at pH values above 6 since the chromium hydroxide precipitates and interferes with the measurement of viscosity. (ii) Contrary to what is observed in the study of most of the properties of gelatin there is no discontinuity in the curves at the isoelectric pM. (iii) The optimum pH depends on the reaction time and decreases as the latter in- creases. This observation should be compared with the results obtained by Houck and Dittmar 6 with more concentrated solutions. The phenomena are more complicated when the gelatin solutions are sufficiently dilute for the addition of chromium salt to bring about a diminution in viscosity at certain pH values.These experimental conditions have never been studied to our knowledge. However, they are very interesting from the point of view of explaining the mechanism of tanning, since at low concentrations the molecular interactions are so small that the phenomena may be analyzed into their components. The most characteristic measurements were made on 0.85 % gelatin solutions, the pH of which was buffered by a mixture of acetic acid and sodium acetate in suitable FIG. 7.-Variation of hardening as a function of the reaction time. Concentration of the gelatin solution 0.85 % ; chrome alum concentrations are indicated on the curves ; buffer : acetic acid + sodium acetate ; pH = 4.00, t = 38" C ; SO$- concentration 8 x 10-3 M.proportions. The results of measurements made at pH = 4.7 are aIready set out in fig. 1. According to these experiments, whatever the quantity of chrome alum added and what- ever the reaction time, the addition of the chromium salt brings about a diminution in viscosity. On the other hand, in studying the same solutions at more acid pH values, it is seen that the addition of chrome alum produces an increase in viscosity. The results of measurements made at pH 4.0 are brought together in fig. 7. It should be noted, moreover, that analogous results to those corresponding to a pH of 4.0 were obtained by treating the gelatin at a high pH in the presence of salts capable of forming chromium complexes and preventing the precipitation of chromium hydroxide.DISCUSSION In order to explain the variations in mechanical properties of chrome-tanned collagens, Spiers 7 in 1934 suggested that the chromium atoms would link together two adjacent polypeptide chains, one being attached to the chromium by a car- boxyl group and the other by an amino group. This hypothesis was taken up by Gustavson,* who suggested that the chromium complexes form bridges by184 HARDENING OF GELATIN attaching themselves with covalent forces to the acid groups of one chain and with co-ordination valencies to the basic groups of the other chain. We shall show that this hypothesis of bridge formation between the polypeptide chains can be applied to gelatin provided that factors inherent in the structure of that protein are taken into account.If the chromium can join together two neighbouring molecdes by attaching itself to a group R1 of the one, and to a group Rz of the other, it should be just as capable of linking two groups, Rl and R2, of the same molecule, thus forming an intramolecular bridge. Together with intermolecular bridges, intramolecular bridges may also be formed, and the relative proportions of the two kinds of bridge must depend on experimental conditions. It is probable that an intramolec- ular bridge is formed when two groups R1 and R2 of the same molecule are neighbours, and that, on the other hand, the chromium forms an intermolecular bridge when two groups belong to different chains which are close to one another. This observation is valid for any kind of process of fixation of chromium and in particular when that reagent is attached simultaneously or successively with the two groups, R1 and R2.A complete theory of the action of chromium salts on gelatin must therefore take account of the existence of these two kinds of bridges which modify the physical and mechanical properties of gelatin in different ways. The intermolec- ular bridges by linking together the molecules increase the apparent molecular weight of the treated gelatin and bring about an increase in cohesion. When the number of these bridges is sufficiently large, all the molecules are united into a rigid three-dimensional lattice. On the other hand, the intramolecular bridges by bringing together different parts of the same molecule do not contribute to the cohesion of the system. Moreover, it should not be forgotten that when it is attached to the polar groups of the gelatin the chromium modifies the interactions between the gelatin and water and between the molecules of gelatin.Consequently, every time the chromium, in order to form an intramolecular bridge, blocks groups which entered into the linking of the molecules among themselves, it diminishes the cohesion of the gelatin. If intramolecular bridges only were formed, the treated gelatin could be represented diagrammatically by a structure like grains of rice. In fact, intermolecular and intramolecular bridges are formed sim~iltaneously and the properties of the hardened gelatin depend on the relative proportion of each type of bridge. Finally, it is possible that in the presence of a substance capable of actively forming complexes with the chromium, the latter is attached to a single group of the gelatin and that its action is limited in this way to blocking the groups under consideration.Since the probability of intra- or intermolecular bridge formation depends on the proximity of two groups, R1 and R2, of one and the same chain or of different chains, it is logical to conclude that the concentration of the gelatin solution at the time of tanning should have an effect on the properties of the hardened gelatin. If the solution is very dilute, the gelatin molecules in solution are dispersed at a distance from one another, and, in the main, intramolecular bridges should be formed. These diminish the attractive forces which unite the different molecules and consequently bring about a lowering of the viscosity and similarly a lowering of melting point of the gels.On the other hand, in concentrated solutions there should be a relatively high proportion of intermolecular bridges tending to form a rigid three-dimensional lattice. The influence of pH on hardening may be explained by taking into account at the same time the possibilities of reaction of the chromium salt with the different groups of the gelatin, and of the degree of unfolding or of coiling of the polypeptide chains. It has been shown earlier 299 that the gelatin molecule, which has the form of a more or less tight ball at the isoelectric point, unfolds when the pH is varied and is more spread out as the pH becomes farther from the isoelectric point.J .POURADIER 185 Since the maximum coiling into a ball occurs at the isoelectric point, it is at that pH that one group R1 of a molecule of gelatin is most likely to be next to a group IR2 of the same molecule, and consequently it is at this pH where there is the greatest likelihood of finding intramolecular bridges. If the pH is made to vary, for example, by acidifying the solution, an unfolding of the gelatin molecule is brought about and at the same time the formation of intermolecular bridges is encouraged. This analysis of the phenomena makes it possible to explain the difference in behaviour of 0.85 % gelatin solution treated with chrome alum at pH 4.75 and pH 4.0. In an isoelectric solution at this dilution, the ball- like molecules are at a distance from one another and intramolecular bridges are formed almost exclusively, bringing about a decrease in viscosity, whereas at pH 4.0 the molecules are sufficiently expanded for them to form intermolecular bridges in sufficient number to increase the cohesion appreciably.These few considerations show the interest offered by the present hypothesis of the formation of inter- and intramolecular bridges, a hypothesis which makes it possible to explain qualitatively most of the results obtained." * The reaction of chrome alum on gelatin causes variations in the melting point of the gels and modifies the molecular weight of the treated gelatin. The results of our measurements on this subject have already been published.10 1 Pouradier and Roman, Compt. rend., 1949, 229, 1325. 2 Pouradier and Venet, J. Chim. Phys., 1950, 47, 11. 3 Pouradier and Venet, J. Chim. Phys., 1950,47, 391. 4 Crabtree and Russell, Sci. Znd. Phot., 1930, (2nd series), 1, 271, 309, 352, 393, 437, 5 Rousselot, Sci. Znd. Phot., 1936 (2nd series), 7, 193. 6 Houck and Dittmar quoted in Mees' The Theory of the Photographic Process (The 7 Spiers, J. Int. SOC. Leather Trades Chem., 1934, 18, 114. 8 Gustavson, J. Int. SOC. Leather Trades Chem., 1936, 20, 398. 9 Abribat, Pouradier and Venet, J. Polymer Sci., 1949, 4, 523. 463. Macmillan Company, New York, 1942). 10 Pouradier, Roman, Venet, Chateau and Accary, Bull. SOC. Chim., 1952, 19, 928.

ISSN:0366-9033    

DOI:10.1039/DF9541600180

出版商:RSC    

年代:1954

数据来源: RSC