Coil-Globule transition of a single short polymer chain - an exact enumeration study

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1、Coil-Globuletransitionofasingleshortpolymerchain-anexactenumerationstudyM.Ponmurugan1,S.L.Narasimhan2,∗,P.S.R.Krishna2andK.P.N.Murthy1,31MaterialsScienceDivision,IndiraGandhiCenterofAtomicReasearch,Kalpakkam-603102,TamilNadu,India.2SolidStatePhysicsDivision,BhabhaAtomicRes

2、earchCentre,Mumbai-400085,India.3SchoolofPhysics,UniversityofHyderabad,CentralUniversityP.O,Gachibowli,Hyderabad-500046,AndhraPradesh,India.WepresentanexactenumerationstudyofshortSAWsintwoaswellasthreedimensionsthataddressesthequestion,`whatistheshortestwalkforwhichtheexis

3、tenceofallthethreephases-coil,globuleandthetheta-couldbedemonstrated'.EventhoughwecouldeasilydemonstratethecoilandtheglobulephasesfromFreeEnergyconsiderations,wecoulddemonstratetheexistenceofathetaphaseonlybyusingascalingformforthedistributionofgyrationradius.Thatevensuchs

4、hortwalkshaveascalingbehaviorisanunexpectedresultofthiswork.PACSnumbers:05.70Fh,36.20.Ey,64.60.KwProteinsarebiologicallyactive,longchainheteropolymersthatbelongtothewalk[5].So,aconformationwithnsuchthatexisteitherinthecollapsed(nativefoldedormoltenglob-pairsofsites,alsocal

5、ledcontacts,hasenergyE=nǫ.Atanyule)phaseorintheextendedcoilphase,dependingontheirgiveninversetemperature,β,thecanonicalPartitionFunctionenvironmentalconditions[1].Simplelatticemodels[2]haveforN-stepSAWscanbewrittenasbeendevisedforunderstandingtheroleofenergy-entropybal-n=X

6、nX(N)anceinrealizingthesephases.Infact,evenshortlatticechainsC(β)=e−nǫβc(n)(1)consistingofonlysixteenmonomersorlesshavebeenshownNN[3]tobelongenoughtothrowlightonthevariousphasesn=0ofproteins.ThesechainsarebasicallySelfAvoidingWalkswherenX(N)isthemaximumnumberofcontactsanN-

7、step(SAW)onaregularlattice,modelinghomopolypeptideswithwalkcanhave,andcN(n)isthenumberofN-stepSAWcon-appropriatelyparametrizedintrachaininteractions.formationswithncontacts.ItisclearthatconformationswithLongchainmolecules,modeledasSAWs,areknowntoex-agivennumberofcontactswi

8、llacquiremore(less)weightsifistinoneofthethreeconformationalphases[4]-namely,ex-ǫisnegati