Jha, S. K.

Khatri, J. C.

Singh, Mukrtar

English

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INDIAN J. CHEM., VOL. 15A, JUNE 1977Ag-{ (nitrate) and Cd-O (nitrate) stretchingmode couldnot be observedabove200.W thank Prof. O. P. l\falhotra,Head of theChen'stry Department.BHU, Varanasi,for pro-vidi facilities.Refer,nces1. A$:UJA, I. S. & RASTOGI, P., ]. chem.Soc., (1970),2161,nd refs. 9-13 therein.2. AiTJA' I. S. & GARG, A., Indian]. Chem.,9 (1971), 1307.3 V GEL, A. I., A textbookof quantitativeinorganicanalysis( ongmans. Green, London), 1971.4. F LD, B. O. & HARDY, C. ]., Q. R v. chem.Soc., 18964), 361; ADDISON, C. C., LOGAN, N., WALLWORK,· C. & GARNER, C. D., Q. Rev. chem.Soc.,25 (1971),89; ADDISON, C. C. & SUTTON, D., Prog. inorg. Chem.,(1967), 195.5. G4TEHOUSE, B. M., LIVINGSTONE, S. E. & NYHOLM, R. S.,· chem.Soc., (1957), 4222.6. C1fRTIS, N. F. & Cl:RTIS, Y. M., Inorg. Chem.,5 (1965),04.7. AJ)DISON, C. C. & GATEHOUSE, B. M., ]. chem.Soc.,960), 613.8. HbT, F. A. & LAMING, F. P., ]. inorg.nucl. Chem.,27965), 1605; 1825.9. Blj'LLOCK, ]. I., J.inorg. nucl. Chem.,29 (1967), 2257.10 LnvER, A. B. P., MANTOVANI, E. & RAMASWAMY B. S.,an. J. Chem.,49 (1971), 1957. KARAYANNIS, N. M.,IKULSKI, C. M., PVTLEWSKI, L. L. & LABES, M. M.,· inorg.nucl. Chem.,34(1972), 3139; Inorg. Chem.,13974), 1146. SPECA, A. N., PYTLEWSKI, L. L., KARA-ANNIS, N. M. & OWENS, C., J. inorg. nucl. Chem.,6 (1974), 3151; AHUJA, 1. S., SINGH, Ro\GHUVIR &INGH, RAJINDAR, SPectrochim.Acta, 32A (1976), 547.11. R~SENTHALL' M. R. & DRAGO, R. S., Inorg. Chem.,4( 965), 840.12. F RRARO, J. R. & WALKER, A., ]. chem.Phys., 42( 965), 1273.PolarographicStudyof Zn(II)-TryptophanSystemJ. C. KHATRI, MUKRTAR SINGH & S. K. JRAepartmentof Chemistry,AgraCollege,Agraceived9 March 1976; revised24 December1976accepted6 January 1977Pol rographicbehaviourofZn(I1)in thepresenceofDL-trptophanand NaCIO as supportingelectrolytehas een studied.The systemyields two waves,howeer,thesecondis maskedbya maximumat lowtrypt hanjZn(I1)ratios. The maximumdisappearson in reasingthe [tryptophan]but at this stagethesecon waveis considerablysuppressedandis finalIyelimi atedon furtherincreaseof tryptophanjZn(I1)ratio. Thefirstwavewhichrepresentsanirreversibleelectrdeprocessis duetoZn(I1)-tryptophancomplex.Ther teconstantandtheproduct'ana' for theelec-trode eactionhavebeenevaluated.CH LATES of Pb(II), Cu(II) and Cd(II) withL tryptophanwere first reportedby Quintinand oglizzo1.Pleticha2hasreportedpolarographicstudi s of complexesof Co(II), Ni(II), Fe(II) andMn(! ) with severalaminoacidsincludingL-trypto-phan. ChandraandSrivastava3andLal andChris-tian4 have also dealt with different aspectsofNi(II -L-tryptophansystem.Th presentnotedealswith polarographicstudyof Zn II)-tryptophansystemin NaC104assupporting564electrolyte.Sodiumperchloratehas beenspeciallyusedto avoidany possibilityof complexformationof Zn(Il) with the anionof the supportingelectro-lyte. The use of buffer has also been avoidedfor thesamereason, Sincethekineticstudieswereenvisaged,useof any surface-activeagenthasalsobeenavoided.The d.m.e. (Sargent,USA) had the followingcharacteristicsm2J3tlJ6 =2·140mg2J3 sec-l/2 in O·lMNaCl04 at -0,11 V versusSCE. All thechemicalsusedwereof BDH or E. Merck (AR grade). ZnC12was used as ,the depolarizer.The experimentalset up and the procedurewere similar to thosereportedearlier5.ThediffusioncoefficientshavebeenexperimentallydeterminedusingDawsoncell6 and tn' calculatedthereafterby Ilkovic equation,correspondingto thefirst wavehas beenfound to be between1·7and2·2. Suchdiscrepanciesin calculatedvaluesof "n'are not unusual7.The potentialdependentheterogeneousrate con-stant kJ,h is relatedto E by the followingtworelations8,9(1) and (2).kJ,h =k/h exp[-a.:naF(E+O·2412)(RTJ ... (1)[-LlGt+a.:naF(E +0'2412)]kJ,h = KT (h'O exp RT ... (2)Equatingthevalueof log kJ,h at E =° from thetworelationswegetLlGt (kcal)at 25°ar.disobtainedby the relation(3).+ -5·706') 0 816 7 '!J.G+= 4.18 Log kJ,h-' rxna-6· 9J ... (3)Zn(II) yields a singlewell definedwave withE1/2 =-1·0365 V (versusSCE) and slope0·040Vin O·lM NaCl04. On the additionof tryptophanto thesystem[1mM Zn(II), 1mM tryptophanandO·lM NaCl04J the followingsignificantchangesareobservedin the current-potentialcurves:(a)E1/2 is shiftedto morenegativepotentialandbecomes0·1066V.(b) The wave becomesmore drawn out withslope=0'095V.(c) The waveis closelyfollowedby a maximum.However,it is not on the rising portion and thusdoes not interfere with the quantitativestudyof the wave.AsthetryptophanjZn(II)ratiois increasedkeepingZn(II) constant at 1 mM, the wave records agradualshift towardsmorenegativepotentialstill[tryptophan]reaches5 mM. There is no changeat [tryptophan]=6 mM. This is followedby apositiveshift at 7 mM and between[tryptophan]7 mM to 20 mM, the E1/2 remainspracticallyconstant.The heightof the maximiumgraduallydecrease~with an increasein [tryptophan]till 4 roM andfrom 4 mM to 6 mM it is reducedto a roundedhump.. At 7 mM theroundedhumpalsodisappearsandIII Its placea smallsecondwaveappearswhichchangesneitherin shapenor in positiontill 15roMtryptophan(id =1·088and-Et =1·225V). How-ever, this secondwave disappearscompletelyat20 mM tryptophan.The ~act~haton the addition of tryptophanthe Et IS shIftedto morenegativepotentialsandI ."~' I"III----------~---1INOTESTABLE 1- IRREVERSIBILITYANDKINETIC PARAMETERDATA[Tryptophan]E314-El/4By Meitesand Israel treatment(mM) cxnaLlGtkl"(kcal)10·130,5728·902·3X 10-1120 69 4953'31'34-6 2457 57 051 40 58,06' 9 386'70 ,60' 15 -81-639x98' -100'4 2X 0-115,2·*cxis derived from the relation E314-E114=0'0564focnand cx<0'5 at n=2 is regarded as a condition for totalirreversibility11.that the slopeincreasedsignificantlyrenderingtheelectrodeprocessfrom near reversibleto totallyirreversible(Table 1), indicateda changein basicnatureof the reactionard in analogywith Ni(II)-tryptophansystemit can be concludedthat thefirst wave correspondsto anirreversiblereductionof Zn(II)-tryptophan complex.Similar to Ni(II)-tryptophansystemreportedby Lal andChristian4thereis a secondwavealsobut it is maskedby amaximiumatlower[tryptophan].Theroleofaminoacids as maximiumsuppressors2is alreadyknownandasthe [tryptophan]is increasedin the presentstudy the maximiumgradually disappearsandthe secondwavecan be observed.However,theconcentrationof the maximiumsuppressor(i.e.tryptophan)at this stageis ratherhigh (7X to-3M)and possiblybecauseof this the height of thesecondwave is very much reducedrenderingareliable quantitativestudy of this secondwaveat this stagedoubtful. At 20 mM tryptophanit iscompletelyeliminated.Studiesregardingtheorigin,natureandkineticsof this waveunderalternativeexperimentalconditionsarein progress.The positive shift of the Et (first wave) at[tryptophan]>6 mM may be attributedto thedouble layer effectlO due to high [tryptophan].Tryptophanbeingchargedspeciesin solution(duetozwitterionformation)andalsosurface-activeis quitelikely to bring changesin doublelayer structurewhichmayleadto a positiveshift in Et·Authors are thankful to the Principal, AgraCollege,Agra, for providingthenecessaryfacilities.References1. QUINTIN, M. & FOGLIZZO,R., c.r. hebd.Acad. Sci. Ser.C., 262 (1966),1500.2. PLETICHA, R., Colln Czech.chem.Commun.,15 (1950),807; Chem.Listy, 45 (1951),185.3. CHANDRA,S. & SRIVASTAVA,S. N., Indian]. Chem.,7(1969),829.4. LAL, S. & CHRISTIAN,G. D., J. prakt. Chem.,313 (1971),99.5. JHA, S. K., JHA, S. & SRIVASTAVA,S. N., Z. Naturforsch.,30b (1975),859.6. ROBINSON,R. A., Electrolytesolutions (Butterworths,London), 1955,33.7. CHATURVEDI,R. K., Physico-chemicalstudiesonmurexide,Ph.D. thesis,Agra University, Agra, 1960.8. MEITES, L., PolarograPhictechniques(IntersciencePub-lishers),1965,239.9. STRASSNER,J. E. & DELAHAY, P., J. Am. chem.SQC.,74 (1952),6232.10. MEITES, L., PolarograPhictechniques(IntersciencePub-lishers),1965,291.11.GOTO, R. & TACHI, I., Proc. Intern.PolarograPhyCongr.,Prague,Vol.1(HrirodovedeckeVydavatelstvi,Prague),1951.69.ThermodynamicFunctions& StabilityConstantsof SomeRare Earths withPhloroglucinolSANTOSHD. MAKHIJANI* & SATENDRAP. SANGALtLaxminarayan Institute of Technology, NagpurReceived27 August 1976;accepted12 January 1977StabilityconstantsofthecomplexesofphloroglucinolwithSc(III),Y(III), La(III), Ce(III),Pr(III) andNd(III)havebeenevaluatedin aqueousmediumat J1=O·02M(NaCI04), employingBjerrum-CalvinpH-titrationtech-nique,asusedby IrvingandRossoW. Thevaluesofoverallchangesin free energy(LlG), enthalpy(!i.H)andentropy(LlS) accompanyingthecomplexformationhavebeenreported.The order of stabilitycons-tant is Sc(III)>Y(III)>La(III) and La(III)<Ce(III)<pr(III) <Nd(III).IN this note the thermodynamicfULctionsandstability constants of some rare earths withphloroglucinolhave been evaluatedin aqueousmedium.Themethodsusedwerethesameas describedinpreviouscommunications1,2.The practicalproton-ligandstabilityconSlantsandmetal-ligar,dstabilityconstantsat various temperatureswere obtainedemployingBjerrum-CalvinpH-titrationtechrique3,4,as usedby Irving and Rossotti5.All the chemicalsusedwereof AR grade. Thestocksolution(O'OlM) of phloroglucinol(E. Merck)was preFaredin CO2-freedoubly distilled water.All other solutiors werepreFaredas describedinprevious papers1,2. Titratiols were carried outunder N2 atmosphereand temperaturewasmain-tainedwith an accuracyof ±0·10c.Titrationswerecarriedout with Q'909M NaOHas in previouspapers1,2at (J. =0'02M (NaCl04);total volumewas 100ml.The proton-ligandandmetal-ligandstabilityCon-stants were calculatedas describedin previouspapers1,2. Thevaluesofstabilityconstantsobtainedby interpolationat half n-values5methodaregivenin Table 1.The temperaturecoefficientandGibbs-Helmhc>ltzequationwereusedto determinetheoverallchangesin free energy(LlG), enthalpy(LlS) , and entropy(LlS). The total freeenergychangewas obtainedfromthe equationLlG =- RT ln ~,where~is the*Present address: National Environmental EngineeringResearchInstitute, Nehru Marg, Nagpur 440020.tAuthor to whom correspondencemay be addressed.565

Polarographic Study of Zn(II)-Tryptophan System

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Polarographic Study of Zn(II)-Tryptophan System

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