摘要:

1982 561Effect of Copper(ii) Ternary Complex Formation on the Co-ordinationBehaviour of Dipeptides in Aqueous SolutionBy Madhavan Sivasankaran Nair." Central Leather Research Institute, Adyar, Madras-600 020, Tamilnadu,IndiaBy evaluating the multip!s equilibria involved in the copper(ll)-glycylglycine (GlyGly) or glycinamide (Glam)(A)-DL-2-aminobutyric acid (2-aba), DL-3-aminobutyric acid (3-aba), DL-2.3-diaminopropionic acid (dapa),DL-2,4-diaminobutyric acid (daba), and DL-ornithine (Orn) (B), and also copper(l1)-GlyGly (A)-Glam (B)ternary systems under biologically important conditions by potentiometry using advanced computer techniques, thetendency to complexation of dipeptides in the ternary complex species of the type CuABH, CuAB, CuABH-,, andCuABH-, is discussed.It appears that the extra proton in the CuABH complexes in copper(l1)-GlyGly or Glam(A)-dapa, daba, and Orn (B) systems resides with the ligand B. In the CuABH and CuAB types of complexes, co-ordination of the dipeptides (A) gives a five-membered chelate ring involving a terminal amino-moiety and anoxygen of the neighbouring amide group. The present investigation shows that the amide-deprotonated dipeptides(AH-,)are bidentate in the CuABH-, and CuABH-, ternary complexes when the ligand B is bidentate or tridentate.IN recent years, considerable attention has been paid to resembles a dipeptide without a carboxyl group. Thethe co-ordination behaviour of dipeptides in their copper- amino-acids (B) chosen are DL-%aminobutyric acid(11) binary and ternary complexes, towards a better (2-aba), DL-3-aminobutyric acid (3-aba), ~~-2,3-diamino-understanding of metal ion-enzyme-substrate com- propionic acid (dapa), ~~-2,4-diaminobutyric acid (daba),plexes.1.2 It was generally accepted 1-12 that initial and DL-Ornithine (Om).In addition to these ten ternarycomplex formation between a dipeptide and copper(I1) systems, the copper(I1)-GlyGly (A)-Glam (B) systemin both the binary and ternary systems results in a was also studied. All these investigations were carriedTABLE 1Stability constant data for the copper(11)-2-aba, 3-aba, dapa, daba, Orn, GlyGly, and Glam binary systems at 37 "C andI = 0.15 mol dmV3 (Na[ClO,]). Standard deviations are given in parenthesesLigands B2-aba 3-aba dapa b daba b Om b GlyGly CJ Glam c d7 h r--log P13B 9.43(1) 9.95( 1) 9.37 (2) 9.93 (2) 10.22( 1) 7.99(1) 7.89(1)11.26( 1) - log P H ~ B- - 1 5.3 7 (4) 1 6.99 (3) 17.67(2) -log P H ~ B8.10(2) 7.16(2) 10.6 1 (4) 10.94(3) - 5.70 (8) 5.53(5)log P C ~ B , H ~ - - 30.16(5) 32.92 (4) 34.3 2 (3) - -log P C ~ B ~ R - - 25.32 (6) 2 6.8 9 (4) 26.12(6) - -log PGuBa 15.13(4) 12.90(5) 20.18(5) 19.15(6) - - -log Po~BH-,11.54(1) 13.30( 1) 15.98(3) 1 8.02 (4) 18.85( 2) - 20.99 (4) - 1 7.37 (5) 19.88(6) - -- log PCuBHlog PCuB- 1.62(2) - 1.14(9) - - - -- - - 5.50( 10) 3.18(9) - - log PCul3sH-1(I Refs.19 and 20. Ref. 13. Refs. 8 and 20. GlyGly and Glam become primary ligands A in the ternary systems (Tables 2out by potentiometry at 37 "C and I = 0.15 mol dm-3(Na[C104]) in aqueous perchlorate media.and 3).However, Glam is the secondary ligand B in the copper(::)-GlyGly (A)-Glam (B) ternary system.chelate involving a terminal amino-moiety and oxygenof the neighbouring amide group. At higher pH values,the dipeptide undergoes deprotonation of the amidegroup and it becomes tridentate via N-amino, N-pep-tido, and O-carboxylate groups as in the CuAH-, glycyl-glycinate (GlyGlyO) binary complexSolutions of all the ligands (Fluka Puriss) were preparedimmediately before use in doubly-distilled water fromperchlorate solution was prepared by neutralising copper(I1)However, interpretations with regard to the bonding dried under vacuum Over p2°!i* CoPPer(ll)mode Of amide-deProtonated diPePtides in the carbonate with perchloric acid.The concentration of the systems Of copper(11) differ* work- metal stock solution was determined by titration withers 4'9p10 are of the view that the amide-deprotonated ethylenediaminetetra-acetate. Acid-washed glassware anddipeptides are bidentate via N-amino- and N-peptido- reagent grade chemicals were used throughout the work.groups in the copper(I1) ternary complex systems. Examinations by potentiometry were made at 37 "C underOthers 9911p12 favour the tridentate binding through N- nitrogen with 0.15 mol dm-3 Na[C10,] as backgroundamino, N-peptido, and O-carboxylate groups in the electrolyte. The equipment and electrode standardisationternary systems, as is also the case with the C u ~ H - , procedures have been described elsewhere.13-17 The stab-GlyGlyO binary complex species.Q, considering these ility constants for the ternary systems were computed frompoints, I thought it worthwhile to study the stability and titrations in which total concentrations of the metal, ligandA, and ligand B were in 1 : 1 : 1 and 1 : 2 : 2 molar ratios. structure of various ternary complex species for some * Present address: Department of Chemistry, Post GraduateExtension Centre, Madurai Kamaraj University, St. John's College(A)-amino-acid (B) systems. The compound Glam Campus, Palayamkottai-627 002, Tamilnadu, India.copper(rr)-glycylglycine (G1yG1y) Or glycinamide (G1am562 J.C.S. DaltonThe potentiometric data were treated with the MINIQUAD-75 computer program la on an IBM-370 computer.Whilerefining the ternary complex constants, the values of overallprotonation constants of the ligands A and B, and the overallassociation constants of the parent binary complex species13, 19, 2o measured at 37 "C and 1 = 0.15 mol dm-3 (Na[ClO,])by potentiometry using MTNIQUAD-75 (Table l ) , werefixed without further refinement. The ionic product ofwater, i.e. the pK, value of 13.62 a t 37 "C, was also treatedas a non-refinable parameter. The model selected was thatwhich gave the best statistical fit, consistent with chemicallogic, to the titration data without giving any systematicdrifts in the magnitudes of various residuals as describedelsewhere.la The results obtained are listed in Tables 2and 3. The charges of all the complex species reported inthis paper are omitted for clarity.RESULTS AND DISCUSSIONThe copper(r1)-GlyGly or Glam (A)-2-aba and 3-aba(B) systems showed the presence of two ternary com-plexes (CuAB and CuABH-,) in addition to the binarycomplex species [HA, CuA, CuAH-,, CuA,H-,, HB,H,B, CUB, CUB,, and also H,A in the GlyGly (A) ligandsystems]. In the copper(I1)-GlyGly or Glam (A)-dapa,daba, and Orn (B) systems, three ternary complex speciesplexes in all the six ternary systems mentioned aboveresides with the dapa, daba, or Orn secondary ligands (B),because in the copper(I1)-GlyGly or Glam (A) binarysystems, no protonated species were detected.8P2O Ithas already been established 13*21,22 that the site ofprotonation in the CuBH or CuB,H dapa, daba, and Orncomplexes is their respective terminal amino-groups.Hence it may be inferred that in the CuABH complexesdetected in the systems also under study, the extraproton is attached to the terminal amino-group of thedapa, daba, or Orn (B) ligands.The same point mayfurther be confirmed by noting that the log PcuhBH,pK&ABH, and log Kg:iBH values in Tables 2 and 3follow the trends of the log ~ R R or log pcuBEE values inTable 1 for the copper(r1)-dapa, daba, or Orn (B)binary systems. The log K%tgE values in Table 2for the copper(I1)-GlyGly (A)-dapa, daba, and Orn (B)systems are comparable to the log PcuR value in Table 1for the copper(I1)-GlyGly binary system suggest-ing that GlyGly is bidentate via N-amino- and 0-peptido-groups in these CuABH ternary complexes.Thus, the CuARH complexes in the copper(I1)-GlyGly(A)-dapa, daba, and Orn (B) systems would haveTABLE 2Stability constants for the copper(I1)-GlyGly(A)-secondary ligand(B) systems a t 37 "C and I = 0.15 mol dm-3 (Na[ClO,]).Standard deviations are given in parenthesesSecondary ligands B2-aba13.40 (1 0)6.54(7)--7.705.306.864.92- 0.40- 1.56-3.183-aba12.94( 17)5.91(5)--7.245.780.087.034.29- 1.25- 2.87of stoicheiometry CuABH, CuAR, and CuARH-, wereevident in addition to the binary species [HA, CuA,CuAH-,, CuA,H-,, HB, H,B, H,B, CuBH, CuB,H,,CuB,H; also H,A in the GlyGly (A) ligand systems, andCUB and CUB, in the dapa, daba (B) ligand systems].The CuAB, CuARH-,, and CuABH-, ternary complexeswere detected in the copper(I1)-GlyGly (A)-Glam (R)system in addition to the binary complexes (HA,H,A, CuA, CuAH-,, CuA,H-,, HB, CUB, CuRH-,, andCuBH-,).1.Stability and Structure of the CuABH TernaryComplexes in CojbPer(II)-GlyGly OY Glam (A)-dapa,daba, and Orn (B) Systems.-It appears more reasonableto suggest that the extra proton in the CuABH com-dapa20.92 (10)16.05( 12)8.7 9 (4)c4.8715.225.55-0.1510.355.44-0.267.267.17- 1.82- 3.44daba2 2.58 (5)1 6.1 1 (4)8.49 (4)6.4716.885.59-0.1110.415.177.626.87--0.53- 2.45- 4.07Om23.2 5 (9)1 6.55 ( 10)8.2 8 (22)6.7017.555.58-0.1210.85--8.276.66Glam11.25(8)-4.19( 10)-2.74(15)--5.556.680.027.062.57- 1.34- 2.966.933.22enhanced stability due to the electrostatic interactionbetween the terminal -NH,+ group of the B ligand andthe unbound COO- group of GlyGly (A).However,such interactions are not possible in the CuABH com-plexes in copper(I1)-Glam (A)-dapa, daba, and Orn (B)systems because Glam (A) does not contain a COO-group.In order to characterise the stability of the CuABHternary complex with that of the binary complexes CuAor CuBH, the parameter A log KCuABH was calculatedusing equation (2) for the equilibrium reaction (1). Forcopper(r1) having a square-planar co-ordination sphere towhich two bidentate ligands co-ordinate, on statisticalgrounds 2923p24 a A log K value of -0.6 is expected an1982TABLE 3Stability constants for the copper(n)-Glam (A)-secondary ligand (B) systems a t 37 "C and I = 0.16 mol dm'-s(Na[C10,]).Standard deviations are given in parenthesesSecondary ligands B5632-aba1 2.64 (9)5.71(5)-----7.114.54-0.996.936.85-2.39- 1.253-aba -1 1.89(9)4.89 (4)----6.364.73-0.807.006.03- 2.27 - 1.13values greater than this indicate higher stability of theCuA + CuBH CuABH + Cu (1)A log KC~ABH = log PC~ABH -ternary complexes than the binary complexes. TheA log KCuABH values in Table 2 for the copper(I1)-GlyGly (A)-dapa, daba, and Orn (B) systems follow thistrend. However, the same parameter in Table 3 for theCuABH complexes in the ternary systems with (A) =Glam suggest that they do not have marked stabilities.2.Stability and Structure of CuAB Ternary CompEexes inthe Systems under Study.-As in the monoprotonatedternary complexes CuABH discussed above, it is clearfrom the log KgsB values in Tables 2 and 3 that in theCuAB complexes in all these ternary systems the GlyGlyor Glam (A) ligand binds the metal in a bidentate modevia N-amino- and O-peptido-groups. The log KpdBvalues in Tables 2 and 3 for the systems with (B) =2-aba and 3-aba agree closely with the corresponding logPCuB values in Table 1 for the copper(11)-2-aba and 3-aba(B) binary systems, demonstrating that bonding of 2-abaand 3-aba in the CuAB ternary complexes in the presenceof GlyGly or Glam (A) ligands involves respectively five-and six-membered chelate rings.Thus, the copper(@-GlyGly or Glam (A)-2-aba and 3-aba (B) systems wouldrespectively contain five- and five-, and five- and six-membered chelate rings, of which the latter would bemore preferred 2~19920*23-25 due to the fact that the ringsof different sizes introduce more ligand-field asymmetryand stabilize the ternary complexes. Also, it may beconcluded from the log Kg:iB values in Tables 2 and 3for the copper(I1)-GlyGly or Glam (A)-dapa, daba, andOrn (B) systems that all these secondary ligands (B) aretridentate in their CuAB complexes. The log Kg:zB andlog K8;iB values in Table 2 for the copper(I1)-GlyGly(A)-Glam (B) system clearly indicate that both GlyGly(A) and Glam (B) are bidentate in the CuAB complexresulting in two five-membered chelate rings.Thus,the copper(I1)-GlyGly or Glam (A)-Z-aba and 3-aba, and(log PCuA + log PCuBH) (2)dapa20.07(43)15.30( 8)8.14(4)4.7714.444.70 - 0.839.774.69-0.667.169.28- 2.47- 1.33daba21.82(4)1 5.58 (3)8.10(2)6.2416.294.8310.054.64-0.897.489.24-0.70- 2.84- 1.70Om22.11 (8)14.95( 7)6.65(8)7.1616.684.44- 1.099.42--8.307.79--also copper(I1)-GlyGly (A)-Glam (B) ternary systemswould have a square-planar geometry, and hence aA log KcuAB value [equations (3) and (a)] of -0.6 isexpected. However, in the copper(I1)-GlyGly or Glam(A)-dapa, daba, and Orn (B) systems, the statisticallyexpected value 2*19924 of A log K C ~ B is -0.9, because theco-ordination sphere of copper(I1) in these complexesbecomes distorted due to the tridentate binding of thedapa, daba, or Om (B) ligands.Comparison of the A logKcuA~ values for the copper (Iz)-GlyGly (A)-secondaryligand (B) systems in Table 2 with the above statisticallyexpected values clearly demonstrates that the CuABcomplexes in all these six ternary systems do have markedstabilities. However, the A log KcuAB values in Table 3CuA + CUB T- CuAB + Cu (3)(4) A log KC~AB = log PC~AB - (log PCUA + log @CUB)for the systems with (A) = Glam do not deviate muchfrom their statistically expected values. The positiveA log KcuAB values obtained in the copper(I1)-GlyGly(A)-3-aba and Glam (B) ternary systems (Table 2) sug-gest that 3-aba or Glam (B) prefers to add to the CuA Gly-Gly binary complex rather than to aquated copper(I1).Again, it may be noted from Tables 2 and 3 that A logK&AB values for the copper(I1)-GlyGly or Glam (A)-3-aba (B) systems are more positive compared to thosevalues for the copper(I1)-GlyGly or Glam (A)-2-aba (B)systems.This may be attributed to the preference forfive- and six-membered chelate rings in the formersystems compared to the five- and five-membered chelaterings in the latter as described earlier.3. Stability and Structure of CuABH-, Ternary Com-plexes.-With rise in pH, the amide group of the dipep-tides [GlyGly or Glam (A)] becomes deprotonated andCuABH-, ternary complexes are formed. A questionarises with regard to the mode of bonding of theseamide-deprotonated dipeptides (AH-,) and the secondaryligands (B).Regarding the mode of bonding of thesecondary ligands (B), one may expect the bidentatebinding of 2-aba and 3-aba, and tridentate binding o564 J.C.S. Daltondapa, daba, and Orn (B) in the CuABH-, complexes also,as their binding in CuAB complexes in the copper(I1)-GlyGly or Glam (A)-2-aba, 3-aba, dapa, daba, and Orn(B) systems described above. If so, the log Kg& andlog Kg:kgg-, values in each of these systems must becomparable. But it may be noted from Tables 2 and 3that the copper(I1)-Glam (A)-(B) systems follow thistrend, while in the copper(I1)-GlyGly (A)-(B) systemsthe log Kg:iEs- values in all the systems are ca. 3 logunits less than the corresponding value for log Kg;iB.This may be easily accounted for by considering thebidentate binding of the amide-deprotonated GlyGlyvia N-amino and N-peptide groups in the CuABH-,complexes unlike its binding in a tridentate mannervia N-amino, N-peptide, and 0-carboxylate groups in theCuAH-, GlyGly binary complex; 4 ~ 8 2.e.for computinglog using equation (5), the log ~ c ~ h ~ - , valueused was that for the tridentate binding of the amide-deprotonated GlyGly in its CuAH-, binary complexirrespective of its bidentate binding in the CuABH-,ternary complex species. Thus, log KgLyg-, values getreduced by ca. 3 log units in all the systems. This bi-dentate binding of the amide-deprotonated GlyGly in theternary systems under study may further be confirmedby noting that the pKgUAB values in all the copper(I1)-GlyGly (A)-(B) systems in Table 2 are nearly identicalloo Ica# 8 40d E2002.5 3.5 4.5 5.5 6 5 75 8.5PHFIGURE 1 Species distribution for the copper(I1)-GlyGly(A)-daba(B) ternary system at a metal : A : B ratio 1 : 1 : 1 : (1) unboundcopper(n), (2) CuA, (3) CuAH-,, (4) CuA,H-,, (6) CuBH, (6)CUB, (7) CuB,H,, (8) CuB,H, (9) CUB,, (10) CuABH, (11) CuAB,and (12) CuABH-,within the limits of experimental error to those values inTable 3 for the corresponding copper(I1)-Glam (A)-(B)ternary systems, i.e.the bonding modes of amide-de-protonated GlyGly and Glam are same in the CuABH,,complexes in all the ternary systems reported here. Ifthe carboxylate group of amide-deprotonated GlyGly isalso co-ordinated with the metal in its CuABH-, ternaryspecies, then it should have been reflected in the pK&ABvalue as is the case with pKZuA values in the copper(I1)-GlyGly and Glam (A) binary systems.4~~The different mode of bonding of amide-deprotonatedGlyGly in the CuAH-, binary and CuABH-, ternarycomplex species is also reflected in the A log KCuhRH-,values in Table 2 ; i.e.this parameter is negative withhigh magnitude which may be explained by consideringthe fact that for calculating A log KauABIX-l using equa-tion (7), the log PcuAH-, value used was that for thetridentate binding of the amide-deprotonated GlyGly inCuAH-, + CUB CuABH-, + Cu (6)its CuAH-, binary complex, although it is bidentate inthe CuABH-, ternary complex species.With regard to the ternary complexes, CuABH-, andCuARH, in the copper(I1)-GlyGly (A)-Glam (B) system,PHFIGURE 2 Species distribution for the copper(I1)-Glam (A)-dabaSpecies (B).ternary system at a metal : A : B ratio of 1 : 1 : 1.as in Figure 1it seems that the CuABH-, complex is formed due to thedeprotonation of the amide group of GlyGly (A) becausethe discrepancies described above in the log Kand A log KCuABn-1 values in copper(I1)-GlyGly (A)-2-aba,3-aba, dapa, daba, and Om (B) systems are also seen inthese values in Table 2 for the copper(I1)-GlyGly (A)-Glam (B) ternary system. In the CuABH-, species inthis system, one may easily suggest that the amidegroup of both GlyGly (A) and Glam (B) is deprotonatedand thus this complex species would have a square-planar geometry where the four positions would be filledup by the amino- and peptido-nitrogens of GlyGly (A)CuAH-1OUABH-1982 565and Glam (B) ligands.The comparable pKEuAB andpK~uABH-, values in Table 2 for this system further con-firms that both the amide-deprotonated GlyGly (A) andGlam (€3) are bidentate in its CuABH-, complex. Theparameter A log KC^^^^^-, included in Table 2 was com-puted using equation (9). This value is more negative,which may be accounted by putting forward the sameCuAH-, + CuBH-, CuARH-, + Cu (8)log Pc~BH-,) (9)A log KCUARH-~ = log P c ~ A B H - ~ - (log PC~AH-, +arguments described above for explaining more negativeA log KcUAHH-, values in the copper(I1)-GlyGly (A)-2-aba, 3-aba, dapa, daba, and Orn (B) ternary systems.Now it seems to be more interesting to correlate thepresent results on the bonding mode of the amide-deprotonated dipeptides in the copper(I1) ternary com-plex systems with earlier studies.Martin et aL9 sug-gested two equilibrium structures for the CuABH-,complex species in the copper( II)-GlyGly (A)-glycine(B) ternary system where in one structure, GlyGly (A)binds the metal in a bidentate mode via amino- andpeptido-nitrogens, while in the other structure, GlyGly istridentate through N-amino, N-peptido, and O-carboxy-late groups. Glycine (B) in this system is bidentate inthe first structure, while it is unchelated in the other.Sigel and co-workers 49% showed that the amide-de-protonated dipeptide is bidentate via N-amino and N -peptide groups in the CuABH-, complexes in the copper-(11) -di peptide (A) -2,Z'-bipyridyl (B) ternary systems.Brookes and Pettit 27 attributed the absence of CuABH-,ternary complex species in copper( 11)-glycyl-L-valine andL-valyl-L-valine (A)-D- or L-histidine (B) systems even atpH 9 to the factor: ' the driving force for the ionizationof the amide proton in these dipeptides (A) is drasticallyreduced due to the tridentate character of histidine (A)ligand '.However, Nair et aZ.1° reported that in thepresence of a bidentate ligand such as histamine or atridentate ligand such as L-histidine, the amide-depro-tonated dipeptides in the CuABH-, ternary species bindin a bidentate mode.The same group of workers28predicted that in the presence of a monodentate ligandlike unsubstituted imidazole, the amide-deprotonated di-peptide can bind both in bidentate and tridentate modesand two equilibrium structures were postulated. Nagy-pal and Gergely l1 suggested tridentate binding of theamide-deprotonated dipeptides in the CuABH-, com-plexes in the copper(I1)-dipeptide (A)-amino-acid (B)systems on the basis that log PCuABR-, values in thecopper(I1)-dipeptide (A)-a- and p-amino-acid (B) systemsare comparable. However, the validity of such argu-ments is doubtful because while comparing the relativestabilities of two ternary complex species, one must takeinto consideration the basicities of the ligands involvedin the complexation.Thus following Sigel 2p23*24 itappears that the parameter A log K , the difference instability of the ternary complex with that of the binarycomplex, is the best way to compare the relative sta-bilities. The A log K c ~ ~ ~ H - ~ values in Table 2 for thecopper(I1)-GlyGly (A)-Z-aba and 3-aba (B) ternarysystems clearly indicate that the CuABH-, ternaryspecies in the system with B = 3-aba is more stable thanthat species in the system with B = 2-aba, which is in ac-cordance with the preference for copper(I1) ternary che-lates containing five- and five-membered rings.2J9* 20*23-25A recent crystal structure analysis of the CuABH-, 'Oh 805 1 0, 60 fPHFIGURE 3 Species distribution for the copper(I1)-GlyGly (A)-Glam (B) ternary system at a metal : A : B ratio of 1 : 1 : 1; (1)unbound copper(Ir), (2) CuA, (3) CuAH-,, (4) CuA,H-,, (5) CUB,(6) CuBH-,, (7) CuB,H-,, (8) CuAB, (9) CuABH-,, and (10)CuABH-,(A = GlyGly, B = 1,lO-phenanthroline) ternary speciesby Lim et aZ.12 indicates that the amide-deprotonatedGlyGly is tridentate.On the basis of the visible spectra,these workers suggested that in aqueous solution also,tridentate binding of the amide-deprotonated dipeptidescan be expected in the ternary complex systems. How-ever, the interpretation of the absorption spectra of suchsystems at higher pH is difficult due to the manyhydrolysed species. Hence without detailed knowledgeof the concentrations of all these complexes from theirabsorption maxima and absorption coefficients, onecannot easily draw any conclusions regarding theirsolution structures.Thus, the present studies on thecopper(I1)-GlyGly or Glam (A)-amino-acid (B) systemsdemonstrate beyond doubt that the amide-deprotonateddipeptides in the presence of bidentate or tridentateligands in the ternary systems of copper(1i) in aqueoussolution bind the metal through N-amino and N-peptidodonor groups, which is in agreement with the studiesreported previously by Sigel et al.4926 and also by Nairet aZ.1° However, one cannot rule out the possibility ofthe tridentate binding of the amide-deprotonated di566 J.C.S. Daltonpeptides in the copper@) ternary chelate systems in pre-sence of a monodentate ligand as reported by Nair et a1.a4. Distribution of Species as a Function of pH for theTernary Systems under Study.-The distribution ofvarious binary and ternary complexes (as percentages oftotal metal) as a function of pH has been calculated forall the eleven ternary systems reported in this paper.The monoprotonated ternary complexes CuABH in thecopper(I1)-GlyGly or Glam (A)-dapa, daba, and Om (B)systems were found to be more favoured in the pH range4.5-6.5.As expected, the pH region for the predomin-ancy of the CuAB complexes was found to be dependentupon the basicity of the secondary ligand. For example,the CuAB ternary complex species in the system withB = 2-aba attained its maximum concentration at pH 5,while in the system with B = Orn the concentration ofthe CuAB species did not reach its maximum even at pH8 and there is a steady increase in its formation withfurther rise in pH.Again, the concentration of theCuAB complexes in the system with 13 = 2-aba and3-aba was found to be only below 10% of the total metalin 1 : 1 : 1 solutions, however they were found in appre-ciable concentrations in 1 : 2 : 2 solutions. For example,in the 1 : 2 : 2 solution of copper(r1)-GlyGly (A)-2-aba(B), about 22% of the total metal was found to bepresent in the form of CuAB. In all the copper(I1)-GlyGly or Glam (A)-secondary ligand (B) systems in thisstudy, the formation of the CuABH-, ternary speciesbegan near pH 6.5 and there is a steady increase in itsconcentration with the rise in pH. The typical distri-bution pattern of the species for the copper(I1)-GlyGly orGlam (A)-daba (B) and also copper(I1)-GlyGly (A)-Glam (B) ternary systems are given in Figures 1-3.The diagrams for the other systems in the presentinvestigation showed the qualitative features of Figures1-3.I wish to thank Professor M.Santappa, Director, CentralLeather Research Institute, Adyar, Madras-20 for his keeninterest in this work.[1/848 Received, 27th May, 19811REFERENCES‘ Inorganic Biochemistry,’ ed. G. L. Eichhorn, Elsevier,Amsterdam, 1973, vols. 1 and 2.‘ Metal Ions in Biological Systems,’ ed. H. Sigel, MarcelDekker, New York, 1973, vol. 2.L. G. Sillen and A. E. Martell, ‘ Stability Constants of MetalIon Complexes,’ Spec. PubI., The Chemical Society, London, 1964and 1971, nos.17 and 25.H. Sigel, Inorg. Chem., 1975, 14, 1535.R. P. Agarwal and D. D. Perrin, J . Chem. SOC., DaltonG. Brookes and L. D. Pettit, J. Chem. SOC., Dalton Trans.,Trans., 1975, 268.1975, 2112.A. Gergely and I. Nagypal, J . Chem. SOC., Dalton Trans.,1977, 1104.M. S. Nair, M. Santappa, and P. Natarajan, Indian J . Chem.,R. P. Martin, L. Mosoni, and B. Sarkar, J . Biol. Chem., 1971,lo M. S. Nair, M. Santappa, and P. Natarajan, J . Chem. SOC.,1980, lOA, 672.246, 5944.Dalton Trans., 1980, 2138.11 I. Nagypal and A. Gergely, J . Chem. SOC., Dalton Trans.,1977, 1109.l2 M. C. Lim, E. Sinn, and R. B. Martin, Inorg. Chem., 1976,15,l3 M. S. Nair and M. Santappa, J . Chem. SOC., Dalton Trans.,M . S . Nair, K. V. Chalapathi, M. Santappa, and P. K.l6 M. S. Nair, M. Santappa, and P. K. Murugan, Inorg. Chem.,l6 M. S . Nair, K. V. Chalapatni, and M. Santappa, precedingl7 M. S. Nair and M. Santappa, Indian J . Chem., in the press.Is P. Gans, A. Vacca, and A. Sabatini, Inorg. Chim. Acta, 1976,M. S. Nair and M. Santappa, Indian J . Chem., in the press.2o M. S. Nair, Ph.D. Thesis, University of Madras, 1979.21 G. Brookes and L. D. Pettit, J . Chem. SOC., Dalton Trans.,1976, 42.22 A. Gergely, E. Farkas, I. Nagypal, and E. Kas, J . Inovg.Nucl. Chem., 197!, 40, 1709.23 H. Sigel in IUPAC Coordination Chemistry-20,’ ed. D.Banerjea, Pergamon Press, Oxford and New York, 1980, pp.2( H. Sigel, Angew. Chem. Int. Ed. Engl., 1975, 14, 394.s5 M. S. Nair, M. Santappa, and P. Natarajan, J . Chem. SOC.,26 H. Sigel, C. F. Naumann, B. Prijs, D. B. McCormick, and27 G. Brookes and L. D. Pettit, J . Chem. SOC., Dalton Trans.,28 M. S. Nair, M. Santappa, and P. Natarajan, Inorg. Chim.807.1981, 992.Murugan, J . Chem. SOC., Dalton Trans., 1982, 55.in the press.paper.18, 237.27-45.Dalton Trans., 1980, 1312.M . C. Falk, Inorg. Chem., 1977, 16, 790.1977, 1918.Acta, 1980, 41, 7

ISSN:1477-9226    

DOI:10.1039/DT9820000561

出版商:RSC    

年代:1982

数据来源: RSC