thepeptidebersactastemplatesforvariousTiOHerewereportthatbysimplyrepl - PDF document

1 thepeptide“bersactastemplatesforvariousT
thepeptide“bersactastemplatesforvariousTiOHerewereportthatbysimplyreplacingtheC-terminalvalinewithabenzyl-protectedcysteine,Scheme1,thesameoligo-valinefamilycanbeusedforthefabricationofsupramolecularscaffoldsforsilvernanoparticlemineralization.Theratioofthepureoligovalinethesulfur-containingpeptideinthegelallowsforasimplecontroloverthesilver-mineralizationreaction.GelsbeforemineralizationThestructuralsimilaritybetweengelsofeitherpureorpureandmixedgelscontainingwasstudiedbyX-raydiffractionandIRspectroscopy.Fig.1showsIRspectraofvariousgels.IRspectroscopyrevealsthatthegelsformthrough-sheetformationoftheindividualpeptidebuildingblocks.TheIRspectraofallgelsarevirtuallyindistinguishable,indicatingthattheyallhavethesamestructuralorganization.However,muchlikeinourpreviouswecannotunambiguouslydistinguishbetweenparallelor-sheetsduetothepresenceofthecarbamateandmethylestercarbonylbands,whichoverlapwiththediagnostic-sheetvibrationsat1700cmFig.2showsX-raypatternsofthesamegels.Overall,XRDindicatesamoderatelyorderedstructurewithoutanyparticularfeatures.XRDpatternsofgelsofpureexhibittwore”ectionsat18.8(-spacingof4.7A)and22.2(-spacingof3.9A)degrees2whichweearlierassignedtoa“berstructuresimilartopolyInterestingly,thecurrentXRDdatashowthattheadditionofpeptidetopeptideimprovestheorderwithinthe“bers.Theincreasingnumberof(narrow)re”ectionsobservedwithincreasingfractionofinthegelssuggeststhattheadditionalthioetherfunctionalityandtheadditionalaromaticringfurtherstabilizethepeptidewhencomparedtothepuretri-valinepeptide.Italsosuggeststhatpeptideleadstoasomewhatmorecrystallineorderinthe“bers.Overall,XRDshowsthatallsampleshaveasimilarstructuralorganization,whichisconsistentwithIRspectroscopy.Closerinspectionrevealsminuteshifts(below0.8degrees2)intheXRDpatternsofthed

2 ifferentsamples.Thisindicatesthattherear
ifferentsamples.Thisindicatesthatthereareslightdifferencesbetweensamplescontainingdifferentfrac-tionsof,whichhoweverdoesnotaffecttheoverallorganizationofthepeptideassemblies.Thesedifferencesareattributedtominorsizedifferencesbetween,similartoastudybySundeetal.Thefactthatthetransitionbetween“bersofpureandpuredoesnotshowabruptstructuralchangesimpliesthatthetwopeptidesarestructurallysimilarenoughtonotdisturbtheirrespectivesupramolecularorderuponco-assembly.Finally,XRDindicatesthatallpeptides“bersadoptanamyloidquaternarystructureupongelation,regardlessoftheircomposition(purepeptidesormixturesof).Thehelicalpitchofthestructureis115A,asdeterminedfromthere”ectionsat18.3(5),18.8(3),30.9(0),39.6(9)degrees2.ThismatchesearlierdatabySundeetal.onproteinsself-assemblingintoamyloid“brils.Thepitchcorrespondsto25peptidesinthehelicalrepeatingunitasisclassicallyacceptedforamyloid Fig.1IRspectraofgelswith(a)pure,(b)50%ofand50%of,and(c)pure Fig.2XRDpatternsofgelswith(a)pure,(b)50%ofand50%ofand(c)pure Fig.3SEMimagesofgelsbeforemineralization.(a)Pure,and(b) Fig.3showsrepresentativeSEMimagesofsomegels.SEMshowsthatinallcasesthepeptidesself-assembleintolong“berswithadiameterof60nm(pure),25nm(mixturesof),and500nm(pure).Thelattervaluemaynotbefromtheindividual“bers,asthoselarge“bersseemtobecomposedofthinner“bersaswell.Thesecould,however,notberesolved.The“bersofpureoftenappearsomewhatcrystallineinthattheyexhibitedgesor”atareasthatcouldbepoorlydevel-opedcrystalfaces.Thisisfurthersupportedbythefactthatgelsformedfrompureshowadditionalre”ectionsinXRD,Fig.2.Wethereforeconcludethatformspeptide“bersandgels,butSEMandXRDalsoprovidecircumstantialevidencecrystallizesmorereadilythan.Thishighertendencytowardscrystallizationisassignedtothepresenceofanaddi-tionalaromaticringinthe

3 thioethermoietyof.Theresultingstackingin
thioethermoietyof.Theresultingstackinginteractionatleastpartiallyfavorscrystallization.Thecombinationofinone“ber,however,completelyinhibitstheformationoflargercrystallineunits.This“ndingisfurtherevidencedbythefactthatthegelswith(largefractions)ofareopaque,whereasthegelswithmixturesofaretransparenttoveryslightlyopaque.MineralizedgelsFig.4showsthattheIRspectraremainunaffectedbytheminer-alizationprocess.Thisindicatesthatthereisnochangeinthesupramolecularstructureoftheself-organized“bersuponsilverdeposition.Speci“cally,IRspectroscopyshowsthatthevibra-tionat1634cmindicativeofthe-sheetisconserved.Furthermore,IRshowsthatthechemicalintegrityofthepeptidesismaintainedandthepeptidesarenotdamagedduringmineralizationbecausethespectraoftheprecursorgelsandthemineralizedgelsareidentical.Eventhethioethermoietyisunaf-fectedbysilvermineralization.Thisisevidencedbythefactthatno…SHband(indicativeofthioethercleavage)isobservedat2550cm.Moreover,therearenosulfoneorsulfoxidebandsat1100…1300andat1050cmindicativeofsulfuroxidation.Theonlysigni“cantchangebetweenthenon-mineralizedandthemineralizedgelsareseveralpeakshifts.Thecarbonylbandofthemethylesterat1738cmshiftsby24cmcomparedtothepureorganogel.Thisshowsthatthemethylesterisnothydrolyzed,becausethebandpersists,butthatitslocalenviron-mentchanges.ContrarytotheworkofSiandMandal,approachtosilverdepositiondoesnotinvolvestrongbasesoralkalineconditions.Asaresult,themethylesterisnotcleavedandremainsintact.Furthermore,theamideIIbandat1529shiftsby3cm,butremainsstrongandintact,showingthattheintegrityofthepeptidebackboneisunaffectedbythesilverdepositionandthereisnosigni“cantstructuralchangeOverall,IRspectroscopyshowsthattherearesomeinterac-tionsofthepeptideswiththesilvercrystals,mostprominentlythecarbonylgroupofthemethylester.T

4 hequitelargeshiftofover20cmindicatesthat
hequitelargeshiftofover20cmindicatesthattheinteractionisquitestrong.However,thefactthatthebanddoesnotdisappearuponminer-alizationalsoshowsthatthemethylesterisnotcleavedduringmineralization.IRspectroscopythereforeclearlycon“rmsthatthesilverdepositionusingDMFinoligovalineorganogelsisasoftmethodleavingthepeptidescaffoldintact.Fig.5showsSEMimagesofthemineralizedgels.Theimagesclearlyshowthatthegelstructureisconserved,thatis,thatthe“bersareintactevenaftermineralization.Inallcases,thepeptide“bersarecomparabletotheirnon-mineralizedanalogs,buttheyarecoveredwithparticlesofdifferentshapesandsizes.The“berscontainingonlyoralargefractionofaredenselycoveredwithsmallparticleswithadiameterof9nm.Somelargerparticlesarealsopresent.Asthefractionofinthe“bersdecreases,theparticlesgrowlarger.Also,thedecreasingfractionleadstotheformationofmorediverseparticleshapes.Parti-cleswithtriangularandrelatedshapesarethepredominantspeciesat50%of.Atevenlowercontentsof25%of,mostsilverparticlesareabove100nminsizeandpartlyhavewell-de“nedtriangularandrelatedshapes.Mineralizationofgelsofpureleadstosampleswithlargeparticlesofvariousshapeswherethesilverparticlesappeartobenolongertightlyassociatedwiththepeptide“bers.Inallcasessomefractionof9nmparticlesisalsovisible.Thesedatashowthatthegelscomposedonlyofpeptideonlyweakgrowthmodi“ersorinhibitorsforsilver,whereasincreasingfractionsofmakethemmoreandmoreef“cient Fig.4IRofthegelsaftermineralization.(a)Puregelof,(b)mixtureof,and(c)pure Fig.5SEMimagesofthegelsaftermineralization.(a,b)Gelwithpure,(c,d)gelwithpure bands.Thebandsat340…355nm,360…385,400…430,and455…490nmareattributedtooverlappingpeaksfromscatteringandplasmonresonancesofthesilverparticles.Thesebandsvaryfromsampletosample,whichcanagainbeexplainedbythepresenceofparticleswithdiffere

5 ntsizesandshapes.Bandsbetween525and575nm
ntsizesandshapes.Bandsbetween525and575nmcanbeattributedtodistortednanopar-ticles(bentplatesorparticleswithdistortionsinthecrystallattice).Iftheamountofis75%orlower,twobandsataround525and660nmarefound.Theformerisagainassignedtodistortedparticlesandthelatterbandisduetothepresenceof(truncated)triangularnanoparticles.Afurtherdecreaseofthefractionofinthegelsleadstoanotherbroadpeakbetween630and665nm,whichcanbeassignedtotheformationofpolygon(twinned)crystalsandtriangularparticles.Samplesgrowningelscontainingonly25%of,exhibitanotherbroadbandataround920nm.Thisbandhasearlierbeenassignedtoaself-assembledraspberry-likestructureorsilvernanowires.,theparticlesbehavespectroscopicallyasbulkmaterial,althoughSEMandTEMshowthatthesesamplescontainnanoparticlesaswell.Essentially,UVspectroscopyprovidesevidencethatthemineral-izedgelscontainparticlesofadiversesizeandshape,whichisconsistentwithSEMandTEM,seeFig.6andFig.7.Table1summarizestheabsorptionbandpositionsobtainedafterdecon-volutionusingGaussianpro“les.Fig.9showsX-raypatternsofsomemineralizedgels.Thepatternsagainexhibitmoreandsharperpeaksasthefractionincreases.Thisshowsthattheintegrityofthepeptide“bersisunaffectedbythemineralizationprocess,althoughslightshiftsinthepeakpositionsindicativeofminutechangesarefound.XRDthereforecon“rmsIRspectroscopy,Fig.4,whichshowsthatoverallthepeptide“bersdonotchangeuponmineralization.Furthermore,XRDcon“rmsthepresenceofmetallicsilverasadditionalre”ectionsbetween20and80degrees2canbeassignedtosilver(JPCPS04-0783).Athighfractionsofinthe“bers,thesilverre”ectionsarebroad.Theybecomeincreasinglynarrow,asthefractionofdecreases.XRDthereforeshowsatransitionfromsilvernanoparticleswithpuretoratherwell-crystallizedparticleswithpure.Thisindicatesthattheinteractionofthepeptidewiththegrowingsil

6 vercrystalsismuchstrongerthanwithpeptide
vercrystalsismuchstrongerthanwithpeptide.XRDthereforesupportsSEM,TEM,andUVdatashowingthatadirecttuningoftheinteractionbetweenthepeptideandthegrowingparticlesispossiblewithourgels.Therelativeintensitiesofthere”ectionsallowforaqualitativeanalysisofthestructure-directingpropertiesof,althoughtheymaycontainsomeexperimentalerrorduetopreferredorienta-tioneffectsof,forexample,thesilverplatesobservedintheTEM.Aslongasispresentinthe“bersinlargeamounts(over50%),allre”ectionsarebroad.The(200)re”ectionisnotobservedintheseXRDpatterns,presumablyduetothefactthatthepeakistoobroadtobedetected.Thisindicatesthepres-enceofverysmallparticlesconsistentwithTEM.Thepresenceofsmallisotropicparticlesisfurthersupportedbythe(220)/(111)intensityratio,whichis0.25.Thisvalueisequaltothatreportedforbulksilver(0.25,JPCPS04-0783).Thisindicatesthatthesilverparticleshavearoughlyisotropicdistributionandorientationin Fig.8UV/Visspectrumofparticlesisolatedfromasamplecontaining50%ofand50%ofdissolvedinmethanol. Table1UVbandsdeterminedfromGaussian“tting.wt%ofinthegel“bersBandposition/nm100352,379,416,472,559,(977,weak)75355,385,428,490,57350350,376,411,458,533,63325342,363,401,456,525,663,9240Noabsorptiondetected Fig.9(a)XRDpatternofamineralizedgelwith50%ofand50%of.Althoughthereareslightshiftsinthepeakpositionscomparedtothecontrolsample,thesignalofthepeptide“bersisnotaffectedbythemineralization.(b)XRDpatternsofgelsmineralizedwithsilver.Magni-“edviewoftheareashowingtheAgre”ections.(i)pure,(ii)75%ofand25%of,(iii)50%each,(iv)25%ofand75%of,and(v)pureTheunlabeledre”ectionsarefromthepeptide“bers. ParticleformationPeptide-controlledmineralizationofsilverparticleshassofarbeenachievedwithredox-activepeptides,mostoftenbasedontyrosineortryptophan.Theywereeitherinsolutionorincorpo-ratedintogels.

7 Histidine-richpeptideshavealsobeenusedas
Histidine-richpeptideshavealsobeenusedasscaffolds,butthere,anadditionalreducingagent,sodiumborohydride,wasused.Themajordrawbackofthisapproachisthatthesamplesrequireextensivepuri“cationaftersynthesis.Bothapproachesusingsodiumborohydrideandusingredox-activepeptidesarethereforedifferentfromthecurrentapproach,whichusesDMFasareducingagent.Avoidinganexternalreducingagentmayseemanadvantage,butthedisadvantageisthatthetemplate(peptide)concentra-tion,thesilverionconcentration,andthereactiontemperaturearetheonlyvariablesinthesystem.Thisallowsforsomecontrolovernucleationandgrowth,buttheuseofanindependentreducingagentoffersmanymorepossibilitiesforreactiontuning.Forexample,iftheconcentrationofthereducingpeptideisincreased,alsotheamountofthepeptidescaffoldandthere-foretheinternalsurface,whichinteractswiththegrowingparti-cles,changes.Thatis,thereisnoindependentvariationofboththescaffoldandthereducingagent.Thecurrentpaperhowevershowsthatmixturesoftwodifferentpeptidescaninsomecasesbequiteinterestingforthefabricationandtuningoforganic…inorganiccomposites.Thisisinparticulartrueifonepeptideisregarded(anddesigned)asastructuralunit,whichdoesnotinteractwiththegrowinginorganic.Inourcasethiswouldina“rstapproximationbethepeptide.Ifhowever,theotherpeptidecontainsfunctionalgroups,forexamplethiols(thatis,coordinationornucleationpromoters)oralcoholmoieties(thatis,reducingagents)itispossibletocombineawidevarietyoffunctionsinoneself-assemblingsystem.Becausethepeptidescanbefabricatedindividuallyandcombinedlater,mixturesof,andapeptidecontainingtyrosinecanbeenvisioned.Theresultinggelswouldprovideaninterestingreactivescaffoldforsilver…peptidehybridmaterials.Assuch,thecurrentpaperisjustoneexampleofsuchamodularpeptidetoolbox.Proteins,whichalsoprovidecontroloverthespatialor

8 ganiza-tionofnucleationandgrowth,canbevi
ganiza-tionofnucleationandgrowth,canbeviewedasmorecomplexvarietiesofourapproach.Thatis,thepeptidesusedhereformaprimitive,butstillfunctional,proteinscaffoldforcontrollingsilvermineralization.AsXRDandIRdonotshowaclearsegre-gationofbothpeptideswithinthe“bers,mixed“bersofcanbeviewedasasimpli“edlargeproteinwithstatisticallydistributedsulfurmoietiesonthesurface.Earlierstudieshavemainlycommentedonthereductionmechanisms,whichhavebeenstudiedbyexploitingthetrypto-phanortyrosine”uorescence,orIR,solidstateCNMR,andUV/Visspectroscopy.Thepresentstudyalsoreportsontheinteractionsofthepeptideswiththesilversurface.Basedonthecurrentdata,thefollowingmodelcanbederived.NMRandUV/Vistitrationsprovideevidenceforanassocia-tionofthesilvercationswiththesulfuratominthethioether.Thisisthe“rststeprequiredforcontrolledparticlenucleationandgrowthandsimilarsurface-enrichmentprocessesclosetopeptidemoietieshavebeendescribedforhistidine,methionine,cysteine,tryptophan,andarginine-richpeptides.Oncenucleationhasoccurredandthesilvercolloidsstartforming,theoutcomeofthemineralizationprocessislargelygovernedbytheconcentra-tionofthethioethermoietiesonthepeptide“bersurface,becausethemaininteractionbetweenthepeptidesandthegrowingsilverparticlesoccursbondingofthethioether(thiol),amide,andbenzylgroupsofthepeptide,asevidencedbyXPSandSERS.Themaininteractionisasilver…sulfurinteraction.Thisapproachthereforeaddsanothertypeoffunctionalgrouptothepeptidefamily,whichcanbeusedbesidesamines,freethiols,andunspeci“cadsorptionofthepeptidestosilverfornucle-ationandcrystallizationcontrol.AstheAg…Sinteractionisquitestrong,thepeptide“berswithhighcontentsofareef“cientgrowthmodi“ersandhencethese“bersarecoveredwithsilverparticlesof9nmindiameter.Theparticlesaretrappedandfurthergrowth(forexampleOstwaldripe

9 ning)isprevented.Becauseofthestrongbindi
ning)isprevented.Becauseofthestrongbindingofthesilvertothesulfur,theresultingparticleshavearatherlowmobilityandessentiallyremainattachedtothelocationwheretheyinitiallyform.Asthecontentofinthe“bersdecreasestobelow50%,theinter-actionbetweenthesilverions,silverparticles,andthepeptide“bersdecreases.Nucleationinsolution(thatis,homogeneousnucle-ation)isstillnotfavorableduetothepresenceofahighinternalsurfaceprovidedbythepeptide“bers.However,thesurfaceener-giesofthepeptide“berschange,asthethioetherisincreasinglyremoved.Assumingthattheparticlesstillformnucleation,theformationoflargeparticlesobservedwithlowcontentsofcanbeexplainedwithOstwaldripening.Initiallythereisasilver…peptideinteraction,asevidencedbyCNMR.However,afternucleation,theinteractionbetweentheparticlesandthepeptide“bersistooweaktocompletelysuppressOstwaldripeningandratherlargecrystalswithvariousshapesform.Asthecontentofdecreasesbelow25%,nucleationandgrowthislargelygovernedbythehydrophobicsurfaceofthepeptide“bers.Sulfur-containingpeptidesstillinteractwiththegrowingclusters.Asthesulfur-containingmoietiesarebeingcoveredbythegrowinglargecrystals,furtherreductionofsilverionsleadstogrowthaccordingtoamodeldevelopedbyNaiketal.Accordingtothismodel,peptidesmodifycrystalgrowthbyallowingaccumulationofthesilveratomsonthelowestsurface-energyfacewherethepeptideisaccumulated.Further-more,thesurfaceenergyofdifferentcrystalfacesinface-centeredcubicmetalsislowerfor111facesthanforothersAsaresult,thereisapreferentialinteractionofthepeptide“berswiththe111faces.Therefore,growthwillhavetooccuralongothercrystallographicaxesandtheresultinganisotropicparticleswillhavelarge111faces.ThisisevidencedbyTEMandelectrondiffractiondata,consis-tentwithexistingtheoriesofcrystalgrowth.Finally,thepeptidesnotonlycontrolthegr

10 owthoftheparti-cles,theyalsocontroltheir
owthoftheparti-cles,theyalsocontroltheirorganization.Thepresenceofthethioethermoietiesonthe“bersurfaceprovidesasimple,yetef“cient,scaffoldbecausethestrongsilver…sulfurinteractionde“nesthelocationofnanoparticlenucleationandgrowthandtheorientationoftheparticlesonthe“bers.Thisisagainsimilartoearlierreportsintheliterature.Naiketal.haveshownthatpeptidesinteractwithlowerenergysurfacetoin”uencetheshapeoftheparticle.Moetal.haveshownthatsilvercolloidscanbeorganizedonaproteinlikescaffold. FytikandtheChemstationAgilentsoftwarewasusedtoretrievedatavalues.SurfaceenhancedRamanscatteringSilverwafersof10.05cmweredegreasedwithacetone,driedwithargon,andetchedfor3minin3.5MnitricacidunderThesilverwasdriedwithargonandimmersedinahotmethanolic,approximately1mMpeptidesolution.After10minutes,thewaferwasremovedfromthesolution,theexcessofsolutionwasremovedbyargon”ushing,andthewaferwasdriedat40Cinavacuumovenovernight.MicroscopywasdonewithanOlympusBX41(100objective)opticalmicro-scopecoupledtoaLabramHR800JobinYvonHoribaRamanspectrometerwitha514nmlaserandapowerof5.20mW.Theconfocalholewas400mandtheslit150ScanningelectronmicroscopywasdoneonaHitachiS-4800operatedat10kV.Samplesweresputteredwith5nmofplat-inumpriortoimaging.TEMimagesweretakenusinganFEIMorgani268Doperatedat80kV.Samplesweredepositedoncarbon-coatedcoppergridsanddirectlyimagedafterdryinginair.Somesamplesweredilutedpriortoimagingtoallowforbetterimagingconditions.X-RaydiffractionX-RaypatternsweremeasuredatroomtemperatureonaStoeStadiPdiffractometerequippedwithacurvedgermaniummonochromator.X-RayradiationwasCuKradiationanddataanalysiswasdonewithOriginLabOrigin6.1.X-RayphotoelectronspectroscopyXPSwasdoneonaVGESCALab220iXLwithaMgK(1253.6eV)source.Take-offanglewas90andthepressureduringmeasurementswas10mbar.Thesilverwafe

11 rhaddimensionsof0.05cm.Waferswere“rstdeg
rhaddimensionsof0.05cm.Waferswere“rstdegreasedwithacetone,thenchemicallyetchedthreetimeswithconcentratednitricacid,rinsedwithdistilledwater,and“nallydriedwithargon.Thecleansilverwaferswereimmersedinarapidlystirred,hotmethanolicsolutionofthepeptidesorinneatmethanolforthecontrolmeasurements.Aftertenminutesandtwohoursofimmersing,thewaferswereremovedfromthesolution,theexcesssolutionwasremovedby”ushingthewaferwithargonandthewaferswerethendriedovernightundervacuumat40C.DataanalysiswasdoneusingUni“t2006(evaluationversion)andXPSPEAKS4.1.Insummary,wehaveintroducedasimpletoolforthecontrolledfabricationofpeptide…silvernanoparticlehybrid“bersandgelswithapre-programmedsilvernanoparticlesizeandshape.ThisstudyshowsthattheBrust…Shiffrinconceptofnanoparticlesizeselectionbymetalion…thiolratiovariationalsoworkswhenthethiolsorthioethersareincorporatedinaratherstiffsupramolecularassemblylikepeptide“bers.Thepaperalsoshowsthatmixturesofsimple-valine-basedoligopeptidesprovidea”exiblemineralizationplatformforthetuningofhybridnanostructures.Asaresult,our“ndingsopenthewaytowardsabettercontrolofmetal…organichybridmaterialsthevariableincorporationoffunctional(peptide)and(almost)purelystructural(peptide)buildingblocksintoasupramolec-ularscaffold.Formationkineticsandrelatedquestionsarecurrentlyunderinvestigation.WethankProf.E.C.ConstableforaccesstohisIRspectrom-eter,M.Duggelin,D.Mathys,andG.MorsonforSEMmeasurements,Prof.L.DiamondforaccesstohisRamanmicro-scope,andProf.J.WirzforaccesstotheAgilentspectrophotom-eter.TheSwissNationalScienceFoundation,theUniversityofPotsdam,theMax-Planck-InstituteofColloidsandInterfaces,andtheNCCRNanosciencesareacknowledgedfor“nancialsupport.A.T.thankstheHolcimStiftungWissenforaHabilita-tionFellowship.1M.Faraday,Philos.Trans.R.Soc.London,185

12 7,,145.2U.Kreibig,Z.Phys.D,1986,,239.3A.
7,,145.2U.Kreibig,Z.Phys.D,1986,,239.3A.Henglein,Chem.Rev.,1989,,1861.4M.Brust,J.Fink,D.Bethell,D.J.ShiffrinandC.Kiely,J.Chem.Soc.,Chem.Commun.,1995,1655.5M.Brust,M.Walker,D.Bethell,D.J.ShiffrinandR.Whyman,J.Chem.Soc.,Chem.Commun.,1994,801.6G.Schmid,Nanoparticles.FromTheorytoApplication,Wiley-VCH,Weinheim,2003.7M.C.DanielandD.Astruc,Chem.Rev.,2004,,293.8C.Zhan,J.Wang,J.Juan,H.GongandM.Liu,,2003,9C.S.Love,V.Chechik,D.K.Smith,K.Wilson,I.AshworthandC.Brennan,Chem.Commun.,2005,1971.10P.Gao,C.ZhanandM.Liu,,2006,11S.SiandT.K.Mandal,Chem.…Eur.J.,2007,,3160.12S.Bhattacharya,A.K.Das,A.BanerjeeandD.Chakravorty,J.Phys.Chem.B,2006,,10757.13S.Ray,A.K.DasandA.Banerjee,Chem.Commun.,2006,2816.14Y.-F.DjalaliandH.M.Chen,J.Am.Chem.Soc.,2003,,5873.15J.M.SlocikandD.M.Wright,Biomacromolecules,2003,,1135.16X.Mo,M.P.KrebsandS.M.Yu,,2006,,526.17Q.Dong,H.SuandD.Zhang,J.Phys.Chem.B,2005,,17429.18A.MantionandA.Taubert,Macromol.Biosci.,2007,,208.19M.Sunde,L.C.Serpell,M.Bartlam,P.E.Fraser,M.B.PepysandC.C.F.Blake,J.Mol.Biol.,1997,,729.20J.A.Jarvis,D.J.CraikandM.C.J.Wilce,Biochem.Biophys.Res.,1993,,991.21A.Manna,B.D.Kulkarni,K.BandyopadhyayandK.Vijayamohanan,Chem.Mater.,1997,,3032.22J.J.Mock,M.Barbic,D.R.Smith,D.A.SchultzandS.Schultz,J.Chem.Phys.,2002,,6755.23I.O.Sosa,C.NoguezandR.G.Barrera,J.Phys.Chem.B,2003,24K.L.Kelly,E.Coronado,L.L.ZhaoandG.C.Schatz,J.Phys.Chem.B,2003,,668.25T.C.Deivaraj,N.L.LalaandJ.Y.Lee,J.ColloidInterfaceSci.,402.26S.Y.KangandK.Kim,,1998,,226.27A.Kumar,H.Joshi,R.Pasricha,A.B.MandaleandM.Sastry,J.ColloidInterfaceSci.,2003,,396.28C.D.Wagner,W.M.Riggs,C.E.Davis,J.F.Moulder,inofX-RayPhotoelectronSpectroscopy,ed.G.E.Muilenberg,Perkin-ElmerCorporation,EdenPraire,1979,p.122.29J.C.MunroandC.W.Frank,,2003,,6335.30C.J.SandroffandD.R.Herschbach,J.Phys.Chem.