物理化学学报(WuliHuaxueXuebao)ActaPhys. 鄄Chim.Sin., 2007,23(7)：1007-1012Received:January22,2007;Revised:April3,2007;PublishedonWeb:May10,2007.Englisheditionavailableonlineatwww.sciencedirect.com鄢Correspondingauthor.Email:anwar_jmiyahoo.co.in鬁EditorialofficeofActaPhysico鄄ChimicaSinicaArticlewww.whxb.pku.edu.cnJulyVolumetricandRefractiveIndexBehaviourof 琢鄄AminoAcidsinAqueousCTABatDifferentTemperaturesALIAnwar鄢 SABIRS. SHAHJAHAN HYDERS.(DepartmentofChemistry,JamiaMilliaIslamia(CentralUniversity),NewDelhi鄄110025,India)Abstract： Densities(籽)andrefractiveindices(nD)ofglycine(Gly),DL鄄alanine(Ala),DL鄄valine(Val)(0.02,0.04,0.06,0.08,and0.10molL-1)in0.005and0.008molL-1 aqueouscetyltrimethylammoniumbromide(CTAB)havebeenmeasuredat298.15,303.15,308.15,and313.15K.Thedensitydatahavebeenutilizedtocalculateapparentmolarvolumes(准v),partialmolarvolumes(准0v),atinfinitedilutionandpartialmolarvolumesoftransfer 准0v (tr)ofaminoacids.Therefractiveindexdatahavebeenusedtocalculatemolarrefractivity(RD)ofaminoacidsinaqueouscetyltrimethylammoniumbromide.Ithasbeenobservedthat 准0v varieslinearlywithincreasingnumberofcarbonatomsinthealkylchainofaminoacids,andhence,wassplittogetcontributionsfromthezwitterionicendgroups(NH +3 ,COO-)andmethylenegroup(CH2)oftheaminoacids.Thebehaviouroftheseparametershasbeenusedtoinvestigatethesolute鄄solute,solute鄄solventinteractionsandtheeffectofcetyltrimethylammoniumcationontheseinteractions.KeyWords： Aminoacid; Cetyltrimethylammoniumbromide; Partialmolarvolume; Refractiveindex;Solute鄄soluteandsolute鄄solventinteractionsSurfactantsaretoolswidelyemployedinthefieldofphar-maceuticals1,2 andbiotechnologicalprocesses3,4.Thesurfactantsaffectthefunctionalpropertiesofprotein,soprotein鄄surfactantinteractionsareconsideredtobesignificant.Surfactantscausechangesinthemolecularcharacteristicsofglobularproteinandthesechangeshelpproteinmoleculestobindwithothermolecules.Severalstudiesareavailableondirectprotein鄄surfac-tantinteractionsusingvarioustechniquessuchasresonance鄄lightscattering5,conductivity6,7,fluorescence8,9,anddirectcalorimetry10-13.Thereportoninteractionoftheconstituentgroupsoftheproteinswithsurfactantsisrarelyavailableintheliterature14.Theproteinsarecomplexbiomolecules,soaminoacidsareusedasmodelcompoundstounderstandthedetailsofprotein鄄surfac-tantinteractions.Inourpresentstudy,thepartialmolarvolumes(准0v)atinfi-nitedilution,partialmolarvolumesoftransfer(准0v(tr)andrefrac-tiveindices(RD)of(0.02,0.04,0.06,0.08,and0.10molL-1)aminoacidsin(0.005and0.008molL-1)aqueoussolutionsofCTABatdifferenttemperatureswerereported.Sincesurfactantsconsistoftwodistinctparts,polarheadgroupandapolarhy-drophobictailgroup,theself鄄aggregationofapolarhydrophobicgroupsleadstotheformationofmicellesabovecriticalmicelleconcentration(cmc).Whilethehydrophobicinteractionactsasthevitaldrivingforcefortheformationofmicellaraggregatesandforbindingofsurfactanttoprotein,theelectrostaticrepulsionbetweenpolarheadgroupsaffectsthesizeofmicelle.ThecmcofCTABisreported15 as0.82mmolL-1.Thus,thesurfactantusedactsasmicellesinthepresentstudy.1 ExperimentalmethodsTheaminoacidschosenforthepresentstudyareglycine(Gly)(Merck,massfraction跃0.99),DL鄄alanine(Ala)(LobaChemie,massfraction跃0.98),andDL鄄valine(Val)(LobaChemie,massfraction跃0.99).TheseaminoacidswererecrystallizedfromaqueousethanolsolutionanddriedundervacuumoverP2O5atroomtemperatureforabout72h.Cetyltrimethylammoniumbro-mide(CTAB)ofextrapureanalyticalreagentgradewasalsore-crystallizedbeforeuseastoattainmaximumpurityanddriedinvacuum.Thedoublydistilledanddeionizedwaterwasusedforthepreparationof0.005molL -1 and0.008molL -1 aqueousCTABsolutions,andthesewereusedassolventstoprepare0.02,0.04,0.06,0.08,and0.10molL-1 Gly,Ala,andValsolu-tions.Allthesolutionswerepreparedafreshbyvolume.TheweighingsweredoneonPrecisaXB鄄220ASwiss-madeelectron-icbalancewithaprecisionof 依0.000lg.Allthenecessarypre-cautionsweretakenintoconsiderationduringthepreparationofsolutions.Theerrorinconcentrationduetotemperatureisfoundtobe 依0.002.Thedensitiesofternarysolutions(aminoacids+aqueousCTAB)weremeasuredat298.15,303.15,308.15,and313.15K,1007ActaPhys. 鄄Chim.Sin.,2007 Vol.23intheconcentrationrangeof0.02 -0.10molL -1,usingsinglestempycnometermadeofBorosilglasswithabulbcapacity 8伊10 -6 m3.Thestemhadgraduatedmarksandawell鄄fittedglasscap.Themarksonthestemwerecalibratedusingdoublydis-tilledwater.Thepycnometercontainingtestsolutionwaskeptforabout20mininanelectronicallycontrolledthermostaticwa-terbath(JULABO,Model鄄MD,Germany)havingprecisionof依0.02K,inordertominimizethethermalfluctuations.Refrac-tiveindicesweremeasuredwiththehelpofthermostatedAbbe鄄refractometeraftercalibratingitwithdoublydistilledwaterandtolueneatknowntemperatureasdescribedintheliterature 16.Theerrorsinthemeasurementof 籽 and nD werefoundtobe依0.01kgm-3 and 依0.0002,respectively.2 ResultsanddiscussionThedensity(籽)andrefractiveindex(nD)determinedfortheaminoacidsolutionsin0.005and0.008molL-1 aqueousCTABfrom298.15to313.15KarelistedinTable1.Themeasured 籽datawereutilizedfor