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J . POURADIER 185 SOME ASPECTS OF TME REACTION OF BASIC CHROMIUM SALTS WITH HIDE PROTEIN BY K. H. GUSTAVSON Garvcrinaringens Forskningsinstitut, Stockholm, Sweden Received 2nd July, 1953 Experimental evidence of the dominating function of the ionized carboxyl groups of collagen for the fixation of cationic chromium complexes is given. Thus, collagen with its carboxylic groups completely discharged loses its affinity for cationic chromium compounds completely. By complete esterification of the carboxyl groups, the binding of these chromium complexes is prevented. Results from interactions of basic chromium chlorides and sulphates with gelatin, in 1 % solution, removing the uncombined chromium by means of cation exchanger, show that the basic salts are preponderantly uni-pointly fixed by gelatin.From data on the average charge of the cationic chromium complexes and the available number of carboxylic groups of collagen for fixation of the electro- positive chromium complexes, an approximation of the proportion of the uni- and multi- point fixation of these complexes by collagen indicates that at least 90 % of the amount of chromium held by collagen is unipointly fixed, 10 % being bipointly attached to the protein. The chromium complexes functioning as the cross-linking agent are to be found among the small amount of bipointly fixed chromium.186 REACTION OF CHROMIUM SALTS WITH HIDE Chrome tannage concerns generally reactions between aqueous solutions of basic sulphates and chlorides of chromium and collagen, the greatest part of the chromium complexes removed by collagen being in irreversible combination with the protein.The fixed chromium salt makes collagen resistant to the action of proteolytic enzymes and to hot water, even to boiling water by rationally performed tanning. This stabilization of the collagen lattice by chromium complexes is generally considered to be due to the cross-linking of the collagen chains through stable chromium bridges. Various types of chromium complexes, differing in composition, molecular size and electrical charge, are present in solutions of the baFic salts. In the present paper, some recent investigations of these systems will be discussed, selecting €or the main experiments as simple systems as possible that contain cationic chromium complexes mainly, to facilitate theoretical discussion and for didactic reasons.Results of recent investigations of the reaction of basic chromium salts with collagen, some modified collagens and polyamides are surveyed in this paper. EXPERIMENTAL THE COMPONENTS.-C~~~~~WH compounds.-A standard solution of basic chromium chloride with composition corresponding to the empirical formula : Cr2(0H)2Cl4 . 2NaC1, prepared by adding one mole of sodium hydroxide to one mole of chromium chloride, cr(oH&c13, represented the type of chromium salts with ions of little or no compkxing tendency. The basic chromium salts are in the following characterized by their acidity percentage, i.e. the number of equivalents of Cl or SO4 groups associated with chromium expressed in per cent. The chromium chloride is thus 67 % acid.The solution of basic chromium sulphate investigated was prepared by reducing a solution of sodium bichromate with sulphur dioxide, boiling the solution after complete reduction. The equilibrated solutions contained 0.6 equiv. Cr/l. (15.2 g/l. Cr203). By ion exchange analysis of the solutions of the chromium salts, employing Dowex 50 in the sodium cycle 1 and Amberlite IRA 400 as hydrochloride,2 only cationic chromium complexes were found in the basic chromium chloride. No complex-bound C1-groups were present in the chloride. From determination of the diffusion coefficient,3 it is known that there are two atoms of chromium present in the molecule of the 67 % acid chlorides and sulphates on the average. Hence, the complexes present in the chromium chloride may be represented by the formula (Cr2(QH)2)4+.The analysis of the solution of the 67 % acid chromium sulphate gave 96 % cationic and 4 % non-ionic chromium complexes. The acidity of the sulphato-chromium cations by means of the cationic and anionic resins, according to methods earlier described, gave a mean value of 33 %. Hence, the cationic complexes are represented by the general type of cations (Cr2(QH)2S04)2+. Whereas the electrochemical composition of the solutjon of the basic chromium chIoride does not change by increasing the chrome concentration, only positively charged chromium complexes being present, the formation of non-ionic and anionic chromium is greatly facilitated by increasing the concentration of the solutions of the type of basic chromium sulphate concerned.4 At a concentration of 6 equiv.Cr/l., for example, the solution contained 45 % cationic, 50 % non-ionic and 5 % anionic chromium complexes. In some experiments, solutions of masked chromium salts of greater complexity were employed : sulphito-chromium sulphates, obtained by adding increasing amounts of sodium sulphite to a solution of a neutral salt-free 67 % acid chromium sulphate, cor- responding to Cr2(OH)2(SO4)2 ; and further phthalato-chromium sulphate, obtained by adding 0.5 mole of sodium phthalate per mole Cr of the aforementioned chemically pure chromium sulphate.5 The complex composition of these solutions is given in connection with the experimental results. Substrates.-Hide powder &yon) and iso-electric calf skin pelt (split) served as intact collagen substrates.Further, the following modified specimens of collagen were used : hide powder with its carboxyl groups practically completely inactivated by esterifi- cation and hide powder with its ionic groups bIocked by irreversibly fixed condensed naphthalene-disulphonic acid. The methylated collagen prepared by the method of Fraenkel-Conrat and Olcott,6 as described in an earlier paper 7 contained 17.4 % N, 2 6 % OCH3 groups and 2-7 % Cl present as HCl attached to the basic protein groups.K. H. GUSTAVSON 187 Its acid binding capacity was 0.1 niequiv./g collagen (0.1 N HCl). The hide powder which had its ionic groups blocked by condensed naphthalene disulphonic acid (three consecutive treatments of hide powder in 5 % solution of the acid at a final pH of 1.2) contained 27.5 % fixed sulpho acid based on the weight of collagen. Its acid binding capacity was 0.07 mequiv.H ion per g collagen (as 0.1 N HCl). Finally, a hydrated polyamide, earlier described,g represented a substrate with free -CO . NH- groups as the main reacting group. Its N content was 12.5 % of the weight of polyamide. Its acid binding capacity 0.05 mequiv. H+ and base binding 0 0 2 mequiv. OH- per g polyamide. In some experiments, a cation exchanger with carboxyl ions as functional groups was used. It was equilibrated against Na ions at pH 7-0 and contained 4.8 mequiv. free carboxyl ions per g dry resin.9 GENERAL 0RIENTATION.The reactive sites of collagen are : (i) ionic groups, such as the carboxyl and ammonium groups (the e-amino group of the lysine residue and the guanidyl group of arginine); (ii) non-ionic groups, such as the peptide link and the hydroxy groups of the residues of serine, threonine and hydroxyproline.In reactions of metal ions with proteins, any of these groups may be involved. The Zn ion appears to have preferential affinity for the imidazole group of the histidine residue of globular proteins.10 Collagen also binds Ag and Pb ions in the same manner as a recent investiga- tion of Grassmann and Kusch 11 shows. Cu2+ ion reacts primarily with carboxyl ions of amino acids, forming stable internal complex salts.12 With collagen and gelatin the copper ion Cu2+ is attached to the carboxyl groups,l3 whereas in some globular proteins the imidazole group forms the binding site.14 Hence, apparently various types of binding groups are involved in the interaction with cations of heavy metals, according to the nature of the protein, the pH of the reacting system and the specific environment.The mechanism of chrome tanning was conceived by Wilson 15 as a reaction between the carboxyl group of collagen and chromium ion. However, it was difficult to conceive such a reaction from the general reactivity of proteins, postulated by the classical concept of protein reactions. The introduction and application of the zwitter-ion concept to protein reactions removed the theoretical apprehensions and, indeed, the attraction and fixation of cationic chromium complexes by the carboxyl ions should be the logical out- come.16 Hence, since chrome tanning takes place in an acidic medium, a competition between protons and cationic chromium complexes should be set up in the chrome tanning process.This deduction agrees with the established facts of the process. Before discussing the principal evidence for the rnechani sm of the chrome fixation, it is appropriate to mention that certain findings have long been known which indicate the carboxyl group to be the main reacting group of collagen in the fixation of ordinary chromium salts. For instance, basic chromium complexes of green colour diffusing into gelatin gel colour the gel violet,l' the colour of the chromium carboxylate. The light absorption curve of solutions of slightly degraded gelatin treated with chromium salts is similar to that of chromium-amino acid complexes,l8 in which compounds the binding of the carboxyl group directly on the chromium atom has been proved.RESULTS AND DISCUSSION EXPERIMENTAL EVIDENCE FOR THE BINDING OF CATIONIC CHROMIUM COMPLEXES BY THE CARBOXYL IONS OF coLLAGEN.-The following experimental evidence for the function of the carboxyl ion as the main binding group of cationic chromium complexes may be cited. The eflect of inactivating the ionic protein groups by sulpho-acids.-In com- parative experiments using regular hide powder and the hide powder devoid of ionic groups (combined with the maximum amount of the condensed naphthalene disulphonic acid) the fixation of basic chromium sulphate was determined by running simultaneously series with intact hide powder. Upon treating portions of substrate equal to 2.0 g collagen with 100 ml of the solution of basic chromium sulphate for 6h, intact hide powder fixed 5.0 % Cr2O3 and the inactivated hide powder 1.4 % Cr203, on the basis of collagen.At a concentration of 3.0 equiv. Cr/l. the corresponding figures were 6-9 and 2.4 %. The condensed naphthalene disulphonic acid was selected as the inactivating agent of the ionic protein groups because it does not form insoluble compounds with the basic chromium sulphate and moreover, since it would be expected not188 REACTION OF CHROMIUM SALTS WITH HIDE to interfere with the reactivity of the non-ionic protein groups, primarily the peptide links. The data show that the uptake of chromium by the hide powder devoid of ionic groups is considerably greater than the amount which can be bound by the free carboxyl groups (0.07 mequiv.per g collagen) which is estimated to be about 0.4 % Cr2O3. The additional fixation is probably due to secondary interaction of the chromium complexes with free sulphonic acid groups in the sulpho acid fixed by collagen, i.e. an example of cation exchange. This explanation is supported by the finding that basic chromium chlorides are still more heavily fixed, these complexes evidently being capable of a still more extensive co-ordination with these sulpho groups. However, this experiment indicates the ionic protein groups to be the main binding sites of cationic chromium complexes. The efect of the discharge of the carboxyl ions of collagen.-The first conclusive evidence for the dominant role of the carboxyl ions of collagen in the binding of cationic chromium complexes was obtained by investigation of the behaviour of basic chromium chloride towards collagen which had its carboxyls in the non-ionized state, the ionic groups being discharged by equilibrating the collagen in solution of hydrochlorjc acid The calf skin split was pickled with hydrochloric acid in 5 % solution of sodium chloride to an equilibrium pH of 1.1.Under these conditions the ionized carboxyl groups of collagen are completely discharged. The solution of the 67 % acid chromium of PH 1.0.19 FIG. 1.-The fixation of 67 % acid chromium chloride by collagen (I) and HC1-saturated collagen 01) as a function of the concentration of chromium. chloride at a concentration of 6 equiv. Cr/l.was boiled for 30 min to increase its resistanca to acids. Solutions of various chrome content containing 5 vol-% NaCl and a sufficient amount of hydrochloric acid to give pH 1.0 were made up immediately before use. Portions of lightly pressed pickled pelt of pH 1.0 (= 4 g collagen) were treated in 200 ml of these solutions for 6 h. This rather short time was selected to minimize the interaction of the added hydrochloric acid with the basic chromic chloride. Blank series were run in the same manner with untreated calf skin split (isoelectric), except that no acid was added to the solutions of the boiled chromium chloride. The results are given graphically in fig. 1, showing the chrome fixation as a function of the chrome concentration of the solutions.No chromium is fixed by collagen with completely discharged carboxyl groups from solutions of basic chlorides adjusted to pH 1.0 in concentrations up to 60 g/l. Cr2O3. In the more highly concentrated solutions, only smalI amounts of chromium are fixed. Hence, the curves prove the chrome fixation by collagen from solutions of purely cationic chromium chlorides to take place on the ionized carboxyl groups of the protein. The results of the corresponding experiment with the basic chromium sulphate em- ploying pelt equilibrated with sulphuric acid at pH 1.1 in 5 volume % sodium sulphate, are graphically represented by fig. 2. It is to be noted that by increased concentration of the basic chromium sulphate the formation of non-cationic chromium complexes will be prominent whereas with the basic chloride of fig.1 such formation does not occur. The curves of fig. 2 show that no chromium is fixed by the acid-saturated collagen from solutions of chromium concentrations less than about 20 g/l. Cr2O3. However, withK . H . GUSTAVSON 189 increasing chrome concentration, collagen devoid of ionized carboxyl groups gradually commences to bind chromium. This fixation consists probably mainly of non-ionic complexes which are attached to non-ionic protein groups. Hence, in tanning with basic chrome sulphate liquors of considerable chromi um content, at least two types of reaction are to be recognized : (i) the ionic fixation of cationic chromium complexes and (ii) the fixation of non-ionic chromium complexes by means of groups other than the carboxyl.The former reaction has been proved to involve that type of chromium fixation which is effecting the high degree of hydpothermal stabiliza- tion of the collagen lattice in the chrome tannage. The egect of esterifying the carboxyl groups u f colhgen. -The above experiments of demonstrating the complete blocking of the fixation of cationic chromium complexes by discharge of the carboxyl ions of collagen, is limited to the low pH mentioned. By per- manent inactivation of the carboxyl groups, for instance by their esterification, investiga- tion of the mechanism of the chrome tannage in a more desirable pH range, or that of the ordinary chrome tanning bath, such as pH 2.5-4 is feasible. Such experiments have been performed by Bowes and Kenten,zo who have methylated collagen by means of methyl sulphate, and methyl bromide.In view of the non- specificity of these agents for the carboxyl group and the marked hydrolytic breakdown of the protein incurred by the large number of treatments necessary for complete esterifica- tion, care must be taken in the interpretation of the data. Bowes and Kenten20 found that methylation of collagen decreased the chromium fixation from basic sulphates very markedly. Thus, the amounts of chromium fixed at final pH values below 3 were less than FIG. 2.-The fixation of 67 % acid chromium sulphate by collagen (I) and HzSO4-saturated collagen (11) as a function of the concentration of chromium. 1 % Cr2O3. At pH values about 4, amounts of 2-3 % CrzO3 were fixed by collagen.The authors were convinced that it is not unreasonable to assume that in the absence of carboxyl groups no chromium would be bound by collagen. By means of the method of esterifkation devised by Fraenkel-Conrat and Olcott,6 employing methanol as the esterifying agent in the presence of small amounts of hydrochloric acid, it is possible to inactivate the carboxyl groups of collagen completely without markedly interfering with other protein groups and with a minimum risk of degradation.7 No chromium was fixed by the methylated collagen from solutions of basic chromium chlorides and perchlorates of the cationic type? The same was found to apply to the reaction of the dilute solutions of basic sulphates. Highly con- centrated solutions of the chromium sulphate which contain large amounts of non-cationic chromium possess some affinity for the collagen devoid of carboxylic groups, exactly as found in the experiments of fig.2, although the amounts of fixed chromium were considerably less. Some reactions of chromium complexes of various electrochemical type.-This non- ionic fixation of chromium reaches very large proportions and is dominating in systems of esterified collagen and certain complexed (“ masked ”) chromium salts, as the following experiments will demonstrate. To a stock solution of the 67 % acid chemically pure chromium sulphate increasing amounts of sodium sulphite were added, as noted in table 1. The solutions were adjusted to contain 0.8 equiv. Crll. and aged 3 weeks before use. The complex composition of these solutions given in table 1 was determined by the ion exchange method (Dowex 50, operated in the sodium cycle and Ainberlite IRA 400, in the form of hydrochIoride’).7190 REACTION OF CHROMIUM SALTS WITH HIDE Untreated hide powder and methylated hide powder (= 0 5 g protein) were shaken with 20.0 ml portions of these solutions for such a short period as 2 h, in order to eliminate hydrolysis of the methylated carboxyls.Since it should be of interest to ascertain the behaviour of a substrate with carboxylic ions as the only functional group towards these chromium complexes, series with a carboxyl type of cation exchanger (Amberlite IRC 50) were included. Portions of 0.5 g of dry resin were shaken for 2 h in 100 ml of solutions. The results of these experiments are graphically shown in fig.3. The data of fig. 3 show that the cationic chromium complexes of the blank solution (no. 1) possess a slight affinity for the protein devoid of carboxyl groups TABLE 1 .-ELECTROCHEMICAL COMPOSITION OF CHROMIUM COMPOUNDS % chromium present as cationic non-ionic anionic no. composition PH - 1. cr2(oH)2(s04)2 2 9 96 4 0 2. WOH)2(S04)2 + Na2SO3 3.4 63 37 0 3. @r2(QH)2(SO4)2 + 2 Na2SQ3 40 12 79 9 5. WOH)2(SO4)2 + 3 Na2SO3 5.7 86 12 (2) 0 85 15 4. Cr2(QH)2(SO& + 2 5 Na2S03 4-8 only. On the other hand, the untreated hide powder binds considerable amounts of chromium. By the addition of sodium sulphite to the solution of the chromium sulphate, the pH is increased which connotes increase of ionized carboxyl groups of collagen, and hence of fixation of cationic chromium.Further, non-cationic complexes are gradually formed by the penetration of sulphite groups into the chromium complexes. These complexes are fixed by both types of hide powder. Solutions no. 4 and 5, mainly containing non-ionic chromium, react more ex- tensively with the esterified collagen than with the intact protein. This is probably due to increase of the number of co-ordination active sites of the collagen chains, FIG. 3.-The fixation of chromium from solutions of basic chromium sulphate complexed by means of sodium sulphite by : -x-x-x- intact collagen, -e--@--@-- collagen with inactivated carboxyls, -0-0-0- cation exchange resin of carboxylic type. i.e. non-ionic groups, resulting from rupture of cross-links, probably H-bonds, which has been indicated to occur in the methylation process as shown by the findings of Bowes and Kenten 20 and by the author.21 The reactivity of the car- boxyl ions of the resin is evidently restricted to the positively charged chromium complexes.Comparing the curves of resin and collagens, the predominance of the fixation of non-cationic chromium by collagen in systems containing 2-3 moles sulphite per mole of Cr203 is evident. A number of earlier findings, particularly on the influence of pretreatment of collagen in concentrated solution of lyotropic agents and the effect of hydrothermal shrinkage (denaturation) ofK . H. GUSTAVSON 191 collagen, point to the binding of non-ionic complexes of chromium to non-ionic protein groups, such as the peptide link by co-ordination (W-bondings).The hydroxy group of serine and hydroxy-proline may also be involved.21 The find- ings discussed prove the exclusive function of the ionized carboxyl groups of collagen for the initial attraction of electropositive chromium complexes and for the final irreversible fixation of these complexes by collagen, the high complexing power of the carboxyl group directing the ultimate attachment. The great avidity of collagen lacking in carboxyl groups for non-ionic complexes also provides evidence for the participation of groups other than the carboxylic group in the binding of these chromium complexes by hide protein. THE REACTION OF POLYAMIDES WITH CHROMIUM sALTs.--In this connection, the behaviour of basic chromium salts to an artificial substrate with the -CO.NH- link as its main reacting groups and practically devoid of ionic reactivity is of interest. The modified polyamide, in the hydrated state has been found to be exceedingly reactive towards agents which possess hydrogen-bonding ability, for instance, polyphenols of which vegetable tannins are an outstanding example.8 The cationic chromium complexes present in the standard solutions of the basic chloride and sulphate were not taken up by the polyamide. A mirior fixation of chromium from concentrated solutions of the sulphate was found, however. From dilute solutions of extremely basic chromium perchlorate (33 % acidity), the polyamide fixed large amounts of chromium, amounting to 7.1 % Cr2O3 of its weight. This solution contained 70 % of its chromium in the form of non-ionic complexes.Also the solution of the phthalato-chromium sulphate which consisted of 65 % non-ionic and 35 % cationic chromium complexes, showed affinity for the polyamide, which fixed irreversibly 4.5 % Cr203. The experiments 4 with the polyamide constitute an additional proof of the non- participation of the -CO . NH- group in the fixation of cationic chromium and indicate also that certain non-ionic chromium complexes may be fixed by this link, the most frequently occurring group in proteins. UNI- AND MULTI-POINT FIXATION OF CHROMIUM COMPOUNDS.-with practically conclusive evidence that the ionized carboxyl groups of collagen are governing its fixation of ordinary chromium salts, it is possible to proceed with th.e second part of the problem of the nature of chrome tanning, i.e.the extent of ionic dis- charge of the polyvalent cationic complexes by the carboxyl ion of the protein, on the proportion of unipointly and multipointly fixed complexes. As pointed out earlier, the 67 % acid chromium chloride contains mainly complexes of the type (Crz(OH)#+. It is reasonable to expect from steric considerations that there is a remote possibility for complete reaction of such a complex with four carboxyl ions of collagen. The length of a Cr-O-Cr--chain is estimated to be about 6A and by protolysis small amounts of complexes containing four atoms of chromium may be formed which would have an extension of ca. 18 A. The formation of complexes in situ is more likely to occur with the basic sulphates than the chlorides.EXPERIMENTS WITH GELATIN soLmoN.-Since the collagen lattice is a rigid structure with the ionized carboxyl groups probably interspaced at a considerable distance and the inaccessibility of some reactive groups are to be expected, some preliminary experiments were carried out with gelatin in 1 % solution, in order to avoid the interference of spatial factors. These experiments were followed up by series on tanning with hide powder. The following series of experiments will give an idea of the general approach. To portions of 10.0 ml of 1 % gelatin, quantities of the standard solutions of basic chloride and sulphate equal to 1.0 mequiv. Cr (25-3 mg Cr203) were added. The solutions were shaken after the addition of the chromium salt and left for various lengths of time for reaction to take place.They were then shaken for 20 min with moist Dowex-50, employed as the sodium salt (= 2 g dry resin) in order to remove the uncombined chromium. The chromium combined with gelatin was determined in the filtrate from the cation exchanger. The amount of ion exchanger used corresponded to 10 mequiv. cation and the quantity of cations added to the gelatin solution was less than I mequiv. using the ionic equivalent of the chromium salts. The amount of chromium present in the form of non-ionic192 REACTION OF CHROMIUM SALTS WITH HIDE complexes of the basic sulphate was corrected for. Fig. 4 shows the binding of chromium by gelatin as a function of the time of interaction. It is interesting to note that the chromium chloride + gelatin system reaches the equilibrium state practically instan- taneously (in less than 1 min), whereas a few hours is required for the sulphate systems to reach the maximum chrome fixation, being particularly pronounced for the neutral salt-free chromium sulphate. The gelatin solutions treated with the basic chromium chloride contained generally 14-15 % CrzO3 in combination with gelatin.Since gelatin contains 1.0-1.1 mequiv. carboxyl ions per g gelatin, and assuming about 90 % of these groups to be present as COO- groups at the pH value of 3.5 employed and to have reacted quantitatively with chromium, values of the mean equivalent weight of 140-150, in terms of Cr2O3, are obtained for the cationic chromium complexes fixed by gelatin.Hence, practically all of the chromium complexes combining with gelatin must be attached in the form of complexes of the general type (Cr2(0H)~C13+. With a mean equivalent weight of 38 for the cationic complexes present in the original solution, expressed as Cr2O3, or (Cr2(OH2)/4, the maximum amount of chromium bound by gelatin should only be about 3-6-34 % on the basis of protein. Accordingly, it is shown that in systems with readily accessible reactive protein groups, such as gelatin in dilute solution, the basic chromium chloride behaves towards the protein mainly as a unifunctional agent. FIG. 4.-The fixation of chromium by gelatin (in 1 % solution) as a function of the time of interaction from solutions of I: 67 % acid chromium sulphate, Cr2(0H)2(SO& ; 11: 67 % acid chromium sulphate liquor, Cr2(0H)2(SO& .Na2SO4 ; 111: 67 % acid chromium chloride, Cr2(OH)2Cl4. EXPERIMENTS WITH COLLAGEN.-In tanning of hide powder with the standard solution of the chromium chloride at a concentration of 25 g/l. Cr203, the following figures of the composition of the chromed hide powder were recorded. The amount of chromium fixed was 9.6 % and the amount of combined C1 found was 7.4 % Cl, both values calculated on the weight of collagen. Since the binding capacity of collagen for hydro- chloric acidis 0.9 mequiv. HCl per g collagen (= 3.2 % Cl), at least 4.2 % C1, based on the weight of the protein, should be associated with the chromium complexes fixed by collagen. Since according to the ion exchange analysis, the chloride quantitatively is in the ionic form, no chloro groups being present, the chloride groups in excess of the amount of the maximum binding capacity of collagen for HC1 must be associated with the hydroxo-chromium complexes fixed by collagen as compensating ions to the posi- tively charged chromium complexes which are not completely discharged by the carboxyl ions of collagen.The mean equivalent weight of the hydroxo-chromium complexes fixed by collagen should be of the order of 120 assuming 80 % of the available carboxyl groups (about 0.8 mequiv. per g collagen) to be partaking in the binding at the pH of the system, i.e. a pH 3. Thus, the main part of the chromium combined with collagen must have been fixed as unifunctional complexes. The data indicate that only a small percentage of the fixed chromium is multipointly attached, which is the potential cross-linking agent.The relatively low degree of hydrothermal stability imparted to collagen in tanning with basic chromium chlorides, compared to the corresponding tanning with basic sulphates, may possibly be due to this preference of the cationic complexes of chromium chlorides for unipoint combination with collagen.K. H. GUSTAVSON 193 The drastic improvement of the hydrothermal stability of chromium chloride tanned leather by its subsequent treatment in solutions of salts of bifunctional carboxylic acids, such as adipate, was explained by Holland 22 as due to an increase in the number of cross- linkages between the collagen chains, the bifunctional residue of the dicarboxylic acid joining two chromium complexes in collagen tanned with chromium chloride. Thus, for instance, a chloride-tanned leather showing an area loss of 60 % in the boiling test, is made shrinkproof after 2 days’ immersion in a 0.25 M solution of sodium adipate.Since the length of an adipate bridge of the type, Cr-0-Cr-OCO . (CH2)4. OCO . Cr-0-Cr, should be about 23& and the side chain distance between protein chains of hydrated collagen is about 17 A, the steric conditions for the postulated cross-linking are favourable. Corresponding series of experiments were run with the standard solution of the 67 % acid chromium sulphate. The chrome fixation curve of gelatin (no. I1 of fig. 4) shows at equilibrium a value of fixed chromium of 13.2 % Cr203 on the basis of gelatin, which proves beyond any doubt that the largest part of the chrome fixation takes place as unipoint binding of cations of the type (Cr2(OH)2S04)(S04/2)+.Nevertheless, the multi- point interaction and binding, necessary for the cross-linking function of the chromium complexes, is as a rule considerably more pronounced for the basic sulphates than for the corresponding chlorides. In tanning experiments with the basic chromium sulphate in solutions of 25 g/l. Cr203 the hide powder fixed 11.0 % Cr2O3 on the weight of collagen. The total sulphate content was 13.7 %. By removing the ionically-held SO4 groups by shaking the chromed hide (= 2-0 g collagen) in 50 ml of 4 % solution of pyridine €or 1 h,23 the sulphate content was reduced to 6-7 % SO4, on the basis of collagen.Hence, an amount of 7.0 % SO4 was present outside the chromium complexes probably in the form of protein-bound sulphate and as sulphate ions compensating the charged chromium complexes attached to collagen by unipoint binding. Since the maximum binding capacity of collagen for sulphuric acid at equilibrium pH > 1.2 is about 4 5 % SO4, on the basis of collagen, an amount of 2.4 % SO4 at least should be present in the third form, assumed to function as compensating ion to the charged, unipointly fixed sulphato-chromium complex. Basing the calculations on the figures given and assuming 80 % of the ionized carboxyl groups of collagen at a final pH value of about 3.2 (0.8 mequiv. per g collagen) to be in- volved in the fixation of the cationic chromium complexes, the chromium compounds fixed by collagen should consist of about 20 % bipointly attached (Crz(OH)zS04)- complexes (= 1.1 % Cr2O3 on the weight of collagen) and of 80 % unipointly attached complexes of the general type : (Cr2(OH)zSO4)(SO4/2)+ (= 9.9 % Cr203).These figures refer to the amount of available carboxyl groups. Hence, the amount of Cr2O3 incor- porated with collagen is composed of about 90 % of the unifunctional complexes carrying residual electrical charge and 10 % of bifunctional complexes containing both of the valencies compensated by the carboxyls of collagen. CROSS-LINKING BY CHROMIUM coMPLExEs.-The cross-linking complexes are among the 1 % chromium oxide which is bipointly fixed by collagen. Although the uncertain factor in these approximations is the amount of the carboxyl ions reacting with chromium, the result probably gives a fair picture of the actual conditions.Weir’s finding 24 that the optimal stability of collagen is obtained by fixation of such small amounts of chromium as 1 % Cr2O3, estimated from data of the thermodynamic quantities, is no Ionger a puzzle. The decreased stabil- ity of collagen indicated by Weir’s thermodynamic data to result from the binding of large amounts of chromium may then be explained by the predominance of unipoint binding of the chromium complexes by single carboxyl groups which connotes rupture and elimination of a part of the ionic cross-links of the original collagen, which bridges in a small way contribute to the organization of the protein structure .Weir24 believes that only a fraction of the acidic and basic protein groups possess the required spatial orientation for reaction with the chromium complexes forming cross-links. He suggested that the amount of chromium bound to collagen in excess of 1 % Cr203 probably is combined in a similar manner as are other types of tanning agents which decrease the entropy of activation. Weir concluded that this additional chrome will add nothing to the orientation of the G194 REACTION OF CHROMIUM SALTS WITH HIDE protein chains and their stabilization. On the contrary, incorporation of large amounts of chromium will mean some loss of orientation of the protein lattice. These suggestions are in harmony with the findings and the deductions of the present paper and with the concept of the dual nature of chrome fixation based on the present and previous experimental data.It is interesting to note that by interaction of chromium sulphate with gelatin solution, the resulting chromed gel will withstand the action of boiling water even at such low chromium contents as 0-2-0.3 % bound chromic oxide, whereas about 3-4 % Cr203 is the minimum amount of fixed chromium required to render collagen resistant to boiling water. This point has been stressed particularly by ElOd.25 This comparison is a striking illustration of the importance of the steric conditions in reactions of fibrous proteins . CONCLUDING COMMENTS.-The chrome tanning process exemplified by the interaction of collagen with basic chromium sulphate, mainly present in dilute aqueous solutions as (Cr~(OH)~S0~)-complexes, may in the light of modern researches be described as follows.The complexes and protons, present in the protolyzed solution of the basic salt, are attracted to and compete for the carboxyl ions of collagen. In order to maintain the electro-neutrality of the system, the corresponding sulphate ions are simultaneously attracted to the cationic protein groups, the main part of these sulphate ions being originally associated with the sulphato-chromium cations which are in great excess over the protons. In view of the considerable distance between adjacent ionized carboxyl groups, which is made probable from considerations of the chemical composition of collagen, and the rather small size of the sulphato- 0x0-chromium complexes of moderately basic chromium sulphates, with an estimated length of 6-12& it seems probable that the main part of the complexes are only able to react with one carboxyl ion, the unipointly fixed complex balancing its residual charge by an equivalent of sulphate ions.The initial ionic reaction with the discharge of electrostatically attracted complexes by the carboxyl ions is probably followed by the penetration of the carboxyl group into the chromium complex, forming a co-ordinate-covalent type of linking of great strength. The direct attachment of the carboxyl group to the chromium atom is indicated by a number of observations. It seems reasonable to believe that only a small part of the complexes, probably not more than one-tenth of the total amount of chromium present in heavily chromed leather, will be able to combine with two carboxyl ions of such close proximity as required for incorporating two carboxyls in the chromium complex.There are two possibilities for this bifunctional fixation (i) intra-molecular binding, which does not contribute to the stabilization of the protein, and (ii) inter-molecular, which combination results in cross-linking of adjacent collagen chains and increased stability of the collagen lattice. In view of the uncertain and unsatisfactory state of our present conception of the structure of collagen, particularly agpavated by the introduction of the helical concept, which appears not to have advanced far enough for the application to intricate chemical reactions of collagen, the discussion of the steric possibilities has been avoided in the present communication although in the final analysis it is likely to be the crucial factor. 1 Gustavson, J. Amer. Leather Chem. Assoc., 1950, 45, 536 ; J. SOC. Leather Trades 2 Gustavson, J. Soc. Leather Trades Chem., 1951, 35, 270. 3 Riess and Barth, Collegium., 1935, 62. Jander and Scheele, 2. anorg. Chem., 1932, 4 Gustavson, Svensk. Kem. Tidskv., 1944,56, 14 ; J. Colloid Sci., 1946, 1, 397 ; J. Soc. 5 Gustavson, J. SOC. Leather Trades Chem., 1951, 35, 160. 6 Fraenkel-Conrat and Olcott, J. Biol. Chem., 1945, 161, 259, 7 Gustavson, J. Amer. Chem. SOC., 1952, 74,4608. Chem., 1950, 34,259. 206, 241. Leather Trades Chem., 1946, 30, 264.K. H. GUSTAVSON 195 8 Gustavson and Holm, J. Amer. Leather Chem. ASSOC., 1952, 47, 700. 9 Gustavson, J. SOC. Leather Trades Chem., 1952, 36, 182. 10 Tanford, J. Amer. Chem. SOC., 1951, 73, 504. Gurd and Goodman, J. Amer. Chem. 11 Grassmann and Kusch, Z. physiol. Chem., 1952, 290, 216. 12 Ley, Z. Elektrochem., 1904, lQ, 954. 13 Thomas and Seymour-Jones, Ind. Eng. Chem., 1924,16,157. Northrop and Kunitz, 14 Tanford, J. Amer. Chem. SOC., 1951, 43, 504. 15 Wilson, J. Amer. Leather Chem. Assoc., 1917, 12, 108. 16 Gustavson and Widen, Ind. Eng. Chem., 1925,17, 577 ; Collegium, 1932, 775. 17 Kuntzel and Riess, Collegium, 1936, 138. 18 Kuntzel, Kolloid-Z., 1940, 91, 152. 19 Gustavson, Svensk Kem. Tidskr., 1940, 52, 75. 20 Bowes and Kenten, Biochem. J., 1949,44, 142. 21 Gustavson, Acta Chem. Scand., 1952, 6, 1443. 22 Holland, J. Int. SOC. Leather Trades Chem., 1940, 24, 221. 23 Gustavson, J. Amer. Leather Chem. Assoc., 1927,22, 60 ; Leder, 1952, 3, 293. 24 Weir, J. Amer Leather Chem. ASSOC., 1949, 44, 142 ; J. Res. Nat. Bur. Stand., 1949, Weir and Carter, J. Res. Nat. Bur. Stand., 1950, 44, 599. 25 Elod and Schachowskoy, Cullegium, 1933, 701. Suc., 1952, 74, 670. See also Edsall, Faraday SOC. Discussions, 1953, 20. J. Gen. Physiol., 1928, 11, 481. 42, 17.

ISSN:0366-9033    

DOI:10.1039/DF9541600185

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

K. H. GUSTAVSON 195 MUCQPD MATERIAL IN HIDES AND SKINS AND ITS SIGNIFICANCE IN TANNING AND DYEING BY D. BURTON AND R. REED The Leather Industries’ Dept., The University, Leeds 2 Receiced 16th July, 1953 The purpose of the paper is to review recent knowledge of the interfibrillary material and discuss its significance in leather manufacture, The early literature contains many references to a cement substance between the fibres. Eitner, Procter and van Licr regarded it as mucoid in character but McLaughlin and Theis, and Kritzinger, considered that the bulk of the interfibrillary material consisted of globular proteins. Researches in the medical field by Meyer, Watson and Pearce, and Wohnlich, are discussed in conjunction with histological, electron microscope and physiological in- vestigations.It is concluded that mucoid material is always associated with protein fibres in their growth and that it plays an important part in determining tissue cohesion and stability. There are two mucoid components. Day considers that the hyaluronic acid of the interfibre fluid coats the collagen fibrils and renders them water-repellent, but Meyer has shown that chondroitin sulphate is inore firmly bound in the skin. There is a considerable amount present at the junction of the epidermis and the coriuin and in parts of the skin which are rich in elastic tissues. It is shown that mucolytic enzymes are much more efficient in removing this material than solutions containing lime and sulphide and they leave the fibre structure in a well-opened-up condition ready for tanning without the usual subsequent treatment with tryptic enzymes. If this mucoid inaterial is not completely removed before tanning it remains in the leather and interferes with the dyeing where even pale shades are required. The importance of the interfibrillary material in hides and skins has long been recognized in the leather industry.In the past, however, information regarding its nature and function has been somewhat vague. Thus, although the tanner has appreciated that some, if not all, the interfibrillary material must be removed during preparation of the pelt for tannage, he has been uncertain196 MUCOID MATERIAL as to the corresponding changes brought about in the pelt structure. The purpose of the present paper is to review the recent knowledge of the interfibrillary material of skin and to discuss its significance in the preparation of pelt for tanning and dyeing.In the early literature of leather chemistry there are many references to a material between the fibres of hides and skins. In 1880, Eitner 1 referred to it as rnucoid and observed that if the skin were dried, this material becomes less soluble in salt solutions. Procter2 in 1903 first drew attention to its complex character and stated that, although mucoid material was present, the major component was protein in nature. He considered that the function of this com- plex material was to cement the fine fibrils of collagen and so form the large white fibre bundles which are characteristic of loose connective tissue. Further, Procter maintained that for satisfactory soaking back, it was necessary to remove as much as possible of this interfibrillary material.van Lier 3 in 1909 obtained interfibrillary material by extraction of skin with half saturated lime-water. He found there was a limit to the amount of material extracted by this reagent and hence he concluded that it was not a decomposition product of collagen. He established that the substance extracted by lime-water could be precipitated by acetic acid, although it became soluble in excess of this precipitant. The material precipitated by acetic acid was soluble also in weak hydrochloric acid and the solution after boiling reduced Fehling’s solution. On the basis of this work, van Lier considered that interfibrillary material was mostly mucoid in character, containing a little nucleoprotein as a contaminant.Like Proctor, van Lier regarded the interfibrillary material as a cement aiding in-the cohesion of the fibrils within the large fibre bundles. Working along similar lines, Rosenthal,4 and later, Mclaughlin and Theis 5 also showed the presence of both protein and mucoid material in hides and skins, but contrary to van Lier, they considered that the bulk of the interfibrillary material consisted of globular proteins. Rosenthal also drew attention to the uneven distribution of interfibrillary material in animal skin. Of the total amount present (about 10 % of the dry weight), only 30 % is located in the fibre layer of the corium, and this amount is evenIy distributed; the remaining 70 % is concentrated in the papillary layer, especially at the junction of the epidermal and papillary layers.McLaughlin and Theis stated that the mucoid component contains about 12 % nitrogen and about 2.4 % sulphur, the latter apparently combined as sul- phuric acid. Halogens and phosphorus are absent. As would be expected with a mucoid material, the Molisch reaction was strongly positive, but Fehling’s solution was not reduced until after hydrolysis with hydrochloric acid. Grassman et aL,6 in a study of the mucoid component, showed that it contained about 8 % of glucose + galactose, and 1.53 % of a hexosamine. Kuntzel,7 in 1924, main- tained that the albumins, globulins and mucoid material which could be extracted from skin were derived from the fibroblasts. He showed also that the removal of these materials resulted in a marked loosening and swelling of the fibre structure and considered that the interfibrillary substance not only acted as a cement sub- stance for the collagen fibrils, but also determined their degree of hydration. In 1937, Schneider 8 found that the protein fraction of ox hide, extracted in the cold by means of 10 % salt solution, corresponded to 0.84 % of the original nitro- gen; the albumin and globulin fractions contained mannose and galactose in equimolecular proportions.After extraction of the hide with 10 % salt solution, to remove the bulk of the interfibrillar proteins, Schneider further extracted with lime-water and obtained a product containing 0.26 % of the original nitrogen This was identified as a mucoid material containing some protein, and acid hydro- lysis of the mucoid gave rise to equimolecular amounts of the sugars glucose and galactose.Kritzinger 9 has made a comprehensive study of the interfibrillary proteins of skin and has confirmed and extended much of the earlier work. ThroughoutD. BURTON AND R . REED 197 these studies, however, Kritzinger has paid little attention to the mucoid com- ponent of interfibrillary material, and considers that since the larger proportion is protein in nature, the lime-yard processes can best be explained in terms of the removal of globular protein material alone. He has found that a 10 % salt solution is the most effective for removing the interfibrillary proteins, which make up roughly 10 % of the total protein matter in hide.Further, he has confirmed Rosenthal's observations that in the fibre layer of the corium, there is an even distribution of interfibrillary material, making up about 30 % of the total present in the whole hide. The remaining 70 % is located in the papillary layer, the site of densest deposition being the epidermal-papillary layer junction. Kritzinger has explained the role of interfibrillary proteins in many of the lime-yard processes. For example, the difficulties associated with the soaking back of sun dried hides is due essentially to the denaturation and coagulation of the globular proteins to form hard and dry material. These changes are irreversible and the dried protein material is extremely difficult to wet back. Kritzinger further considers that interfibrillary protein may be coagulated in the tissue spaces during wet curing, by the process of salting out; unless care is taken, the coagulated protein may prove difficult to disperse.The same author has also produced evidence for the importance of the interfibrillary proteins in the liming process, both from the aspect of unhairing and from the opening up of the fibre structure of the pelt. Kritzinger points out that R o s s , ~ ~ in 1924, first put forward the suggestion that unhairing involved the loosening of the interfibrillary proteins of the epidermal- papillary junction. Kritzinger has developed this idea and draws attention to the fact that the theory of unhairing by means of lime, which involves a partial breakdown of the keratin molecule, cannot apply generally.That is, he regards unhairing by lime as a special case of depilation. Other unhairing reagents, such as enzymes, acetic acid, hydrochloric acid, sodium chloride, hot water, sodium fluosilicate, urea, etc., he considers to act by virtue of their solvent and dispersive effect on the interfibrillary proteins. In his view, the general process underlying all methods of depilation, is the removal of the globular proteins. Further, the loosening action on the fibre structure of the pelt is a necessary consequence of the removal of globular protein material. Gustavson,ll in a study of the unhairing and loosening action of sodium chloride and urea, holds a similar view. Kritzinger also states that in his opinion, bating is essentially a continuation of the liming process, whereby the interfibrillary protein remaining after liming, is finally and completely removed, so bringing about the characteristic softness, porosity and fallen condition of bated stock.It is seen, therefore, that the current tendency in the leather field is to regard only the protein component of interfibrillary material as the important one, and to attempt to explain the changes taking place in the pelt, during preparation for tannage, solely in terms of the removal of protein matter only. Current research work into the nature of interfibrillary material, carried out by workers in the medical field, suggests, however, that the mucoid component of this material is also of great importance in determining the stability and cohesion of the skin structure, and also the flow of liquids through skin and the state of hydration of the collagen fibrils.Such considerations may have great implications in the preparation of pelt and hence it is necessary to review the more important aspects of this work. RESEARCHES IN THE MEDICAL FIELD.-Meyer 12 has been chiefly responsible for developing the recent chemistry of the mucoid material of skin. After freeing the corium of skin from protein components by extraction with 10 % solution of sodium chloride, Meyer has confirmed that the mucoid component of interfibi-illary material can be loosened from the remaining structures only if treatment with alkali is employed. Once the bulk of the interfibrillary protein has been removed by extraction with salt solution, no mucoid material can be extracted by water alone ; alkali, e.g.lime-water, is essential. This fact alone indicates that whereas198 MUCOID MATERIAL the bulk of the interfibrillary protein is only loosely bound, existing free in the tissue spaces, the mucoid component is somehow bound to the collagen fibrils of the corium. The lime-water extract of corium does in fact contain some protein material, but Meyer considers that it is bound very loosely to the mucoid material (which is precipitated at pH4 by means of acetic acid) since the protein can be separated from the mucoid by physico-chemical means alone. The mucoid material obtained in this way has been characterized by Meyer as hyaluronic acid, and it is obtained as a thick, viscous solution, indicating a long chain, polymeric molecule.It is a mucoid, or mucopolysaccharide, in that it is essentially a polymer produced by the end-to-end linking of a disaccharide unit, acetyl glucosamine and glucuronic acid. From such considerations, Meyer suggests that hyaluronic acid exists free in the interfibrillary material of skin, that is, it is not attached chemically either to the interfibrillary proteins or to the collagen fibrils themselves. By a similar procedure, a further mucopolysaccharide has been shown to be present in skin, namely, chondroitin sulphate. More drastic pretreatment with alkali, however, which involves breakdown of the collagen fibrils of the skin, is needed and so far Meyer has been unable to obtain the chondroitin sulphate component of skin in highly viscous and relatively undegraded form.Thus Meyer recognizes two mucoid components of skin, one of which, hyaluronic acid, is present in the interfibrillary material in loose association both with the collagen fibrils and the interfibrillary proteins ; the other, chondroitin sulphate, which most probably should be regarded not as an interfibrillary component, but as integral with the collagen fibril structure itself. This indication that chondroitin sulphate seems to be an integral part of the native collagen fibril is borne out by work carried out with other tissues. It is, for example, somewhat easier to prepare chondroitin sulphate from tendon or cartilage, but even so, no preparation of this material can be said to represent pure and undegraded chondroitin sulphate.Great diffi- culty is also experienced in isolating this material from bone collagen and it seems necessary first to destroy the collagen fibrils before the mucoid component is re- leased. Watson and Pearce 13 have also shown by chemical estimation that the chondroitin sulphate of skin is in firm association with the collagen fibrils, whilst the hyaluronic acid appears to exkt relatively free in the interfibrillary material. Other mucoids are lcnown to exist in skin, but as yet little is known about them. Recently Wohnlich14 has shown that the basal layer of the epidermis contains large amounts of a polysaccharide which is probably a poly-oxy sugar acid. The fibres of elastic tissue in skin and the walls of the blood vessels also are associated with an unidentified mucoid material.material of skin has been studied by histological methods. Two major staining techniques have been used to study the mucoid components of interfibrillary material. Firstly, there is the metachromatic effect shown by certain thiazine dyes ; mucoids, in combining with the dyes, are thought to induce polymerization of the latter, with a consequent change in colour. For example, when toluidine blue is used, the normal colour is blue, but the metachromatic colours range from violet to red, depending on the degree of polymerization of the dye. Secondly, there is the periodic acid Schiff method; mucoids often contain the 1 : 2 glycol grouping -CHQH-CHQH- which is oxidized by periodic acid to aldehydic groupings. These can react with the colourless leuco-fuchsin compound to form red colours in histological sections.In a study of the interfibrillary material of human skin, Wislocki et aZ.15 found that the papillary layer of the corium and the intercellular material around the hair follicles, were the only regions to show metachromatic staining. Moreover, the intensity of this staining was variable. Treatment of the section with the mucolytic enzyme hyaluronidase, however, brought about a marked reduction in the intensity of metachromatic staining. Stoughton and Wells,l6 using the McManus technique on normal human skin, found a vivid red band staining material at the epidermal corium junction, HISTOLOGICAL EVIDENCE FOR INTERFIBRILLARY MATERIAL .-The inter fi br i 1 la r yD .BURTON AND R. REED 199 that is, around all the epidermal intrusions into the corium. In addition, a similar intense red coloration was seen in the walls of the blood vessels, and a less intense coloration was observed throughout the fibre layer of the corium. This work indicated that though the actual distribution of mucoid may vary in amount in different regions of the skin, it seems associated with all the skin components. Stoughton and Wells were unable to identify this red staining material, but they were able to show that it was not glycogen or hyaluronic acid. Gersh and Catchpole17 found that mouse and rat skin present a similar staining pattern with the McManus technique and considered that the red coloration is due essenti- ally to a homogeneous interfibrillar and extracellular component which forms a continuum in which the protein fibre structures, such as collagen and reticulin, are embedded. Further, they found with increasing age, the interfibrillary material becomes harder and harder to extract from the skin (rat).This was interpreted in terms of it being a muco-protein which progressively polymerizes with age. In young skin which had been treated with proteolytic enzymes, such as pepsin or trypsin, and the mucolytic enzyme hyaluronidase, the red coloration could not be obtained, indicating that the muco-protein interfibrillary material had been removed by such treatments. The fibrils of reticulin and elastin in the collagen structure, although remaining after this treatment with enzymes, appeared morphologically intact but far more fragile.They conclude that interfibrillary material is essentially a cement substance which when present determines the strength and cohesion of the collagenous framework of the tissue; further it is a muco-protein, i.e. protein containing mucoid, which may be highly polymerized, relatively inert and difficult to extract. ELECTRON MICROSCOPE REsEARcms.-The direct observation of interfibrillary material in skin by means of the electron microscope has also been attempted. Progress along these lines is, however, difficult since it is well established that drying brings about profound changes in this material and it has not been possible so far to carry out observations on wet tissue. Wolpers 18 first found evidence of an amorphous material which is only weakly attached to the collagen fibrils of skin.Gross 19 has studied fragmented human skin of a variety of ages and has identified the amorphous material which is always observed in close associ- ation with the collagen fibrils, as ground substance or interfibrillary material. Recently, Day and Eaves 20 have shown that the bulk of the interfibrillary material of interstitial connective tissue consists of minute membranes. Further, whilst treatment of the tissue with the enzyme hyaluronidase affects the flow of saline throughout its structure, this enzyme appears to have no effect on the membranous structure . been recognized that the material between the fibres in a fresh skin must be in a fluid condition, for it appears to offer no resistance either to the swelling or the separation of the fibres.Further, it possesses a sticky, viscous nature and is smooth and slimy to the touch. From the colloidal aspect it is intermediate between a sol and a gel. It does not flow as easily as a sol, nor does it resist deformation in the manner of a gel. The material is elastic and its viscosity varies with the pH value of the fluid. Thus, in the natural state, interfibrillary material possesses many of the physical characteristics of mucous material. Physiological evidence suggests that mucoid material at least enters into part of the make-up of inter- fibrillary material. It is now well known that great resistance is offered to the diffusion of certain fluids which are injected into this fluid filling the interfibre spaces. Moreover, this resistance to diffusion can be rapidly and strikingly over- come by treatment of the tissue with mucolytic enzymes.Almost immediately after such an enzyme has been injected into the interfibrillary spaces, the flow of many injected fluids is greatly increased. This is the so-called “spreading phenomenon ” discovered by Duran-Reynals.21 Many workers have considered that hyaluronidase, an enzyme which brings about this striking change, acts by PHYSIOLOGICAL CONSIDERATIONS OF INTERFIBRILLARY MATERIAL.-It has long200 MUCOID MATERIAL depolymerizing the hyaluronic acid component of the interfibrillary fluid. Day,22 however, considers that the rate of depolymerization of hyaluronic acid by this enzyme in uitro is far too slow to account for its surprisingly rapid action in vivo.He suggests that it is more likely that the hyaluronic acid of the interfibre fluid coats the collagen fibrils and renders them water-repellent. Thus the flow of fluids through the tissue structure is impeded. The sudden effect of hyaluronidase on the rate of fluid flow he attributes, not to a depolymerization of the hyaluronic acid, that is, a lowering in the viscosity of the interfibrillary fluid, but merely to a removal of the hyaluronic acid from the collagen fibrils. The latter are no longer water-repellent. They become hydrophilic and fluids can now flow easily through- out the tissue structure. This effect has important implications for the tanner. It establishes that it is the mucoid component of the interfibrillary material, which determines the degree of hydration of the collagen structure and the flow of liquids through it.Thus, if the tanner wishes to open up the fibre structure of pelt, and remove the whole of the interfibrillar material, it seems to be essential to detach the hyaluronic acid from the collagen fibrils. Only if this is done will it be possible to achieve thorough wetting of the pelt structure. There is, therefore, much evidence that the mucoid material is of fundamental importance in hides and skins. It is always associated in considerable quantity with collagen, reticulin, and elastic tissue fibres during their development. As the tissues mature, the mucoid material appears to become less necessary, because the fibres rigidify and crystallize out in a regular manner.Mucoid seems to be needed as a protection for the young, tender collagen, which would be easily re- dispersed if it were not present. This accounts for the difficulty in liming calf skins as compared with older ox hides. It is also known that corresponding changes in the mucoid component of interfibrillary material are involved in certain pathological conditions of skin, many of which manifest changes in the cohesion of the collagen fibrils. The mucoid component, therefore, plays a very important part in determining tissue cohesion and stability. Its removal appears to relax the fibre structure and open it up, since muco-collagen links of stabilization are broken. It still has to be proved which of the two mucoid components is the more important as regards tissue cohesion and general stability.The suggestion of Day that the hyaluronic acid of the interfibrillary fluid coats the collagen fibrils and so renders them water-repellent, takes no account of the mucoid which seems firmly bound to the sclero-protein structures. The difficulty in obtaining chondroitin sulphate in a highly polymerized and viscous form has been mentioned; if it were associated only with the globular proteins of interfibrillary material, it should be easily obtainable. Moreover, the work of Jackson 24 is direct evidence for the stabilizing effect of chondroitin sulphate. Tendon collagen is insoluble in acetic acid unless this mucoid component is removed either by alkali or by mucolytic enzymes. Thus the tanner starts with a hide or skin which contains mucoid materials.Further, this is present in considerable amount at the juncture of the epidermis and the corium as well as in those sites in the skin which are rich in elastin tissue. It has already been shown 23 that the ‘‘ liming process ” consists in the removal of these mucoids with a consequent loosening in the hair and a change in the cohesion of the collagen fibre structure. This process, however, does not remove the mucoid material sufficiently in the cases of skins or hides which have to be made into pliable leathers with the desired degree of softness. It is, therefore, common practice to bate by treating them with a proteolytic enzyme. In experi- ments extending over the past year, it has been found that mucolytic enzymes are much more efficient than lime.They remove the mucoid material and leave the fibre structure in a well-opened-up condition ready for tanning. This conception is important not only with reference to tanning but also to dyeing. It follows that if mucoid material is not removed before tanning it will THE SIGNIFICANCE OF THE INTERFIBRTLLARY MATTER IN TANNING AND DYEING.-D. BURTON AND R. REED 201 remain in the leather and interfere with dyeing especially where pale shades are required. In our experiments, comparative experiments with skins unhaired in the usual way and skins treated with mucolytic enzymes, it has been found that paler and more even shades are obtained after mucolytic enzyme treatment. 1 Eitner, Gerber, 1880, 111 et seq. 2 Procter, Principles of Leather Marzufacture, 1903, 50 ; Colloid Chem. Reports, 1917, 3 van Lier, 2. Physiol Chem., 1909, 61, 117. 4 Rosenthal, J. Amer. Leather Chem. Ass., 1916, 11,463. 5 McLaughlin and Theis, J. Amer. Leather Chem. Ass., 1924, 19,428. 6 Grassman, et al., quoted by McLaughlin and Theis, Chemistry of Leather Manu- 7 Kuntzel, Collequim, 1924, 212. 8 Schneider, Collequim, 1937, 522 ; J. SOC. Leather Trades Chem., 1938, 22, 569. 9 Kritzinger, J. Amer. Leather Chem. Ass., 1948, 43, 243. 10 Ross, J. Soc. Chem. Ind., 1924, 43, 55. 11 Gustavson, J. SOC. Leather Trades Chem., 1934, 33, 162. 12 Meyer, Ann. N. Y. Acad. Sci., 1950, 52,961 ; Advances in Enzymology, 1952,13, 199. 13 Watson and Pearce, Ann. N. Y. Acad. Sci., 1950, 52, 987. 14 Wohnlich, Biochem. Z., 1951, 322 (l), 78. 15 Wislocki, Bunting and Dempsey, Ann. J. Anat., 1947, 81, 1. 16 Stoughton and Wells, J. Invest. Derm., 1950, 14, 37. 17 Gersh and Catchpole, Ann. J. Anat., 1949, 85, 457. 18 Wolpers, Deutsche. Med. Woch., 1944, 70, 435. 19 Gross, Ann. N. Y. Acad. Sci.,1950, 52, 964. 20 Day and Eaves, Biochim. Biophysica, 1953, 10, 203. 21 Duran-Reynals, J. Expt. Med., 1929, 50, 327 ; Ann. N. Y. Acad. Sci., 1950, 52, 946. 22 Day, J. Physiol., 1952, 617, 1. 23 Burton and Reed, J. SQC. Leather Trades Chem., 1953, 37, 82; 1953, 37, 75. 24 Jackson, Biochem. J., 1952. 10. facture (1943, p. 44.

ISSN:0366-9033    

DOI:10.1039/DF9541600195

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

D. BURTON AND R. REED 201 MECHANISM OF ABSORPTION OF NON-IONIC DYES BY BQLYETHYLENE TEWEPHTHALATE * BY M. J. SCHULER AND W. R. REMINGTON E. I. duPoiit de Nemours and Company, Jiic., Wilmington 99, Delaware, U.S.A. Received 29th June, 1953 Isotherms were measured for the distribution of three pure non-ionic dyes and their binary mixtures between polyethylene terephthalate and water in the presence and absence of benzoic acid. In each case, the equilibrium concentration of dye in the fibre was directly proportional to the concentration in the water. For a binary mixture of greatly dissimilar dyes, each behaved completely independently of the other, while for a mixture of two closely related dyes some interference was noted. The solubilities of the dyes in both the fibre and the water increased with a temperature increase and the isotherm was displaced toward the water.The presence of benzoic acid displaced all isotherms toward the water. It is concluded that sorption of non-ionic dyes by polyethylene terephthalate takes place by a solution mechanism. Non-ionic dyes are used almost exclusively in the dyeing of polyethylene ter-ephthalate fibres.1 However, no study of the mechanism of this dyeing system has been published. The rates of dyeing at different temperatures and * Contribution no. 147 from Jackson Laboratory.202 ABSORPTION OF NON-IONIC DYES the use of carriers to increase the dyeing rates have been studied by Waters2 and others 3 using commercial dyes. A graphic description of the physical process of dye transport through the fibre fine structure was given by Remington.4 Reith and Andres 5 suggested that the dyeing of polyethylene terephthalate resembles a solution of the dye in the fibre since the dyes appeared to behave independently in mixtures.Non-ionic dyes of the type used in this study have very low solubility in water and are commonly used as aqueous dispersions. For this reason they are called dispersed dyes. We have attempted to avoid obvious difficulties 6 in the study of dispersed dyes by (1) using dyes which were sufficiently soluble in water to permit reliable measurements of solution concentrations, (2) approaching equilibrium from both directions, (3) using pure dyes. EXPERIMENTAL MATERIALS.-The fibre used was spun from polyethylene terephthalate polymer con- taining 0.3 % TiOz.It was drawn to 3.5 times its original length and was finished as FIG. 1.-Dyeing chamber for 120" C sorption. a crimped tow. The fibre diameter was 18 microns. No finishing agents were used in its preparation. It was washed 15 min in a solu- tion of Duponol D fatty alcohol sulphate (5 g/l.) at 90-100" C, rinsed, and dried before use. The fibre was prepared without using finishing agents, but this precaution was apparently not required. Similar experimental results were obtained with other samples of fibre prepared with standard finishing agents and given the above scour. thesized by a condensation of hydroquinone and phthalic anhydride and was purified by the procedure described in Organic Syntheses.7 The product melted at 199.5" C on a copper block.This synthesis eliminates the formation of the difficultly-removable chloro compounds found in commercial samples. Its purity was demon- strated by the absence of extraneous bands when adsorbed from benzene on a mixture of mag- nesium oxide and Hyflo Super-Cel and de- veloped with 0.05 "/, acetic acid in benzene. 1 : 4-DIHYDROXYANTHRAQUlNONE was syn- This method can detect small amounts of pur- purin, 2-chloroquinizarin or l -chloro-4-hydroxyanthraquinone in l : 4-dihydroxyanthra- quinone. ~-AMINO-~-HYDROXYANTHRAQUINONE (a commercial product) was crystallized from acetone and further purified by passing a benzene solution through a column of Hyflo Super-Cel. A blue to violet band of unknown composition remained on the column. The solid dye, crystallized from benzene as large ribbon-like crystals, gave no extraneous bands on adsorption columns and melted at 216.5" C on a copper block.2-nitro-4-benzenesulphonchloride with excess aniline. The excess aniline was removed from an alkaline solution by steam distillation. The sample crystallized from 95 % alcohol as yellow needles. No extraneous compounds were detected by chromatographic methods. This compound analyzed N-11.4 %, C-58-4 %, S-8-78 %, N02-12.6 % (theory N-I 1.4, C-58.6, S-8.68, N02--12.5). BENZOIC ACID was analytical reagent grade benzoic acid, melting range 122-123" C (Mallinckrodt Chemical Works). PRocmum-During equilibration, all dyebaths were agitated at temperatures con- trolled to & 0.05" C. At 89.3 and 100" C, screw-capped bottles were used, with cap liners made of Teflon polytetrafluoroethylene plastic.Two procedures were used for equilibra- tion, sorption and desorption. In the sorption process at 89.3 and 100" C a dilute solution of the dyc in acetone was pipetted into the bottle and the acetone evaporated. The fibre N1 : N4-DIPHENYL-3-NITROSULPHANILAMIDE Was synthesized by heating 1 - c ~ I o ~ o -M . J . SCHULER A N D W. R. REMINQTON 203 and water (50 mg in 50 ml or 1 g in 150 nil) were then added. At 120" C the same prepara- tion was made except that the dyeing was accomplished in the special dyeing chamber illus- trated in fig. 1. The percent transmission of the solution was determined against air by inserting the dyeing chamber directly into a Cenco Photelometer (Central Scientific Co.).Equilibrium was usually attained within 2 h. The length of the light path through the solution was decreased by inserting plate glass between the windows so that a sufficiently great concentration range could be covered. At equilibrium the solution was " blown " through the valve and the fibre was treated by the standard procedure. In the desorption process, fibre was dyed at 120" C and analyzed for dye concentration. It was then placed in distilled water for desorption or in a dyebath whose concentration was adjusted so that it would be at equilibrium with the fibre. The latter method was used to shorten the time for equilibration. Samples were taken during the sorption or desorption process until no further significant change in the dye concentration in the fibre or bath was noted.The times involved were 3-5 days for desorption at 89" and 100" C, 2 weeks for sorption at 89", 1 week at 100" and 2 h at 120" C. bath and the fibre extracts were determined optically: for the individual dyes, with a Cenco Photelometer ; for mixtures, with a model B, Beckman spectrophotometer (Beckman Instruments Inc.). The absorbancy indices as determined with the spectrophotometer are given in table 1. They were not affected by the presence of other dyes or benzoic acid. ANALYTICAL METHODS.-PHOTOMETRY.-The concentrations Of the dyes in both the TABLE 1 .-ABSORBANCY INDICES dye K m d 535 9 9 415 Y Y 530 Y, 1 -amino-4-hydroxyan thraquinone 535 Y, 420 Y , 480 ,Y 530 Y, 415 ,Y 490 9 , 480 Y ? 535 9 , 490 ¶, 530 9 , N1 : N4-diphenyl-3-nitrosulphanilamide 420 max.1 : 4-dihydroxyanthraquinone as*s 8.1 0.1 15.5 0.07 1 *22 9-70 24.2 40- 1 2.5 26.5 17-8 2.3 34-6 14.0 solvent Cellosohe H20 50 % v./v. Cellosolve H20 50 % ,, chlorobenzene chlorobenzene Cellosolve H20 50 % v./v. Cellosolve H20 50 y y Cellosolve H20 50 % ,, chlorobenzene chlorobenzene chlorobenzene Cellosolve H20 50 % v./v. Cellosolve H20 50 % ,, chlorobenzene chlorobenzene * a, = As/bc ; A, = loglo (l/T,) ; c = mg of dye/cm3 ; b = cell thickness in cm ; T, = transmission solution/transmission solvent. DETERMINATION OF DYE IN THE FInRE.-Approximately 50mg samples of fibre were removed at the temperature of the isotherm, squeezed dry between paper towels, rinsed in acetone at 0-2" C, squeezed between paper towels, and dried in air at 60" C.They were then weighed and extracted in boiling chlorobenzene. The dye was completely extracted with four or five 5-ml portions of boiling solvent. The extract was then diluted to volume, and the concentration determined by optical methods. The con- centration of the dye in the fibre was calculated by dividing the weight of the dye extracted from the fibre by the weight of the fibre minus the weight of the dye. No correction was made for the weight of benzoic acid in the fibre. When fibres containing varying amounts of dye less than saturation were rinsed with cold acetone no dye was removed. At saturation, where there was a significant amount of excess dye solid in the bath, a cold water rinse was given to remove the solid enmeshed in the fibres. The acetone rinse completed the removal.In any case further rinses with cold acetone removed essentially no dye. DETERMINATION OF DYE IN THE BATH.-^ : 4-Di~yduoxyanthruquinone.-Samples were removed in a pipette preheated to the temperature of the bath and discharged into 30 % sodium hydroxide solution. A blue-violet colour developed which was sufficiently stable for quantitative determination colorirnetrically.204 ABSORPTION OF NON-IONIC DYES 1 -Amino-4-hydroxyanthraguinone, N1: N4-diphenyl-3-nifrosulphanilarnidey and all dye mixtures.-Samples were removed in a pipette preheated to the temperature of the bath and discharged into Cellosolve ethylene glycol monomethyl ether solvent. The concentra- tion of dye was determined optically. At saturation, samples of the dye solution were removed in a preheated pipette with a wad of fine glass-wool wrapped on the end to insure removal of dye particles.RESULTS Hereafter? the symbols C f , Cb and K are used; C' represents the concentration of dye in the fibre in mg/g, Cb, the concentration of dye in the bath in mg/ml, and K = C'/Cb. FIG. 2.-A sorption. 0, 0 desorption. Distribution of 1 : 4 - dihydroxyanthra- quinone between fibre and water at 100" C. I I I FIG. 3.-0 89~3°C; A 100" C ; 0 120°C. Effect of temperature on the distribution of 1 -amino-4-hydroxyanthraquinone be- tween fibre and water. FIG. 4.-A no benzoic acid; 0 0.5 %; 0 1.0 %; A 1.5 %; Effect of benzoic acid concentration on the distribution of 1 : 4-dihydroxyanthraquinone between fibre and water at 89-3" C. 0 2.0 %; $I 3.0 % benzoic acid.M.J. SCHULER AND W. R . REMINGTON 205 The distributions of three dyes, individually, between fibre and water are given in fig. 2, 3, 4 and 6. For each dye, at each temperature, a single straight line best represents the data. As the temperature increases, K decreases, and the solubility of the dye increases FIG. 5.-A no benzoic acid; 0 0.5 % ; 1.0 % ; a 2-0 % benzoic acid. Effect of benzoic acid concentration on the distribution of 1-amino-4-hydroxyanthra- quinone at 89.3" C . ~~ ~ FIG. 6.--h no benzoic acid; 0 0.5 %; 0 1.0 %; P 1.5 %; 2.0 %; E 3.0 % benzoic acid. Effect of benzoic acid concentration on the distribution of N1 : N4-diphenyl-3-nitro- sulphanilamide at 89.3" C . in each phase, In the absence of experimental determination of the solubility of dye in water, the isotherms in fig.3 for 100" and 120" C have been extrapolated to reach the experimentally determined fibre saturation value. The saturation value at 89.3" includes experimental values for both fibre and bath.206 ABSORPTION OF NON-IONIC DYES Similarly, the distributions of these dyes between fibre and water in systems containing various amounts of benzoic acid are given in fig. 4-6. In each case, as the concentration of benzoic acid increases, K decreases. Also, the first additions of benzoic acid decrease the solubilities of the dyes in the fibre. The dashed lines represent the change in solu- bility of the dyes in the fibre with change in benzoic acid concentration. Although ~~ ~ i-i FIG. 7.-0 1.4-dihydroxyanthraquinone ; 0 1-amino-4-hydroxyanthraquinone. Binary mixtures-distribution of dye between fibre and water at 89.3" C with 2 % benzoic acid.FIG, 8.-0 1 : 4-dihydroxy- anthraquinone ; 17 1 -amino-4-hydroxyanthra- quinone. Binary mixtures-distribution of dye between fibre and water at 89.3" C . FIG. 9.-0 N1 : N4-diphenyl-3-nitrosulphanilamide ; 0 1-amino-4-hydroxyanthraquinone. Binary mixtures-distribution of dye between fibre and water at 89.3" C with 2 % benzoic acid. FIG. 10.-0 N1: N4-diphenyl-3- nitrosulphanilamide ; 0 1-amino-4-hydroxyanthraquinone. Binary mixtures-distribution of dye between fibre and water at 89.3" C.M. J . SCHULER AND W. R . REMINGTON 207 some of the benzoic acid must have been absorbed by the fibre, its concentration is given in per cent based on the water phase.The error so introduced is small since the fibre to bath ratio was large and the partition of benzoic acid does not greatly favour the fibre. In the absence of dye, K = 2-4 at 100" C.9 Data concerning mixtures of the red dye with an orange and a yellow dye in the presence and absence of benzoic acid are presented in fig. 7-10. The points represent the coinplete spectrum of mixtures presented in tables 2 and 3. Table 2 shows that as the C' of one of the dyes increases, the solubility of the other tends to decrease. Table 3, for a different mixture, shows that the saturation level of one dye is very slightly affected TABLE 2.--DISTRIBUTION OF DYES IN MIXTURES AT DIFFERENT CONCENTRATION LEVELS (89.3" C ) A = 1 : 4-dihydroxyanthraquinone (orange) B = 1-amiiio-4-hydroxyanthraqui1lone (red) 2 % benzoic acid Cf c b A B A B 12.2 14.8 15.4 18.1:': 21.5" 21.4" 22.5" 22.0" 22.2" 8.5 8.4 5.1 24.4" 23.5" 23.8" 20.1" 17.9 14.3 13-8 7.1 5-8 9.6 9.6 5.3 0.0151 00183 00176 0,0235" 0.0261" 0.0261 * 0.0266" 0-0253* 0.0250" 0*0102 0.0 107 0.0063 No benzoic acid ~~ Cf A B a 4.9 23.0 25.7" 26.0" 28.7" 29.7" 29.8* 26-6 23.4 9.5 6.8 5.1 32.4" 28.3" 25.8:': 24.5 16.1 14.2 5-3 6.0 15.3 8.1 8.4 4.8 0.00 1 3 0.0062 0.0073" 0.007 1 * 0.0087:': 0.0078" 0.0076" 0.0082 0.007 1 0.0027 0.0020 0.001 3 0*0627* 0.0618" 0.0610" 0.050" 0.0427 0.0345 0.0334 0.0159 0.0138 0.0234 0.0237 0.01 23 c b B 0.020" 0.01 72* 0.01 59" 0,0152 0.009 1 0.0083 0.0025 0,0035 0.0 107 0.0046 0.0053 0.0250 * saturated.by the introduction of the other. In all cases the data appear to be best represented by straight lines and they have approximately the same slopes as those obtained for each dye distributed individually.Since the fibre can absorb the individual components of binary mixtures so nearly independently, especially critical demands are made upon the purity of the dyes used. In the work reported, as much as 800 times the amount of dye required to saturate the system was present in one case, but no increase in either Cf or cb was noted. With this extraordinarily large excess of dye, as little as 0.1 to 0-2 % of a minor dye component would have been sufficient to saturate the system therewith. As a further check on the composition of the dye in the fibre the chlorobenzene extracts were analyzed chromato- graphically.No extraneous bands were detected.208 ABSORPTION OF NON-IONIC DYES TABLE 3 .-DISTRIBUTION OF DYES IN MIXTURES AT DIFFERENT CONCENTRATION LEVELS (89.3" C) A = N1: N4-diphenyl-3-nitrosulphanilarnide (yellow) B = 1 -aniino-4-hydroxyanthraquinone (red) 2 % benzoic acid A 30.7" 30.6* 14.0 13.2 5.0 4-8 14.2 14.6 12.0 Cf -- B 23.2" 23.5" 23.7" 23.9" 24.3" 24.0" 15.7 14.4 10-4 c b A 0.0357" 0.0346" 0.0176 0.01 63 0.0064 0.0065 0.01 79 0.01 80 0.0138 B 0-0644* 0.0625" 0.0654" 0.062 1 * 0.0653" 0.0623" 0.0406 0-0380 0.0264 No beiizoic acid cb - Cf A B A B 30.5* 27.1 0.0135" 0.0189 16.1 3 l.O* 0.0072 0.0208 * 15.1 30.9" 0.0066 0~0200" 5.0 3 1.4* 0.0022 0*0200* 14.6 14.2 0.0073 0.0090 * saturated. DISCUSSION ISOTHERMS.-AII of the data presented indicate that at equilibrium the distribu- tion of non-ionic dyes between polyethylene terephthalate fibre and water obeys the equation at all concentrations including saturation.EFFECT OF PARTICLE sIzE.---It has been reported that the particle size distribu- tion of dispersed dyes is a very important parameter in the dyeing of acetate.10 In this work we have been particularly careful to work with solutions, so that all data up to but not including saturation were obtained with no solid dye in the bath. However, several points at saturation were checked with dye ranging in particle size from large crystals to less than 1 micron. At equilibrium, variation of particle size had no effect whatsoever. EFFECT OF BENZOIC AcID.-The widespread use of benzoic acid to increase the rate of dyeing of polyethylene terephthalate made it important to determine its effect on the equilibrium system.The decrease in the solubility of the dyes in fibre containing benzoic acid is only partially accounted for by making a correc- tion for the weight of the benzoic acid present. For the dyes studied this cor- rection would amount to a decrease of about 1 mglg in the solubility. Since the effect is greater than this (2 to 6 mg/g), the slight increase in the activity of the dye in the fibre containing benzoic acid is real. The decrease in solubility is not without exception : the solubility of N1: N4-diphenyl-3-nitrosulphanilamide in the fibre first decreases, and then increases as the concentration of benzoic acid is increased. No explanation is advanced for these phenomena.BINARY MmTuREs.--The mixtures studied, tables 2 and 3, exhi bit non-additivity and additivity of solubilities respectively. The dyes in th.e non-additive mixture are very similar, differing only in the substitution of an amino for an hydroxy K = cf/cb7M. J . SCHULER AND W. R. REMINGTON 209 group. The solubility of each dye in the fibre and in the bath, in the presence of a large amount of the other, is decreased by about 20 %. It is evident that the activity of each dye is increased in the presence of the other. Further work will be required to ascertain the minimum structural differences required to permit additive solubilities. The dyes in the additive mixture have very different structures, and their solu- bilities are additive even in the pres,eixe of benzoic acid, At 89.3" C, the fibre has dissolved 3 % N1: N4-diphenyl-3-nitrosulphanilamide, 2.4 % 1 -amino-4- hydroxyanthraquinone and probably about 5 % benzoic acid, a total of 10 %, and there is no reason to believe that this is an upper limit.Clearly, polyethylene terephthalate is an excellent solvent. CoNcLusI0Ns.-The independence of the solubility of dyes and other organic compounds in polyethylene terephthalate shows clearly that in the sorption of non-ionic dyes by this fibre there is no requirement that the dye molecules be associated with a limited number of sites. Furthermore, the linearity of the iso- therms, under all of the conditions studied, strongly suggests that the dye is similarly dispersed in both phases, almost certainly as single molecules.Ac- cordingly, we conclude that the dyeing mechanism is best described as solution in the fibre, presumably in the non-crystalline regions only. The heat of dyeing, calculated from the data in fig. 3, is - 14.7 kcal/mole. This large value indicates that the solution is not ideal, but rather that there is an interaction between the dyes and the fibre, possibly hydrogen-bonding. The authors wish to acknowledge the particularly helpful assistance of Dr. B. F. Faris, J. D. Lehmicke, G. Pamm and H. E. Schroeder and Messrs. E. W. Bassett, H. F. Hume and A. J. Johnson. 1 Carmichael, Text. Age, 1951, 15, 32. Gamble and Parks, Amer. Dyestuf Reptr., 1952, 41, 223. Kramrisch, Dyer, 1952, 108, 709. Lyle, Iannarone and Thomas. Amer. Dyestuf Reptr., 1951, 40, 585. Meunier, Amer. Dyestuf Report, 1951, 40, 51. Roy, Amer. Dyestuf Reptr., 1952, 41, 35. Turnbull, Amer. Dyestuf Reptr., 1952, 41, 75. Tech. Bull. (DuPont), 1951, 4, 198. 2 Waters, J. SOC. Dyers Col., 1950, 66, 609. 3 The Dyeing of Terylene Polyester Fibre (Imperial Chemical Industries Ltd., Dye- Tech. Bull. (DuPont), 1952, 2, 69. Tech. Bull. stuffs Division, Great Britain). (DuPont), 1952, 2,99. 4 Remington, Amer. Dyestuf Report, 1952,41, 859. 5 Reitli and Andres, Amer. DyestufReport, 1953, 42, 35. 6 Vickerstaff, The Physical Chemistry of Dyeing (Interscience Publishers Inc., New 7 Organic Syntheses (Collective Volume 1) (John Wiley and Sons Inc., New York, 8 National Bureau of Standards (Letter Circular LC-857, 1947). 9 Hayward, this laboratory ; personal communication. 10 Vickerstaff and Waters, J. SOC. Dyers Col., 1942, 58, 116. York, 1950), 1st ed., p. 259. 1932), 1st ed., p. 464.

ISSN:0366-9033    

DOI:10.1039/DF9541600201

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

THE DYEING OF POEYACRYLONITRIEE FIBRES WITH ANIONIC DYES BY R. H. BLAKER, S. M. KATZ, J. F. LAUCIUS, W. R. REMINGTON AND H. E. SCHROEDER Contribution No. 145 from Jackson Laboratory, E. I. duPont de Nemours and Company, Wilmington, Delaware, U.S.A. Received 15th June, 1953 The mechanism of dyeing polyacrylonitrile fibres is discussed for two cases in which the fibre, through its affinity for H+ and Cu+ respectively, acquires cationic centres capable of permitting absorption of dye anions. In the first, affinity for H+ is created by basic sites introduced through copolymerization and the dyeing reactions are best described by a mechanism involving sites differing in basicity. In the other, every cyan0 group in polyacrylonitrile appears inherently capable of absorbing cuprous copper through formation of a complex of the type (RCN)Cu+, which acts as a site for fixation of dye anions.The new acrylic fibres made wholly from polyacrylonitrile are difficult to dye by conventional procedures. Until recently they were considered undyeable with anionic (acid or direct) dyes 1 and in early work showed only limited affinity for dispersed, basic and vat dyes. Two new methods for producing dyeing sites in polyacrylonitrile fibres have made them easily dyeable with typical anionic dyes. The fist involves the incorporation of a limited number of basic groups into- the polymer structure through copolymerization of acrylonitrile with basic monomers, such as vinylpyridine.2 The other has resulted from the discovery that cuprous copper is readily absorbed by acrylonitrile copolymers which then acquire almost unlimited affiiiity for many anionic dyes.3 This discovery has been extended to homopolymers and has led to practical dyeing procedures which are widely used.4 This paper covers initial phases of a study of the absorption of anionic dyes by a copolymer of acrylonitrile and vinylpyridine in the presence of hydrogen ions and by polyacrylonitrile in the presence of cuprous ions.The two processes have several features in common. In each case the polymer shows substantially no affinity for anions until the appropriate cation is added. Thus the basified copolymer will absorb anionic dyes only from solutions having a relatively low pH and the homopolymer absorbs dye only in the presence of Cu+.* Adsorption of dye may therefore be represented by a simplified general expression : We have assumed that each polymer contains specific chemical features, i.e.sites, which possess affinity for the cations (Hf or Cu+) and cause their absorption together with associated anions. The data were then treated using concepts similar to those developed by Gilbert and Rideal for the absorption of acids by ~ 0 0 1 . 5 For the basic copolymer, reasonable agreement with the theory of equivalent sites was obtained under selected conditions, but not all of the data can be inter- preted satisfactorily on this basis. Accordingly, we have been forced to postulate the existence of sites differing in activity, i.e., basicity. Satisfactory explanation of the experimental results has been achieved on the basis of two kinds of sites.* Copolymer will also absorb dye anions in the presence of Cu+. This case is not considered in the present study. dye- + cation+ + fibre + dyed fibre. (1) 210BLAKEII, KATZ, LAUCIUS, REMINGTON AND SCHROEDER 21 1 The more affinitive possess an equilibrium constant 100 times as great as the others and represent 6 % of the total. The total number of sites approximates to the pyridine content of the copolymer. With the homopolymer, the situation appears relatively simple. The basic reaction appears to be one of complex formation between cuprous ion and nitrile groups of the polymer with every nitrile group a potential site for Cu+. A plot of copper in the fibre * (CLIJ)~ against copper in the bath (Cu,) derived on the assumption that copper is absorbed through a reaction of the type +Cu22+ + N ES C-polymer + Cu+, N = C polymer (2) is almost a straight line as predicted.A very high concentration of sites of only one type is indicated. Once either of the above fibres has accepted its cation and the accompanying anion, dyeing can occur by a simple anion exchange reaction : fibre. cation+. anion- + dye- + fibre . cation'. dye- + anion-. (3) This reaction is the same for both polymers, with all cationic centres equivalent in either case. The total amount of dye absorbable (by extrapolation) is equal to the number of cations present in the fibre. T. STUDIES OF THE ACRYLONITRILE -l- VINYL PYRIDINE COPOLYMER EXPERIMENTAL MA'I.miALs.-The basified fibre studied in this investigation was prepared from a copolymer containing approximately 94 % acrylonitrile and 6 % 2-vinylpyridine.A single lot of 4.0 denier bright rawstock was used in all the experiments. The fibre was scoured at the boiI with 0.5 % soap solution, rinsed, dried and thoroughly blended. The dye, 1 -phenyl-3-methyl-4-(4-sulphophenylazo)-pyrazolone-5, was selected because it is easily prepared and purified, has low neutral dyeing affinity, is not affected by pH, and had adequate stability in boiling solutions. The dye as prepared was shown to be pure by chromatographic analysis and from the absorption spectra of successive fractions recrystallized from and extracted with a variety of solvents. It was recrystallized several times from a mixture of 2-ethoxyethanol and water before use.DYEING ExPERnmNTs.-Each series of dyeings was made at constant pH with the aid of a buffer system of hydrochloric acid and sodium chloride. Experiments were made at three pH values, 1.0, 1.5 and 2.3 with a constant ionic strength of 0.1. The fibre was equilibrated with the dye solution in cylindrical glass tubes partially immersed in a constant temperature bath. Each tube was fitted with a thermometer and two ground- glass joints for insertion of electrodes for pH measurement. The solution temperature was 99.9 rt 0.1" C. The tubes containing 135 to 150 ml of buffered dye solution and 50 to 500 mg of fibre were closed during the dyeing with ground-glass stoppers held in place with springs. After the solution and fibre were equilibrated, the pH of the solution was measured 0.2" C below the dyeing temperature.The fibre was then removed from the solution, rinsed, and stored in a desiccator over a saturated solution of sodium dichromate (relative humidity approximately 50 %). Both the fibre and the solution were then analyzed for dye and chloride. The equilibrium absorption of the dye at the 3 pH's studied is presented in fig. 1. ANALYTICAL.-Dye concentrations were determined with the aid of a spectrophoto- meter. The concentration of dye on the fibre was determined by dissolving the dyed fibre in butyrolactone and measuring the optical density of this solution, The concentra- tion of the dye in the aqueous solution was determined by spectrophotometry of the solution (Amax = 3900& molar absorbancy index = 2.78 x 104 1. mole-1 cm-1).Chloride analyses were made by a potentiometric titration with silver nitrate. For the fibre analysis a sample was burned with oxygen in a bomb. * Throughout this paper subscripts f and s indicate fibre and solution respectively.212 DYEING OF POLYACRYLONITRILE FIBRES ACCURACY OF EXPERIMENTAL RESULTS.-Three dyeing experiments were made for each set of conditions and all the experimental data are shown on the accompanying plots. Many of these repetitive groups of three were duplicated for longer time intervals to determine whether equilibrium had been reached. Sufficient dye solution was pre- pared in one lot for all repetitions so that the initial conditions could be considered to be the same in all three (or six) dye vessels. In all cases the chloride ions in the solution (for the same period of dyeing) agreed within 10 % among the repetitive samples, and in most cases within 5 %, but wider variations were observed in chloride determinations from one set of runs to another at the same pH, although the solutions were always made up from the same stock buffer at each pH.5 10 15 20 25 FIG. 1 .-Experimental data for absorption of dye by copolymer. Duplicate experiments were usually run for both 96 or 168 h. A somewhat lower dye concentration in both solution and fibre was observed for the longer dyeing time. This loss of dye may be attributable to thermal decomposition. When the results were corrected for this loss of dye, the results for 96 and 168 h were in excellent agreement and indicated that equilibrium had been reached.Two attempts to confirm the attain- ment of equilibrium by desorption from material dyed to saturation indicated that more colour remained on the fibre than would have been predicted from absorption experiments. Presumably the excess of dye in the fibre after desorption must be attributed to a hys- TABLE ~.-DESORPTION EXPERIMENTS desorption relative amount teresis effect, unless the fibre suffered a per- time, ofdyein manent change through being dyed to h fibre * saturation. This point was not investigated PH 1.0 96 1.39 further. 240 Although the pH of the dyebath is an im- 2.3 96 2.43 portant factor in the postulated dyeingmechan- 240 2-4 1 ism, pH at 100" C is not well defined. Our measurements were made with a Beckman model G pH meter using high-temperature calomel (8970-90) and glass (8990-90) elec- trodes.The reference was a standard buffer solution at the same temperature as the dyebath. The pH of the standard buffer is not known at this temperature but was estimated by extrapolating from lower temperatures. Consequently, all pH deter- minations on the solutions are uncertain by an amount equal to the uncertainty in this extrapolation. This uncertainty is a constant additive term to all the pH values in this section and accordingly affects the absolute magnitudes of the dyeing equilibrium constants. The random errors involved in pH measurement amounted to about 0.004 pH units. 1.35 *This factor represents the observed amount of dye divided by the amount of dye which would have been predicted from absorption experiments.BLAKER, KATZ, LAUCIUS, REMINGTON AND SCHROEDER 213 DISCUSSION We propose that anionic dyes are absorbed by the copolymer as indicated in the following equation : The equilibrium constant of this reaction is where Of = concentration of dye in fibre (moles/kg), Hs = hydrogen ion activity in solution, Ds = activity of dye anion in solution, Ds- + Hsf + site + (site Hf D-) = Df(dyed fibre).(4) Kd = Df/HsDsC, (5) C = concentration of unoccupied sites in the fibre (mmoles/kg). Since the buffer anion is absorbed also and competes with the dye for protonated sites, the magnitude of C is given by C = S - D f - AS, (6) FIG. 2.-Determination of A f . where S = total number of basic sites in the fibre (mmoleslkg), Af = concentration of buffer anion in the fibre (mmoles/kg) and, just as for the dye, the absorption of buffer anion is given by Af]C = Aj*/(S - Df - A ) = KaHsAs, where A, = buffer anion activity in solution, Ka = equilibrium constant for the absorption of buffer anion. By substituting for C, and rearranging, eqn.(5) becomes (7) Df/HsDs == KdS - G(Df Af). (8) According to eqn. (8), then, a plot of Df/HsDs against ( O f + Af) should give a straight line with slope - Kd and intercept S, on the abscissa, and KdS on the ordinate. Since the experimental determinations of Af gave a large variation in this quantity, eqn. (7) was rearranged so that average values of Af could be determined : where a -- Sb and b = KaHsAs/(l + KaHsAs). The values of a and b were determined from plots of measured values of Af against Of for each pH, as shown in fig.2. The straight lines of this plot are least Af = a - bDf, (9)214 DYEING OF POLYACRYLONITRILE FIBRES square curves, from which the values given in table 2 are taken. The constants, a and b, were then used to calculate smoothed values of Af. A plot according to eqn. (S), using the calculated values for Af, together with the experimental values of Df, Ds and Hs, is shown in fig. 3. It can be seen that the data for pH 1.036 agree very well with the proposed equation, since a straight line can be drawn through the experimental points. There is less agreement at pH 1.513 and no agreement at all at pH 2,305. Clearly, if dyeing does proceed according to eqn. (3), different types of sites, having different equilibrium constants, must be involved.Thus, if there were a relatively small number of highly affinitive basic sites, TABLE 2s-VALUES OF a ANDb essentially all of them might be dyed in 1.036 0.1 178 0.2079 apparently straight line would result. At 1.513 0.0496 0.0823 the higher pH of 2.305, with a hydrogen 2.305 0.0262 0.0674 ion activity one-twentieth as great, dis- crimination between sites of different basicity would be possible and the observed curve could result. Quite possibly, then, the basic sites in the fibre exhibit a range of basicity but we have found the assumption of only two types of sites adequate. On the assumption that two types of site, S1 and S2, exist in the fibre, differing from each other in their affinities for protons, a new equation for Of can be written : A similar equation can be written for Af, and by combining the two, the following expression for Df can be obtained: PH a b all the experiments at pH 1.036, and the of = Dfl + Dh = Kd,-f&Ds(sI - Dfl - Afl) -k Kd2HsDs(S2 - Df2Af2)- (10) 0.1 0.2 0.3 0.4 0.5 FIG.3.-Absorption of dye by copolymer. Afcan be expressed by a similar equation. It is then possible to plot Df/HsDs as a function of Df -k &in terms of the parameters S1, 5'2, Kdl, Kd2, K,, and Ka2. The values of these parameters are given in table 3 and the plot is shown as the solid line in fig. 3. As a first approximation the values for one class of sites S1, Kdl and K,, were calculated from the experimental data at pH 1'036, since these data, as shown by fig. 3, agree with a single site mechanism.These values were then used in eqn. (8) to calculate Dfl. Dh was estimated as the difference between Of and Dfl. The values of the parameters given in table 3 were estimated as follows.BLAKER, KATZ, LAUCIUS, REMINGTON A N D SCHROEDER 21 5 Ah, S2, Kd2 and Kaz were then obtained from the following equations employing the data at pH 2.305 : Afi DfiKa,AS/Kd,Ds, (12) (1 3) Ka2 = KdZKa1/Kdl. (14) Eqn. (14) constitutes the reasonable assumption that the differences among sites are solely in their affinity for protons. In other words, all cationic centres in the polymer are regarded as having equivalent affinity for any given anion. These values of Kd2, Ka2, S2 and Af2 were then used to recalculate the values of Kd, Ka, S1 and Affrom the data at pH 1.036.This process was then repeated until no further changes in Kd,, Kd2, S1 and S2 were observed. It has been shown that it is necessary to postulate the presence in the fibre of dyeing sites of different affinities in order to account for experimental data. It is not unreasonable to assume that the basicity of the pyridine centres in the copolymer can be affected by interactions with neighbouring groups in the individual molecules of polyacrylonitrile or interactions between adjacent molecules of the polymer. Thus the crystallinity of the fibre may be involved as well as the dis- tribution of pyridine centres along the polymer chain, the number of pyridine end- groups, and the effect of sulphonic acid end-groups on the basicity of neighbouring pyridine centres.These sulphonic acid sulphate-catalyst. determined by the analysis of the experi- si 0.558 equiv./kg mental data (0.589 equiv./kg) agrees with s 2 0.03 1 equiv./kg 7.94 x 103 1.2/equiv.2 7.66 x 1 0 5 1.2/equiv.2 the pyridine content of the fibre (0.570 Kdl 2.85 x 101 1.2/equiv.2 equiv./kg). This agreement supports the Kdz 2.75 x l o 3 1.2/equiv.2. hypothesis that the anionic dye is absorbed on the pyridine centres in the copolymer. If the sulphonic end-groups are ionized, a dyeing mechanism based only on two types of basic sites would not be valid. However, the data have not been analyzed in terms of a zwitter-ionic fibre because the resulting equations would be much more complicated and the simpler mechanism adequately describes the experimental results. Df2 4- A, = s2 - Af2/HSDSK&, end-groups have their origin in the per- TABLE 3*-EST1MATED VALUES OF PARA- METERS FOR EQN.(11) estimated value The total number of sites, S1 + 5'2, as parameter Kal KQz TI. STUDIES OF ACRYLONITRILE HOMOPOLYMER EXPERIMENTAL MATERIALS.-A single lot of 3 denier polyacrylonitrile staple fabric containing 0.4 % titanium dioxide as a delusterant was used in all experiments. The fabric, a 2 x 2 twill weave of singles yarn, was scoured at 70" C with 0.3 % lauryl sulphate, rinsed and dried in a pin tenter at 130" C. The anionic dye, the pure sodium salt of l-amino-4-anilino-anthraquinone-2-sulphonic acid, was prepared by four recrystallizations of the commercial dye from distilled water. A paper chromatogram indicated that the recrystallized material consisted of a single component.ANALYTICAL PRoCEDuRES.-Copper in the fibre was determined electrolytically sub- sequent to solution of the fibre in hot nitric and sulphuric acids. Copper in solution was determined colorimetrically using zinc dibenzyl-dithiocarbamate. The analysis of solutions for dye was made by measuring the transmission of a sample with a Cenco photelometer and comparing the transmission measurements with a standard curve of transmission against concentration for the purified dye. Analysis of dye on dyed fibre was made as follows. The dye was stripped from the fabric by boiling with ethylene glycol for 20 min. The analysis of dye in solution in ethylene glycol was made by optical means as above. Preliminary experiments indicated that with this particular216 DYEING OF POLYACRYLONITRILE FIBRES dye and fibre combination, no dye was lost by this procedure for recovering the dye fsom the fibre.VALENCE OF THE CoPPrx-The fibre does not absorb copper readily from solutions of cupric salts unless reducing agents are present. This suggests that copper must be in the cuprous valence state to be absorbed by polyacrylonitrile. A large amount of indirect evidence supports this conclusion ; for example, if glutaronitrile was shaken with an aqueous solution of copper sulphate and a blue anionic dye, 1-amino-4-anilino- anthraquinone-2-sodium sulphonate, only the water layer was coloured. If then a reducing agent, such as sodium bisulphite, was added and the solution shaken, the dye immediately transferred to the glutaronitrile layer.The relative amounts of copper and chloride found in the fibre after the following experiments also indicated that the copper entered the fibre as the cuprous ion. Two samples of polyacrylonitrile fibre were boiled in aqueous solutions to which were added different amounts of cupric chloride, cuprous chloride, and hydrochloric acid. The fibre was then analyzed for copper and chloride. expt. TABLE 4.-cHLORIDE/COPPER RATIO analysis, % ~- copper chloride atomic ratio, Cl/CU 1 4 .O 2.06 0.93 2 5.7 2.98 0.94 These results suggest that a single chloride ion accompanied each copper ion which entered the fibre. NATURE OF ATTACHMENT OF THE COPPER.-The fact that copper is readily absorbed by polyacrylonitrile only when it is in the cuprous valence state suggests that the nitrile groups of the polymer are probably involved in the formation of complexes analogous to those described by Morgan for simple nitriles.6 These complexes are probably of the 7~ type since those metals, Cu+, Ag+, and Pt+, which are unique in their ability to accept 7~ electrons are also unique in exhibiting affinity for polyacrylonitrile and in pro- moting the dyeability of these fibres with anionic dyes.The strength of these co-ordinate bonds between the cuprous ion and the nitrile groups would be expected to be small. The apparently slight temperature dependence of the equilibrium copper absorption, described below, supports the belief. Further confirma- tion was obtained from the observation that the cyanide ion, which forms strong complexes with cuprous ion, completely inhibited the absorption of copper.The weaker-complexing citrate ion had less effect on the absorption of copper by the fibre. METHODS FOR USE OF CoPPER.-The cuprous copper is best produced in solution from cupric salts and reducing agents. Some of the first reducing agents used were ferrous sulphate, sodium hydrosulphite, and sodium formaldehyde sulphoxylate. Extreme care had to be used with these reducing agents since, if the concentration was too high or if the solution was heated too rapidly, metallic copper was formed. To avoid this difficulty it is necessary to generate the cuprous ion only as fast as it can be absorbed by polyacrylonitrile or to form a weak complex of cuprous ion in solution. This complex must be stable enough to prevent the disproportionation but weak enough for the cuprous ion to be available for absorption by the polyacrylonitrile.Hydroxylamine sulphate has been found to be particularly effective in reducing the cupric ion and at the same time maintaining the free cuprous ion at a sufficiently low con- centration to avoid the disproportionation. This stabilization is apparently due to the formation of a weak complex between hydroxylamine and the cuprous ion. The complex ion probably involves hydroxylamine itself, rather than its decomposition products, since the cuprous ion is not stabilized unless an excess of hydroxylamine is present in solution. Efforts to identify this complex from spectral and polarographic data have not been entirely successful.An alternative method of reducing the cupric ion and still avoiding the danger of disproportionation of the cuprous ion is to employ the common reducing agents, such as sodium or zinc sulphoxylate, under controlled redox potential conditions.7 EFFECT OF TEMPERATURE ON ABSORPTION OF COPPER.-Preliminary experiments indicated that polyacrylonitrile fibres absorb copper rapidly from a boiling solution containing copper sulphate and hydroxylamhe sulphate. The effect of temperature on the rate of copper absorption is shown in fig. 4. Also shown on the figure is the rate of copper absorption from a solution containing only cupric sulphate.BLAKER, KATZ, LAUCIUS, REMINGTON A N D SCHROEDER 21 7 The data presented in the figure indicate that the rate of absorption is strongly dependent on the temperature and is very slow below 93" C.Other experiments not shown on the figure indicated that, at 93" C, 17 h were required for the same amount of copper to be absorbed as in 1 h at 100' C. EFFECT OF pH ON COPPER AssoRPTroN.-Preliminary experiments indicated that pH of the solution has a large effect on the amount of copper which is absorbed by poly- acrylonitrile. The effect of pH on copper absorption is shown by fig. 5. These data 9 8 7 6 1 5 5 g4 2.5% Copper Sulphate J 2.5 Hydroxylomino Sul p hate (v u- u 3 2 I 0 B 2 3 4 FIG. 4.-Effect of temperature on rate of copper absorption. - r I I I I 1 0- - 0.5 - - 4Y0 Copper Sulp hote 4% Hydroxyiamine Sulphote 2.5gFibre in 100ml. 2 Hours at 100°C 0.4 - 0.3 - - - 0.2 - - 0.1 - - I I I I show that the absorption of copper was decreased rapidly as the pH of the solution was decreased and that relativeJy little copper was absorbed if the solution had a pH of less than 1.0.EQUILIBRIUM ABSORPTION OF CoPPER.-The equilibrium absorption of copper by POlY- acrylonitrile is affected by copper concentration as is shown by fig. 6. The experiments at 100" C were run for 15 h. In each case 2.5 g of fibre was dyed in a 100 ml dyebath FIG. 5.-Effect of pH on copper absorption. containing equal weights of CuSO4. 5)3[20 and (NH20H)2 . H2SO4. In addition the equilibrium absorption of copper up to a concentration of 150 mmoles/kg fibre was measured at 93" and 97" C. The results were nearly identical with those obtained at 100" C and therefore indicated a low heat of absorption.ROLE OF COPPER IN THE DYEING REACTION.-^ the actual dyeing of the polyacrylo- nitrile fibres, cuprous ion is absorbed with an accompanying anion. This may be an218 DYEING OF POLYACRYLONITRILE FIBRES anion from the solution or a dye anion. Fig. 7 shows the changes which take place during dyeing in a dyebath which originally contained cupric sulphate, hydroxylamine sulphate, pure sodium salt of the anionic dye, and a sample of polyacrylonitrile fibre. Cuprous ions are first absorbed by the fibre, presumably through formation of a complex with nitrile groups of the polymer. To maintain electrostatic neutrality, the cuprous ions FIG. 6.-Experimental data for equilibrium absorption of copper. are accompanied by sulphate ions and dye anions. Sulphate ions are absorbed more rapidly in the initial stages of the dyeing.Eventually the dye anion, because of its intrinsically greater affinity for the copper containing fibre begins to displace the sulphate ion from the fibre and the concentration of sulphate in the bath increases. In the case where polyacrylonitrile is treated with Cu+ and sulphate ions, dye ions can later be ex- changed for the sulphate ions. A 5 g sample of fibre was boiled for 2 h in 100 ml of water which contained 0.56 g cuprous oxide and 10 m.equiv. of sulphuric acid. The coppered fibre was then removed, FIG. 7.-Interchange of copper, dye and sulphate with fibre during dyeing. rinsed thoroughly, and added to 100 ml of water containing 100 mg of pure monovalent anionic dye. The solution was heated at the boil until all of the dye was absorbed by the fibre, The solution was then analyzed for copper and sulphate ion.The analytical data iiidicate that 2.2 X 10-4mole of dye was absorbed by the fibre and that 5.2 x 10-4 mole of copper and 7.1 X 19-4 mole of sulphate ion appeared inBLAKER, KATZ, LAUCIUS, REMINGTON AND SCHRODER 219 the bath. These data are consistent with the hypothesis that a univalent dye ion replaces a univalent bisulphate ion in the fibre. ments were made with 2-5 g samples of polyacrylonitrile fibre which had been boiled for 111 in 100 ml of aqueous solution containing 0.063 g CuSO4. 5H20 and 0.063 g (NH2OH)2H2SO4. This fibre was rinsed thoroughly with hot water and was then used for the dyeing experiments. The dyeings were made in the glass tubes described for the copolymer.The closed tubes were placed in an oil bath maintained at 100” C 4 0.1”C. The dyeings were continued for 178 h since preliminary experiments indicated that this was sufficient time for equilibrium to be reached. DYEING EXPERIMENTS WITH COPPER-TREATED POLYACRYLONITRILE.-Dy&g experi- TABLE 5.-EQUILIBRIUM ABSORPTION OF DYE BY COPPER TREATED FIBRE dye in bath (equiv./l. x 105) 0.5 4.6 18.0 5-8 67.0 175.0 5-6 11.0 26 -0 11.0 27.0 108.0 dye on fibre (equiv./l. x 103) 10 23 30 5 23 30 9 15 24 18 27 36 sulphate in bath (mole/I.) none added ” 0.07” 0.07 0.07 0.10 0.10 0.10 0.24 0.24 0.24 A series of dyeings were made with the copper treated fabric and solutions of dye, sodium sulphate, and sufficient sulphuric acid to give an initial pH of 3.0.After the dyeings were completed the dyebath and the fibre were analyzed for dye and copper. The samples had an average copper content of 4.2 x 10-2 molelkg before equilibration. The dye analyses are tabulated in table 5. DISCUSSION THE REACTION OF COPPER WITH POLYACRYLONITRILE.-~t iS Clear from the evidence presented above that cuprous ions are absorbed by polyacrylonitrile because of the presence in the polymer of nitrile groups. The large number of groups, one for each monomer unit in the polymer, which could combine with the cuprous ion might be expected to lead to solution of the copper in the polymer. The experimental data indicate that a simple solution mechanism is not obeyed since, as shown by fig. 6, a linear plot is not obtained when Cufis plotted against Cu,.This, together with the other experiments which have been described, suggests a chemical reaction wherein Cu+ and CN groups interact to form a moder- ately strong co-ordination complex. The interpretation of the data is greatly complicated by the fact that most of the cuprous copper in solution exists in the form of a cuprous ion + hydroxyl- amine complex. The exact composition of this complex is not known but there is some indication (from polarography) that it may contain two atoms of copper.8 On this basis, the reaction for copper absorption might be written : (1 5 ) 2 sites + (Cu2. hydroxylamine)x + 2HS04- + 2 (CuHS04 . . . site) + x hydroxylamine. If variations in concentration of the bisulphate ion and hydroxylamine are neglected, then the reaction may be described by the simplified expression, (Cu22+)s s 2CUff.(1 6) Then if the cuprous ion + hydroxylamine complex contains two cuprous ions, a plot of (CUJ)~ against Cus should give a straight line. Fig. 8 shows that220 DYEING OF POLYACRYLONITRILE FIBRES this method of plotting the data does approach a straight line as does a similar plot or (Cuf)3 against Cu,. Better agreement with a straight line, however, is given by a plot of (Cuf)2*5 against Cus. ]In the absence of detailed knowledge about the structure of the cuprous ion+ hydroxylamine complex but with the realization that its composition may be influenced by relative concentration of hydroxylamine in solution and the pH of the solution, it is plausible that the absorption of copper over a wide range of concentrations can be interpreted in terms of a single complex for Cus involving an average ncmber of cuprous ions.If this mechanism is accepted it follows that the absorption of copper is not dependent on the existence of a limited number of specific configurations, or sites, and in all probability that each of the nitrile groups of the homopolymer is a potential site for absorption. 0.6 0.5 0.4 0.3 0.2 0.1 FIG. 8.-Equilibrium absorption of copper. THE ION EXCHANGE REACTION.-The experiments described above suggest that once cuprous ions are absorbed by polyacrylonitrile, they will function as cationic centres which are capable of exchanging a simple a dye anion from a dyebath. For this exchange, the expression may be written : K = AsDjIDsAf, where A, = activity of simple anion in bath (moles/l.), Ds = activity of dye in bath (moles/l.), neutralizing anion for following equi I i brium Df = concentration of dye in fibre (mmoles/kg), AJ = concentration of simple anion in fibre (mmoleslkg). If we represent the total (assumed constant) concentration of cationic sites in the fibre by S, it follows that (1 8) Thus, if the quantity (hereafter referred to as A) on the left side of this equation is plotted against Df a straight line should result.However, when the data from the section on dyeing copper-treated poly- acrylonitrile are plotted (fig. 9) according to eqn. (18), they define a separate straight line for each value of As, if activity coefficients are set equal to unity. Allowance for the effect of sodium sulphate concentration on activities may be made by writing DfASf Ds = KS - KDf. R[y = Ks - KDJ. (19)2 0.07 Molesll. NatSo+ 3. 0.10 Molesll. No2504 4.0.24 MolesII. NagS04 FIG. 9.-Absorption of dye by homopol!7mer. 1 I 1 . 1 I 1 I I I 0 0.24 molesll. Nap304 7=600 4 0.10 moles/l.No2S04 1-240 n 0.07 moleslL Na2S04 7.60 6- - number of dyeing sites is approximately the same for all samples of fibre and is independent of the amount of salt. The same is true for fig. 10. The number of dyeing sites, approximately 4 X 10-2 equiv./kg, as determined from fig, 9 is in excellent agreement with the analyzed amount of copper on the fibre at the beginning of the dyeing experiments (4.2 x 10-2 mole/kg). This is added support222 DYEING OF POLYPEPTlDES for the hypothesis that at equilibrium each cuprous ion in the homopolymer is a potential dyeing site for a monovalent dye anion. A better understanding of the reactions involved will undoubtedly result as further studies show more precisely the effect of pH and anion concentration and the nature of the cuprous copper complex in the aqueous dyebath. The authors wish to acknowledge the particularly helpful assistance of DT. J . H. Trepagnier, A. W. Bauer, C. A. Young, J. Hyde and E. K. Gladding. 1 Thomas and Meunier, Amer. Dyest. Report, 1949, 38, 925. 2 Arnold, U.S. Pat. no. 2,491,471 (1949). 3 Feild and Fremon, Text Res. J., 1951, 26, 531. 4 BIaker and Laucius, Amer. Dyest. Report, 1952, 41, 39. 5 Gilbert and Rideal, Proc. Roy. SOC. A, 1944, 182, 335. Remington and Gladding, 6 Morgan, J. Chem. SOC., 1923, 123,2901. 7 Blaker, Amer. Dyest. Report, 1953, 42, 76. 8 Marcali, private communication. J . Amer. Chem. SOC., 1950, '72, 2553.

ISSN:0366-9033    

DOI:10.1039/DF9541600210

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

222 DYEING OF POLYPEPTlDES THE DYEING QF SYNTHETIC POLYPEPTIDES BY C. H. BAMFORD, J. BOULTON, W. E. HANBY AND J. S. WARD Courtaulds Ltd., Droylsden and Maidenhead Received 30th June, 1953 A study of the dyeing of a number of synthetic polypeptides has been made in an attempt to obtain information bearing on the dyeing of natural proteins, and the mechanism of dyeing in general. The main concIusions are that dyeing of the polymers studied may involve sites located in the backbone, the side chains and the amino end- groups. The conditions affecting the dyeing of these groups of sites are discussed. So far no evidence has been obtained which indicates any difference in the dye uptake of synthetic polypeptides in the cc and /3 configurations. The study of synthetic polypeptides has, in recent years, provided information which has been of value in furthering our understanding of the behaviour and constitution of proteins.192, 3 The advance has resulted from the use of polymers carrying side chains of simple types which can be varied at will; this has per- mitted assessment of the separate contributions of the backbone and side chains to the properties of polypeptides. It seemed likely that these compounds would be useful in a similar way in elucidating some features of the dyeing of proteins and the chemically related polyamides, and perhaps in improving our under- standing of dyeing phenomena generally.In particular, it should be possible to determine the site of adsorption of a given dye, e.g. whether the latter is attached to the polypeptide backbone or to the side chains, and to examine the contribution of the amino end-groups.Further, the synthetic polypeptides generally can exist in folded (a) and extended (p) configurations in which the dispositions of the peptide hydrogen bonds are essentially different, being intra-molecular and intermolecular respectively ; 1 9 2 s 3 therefore some idea of the importance of hydrogen bonding in the attachment of dye molecules to the polypeptide backbone should be obtainable. This paper describes a preliminary investigation of the dyeing of synthetic polypeptides, designed to supply some of the above information. The polymers used in this investigation were :c. H. BAMFORD, J . BOULTON, w. E. HANBY AND J. s. WARD 223 (i) polyglycine (I; R = H), (ii) 1 : 1 copolymer of DL-P-phenylalanine and DL-leucine (I ; X = -CH2C&€5 (iii) 1 : 2 copolymer of DL-P-methyl aspartate and or -CH2CH(CH3)2), DL-leucine (I; R = -CH2COOCH3 or --C&CH(CI-I3)2 in ratio 1 : 2), (iv) poly-L-alanine (I; R = -CH3).X-(NHCHRCO), - Y . EXPERIMENTAL The polymers were prepared from the N-carboxy-a-amino acid anhydrides by poly- merization in nitrobenzene solution at 50" C.4 To prepare the small polymers the cal- culated amounts of m-leucine dimethylamide were used as initiator ; in these cases the end-groups are therefore -NH2 and -CON(CH3)2 (I ; X = H, Y = -N(CH3)2). For the larger polymers no initiator was added, the traces of water normally present being sufficient. The end-groups of these polypeptides are therefore -NH2 and -COOK (I ; X = H, Y = OH).Isolation of the polymers was effected by pouring the reaction mixtures into low-boiling petroleum ether. Residual nitrobenzene was extracted by boiling the polymers for several hours with ether or acetone. The chain lengths of the polymers were determined by end-group analysis for -NH2 using van Slyke and con- ductimetric techniques. For the latter a solution of the polypeptide in a mixture of phenol and methanol was used.5 Since polyglycine and polyalanine are insoluble in this liquid the technique could not be applied to them. Direct estimation of terminal di- methylamide groups of the low copolymers of DL-p-phenylalanine and DL-leucine was carried out. Whenever comparison was possible the three methods gave satisfactorily similar values for the degree of polymerization. For the dyeing experiments the polymers were prepared, when possible, as films by casting from suitable solvents ; when film preparation was not possible, finely divided powders were used.The copolymers of DL-phenylalanine and m-leucine with degrees of polymerization (D.P.) of 45 and 640 were prepared in both a and /3 forms by techniques already described.3 The 1Zmer could not be obtained as the pure a form but always contained at least 50 % p. The pure fi form was, however, available. With the exception of polyglycine, all the specimens used appeared poorly crystalline when examined by X-ray diffraction. The general dyeing behaviour of the polymers was exanlined by determining the equilibrium exhaustion of a selected range of dyes under representative dyeing conditions.Commercial dyes were used without further purification except when otherwise indicated. (It was not thought necessary to determine complete isotherms at this stage.) Following this, further dyeings were carried out to elucidate particular points. Kinetic studies were not attempted, owing to the differences in the state of subdivision of the various polymers. The conditions under which the dyeing properties were examined are given in tables 1 and 2. RESULTS AND DISCUSSION PoLyGLyciNE.-PoIyglycine, the simplest possible polypeptide, represents the basis, or " backbone" of all other polypeptides, which may be regarded as derived from polyglycine by substitution at the methylene carbon atom. Poly- glycine of very high molecular weight, comparable in degree of polymerization with, e.g., wool or silk was not available when these experiments were done.The sample examined had D.P. - 100 and was a powder which appeared to have a moderate degree of crystallinity when examined by X-rays. It was in the Is- configuration. The polymer was found to dye very readily with the whole range of dyes used (table 1). The high equilibrium exhaustion of dyes generally indicates that the polypeptide backbone offers suitable absorption sites for these dyes. Further experiments showed that for the anionic dyes (table 1 ; 3, 4, 7, 8) the equilibrium dye absorption was dependent upon dyebath pH, indicating that the basic groups in the polymer were contributing to this absorption. InTABLE PERCENTAGE EQUILIBRIUM EXHAUSTION.Liquor ratio 50 : 1, temp. 95" C Duranol Red 2B 300 powder (I.C.I.) constitution 0 OH M . A "\(k) I 0 NH2 2. Dispersol F Crimson c1 dye B 300 powder (I.C.I.) GHS N02<$N==NC,-N< C2H40H 1 : 1 copoly- 1 : 1 copoly- 1 : 2 copoly- I3 1 c o ~ ~ y ~ ~ ~ rner of DL-B mer of DL-B- mer of m-8- Of DL-B-pheny- phenyl al- phenyl al- methyl as- anineand partateand poly- p acetyl- alanine and anine and initial dyebath poly- ated composition glycme poly- DLfpz$; DL-leucme ; DL-leucine; DL-leucine; I,-+ 45-mer 640-mer 609-mer mine d 1 . glycine cc ~ origi- modi- G - t P B nal fied dye 0.4 100 100 85 90 64 72 60 65 60 66 100 3. Solacet F Blue 2BS 0 NHa dye NaCl ()&SO 3Na (I.C.I.) 4. Solacet F Crimson c1 dye BS (I.C.1.) (2% NaCl CzH40SOzNa 5.Durazol Red 2BS (I.C.I.) 6. Solophenyl Yellow FFL (Geigy) 7. Azogeranine 2 GS (I.C.I.) 8. Coomassie Red PGS (I.C.I.) 9. Rhodamine BS (I.C.I.) C.I. 278 C.I. 814 C.I. 31 C.I. 749 60 76 - * Z 0 0 0.4 - - - - 82 83 - - E crl 0.4 95 69 100 100 11 33 0 0 3 35 36 cd 0 6.0 0.4 73 52 100 100 27 44 0 0 5 50 56 6.0 vl dye 0.4 96 93 33 58 o o o a a 2 43 NaCl 6.0 dye 0.4 100 100 75 100 14 29 0 0 0 0 53 NaCl 6.0 dye 0.4 89 56 30 55 0 0 0 0 0 0 17 NazSO, 3.5 dye 0-4 100 97 28 45 2 5 0 0 0 23 46 NazSO, 3.5 dye 0.2 45 69 33 18 13 7 0 0 2 66 43 HZSO, 0.8 CH3COONH4 0.8 CH&OOH 0.2c . H. BAMFORD, J . BOULTON, w. E. HANBY AND J . s. WARD TABLE 2 225 Composition of dyebath : Naphthalene Scarlet 4RS 2.0 g/l. temp. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. CHsCOOH polymer pol yglycine ace tyla ted poly gly cine Nylon-66 acetylated Nylon-66 copolymer DL-P-phenyl-alanine and DL-leucine 1Zmer (a + p) 12-mer @) 45-mer (E) 45-mer (p) 640-mer (a) 640-mer (p) 1 : 2 copolymer of DL-p-methyl aspartate and DL-leucine 1 : 2 copolymer of DL-/%methyl aspartate and DL-leucine modi- fied by treatment with ammonia amino end-group content, ji equiv./g polymer 164 104 34 7.5 591 65 5 170 169 12 12 14 >14 * 0.5 g/l.95" C total dye absorbed at saturation, p equiv.jg polymer 101 24 46 12 188 188 1.4 14 0 0 0 0 * Attempts to estimate this were unsuccessful owing to traces of ammonia remaining in the polymer. this connection a sample of polyglycine was acetylated by refluxing with acetic anhydride for 15 min, in order to reduce the basic end-group content.A con- siderable reduction was observed in the uptake of the acid dye Azogeranine 2G by the acetylated polymer, whilst on the other hand the absorption of direct cotton dyes (table 1 ; 5, 6) was little affected. Similar behaviour was observed by Peters6 and by Munden and Palmer7 with Nylon-66. These authors also showed that in the case of Nylon-66 the saturation absorption of a level dyeing acid dye such as Naphthalene Scarlet 4RS (C.I. 185), from an acetic acid dyebath containing excess dye, was closely related to the amino end-group content. To ascertain whether a similar relation holds with polyglycine the saturation ab- sorption of this dye was determined for polyglycine and acetylated polyglycine, with results given in table 2. For comparison, similar experiments were carried out with Nylon-66.It is clear that for both polyglycines the dye absorption is considerably less than corresponds to the number of amino groups. This is pre- sumably due to the crystalline nature of the polymer; the latter is not highly swollen during dyeing and amino groups in the crystalline regions, which probably remain intact, are not accessible to dye molecules. After acetylation the dye absorption is reduced proportionately to a much greater extent than the number of end-groups. This again can be attributed to the presence of amorphous and crystalline phases. We would expect the amino groups which are accessible to dye molecules to react more readily during the heterogeneous acetylation than those in the crystalline regions. After acetylation, the free amino groups in the accessible regions are responsible for the uptake of the dye (24 micro equivalents per g).It is clear therefore that the fraction of free amino groups in the accessible regions, and hence the dye uptake, will be reduced by acetylation to a* greater extent than the total amino group content. A simple calculation based on these ideas shows that, in order to account for the results in table 2, the percentage of end-groups inaccessible to dye in the polyglycine before acetylation is about 40; after acetylation this has increased to about 49. A small decrease in accessibility during acetylation, corresponding perhaps to an increase in crystallinity, is not surprising. H226 DYEING OF POLYPEPTIDES It appears therefore that the amino end-groups of polyglycine contribute to dye absorption in a manner similar to those in Nylon 66, and that in the case of the level-dyeing acid dye Naphthalene Scarlet 4RS the interaction between dye and backbone is, for both polyglycine and Nylon-66, insufficiently strong to allow dyeing when the amino end groups are blocked.On the other hand, the inter- action between direct dyes (table 1; 5, 6) and the backbone in polygiycine and Nylon 66, may be so strong that dyeing becomes independent of amino end-group content. These dyes are probably attached to the backbone primarily by hydrogen bonds. The 1 : 1 COPOLYMER OF DL-13-PHENYLALANINE AND DL-LEUCINE.-The amide group content of this copolymer is not very different from that of Nylon-66, which has the repeating unit (-CO . (CH2)4.CO . NH . (CH2)6. NH-). The amino group content of the 640-mer is about one-third of that of Nylon, while the lower polymers have correspondingly more amino groups (table 2 ; 6-1 1). In view of this similarity, and considering the results obtained with polyglycine, it might be anticipated that the dyeing properties of these polypeptides, particularly with respect to acid dyes, would be similar to those of Nylon, allowing for any differ- ence in amino end-group content. It was surprising therefore to find that films of the 640-mer could not be dyed with acid dyes (table 1 ; 3, 4, 7, 8 ; table 2 ; 10, 11). Tables 1 and 2 show, however, that the lower polymers (45- and 12-mers) took up some acid dyes. Azogeranine 2GS dyed only the 12-mer, the 45-mer remaining undyed after a prolonged period even when the pH of the dyebath was reduced to 2 by the use of sulphuric instead of acetic acid.Solway Blue B (C.I. 1054) gave similar results. Using a wide range of dyes and conditions of appIication we found that the 640-mer would take up only dispersed dyes (table 1 ; 1). These results show that there is a profound difference in dyeing behaviour between the 640-mer and Nylon of comparable amino group content. A possible reason for this is the much lower uptake of water by the polypeptide. Water imbibition by the Iatter is 2 % by weight, while that of Nylon is 11 %. The partially acetylated Nylon, of amino group content 7.5 pequiv./g, was found to imbibe water to ap- proximately the same extent as the unmodified Nylon.It appears therefore that the water absorption of Nylon is primarily due to its -CONH- groups and not to its end groups, and we may reasonably suppose that the comparatively low water imbibition of the copolymer is not caused by its somewhat lower pro- portion of end-groups. This low imbibition and swelling of the co-polymer make the polar groups inaccessible to dye molecules. Although the overall compositions are similar the different chemical structures of Nylon and the copolymer can readily account for the different water imbibitions. The hydrocarbon portions of the copolymer are side chains and it is possible that they shield the polar peptide groups of the backbone, rendering them inaccessible to water molecules. Whether each individual chain is enclosed, as it were, in a hydrocarbon sheath, or whether sheets of neighbouring chains are enclosed by hydrocarbon layers, will depend on the configuration of the polypeptide chains.In both cases, however, the final results are similar. Such a shielding effect is less probable with Nylon, in which the hydrocarbon and amide groups follow one another along the chains. In polyglycine there are no side chains, hence it is not surprising to find that the swelling in water is suEcient to allow dye molecules to enter the structure. We have not measured directly the water imbibition of polyglycine powder, but measurements of the water absorption from the vapour phase 8 indicate that it is considerable for low peptides of glycine. Tables 1 and 2 show that the 12-mers of this copolymer are much more readily dyeable than the high polymers, although less so than a Nylon of similar amino group content. These small polymers are probably appreciably more hydro- philic than the larger ones, on account of the increased amino-group and dimethylamide-group contents.Differences between the molecular weightc. H . BAMFORD, J . BOULTON, w. E. HANBY AND J . s . WARD 227 distributions of the 12-mer and the higher polymers will be such as to enhance differences in dyeing. The distribution for the 12-mer is comparatively broad, and the polymer will contain a significant amount of low molecular weight, com- paratively hydrophilic, material. This is presumably the portion which dyes most readily. The 45-mer, and higher polymers will have sharper distributions and would be expected to contain relatively little low molecular weight hydrophilic material.Table 1 shows that the a and /? forms of this copolymer with degrees of polymerization of 12 and 45 have different equilibrium exhaustions when dyed with the ionic dyes 3-9. While this may be a real effect due to the different back- bone configurations, it must be remembered that the /? form was obtained by treating the a material with 98 % formic acid, followed by drying in vacuo. Traces of residual formic acid would enhance the uptake of anionic dyes and retard the uptake of the basic dye 9 by the polymer, while not affecting the ab- sorption of the dispersed dyes appreciably. The uptake of dispersed dyes is not significantly affected by the backbone configuration (table 1).Since the latter is so different in the a and P forms it seems that either the two modifications dye with equal ease, or the backbone does not participate significantly in the inter- actions between the polymer and the dispersed dyes. The dispersed dyes appear to be able to enter the polymer although the latter is practically unswollen, and they may do this by dissolving in the hydrocarbon side chains. (Note that it is possible to dye cellulose acetate in vacuo with amino-anthraquinone dyes.9) Table 1 shows that the absorption of dispersed dyes decreases with increasing degree of polymerization. In the smaller polymers the larger number of chain ends per unit weight and the broad molecular weight distribution may result in a lower average degree of order, and a higher accessibility to dyes.polymer @.P. - 609) exhibited dyeing properties very similar to those of the previous copolymer of highest molecular weight (D.P. - 640) (table 1). In this case also the water imbibition is very low (< 2 %), due to the predominantly hydrophobic character of the side chains. It was found possible to replace the side chain ester groups by amide and carboxyl by treatment with aqueous ammonia. Thus, if samples of the film were treated with 0.880 ammonia at 50" C for 18 h, 90 % of the methoxyl groups were removed ; these were replaced by NH2 and OH in the ratio 4/1. The resulting polymer, having side chains -CH2CONH2, -COOH and -CH2CH(CH3)2 and a small amount of residual ester, sweJls in water at room temperatures; the degree of swelling depends on the pH of the surrounding medium.At pN 9, a film of the modified polymer imbibes 50 % of its weight of water, while at pH 3.5 it takes up only 13 %. The modified films had very different dyeing properties from the original (table 1). Clearly the increased swelling facilitates dyeing in general. This is particularly noticeable with dyes 3, 4, 8, 9. Further experiments indicated that the acid dyes 3, 4, 8 were not taken up by the modified polymer in the absence of salt, even when acetic acid was added. This suggests that the amino end-groups are not responsible for the dye uptake. Experiments with Azogeranine 2GS and Naphthalene Scarlet 4RS (tables 1 and 2) confirmed that true acid dyeing properties are not shown by this polymer. These dyes, the absorption of which is believed to depend exclusively on basic groups, were not taken up by the original or modified material from baths containing neutral salt or free acid.This lack of acid dyeing may be caused by some kind of shielding of the amino groups by the side chains, but we are inclined to think that a significant factor is the low degree of swelling of the polymer in acid baths. The carboxylate ions would be expected to be much more effective in promoting swelling of the polymer than the unionized carboxyl groups. An analogous swelling effect is found with the polypeptide prepared from L-glutamic acid.10 The general dyeing properties of the modified copolymer resemble closely those of commercial cellulose acetate. Like the fatter, the modified polymer THE 2 1 COPOLYMER OF DL-LEUCINE AND DL-P-METHYL ASPARTATE-This228 DYEING OF POLYPEPTIDES does not absorb the direct dyes 5 and 6.This may be due to the much greater molecular size of these dyes. However, it is known that even highly swollen cellulose acetate does not absorb these direct dyes appreciably. Thus no suitable sites may be available in either polymer. PoLY-L-ALANmE.-Poly-L-alanine of moderately high degree of polymeriza- tion was available as film in the cc form. This polymer is of interest since it has hydrocarbon side chains which are much smaller than those of the two copolymers already discussed. It will be seen from table I that dye absorption is sufficiently high over a wide range of dyes to indicate a close similarity to polyglycine. Any differences between the two could be due to the different physical conditions of the polymers, or to differences in crystallinity, or to the different backbone con- figurations.The similarity is sufficient to indicate that methyl substitution of polyglycine does not prevent access of dye molecules to the backbone. DYEING WITH DISPERSOL FAST ORANGE G.-The dispersed dye Dispersol Fast Orange G dyes cellulose acetate to a yellow-orange colour, and Nylon to a brick- red colour. It appears likely that this colour change results from a difference in the mode of attachment of dye to substrate. When the polypeptides were dyed with this dye the following colours were obtained : polyglycine brick-red poly-1 : 1 DL-leucine-DL-/?-phenylalanine yellow-orange poly-2 : 1 DL-leucine-DL-p-methylaspartate yellow-orange poly-L-alanine brick-red (modified as described above) Since the brick-red colour is produced with polyglycine, poly-L-alanine and Nylon it may be diagnostic of the attachment of the dye to peptide groups and therefore may indicate the accessibility of these groups in a given polymer.The relative extents to which the backbone and side chains are dyed depend not only on the accessibility, but also on their relative affinities for the dye, and the proportion of each present. In the case of the modified aspartate copolymer the yellow- orange colour suggests that the backbone is not dyed. If this is accepted it must be assumed that the interaction between dye and side chain amide or carboxyl groups is similar to that occurring with cellulose acetate, or that the dye is dis- solved in the hydrocarbon side chains. Any attachment of the dye to the side chain amide groups does not result in the production of the brick-red colour.CoNcLusIoN.-The experiments described have shown that the three groups of possible dye sites in the synthetic polypeptides studied do in fact take up dye under suitable conditions. The locations of these groups are (i) the polypeptide backbones, (ii) the amino groups at the ends of the chains and (iii) the side chains. Which of these (if any) will be operative depends on the conditions of dyeing as well as on the dye and the polymer. In general, the greater the degree of swelling of the polymer the easier dyeing becomes, and the role of the side chains is especi- ally important in this connection.Although the polypeptide chain itself is appreciably hydrophilic, swelling may be reduced to an insignificant amount if sufficient hydrophobic side chains are present. It would appear that the chemical structure of the polypeptides enhances the importance of the side chains as far as swelling properties in water are concerned. The simple polypeptides polyglycine and poly-L-alanine may be dyed without difficulty by using sites of groups (i) and (ii); apparently the polypeptide chain offers suitable sites for all the dyes we have examined, except perhaps some acid dyes. With polypeptides carrying comparatively large side chains the situation is more complicated. It would seem that in some cases dispersed dyes may pene- trate these materials even when there is no appreciable swelling in aqueous media, i.e.some dye becomes attached to type (iii) sites. Under these conditions, no other classes of dye are effective. When these polymers are swollen in waterc. H . BAMFORD, J. BOULTON, w. E. HANBY AND J. s. WARD 229 dyeing is facilitated, but it is not clear whether this necessarily implies that all three types of site become accessible. Some evidence which has been presented for the modified aspartate copolymer seems to indicate that under these conditions at least one dye-Dispersol Fast Orange G-becomes attached preferentially to the side chains. Whether this indicates that even under conditions of high swelling the side chains can prevent access of dyes to the polypeptide backbones, or whether it is merely a result of a much larger affinity of the dye for the side chains, can only be decided by further work.For the copolymer of DL-P-phenylalanine and DL-leucine the backbone con- figuration appears to have little or no effect on the dyeing properties. A com- parison of polyglycine (p) and poly-L-alanine (a) also leads to the same conclusion. It is not certain that either form of these polymers is uncontaminated by small amounts of the other modification, but it is difficult to see how this could affect the main conclusion. One explanation of the results would be that during dyeing an appreciable amount of interconversion of the two forms occurs. This possi- bility is being investigated. The similarity between the a and P forms in dyeing behaviour inevitably raises the question as to how dyes are attached to poly- peptide chains. If hydrogen bonding is involved (as appears to be currently supposed) the two forms would be expected to show different behaviour. The ease with which polyglycine and poly-L-alanine may be dyed recalls the similar behaviour of silk, although of course the latter also shows properties characteristic of its (small) content of basic and acidic side chains. We consider that a better understanding of the dyeing properties of this and other protein fibres will be possible after more work on simple models has been done. 1 Bamford, Hanby and Happey, Proc. Roy. SOC. A , 1951,205, 30. 2 Ambrose and Elliott, Proc. Roy. SOC. A, 1950, 205,47. 3 Bamford, Hanby and Happey, Proc. Roy. SOC. A , 1951,206,407. 4 Hanby, Waley and Watson, J. Chem. SOC., 1950, 3009. 5 Waltz and Taylor, Anal. Chem., 1947, 19, 448. 6 Peters, J. SOC. Dyers Col., 1945, 61, 95. 7 Munden and Palmer, J. SOC. Dyers Col., 1951, 67, 612. 8 Mellon, Korn and Hoover, J. Amer. Chem. SOC., 1948, 70, 3040. 9 Johnson, referred to in Vickerstaff, The Physical Chemistry of Dyeing (Oliver and 10 Hanby, Waley and Watson, J. Chem. SOC., 1950, 3239. Boyd, London, 1950), p. 260.

ISSN:0366-9033    

DOI:10.1039/DF9541600222

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

c. H . BAMFORD J. BOULTON w. E . HANBY AND J. s. WARD 229 GENERAL DISCUSSION Dr. H. Zollinger (Bade University) (communicated) I think that the ad- vantages of Dr. Robinson’s models are their usefulness for sterically strained molecules. Dr. Robinson demonstrated a model of Caledon Jade Green (his fig. 54 in which one of the methoxy groups was left out. If we put both methoxy groups on the dibenzanthrone nucleus one recognizes that only 4 or 5 of the 34 aromatic carbon atoms are distorted out of the plane. In spite of this distortion the model fits well on the cellulose chain. This explains why Caledon Jade Green has not a lower substantivity than the unsubstituted dibenzanthrone dyestuff. On the other hand I think that we should not forget that very detailed spatial problems cannot be soIved with any model.Dr. C. H. Bamford (Courtaulds Ltd. Maidenhead) said Dr. Robinson has mentioned the “ hydrogen bond ” and “ conjugation ” hypotheses which have been put forward to account for substantivity. Further advances in our under- standing of this complex subject seem most likely to result from work on model systems in which specific interactions may be studied. As an example one may cite the interaction between hydroxyl groups and aromatic or unsaturated GENERAL DISCUSSION 230 hydrocarbons ; the experimental evidence described below suggests that this should be considered as a possible factor contributing to substantivity. As long ago as 1940 Badger 1 pointed out that benzene “ appears to exhibit an interaction with proton donor substances which may probably be described as the formation of a weak hydrogen bond”.In a more recent paper Jones and Badger2 have made observations on the frequency of the third harmonic OH band of methanol in a number of solvents and have concluded that in aromatic liquids a frequency shift occurs which is of the order of magnitude found when a hydrogen bond is formed between two oxygen atoms. This is taken to indicate the formation through the hydroxyl hydrogen of a hydrogen bond of moderate strength between the alcohol and hydrocarbon. Somewhat similar conclusions have been reached by Mecke.3 From the two papers by Badger a value of 2-3 kcal for the energy of the hydrogen bond between methanol and benzene may extensive conjugated systems e.g.the bond energy in the methanol + mesitylene be estimated. Stronger bonds can be formed with suitably substituted or more system appears to be about 4 kcal. Dye molecules might be expected to behave similarly. The precise nature of the intermolecular bond in these complexes is uncertain. It may result from the interaction of the H atom of the OH group with the n electrons of the aromatic system (or double bond) i.e. in Mulliken’s terminology the complex would be of the (hUkou) type. This appears to be Mecke’s view.3 On the other hand Mulliken4 does not favour the idea of a the “ somewhat negatively charged carbons of the benzene ring ”. dative complex but suggests weak hydrogen bonding between the H atom and Models show that a dye molecule may be placed on a cellulose chain in such a way that a considerable number of suitable contacts with hydroxyl groups may be obtained.The net contribution to substantivity is however always determined by competing interactions; in this case the competition is between water mole- cules and the conjugated system for the hydroxyl groups of the cellulose. The results of this cannot be calculated at present with any certainty because the relevant hydrogen bond energies are not known sufficiently accurately. How- ever consideration of the current values suggests that a net contribution towards the binding energy between the dye and substrate of the order of 1 kcal from each contact is within the range of possibilities. The entropy change accompanying the displacement of several water molecules from a cellulose chain by a dye molecule will also favour attachment of the dye although of course it will not contribute to the measured heat of dyeing.It is known that the absorption spectra of dyes frequently change on ad- sorption. This is consistent with but of course does not establish the presence of interactions of the type discussed. Dr. A. S . Dunn (Brit. Rayon Rex. Assn. Manchester) said Data bearing on the substantivating properties of the amide group can be derived froin studies of the sorption by cellulose of naphthols which have the structure X’ These molecules have but a single group the amide group capable of taking part in hydrogen bond formation. The introduction of substituents X Y increases the substantivity of naphthols there is an increase in the heat of dyeing and 1 Badger J.Chem. Physics 1940 8 288. 2 Jones and Badger J. Amer. Chem. SOC. 1951 73 3132. 3 Mecke Faraday Suc. Discussions 1950 9 161. 4 Mulliken J. Physic. Chem. 1952 56 801. substituent Brenthol - GENERAL DISCUSSION HEATS FREE ENERGIES AND ENTROPIES OF SORPTION OF NAPHTHOLS - AH" slopc of ionic product plot kcal/mole 23 I presumably in the- strength of any hydrogen bond formed though this bond strength cannot be estimated in the absence of further data on cellulosc -I- water dye + water and dye + dye interaction. The heats of dyeing have been derived from the adsorption isotherms determined in the absence of salt and surface- active agents at 25" and 50". - AS" cal/deg.mole -AGO cal/molc 5-6 6.6 CH3 - X CH3O - 0.75 1.0 0.89 0.81 8.4 11.3 13-7 14.8 AS OT FR PA 3100 3240 3330 3490 Y - - CH30 7.4 7.9 - Affinities and entropies of dyeing have been deduced by applying the Peters- Vickerstaff theory. Variation of the concentration of excess sodium hydroxide between 0.015 N and 0.035 N produces no change in the equilibrium absorption of Brenthol AS on viscose model filament. Neale 1 has measured the uptake of sodium hydroxide by cellulose. When the affinity is calculated using values for the sodium concentration in the fibre derived from Ncale's data it is found not to vary with sodium hydroxide concentration. However the slopes of plots of the logarithm of the ionic product in the fibre against the ionic product in solution do not have the theoretical value of unity and do not increase with temperature.Hence it is doubtful whether the theory may be properly applicd. The entropy of dyeing is not constant as might have been expected if binding of the dye to the cellulose takes place through a hydrogen bonding mechanism exclusively in fact the entropy increases linearly with the heat of dyeing. Of the nine direct dyes for which heats and entropies of dyeing have been evaluated five are related by the same linear expression AH = 0.38 AS + 2.3. Linear relations of this kind may be general especially among series of related reactions.2 If as seems likely the binding of dyes to cellulose is not to be at- tributed to interaction of a single type such as hydrogen bonding but is due to the co-operation of several intermolecular forces compliancc with or deviation from a relation of this type may indicate identity or alteration in the contributions of the various forces acting.Dr. H. E. Nursten (Nottingham and District Tech. Coll.) said Amongst direct cotton dyes the class consisting of derivatives of benzidine tolidinc and di- anisidine is preeminent. When Paine and Rose 3 state that in many dyes the distance between groups capable of taking part in hydrogen-bond formation is 10.8 A they are presumably referring to this class. I confirmed this distance from drawings using essentially Pauling's covalent radii and valency angles and assuming the molecules to be perfectly planar.It is not surprising that as the repeat of a cellulose chain occurs at 10*3& the nearness of these two figures was considered very suggestive. However Paine and Rose found that for the second most important class of direct cotton dyes the straight-chain polyazo compounds the spacing of azo groups occurred at 7.5A. I find this distance to be 6.5& though the distance between the extreme nitrogen atoms in an all-trans azo-benzene-azo group is 7.3 A. It can be shown that in an all-trans trisazo dye containing J-acid as end- component (a very common feature) the distance between the first azo group and 1 Neale Shirley Inst. Mem. 1931 10 1. 2 Evans and Polanyi Truns. Furuduy SOC. 1936,32 1333. 3 Vickerstaff The Physical Chemistry :of Dyeing (Oliver and Boyd London 1950) p.164. GENERAL DISCUSSION 232 the amino group of the J-acid is in the region of 20-21 A i.e. equivalent to two repeats of the cellulose chain. In primary disazo dyes using carbonyl-J-acid as middle component the distance between an azo group and the imide-nitrogen farthest from it is 10.3 A. In 4 4'-diaminodiphenylurea the amino groups are 12.8 8 apart and dyes derived from it therefore contain no such distance as 10.3 A. On examination of a drawing of the stilbene derivative Chrysophenine G (Colour Index no. 365) I confirm Dr. H. Zollinger's findings namely that there is no distance of 10-11 8 between groups capable of taking part in hydrogen bonds. The distance between oxygen atoms is 24-7A assuming that the azo and ethylene groups in the traizs-form themselves are cis to one another and the distance between amino groups in 4 4'-diaminostilbene is 12.1 A.Thiazole derivatives form another class of direct dyes. In dehydrothio- p-toluidinc the distanccs between the amino-nitrogen and the cyclic nitrogen and sulphur atoms are about 6-7A. In Chlorophenine (Colour Index no. 814) there is no distance between groups able to participate in hydrogen bonds which lies near lO-llW and in Primuline (Colour Index no. 812) the nearest distance is about 11 A being that between a sulphur atom and the amino group in the form in which the two thiazole rings are cis to one another. It is doubtful whether sulphur can act as a hydrogen acceptor.Although I have not examined all classes of dyestuffs which show affinity for cellulose fibres I have mentioned most of the important ones and it does appear from such a consideration that a distance of 10-11 A between groups able to accept or donate hydrogen is of no particular significance. It is therefore gratifying to find that Dr. C. Robinson has shown by means of his very welcome models that the surface of the celIulose chain is such that hydrogen bonding by means of one or other hydroxyl group can occur at any position along its length and that therefore the repeat of 10.3 A is unlikely to be of importance. Naturally these remarks have no bearing on the question of whether hydrogen bonding does or does not take place between the dye and the cellulose during the process of dyeing.Dr. K. H. Gustavson (Stockholm) (contributed) said According to the findings reported the absence of heat of reaction in the binding of the sulpho-acid dyestuff Naphthalene Orange G by the amino acids which form the cationic sites in proteins i.e. the lysine and arginine should imply that the heat of reaction about - 9 kcal/mole obtained for the system wool + colour acid is not due to a partial discharge of the cationic protein groups by the sulpho-acid anions. In reading the interesting paper by Derbyshire and Marshall the figures of table 3 with the exceptionally large heat change obtained by mixing arginine hydrochloride with the colour acid was noted with satisfaction which however declined upon consulting table 4 with the corrected arginine value.This subject interests me greatly because the AH values of reactions between collagen and polyacids form the basis for attempted estimation of the number of the cationic groups of collagen which are directly involved and discharged in the irreversible binding of polyvalent aromatic anions by collagen such as for instance poly- sulphonic acids of synthetic tannins and various fractions of lignosulphonic acids. In these attempts to apply thermodynamics to the collagen systems the lucid text of Dr. Vickerstaff has been very helpful. Since Dr. Vickerstaff is present and the paper under consideration emanates from his laboratory I should like to ask him if the corrections applied to the reaction of arginine with the colour acid are valid and further whether he would support the following approach to the system collagen + solutions of polyacids.From the titration curves obtained at lo" 20" and 30" C the concentration of the solutions of the polyacid in equilibrium with the same amount of acid in the fibre at two of the temperatures given were noted. The values were inserted in the Clapeyron equation and thus the values of AH were obtained. With due 23 3 GENERAL DISCUSSION consideration of the fact that the complete discharge of the cationic protein 4- groups by hydroxyl ions (-NH3 -f -NH2) involves AH values of the order of - 12 to - 14 kcal/mole whereas the AH values obtained for the maximum fixa- tion of the sulpho acids amounted to about -6 kcal/equiv. correcting for the AH value of the carboxyl ions of collagen (HCl) it was inferred that about half of the total number of the cationic groups of collagen had been inactivated and discharged by the sulphonic acid groups of the polyvalent anions attached to collagen.Accordingly this method rests on the assumption that the changes in the heat of reaction are due chiefly to alterations in the thermodynamic state of the basic protein groups. The corrected value for the AH of the reaction between By anion exchange between esterified (methylated) collagen assumption. this will acid pH - lo) arginine with all and its colour cationic groups apparently compensated invalidate by C1 ions and (isoelectric anions of the at polysulphonic acids it was also found that only about one-half of the total number of Cl ions were exchanged for sulphonic acid anions at the point of maximum fixation of the sulpho-acids.It is to be noted that only a partial dis- placement of the anions of the sulpho-acids studied was obtained upon repeated extraction with 2 M sodium chloride indicating a high degree of irreversibility of the binding. Mr. A. N . Derbyshire (I.C.I. Dyestufi Blackley) (communicated) In reply to Dr. Gustavson the correction applied to the measured heat of reaction between dye acid and arginine hydrochloride is not rigidly valid since the binding forces in the solid complex will not necessarily be the same as in the solid constituents. However the greater part of the correction is due to the heat of precipitation of the dye whose large hydrophobic surface will in aqueous solution cause scparation of water molccules against their mutual attraction.This contribution will persist in whatever form the dye is precipitated. We believe that the correction leads to a reasonable approximation for the heat of interaction of dye with arginine. It should also be noted that the heat changes on mixing dye and arginine in ncutral solution at concentrations below the point at which precipitation occurs are very small in agreement with the corrected figure from acid solution. Dr. Gustavson’s work with sulphonic acids on collagen is very interesting. Our work shows that there is specific interaction between dye anions and guanidine groups but not with free amino groups.If this is characteristic of sulphonic acids it would explain his finding that only one half of the chloride ions in methylated collagen were displaced by sulphonic acid in agreement with analysis showing about one-half of the basic groups of collagen to be guanidine. I t is suggested that the measured heat of adsorption of - 6 kcal/g equiv. consists of the heat of interaction together with the heat change accompanying the transfcr NH3+ -I- OH- -+ NH2 + H20 involving the heat of formation of water from of the acid from aqueous medium to the collagen phase. The postulated reaction its ions appears unlikely to occur in a reaction of this kind. Dr. C. H. Giles (Royal Tech. Coll. Glasgow) (communicated) The results of Derbyshire and Marshall while interesting and important in themselves do not necessarily disprove that the peptide groups in proteins may be bound to dye molecules by hydrogen bonds.If the anionic group of the dye is associated with the cationic group of the dipeptide then it is not possible for steric reasons for the peptide group of the latter to form a bond simultaneously with the azo group of the dye. Mr. W. J . Marshall (I.C.I. Dyestufi Blackley) (communicated) In reply to Dr. Giles in aqueous solutions the reaction between hydrochloric acid and amino acids is entirely due to the latter combining with the hydrogen ion C1- being completely dissociated as in dilute solution of salts. If association of the dye with the peptide linkage did tend to occur there is no reason why the anionic group of the dye should be associated with the cationic group of the same dipeptide.GENERAL DISCUSSION 234 The question of steric effects therefore does not arise. In our experiments we could not detect any heat change due to this type of interaction. Dr. G. A. Gilbert (Birmingham University) said Meggy is considering a very important property of dyes in his paper since although the relation between dye activity and dye concentration is basic to any theory of dyeing lack of data has almost always made it necessary to equate activity in solution with conccntration. In the present case of Orange I1 (sulphanilic acid -> p-naphthol C.I. 151) Meggy shows that the dye is of the order of a thousand times less soluble at 25" in N NaCl than would be expected from its solubility in pure water and that therefore for saturated solutions of this dye under these conditions this assumption is quite untenable.In explanation Meggy suggests that the increase of activity co- efficient which this decrease in solubility implies is in line with the fact that in general electrolytes increase thc activity of organic substances in aqucous solu- tions. Howcver such general considerations which led to the introduction of the " salting-out " term in the Debye-Huckel equations and which have been tested for various organic substances,l can account for only an insignificant part of the ob- served increase of activity coefficient. (It may be remarked further that over the range of NaCl concentration 0.0 to 0.05 N the ionic strength as calculated from the sum of the dye and NaCl concentrations is actually decreasing as NaCl is increased.) A more likely explanation is that the ions of the dye are aggregated in solution and that the degree of their aggregation is strongly dependent on conccntration.By adding the common ion Na+ as NaCl or Na2S04 to the saturated solution of the dye the solubility of the dye is decreased and dissociation of the aggregatcs is favoured with a consequent increase of activity coefficient. This effect would not be found in any but a saturated solution of dye where the expected tendency of the added electrolyte to encourage dye aggregation is completely outweighed by the opposite effect of decrease of dye concentration. It is possible to find support for this explanation by working out what should happen when NaCl is added to the saturated solution of the sodium salt of a hypothetical dye chosen to have the property of aggregating in solution to form predominantly aggregates containing four dye ions D4 in equilibrium with single ions D.It may be assumed that the formation of these aggregates is governed by the law of mass action according to the equation [D]4/[D4] = Kd and that the solubility of the sodium salt of the dye is governed by the equation [Na][D]=Ks. It will be assumed further that activities may be replaced by molar concentrations. Inspection of the results of Meggy leads to the choice of 4.65 x 10-13 for ( p 4 ] + [D]) of the dye has been calculated as a function of "a+] and hence the value of Kcr and 7.1 x 10-5 for Ks.Using these figures the solubility of added salt. The result of this calculation is shown by the line in the figure in which the logarithm of the dye concentration (expressed in mole of single ions) of the saturated solution has been plotted against the logarithm of the Na ion concentrations. On the same figure are plotted the experimental results of Meggy for Orange 11. There is clearly a correlation between the behaviour of the hypothetical dye and of the real dye over a considerable range of salt concentration and hence support of the hypothesis of aggregation but no correlation at low salt concentra- tion. In the latter region however the concentration of dye and of Na ion are both falling (the concentration of Na ion being of course equal to the sum of the concentrations of dye and added electrolyte).I believe that this can happen only if true equilibrium has not been attained and if the first additions of salt are removing supersaturation or precipitating a suspendcd colloid. True equi- librium seems to begin at about 0.1 N salt and by analogy with the hypothetical dye the real solubility of the pure dye might be guessed to be about 0.11 M. 1 Harned and Owen The Physical Chemistry of Electrolytic Solutions 2nd cd. (Rein- hold Publishing Corp. N. York 1950) pp. 51 and 397. GENERAL DISCUSSION 235 The solubility of Orange I1 at 60" in N NaCl calls for a remark. Meggy finds an increase of nearly 4,000 times over the interval 25-60'. This extraordinarily high temperature coefficient of solubility is the clearest possible indication of an increase of aggregation with rise of temperature of the saturated solution.From being comparatively unaggregated at 25" in N NaCl the solution must become highly aggregated and have a correspondingly low activity coefficient at 60". Once again of two opposing tendencies this time the disaggregating effect of rise of temperature and the aggregating effect of increase of concentration the influence of concentration predominates provided saturated solutions are being considered. The distribution of dye between amyl alcohol and water is difficult to discuss without information about the state of the dye in the alcohol. It is possible to say however that the hypothetical dye above if present in solution in the alcohol as simple undissociated molecules of its sodium salt would have a distribution coefficient which would increase rapidly in favour of the aqueous layer as the dye concentration increased.For example at a constant concentration of sodium ion the coefficient cw/cA would have for the respective concentrations of dye of I - 1 - theory. FIG. I.-Salting out of Orange IT by NaCl and Na2S04 at 25". >.( Na2SO4. 0 NaCI. 10-5 10-4 10-3 and 10-2 M the relative values of 1.0 1.3,5 and 27 figures which agree quite well with the trend shown in the paper for Orange 11. In conclusion it must be stressed that the properties of the hypothetical dye have been chosen only to make possible a simple demonstration.At the same time it seems likely that further experiments based on the valuable methods that Meggy has initiated will greatly help the discovery of the actual degrees of aggrega- tion heats of solution and of aggregation etc. of real dyes. Dr. A. €3. Meggy (Lpeds University) said Dr. Gilbert's suggestion is a very interesting one. If it is correct the change in the activity of Orange I1 should be less in CaC12 solutions than it is in NaCl or NaZS04 as the solubility of the calcium salt i s much less than that of the sodium salt. I think it is necessary to be cautious in applying the results of the Debye-Huckel theory to dye solutions. Dye ions are large in size highly symmetric and have a considerable area of water- hydrocarbon interface ; a change in the surface energy at this interface will greatly modify their activity quite apart from any electrical influences on the charged -SO3- groups.Prof. W. Bradley (University of Leeds) said Although it was intended to limit the scope of our paper to a demonstration that quite a number of derivatives GENERAL DISCUSSION ‘Y 236 of mandelic acid can be resolved on wool and hence that the corresponding anions are present in some degree in the form of typical ammonium-salt groups the paper contains one experiment which suggests that the majority of the mandelate anions are bound in the same manner at ammonium sites. When wool combined with (&)-mandelic acid is immersed in water transfer of the acid from wool to medium occurs almost completely within a few minutes if the relative amount of water is large.If however the acid combined with the wool is (-)-mandelic acid and the aqueous medium contains (A)-mandelic acid at an appropriate concen- tration the exchange of (+)-anions for (-)-anions on the fibre occurs very slowly indeed. We interpret this result as meaning that the loss of acid from wool com- bined with mandelic acid is the result of two rapid but consecutivc reactions. First protons leave then anions as a negative charge accumulates on the fibre. Wool combined with (-)-mandelic acid when immersed in aqueous (&)-mandelic acid cannot undergo rapid loss of the (-)-acid for the reason that the essential first stage of reaction the loss of protons cannot take place. Even so it remzins remarkable that the rate of exchange of anions is so low and the result is difficult to understand if the (-)-anions are merely present in solution or absorbed on a surface.On the other hand the result is feasible if the anions are bound more intimately at positively charged (ammonium) sites. FIG. l.-Crystalline (A) and Dr. G. D. Coumoulos (Nat. Tech. University Athens) said The final dyeing effect i.e. the formation of a system “ dyeing molecule-substrate fibre” may be due as pointed out in different papers to different reasons adsorption absorp- tion solubility salt formation diffusion etc. The dyer is of course interested that the final effect should be a non-reversible one. While in all papers the dye is considered as a molecular unit the reference to the substrate is made to the fibre being of the ultimate size.At this point it should be pointed out that the fibre is built-up from natural or artificial polymer mole- cules aligned in the general direction of the axis of the fibre. It is now well known that the state fibre. orderly (B) regions in a of these macro-molecular units in the fibre varies from completely amorphous to crystalline with all the possible intermediate states. Even the amorphous state may have regions where a certain degree of orientation persists.1 Both the crystalline and the amorphous regions are formed from parts of the macro-molecules (see fig. 1). The dyeing is effected by the interactions of the dyeing molecule with a part of the macro-molecular configuration and it will depend on the nature of the groups comprising the dyeing and the polymer molecules their shape and size and also the state of matter as to what type of forces will develop between them in order to effect dyeing.Prof. Bradley and his co-workers in their paper on the selective absorption of optical antipodes on wool found differences in the degree of rcsolution as the chain length attached to the mandelic acid was increased. He also pointed out that there is a difference in the rate of absorption for the amorphous and crystallinc regions of the wool fibre. Optical activity may be due to the existence of an asymmetric atom in the molecule and/or an asymmetric lattice in the crystal. It is reasonable to accept that the asymmetric carbon atom in the mandelic acid combines more easily with the more flexible asymmetric atom in the amorphous rcgion of the wool fibre.While for its absorption on the crystal more rigid steric conditions should be fulfilled.2 Except for the existence of an asymmetric atom 1 Coumoulos Proc. Roy. SOC. A 1943 182 166. 2 Coumoulos Thesis (Athens University 1938). 237 the dimensions of the lattice crystallites should be suitable. This may explain the observed difference in rate of absorption. With the increase of the chain length attached to the mandelic acid one would expect the development of another type of force between the long chain of the dyeing molecule and that of the macro- molecule in the fibre and there exists a critical length over which the dyeing mole- cuIe attaches itself to the fibre by lateral forces.1 In all cases the molecular scale for both the dye and the fibre should be con- sidered in dyeing.In that respect Dr. Robinson’s paper on atomic models is of the system dyeing molecule + substrate fibre before proceeding with theoret- very interesting and it is suggested that it will always be helpful to make a model ical explanations. Dr. K. H. Gustavson (Stockholm) said In the extremely suggestive paper of Schulman and Dogan there is a wealth of points which invite discussion. My comments will be restricted to a few of these. The first important point is the finding that monolayers of proteins which contain free carboxylic groups such as serum albumin react with chromium forming two-dimensional solid lattices probably by the interlinking of the protein chains through the hydroxy-chromium complexes.An important fact clearly brought out by the monolayer technique is indeed that the steric factor is much in evidence in this cross-linking. On the other hand proteins lacking in free carboxylic groups such as gliadin do not solidify upon treatment with chromium salts. This is certainly an unambiguous proof of the primary importance of the carboxyl ion of proteins in the binding of cationic chromium complexes. As additional evidence for the governing role of the charged carboxyls of the proteins for their reactivity towards cationic chromium complexes the following mainly unpublished data from investigations related to the mechanism of chrome tanning 2 are of interest.Two g portions of the various proteins (hydrated) equilibriated in 1 0 m l of solutions of 67 % acid chromium sulphate 2Og/l. CrzO3. The amounts of Cr2O3 fixed by the proteins and the proportion of free carboxylic groups of the proteins are shown in the following table. % Cr2 0 3 fixed by the protein 10.8 2.6 100 25 35 70 125 110 100 0 GENERAL DISCUSSION ‘rABLE 1 free acid groups typc of protein collagen elastin silk fibroin keratin (wool) serum albumin ovalbumin fibrinogen gliadin myosine (rabbit muscle) casein 130 100 8.9 0.9 0.3 11.2 10.7 1.2 14.5 10.1 With the exception of keratin and silk the chrome fixation of the various proteins can be fairly well correlated with the carboxylic content of the proteins.With keratin the steric conditions and the inaccessibility of the carboxyl ions (crystalline region) may be responsible for its anomalous behaviour towards polynuclear chromium complexes. Further it should also be noted that the number of cationic protein groups are of importance indirectly for the fixation of the chromium cations since the anions of the system must be compensated by the cationic protein groups in order to maintain the electro-neutrality of the 1 Coumoulos Proc. Roy. Soc. A 1943 182 166. 2 Gustavson J. Physic. Chern. 1947 51 1181. GENERAL DISCUSSION 238 system. This point is stressed by the authors in stating that the positive potential barrier of the amine groups in the protein monolayer has to be overcome.As to the action of Cu2f ions on gelatin 1 and collagen 2 Cu is fixed by the carboxyl ions of these proteins mainly irreversibly. The resulting Cu-collagen compounds possess a lower degree of stability than the original collagen hydro- thermal as well as proteolytic. The reason is probably that the Cu2+ ion only reacts as a unifunctional hydroxo-cation ; the unipoint fixation of Cu(0H)-+ complexes by the carboxyls of collagen then connotes dislocation of some of the salt-like crosslinks of the original collagen which links contribute in a small measure to its stability. The effect of C U ~ + ions on collagen is indeed indirect cvidence for the requirement of multipoint attachment of the agent to adjacent chains of the protein and the fulfilment of certain steric conditions for tanning to take place.I do not follow the authors’ formulation of the hydrogen bonded monatomic chromium complex with the link c- 4 C O . &-OH- - -O==C’ \O- nor the suggested structure of the dinuclear complex with two hydroxy groups co-ordinatcd as Is not the formation of structures of thc type more likely since the basic sulphates are sulphato-ol-chromium sulphates ? Is there experimental evidence for the existence of structures of chromed proteins of the type given in the paper ? Further it appears problematical if complexes of the type Cr(OH)2’ can be formed on the addition of alkali to solutions of chromic sulphate because the chromium of basic salts tends to form a polynuclear chromium complex and such a highly basic sulphate is insoluble.It would be of further interest to be informed by Dr. Schulman whether his findings of the behaviour of the chrome-protein monolayers might be explained on the basis of the interaction of di- or poly- nuclear chromium complexes with the protein. Concluding I cannot refrain from stating that the fundamental investigations of tanning introduced by the Rideal school and so ably continued by Dr. Schulman have greatly strengthened our present conception of the mechanism of tanning processes. The use of individual protein chains eliminates the many complicating factors present in the macro-structure of skin and represents the simpler chemical reaction between proteins and the tanning agents.Dr. J. H. Schulman (Cambridge) said We consider that hydrogen bonding between the basic metal ions is the initial stage in their aggregation or their inter- linking of the polypeptide chains. This is obtained by their adlineation after being adsorbed on to the available negative carboxyl groups in the protein lattice. This conccpt is experimentally supported by the fact that fatty acid and protein monolayers are made insoluble and are solidified at high areas per fatty acid moleculc and amino acid residue in solid lattices which are produced only at the 1 Northrop and Kunitz J . Gen. Pliysiol. 1928 11 481. 2 Thomas and Seymour-Jones Ind. Eng. Chein. 1924 16 157. GENERAL DISCUSSION 239 pH of formation of basic metal ions.These vary for each metal ion (e.g. pH 2.3 for Fe3-'- pH 4.2 for AP+ pH 5.3 for Cr3+ pH 6.7 for Cu2t-). Any theory valid for the chromium system would equally well have to apply for the other metal ionic system. Further experimental support is given by the infra-red absorption studies on the aluminium soap systems which solidify or gel in hydrocarbons only when the aluminium has an hydroxyl group attached to it in the presence of the di-soap. The hydrogen bonding can be easily established by the infra-red absorption bands and any interference with this bonding prevents or breaks down the structure. The structure given by Gustavson could equaIIy well interlink by hydrogen bonding between the ions after adsorption on to the carboxyl groups in the protein lattice.Dr. K. G. A. Pankhurst (Brit. Leather Manuf. Res. Assn.) said I was inter- ested in the large increase in surface area reported by Allingham Giles and Neustadter and wonder whether all of these changes are due to crosslinking as they suggest. Some years ago we found 1 that many small comparatively simple substances such as butyl alcohol phenol etc. were capable of non-specific pene- tration into monolayers of fatty acids alcohols etc. with the production of films that were expanded at least at high areas and frequently at low areas also. I would suggest that surface potentials and viscosities of the systems mentioned by Allingham et al. would be very informative on this point. Dr. C . H. Gila (Royal Tech. CoZZ. Glasgow) (communicated) Some non- specific penetration of the film may perhaps occur when solutes are used which contain a large proportion of hydrophobic groups e.g.molecules VI VII VIII IX IV,* and this might account for the fact that VII and VIII which contain the largest proportion of such groups produce area increases significantly higher than those predicted. Even so specific cross-bonding must also be involved because it seems most unlikely that the large area increases observed can be attributed solely to non-specific penetration e.g. if the tricarbocyanine molecule (VIII) is assumed to penetrate the film in this manner and to stand vertically to the water surface the observed area increase would represent the association of about 1.5 solute molecules with each one of the cetyl acetate.A consideration of the size and shape of these two molecules does not suggest that such a ratio of association is likely. Cross-bonding appears to be the most reasonable mechanism to account for the observed effects of the highly hydrophilic compounds particularly those whose molecules are completely surrounded by strongly hydrophilic groups e.g. Alizarine Cyanine and mannitol (cf. also ref. (4)). possible sizes and orientations of the postulated monolayer + solute complexes. Since this paper was submitted a more detailed study has been made of the The revised data for the predicted molecular areas now given in table 3 show that in each case (except VII and VIII as just discussed) the observed value is quite close to that predicted on the assumption of specific cross-bonding alone.Regarding our suggestion that compounds VI-VIII are bifunctional we may state that cyanines are regarded as resonance hybrids the charge in symmetrical compounds of the present type being distributed equally between the two nitrogen atoms. This being so it would appear that the only position they could reason- ably be expected to occupy in the film is one where the longest axis is parallel with the water surface. While the data seem to support the cross-bonding hypothesis it is admittedly difficult to decide which groups in these cyanine molecules can be responsible for bonding. We have here supposed that the nitrogen atoms form hydrogen bonds. The positive charge which they hold may make such a link impossible and the following alternatives may be suggested (i) electrostatic 1 Adam Askew and Pankhurst Proc.Roy. SOC. A 1939,170,485 ; Pankhurst ibid. 1942 179 393. * see my paper. GENERAL DISCUSSION 240 attraction of the cationic nitrogen atom for the weakly negative carbonyl oxygen of the acetyl group or (ii) hydrogen bonding between the latter and hydrogen attached to the carbon atoms of the methin chain (cf. the greater attraction for water known to be imparted to an alkyl chain by the insertion of a C=C double bond therein). This matter will be investigated further and surface potential measurements will also be carried out. Dr. K. G. A. Pankhurst (Brit. Leather Manuf. Rex. A m . ) said Since carrying out the work described in our paper Mr. A. F.Lanham and I have investigated the tanning of monolayers of a 33 % N-methyl-methoxy Nylon with mimosa tannin and have found a similar increase in surface viscosity to that obtained with collagen monolayers at pH values between 2 and 5. This supports our contention that tanning with phenolic vegetable tannins is essentially non-ionic. Dr. I(. H. Gustavson (Stockholm) said The drastic alteration of the character- istic properties of collagen monolayers by their interaction with tanning agents makes the technique of Ellis and Pankhurst a very sensitive indicator of tanning potency of a substance. It apparently also yields important theoretical informa- tion on systems of tanning as already noted in the researches of the Rideal school. The pronounced effect of mimosa tannin in solutions containing 1 mg tannin per 1.on the surface viscosity of the film is remarkable. It is interesting to find that the behaviour of basic chromium salts indicates that anionic groups of collagen are the sites for the fixation of the chromium complexes the reaction being ionic in its initial stage. It is aLso pleasing to note that the results from chrome tanning of collagen monolayers strikingly confirm the present concept of chrome tanning which has been developed for macro systems. As to the vegetable tannage the fixation of mimosa tannins is interpreted to be mainly a multipoint binding of the tannin molecule on collagen. At pH values above 3 evidence for dipolar (ionic) interaction between tannin and collagen is presented.Since mimosa tannins are usually employed in the natural pH range of the extract (PH 4-5-5.0) the participation of ionic protein groups in the ordinary mimosa tannage should not be disregarded in framing theoretical con- cepts. It should also be noted that in the unpublished electrophoretic investiga- tion of purified vegetable tannins by Danielson referred to by the authors solu- tions with the natural pH of the tannins were used i.e. for mimosa tannins a pH of 5.0. The experiments indicated that the negatively charged fraction was of lower molecular weight than the non-migrating main part of this tannin. A considerable part of the tannins of the hydrolyzable class such as tannic acid and valonea migrate in the electric field even in solutions of such low pH values as 3 and the fixation of these tannins occurs to a very marked extent by ionic protein groups as pointed out in the discussion of the dual nature of the vegetable tannage.Also in the work of Rideal and his co-workers the interaction of tannic acid with the cationic groups of monolayers of globular proteins and with amines has been proved conclusively. It is a pleasure to note that the authors justly credit Freudenberg with the concept of vegetable tannage as being the formation of co-ordinate compounds -an idea of thirty years’ standing. Actually prototypes of collagen + tannin compounds in the form of co-ordinated diketopiperazine (with the -CO . NH link) and polyphenols with the characteristic CO / . . HO( bond date back \ NH to Pfeiffer’s fundamental work on Mulekul- Verbindungen.This historical fact emphasizes the debt which we owe to the originators of the co-ordination concept (or hydrogen bond formation). / The authors’ finding that the monomers of benzoquinone and catechin are lacking in tanning potency is a fundamental contribution. It is proved that these substances first acquire this property upon polymerization. This is a GENERAL DISCUSSION 241 striking illustration of the requirement of multipoint attachment of tanning agents to different collagen chains (interchain cross-linking) and consequently in order to attain this cross-linking that the size of the molecule of the tanning agent the distribution of its reactive groups and the spatial conditions of the reacting protein groups of adjacent protein chains are the decisive factors.Once more I would like to sound a note of warning with regard to the trend of treating the tanning process as a hydrogen bonding process entirely assuming all vegetable tannins to behave alike and hence overlooking their chemical individuality. Dr. H. Phillips (Brit. Leather Manuf Res. Assn.) said We have argued about a definition of tanning and I suggested that it might be defined as covering those processes which were used to stabilize the collagen fibre (and other protein fibres) against the action of water and bacteria. But before collagen fibres in a hide or skin can be tanned the hair wool epi- dermis and the interfibrillary proteins must be removed to make the fibres more accessible to tannins.The processes used-soaking liming bating sometimes pickling-also help to decide what kind of collagen fibre the tanner will tan and hence the physical characteristics of the final leather. The value of the paper of Burton and Reed is that it stresses the importance of mucoids as substances which influence the physical state of collagen fibres. Collagen fibres as they exist in hides and skins are not such d e ~ t e entities as the single fibres of wool and cotton. They are bundles of fibres which can be split during the pretanning processes into fibres and into fibrils. The wool textile manufacturer when he wishes to make a soft handling fabric will choose fine wool fibres spin them into lightly twisted yarns and weave the yarns loosely into a fabric.On the other hand if he is manufacturing a fabric for hard wear and strength he will use coarser fibres and spin them into highly twisted yarns which he will weave into a compact fabric. In effect the tanner’s fibre bundles can be compared with the yarns of the textile manufacturer. The tanner has a very wide choice of skins containing “ yarns ” of various sizes and woven either loosely or compactly. By his pretanning processes he can alter the size of the individual fibrils in the fibre bundles. There is much evidence that mucoids or mucopolysaccharides are concerned in this breakdown of fibre bundles to fibres and of fibres to fibrils. On the other hand chemical evidence is lacking to support the view that hides and skins skins contain relatively large amounts of mucoids.Dr. Bowes has estimated the amounts present by determinations of the glucosamine content her results show about 1.0 % mucopolysaccharide 1 for the full thickness of fresh ox-hide and about 0.7 % for the middle corium split of the same ox-hide after extraction with sodium chloride solution. The mucoid content of the middle corium split was halved by liming. The close connection between some mucopolysaccharides and the molecular cohesion of collagen is indicated by the increase in water uptake produced by treatments which are known to extract polysaccharides from collagen. Both dyeing and tanning are concerned with the interaction of large molecules. The large molecules of fibres are linear molecules whilst those of the dyes and tannins are smaller molecules which may however be bulky.Generally speak- ing the linear molecules in all fibres are arranged with their long axes parallel to the length of the fibre. Because we dye and tan fibres both processes are concerned with diffusion and absorption. Technologically textile fibres are more often dyed after they have been spun into yarns and woven into fabrics. This increases the difficulties of the dyer. In the same manner the tanner is faced with a similar problem in a somewhat accentuated form since the fibres of hides and skins are interwoven in an intricate manner. 1 Bowes Research 1951 4 155. GENERAL DISCUSSION 242 From there on the similarity ends. It is true there are anionic tannins natural vegetable tannins with carboxyl groups such as myrabolam and chestnut and so-called syntans with sulphuric acid groups.There are also non-ionic tannins whose functional groups are entirely hydroxyl such as mimosa which was men- tioned in the discussion on Mr. Amstrong’s paper. But tannins cannot tan by combining with one linear molecule in the fibre; they must crosslink adjacent linear molecules and form what Dr. Pankhurst has described as multipoint attachments. The reason for this is that tanning is essentially a process by which collagen fibres are stabilized against the action of water and micro-organisms. The collagen fibre is a much more reactive fibre than any textile fibre. It will readily absorb many times its own weight of water even when neutral and will swell to many times its original size in alkaline and acid solutions.Tannins by cross-linking the polypeptide chains restrict their degree of hydration and their capacity to swell. In chrome tanning for instance there is much evidence as Dr. Gustavson has shown that when co-ordinate linkages are formed through chromium with carboxyl groups of adjacent poly- peptide chains the collagen becomes resistant even to boiling water. In order to attain this widespread cross-linking it is necessary that the tanning molecule should be large much larger than is necessary with dyestuffs. Very generally speaking tannins must have a molecular weight of about 2000. But tanning itself remains a mystery unless one realizes the amount of organic tannins that can penetrate the collagen fibre.A fully tanned collagen fibre can accommodate half its own weight of vegetable tannins. So that technologically speaking although tanning is the multipoint cross-linking of the linear molecules of the fibres by tannins-ither with co-ordinate linkages as with chrome tannins or hydrogen bonding and salt linkages with vegetable or organic tannins-there is this further build-up of tannin in the fibre which alters its physical properties besides making it resistant to water. The dyer uses the minimum amount of dye consistent with obtaining the coloration he desires. But the tanner varies the amount of tannin in the fibre depending on the physical characteristics of the leather he wishes to produce. When he is producing a flexible leather such as that needed for the uppers of shoes or for upholstery then he finds that when the fibres have absorbed half their own weight of tannin they are satisfactory for his purpose.There is much evidence that this amount of tannin is absorbed freely and that it corresponds to the amount of tannin needed to fill the less organized amorphous or less crystalline parts of the fibre. This is the type of tannage which is undertaken by what is known in the in- dustry as the light leather tanner. But there is another section of the industry- the heavy leather tanners manufacturing sole leather who consider their type of tannage so complex that they almost object to the light leather manufacturers calling themselves tanners. And the reason for this is that to make sole leather which should be firm and waterproof the collagen fibre must be made to absorb almost its own weight of tannin-ertainly more than half its own weight.Scientifically speaking this means that the molecular structure of the fibre must be made more accessible to tannins-in other words during tannage the more organized or more crystalline and therefore less accessible regions in the fibre must be opened up so that tannins can enter. This change must not be taken too far; the strength of even the tanned collagen fibre depends on the degree of cross-linking between the linear molecules of the more organized parts of the fibres. But strength is not essential for sole leather so that the heavy leather tanner finds he can break down part of the molecular structure and then fill it with tannin obtaining thereby a coarser or thicker fibre and hence a firmer leather.The methods he uses-weak acids and heat-are similar to the methods we should use in the laboratory to disperse and dissolve protein fibres. For many years it remained a mystery to the tanner himself because he did not know that certain CiENERAL DISCUSSION 243 vegetable tanning materials he used to produce this change contained weak acids and indeed he was of course unfamiliar with the nature of weak acids and of their action on fibrous protein. Essentially although on the molecular scale there are many similarities between dyeing and tanning I think it is evident that the modifications in the physical characteristics of fibres produced by tanning are more profound than those pro- duced by dyeing.Dr. K. H. Gustavson (Stockholm) said Before discussing Dr. Pouradier’s contribution on the chrome tanning of gelatin in aqueous solution it is a personal privilege to stress the originality of the researches of his group and their im- portance for the theory of the chrome tanning process. The fkst experimental evidence of the cross-linking of gelatin (collagen) by chromium salts proved by the increased mean molecular weight of gelatin was in fact given in the informative paper in Bull. SOC. Chim. 1952 19 928. The data and the discussion of that paper particularly concerning the effect of the concentration of the solution of gelatin on the relative importance of inter- and intra-chain cross-linking of the gelatin molecules by chromium complexes and the effect of the pH on the steric proved to molecules gelatin possibilities of great of the value in the interpretation for such of cross-linking the system collagen occur + have chromium already salts as already pointed out in a recent paper,l bearing on the uni- and multi- point fixation of chromium complexes by collagen.I am very anxious to state these facts in view of the omission of reference to the 1952 paper of the Pouradier group in the brief outline of the chrome fixation by collagen presented in my condensed contribution at this Discussion. In Pouradier’s paper it is shown that the viscosity of dilute solutions of gelatin (0.85 %) is diminished by the addition of chrome alum while an increase is found in chroming more concentrated solutions of gelatin.I should venture to say that the main reason for the decline in viscosity is probably due to the preponderance of unipointly attached cationic chromium complexes to the car- boxyl ions of gelatin in the dilute solutions which mode of combination lessens the number of electrostatic bridges between the peptide chains by partial discharge of its anionic sites. The hydroxo-chromium cations were found to be practically quantitatively fixed by means of single bonds to gelatin in rhe experiments with the basic chromium chloride presented in my paper. The increase in viscosity of the more concentrated solutions of gelatin resulting from the addition of chrome alum is probably due to and logically explained by the inter- chain cross-linking of gelatin by the chromium complexes the higher concentra- tion of gelatin facilitating inter-chain cross linking by the chromium complexes.The interpretation of the findings given by Dr. Pouradier is convincing and let me say without disparaging the originality of Dr. Pouradier’s deductions that his ideas are in harmony with the trend of thought with which I have long familiarized myself in investigating the interaction of chromium complexes with hide protein. Concluding with a question it would be of interest to know whether Dr. Pouradier has formed any opinion regarding the type of protein groups involved jn the chrome fixation by gelatin? Dr. J. Pouradier (Vincennes) (communicated) The theory which we have worked out to explain our observations is extended to gelatin subject to allowance for the factors inherent in that protein of the well-known work of Spiers and Dr.Gustavson. The chromium complexes fixed on a single carboxyl ion of gelatin certainly have a considerable effect on the physical and mechanical properties of tanned gelatin. We tried to take account of this in interpreting our results but in the absence of quantitative information we were reduced to making hypotheses. As Dr. Gustavson’s recent work has provided some extremely interesting facts about 1 Gustavson J. Amer. Leather Chem. ASSOC. 1953 48 559. GENERAL DISCUSSION 244 the relative proportions of the uni- and multi-point binding of chromium complexes we intend to continue our study.We have not yet been able to de;ermine with certainty the natuie of the gelatin groups capable of fixing chromium salts but probably they are the same groups as for collagen. In order to establish this however we are at present trying to establish the pK of the groups which come into the tanning with the variations in the chromium content of gelatins treated at different pH values up to the point of equilibrium. Dr. H. Phillips (Brit. Leather Manuf. Res. Axsn.) said Whilst it may be true that tannic acid is linked to the basic groups of collagen whereas non-ionic tannins such as mimosa may be linked through hydrogen bonds it should be are not. The collagen + tannic acid complex is therefore more easily broken remembered that tannic acid is highly hydroxylated whereas the mimosa tannins down by water than the collagen + mimosa complex which may tend to be hydro- phobic.Dr. K. H. Gustavson (Stockholm) said The important functions of the much- neglected constituents of skin the mucoids and related compounds in the unhairing of skin and for the physical properties of collagen and leather have been brought out in the important researches of Prof. Burton and Dr. Reed. The use of muco- lytic enzymes in the preparatory processing demonstrated by the authors is a decided technological advance and the further development of this natural method of unhairing and freeing the hide fibres from their restraint will be followed with great interest. Modern work on the unhairing problem has put undue stress on the keratolytic mode of unhairing which actually is an artificial method of removing hair and other epidermal matter by a more or less complete destruction of the keratin molecule.A few questions are provoked by their paper firstly I have long been puzzled by the fact that tendon collagen which has not a weave structure like corium of the skin but which is built up from parallelly alignzd fibres is not soluble in dilute solutions of weak organic acids while rat tail collagen is. It is contended that the presence of cementing layers of some mucoid component is the reason for the tendon not dissolving since pretreatment with mucolytic enzymes will make the tendon soluble in dilute organic acids. From the important investigations of Partridge concerning the state of combination of chondroitin sulphate with collagen in cartilage one is inclined to agree with Partridge that the chondroitin sulphate may act as a cross-linking agent on the collagen fibrils and fibres.And further that this type of compounds may have something to do with the orientation of collagen in the formation of connective tissue. The chondroitin sulphate should then react as a multifunctional anion cross-linking and orienting the fibrils into collagen macromolecules. In our own determin- ation of ester sulphate of bovine collagen in native and limed skins about the same amounts of ester sulphate jn such small quantities as equivalent to 0-02- 0.04 % S on a protein basis have been found.Perhaps Dr. Reed will have some views on this particular problem ? Secondly a question of a more practical importance it appears from the paper that the removal of the mucoid component from the skin by mucolytic enzymes in the preliminary processing should have a favourable effect on the subsequent processing particularly the tanning. Does the tannage of the mucolytic-treated skin proceed more smoothly and uniformly than that of ordinarily limed skin and is thereby the quality of the leather improved ? It should also be of interest to know whether skin which has been chrome-tanned after the removal of the mucoids resists the action of water after drying in “the b1ue”as is the case with regular chrome leather which is not wettable after being “ bone- dried ” in the non-fat liquored state.This question obviously has a bearing on the explanation given for the unique hydrophobic character of dried chrome leather i.e. whether this is due to the changes of the surface of the leather fibres GENERAL DISCUSSION 245 by the fixed chromium complexes or to the presence of fatty matter in the skin which forms non-wetting chromium soaps. Finally are there any data regarding the minimum amount of chromium required for producing a chrome leather stable to boiling water ? Prof. D. Burton (Leeds University) said Little is known as to the mechanism whereby chondroitin sulphate determines the stability of the chondroitin fibre structure. Much of the available evidence however indicates that the chondroitin sulphate is very firmly joined to the molecular chains of collagen and that if it is removed the cohesion of the molecular chains is profoundly modified.We have no definite information regarding Dr. Gustavson's second point concerning the effect of the removal of mucoid material on the water uptake of the dried leather. From the work so far carried out however we think that chromed pelt prepared by means of mucolytic enzymes wets back easily and in a most even manner. Dr. R. Reed (Leeds University) said Most mucoid materials are insoluble in the common organic solvents. They are however usually freely soluble in alkalis. Thus it is doubtful whether the epicuticle of the wool fibre would be modified in the manner suggested even if it is of a mucoid nature unless the scouring operation involves alkaline conditions.Dr. H. H. Sumner (I.C.I. Dyestufs Blackley) said I would like to ask Dr. Schroeder whether the authors have investigated the rate effects which occur in the dyeing of polyethylene terephthalate in the presence of carriers. We have I-' I FIG. 1.-Phenol as carrier. Dyebaths contain 025 g/l. Dispersol Fast Scarlet B 150 ; carrier concentration used in all cases 0.5 g/l. been concerned with this aspect because it was thought that both rate and equilibrium effects must be considered in order to obtain a complete understand- ing of the mechanism of carrier dyeing. It must be pointed out however that whilst the paper of Schuler and Remington deals with dyes in solution in the dye- bath our work has been carried out in the main using dispersions of dye because it appeared possible that carrier action is a result of having a dispersed system.The following is a brief account of those results which are relevant to this discussion. Fig. 1 shows rate of dyeing curves obtained for a dispersed dye with a soluble carrier in this case phenol the four curves shown being for (A) no carrier ; (B) carrier and dye in the dyebath i.e. both applied to the fibre simultaneously; GENERAL DISCUSSION 246 (C) fibre pretreated with and then dyed in the absence of a carrier; (D) fibre pretreated with and then dyed in the presence of carrier. The results shown by A and B are in accord with those described by the authors i.e. an increased rate of initial dyeing in the presence of carrier and a decrease in the amount of dye taken up for the longer times of dyeing.The rapid decrease in the slope of curve C must be due to the carrier diffusing out of the fibre. If the relative positions of the curves after 1 h are considered it appears that pretreatment with carrier is not advantageous. This is not the case when we consider an insoluble carrier such as diphenyl. The four curves in fig. 2 (in which it should be noted that the dye on fibre scale is 25 times greater than in fig. 1) are again the results of similar experiments A B C and D and here it is obvious that pretreatment of the fibre in carrier is ad- vantageous (C and D). Again the effect of carrier being removed from the fibre ---I FIG. 2.-Diphenyl as carrier.r Dyebaths contain 0.25 g/I. Dispersol Fast Scarlet B 150 ; carrier concentration used in all cases 0.5 g/l. is shown in curve C. It is only the initial rate of dyeing that is different in B and D and the slower rate of B must be due to the fact that there is no carrier in the fibre so that the rate of up-take of carrier by the fibre becomes one of the controlling factors. The relative action of soluble and insoluble carriers when they are applied in equal concentration is clearly shown by these results. Also it is evident that over normal dyeing times of approximately 1 h pretreatrncnt of the fibre in carrier is beneficial for insoluble carriers but of doubtful value for soluble carriers. It must therefore be concluded that an effective carrier must be capable of being taken up by the fibre and that for maximum effect on the initial rate of dyeing when carrier and dye are applied together this process must be rapid.Dr. M. J. Schuler and Dr. W. R. Remington (du Pont de Nemours Co. Dela- ware) (communicated) Data for sorption of the dycs 1 -amino-4-hydroxyan thra- quinone and 1 4-dihydroxyanthraquinone from binary mixtures yieldcd linear isotherms but at saturation the conccntration of each dye in solution in both fibre and H20 was less than when either dye was used alone. The solubilities were not additive. The tentative explanation of ‘‘ interaction ” was offered for this behaviour. Further experiments have demonstrated that these dyes form solid solutions (mixed crystals) with one another over the complete composition range; the GENERAL DISCUSSION 247 activities of the dyes in the saturated aqueous solution vary with the composition of the solid phase.The solubility data reported in the paper are in excellent agreement with those obtained with the mixed crystals. .Therefore there is no need to postulate " interaction " between dyes in the fibre. Dr. D. Patterson (I.C.I. Ltd. Welwyn Garden City) said The suggestion by Schuler and Remington 1 that the solution of dispersed dyes in polyethylene terephthalate is non-ideal and that there is a possibility of hydrogen bonding between dye and substrate is borne out by the following experiments in which the dye Dispersol Fast Scarlet B was used. Amorphous film was given a low temperature surface dyeing and then drawn on a continuous drawing machine so that its length was increased by known ratios UP to 4.5 times its original length.Optical densities at the peak of the absorption curve of the dye were then measured using light plane polarized first parallel and then perpendicular to the direction of stretch. The dichroic ratio increases with the degree of stretching as shown in the figure. The dye molecdes are 1 I I I I 1.4 ' FIG. 1 .-The orientation of Dispersol Fast Scarlet 3 in polyethylene terephthalate film. constrained to follow the straightening of the long chain molecules of the poly- ethylene terephthalate which occurs in the drawing process. This could be brought about by hydrogen bonding or simply by mechanical entanglement but it is clear that there is marked orientation of the dye molecules with their long axes parallel to the polymer molecule chains.It is therefore not surprising that the solution is non-ideal. Dr. C. H. Bamford (Courtaulds Lrd. Maidenhead) said I should like to comment on Dr. Patterson's conclusion based on measurements of the dichroism of dyes adsorbed on polyethylene terephthalate that some dyes can be strongly bound to the polymer chains. Additional valuable information might be ob- tained if simultaneous measurements of dye and fibre orientations could be made. Observation of the dichroism of a suitable infra-red band e.g. that corresponding to the CO stretching vibration might be suitable for estimating the mean fibre orientation. If during the extension of the polymer film the dye orientation were found to lag significantly behind the orientation of the fibre the conclusion could be drawn that the crystallization of the polymer tends to squeeze out dye molecules into the (less oriented) amorphous regions.On the other hand if the dye is attached sufficiently strongly it may be expected to show comparable orientation to that in the fibre. Could Dr. Patterson say whether any observations of this kind have been made ? Dr. D. Patterson (I. C.I. Plastics Welwyn) (partly communicated) In reply to Dr. Bamford no infra-red examination of the films was possible owing to their thickness but density and birefringence have been measured and X-ray analysis 1 this Discussion. GENERAL DISCUSSION 248 carried out.The orientation measured by these methods does not increase steadily with increased drawing as does the dichroism shown by the dye. Instead at draw ratios above 2-5 there is a marked increase in both density and birefring- ence and the X-ray photographs reveal the onset1of crystallization. The reason for this is that the overall orientation is being measured and density and bire- fringence are much more sensitive to the (strain-induced) crystallization than to the increase in order in the amorphous regions. It seems possible that in the same way the infra-red dichroism of the CO stretching vibration would measure the orientation of both crystalline and amorphous regions and show a similar dependence on draw ratio. This view is confirmed in a private communication from Miller who has already used infra- red dichroism methods in a similar connection.1 The suggestion that the migration of dyes from crystalline to amorphous regions might be shown by an independent measure of orientation does not seem likely to be fulfilled in view of these complications.Further in the dyed portions of the films there is about one dye molecule for each polymer chain and since the latter are so much the larger the chances would seem to be that the polymer chains could pass through crystalline regions without requiring a shift in the point of attachment of the dye molecules. The evidence points to the dichroism of the dye molecules being a measure of the orientation of the amorphous regions independent of that of the crystalline parts.An examination of the infra-red absorption of the dyestuff rather than the polymer however might throw light on the method of their mutual attachment. Dr. T. Vickerstaff (I.C.I. DyestuB Blackley) said One possible mechanism by which carriers may promote the dyeing of polyester fibre is by adsorption on the polymer chains to reduce intermolecular cohesion and so reduce the activation energy required for dye diffusion. This molecular lubrication might be revealed by a reduction in the rigidity of fibres and some recent measurements support this view as shown below treatment flexural rigidity (g cm2) 1.096 X 10-2 untreated fibre treated in blank aqueous dyebath treated in dyebath with 6 % diphenyl treated in dyebath with 6 % phenylphenol 0789 x 10-2 1.068 X 10-2 0*800 x 10-2 Dr.C. H. Giles (Royal Tech. Cull. Glasgow) said As already stated (see comment on paper by Bird et al.) a straight line isotherm may not be inconsistent with specific attraction between substrate and dye. It may be significant that both the substrate and the solutes used in the paper of Schuler and Remington contain benzene nuclei. It is well known that such nuclei associate together closely in parallel e.g. in monolayers on water and we may therefore assume that when carriers or dyr;J are applied to polyethylene terephthalate their aromatic nuclei associate in this way with those of the substrate. If this is so then we should not expect aromatic compounds to act as carriers for fibres devoid of aromatic nuclei e.g.cellulose acetate or Nylon. Neither should aliphatic com- pounds act as carriers with polyethylene terephthalate. Perhaps also the intro- duction of bulky non-hydrogen bonding substituents into the aromatic nuclei of carriers or dyes would reduce their affinity for this substrate by preventing close packing. The solid solution mechanism of sorption of solutes by polyethylene tereph- thalate suggested by the authors may therefore be tentatively interpreted as association between aromatic nuclei in solute and substrate coupled with hydrogen bonding where suitable groups are present in the solute. The hydrogen 1 Miller and Willis,:Trans. Faraday Soc. 1953 49 433. GENERAL DISCUSSION bonding may involve the methylene groups in the substrate as suggested in the paper by Allingham et aI.24 9 Dr. M. J. Schlaler and Dr. W. R. Remington (du Pont de Nemours Co. Delaware) (communicated) We thank Dr. Giles for his suggestion regarding the possible " association between aromatic nuclei in solute and substrate ',. This suggestion might be checked using model compounds such as dimethyl terephthalate with phenol aniline and dimethylaniline. For association or n complex formation there would be a marked change in the absorption spectrum. of sorption of dyes ". We would like to clarify this point. The mechanism Dr. Giles also attributes to us the suggestion of" the solid solution mechanism of dyeing proposed is one of solution of dyes in the fibre probably in the amorphous rcgions. We do not wish to suggest that " solid solution " or " mixed crystal " formation takes place.Dr. €3. Zollinger (Basle University) said I would contribute two remarks to the dyeing mechanism in the presence of Cu-t- ions. The first remark supports the view of Dr. Schroeder that cationic complexcs containing the Cu-t- ion act as sites for fixation of dye anions. Field and Fremon 1 already mentioned that other mctal ions will also be adsorbed. In thc course of investigations made in the laboratories of Ciba Ltd. with the purpose of overcoming some practical disadvantages of the copper method we extended the work of Field and Fremon to a series of 22 metal salts. All of these salts were adsorbed more or less part of them to a much higher extent than copper. With respect to the correlation with Dr.Schroeder's mechanism there is the interesting fact that polyacrylonitrile fibres (Orlon 41) treated with anionic Cr3-c salts (e.g. by treatment with sodium dichromate and reduction by the Bucherer process2) have a lower affinity for a simple acidic azo dyestuff namely Kiton Fast Orange G than fibres which have not been treated at all. Under standard conditions thc relation was approximately as follows (arbitrary units) Orlon 41 treated by the copper process Orlon 41 untreated Orlon 41 treated with anionic Cr Orlon 41 untreated Orlon 41 + o-phenylphenol OrIon 41 I- CuSO4 + NH2OH 1.0 0.01 The fact that " anionized polyacrylonitrile " has a lower affinity is in agreement with Dr. Schroeder's paper. The second remark concerns a point which in my opinion must be considered in this dyeing process i s .the swelling of polyacrylonitrile fibres when treated with monovalent copper salts. As is well known carriers like benzoic acid phenylphcnol etc. promote the up-take of dyestuffs. At the same time the amor- phous regions of the fibres swell. We estimated this swelling by measuring the decrease of the refractive index of these fibres using polarized light.3 We obtained the following values 0.05 nD" (11) 1 -509 ca. 1.505 "D' (1) 1.510 1.509 1.505 (expcrimcntal error ca. 0.001) This shows that copper ions have an unexpectedly large swelling effect. Although it has been pointed out in the discussion on the polyethylene terephthal- ate paper that it is difficult to prove definitely a correlation between swelling and dyeing affinity of such fibres this effect has to be considered in my opinion as well as the pure ionic exchange mechanism.1 Field and Fremon J. Text. Res. 1951 21 536 table 8. 2 D.R.P. 587,361. 3Lunpublished measurements of H. Labhart Physics Laboratory Ciba Ltd. Basle. 1.509 GENERAL DISCUSSION 250 Dr. P. Mares (Aberdeen) said It would be interesting to know from Dr. Schroeder whether the 2-vinylpyridine copolymerized with the acrylonitrile may have contained a minor quantity of 4-vinylpyridine. Fuoss has shown that the nitrogen atoms in poly4vinylpyridine are more readily available for quaterniza- tion with alkyl halides than are those in poly-2-vinylpyridine. Mr.Mackie of this department has found that this is true to an even more marked extent in the quaternization of copolymers of 2- and 4-vinylpyridines with styrene containing about 5 % of the former. The presence of a few 4vinylpyridine units among the 2-vinylpyridine units in the copolymers with acrylonitrile would tively small number of highly affinitive basic sites ". therefore provide a possible interpretation of the suggested existence of " a rela- Dr. T. Vickerstaff and Dr. J. Simons (I.C.I. DyestuB Blackley) (communicated) If we regard dyeing as a displacement of chloride by dye ions it is possible to calculate the affinity of the dye ion relative to the chloride ion at the three pH values used in the work of Blaker et al. The concentrations of dye in the fibre and in solution ([DF] and [Ds]) can be read off fig.1 of Dr. Schroeder's paper while the concentration of chloride ions [CIS] in the solution is assumed equal to that initially present. The concentra- tion of chloride ions in the fibre [Cl,] can be derived from his fig. 2 (= AP) al- though there is clearly an error in the lowest of the three lines which does not pass through the experimental points. The results obtained in this way for four points on each isotherm are as follows 2510 2420 2260 2070 1540 2280 2430 1530 2610 2500 1950 1810 1800 2220 1790 1930 1.04 1.5 1 2-3 1 2-31* The relative values at pH 2.31 are calculated for the line shown in the figure while the values at pH 2.3 1 * have been derived for a line through the experimental points.These results are necessarily approximate by virtue of their graphical derivation but show no evidence of sites of differing affinity for dye ions. Dr. M. J. Schuler and DP. W. R. Remington (du Pont de Nemours Co. Dela- ware) (communicated) We are grateful to Dr. Vickerstaff and Dr. Simons for showing that our data support our hypothesis that for the displacement of chloride by dye ions " . . . all cationic centres " are as stated in the paper " equivalent . . .". Using our data they have shown that This is equivalent to our equation (14) which we had regarded only as a logical assumption. However we wish to reemphasize that this discussion of the ion-exchange reaction of the protonated fibre has no bearing on the number of different types of sites in the unprotonated fibre ; it implies only that onceprotonated all pyridine nuclei behave alike.It carries no implication regarding the identity of un- protonated pyridine nuclei. As we have shown (cf. table 3) our results are best accounted for by two types of sites 6 % of the sites being 96 times as basic as the remainder. A number of reasonable possibilities can be advanced to explain this difference in basic character beside those already mentioned in the paper. Thus the steric situation of the basic pyridine nuclei might be particularly important. GENERAL DISCUSSION 25 1 In this connection Dr. Meares has made a very plausible suggestion that a low concentration of 4-vinyl isomer in the vinyl pyridine might account for the more amitive or more basic sites.Any 4-isomer would place a basic centre farther from the main polymer chain where it would be more available for reaction. The 2-vinyl pyridine used in these studies actually contained too little probably less than 1 % of the 4-isomer to explain completely the difference in basicity validity . in the fibre. For the present we believe the other explanations are of equal c. H . BAMFORD J. BOULTON w. E . HANBY AND J. s. WARD 229 GENERAL DISCUSSION Dr. H. Zollinger (Bade University) (communicated) I think that the ad-vantages of Dr. Robinson’s models are their usefulness for sterically strained molecules. Dr. Robinson demonstrated a model of Caledon Jade Green (his fig. 54 in which one of the methoxy groups was left out.If we put both methoxy groups on the dibenzanthrone nucleus one recognizes that only 4 or 5 of the 34 aromatic carbon atoms are distorted out of the plane. In spite of this distortion the model fits well on the cellulose chain. This explains why Caledon Jade Green has not a lower substantivity than the unsubstituted dibenzanthrone dyestuff. On the other hand I think that we should not forget that very detailed spatial problems cannot be soIved with any model. Dr. C. H. Bamford (Courtaulds Ltd. Maidenhead) said Dr. Robinson has mentioned the “ hydrogen bond ” and “ conjugation ” hypotheses which have been put forward to account for substantivity. Further advances in our under-standing of this complex subject seem most likely to result from work on model systems in which specific interactions may be studied.As an example one may cite the interaction between hydroxyl groups and aromatic or unsaturate 230 GENERAL DISCUSSION hydrocarbons ; the experimental evidence described below suggests that this should be considered as a possible factor contributing to substantivity. As long ago as 1940 Badger 1 pointed out that benzene “ appears to exhibit an interaction with proton donor substances which may probably be described as the formation of a weak hydrogen bond”. In a more recent paper Jones and Badger2 have made observations on the frequency of the third harmonic OH band of methanol in a number of solvents and have concluded that in aromatic liquids a frequency shift occurs which is of the order of magnitude found when a hydrogen bond is formed between two oxygen atoms.This is taken to indicate the formation through the hydroxyl hydrogen of a hydrogen bond of moderate strength between the alcohol and hydrocarbon. Somewhat similar conclusions have been reached by Mecke.3 From the two papers by Badger a value of 2-3 kcal for the energy of the hydrogen bond between methanol and benzene may be estimated. Stronger bonds can be formed with suitably substituted or more extensive conjugated systems e.g. the bond energy in the methanol + mesitylene system appears to be about 4 kcal. Dye molecules might be expected to behave similarly. The precise nature of the intermolecular bond in these complexes is uncertain. It may result from the interaction of the H atom of the OH group with the n electrons of the aromatic system (or double bond) i.e.in Mulliken’s terminology the complex would be of the (hUkou) type. This appears to be Mecke’s view.3 On the other hand Mulliken4 does not favour the idea of a dative complex but suggests weak hydrogen bonding between the H atom and the “ somewhat negatively charged carbons of the benzene ring ”. Models show that a dye molecule may be placed on a cellulose chain in such a way that a considerable number of suitable contacts with hydroxyl groups may be obtained. The net contribution to substantivity is however always determined by competing interactions; in this case the competition is between water mole-cules and the conjugated system for the hydroxyl groups of the cellulose. The results of this cannot be calculated at present with any certainty because the relevant hydrogen bond energies are not known sufficiently accurately.How-ever consideration of the current values suggests that a net contribution towards the binding energy between the dye and substrate of the order of 1 kcal from each contact is within the range of possibilities. The entropy change accompanying the displacement of several water molecules from a cellulose chain by a dye molecule will also favour attachment of the dye although of course it will not contribute to the measured heat of dyeing. It is known that the absorption spectra of dyes frequently change on ad-sorption. This is consistent with but of course does not establish the presence of interactions of the type discussed.Dr. A. S . Dunn (Brit. Rayon Rex. Assn. Manchester) said Data bearing on the substantivating properties of the amide group can be derived froin studies of the sorption by cellulose of naphthols which have the structure X’ These molecules have but a single group the amide group capable of taking part in hydrogen bond formation. The introduction of substituents X Y increases the substantivity of naphthols there is an increase in the heat of dyeing and, 1 Badger J. Chem. Physics 1940 8 288. 2 Jones and Badger J. Amer. Chem. SOC. 1951 73 3132. 3 Mecke Faraday Suc. Discussions 1950 9 161. 4 Mulliken J. Physic. Chem. 1952 56 801 GENERAL DISCUSSION 23 I presumably in the- strength of any hydrogen bond formed though this bond strength cannot be estimated in the absence of further data on cellulosc -I- water, dye + water and dye + dye interaction.The heats of dyeing have been derived from the adsorption isotherms determined in the absence of salt and surface-active agents at 25" and 50". HEATS FREE ENERGIES AND ENTROPIES OF SORPTION OF NAPHTHOLS - AS" substituent X Y - AH" slopc of ionic -AGO kcal/mole product plot cal/molc cal/deg. mole Brenthol -AS - - 5-6 0.75 3100 8.4 OT CH3 - 6.6 1.0 3240 11.3 FR CH3O - 7.4 0.89 3330 13-7 PA - CH30 7.9 0.81 3490 14.8 Affinities and entropies of dyeing have been deduced by applying the Peters-Vickerstaff theory. Variation of the concentration of excess sodium hydroxide between 0.015 N and 0.035 N produces no change in the equilibrium absorption of Brenthol AS on viscose model filament.Neale 1 has measured the uptake of sodium hydroxide by cellulose. When the affinity is calculated using values for the sodium concentration in the fibre derived from Ncale's data it is found not to vary with sodium hydroxide concentration. However the slopes of plots of the logarithm of the ionic product in the fibre against the ionic product in solution do not have the theoretical value of unity and do not increase with temperature. Hence it is doubtful whether the theory may be properly applicd. The entropy of dyeing is not constant as might have been expected if binding of the dye to the cellulose takes place through a hydrogen bonding mechanism exclusively in fact the entropy increases linearly with the heat of dyeing. Of the nine direct dyes for which heats and entropies of dyeing have been evaluated, five are related by the same linear expression AH = 0.38 AS + 2.3.Linear relations of this kind may be general especially among series of related reactions.2 If as seems likely the binding of dyes to cellulose is not to be at-tributed to interaction of a single type such as hydrogen bonding but is due to the co-operation of several intermolecular forces compliancc with or deviation from a relation of this type may indicate identity or alteration in the contributions of the various forces acting. Dr. H. E. Nursten (Nottingham and District Tech. Coll.) said Amongst direct cotton dyes the class consisting of derivatives of benzidine tolidinc and di-anisidine is preeminent. When Paine and Rose 3 state that in many dyes the distance between groups capable of taking part in hydrogen-bond formation is 10.8 A they are presumably referring to this class.I confirmed this distance from drawings using essentially Pauling's covalent radii and valency angles and assuming the molecules to be perfectly planar. It is not surprising that as the repeat of a cellulose chain occurs at 10*3& the nearness of these two figures was considered very suggestive. However Paine and Rose found that for the second most important class of direct cotton dyes the straight-chain polyazo compounds the spacing of azo groups occurred at 7.5A. I find this distance to be 6.5& though the distance between the extreme nitrogen atoms in an all-trans azo-benzene-azo group is 7.3 A.It can be shown that in an all-trans trisazo dye containing J-acid as end-component (a very common feature) the distance between the first azo group and 1 Neale Shirley Inst. Mem. 1931 10 1. 2 Evans and Polanyi Truns. Furuduy SOC. 1936,32 1333. 3 Vickerstaff The Physical Chemistry :of Dyeing (Oliver and Boyd London 1950), p. 164 232 GENERAL DISCUSSION the amino group of the J-acid is in the region of 20-21 A i.e. equivalent to two repeats of the cellulose chain. In primary disazo dyes using carbonyl-J-acid as middle component the distance between an azo group and the imide-nitrogen farthest from it is 10.3 A. In 4 4'-diaminodiphenylurea the amino groups are 12.8 8 apart and dyes derived from it therefore contain no such distance as 10.3 A. On examination of a drawing of the stilbene derivative Chrysophenine G (Colour Index no.365) I confirm Dr. H. Zollinger's findings namely that there is no distance of 10-11 8 between groups capable of taking part in hydrogen bonds. The distance between oxygen atoms is 24-7A assuming that the azo and ethylene groups in the traizs-form themselves are cis to one another and the distance between amino groups in 4 4'-diaminostilbene is 12.1 A. Thiazole derivatives form another class of direct dyes. In dehydrothio-p-toluidinc the distanccs between the amino-nitrogen and the cyclic nitrogen and sulphur atoms are about 6-7A. In Chlorophenine (Colour Index no. 814) there is no distance between groups able to participate in hydrogen bonds which lies near lO-llW and in Primuline (Colour Index no.812) the nearest distance is about 11 A being that between a sulphur atom and the amino group in the form in which the two thiazole rings are cis to one another. It is doubtful whether sulphur can act as a hydrogen acceptor. Although I have not examined all classes of dyestuffs which show affinity for cellulose fibres I have mentioned most of the important ones and it does appear from such a consideration that a distance of 10-11 A between groups able to accept or donate hydrogen is of no particular significance. It is therefore gratifying to find that Dr. C. Robinson has shown by means of his very welcome models that the surface of the celIulose chain is such that hydrogen bonding by means of one or other hydroxyl group can occur at any position along its length and that therefore the repeat of 10.3 A is unlikely to be of importance.Naturally, these remarks have no bearing on the question of whether hydrogen bonding does or does not take place between the dye and the cellulose during the process of dyeing. Dr. K. H. Gustavson (Stockholm) (contributed) said According to the findings reported the absence of heat of reaction in the binding of the sulpho-acid dyestuff, Naphthalene Orange G by the amino acids which form the cationic sites in proteins i.e. the lysine and arginine should imply that the heat of reaction about - 9 kcal/mole obtained for the system wool + colour acid is not due to a partial discharge of the cationic protein groups by the sulpho-acid anions. In reading the interesting paper by Derbyshire and Marshall the figures of table 3 with the exceptionally large heat change obtained by mixing arginine hydrochloride with the colour acid was noted with satisfaction which however, declined upon consulting table 4 with the corrected arginine value.This subject interests me greatly because the AH values of reactions between collagen and polyacids form the basis for attempted estimation of the number of the cationic groups of collagen which are directly involved and discharged in the irreversible binding of polyvalent aromatic anions by collagen such as for instance poly-sulphonic acids of synthetic tannins and various fractions of lignosulphonic acids. In these attempts to apply thermodynamics to the collagen systems the lucid text of Dr. Vickerstaff has been very helpful.Since Dr. Vickerstaff is present, and the paper under consideration emanates from his laboratory I should like to ask him if the corrections applied to the reaction of arginine with the colour acid are valid and further whether he would support the following approach to the system collagen + solutions of polyacids. From the titration curves obtained at lo" 20" and 30" C the concentration of the solutions of the polyacid in equilibrium with the same amount of acid in the fibre at two of the temperatures given were noted. The values were inserted in the Clapeyron equation and thus the values of AH were obtained. With du GENERAL DISCUSSION 23 3 consideration of the fact that the complete discharge of the cationic protein groups by hydroxyl ions (-NH3 -f -NH2) involves AH values of the order of - 12 to - 14 kcal/mole whereas the AH values obtained for the maximum fixa-tion of the sulpho acids amounted to about -6 kcal/equiv.correcting for the AH value of the carboxyl ions of collagen (HCl) it was inferred that about half of the total number of the cationic groups of collagen had been inactivated and discharged by the sulphonic acid groups of the polyvalent anions attached to collagen. Accordingly this method rests on the assumption that the changes in the heat of reaction are due chiefly to alterations in the thermodynamic state of the basic protein groups. The corrected value for the AH of the reaction between arginine and colour acid will apparently invalidate this assumption. By anion exchange between esterified (methylated) collagen (isoelectric at pH - lo) with all its cationic groups compensated by C1 ions and anions of the polysulphonic acids it was also found that only about one-half of the total number of Cl ions were exchanged for sulphonic acid anions at the point of maximum fixation of the sulpho-acids.It is to be noted that only a partial dis-placement of the anions of the sulpho-acids studied was obtained upon repeated extraction with 2 M sodium chloride indicating a high degree of irreversibility of the binding. Mr. A. N . Derbyshire (I.C.I. Dyestufi Blackley) (communicated) In reply to Dr. Gustavson the correction applied to the measured heat of reaction between dye acid and arginine hydrochloride is not rigidly valid since the binding forces in the solid complex will not necessarily be the same as in the solid constituents.However the greater part of the correction is due to the heat of precipitation of the dye whose large hydrophobic surface will in aqueous solution cause scparation of water molccules against their mutual attraction. This contribution will persist in whatever form the dye is precipitated. We believe that the correction leads to a reasonable approximation for the heat of interaction of dye with arginine. It should also be noted that the heat changes on mixing dye and arginine in ncutral solution at concentrations below the point at which precipitation occurs are very small in agreement with the corrected figure from acid solution. Dr. Gustavson’s work with sulphonic acids on collagen is very interesting.Our work shows that there is specific interaction between dye anions and guanidine groups but not with free amino groups. If this is characteristic of sulphonic acids it would explain his finding that only one half of the chloride ions in methylated collagen were displaced by sulphonic acid in agreement with analysis showing about one-half of the basic groups of collagen to be guanidine. I t is suggested that the measured heat of adsorption of - 6 kcal/g equiv. consists of the heat of interaction together with the heat change accompanying the transfcr of the acid from aqueous medium to the collagen phase. The postulated reaction NH3+ -I- OH- -+ NH2 + H20 involving the heat of formation of water from its ions appears unlikely to occur in a reaction of this kind.Dr. C. H. Giles (Royal Tech. Coll. Glasgow) (communicated) The results of Derbyshire and Marshall while interesting and important in themselves do not necessarily disprove that the peptide groups in proteins may be bound to dye molecules by hydrogen bonds. If the anionic group of the dye is associated with the cationic group of the dipeptide then it is not possible for steric reasons for the peptide group of the latter to form a bond simultaneously with the azo group of the dye. Mr. W. J . Marshall (I.C.I. Dyestufi Blackley) (communicated) In reply to Dr. Giles in aqueous solutions the reaction between hydrochloric acid and amino acids is entirely due to the latter combining with the hydrogen ion C1- being completely dissociated as in dilute solution of salts.If association of the dye with the peptide linkage did tend to occur there is no reason why the anionic group of the dye should be associated with the cationic group of the same dipeptide. 4 234 GENERAL DISCUSSION The question of steric effects therefore does not arise. In our experiments we could not detect any heat change due to this type of interaction. Dr. G. A. Gilbert (Birmingham University) said Meggy is considering a very important property of dyes in his paper since although the relation between dye activity and dye concentration is basic to any theory of dyeing lack of data has almost always made it necessary to equate activity in solution with conccntration. In the present case of Orange I1 (sulphanilic acid -> p-naphthol C.I.151) Meggy shows that the dye is of the order of a thousand times less soluble at 25" in N NaCl than would be expected from its solubility in pure water and that therefore for saturated solutions of this dye under these conditions this assumption is quite untenable. In explanation Meggy suggests that the increase of activity co-efficient which this decrease in solubility implies is in line with the fact that in general electrolytes increase thc activity of organic substances in aqucous solu-tions. Howcver such general considerations which led to the introduction of the " salting-out " term in the Debye-Huckel equations and which have been tested for various organic substances,l can account for only an insignificant part of the ob-served increase of activity coefficient.(It may be remarked further that over the range of NaCl concentration 0.0 to 0.05 N the ionic strength as calculated from the sum of the dye and NaCl concentrations is actually decreasing as NaCl is increased.) A more likely explanation is that the ions of the dye are aggregated in solution, and that the degree of their aggregation is strongly dependent on conccntration. By adding the common ion Na+ as NaCl or Na2S04 to the saturated solution of the dye the solubility of the dye is decreased and dissociation of the aggregatcs is favoured with a consequent increase of activity coefficient. This effect would not be found in any but a saturated solution of dye where the expected tendency of the added electrolyte to encourage dye aggregation is completely outweighed by the opposite effect of decrease of dye concentration.It is possible to find support for this explanation by working out what should happen when NaCl is added to the saturated solution of the sodium salt of a hypothetical dye chosen to have the property of aggregating in solution to form, predominantly aggregates containing four dye ions D4 in equilibrium with single ions D. It may be assumed that the formation of these aggregates is governed by the law of mass action according to the equation [D]4/[D4] = Kd and that the solubility of the sodium salt of the dye is governed by the equation [Na][D]=Ks. It will be assumed further that activities may be replaced by molar concentrations. Inspection of the results of Meggy leads to the choice of 4.65 x 10-13 for the value of Kcr and 7.1 x 10-5 for Ks.Using these figures the solubility ( p 4 ] + [D]) of the dye has been calculated as a function of "a+] and hence of added salt. The result of this calculation is shown by the line in the figure in which the logarithm of the dye concentration (expressed in mole of single ions) of the saturated solution has been plotted against the logarithm of the Na ion concentrations. On the same figure are plotted the experimental results of Meggy for Orange 11. There is clearly a correlation between the behaviour of the hypothetical dye and of the real dye over a considerable range of salt concentration and hence support of the hypothesis of aggregation but no correlation at low salt concentra-tion. In the latter region however the concentration of dye and of Na ion are both falling (the concentration of Na ion being of course equal to the sum of the concentrations of dye and added electrolyte).I believe that this can happen only if true equilibrium has not been attained and if the first additions of salt are removing supersaturation or precipitating a suspendcd colloid. True equi-librium seems to begin at about 0.1 N salt and by analogy with the hypothetical dye the real solubility of the pure dye might be guessed to be about 0.11 M. 1 Harned and Owen The Physical Chemistry of Electrolytic Solutions 2nd cd. (Rein-hold Publishing Corp. N. York 1950) pp. 51 and 397 GENERAL DISCUSSION 235 The solubility of Orange I1 at 60" in N NaCl calls for a remark. Meggy finds an increase of nearly 4,000 times over the interval 25-60'.This extraordinarily high temperature coefficient of solubility is the clearest possible indication of an increase of aggregation with rise of temperature of the saturated solution. From being comparatively unaggregated at 25" in N NaCl the solution must become highly aggregated and have a correspondingly low activity coefficient at 60". Once again of two opposing tendencies this time the disaggregating effect of rise of temperature and the aggregating effect of increase of concentration the influence of concentration predominates provided saturated solutions are being considered. The distribution of dye between amyl alcohol and water is difficult to discuss without information about the state of the dye in the alcohol. It is possible to say however that the hypothetical dye above if present in solution in the alcohol as simple undissociated molecules of its sodium salt would have a distribution coefficient which would increase rapidly in favour of the aqueous layer as the dye concentration increased.For example at a constant concentration of sodium ion the coefficient cw/cA would have for the respective concentrations of dye of I - 1 FIG. I.-Salting out of Orange IT by NaCl and Na2S04 at 25". 0 NaCI. >.( Na2SO4. - theory. 10-5 10-4 10-3 and 10-2 M the relative values of 1.0 1.3,5 and 27 figures which agree quite well with the trend shown in the paper for Orange 11. In conclusion it must be stressed that the properties of the hypothetical dye have been chosen only to make possible a simple demonstration.At the same time it seems likely that further experiments based on the valuable methods that Meggy has initiated will greatly help the discovery of the actual degrees of aggrega-tion heats of solution and of aggregation etc. of real dyes. Dr. A. €3. Meggy (Lpeds University) said Dr. Gilbert's suggestion is a very interesting one. If it is correct the change in the activity of Orange I1 should be less in CaC12 solutions than it is in NaCl or NaZS04 as the solubility of the calcium salt i s much less than that of the sodium salt. I think it is necessary to be cautious in applying the results of the Debye-Huckel theory to dye solutions. Dye ions are large in size highly symmetric and have a considerable area of water-hydrocarbon interface ; a change in the surface energy at this interface will greatly modify their activity quite apart from any electrical influences on the charged -SO3- groups.Prof. W. Bradley (University of Leeds) said Although it was intended to limit the scope of our paper to a demonstration that quite a number of derivative 236 GENERAL DISCUSSION of mandelic acid can be resolved on wool and hence that the corresponding anions are present in some degree in the form of typical ammonium-salt groups, the paper contains one experiment which suggests that the majority of the mandelate anions are bound in the same manner at ammonium sites. When wool combined with (&)-mandelic acid is immersed in water transfer of the acid from wool to medium occurs almost completely within a few minutes if the relative amount of water is large.If however the acid combined with the wool is (-)-mandelic acid and the aqueous medium contains (A)-mandelic acid at an appropriate concen-tration the exchange of (+)-anions for (-)-anions on the fibre occurs very slowly indeed. We interpret this result as meaning that the loss of acid from wool com-bined with mandelic acid is the result of two rapid but consecutivc reactions. First protons leave then anions as a negative charge accumulates on the fibre. Wool combined with (-)-mandelic acid when immersed in aqueous (&)-mandelic acid cannot undergo rapid loss of the (-)-acid for the reason that the essential first stage of reaction the loss of protons cannot take place. Even so it remzins remarkable that the rate of exchange of anions is so low and the result is difficult to understand if the (-)-anions are merely present in solution or absorbed on a surface.On the other hand the result is feasible if the anions are bound more intimately at positively charged (ammonium) sites. Dr. G. D. Coumoulos (Nat. Tech. University, Athens) said The final dyeing effect i.e. the formation of a system “ dyeing molecule-substrate fibre” may be due as pointed out in different papers to different reasons adsorption absorp-tion solubility salt formation diffusion etc. The dyer is of course interested that the final effect should be a non-reversible one. While in all papers the dye is considered as a molecular unit the reference to the substrate is made to the fibre being of the ultimate size.At this point it should be pointed out that the fibre is built-up from natural or artificial polymer mole-cules aligned in the general direction of the axis of the fibre. It is now well known that the state of these macro-molecular units in the fibre varies from completely amorphous to crystalline with all the possible intermediate states. Even the amorphous state may have regions where a certain degree of orientation persists.1 Both the crystalline and the amorphous regions are formed from parts of the macro-molecules (see fig. 1). The dyeing is effected by the interactions of the dyeing molecule with a part of the macro-molecular configuration and it will depend on the nature of the groups comprising the dyeing and the polymer molecules their shape and size, and also the state of matter as to what type of forces will develop between them in order to effect dyeing.Prof. Bradley and his co-workers in their paper on the selective absorption of optical antipodes on wool found differences in the degree of rcsolution as the chain length attached to the mandelic acid was increased. He also pointed out that there is a difference in the rate of absorption for the amorphous and crystallinc regions of the wool fibre. Optical activity may be due to the existence of an asymmetric atom in the molecule and/or an asymmetric lattice in the crystal. It is reasonable to accept that the asymmetric carbon atom in the mandelic acid combines more easily with the more flexible asymmetric atom in the amorphous rcgion of the wool fibre.While for its absorption on the crystal more rigid steric conditions should be fulfilled.2 Except for the existence of an asymmetric atom ‘Y FIG. l.-Crystalline (A) and orderly (B) regions in a fibre. 1 Coumoulos Proc. Roy. SOC. A 1943 182 166. 2 Coumoulos Thesis (Athens University 1938) GENERAL DISCUSSION 237 the dimensions of the lattice crystallites should be suitable. This may explain the observed difference in rate of absorption. With the increase of the chain length attached to the mandelic acid one would expect the development of another type of force between the long chain of the dyeing molecule and that of the macro-molecule in the fibre and there exists a critical length over which the dyeing mole-cuIe attaches itself to the fibre by lateral forces.1 In all cases the molecular scale for both the dye and the fibre should be con-sidered in dyeing.In that respect Dr. Robinson’s paper on atomic models is very interesting and it is suggested that it will always be helpful to make a model of the system dyeing molecule + substrate fibre before proceeding with theoret-ical explanations. Dr. K. H. Gustavson (Stockholm) said In the extremely suggestive paper of Schulman and Dogan there is a wealth of points which invite discussion. My comments will be restricted to a few of these. The first important point is the finding that monolayers of proteins which contain free carboxylic groups such as serum albumin react with chromium forming two-dimensional solid lattices, probably by the interlinking of the protein chains through the hydroxy-chromium complexes.An important fact clearly brought out by the monolayer technique, is indeed that the steric factor is much in evidence in this cross-linking. On the other hand proteins lacking in free carboxylic groups such as gliadin do not solidify upon treatment with chromium salts. This is certainly an unambiguous proof of the primary importance of the carboxyl ion of proteins in the binding of cationic chromium complexes. As additional evidence for the governing role of the charged carboxyls of the proteins for their reactivity towards cationic chromium complexes the following, mainly unpublished data from investigations related to the mechanism of chrome tanning 2 are of interest. Two g portions of the various proteins (hydrated) equilibriated in 1 0 m l of solutions of 67 % acid chromium sulphate 2Og/l.CrzO3. The amounts of Cr2O3 fixed by the proteins and the proportion of free carboxylic groups of the proteins are shown in the following table. ‘rABLE 1 % Cr2 0 3 typc of protein free acid groups fixed by the protein collagen elastin silk fibroin keratin (wool) serum albumin ovalbumin fibrinogen gliadin myosine (rabbit muscle) casein 100 25 35 70 125 110 100 0 130 100 10.8 2.6 0.9 0.3 11.2 8.9 10.7 1.2 14.5 10.1 With the exception of keratin and silk the chrome fixation of the various proteins can be fairly well correlated with the carboxylic content of the proteins. With keratin the steric conditions and the inaccessibility of the carboxyl ions (crystalline region) may be responsible for its anomalous behaviour towards polynuclear chromium complexes.Further it should also be noted that the number of cationic protein groups are of importance indirectly for the fixation of the chromium cations since the anions of the system must be compensated by the cationic protein groups in order to maintain the electro-neutrality of the 1 Coumoulos Proc. Roy. Soc. A 1943 182 166. 2 Gustavson J. Physic. Chern. 1947 51 1181 238 GENERAL DISCUSSION system. This point is stressed by the authors in stating that the positive potential barrier of the amine groups in the protein monolayer has to be overcome. As to the action of Cu2f ions on gelatin 1 and collagen 2 Cu is fixed by the carboxyl ions of these proteins mainly irreversibly.The resulting Cu-collagen compounds possess a lower degree of stability than the original collagen hydro-thermal as well as proteolytic. The reason is probably that the Cu2+ ion only reacts as a unifunctional hydroxo-cation ; the unipoint fixation of Cu(0H)-+ complexes by the carboxyls of collagen then connotes dislocation of some of the salt-like crosslinks of the original collagen which links contribute in a small measure to its stability. The effect of C U ~ + ions on collagen is indeed indirect cvidence for the requirement of multipoint attachment of the agent to adjacent chains of the protein and the fulfilment of certain steric conditions for tanning to take place. I do not follow the authors’ formulation of the hydrogen bonded monatomic chromium complex with the link c-4 C O .&-OH- - -O==C’ , nor the suggested structure of the dinuclear complex with two hydroxy groups co-ordinatcd as \O-Is not the formation of structures of thc type more likely since the basic sulphates are sulphato-ol-chromium sulphates ? Is there experimental evidence for the existence of structures of chromed proteins of the type given in the paper ? Further it appears problematical if complexes of the type Cr(OH)2’ can be formed on the addition of alkali to solutions of chromic sulphate because the chromium of basic salts tends to form a polynuclear chromium complex and such a highly basic sulphate is insoluble. It would be of further interest to be informed by Dr. Schulman whether his findings of the behaviour of the chrome-protein monolayers might be explained on the basis of the interaction of di- or poly-nuclear chromium complexes with the protein.Concluding I cannot refrain from stating that the fundamental investigations of tanning introduced by the Rideal school and so ably continued by Dr. Schulman, have greatly strengthened our present conception of the mechanism of tanning processes. The use of individual protein chains eliminates the many complicating factors present in the macro-structure of skin and represents the simpler chemical reaction between proteins and the tanning agents. Dr. J. H. Schulman (Cambridge) said We consider that hydrogen bonding between the basic metal ions is the initial stage in their aggregation or their inter-linking of the polypeptide chains.This is obtained by their adlineation after being adsorbed on to the available negative carboxyl groups in the protein lattice. This conccpt is experimentally supported by the fact that fatty acid and protein monolayers are made insoluble and are solidified at high areas per fatty acid moleculc and amino acid residue in solid lattices which are produced only at the 1 Northrop and Kunitz J . Gen. Pliysiol. 1928 11 481. 2 Thomas and Seymour-Jones Ind. Eng. Chein. 1924 16 157 GENERAL DISCUSSION 239 pH of formation of basic metal ions. These vary for each metal ion (e.g. pH 2.3 for Fe3-'- pH 4.2 for AP+ pH 5.3 for Cr3+ pH 6.7 for Cu2t-). Any theory valid for the chromium system would equally well have to apply for the other metal ionic system.Further experimental support is given by the infra-red absorption studies on the aluminium soap systems which solidify or gel in hydrocarbons only when the aluminium has an hydroxyl group attached to it in the presence of the di-soap. The hydrogen bonding can be easily established by the infra-red absorption bands and any interference with this bonding prevents or breaks down the structure. The structure given by Gustavson could equaIIy well interlink by hydrogen bonding between the ions after adsorption on to the carboxyl groups in the protein lattice. Dr. K. G. A. Pankhurst (Brit. Leather Manuf. Res. Assn.) said I was inter-ested in the large increase in surface area reported by Allingham Giles and Neustadter and wonder whether all of these changes are due to crosslinking as they suggest.Some years ago we found 1 that many small comparatively simple substances such as butyl alcohol phenol etc. were capable of non-specific pene-tration into monolayers of fatty acids alcohols etc. with the production of films that were expanded at least at high areas and frequently at low areas also. I would suggest that surface potentials and viscosities of the systems mentioned by Allingham et al. would be very informative on this point. Dr. C . H. Gila (Royal Tech. CoZZ. Glasgow) (communicated) Some non-specific penetration of the film may perhaps occur when solutes are used which contain a large proportion of hydrophobic groups e.g. molecules VI VII VIII, IX IV,* and this might account for the fact that VII and VIII which contain the largest proportion of such groups produce area increases significantly higher than those predicted.Even so specific cross-bonding must also be involved, because it seems most unlikely that the large area increases observed can be attributed solely to non-specific penetration e.g. if the tricarbocyanine molecule (VIII) is assumed to penetrate the film in this manner and to stand vertically to the water surface the observed area increase would represent the association of about 1.5 solute molecules with each one of the cetyl acetate. A consideration of the size and shape of these two molecules does not suggest that such a ratio of association is likely. Cross-bonding appears to be the most reasonable mechanism to account for the observed effects of the highly hydrophilic compounds particularly those whose molecules are completely surrounded by strongly hydrophilic groups, e.g.Alizarine Cyanine and mannitol (cf. also ref. (4)). Since this paper was submitted a more detailed study has been made of the possible sizes and orientations of the postulated monolayer + solute complexes. The revised data for the predicted molecular areas now given in table 3 show that in each case (except VII and VIII as just discussed) the observed value is quite close to that predicted on the assumption of specific cross-bonding alone. Regarding our suggestion that compounds VI-VIII are bifunctional we may state that cyanines are regarded as resonance hybrids the charge in symmetrical compounds of the present type being distributed equally between the two nitrogen atoms.This being so it would appear that the only position they could reason-ably be expected to occupy in the film is one where the longest axis is parallel with the water surface. While the data seem to support the cross-bonding hypothesis, it is admittedly difficult to decide which groups in these cyanine molecules can be responsible for bonding. We have here supposed that the nitrogen atoms form hydrogen bonds. The positive charge which they hold may make such a link impossible and the following alternatives may be suggested (i) electrostatic 1 Adam Askew and Pankhurst Proc. Roy. SOC. A 1939,170,485 ; Pankhurst ibid., * see my paper. 1942 179 393 240 GENERAL DISCUSSION attraction of the cationic nitrogen atom for the weakly negative carbonyl oxygen of the acetyl group or (ii) hydrogen bonding between the latter and hydrogen attached to the carbon atoms of the methin chain (cf.the greater attraction for water known to be imparted to an alkyl chain by the insertion of a C=C double bond therein). This matter will be investigated further and surface potential measurements will also be carried out. Dr. K. G. A. Pankhurst (Brit. Leather Manuf. Rex. A m . ) said Since carrying out the work described in our paper Mr. A. F. Lanham and I have investigated the tanning of monolayers of a 33 % N-methyl-methoxy Nylon with mimosa tannin and have found a similar increase in surface viscosity to that obtained with collagen monolayers at pH values between 2 and 5.This supports our contention that tanning with phenolic vegetable tannins is essentially non-ionic. Dr. I(. H. Gustavson (Stockholm) said The drastic alteration of the character-istic properties of collagen monolayers by their interaction with tanning agents makes the technique of Ellis and Pankhurst a very sensitive indicator of tanning potency of a substance. It apparently also yields important theoretical informa-tion on systems of tanning as already noted in the researches of the Rideal school. The pronounced effect of mimosa tannin in solutions containing 1 mg tannin per 1. on the surface viscosity of the film is remarkable. It is interesting to find that the behaviour of basic chromium salts indicates that anionic groups of collagen are the sites for the fixation of the chromium complexes the reaction being ionic in its initial stage.It is aLso pleasing to note that the results from chrome tanning of collagen monolayers strikingly confirm the present concept of chrome tanning which has been developed for macro systems. As to the vegetable tannage the fixation of mimosa tannins is interpreted to be mainly a multipoint binding of the tannin molecule on collagen. At pH values above 3 evidence for dipolar (ionic) interaction between tannin and collagen is presented. Since mimosa tannins are usually employed in the natural pH range of the extract (PH 4-5-5.0) the participation of ionic protein groups in the ordinary mimosa tannage should not be disregarded in framing theoretical con-cepts. It should also be noted that in the unpublished electrophoretic investiga-tion of purified vegetable tannins by Danielson referred to by the authors solu-tions with the natural pH of the tannins were used i.e.for mimosa tannins a pH of 5.0. The experiments indicated that the negatively charged fraction was of lower molecular weight than the non-migrating main part of this tannin. A considerable part of the tannins of the hydrolyzable class such as tannic acid and valonea migrate in the electric field even in solutions of such low pH values as 3, and the fixation of these tannins occurs to a very marked extent by ionic protein groups as pointed out in the discussion of the dual nature of the vegetable tannage. Also in the work of Rideal and his co-workers the interaction of tannic acid with the cationic groups of monolayers of globular proteins and with amines has been proved conclusively.It is a pleasure to note that the authors justly credit Freudenberg with the concept of vegetable tannage as being the formation of co-ordinate compounds -an idea of thirty years’ standing. Actually prototypes of collagen + tannin compounds in the form of co-ordinated diketopiperazine (with the -CO . NH link) and polyphenols with the characteristic CO . . HO( bond date back / \ NH / to Pfeiffer’s fundamental work on Mulekul- Verbindungen. This historical fact emphasizes the debt which we owe to the originators of the co-ordination concept (or hydrogen bond formation). The authors’ finding that the monomers of benzoquinone and catechin are lacking in tanning potency is a fundamental contribution.It is proved that these substances first acquire this property upon polymerization. This is GENERAL DISCUSSION 241 striking illustration of the requirement of multipoint attachment of tanning agents to different collagen chains (interchain cross-linking) and consequently, in order to attain this cross-linking that the size of the molecule of the tanning agent the distribution of its reactive groups and the spatial conditions of the reacting protein groups of adjacent protein chains are the decisive factors. Once more I would like to sound a note of warning with regard to the trend of treating the tanning process as a hydrogen bonding process entirely assuming all vegetable tannins to behave alike and hence overlooking their chemical individuality.Dr. H. Phillips (Brit. Leather Manuf Res. Assn.) said We have argued about a definition of tanning and I suggested that it might be defined as covering those processes which were used to stabilize the collagen fibre (and other protein fibres) against the action of water and bacteria. But before collagen fibres in a hide or skin can be tanned the hair wool epi-dermis and the interfibrillary proteins must be removed to make the fibres more accessible to tannins. The processes used-soaking liming bating sometimes pickling-also help to decide what kind of collagen fibre the tanner will tan, and hence the physical characteristics of the final leather. The value of the paper of Burton and Reed is that it stresses the importance of mucoids as substances which influence the physical state of collagen fibres.Collagen fibres as they exist in hides and skins are not such d e ~ t e entities as the single fibres of wool and cotton. They are bundles of fibres which can be split during the pretanning processes into fibres and into fibrils. The wool textile manufacturer when he wishes to make a soft handling fabric will choose fine wool fibres spin them into lightly twisted yarns and weave the yarns loosely into a fabric. On the other hand if he is manufacturing a fabric for hard wear and strength he will use coarser fibres and spin them into highly twisted yarns which he will weave into a compact fabric. In effect the tanner’s fibre bundles can be compared with the yarns of the textile manufacturer. The tanner has a very wide choice of skins containing “ yarns ” of various sizes and woven either loosely or compactly.By his pretanning processes he can alter the size of the individual fibrils in the fibre bundles. There is much evidence that mucoids or mucopolysaccharides are concerned in this breakdown of fibre bundles to fibres and of fibres to fibrils. On the other hand chemical evidence is lacking to support the view that hides and skins skins contain relatively large amounts of mucoids. Dr. Bowes has estimated the amounts present by determinations of the glucosamine content her results show about 1.0 % mucopolysaccharide 1 for the full thickness of fresh ox-hide and about 0.7 % for the middle corium split of the same ox-hide after extraction with sodium chloride solution.The mucoid content of the middle corium split was halved by liming. The close connection between some mucopolysaccharides and the molecular cohesion of collagen is indicated by the increase in water uptake produced by treatments which are known to extract polysaccharides from collagen. Both dyeing and tanning are concerned with the interaction of large molecules. The large molecules of fibres are linear molecules whilst those of the dyes and tannins are smaller molecules which may however be bulky. Generally speak-ing the linear molecules in all fibres are arranged with their long axes parallel to the length of the fibre. Because we dye and tan fibres both processes are concerned with diffusion and absorption. Technologically textile fibres are more often dyed after they have been spun into yarns and woven into fabrics.This increases the difficulties of the dyer. In the same manner the tanner is faced with a similar problem in a somewhat accentuated form since the fibres of hides and skins are interwoven in an intricate manner. 1 Bowes Research 1951 4 155 242 GENERAL DISCUSSION From there on the similarity ends. It is true there are anionic tannins natural vegetable tannins with carboxyl groups such as myrabolam and chestnut and so-called syntans with sulphuric acid groups. There are also non-ionic tannins whose functional groups are entirely hydroxyl such as mimosa which was men-tioned in the discussion on Mr. Amstrong’s paper. But tannins cannot tan by combining with one linear molecule in the fibre; they must crosslink adjacent linear molecules and form what Dr.Pankhurst has described as multipoint attachments. The reason for this is that tanning is essentially a process by which collagen fibres are stabilized against the action of water and micro-organisms. The collagen fibre is a much more reactive fibre than any textile fibre. It will readily absorb many times its own weight of water even when neutral and will swell to many times its original size in alkaline and acid solutions. Tannins by cross-linking the polypeptide chains restrict their degree of hydration and their capacity to swell. In chrome tanning for instance, there is much evidence as Dr. Gustavson has shown that when co-ordinate linkages are formed through chromium with carboxyl groups of adjacent poly-peptide chains the collagen becomes resistant even to boiling water.In order to attain this widespread cross-linking it is necessary that the tanning molecule should be large much larger than is necessary with dyestuffs. Very generally speaking tannins must have a molecular weight of about 2000. But tanning itself remains a mystery unless one realizes the amount of organic tannins that can penetrate the collagen fibre. A fully tanned collagen fibre can accommodate half its own weight of vegetable tannins. So that technologically speaking although tanning is the multipoint cross-linking of the linear molecules of the fibres by tannins-ither with co-ordinate linkages as with chrome tannins, or hydrogen bonding and salt linkages with vegetable or organic tannins-there is this further build-up of tannin in the fibre which alters its physical properties besides making it resistant to water.The dyer uses the minimum amount of dye consistent with obtaining the coloration he desires. But the tanner varies the amount of tannin in the fibre depending on the physical characteristics of the leather he wishes to produce. When he is producing a flexible leather such as that needed for the uppers of shoes or for upholstery then he finds that when the fibres have absorbed half their own weight of tannin they are satisfactory for his purpose. There is much evidence that this amount of tannin is absorbed freely and that it corresponds to the amount of tannin needed to fill the less organized amorphous or less crystalline parts of the fibre.This is the type of tannage which is undertaken by what is known in the in-dustry as the light leather tanner. But there is another section of the industry-the heavy leather tanners manufacturing sole leather who consider their type of tannage so complex that they almost object to the light leather manufacturers calling themselves tanners. And the reason for this is that to make sole leather, which should be firm and waterproof the collagen fibre must be made to absorb almost its own weight of tannin-ertainly more than half its own weight. Scientifically speaking this means that the molecular structure of the fibre must be made more accessible to tannins-in other words during tannage the more organized or more crystalline and therefore less accessible regions in the fibre must be opened up so that tannins can enter.This change must not be taken too far; the strength of even the tanned collagen fibre depends on the degree of cross-linking between the linear molecules of the more organized parts of the fibres. But strength is not essential for sole leather so that the heavy leather tanner finds he can break down part of the molecular structure and then fill it with tannin obtaining thereby a coarser or thicker fibre and hence a firmer leather. The methods he uses-weak acids and heat-are similar to the methods we should use in the laboratory to disperse and dissolve protein fibres. For many years it remained a mystery to the tanner himself because he did not know that certai CiENERAL DISCUSSION 243 vegetable tanning materials he used to produce this change contained weak acids and indeed he was of course unfamiliar with the nature of weak acids and of their action on fibrous protein.Essentially although on the molecular scale there are many similarities between dyeing and tanning I think it is evident that the modifications in the physical characteristics of fibres produced by tanning are more profound than those pro-duced by dyeing. Dr. K. H. Gustavson (Stockholm) said Before discussing Dr. Pouradier’s contribution on the chrome tanning of gelatin in aqueous solution it is a personal privilege to stress the originality of the researches of his group and their im-portance for the theory of the chrome tanning process. The fkst experimental evidence of the cross-linking of gelatin (collagen) by chromium salts proved by the increased mean molecular weight of gelatin was in fact given in the informative paper in Bull.SOC. Chim. 1952 19 928. The data and the discussion of that paper particularly concerning the effect of the concentration of the solution of gelatin on the relative importance of inter- and intra-chain cross-linking of the gelatin molecules by chromium complexes and the effect of the pH on the steric possibilities of the gelatin molecules for such cross-linking to occur have already proved of great value in the interpretation of the system collagen + chromium salts as already pointed out in a recent paper,l bearing on the uni- and multi-point fixation of chromium complexes by collagen. I am very anxious to state these facts in view of the omission of reference to the 1952 paper of the Pouradier group in the brief outline of the chrome fixation by collagen presented in my condensed contribution at this Discussion.In Pouradier’s paper it is shown that the viscosity of dilute solutions of gelatin (0.85 %) is diminished by the addition of chrome alum while an increase is found in chroming more concentrated solutions of gelatin. I should venture to say that the main reason for the decline in viscosity is probably due to the preponderance of unipointly attached cationic chromium complexes to the car-boxyl ions of gelatin in the dilute solutions which mode of combination lessens the number of electrostatic bridges between the peptide chains by partial discharge of its anionic sites.The hydroxo-chromium cations were found to be practically quantitatively fixed by means of single bonds to gelatin in rhe experiments with the basic chromium chloride presented in my paper. The increase in viscosity of the more concentrated solutions of gelatin resulting from the addition of chrome alum is probably due to and logically explained by the inter-chain cross-linking of gelatin by the chromium complexes the higher concentra-tion of gelatin facilitating inter-chain cross linking by the chromium complexes. The interpretation of the findings given by Dr. Pouradier is convincing and let me say without disparaging the originality of Dr. Pouradier’s deductions, that his ideas are in harmony with the trend of thought with which I have long familiarized myself in investigating the interaction of chromium complexes with hide protein.Concluding with a question it would be of interest to know whether Dr. Pouradier has formed any opinion regarding the type of protein groups involved jn the chrome fixation by gelatin? Dr. J. Pouradier (Vincennes) (communicated) The theory which we have worked out to explain our observations is extended to gelatin subject to allowance for the factors inherent in that protein of the well-known work of Spiers and Dr. Gustavson. The chromium complexes fixed on a single carboxyl ion of gelatin certainly have a considerable effect on the physical and mechanical properties of tanned gelatin. We tried to take account of this in interpreting our results but in the absence of quantitative information we were reduced to making hypotheses.As Dr. Gustavson’s recent work has provided some extremely interesting facts about 1 Gustavson J. Amer. Leather Chem. ASSOC. 1953 48 559 244 GENERAL DISCUSSION the relative proportions of the uni- and multi-point binding of chromium complexes we intend to continue our study. We have not yet been able to de;ermine with certainty the natuie of the gelatin groups capable of fixing chromium salts but probably they are the same groups as for collagen. In order to establish this however we are at present trying to establish the pK of the groups which come into the tanning with the variations in the chromium content of gelatins treated at different pH values up to the point of equilibrium. Dr. H. Phillips (Brit.Leather Manuf. Res. Axsn.) said Whilst it may be true that tannic acid is linked to the basic groups of collagen whereas non-ionic tannins such as mimosa may be linked through hydrogen bonds it should be remembered that tannic acid is highly hydroxylated whereas the mimosa tannins are not. The collagen + tannic acid complex is therefore more easily broken down by water than the collagen + mimosa complex which may tend to be hydro-phobic. Dr. K. H. Gustavson (Stockholm) said The important functions of the much-neglected constituents of skin the mucoids and related compounds in the unhairing of skin and for the physical properties of collagen and leather have been brought out in the important researches of Prof. Burton and Dr. Reed. The use of muco-lytic enzymes in the preparatory processing demonstrated by the authors is a decided technological advance and the further development of this natural method of unhairing and freeing the hide fibres from their restraint will be followed with great interest.Modern work on the unhairing problem has put undue stress on the keratolytic mode of unhairing which actually is an artificial method of removing hair and other epidermal matter by a more or less complete destruction of the keratin molecule. A few questions are provoked by their paper firstly I have long been puzzled by the fact that tendon collagen which has not a weave structure like corium of the skin but which is built up from parallelly alignzd fibres is not soluble in dilute solutions of weak organic acids while rat tail collagen is.It is contended that the presence of cementing layers of some mucoid component is the reason for the tendon not dissolving since pretreatment with mucolytic enzymes will make the tendon soluble in dilute organic acids. From the important investigations of Partridge concerning the state of combination of chondroitin sulphate with collagen in cartilage one is inclined to agree with Partridge that the chondroitin sulphate may act as a cross-linking agent on the collagen fibrils and fibres. And further that this type of compounds may have something to do with the orientation of collagen in the formation of connective tissue. The chondroitin sulphate should then react as a multifunctional anion cross-linking and orienting the fibrils into collagen macromolecules.In our own determin-ation of ester sulphate of bovine collagen in native and limed skins about the same amounts of ester sulphate jn such small quantities as equivalent to 0-02-0.04 % S on a protein basis have been found. Perhaps Dr. Reed will have some views on this particular problem ? Secondly a question of a more practical importance it appears from the paper that the removal of the mucoid component from the skin by mucolytic enzymes in the preliminary processing should have a favourable effect on the subsequent processing particularly the tanning. Does the tannage of the mucolytic-treated skin proceed more smoothly and uniformly than that of ordinarily limed skin and is thereby the quality of the leather improved ? It should also be of interest to know whether skin which has been chrome-tanned after the removal of the mucoids resists the action of water after drying in “the b1ue”as is the case with regular chrome leather which is not wettable after being “ bone-dried ” in the non-fat liquored state.This question obviously has a bearing on the explanation given for the unique hydrophobic character of dried chrome leather i.e. whether this is due to the changes of the surface of the leather fibre GENERAL DISCUSSION 245 by the fixed chromium complexes or to the presence of fatty matter in the skin, which forms non-wetting chromium soaps. Finally are there any data regarding the minimum amount of chromium required for producing a chrome leather stable to boiling water ? Prof. D. Burton (Leeds University) said Little is known as to the mechanism whereby chondroitin sulphate determines the stability of the chondroitin fibre structure.Much of the available evidence however indicates that the chondroitin sulphate is very firmly joined to the molecular chains of collagen and that if it is removed the cohesion of the molecular chains is profoundly modified. We have no definite information regarding Dr. Gustavson's second point concerning the effect of the removal of mucoid material on the water uptake of the dried leather. From the work so far carried out however we think that chromed pelt prepared by means of mucolytic enzymes wets back easily and in a most even manner. Dr. R. Reed (Leeds University) said Most mucoid materials are insoluble in the common organic solvents.They are however usually freely soluble in alkalis. Thus it is doubtful whether the epicuticle of the wool fibre would be modified in the manner suggested even if it is of a mucoid nature unless the scouring operation involves alkaline conditions. Dr. H. H. Sumner (I.C.I. Dyestufs Blackley) said I would like to ask Dr. Schroeder whether the authors have investigated the rate effects which occur in the dyeing of polyethylene terephthalate in the presence of carriers. We have I-' I FIG. 1.-Phenol as carrier. Dyebaths contain 025 g/l. Dispersol Fast Scarlet B 150 ; carrier concentration used in all cases 0.5 g/l. been concerned with this aspect because it was thought that both rate and equilibrium effects must be considered in order to obtain a complete understand-ing of the mechanism of carrier dyeing.It must be pointed out however that whilst the paper of Schuler and Remington deals with dyes in solution in the dye-bath our work has been carried out in the main using dispersions of dye because it appeared possible that carrier action is a result of having a dispersed system. The following is a brief account of those results which are relevant to this discussion. Fig. 1 shows rate of dyeing curves obtained for a dispersed dye with a soluble carrier in this case phenol the four curves shown being for (A) no carrier ; (B) carrier and dye in the dyebath i.e. both applied to the fibre simultaneously 246 GENERAL DISCUSSION (C) fibre pretreated with and then dyed in the absence of a carrier; (D) fibre pretreated with and then dyed in the presence of carrier.The results shown by A and B are in accord with those described by the authors i.e. an increased rate of initial dyeing in the presence of carrier and a decrease in the amount of dye taken up for the longer times of dyeing. The rapid decrease in the slope of curve C must be due to the carrier diffusing out of the fibre. If the relative positions of the curves after 1 h are considered it appears that pretreatment with carrier is not advantageous. This is not the case when we consider an insoluble carrier such as diphenyl. The four curves in fig. 2 (in which it should be noted that the dye on fibre scale is 25 times greater than in fig. 1) are again the results of similar experiments A, B C and D and here it is obvious that pretreatment of the fibre in carrier is ad-vantageous (C and D).Again the effect of carrier being removed from the fibre r ---I FIG. 2.-Diphenyl as carrier. Dyebaths contain 0.25 g/I. Dispersol Fast Scarlet B 150 ; carrier concentration used in all cases 0.5 g/l. is shown in curve C. It is only the initial rate of dyeing that is different in B and D and the slower rate of B must be due to the fact that there is no carrier in the fibre so that the rate of up-take of carrier by the fibre becomes one of the controlling factors. The relative action of soluble and insoluble carriers when they are applied in equal concentration is clearly shown by these results. Also it is evident that over normal dyeing times of approximately 1 h pretreatrncnt of the fibre in carrier is beneficial for insoluble carriers but of doubtful value for soluble carriers.It must therefore be concluded that an effective carrier must be capable of being taken up by the fibre and that for maximum effect on the initial rate of dyeing, when carrier and dye are applied together this process must be rapid. Dr. M. J. Schuler and Dr. W. R. Remington (du Pont de Nemours Co. Dela-ware) (communicated) Data for sorption of the dycs 1 -amino-4-hydroxyan thra-quinone and 1 4-dihydroxyanthraquinone from binary mixtures yieldcd linear isotherms but at saturation the conccntration of each dye in solution in both fibre and H20 was less than when either dye was used alone. The solubilities were not additive. The tentative explanation of ‘‘ interaction ” was offered for this behaviour.Further experiments have demonstrated that these dyes form solid solutions (mixed crystals) with one another over the complete composition range; th GENERAL DISCUSSION 247 activities of the dyes in the saturated aqueous solution vary with the composition of the solid phase. The solubility data reported in the paper are in excellent agreement with those obtained with the mixed crystals. .Therefore there is no need to postulate " interaction " between dyes in the fibre. Dr. D. Patterson (I.C.I. Ltd. Welwyn Garden City) said The suggestion by Schuler and Remington 1 that the solution of dispersed dyes in polyethylene terephthalate is non-ideal and that there is a possibility of hydrogen bonding between dye and substrate is borne out by the following experiments in which the dye Dispersol Fast Scarlet B was used.Amorphous film was given a low temperature surface dyeing and then drawn on a continuous drawing machine so that its length was increased by known ratios, UP to 4.5 times its original length. Optical densities at the peak of the absorption curve of the dye were then measured using light plane polarized first parallel and then perpendicular to the direction of stretch. The dichroic ratio increases with the degree of stretching as shown in the figure. The dye molecdes are 1.4 ' I 1 I I I FIG. 1 .-The orientation of Dispersol Fast Scarlet 3 in polyethylene terephthalate film. constrained to follow the straightening of the long chain molecules of the poly-ethylene terephthalate which occurs in the drawing process.This could be brought about by hydrogen bonding or simply by mechanical entanglement but it is clear that there is marked orientation of the dye molecules with their long axes parallel to the polymer molecule chains. It is therefore not surprising that the solution is non-ideal. Dr. C. H. Bamford (Courtaulds Lrd. Maidenhead) said I should like to comment on Dr. Patterson's conclusion based on measurements of the dichroism of dyes adsorbed on polyethylene terephthalate that some dyes can be strongly bound to the polymer chains. Additional valuable information might be ob-tained if simultaneous measurements of dye and fibre orientations could be made. Observation of the dichroism of a suitable infra-red band e.g. that corresponding to the CO stretching vibration might be suitable for estimating the mean fibre orientation.If during the extension of the polymer film the dye orientation were found to lag significantly behind the orientation of the fibre the conclusion could be drawn that the crystallization of the polymer tends to squeeze out dye molecules into the (less oriented) amorphous regions. On the other hand if the dye is attached sufficiently strongly it may be expected to show comparable orientation to that in the fibre. Could Dr. Patterson say whether any observations of this kind have been made ? Dr. D. Patterson (I. C.I. Plastics Welwyn) (partly communicated) In reply to Dr. Bamford no infra-red examination of the films was possible owing to their thickness but density and birefringence have been measured and X-ray analysis 1 this Discussion 248 GENERAL DISCUSSION carried out.The orientation measured by these methods does not increase steadily with increased drawing as does the dichroism shown by the dye. Instead, at draw ratios above 2-5 there is a marked increase in both density and birefring-ence and the X-ray photographs reveal the onset1of crystallization. The reason for this is that the overall orientation is being measured and density and bire-fringence are much more sensitive to the (strain-induced) crystallization than to the increase in order in the amorphous regions. It seems possible that in the same way the infra-red dichroism of the CO stretching vibration would measure the orientation of both crystalline and amorphous regions and show a similar dependence on draw ratio.This view is confirmed in a private communication from Miller who has already used infra-red dichroism methods in a similar connection.1 The suggestion that the migration of dyes from crystalline to amorphous regions might be shown by an independent measure of orientation does not seem likely to be fulfilled in view of these complications. Further in the dyed portions of the films there is about one dye molecule for each polymer chain and since the latter are so much the larger the chances would seem to be that the polymer chains could pass through crystalline regions without requiring a shift in the point of attachment of the dye molecules. The evidence points to the dichroism of the dye molecules being a measure of the orientation of the amorphous regions independent of that of the crystalline parts.An examination of the infra-red absorption of the dyestuff rather than the polymer however might throw light on the method of their mutual attachment. Dr. T. Vickerstaff (I.C.I. DyestuB Blackley) said One possible mechanism by which carriers may promote the dyeing of polyester fibre is by adsorption on the polymer chains to reduce intermolecular cohesion and so reduce the activation energy required for dye diffusion. This molecular lubrication might be revealed by a reduction in the rigidity of fibres and some recent measurements support this view as shown below : treatment flexural rigidity (g cm2) untreated fibre 1.096 X 10-2 treated in blank aqueous dyebath 1.068 X 10-2 0*800 x 10-2 treated in dyebath with 6 % phenylphenol 0789 x 10-2 treated in dyebath with 6 % diphenyl Dr.C. H. Giles (Royal Tech. Cull. Glasgow) said As already stated (see comment on paper by Bird et al.) a straight line isotherm may not be inconsistent with specific attraction between substrate and dye. It may be significant that both the substrate and the solutes used in the paper of Schuler and Remington contain benzene nuclei. It is well known that such nuclei associate together closely in parallel e.g. in monolayers on water and we may therefore assume that when carriers or dyr;J are applied to polyethylene terephthalate their aromatic nuclei associate in this way with those of the substrate. If this is so then we should not expect aromatic compounds to act as carriers for fibres devoid of aromatic nuclei e.g.cellulose acetate or Nylon. Neither should aliphatic com-pounds act as carriers with polyethylene terephthalate. Perhaps also the intro-duction of bulky non-hydrogen bonding substituents into the aromatic nuclei of carriers or dyes would reduce their affinity for this substrate by preventing close packing. The solid solution mechanism of sorption of solutes by polyethylene tereph-thalate suggested by the authors may therefore be tentatively interpreted as association between aromatic nuclei in solute and substrate coupled with hydrogen bonding where suitable groups are present in the solute. The hydrogen 1 Miller and Willis,:Trans. Faraday Soc. 1953 49 433 GENERAL DISCUSSION 24 9 bonding may involve the methylene groups in the substrate as suggested in the paper by Allingham et aI.Dr. M. J. Schlaler and Dr. W. R. Remington (du Pont de Nemours Co. Delaware) (communicated) We thank Dr. Giles for his suggestion regarding the possible " association between aromatic nuclei in solute and substrate ',. This suggestion might be checked using model compounds such as dimethyl terephthalate with phenol aniline and dimethylaniline. For association or n complex formation, there would be a marked change in the absorption spectrum. Dr. Giles also attributes to us the suggestion of" the solid solution mechanism of sorption of dyes ". We would like to clarify this point. The mechanism of dyeing proposed is one of solution of dyes in the fibre probably in the amorphous rcgions.We do not wish to suggest that " solid solution " or " mixed crystal " formation takes place. Dr. €3. Zollinger (Basle University) said I would contribute two remarks to the dyeing mechanism in the presence of Cu-t- ions. The first remark supports the view of Dr. Schroeder that cationic complexcs containing the Cu-t- ion act as sites for fixation of dye anions. Field and Fremon 1 already mentioned that other mctal ions will also be adsorbed. In thc course of investigations made in the laboratories of Ciba Ltd. with the purpose of overcoming some practical disadvantages of the copper method we extended the work of Field and Fremon to a series of 22 metal salts. All of these salts were adsorbed more or less part of them to a much higher extent than copper.With respect to the correlation with Dr. Schroeder's mechanism there is the interesting fact that polyacrylonitrile fibres (Orlon 41) treated with anionic Cr3-c salts (e.g. by treatment with sodium dichromate and reduction by the Bucherer process2) have a lower affinity for a simple acidic azo dyestuff namely Kiton Fast Orange G than fibres which have not been treated at all. Under standard conditions thc relation was approximately as follows (arbitrary units) : Orlon 41 treated by the copper process Orlon 41 untreated Orlon 41 treated with anionic Cr 1.0 0.05 0.01 The fact that " anionized polyacrylonitrile " has a lower affinity is in agreement with Dr. Schroeder's paper. The second remark concerns a point which in my opinion must be considered in this dyeing process i s .the swelling of polyacrylonitrile fibres when treated with monovalent copper salts. As is well known carriers like benzoic acid, phenylphcnol etc. promote the up-take of dyestuffs. At the same time the amor-phous regions of the fibres swell. We estimated this swelling by measuring the decrease of the refractive index of these fibres using polarized light.3 We obtained the following values : "D' (1) nD" (11) Orlon 41 untreated 1.510 1 -509 Orlon 41 + o-phenylphenol 1.509 1.509 OrIon 41 I- CuSO4 + NH2OH 1.505 ca. 1.505 (expcrimcntal error ca. 0.001) This shows that copper ions have an unexpectedly large swelling effect. Although it has been pointed out in the discussion on the polyethylene terephthal-ate paper that it is difficult to prove definitely a correlation between swelling and dyeing affinity of such fibres this effect has to be considered in my opinion as well as the pure ionic exchange mechanism.1 Field and Fremon J. Text. Res. 1951 21 536 table 8. 2 D.R.P. 587,361. 3Lunpublished measurements of H. Labhart Physics Laboratory Ciba Ltd. Basle 250 GENERAL DISCUSSION Dr. P. Mares (Aberdeen) said It would be interesting to know from Dr. Schroeder whether the 2-vinylpyridine copolymerized with the acrylonitrile may have contained a minor quantity of 4-vinylpyridine. Fuoss has shown that the nitrogen atoms in poly4vinylpyridine are more readily available for quaterniza-tion with alkyl halides than are those in poly-2-vinylpyridine. Mr. Mackie, of this department has found that this is true to an even more marked extent in the quaternization of copolymers of 2- and 4-vinylpyridines with styrene, containing about 5 % of the former.The presence of a few 4vinylpyridine units among the 2-vinylpyridine units in the copolymers with acrylonitrile would therefore provide a possible interpretation of the suggested existence of " a rela-tively small number of highly affinitive basic sites ". Dr. T. Vickerstaff and Dr. J. Simons (I.C.I. DyestuB Blackley) (communicated) : If we regard dyeing as a displacement of chloride by dye ions it is possible to calculate the affinity of the dye ion relative to the chloride ion at the three pH values used in the work of Blaker et al., The concentrations of dye in the fibre and in solution ([DF] and [Ds]) can be read off fig. 1 of Dr. Schroeder's paper while the concentration of chloride ions [CIS] in the solution is assumed equal to that initially present. The concentra-tion of chloride ions in the fibre [Cl,] can be derived from his fig. 2 (= AP) al-though there is clearly an error in the lowest of the three lines which does not pass through the experimental points. The results obtained in this way for four points on each isotherm are as follows : 1.04 2260 2510 2610 2280 1.5 1 2070 2420 2500 2430 2-3 1 1540 1790 1950 1530 2-31* 1810 1930 2220 1800 The relative values at pH 2.31 are calculated for the line shown in the figure while the values at pH 2.3 1 * have been derived for a line through the experimental points. These results are necessarily approximate by virtue of their graphical derivation but show no evidence of sites of differing affinity for dye ions. Dr. M. J. Schuler and DP. W. R. Remington (du Pont de Nemours Co. Dela-ware) (communicated) We are grateful to Dr. Vickerstaff and Dr. Simons for showing that our data support our hypothesis that for the displacement of chloride by dye ions " . . . all cationic centres " are as stated in the paper " equivalent . . .". Using our data they have shown that This is equivalent to our equation (14) which we had regarded only as a logical assumption. However we wish to reemphasize that this discussion of the ion-exchange reaction of the protonated fibre has no bearing on the number of different types of sites in the unprotonated fibre ; it implies only that onceprotonated all pyridine nuclei behave alike. It carries no implication regarding the identity of un-protonated pyridine nuclei. As we have shown (cf. table 3) our results are best accounted for by two types of sites 6 % of the sites being 96 times as basic as the remainder. A number of reasonable possibilities can be advanced to explain this difference in basic character beside those already mentioned in the paper. Thus the steric situation of the basic pyridine nuclei might be particularly important GENERAL DISCUSSION 25 1 In this connection Dr. Meares has made a very plausible suggestion that a low concentration of 4-vinyl isomer in the vinyl pyridine might account for the more amitive or more basic sites. Any 4-isomer would place a basic centre farther from the main polymer chain where it would be more available for reaction. The 2-vinyl pyridine used in these studies actually contained too little probably less than 1 % of the 4-isomer to explain completely the difference in basicity in the fibre. For the present we believe the other explanations are of equal validity

ISSN:0366-9033    

DOI:10.1039/DF9541600229

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

GENERAL DISCUSSION 25 1 AUTHOR Allingharn, Margaret M., 92. Armstrong, D. M. G., 45, 112, 117, 119. Bamford, C. H., 222, 229, 247. Barrer, R. M., 106, 111, 117. Bird, C. L., 85. Blaker, R. H., 210. Boulton, J., 222. Bradley, W., 152, 235. Brindley, R. A., 152. Burton, D., 195, 245. Coumoulos, G. D., 236. Derbyshire, A. N., 140, 233. Dogan, M. Z., 158. Dunn, A. S., 230. Easty, G. C., 152. Ellis, S. C., 170. Gilbert, G. A., 110, 234. Giles, C. H., 92, 112, 233, 239, 248. Gustavson, K. H., 108, 113, 185, 232, 237, 240, 243, 244. Hanby, W. E., 222. Harris, P., 85. Homer, J. L., 113. Hudson, R. F., 14, 105, 107. Katz, S. M., 210. King, G., 110. Larose, P., 105, 119. Laucius, J. F., 210. Lister, G. H., 24. Manchester, I?., 85. Mann, H. B., 75. INDEX * Marshall, W. J., 140, 233. Meares, P., 250. Meggy, A. B., 149, 235. Morton, T. H., 75, 122. Neustadter, E. L., 92. Nursten, H. E., 231. Olofsson, Bertil, 34, 105, 11 1, 117. Pankhurst, K. G. A., 170,239,240. Parisot, Andr6, 117. Patterson, D., 247. Peters, L., 24. Phillips, H., 241, 244. Pouradier, J., 180. Reed, R., 195, 245. Rernington, W. R., 201, 210, 246, 249, 250. Rideal, Sir Eric, 9. Robinson, Conmar, 125. Schroeder, H. E., 113, 123, 210. Schuler, M. J., 201, 246, 249, 250. Schulman, J. H., 158, 238. Simons, J., 250. Sumner, H. H., 245. Underwood, D. L., 66, 121. Valentine, L., 118. Vickerstaff, T., 121, 122, 248, 250. Ward, J. S., 222. Whetstone, J., 132. White, H. J., Jr., 66, 121. Wright, M. L., 58, 119. Zollinger, H., 122, 123, 229, 249. * The references in heavy type indicate papers submitted for discussion.

ISSN:0366-9033    

DOI:10.1039/DF9541600251

出版商:RSC    

年代:1954

数据来源: RSC

摘要:

252 REVIEWS OF BOOKS REVIEWS OF BOOKS Metallurgical Equilibrium Diagrams. By W. HUME-ROTHERY, J. W. CHRISTIAN and W. B. PEARSON. (The Institute of Physics, 1952.) Pp. 3 11. Price 50s. The title of this book is misleading for it is not a collection of cquilibrium diagrams. It could morc usefully, though lees briefly be called " Methods of Establishing Metallurgical Equilibrium Diagrams ", for it is devoted almost entirely to experimental techniques. A small proportion of the book-some sixty pages-deals with the general principles of thc rcpresentation of phase equilibria in binary and ternary systems, with slight reference to thermodynamic aspects, to superlattices and to order- disorder changes. The remainder of the book is devoted to the experimental methods used in determining metallurgical equilibrium diagrams.The treatment is clear and thorough and the text is well supported by 239 diagrams and illus- trations. There are 202 references to original papers. Almost cvery aspect of expcrirnental procedurc is mentioned. The authors describe the various types of furnaces available for melting, casting, annealing and equilibrium studies ; they also discuss refractories, temperature scales and fixed points, and the various met hods of temperature measurements. The determination of the liquidus, of the solidus and of phase boundaries in the solid state are described in detail, and in each case there is good discussion of the choice of method. In addition the utility of microscopal, X-ray, dilatometric, electrical conductivity and magnetic methods arc all carefully considered.In a book covering so wide a range of topics, some blemishes are to be ex- pected. It is a little surprising, however, to see that the type of disappearing filament optical pyrometer described in the section on pyrometry is onc which is not satisfactory by present standards. In the discussion of black body holes for optical pyrometry, it is disappointing to find no indication of the minimum ratio of length to diameter required for accurate measurements. It is also a pity that, in the introductory theoretical part, no reference is made to the use of phase diagrams in the calculation of activities in liquid solutions when solid solutions do not occur and when supporting thermal data are available. The book can be recommended to senior undergraduates and to research workers in metallurgy.It is a " must " for all engaged in establishing equilibrium diagrams. It also contains a grcat deal of information and many opinions which could be of use to anyone concerned with chemical or metallurgical researches at high temperatures. It should find a place in any library supporting such activities. F. D. R. Gmelins Handbuch der anorganischen Chemie. (8th ed.). System-Nummer 3, Saucrstoff, Lieferung 2 : Vorkommen, Technologie. 1952. System-Numnier 10, Selen, Teil A, Lieferung 2 : Elektrischen Eigenschaften. 1950. System- Nummer 17, Arsen. 1952. System-Nummer 18, Antimon, Teil A, Lieferung 3 : Bildung und Darstellung des Metalls. 1950. System-Nummer 27, Magnesium, Teil A, Lieferung 4 : Legierungen von Magnesium mit Zink bis Rhenium, Oberfliichenbehandlung.1952. System-Nummer 28, Calcium, Teil A, Lieferung 1 : Geschichtliches. 1950. System-Nummer 41, Titan. 195 1. System-Nummer 62, Gold, Lieferung 1 : Geschichtliches. 1950. System-Nummer 68, Platin, Teil A, Lieferung 6 : Legierungen der Platin- metalle, Osmium, Iridium, Platin. 195 1. System der Letzten Stelle, abkur- mngen, usw. 1950. Verlag Chemie G.m.b.H., Weinhcim/Bergstrasse. These sections are a worthy addition to this exceedingly valuable work of reference. They show that the current edition is being completed as quicklyREVIEWS OF BOOKS 253 as circumstances allow, but without sacrifice of the accuracy and attention to detail so characteristic of " Gmelin ". The volume on titanium, which is complete, is a most useful accession, and in view of current interest in this metal and its compounds its appearance is opportune.Not unexpectedly, the sections on the metallurgy of titanium are brief and in part only historical ; the compounds, however, are treated very thoroughly. A detailed discussion of the crystallography and ferroelectric properties of barium titanate is typical of the close attention given to special physical properties. This same feature, of such importance to readers from the borderlines of chemistry, is also evident in the new part of the selenium volume, in which 120 pages are devoted to the electrical properties of the element. The arsenic volume is also complete. It covers admirably the chemistry of an ehnent often encountered in the chemical industry, although not itself an important industrial product.A very complete account of the toxicology of arsenic is included. The two parts on alloy systems again contain very full information on physical properties, with very clearly drawn phase diagrams and full references to the patent literature (often through the compilations of Grutzner and Gotze). Electrical and mechanical properties receive full prominence and increase the value to engineers of these sections of Gmelin. Electrochemical and chemical surface treatments for magnesium and its alloys are reviewed in considerable detail. The two historical parts (on calcium and gold) are more of academic interest than of practical value, but they represent the fruits of careful study of early literature.The frequent verbatim quotations give the reader full opportunity to evaluate the older records himself. These sections, in rather sharp contrast with the necessarily cold, informative style of most of Gmelin, make fascinating reading. The oxygen part deals exhaustively with the geochemistry of the element (180 pp.). The succeeding section (120 pp.) reviews industrial methods of isolat- ing oxygen by fractional distillation of liquid air and by chemical and electrolytic processes. The technology of ozone and hydrogen peroxide production, and of industrial water-supply are also discussed from the chemical viewpoint. Abundant references to the patent literature are a feature of these sections. A small appendix giving abbreviations, symbols, etc., used in Gmelin is a useful provision at this stage in the issue of so extensive a work.Further parts will be awaited with interest, for it is evident that recent diffi- culties in production have in no way diminished the general value and authori- tative character of this important reference source. A. J. E. W. The Physical Chemistry of Copper Smelting. By R. W. RUDDLE. (The Institution of Mining and Metallurgy, London.) Pp. 156. Price fl. The value of physical chemistry as the fundamental approach to metallurgical problems is now fully recognized, yet little or no attempt has been made to collect and assess the information about non-ferrous extraction metallurgy that is already available. This omission is unfortunate, for the references are widely scattered and the practising metallurgist seldom possesses the facilities that would enable him to undertake so time-consuming a task.The author of this little volume has therefore performed a valuable service by producing a critical and compre- hensive review of the existing information. The subject-matter is divided into seven chapters, the first of which is an ad- mirable, though greatly condensed, survey of the practical operations involved.254 REVIEWS OF BOOKS This provides the background needed by the uninitiated to enable them to appreci- ate the importance of the problems under discussion. The subsequent chapters deal, in turn, with the constitution of matte, the constitution of copper smelting slags, the formation of magnetite, copper losses in smelting and converting, the recovery of sulphur from smelter gases and the elimination of impurities during smelting.The first of two appendices lists the more important thermodynamical data relevant to the subject, and the second gives, for the benefit of the practical man whose chemistry is growing “rusty”, a brief explanation of the physico- chemical terms used in the text. The volume concludes with a list of 189 references and an excellent index. The author is to be congratulated on presenting a complex subject in so pleasantly readable a form, and as the great majority of his deductions and con- clusions will be rcadily accepted, there is little room for comment. Brief rcference may be made, however, to the subject-matter of Chapter IV. The formation of magnctite is so troublesome that it has given rise to much spcculation and ex- perimentation, yet it is surprising that the copper smelter thinks only in terms of magnetite or, possibly, copper ferrite, whereas the lead smelter usually speaks of spinels. Admittedly, therc is frequently more zinc in a lead furnace charge but, in general, thc slag-forming constituents are much the same in both cases, and the increasing use of chrome-magnesite bricks in the reverberatory furnace might be expected to build up a highly refractory chrome spinel in the slag.The possible formation of spinels other than magnetite appears to be a matter that needs further investigation. Where so much is excellent, there is reluctance to indulge in criticism, and although there are some points that call for comment, their relative unimportance may be taken as commendation of the author’s work.The heading of table 1, “ Compositions of Principal Copper Ores ”, is unfortunate, for thesc are minerals, not ores, and the two should not be confused. Fig. 63 is taken, presumably, direct from Aksoy’s Thesis, but the label of the horizontal axis does not makc it clear that FeS + CaS are the collectors employed, nor does it indicatc the pro- portions in which these latter reagents are used. Chapter VI appears to bc out of place, for it would be more logical to complete consideration of the smelting and converting operations before discussing the recovery of a by-product. The author is inclined to be parsimonious in his use of hyphens and commas. The lack of a hyphen reverses the meaning of “ copper oxide-containing minerals ”, and the omission of a comma will often break the reader’s concentration and interrupt his line of thought.There are relatively few misprints, but attention may be drawn to the following. In eqn. (l.l), 2FeS, not FeS, is one of the pro- ducts ; in eqn. (1.6), 302, not S02, is one of the reactants ; eqn. (6.22) is incorrect for it should be a repetition of eqn. (6.11). There is also a reference on page 73 to “ HgCl treatment ”, when HgC12 is the reagent used. While one regrets such minor blemishes, they detract little from a clear, concise and valuable publication. That it will receive a warm welcome from the copper smelter can be safely assumed. If it arouses a wider interest in this attractive field of investigation, it will perform an important service, and it should certainly prove invaluable to every teacher and student of extraction metallurgy.C. W. D. Inorganic Chemistry. A Text-Book for Advanced Students. By E. de B. BARNETT and C. L, WILSON. (Longmans Green and Co., London, 1953.) Pp. xiv + 512. Price 35s. Inorganic chemistry, properly understood, is the study of the chemical in- dividuality of the elements, and not merely a cataloguing of “ preparations and properties”. As such, it provides the field in which the general principles of physical chemistry find their detailed application. Thermodynamics, atomicREVIEWS OF BOOKS 255 structure, molecular theory and kinetic considerations all combine to weave an intriguing pattern in which each of the elements is chemically unique. This is the aspect of the subject which we may hope that an advanced text-book will bring out, and for this purpose quantitative data-free energies, equilibrium constants, electrode potentials, etc.-are quite as essential for a comparison of the elements, and quite as much in place as are the colours of precipitates or the solubilities of salt hydrates.We may also look for a certain breadth of view. For example, compounds containing carbon (other than COY C02 and the car- bonates), need not be relegated to a water-tight compartment labelled “ organic chemistry ”. The acetates, oxalates and cyanides of the heavy metals are quite as important for the chemistry of complex salts as for the systematic chemistry of carbon. By any such criteria as these, the book under review is quite unsatisfactory.After introductory chapters on nomenclature (but see below !), classification or the elements and atomic weights, the authors take up the theory of the atom in chapters on radioactivity, nuclear reactions, isotopy and the extra-nuclear structure. This is an interesting beginning, but treatment of some of these topics on a completely qualitative level is beset with some dangers, and the discussion of electron orbits is open to criticism. Chapters on stereochemistry and crystal chemistry, and the isolation of the elements, make this general section up to about 100 pages. The rest of the book is taken up with a group-by-group treatment of the elements on purely descriptive lines, but without any consistent attempt to apply general principles from the preliminary chapters.There is practically no com- parative discussion of the elements within each group. Indeed, if (as appears to be the case) the authors consider that numerical data belong to a different mental discipline (“ physical chemistry-not to be transplanted ”), it is virtually impossible to do more than enumerate the compounds that exist. Even so, the omissions are astonishing. The index (which is adequate) records some mention of Empedocles, corpse candles, the atomic bomb (twice) and sodyl hydroxide (an extraordinary aberration of nomenclature, guaranteed to obscure the relation between NaOOH and hydrogen peroxide; there is also aluminyl hydroxide, but this is quite different), but there is no reference to electrode poten- tials, cobaltammines, solubility products or austenite.Formulae for one or two cobalt complexes are, to be sure, written down in the chapter on stereochemistry, but no reference whatever is made in chapter 17 either to the ammines or (except for sketchy mentions of c02(so4)3, but not its alums, and of the cobaltinitrites) to the chemistry of trivalent cobalt. Yet another omission, the more surprising in view of the authorship, is that there is no discussion of analytical reactions, nor mention of analytical methods for the elements, in any chapter. The in- structive chemistry of metallurgical processes receives very scanty treatment. The book is quite inadequate as an advanced text-it is marred by too many lost didactic opportunities, inconsistencies of treatment and emphasis, and omissions of important subject-matter.There are also a few factual inaccuracies. It could be recommended only with considerable reservations at the elementary level. J. S. A. The Physical Chemistry of Melts. London, 1953). Pp. 106. (The Institute of Mining and Metallurgy, This small volume contains six valuable papers by authors who have become prominent in the field of molten slags and salts. Dr. J. O’M. Bockris contributes a general discussion of the constitution of molten silicates and the methods that may bc used in its investigation; Dr. J. W. Tomlinson considers the constitution of liquid oxides, especially with regard to the extent and type of their electrical256 REVIEWS OF BOOKS conductivity; Dr. T. B. King reports results on the surface tension of molten silicates, emphasizing the anomalous positive temperature derivatives sometimes found; Dr. H.Flood and his colleagues give a theoretical calculation correlating activity and composition in fused salt mixtures; Prof. M. Rey derives the heat of mixing of ferrous oxide and silica from thermodynamic data; and Dr. F. D. Richardson discusses thermodynamic aspects of molten slags. There is an intro - ductory note by Dr. Richardson and a series of discussions on each paper by the various authors and others. The symposium as a whole is a lively survey of a still somewhat obscure corner of physical chemistry. Dr. Bockris, in so strongly favouring the determination of “ kinetic ” properties such as viscosity and electric conductivity while deprecating the “ equilibrium ” approach to problems of stiucture, seems to overlook the power of thermodynamics when allied to statistical-mechanical models ; the numerical value of an entropy change, interpreted by the Boltzinann relationship and an atomic model, is surely as revealing whether it relates to a completed chemical or physical change or to the formation of a transition state.Dr. Richardson and the thermodynamicists, however, with so large a field of equilibrium data to be obtained and codified, are perhaps a little too shy of sorties into the less tidy region of process rates (even its title is commonly garbled). This and similar somewhat controversial topics form the basis of several interesting discussions throughout the symposium. Knowledge of the properties, structure and general nature of molten slags and salts, however achieved, is of the greatest importance in academic physical chem- istry, and all the present papers are important additions to our understanding. How far these studies will contribute to the solution of practical metallurgical problems and to the invention of new and improved methods remains to be seen ; it is far easier to work out structures and mechanisms than to provide practical working processes, a matter that we who take pride in making so-called “ funda- mental ” contributions to knowledge may find it salutary to ponder.T. P. H. Physical Chemistry. By F. H. MACDOUGALL, 3rd ed. (New York, The Mac- millan Co., 1952.) Pp. xi + 750. Price 41s. This admirable text-book of elementary physical chemistry, which first appeared in 1936, was revised by the author in 1943 and again last year. In the new edition, apart from minor corrections, “ the chief revision has consisted in the rewriting of the chapters on atomic structure and on reaction kinetics”. An attempt has been made to stress the important role that quantum mechanics plays in the solution of chemical problems, and an outline of the theory of absolute reaction rates has been included. The reviewer’s impression of this book is that it represents the quintessence of many years’ painstaking teaching experience. It is both refreshing and stimu- lating to see how Prof. MacDougall anticipates the many difficulties which fre- quently confront those studying the subject for the first time, and how he guides his readers carefully through them. The book is well produced in a form worthy of the Macmillan Co., and the price, in these times, is not too high. C. IF. C.

ISSN:0366-9033    

DOI:10.1039/DF9541600252

出版商:RSC    

年代:1954

数据来源: RSC