钙镁离子对尼古丁的zeta电位和粒径的影响

ColloidsandSurfacesB:Biointerfaces65(2008)54–60ContentslistsavailableatScienceDirectColloidsandSurfacesB:Biointerfacesjournalhomepage::Characterizationofflocculatesize,zetapotentialandnicotineadsorptionbehaviorHatairatSuksri,ThanedPongjanyakul∗FacultyofPharmaceuticalSciences,KhonKaenUniversity,KhonKaen40002,ThailandarticleinfoArticlehistory:Received18January2008Receivedinrevisedform18February2008Accepted23February2008Availableonline29February2008Keywords:NicotineMagnesiumaluminumsilicateFlocculationZetapotentialAdsorptionisothermabstractThepurposesofthisstudyweretopreparedispersionsinvariousratiosofnicotine(NCT)andmagnesiumaluminumsilicate(MAS)atdifferentpHsandtoinvestigateinteractionofNCTwithMASbycharacteriz-ingmicroscopicmorphology,particlesizeandzetapotentialofMAS-NCTflocculates.Moreover,theNCTadsorptionontoMASatdifferentpHswerealsoinvestigated.Atbasicmedium,incorporatingNCTintoMASdispersionbroughtaboutasmalldecreaseinthezetapotentialofMAS,leadingtoaloosefloccu-lateformationofMAS.ThisislikelytobeduetoanadsorptionofunionizedformofNCTontoMASviaintermolecularhydrogenbonding.Thelowerzetapotential,densermatrixstructureandlargersizeoftheflocculateswasfoundatneutralandacidicmediabecausetheprotonatedspeciesofNCTcouldinteractwiththenegativelychargedMASbyelectrostaticforce.InadditiontheflocculatesformedatpH4possiblypossessedahigherdensitythanthoseformedatpH7,suggestingthatthediprotonatedspeciesofNCTatpH4causedstrongerinteractionwithMAS.TheadsorptionisothermsofNCTontoMASatdifferentpHscanbedescribednotonlyusingtheLangmuirmodel,butalsousingtheFreundlichmodel.ThehigheraffinityofNCTadsorptionontoMASatneutralandacidicmediawasfound.However,theadsorptioncapacitytoformNCTmonolayerreducedwithdecreasingthepHofthedispersionsbecauseofanadsorptionofhydroniumionsandadecreaseinsurfaceareaofadsorptionsitebyflocculation.ThesefindingssuggestedthattheflocculationofMASdispersioncouldbeinducedbyincorporationofNCT.Thecharacteristics,suchasparticlesizeandzetapotential,oftheNCT-MASflocculatesandtheadsorptionisothermsofNCTontoMASweredependeduponpHofdispersion,inwhichthedifferentchargedspeciesofNCTwereformed.©2008ElsevierB.V.Allrightsreserved.1.IntroductionNicotine(NCT)isavolatilestronglyalkalineliquidobtainedfromtobaccoplants.Itiscolorlessinnaturebutundergoesauto-oxidationandturnsyellowtobrownonexposuretoairorlight[1].NCTishighlysolublenotonlyinwater,butalsoinhydrophobicsolvents.Ithaswell-separatedpKavalues,whichpKa1andpKa2are3.04and7.84,respectively,leadingtothedifferentchargedspeciesatanyparticularpH(Fig.1a).ThefreebaseformofNCTreadilyper-meatesacrossmembranes[2].AccordingtothevolatilepropertyandoxidativedegradationofNCT,manyresearchersseekamaterialforadsorbingNCTinordertopreventtheevaporationandimprovestability.Cellulosepowderswereasuitablematerialduetoalargesurfaceandporevolume.TheNCTadsorbedontothecellulosepow-dersshowedacompletereleaseinwaterwithin1h[3].TheotherapproachistheadsorptionofNCTusingacationexchangeresin.∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](T.Pongjanyakul).TheadsorptionisothermofNCTontocationexchangeresinscouldbedescribedusingtheLangmuirmodel.Moreover,theNCT–resincomplexesprovidedasustainedreleasebehaviorofNCT[4].Magnesiumaluminumsilicate(MAS)isamixtureofmontmo-rilloniteandsaponiteclays[5],whichhavealayeredstructure.Eachlayerisconstructedfromtetrahedrallycoordinatedsilicaatomsfusedintoanedge-sharedoctahedralplaneofeitheraluminiumhydroxideormagnesiumhydroxide[5–7],whichthestructureofmontmorilloniteclaysisillustratedinFig.1b[6].Thelayerstruc-turesofclayscouldbeseparatedwhentheywerehydratedinwater.OnceMASishydrated,theweaklypositivelychargededgesareattractedtothenegativelychargedfacesofcolloidallayersofMAS.Theattractionoffacetoedgeofthesecolloidallayerscreatesathreedimensionalcolloidalstructurethroughoutthedis-persion,whichexhibitedathixotropicproperty[8].ThepositivelychargededgesofMAScouldinteractwithanionicpolymers,suchasxanthangum[9],carbomer[10],andsodiumalginate[11,12],whichresultedinviscositysynergism.Moreover,thenegativelychargedfacesbroughtaboutastrongelectrostaticinteractionwithapositivelychargedpolysaccharide,suchaschitosan,resultingin0927-7765/$–seefrontmatter©2008ElsevierB.V.Allrightsreserved.doi:10.1016/j.colsurfb.2008.02.016H.Suksri,T.Pongjanyakul/ColloidsandSurfacesB:Biointerfaces65(2008)54–6055Fig.1.MolecularstructureanddifferentchargedspeciesofNCT(a),andstructureofmontmorilloniteclays(b)[6].animprovementofrheologyofcompositedispersionsandafor-mationofpositivelychargedflocculates[13].Furthermore,MAScouldadsorbaminedrugs[14,15],leadingtoaprolongedreleaseofdrug.TheinteractionandadsorptionofNCTwithillite,onetypeofclays,hasbeenpreviouslyreportedbySinghalandSingh[16].How-ever,illitehadaremarkablylowercationexchangecapacityandspecificsurfaceareathanmontmorilloniteclays[17].Itisthusinterestingthatmontmorilloniteclays,particularlyMAS,haveapotentialtouseasanadsorbentofNCTbecausetheypossessa