Electrophoreti

Electrophoresis2001,22,4341–4346Sara-L.Tamisier-Karolak1SabrinaPagliarusco1

ChristineHerrenknecht1MichaelBrettreich2AndreasHirsch2RenéCéolin3

RenéV.Bensasson4HenriSzwarc5FathiMoussa1

1

4341

Electrophoreticbehaviorofahighlywater-solubledendro[60]fullerene

Theaimofthepresentstudywastodevelopananalyticalmethodformeasuringamountsofadendro[60]fullerene(DF)whichisahighlywater-soluble[60]fullerenederi-vative.Wetriedtodefineastraightforwardmethodologyusingcapillaryzoneelectro-phoresis,amethodwhich,toourknowledge,hasnotyetbeenusedtothatpurpose.PreliminaryassaysshowedthatDFhasalmostthesamemobilitythantheelectroos-moticflow(EOF)butintheoppositedirection.

LaboratoiredeChimieAnalytique,Facultéde

EOFandpositiveresultswereobtainedbyPharmacie,UniversitéParisXI,groundelectrolyte.InordertodefineoptimalChâtenay-Malabry,Francementalplanwasusedtostudysimultaneouslytheeffectsofthemainparametersthat2

InstitutfürOrganischearepH,ionicstrength,methanolamountandhydroxypropylcelluloseconcentration.ChemiederUniversitätErlangen-Nürnberg,TwoparametersareoftheutmostimportanceastotheireffectonthemigrationtimeErlangen,Germanyandseparationefficiency:pHandionicstrengthwhoseactionsareopposite.

3

LaboratoiredeChimiePhysique,

FacultédePharmacie,

Keywords:Dendro[60]fullerene/Capillaryzoneelectrophoresis/Hydroxypropylcellulose/

UniversitéParisV,HumanimmunodeficiencyvirusEL4669

Paris,France4

LaboratoiredeBiophysiqueetdePhotobiologie,MuséumNationald’HistoireNaturelle,Paris,France5

LaboratoiredeChimiePhysique,sensitizeformationofsingletoxygen,andcancauseUMR8000duCNRS,photo-inducedDNAcleavage[9].ThenextstepwhoseUniversitéParisXI,

importanceisfundamentalforanyinvivobiologicaleva-Orsay,France

luationistoinvestigatetheirmetabolicfateafteradmin-istration,togetherwiththeirpotentialtoxicity.

Todeterminethepurityofthesecompoundsaswellas1Introduction

theirdistributionafteradministrationandtheirmetabo-lisminvivo,asensitiveanalyticalmethodforseparatingOverthepastfewyears,http://wendang.chazidian.compoundsinmedicinalchemistry[1–4].Fullerenederi-Althoughcapillaryelectrophoresistechniqueshavebeenvativesinhibithumanimmunodeficiencyvirus(HIV)-1usedtoseparatefullerenes[10–12],theyhaveneverbeenprotease[5],exhibitfree-radicalscavengeractivity[6],usedtoanalyzetheirderivatives,toourknowledge.So,includingtheinhibitionofradical-initiatedlipidperoxida-wedecidedtoevaluatethecapillaryzoneelectrophor-tion[7]andtheinterceptionofdeleteriousreactiveoxy-esis(CZE)behaviorofahighlywater-solubledendro[60]-genspecies[8].Duganetal.[8]haveobservedthefullerene(34mg/mLatpH7.4)(Fig.1)[13],whosetoxi-efficiencyofwater-solublemalonicacidderivatives,cityislow,whichisabletoinhibitHIV-1invitro[14]C60[C(COOH2]3,asneuroprotectiveagentsinlivingsys-andwhichisreadilyeliminatedthroughrodentkidneystemsandassessedtheirabilitytoscavengeO2.–and[15].

HO.oxyradicalsinsolutionbyelectronpulseradiologic(EPR)analysis.Fullerenederivativesarealsoableto

2Materialsandmethods

Correspondence:Dr.Sara-LaurenceTamisier-Karolak,Dr.FathiMoussa,LaboratoiredeChimieAnalytique,FacultédePharma-ABeckmanP/ACE2100system(BeckmanInstruments,cie,UniversitéParisXI,RueJ.-B.Clément,F–92260Chateny-Malabry,France

Fullerton,CA,USA)capillaryelectrophoresisinstrumentE-mail:sara.karolak@cep.u-psud.fr,withsingle-wavelengthdetectionwasused.Instrumentfathi.moussa@cep.u-psud.fr,monitoringanddataacquisitionwereperformedusingFax:+33-1-4683-5409

thesoftwareBeckmanGold7.11.DetectionwascarriedAbbreviations:DF,dendro[60]fullerene,HP-cellulose,hydroxy-outat254nmandthecapillarycassettetemperaturewaspropylcellulose

setat307C.Sampleswereintroducedwithhydrody-ªWILEY-VCHVerlagGmbH,69451Weinheim,2001

0173-0835/01/2012–4341$17.50+.50/0

C

ECdnaEC

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4342S.-L.Tamisier-Karolaketal.Figure1.Chemicalstructureofdendro[60]fullerene

namicinjectionsat0.5psifor30s.Fused-silicacapil-laries(40cmeffectivelength,47cmtotallength,50mminternaldiameter)werepurchasedfromBeckmanInstru-ments.Appliedvoltagesvariedfrom615to625kVdependingontherequiredpolarity.Dendro[60]fullerene(DF)wassynthesizedaspreviouslydescribed[10].Diba-sicsodiumphosphate,monobasicpotassiumphos-phate,ortho-phosphoricacid,sodiumhydroxide,metha-nolandacetonitrilewerepurchasedfromProlabo(Paris,France).Hydroxypropylcellulose(HP-cellulose)waspro-videdbySigma-Aldrich(Milwaukee,WI,USA).Back-groundelectrolytes(BGE)containingfrom45to75mMphosphatebufferswereprepareddailyindeionizedwaterandwerefilteredthrougha0.22mmporesizemembranefilter(Millipore,St-QuentinenYvelines,France)beforeuse.Whenused,methanolwasdilutedwithphosphatebufferbeforefiltration.ForHP-celluloseBGE,anappro-priateamountofHP-cellulosewasdissolvedinamixtureofmethanol/phosphatebufferandthensonicatedfor10minbeforefiltration.TheDFstocksolutions(2g/L)werepreparedmonthlyinawater-acetonitrile(50/50v/v)mixtureandstoredat–47Cuntiluse.Afterequilibrationatroomtemperature,anappropriatealiquotofDFstocksolutionwasdilutedinwatertogeta0.2g/Lsolution.Beforeuse,thefused-silicacapillarywasrinsedunderpressurewithwaterduring5min,thenwith0.1Msodiumhydroxidefor10minandthenwithwateragainforduring5min,beforefinallybeingequilibratedwiththerunningBGEfor10min.Aftereachrun,thecapillarywasrinsedwithwaterunderpressurefor10minandthentwicewithBGEduring5minwithBGE.

Electrophoresis2001,22,4341–4346

3Results

Inapreliminaryassay,DFwasanalyzedusinga67mM,pH7.4,phosphatebufferwithanormal25kVpolaritysupply(detectionatthecathode).Undertheseconditions,abroadpeakwasobtainedatabout50minwhichcorre-spondstoanapparentmobilityof5.3610–5cmV–1s–1.AstheEOFwasestimatedas4.8610–4cmV–1s–1byusingthemigrationtimeofacetone,theeffectivemobi-lityofDFwascalculatedas–4.3610–4cmV–1s–1,thatisaboutthesamevalueasthatoftheEOFbutwiththeoppositesign.Sowetriedtoreducethelatterbychemicallyalteringthecapillarysurfacecharge.With0.1%HP-cellulose-BGE,DFmigratedtowardstheanodeandthemigrationtimeincreasedasafunctionofpHtoreach50minatpH6.6(Table1).Undertheseconditions,theelectrophoreticmobilityofDFremainednearlycon-stantbetweenpH5.5and6.6,whereastheEOFin-creasedasafunctionofpH.

Anexperimentalplanwasthendevelopedtoimprovetheseparation.Wedecidedtostudytheeffectsoffourpara-meters–pH,saltconcentration,HP-celluloseconcentra-tionandmethanolamount–onmigrationtimeandeffi-ciencyofseparationexpressedastheasymmetryfactormeasuredat10%ofthepeakheight(Table2).Thisfactorwastakenastheratioofthetwohalfpeakwidthsmea-sured,respectively,afterandbeforethemigrationtimeofthemaximumofthepeak.Thevaluesstudiedforeachparameterwerechoseninordertoimprovethesepara-tionobtainedatpH5.5.ThepHrangewaskeptbetween

Electrophoresis2001,22,4341–4346CZEseparationofdendro[60]fullerene4343

Table1.Determinationoftheelectrophoreticmobilityofdendro[60]fullereneunder

differentbufferconditionspHofaqueousbuffer5.56.16.68.1

Dendro[60]fullereneMigrationtime(min)183550

Nopeak

Electrophoreticmobility(cmV–1s–1)–2.72610–4–2.75610–4–2.93610–4

AcetoneMigrationtime(min)6.255.34.74.3

Electroosmoticmobility(cmV–1s–1)2.02610–42.38610–42.68610–42.93610–4

BGE:0.1%ofHP-cellulosein67mMphosphatebuffer/methanol(75/25v/v).Reversepolarity,25kVforDFdetection;normalpolarityforEOFdetermination

Table2.Taguchiexperimentalplan:migrationtimesofdendro[60]fullereneandpeak

asymmetriesobtainedunderdifferentbufferconditionsBuffer

pH

Methanol(%)

HPCa)(%)

Ionicstrength(mM)606060454545757575

TimeofmigrationMean6SD(n=3)13.661.220.361.423.860.225.462.634.162.951.662.214.061.414.860.417.661.2

Asymmetryfactor

Mean6SD(n=3)0.1060.040.4260.080.2160.020.0560.040.3660.050.2460.030.0860.030.1360.030.2460.02

12345678955.5655.5655.562530202025303020250.10.0750.1250.0750.1250.10.1250.10.075

a)ConcentrationofHP-cellulose

5and6togetsufficientionizationofDFwithoutaggrega-tion[16]andtoavoidastrongEOF.ATaguchiplan[17]wasretainedasitallowsthesimultaneousevaluationoftheeffectsofthefourparameterswithonlynineopera-tionalconditions,eachanalysisbeingrepeatedthreetimes.Theeffectofagivenlevelofaparameteronthedesireddatawascalculatedasthedifferencebetweenthemeanoftheanalysescarriedoutwiththeconsideredlevelandthemeanofallanalyses(Table3).TheseeffectsareallsignificantasprovedbystatisticalAnovastudiesthatleadtoprobabilitydegreeslowerthan0.01%foreachparameter.

AsshowninFig.2,themigrationtimeofDFincreaseswhenpHincreasesandthebufferconcentrationde-creases.ThepHeffectismoreimportantatthelowestbufferconcentration(Fig.2a).Inthesameway,theeffectofbufferconcentrationismoreimportantatthehighestpHlevel(Fig.2b).Theinfluenceoftheamountofmethanolonmigrationtimeisweakerespeciallybetween20and25%wherethecalculatedeffectsremaincloseoneto

another(Table3).HP-celluloseconcentrationhasalmostnoinfluence,asitdoesnotleadtoalinearvariationofthemigrationtime(Table3).

WhatevertheBGEcomposition,DFpeaksappearasym-metricwithzonefronting(Fig.3).AtpHlowerthan6,anunresolvedsmallpeakappearsinfrontoftheDFpeak.Theasymmetryfactorremainsbelow1butislesspronouncedatpH5.5and6andfor60mMbuffercon-centration(Fig.3,peaks2and3).Therelationshipbetweenthepeakasymmetryandtheconsideredpara-meterseemslinearforpHandquiteunclearfortheotherparameters(Table3).Optimalresults–lessasym-metricpeaks–areobtainedforbuffers2and5with0.42and0.36asymmetryfactors,respectively.PeakshapesapproachGaussianprofilesand,usingtheusualGaussequation(N=5.54(tm/d)2wheretmisthemigra-tiontimeofthepeakmaximumanddisthepeakwidthatitshalf-height),allowtocalculateplatenumbersof262800616500and3221006153500(n=3),respec-tively.AtpH=6,asymmetryfactorsarecloseto0.2

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4344S.-L.Tamisier-Karolaketal.Electrophoresis2001,22,4341–4346

differentbehaviors[16].ThefirstdomainliesatpH,5whereDFaggregationisobviouslytakingplace.Thediffer-encesbetweenthepKavaluesarerelativelylarge(0.3–0.5)andincreasewithincreasingdissociationdegrees.Thiscanbeunderstoodbyconsideringtheincreasingchargedensitiesontheclustersurfacewithincreasingdissocia-tiondegrees.Thedeprotonationoftheacidismoreandmoredifficultandconsequentlyincreaseofchargedensi-tiesishindered.TheseconddomainliesbetweenpH5and8.AtpH5,thedifferencebetweentwosuccessivepKavaluesdecreasessteeply(about0.1).Thisisrelatedtothebreakdownoftheclusters.Becauseofthisbreak-down,thesurfaceonwhichnegativechargescanfastenincreasesdrasticallyandthereforedeprotonationoftheacidsiseasier.ThedrivingforceforthedestructionoftheclustersandtheformationofDF-monomersisthechargedensitybuilduponthesurfacewithincreasingpH.Inthelow-pHregion,thedifferencesbetweenpKavaluesincreasewithincreasingpHaswell.ThethirdregionoccursatpHhigherthan8wherethedivergencebetweenthecalculatedandthemeasuredcurveissignificant.InthispHdomain,consumptionofNaOHishigherforthemeasuredcurve.AtpHhigherthan8,hydrolysisoftheDFesterbondsalreadyinfluencesthetitration.InthispHdomain,theprimarilyexistingspeciesarethosecontain-ing17and18ionizedcarboxylicgroups:thesespeciesarehydrolyzedandtheircalculatedpKavaluescannotbeused.ThepKaofthesespeciesshouldbe(withoutsaponi-fication)inthesamerangethantheproceedingpKa,i.e.,between6.5and7.5[16].

TwoofthesecarboxylicfunctionsexhibitanapparentpKaequalto3.3whereastheother16pKavalueslyingbetween5.5and6.5cannotbedeterminedaccurately.AtpH7.4,where14ofitscarboxylicgroupsareionized,DFexhibitsanelectrophoreticmobilityofthesamemag-nitudeastheEOFbutintheoppositedirection.

Figure2.EvolutionofDFmigrationtimeasafunctionof(a)pHand(b)saltconcentrationoftheBGEphosphatebuffer.(BGE,phosphatebuffer/methanol(80–70/20–30,v/v)–HP-cellulose(0.075–1.25%).

althoughtheshortmigrationtimecompensatesforthedeformation.Thus,forbuffer9,theplatenumberis351500647400.

4Discussion

DFisawater-solubleC60derivativecontaining18car-boxylicfunctionswithdifferentpKa[13].NaOHtitrationofDFledtodistinguishthreepHdomainswithsignificantly

Table3.Taguchiexperimentalplan:determinationoftheeffectofeachlevelofstudiedparameters

onthemigrationtimeofdendro[60]fullereneandonthepeakasymmetryEffectofconsideredparameteronmigrationtimeofDFpH55.56

Effect–6.23–0.857.08

Saltconcentration45mM60mM75mM

Effect13.15–4.71–8.44

Methanol20%25%30%

Effect–2.57–2.154.72

HPCa)0.075%0.1%0.125%

Effect–2.812.750.06

EffectofconsideredparameteronasymmetryofDFpeakpH55.56

Effect–0.130.10.23

Saltconcentration45mM60mM75mM

Effect0.010.04–0.05

Methanol20%25%30%

Effect–0.070.030.05

HPCa)0.075%0.1%0.125%

Effect0.03–0.050.01

a)ConcentrationofHP-cellulose

Electrophoresis2001,22,4341–4346

NeutralhydrophilicpolymersareadsorbedoncapillarywallsandusuallydiminishtheEOFbyshieldingsurfacechargesandincreasingviscosity.Theadditionof0.1%HP-cellulosetotheBGEeffectivelydecreasestheEOF.Undertheseconditions,themobilitycalculatedforDFremainsnear2.7610–4cmV–1s–1whateverthepHvaluebetweenpH5.5and6.5.ThisvaluelowerthanthatobtainedwithoutHP-celluloseisprobablyduetotheadditionofmethanoltothebuffer,whichalterstheioniza-tiondegreeofDFandtheviscosityoftheBGE.MethanolwasnecessarytoallowcompletedissolutionofHP-cellu-loseinthebuffer.Actually,themigrationtimeofDFincreasesasafunctionofpH.However,theconcentrationofHP-cellulosewassufficienttodecreasetheEOFbutnottosuppressitcompletely.WhenthepHbufferbecomeshigherthan6,theresultingEOFincreasesandlimitstheneutralizingactionofHP-cellulose.ThefastestseparationwasobtainedatpH5.5withamigrationtimeof18min.

Tooptimizetheseparation,weusedaTaguchiexperi-mentalplan[17].Thisplanisanorthogonalfractionalplanthatallowstostudyeachlevelofanyparameterinassociationwithalllevelsoftheotherthreepara-meters.Thismeansthataneffectobservedforonegivenparameterisindependentonthelevelsoftheotherparameters.However,adrawbackofthisplanisthatitmaymistaketheinfluenceofoneparameterwiththepossibleinfluenceoftwootherinteractingpara-meters.Forinstance,thepHeffectwasassociatedwiththepossibleeffectsduetotheinteractionsbetweensaltconcentrationandmethanolamount,saltconcentrationandHP-celluloseconcentration,methanolamountandHP-celluloseconcentration.Nevertheless,theseparationprocessresultsfromthecombinedeffectsofalltheparameters.

CZEseparationofdendro[60]fullerene4345

Twoparametershaveastronginfluenceonthemigra-tiontimeofDF:pHthatslowsdownmigrationandsaltconcentrationthatspeedsitup.AsshowninFig.3,themagnitudeoftheinfluenceofoneoftheseparametersdependsonthelevelofthesecondone,whichprovestheexistenceofasignificantinteractionbetweenthem.ThisphenomenoncanbeattributedtothefactthattheseparametersactinoppositewaysontheEOF.ThepreliminarystudyshowedthatthemobilityofDFdoesnotvarysignificantlyinthe5.5–6.6pHrange.Thus,thevariationoftheDFmigrationtimeismainlyrelatedtothevariationoftheEOF.TheincreaseofpHleadstoanincreasesoftheEOFandofthemigrationtimetowardstheanode.AhighersaltconcentrationgivesaweakerEOFthatgenerateslessoppositiontotheanionicmigration.TheeffectofpHonthemigrationtimeofDFismoreimportantatthelowestionicstrengthwheretheEOFisbigger.

Underourconditions,HP-celluloseconcentrationdoesnotaffectsignificantlythemigrationprocess(Table3).TheDFmigrationtimeshoulddecreaseastheconcen-trationofHP-celluloseincreasesleadingtoEOFreduc-tion.Table3showsthatthecontraryoccurs.Therefore,theeffectsmeasuredforHP-celluloseconcentrationsshouldbepreferablyrelatedtotheinteractionsbetweenpHandsaltconcentration.Theseinteractionsshouldalsobetakenintoaccountwhenevaluatingtheinfluenceofmethanol.Actually,themeasuredeffectsformethanolareweakandnoclearrelationshipbetweenmethanolamountandDFmigrationtimecameout.Theefficiencyoftheseparationwasstudiedbydeterminingasymmetryfactorsandcalculatingplatenumbers.Twophenomenahaveapredominantinfluenceonefficiency:(i)ionicdis-persionthatresultsfromvariationsoftheelectricfieldbetweenthebufferandthemigratingzoneandleads

to

Figure3.ElectropherogramsofDFobtainedunderdifferentBGEconditions.Numbersinbracketsrefertothebuffer(seeTable2fordetails).