Girdhar, H. L.

Parveen, (Miss) Shamah

Puri, M. K.

English

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The values of ii approach 2 for Gd3t, Dy3+, Er3+and Tb3+ chelates with tyrosine indicating theformation of 1: 1 and 1: 2 complexes. The orderof overall stability constants of these complexesis: Yb3t>Er3+>Dy3~>Gd3+ at 25°, 35° and 45°in accordance with their electronic configura-tions. The data show an increase in log Kl andlog K2 values with increase in temperature whichindicates that higher temperature ::; favourablefor complex formation. .-\ comparison of metal-ligand stability constants of tvrosine with those ofserine reveals that hydroxy gr,up is unionize.i andis not participating in complex formttio.16.l2. Thecoordination appel.rs to be throuzh a-nino nitrogenand carboxylic o;~vg.oa 1),11y. The ire; ,~.1;r6ie, offormation (~GO) have rn ire It';sli:iv\~ values athigher temperatures sl1Jwing tint complex Iorrna-tion is a spo.rtancius p,"Y~~'" The formation ofall the complexes is an e.idotherrnic reactioi whichexplains the increase in the values of Ior.nationconstants with increase in temperature. The ~SOvalues are positive in all the Ch~) indicating Iavour-able entropy change for the [),',nlticn of conplexes,References1. SILLEK, L G, & :\h.RTELL, .\. E., Stability constants ofmetal ion complexes, Special Publication No. 17 (TileChemical Society, Londm). 1964.2, SILLEK, L G. & ':\IARTELL, A. E., Stability constuits ofmetal ion complexes, Special Publication No. 25 (TheChemical Societv, Lo nd on). 1971.3, PERKDfS, D . .T., Biocheni. I, 55 (1953), 649.4. ALBERT, A" Biochcm, I, 50 (1950), 690,5. BIRCH, C. G. &; :\1.'-KAII.\;-';, S. E., Ariatvt, Clieni., 39(1967), 1182.6. LETTER, .T. K & BATDIA)[, .T. E., J . .4.;j/, cic.n: Soc. 92(1970), 443,7. SCHWARZEK.-\BACH, G. & FL\SCHKA. H., Comvlo.cometrictitrations (Methuen & Co. Ltd, London), 1969, 195.8. CALVIK, :VI. & \VILSO:<f, K, W., I .·lm. chcin: s-: 67(1945), 2003.9. BJERRUM, l, JI'!iai c nuninc in {tIlte')I!, soluticn s(P. Haas~ & Sons, 1941-10. IRVIXG, H. & ROSSOTTI, J·1" Soc., (1953), 3397.11. YATSIMIRSKII, K. B. 8: VASPL'EV, V. P., l nsiabilityconstants of complex compounds (D. Van Nostrand Co.Inc., New York), 1963, 63.12. PANASYNK, V. D. & GOL\B, V. A" Russ. J. inorg, Cheni.,14 (1965), 1485.Stability Constants of Glutamic AcidComplexes with Some Metal IonsH. L GIRDHAR, ('lEss) SHA:\!AH PARVEEN & M. K. PURlDepartment of Chernistrv, The University of KashmirSrinagarReceived 5 January 1976; accepted 26 April 1976Stepwise stability constants of glutamic acid com-plexes with a number of metal ions have been deter-mined by Bjerrum-Calvin pH titration method. Thecompositions of the complexes are 1: 1 for Cr", Fe3+,La3+, Nd3+, Pr3+, Zr4+, Th4+ and both 1: 1 and 1: 2 forAg+, Mn2+, C02+,Ni"+, Cu=, Zn2+, UO~+.IN ~pite of known ~helating ability of glutamicacid>", no systematic study on the complexes ofthis ligand with various metal ions has been carriedNOTESout. Further in view of its importance from bio-chemical point of view, we thought it fit to studyits complexes with a number of metal iois in solutionemploying Bjerrum-Calvin PH titration technique+",Glutamic acid (E. :\Ierck, AR) was used to pre-pare 0·005J1 aqueous solution. Stock solutions(0·005J1) of metal ions were prepared using ana-lytical grade reagents and standardized by conven-tional motJuJs6. The complex equilibria werestudied at 25" and 'J. = O·U1. Potassium nitrateand nitric acid were l~;;ed to maintain constant ionicstrength. All /)H measurements were made usingPhilips jJH meter (PR 9405) which was calibratedat·}O a.id 9·2 pH values. The following solutions(total vol. 50 rnl) were titrated separately against0·1.11 KOH; (A) 5 ml of K:W3 (1M) + 10 ml ofH~03 (0·01.V1); (E) A - 10 ml of glutamic acid(0·005J1); and (C) B + 2 ml of metal ion solution(0·005.l1) .From the titration curves of solutions (A) and(B), iiH values at different PH were calculated bythe methol of Irving and RO .ssotti". The calculatedvalues of fIH were plotted against pH and the proto-nation constants computed by interpolation at half11:H values. The values of K1 and K1; are 9·20 and4·15 respectively. From the titration plots ofsolutions (B) and (C), Ii and pL values were calcu-lated and the formation curves were obtained byplotting 71: values against PL values. For eachmetal ion the stepwise stability constants wereevaluated by interpolation at half !I: values and arerecorded in Table 1. Since the values of stabilityconstants for the complexes of Ag1+ to UO~+ are lessthan 2 log units apart, therefore, the stability con-stants for these were also calculated bv the methodof least squares. ~It has been found that the complexes of UO:;+,Cr3+, Fe3+, La3+, Nd3+. Pr3+, Zr4+, Th4+ get hydrolysedin the PH range 3·0 to 8·0. However, in other casesthe complexes are stable towards hydrolysis becausethere is no precipitate formation even \vhen the pHTABLE 1 _. STEPWISE STABILITY CONSTA)[TS OFGLUL\}!IC ACID CO:-!PLEXESCation Log tc« L')g Ka Loe;]{b Log «» LoO' ~n t;.F1 2' 1 2 '" (kcal/mole)t\,cyl+ 4·07 3·20 4-14 3·32 7·46(b) -10'17• bMn2+ 4·07 3·50 4-10 B5 7·65 -10·43C02+ 4·60 3·73 4·74 3·74 8·48 -11,57N"H 5·90 4·37 5·90 4·38 10·28 -14,09" 1Cu2+ 8'23 6·07 8·17 6·11 14·28 -19'48Zn2+ 5-40 4·37 5·37 4'23 9·60 -13-09UO~+ 8·30 6·37 8·23 6·64 14'87 -20'28Cr3> 9·70 9·70(a) -13'23Fe3+ 9·56 9'56 -13-04La3+ 5·50 5·50 -7,50Nd3+ 5·80 5·80 -7·71Pr3+ 4·80 4·80 -6,54Zr4+ 8·30 8·30 -11·32ThH 9·10 9·10 -12,41(a) Values calculated bv half n method.(b) Values calculated by least square method.1021INDIAN J. CHEM., VOL. 14A, DECEMBER 1976is raised to 10. The data in Table 1 show that theCr3+, Fe3+, La3+, Nd3+, Pr3+, Zr4+ and Th4+ form 1: 1complexes only and Agl+, Mn2+, Co", Ni2+, Cu-",Zn-" and UOi+ form both the 1: 1 and 1: 2 com-plexes. The order of stability of 1: 1 and 1: 2complexes of bivalent metal ions is UO~+>CU2+>Ni2+>Znc+>C02+>Mn:'+ which is in agreementwith the general order of stability given by Irvingand Williams",One of us (S.P.) is thankful to the CSIR, NewDelhi, for the award of a junior research fellowship.References1. CHABEREK, S. (Jr) & MARTELL, A. E., j. Alii. che in. Soc.,74 (1952), 6021.2. LI, N. C. & DOODY, E., j. Am. chem. Soc., 74 (1952), 4189.3. PERRIN, D. D., j. chem, Soc., (19591, 290.4. BJERRl:~I, J., Metal ammine formation ill aqueous solutions,(P. Haase & Sons, Copenhagen), 1941.5. CALVIN, 1\1. & \\'ILSON, K. \V., j. Alii. chem. Soc., 67(1945), 2003.6. VOGEL, A. I., A text book of quantitative inorganic analysis(Longmans, London), 1971.7. IRVING, H. :\1. & ROSSOTTI, H. S., j. chcni. Soc., (1954),2904.8. IRVING, H. & \\'ILLIAMS, R. J. P., Nature, Lond., 162(194-8), 74-6.Determination of Hydraz ine, Methylhydr az ine,Semicarbazide & Hexacyanoferrate(II) UsingPeriod ateR. L. KAl:SHIK, O. P. VERMANI & RAJENDRA PROSA[)Department of Chemistry, Regiunal Engineering CollegeKurukshct raReceived 30 [unuary 1976; accepted 17 JJay 1976Hydrazine, methylhydrazine, semicarbazide andhexacyanoferrate(lI) have been oxidized with excessof metaperiodate under suitable conditions. Theequivalent amount of iodate liberated is treated withpotassium iodide in chloroacetic acid buffer and theiodine liberated by titrating with standard sodiumthiosulphate after masking the excess metaperiodatewith molybdate.SI~GH and coworkers have used metapcriodat cas an oxidizing titrant for the determinationof hydrazinc and its derivatives under the conditionsof Andrews and Lang-- 2. In the presence of bicar-bonate, reduction of met aperiodatc with hydrazinc,methylhydrazirie and sernicarbazide goes only up toiodate stage. Similarly, in the presence of boricacid, met aperiodat e is reduced to iodate withhexacyanoferratetl.I)". Since the iodate formedin these reactions is stoichiometrically related tothe amount of hydrazine, methylhydrazinc, semi-carbazide and hexacyanoferrat efl I) taken, it wouldbe better to determine organic compounds bytitrating the iodate and hexacyanoferrate(II) bytitrating the iodate and hexacyanoferratetl H)formed", Under the conditions each organic mole-cule and hexacyanoferraterl I) ion would give riseto twelve and eight iodine atoms respectively. Withthis background, we describe in this note a sensitive1022method for the estimation of hydrazine, methyl-hydrazine, semicarbazid e and hexacyanoferraterl I)using periodate.All the chemicals used were of AR (BDH orE. Merck) grade. Solutions of hydrazine sulphate,methylhydrazinc sulphate, semi carbazide hydro-chloride and potassium hexacyanoferratetl I) wereprepared in distilled water and standardized byiodine.Chloroacetic acid buffer was prepared by dissolving25 g of the substance in 70 ml distilled water andits PH adjusted to 2·9 with strong sodium hydroxidesolution.2.M molybdate solution was obtained by dissolv-ing ammonium molybdate in hot distilled water.Determination of hydrazine, methylbydrazine andsemicarbazido - A suitable aliquot of the substanceto be determined was added to aq. sodium bicar-bonate (10 ml, 1%) containing an excess of potas-sium metaperiodate (50-100 mg). The contentswere shaken for 2-3 min and molybdate solution(10 ml, 2["1/) followed by same volume of chloroaceticacid buffer and 1 g of potassium iodide were, added.The contents of the flask were thoroughly mixedand the iodine liberated was titrated against O·lNsodium thiosulphate. The results are recorded inTable 1.Determination of hexacy(moferrate(II) - To analiquot containing 40-90 mg of hexacyanoferrate(II)was added 0·5 g of boric acid and an excess of1% so.lium mctupcr iodat c solution (5-10 ml). Thereaction mixture was kept at room temperature for2-3 min to complete the reaction and 10 ml of 2Mammonium molybdate followed by 10 ml of chloro-acetic acid buffer were added. The reaction mixturewas then treated with 1 g of potassium iodide and10-lS rnl of 3% zinc sulphate solution and set asidefor 2 min. The liberated iodine was titrated withO'lN sodium thiosulphat e. The results are givenin Table 1.It has been r('Portec~4 that periodat e can bemasked with molybdate whereas iodate remainsTABLE 1 - ESTI'IIATIOX OF HYDRAZIKE, l\[ETHYLHYDRAZINE,SE:\IICARBAZIDE AKD 1-1FXACYAKOFERRATE(II)Hyd razine (rng) l\Iethylhydrazine (mg)Taken Founel Taken Found2'33 2·23 2·85 2·862·72 2-61 3·32 3·34311 2·97 3·80 3·803·50 3·+9 4·27 4·273·89 3·84- 4· 74- 4·75+·28 4·2+ 5·22 5·19Semicarbaz ide Hexacyanofcrrate(II)(mg) (mg)Taken Found Taken Found5·13 5'13 41·98 41·875·99 6·00 55'97 55'926·84 6·75 61·56 61-487·70 7·75 69·96 70·238'55 8·50 75'56 75'539·41 9·38 83·95 84'01

Stability Constants of Glutamic Acid Complexes with Some Metal Ions

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Stability Constants of Glutamic Acid Complexes with Some Metal Ions

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