Effect of Polyelectrolyte Structure on Protein-Polyelectrolyte Coacervates: Coacervates of Bovine Se

文档简介Electrostaticinteractionsbetweensyntheticpolyelectrolytesandproteinscanleadtotheformationofdense,macroion-richliquidphases,withequilibriummicroheterogeneitiesonlengthscalesuptohundredsofnanometers.TheeffectsofpHandionicstrengthontherheologicalandopticalpropertiesofthesecoacervatesindicatemicrostructuressensitivetoprotein-polyelectrolyteinteractions.Wereporthereonthepropertiesofcoacervatesobtainedforbovineserumalbumin(BSA)withthebiopolyelectrolytechitosanandfindremarkabledifferencesrelativetocoacervatesobtainedforBSAwithpoly(diallyldimethylammoniumchloride)(PDADMAC).CoacervationwithchitosanoccursmorereadilythanwithPDADMAC.Viscositiesofcoacervatesobtainedwithchitosanaremorethananorderofmagnitudelargerand,unlikethosewithPDADMAC,showtemperatureandshearratedependence.Forthecoacervateswithchitosan,afastrelaxationtimeindynamiclightscattering,attributabletorelativelyunrestrictedproteindiffusioninbothsystems,isdiminishedinintensitybyafactorof3-4,andtheconsequentdominancebyslowmodesisaccompaniedbyamoreheterogeneousarrayofslowapparentdiffusivities.Inplaceofasmall-angleneutronscatteringGuinierregioninthevicinityof0.004-1,a10-foldincreaseinscatteringintensityisobservedatlowerq.Takentogether,theseresultsconfirmthepresenceofdensedomainsonlengthscalesofhundredsofnanometerstomicrometers,whichincoacervatespreparedwithchitosanarelesssolidlike,moreinterconnected,andoccupyalargervolumefraction.Thedifferencesinpropertiesarethuscorrelatedwithdifferencesinmesophasestructure.