液液界面電子轉(zhuǎn)移研究苯甲酰吡啶-縮氨基硫脲的親脂性

1、AprilArticleActaPhys.鄄Chim.Sin.,2008,24(4)：619-624物理化學(xué)學(xué)報(WuliHuaxueXuebao)619InvestigationoftheLipophilicityof2BenzoylpyridineThiosemicarbazoneBasedontheIonTransferacrosstheLiquid/LiquidInterfaceAKGEMCIEmineG.(DepartmentofChemistry,SelcukUniversity,Meram/KonyaBINGOLHalukOZCELIKMehmet42099,Turkey)ERS

2、OZMustafaAbstract：Theiontransferreactionof2benzoylpyridinethiosemicarbazone(HL),whichhasantimicrobialandantifungalpropertiesandanticanceractivity,hasbeenstudiedtodetermineitslipophilicitybycyclicvoltammetryatthewater/1,2dichloroethane(1,2DCE)interface.Thephysicochemicalparameterssuchasstandardpartit

3、ioncoefficiento(lgPI)andthestandardGibbsenergyoftransfer(G0,w)oftheprotonatedformoftheligandweremeasuredasafunctiontr,IofpHinaqueousphase.Theprotonatedformoftheligandexhibitedreversibleorquasireversiblevoltammogramsatthe1,2DCEintherangeofpH1-5.Theprotonationconstantsoftheligand,pKa1andpKa2,weredeter

4、minedspectrophotometricallywoandwerefoundtobe12.14and3.24,respectively.ThestandardGibbsenergyoftransfer(G0,)andthepartitiontr,Ncoefficientofneutralspecies(lgPN)werealsodeterminedbytheshakeflaskmethod.ThestandardGibbsenergyoftransferofthiscompoundacrossthewater/1,2DCEinterfacewasevaluatedasthequantit

5、ativemeasureofitslipophilicity.ThedifferencebetweenlgPIandlgPNwasrelatedtothedegreeofchargedelocalizationandwasusedtoevaluatequalitativelythelipophilicityoftheligand.KeyWords：Lipophilicity;2Benzoylpyridinethiosemicarbazone;Liquid/liquidinterfaceIontransfer;Protonationconstant;Quantitativestructureac

6、tivityrelationships(QSAR)havebeenextensivelyusedtocorrelatethebiologicalactivityofdrugswithphysicochemicalparameterssuchassolubility,thepartitionco-efficientinoil/watersystems,electroniceffectofsubstituents,electrondensity,andstericeffects,inthelastfewdecades1.Lipophilicityrepresentstheaffinityofaco

7、mpoundforalipidicenvironmentanditisthemostwidelyusedparametertodesigndrugsandtoassesstheirperformances.AquantitativemeasureofthelipophilicityofionsisrelateddirectlytothestandardGibbsenergyoftheiontransferfromwatertoorganicphase2.Theinterfacebetweenanorganicandawaterphasehasbeenfrequentlyinferredasas

8、implemodelofbiologicalmembranes3.noctanolisthemostcommonlyusedsolventinlipophilicityastheorganicphase4.However,thenoctanol/waterinterfaceisnotsufficienttomodelmembranepermeation,owingtothemajordifferencesinthebiophysicalproperties.Forexample,thepres-enceofhydrogenbondsbetweenwaterandnoctanolmolecule

9、sattheinterfaceintroducesimportantchangesintheinterfacialstructure.Ontheotherhand,owingtoveryfewbaseelectrolytesthatcandissolveinthenoctanolphase,thepolarizabilityofthissystemisverydifficultexceptthenanointerfacestudies5.Owingtothewater/1,2DCEinterfacebeingpolarizable,thissystemismoresuitedforelectr

10、ochemicalstudies6.Lipophilicitiesofsomeionizabledrugshavebeendeterminedbycyclicvoltammetryattheinterfacebetweentwoimmiscibleelectrolytesolutions(ITIES)acrossthewater/1,2DCEinterface1,7-10.IthasbeendemonstratedthatcyclicvoltammetryatITIESisthemethodofchoicetodeterminethelipophilicityofcations,inparti

11、culardrugsthatcanbeprotonated4.ThetransferofabaseBH+canberegardedeitherasaclassicalcationtransferreactionorasapro-tontransferreactionassistedbytheconjugatedacid11.Therefore,thesetypesofassistediontransferreactionsconcernwithacidbasepropertiesofmolecules.TheneutralformofacidsandbasesmayreducetheGibbs

12、energyoftransferoftheprotonasaresultofinterfacialprotonationanddeprotonationreactions,re-spectively.Theexplanationofinterfacialmechanismisofgreatimportanceinpharmacology,becausetheprotonconcentrationisverytightlyregulatedinfunctionalbiologicalsystems12.Thepartitioncoefficientofagivensolutebetweentwo

13、immis-ciblesolventsisameasurementofitsrelativeaffinityforbothphases.SincelgPisrelatedtothefreeenergyoftransferofthesolutebetweenthesolvents,itencodesinformationonthediffer-Received:October17,2007;Revised:December11,2007;PublishedonWeb:February19,2008.ECorrespondingauthor.Email:egakgemci;Tel:+9033232

14、38220141;Fax:+903323238225.EditorialofficeofActaPhysicoChimicaSinicaTheprojectwassupportedbytheScientificResearchProjects(BAP)ofSelcukUniversity,Turkey(2003/151).620ActaPhys.鄄Chim.Sin.,2008Vol.24entialsolvationeffectsandhasbeencorrelatedwiththebiologi-calandpharmacologicalprocesseswithregardtoadsorp

15、tion,transportthroughcellmembranes,andhydrophobicbinding13.Thiosemicarbazones(hydrazinecarbothioamides)andtheirmetalcomplexesexhibitawiderangeofmedicinalapplicationsandrepresentsomeofthemostpotentknowninhibitorsofribonucleosidediphosphatereductase14-20.Metalcomplexesof2benzoylpyridinederivedthiosemi

16、carbazonewerecharacterizedbyspectroscopictechniquesandtheirelectrochemicalandbio-logicalpropertieswerealsostudiedindetail21-24.Antifungalac-tivitiesagainstcandidaalbicans22andantibacterialactivitiesinnutrientbrothagainstE.coli1053625ofHLanditsmetalcom-plexeshavebeenstudied.Thecyctotoxicactivityofpal

17、ladium(II)complexesof2benzoylpyridinethiosemicarbazone(HL),anditsN(4)methylandphenylderivativeswerealsotestedagainsttheMCF7,TK10,andUHCC62humantumorcelllines26.TheelectrochemicalbehaviorofHLwasfirstdescribedonthebasisofclassicalanddifferentialpulsepolarographictech-niques27.Thecomplexesof2benzoylpyr

18、idinethiosemicar-bazoneaswellasofitsN(4)methylandN(4)phenylanalogueswithmetalssuchasiron(II),nickel(II),andzinc(II)werechar-acterizedandtheelectrochemicalstudiesrevealedthattheiron(II)complexesundergooxidationgivingtheiron(III)analogues,whichcanbereducedbackbycellularthiolssuchasthioredox-ine,sugges

19、tingthatthisprocesscanoccurinbiologicalmedia22.Theaimofthisstudywastoexaminethevoltammetricbehaviorofthe2benzoylpyridinethiosemicarbazone(HL),whichhasan-timicrobialandantifungalpropertiesandanticanceractivitythatcanhavesomeadvantagesforbiologicalsystems,tocharacterizeitsiontransferreactionacrossthew

20、ater/1,2DCEinterface,andtodeterminethelipophilicityscaletoobtainsomeconclusiontotheoriginofitspharmacologicalactivityinbiologicalsystems.Fig.1Chemicalstructureof2benzoylpyridinethiosemicarbazone(HL)1Experimental1.1ChemicalsDeionizedwater(MilliQSPreagentwatersystem,Millipore)and1,2dichloroethane(1,2D

21、CE)ofthehighestavailablepurity(Merck)wereusedasorganicphase,withoutanytreatment.Theorganicsupportingelectrolytewaspreparedbymetathesisofbis(triphenylphosphoranylidene)ammoniumchloride(BTPPA-Cl)(Fluka)andpotassiumtetrakis(4chlorophenyl)borate(KTP-BCl)(Lancaster,UK)in11methanol/watermixtureprovidingaB

22、TPPATPBClprecipitateasdescribed12.LiCl(Fluka)wastheaqueouselectrolyteandHClorLiOH(Fluka)wasaddedtothewaterphaseofelectrochemicalcelltofixatthedesiredpHvalue.2benzoylpyridinethiosemicarbazone(Fig.1)waspreparedaccordingtothemethodasdescribedintheliterature25.Thestructureofligandwasconfirmedbyelemental

23、analysis,1HNMR,andIRspectrometrictechniques.Inthespectrophotometricexperiments,BrittonandRobinsonbuffersolutionwasusedinpHinterval2-12.1.2CellandapparatusTheiontransferreactionacrossthewater/1,2DCEinterfacewasstudiedbymeansofcyclicvoltammetryusingafourelec-trodecellsystemdescribedelsewhere10.Thecell

24、waspoweredbyafourelectrodepotentiostatfeaturingIRcompensationbyposi-tivefeedback,PAR263/A2(PAR,USA).Theareaoftheinterfacewas0.273cm2andtheexperimentswerecarriedoutatroomtem-perature(24±1).Inallexperiments,thecellwasplacedinaFara-daycage.TheelectrochemicalcellcanberepresentedbyScheme1.Thepotenti

25、alEappliedbetweenthetwoAg/AgClreferenceelectrodesisrelatedtotheGalvani(ortheinner)potentialdiffer-ence(wo)acrosstheinterfaceby:wE=o+Eref(1)+Tetraethylammoniumcation(TEA)wasaddedtotheaqueousphaseaftereachexperiment,toreferencealltheobservedstan-0dardtransferpotentials,Etr,I,deducedfromthepeakpotentia

26、lsinthevoltammograms(Fig.2).Thesevalueswerethentransposedtotheabsolutescalebyapplyingthefollowingrelationship,0w00w0Etr,(2)I-otr,I=Etr,ref-otr,refw0where,otr,IisthestandardGalvanitransferpotentialofprotonatedligand,andwotr,refisthestandardGalvanitransferpotentialofTEA+(wotr,TEA=44mVaccordingtoRef.28

27、).1.3DeterminationofprotonationconstantsTheprotonationconstantsoftheligand,Ka1andKa2,weredeterminedspectrophotometricallyat25andionicstrengthof0.1mol·L-1KNO3.UVVisspectrophotometricmeasurementswerecarriedoutwithShimadzuUV160spectrophotometer.+Scheme1SchematicdiagramoftheelectrochemicalcellNo.4A

28、KGEMCIEmineG.etal.：InvestigationoftheLipophilicityof2鄄BenzoylpyridineThiosemicarbazoneBased621Fig.2ObtainedvoltammogramsforthetransferofTEA+andtheprotonatedformofligand(H2L+)atpHCrisonmicropH2002pHmeterwithcombinedelectrode(MetterToledoInlab412)wasusedforthepHmeasurements.Stan-dardizationsofHClandNa

29、OHsolutionswereadjustedpoten-tiometrically.Theappliedmethoddependsuponthedirectdeterminationoftheratioofmolecularspecies(neutralmolecule)toionizedspec-iesinaseriesofnonabsorbingbuffersolutions,whosepHvaluesareeitherknownormeasured.Allspectrawererecordedintherangeof250-450nm,atslowscanspeed,againstco

30、rrespondingblank(thenumber(n)ofparallelmeasurementswas6).1.4Shake鄄flaskmethodThepartitioncoefficientofneutralformoftheligandinthewater/1,2DCEsystemwasmeasuredbytheshakeflaskmethod29.Priortoeachexperiment,theorganicandaqueousphasesweremutuallysaturatedfor6h.Theligandwasdissolvedinthe1,2DCEphasecontai

31、ning0.01mol·L-1BTPPATPBCl,whiletheaqueousphasecompositionwas0.01mol·L-1LiCl(pH7.4).Bothphaseswereshaken(36h)togetherbeforeseparationandanalysisoftheorganicsolutionwasdonebyUVspectroscopy(n=6).2Resultsanddiscussion2.1ProtonationconstantsFig.3showstheabsorptionspectraatdifferentpHranges1-14.

32、ClearlydiscernibleisosbesticpointsinpHdependentabsorptionspectraindicatethattheacidbaseequilibriumisnotchangedbysidereactions.ThepKa1andpKa2valueswereFig.3PlotsofabsorbancedataversuswavelengthforHLFig.4Distributionofionicspeciesforthethiosemicarbazonecalculatedfromtheclassicalspectrophotometricequat

33、ion30andwerefoundtobeequalto12.14and3.24,respectively.TheligandpossessesoneacidicNHgroupandonebasicpyridylgroup,thus,itbehavesasaweakbaseandaweakacid,andtherefore,ithasthreeindependentspeciesinaqueoussolutions.ThedistributionofionicspeciesforthepHrangefrom1to14isshowninFig.4.Theequilibriumbetweenthe

34、speciesisgivenbytheequilibriumequationsasfollows:L-+H3O+Ka1HL+H2O(3)HL+H3O+Ka2valueisH2L+H(4)ThepK2Oa2lowerthanthatofpyridine(5.25).Comparedtopyridine,itcanbeattributedtothedecreaseinelectrondensityonthepyridinenitrogencausedbytheelectronwithdrawingeffectofthethiureidegroup20.Ithasbeenfoundfromtheda

35、taof1Hand13CNMRspectr-oscopiesthatintheelectronicspectraoftheHL,thesignalsaredoubledasaconsequenceoftheexistenceoftheZandEconfigurationalisomersinsolution22.ItcanbepointedoutthattheisomerandresonanceformsdirectlyaffecttheacidityandbasicpropertiesofHL,i.e.,pyridinenitrogenofHLintheEformwithregardtoth

36、eZformcanbeeasilyprotonatedowingtothehydrogenbondinthemolecules.2.2ThermodynamicparametersLipophilicityofasoluteiscommonlymeasuredbyitspartitioncoefficient(P)inabiphasicsystem.Thermodynamically,thisparameterisdefinedastheratiooftheactivityofaspeciesdissolvedatequilibriumbetweentwoimmisciblesolventph

37、asesanditisoftenexpressedonalogarithmicscaleaslgP.Thepartitioncoefficientofprotonatedform(lgPI)iscalculatedaccording(tolgPI=-)wotr,I0(5)where,lgPIrepresentstheproportionofionspresentineachphaseiftheinterfaceisnotpolarized.Indilutesolutions,thestandardiontransferGalvanipotentialisrelatedtothestandard

38、Gibbsenergyoftransferbythefollowingdefinitionwotr,I0=0,wtr,IoI(6)TheGibbsenergyoftransferfromanorganicsolventtowater622ActaPhys.鄄Chim.Sin.,2008Vol.24Fig.5TypicalcyclicvoltammogramsobtainedforthetransferofprotonatedformofHLacrossthewater/1,2DCEinterfaceatdifferentpHvalueshasbeenusedasaquantitativemea

39、sureofthelipophilicityoforganiccompounds.Inthecaseofchargedcomponents,thestandardGibbsenergyofiontransferisadirectmeasurementofthelipophilicity1.Theneutralform(N)ofanionizablecompoundisdistributedbetweenthetwophases,butitspartitioncoefficientisindependentofwoandisrelatedsimplytoitsstandardGibbsenerg

40、yoftransfer()G0,wtr,NoasdefinedbyEq.(5).lgPN=lgaoNN=-0,wtr,No(7)ThevoltammogramscorrespondingtothetransferoftheprotonatedformoftheligandareshowninFig.5betweenpH1and5.ThevoltammogramsobtainedatdifferentscanrateswereanalyzedatpH1(Fig.6).Thedependenceofthebackgroundsubtractedanodicpeakcurrent(ipa)onthe

41、squarerootofthescanrate(v)isshowninFig.7,indicatingthatthecurrentispropor-tionaltov1/2.Thepeakseparationwas65mVandthemidpointpotentialwasdeterminedas134mVfromEq.(2).Thelineardependenceofthepeakcurrentonthesquarerootofthevintherangeof20to150mV·s-1,andthenegligibleshiftofthepeakpotentialwithvindi

42、catesthatthetransferoftheprotonatedligandatthewater/1,2DCEinterfaceisdiffusioncontrolledandreversibleatpH1.Fig.6TypicalcyclicvoltammogramsobtainedatdifferentscanratesforthetransferofHLacrossthewater/1,2DCEinterfaceatpH1Fig.7Dependenceoftheanodicpeakcurrent(ipa)ofprotonatediontransferofHLonthesquarer

43、ootofthepotentialscanrate(v1/2)atpH1ThepeakseparationwasapproximatelyobtainedasEp=0.091VbetweenpH2and5,indicatingthatthevoltammogramsareofquasireversiblenature,whichcanbepartlyattributedtothelimitedrateofprotonationprecedingiontransferacrosstheinterface31.TheformalGalvanitransferpotentialoftheproton

44、atedligandacrosstheinterfaceshiftedtomorepositivevalueswiththeincreaseofpH(Fig.5).ThediffusioncoefficientoftheprotonatedformoftheligandwascalculatedfromtheRandlesSevcikequation32usingthevoltammetricdataatpH(1:ipa=0.4463zIFAcwI)1/2(vDwI)1/2(8)where,ipaisthevalueofthecurrentpeak,Aistheinterfacialarea,

45、zIisthechargeoftheionI,cwIistheconcentrationofionintheaqueousphase,DwIisthediffusioncoefficientofionintheaqueousphase,andvisthepotentialscanrate.Theothersymbolshavetheirusualmeanings.ThediffusioncoefficientoftheprotonatedformoftheligandinthewaterphasewasfoundtobeDw=(2.09±0.37)×10-6cm2·

46、;s-1.Thediffusioncoefficientofthespeciesinorganicphasewascalculatedas,Do=(2.39±0.37)×10-6cm2·s-1usingtheDwandtheviscosityratioofthecontactingphases(Waldensrule).Theobtainedvaluesareclosetothereportedvaluesforsimilarstructure3.NocurrentwasobservedbetweenpH5and12,indicatingthatassistedi

47、ontransferreactiondoesnottakeplaceundertheseconditions.AbovepH12,aweakwaveappeared(Fig.8),whichcouldbeattributedtothetransferoftheanionicform(L-).However,thenatureofthistransfercouldnotbesatisfactorilyevaluatedbyanalyzingthecyclicvoltammetricdata.Bornsequationprovidesgoodestimatesofionicsolvationene

48、rgies12lgP(=lg.Thedifferencebetweenachargedandneutralspecies,lgPPI-lgPN),canbeexpressedas:=-(GoIS-GwIS)=(z22eN)(or-wr)(9)where,istheemolecularisthechargeradius,oftheproton,0rrNAistheAvogadronumber,r0isthevacuumpermittivity,orandwrareGthedielectricconstantsoftheorganicandaqueousphases,oISandGwISareth

49、edifferencesinthechemicalpotentialbetween1molofionsand1molofneutralmoleculesforequalNo.4AKGEMCIEmineG.etal.：InvestigationoftheLipophilicityof2BenzoylpyridineThiosemicarbazoneBased623Fig.8VoltammogramforthetransferofanionicformatpH12.71numberofmoleculesofequalsizeinorganicandaqueousphases,respectivel

50、y.Asageneralcharacteristic,itcanbeconcludedthatthesmallerlgPcanbeattributedtothehighermolecularradiusofthecompounds.Itindicatesthatthistypeofmoleculehashigherlipophilicity.Bornssolvationmodelshowsthationswithadelocalizedormaskedchargebehaveaslargerionsthanthosethatpossessamorelocalizedcharge12.Inthe

51、water/1,2DCEsystem,thedifferencebetweentheneutralandcationicformsofHL(-3.42)issmallerthanthedifferenceobservedforsimplerprotonablecompounds.Thisresultindicatesthatthepositivechargeinthecationicformislesslocalizedthanregularcations.Thephysicochemicalparametersfortheneutralandprotonatedformoftheligand

52、arefoundasfollows:wo準(zhǔn)0I=134mV,lgPI=-2.27,G0,wtr,Io=12.93kJ·mol-1,lgPN=1.15,G0,wtr,No=-6.56kJ·mol-1,andlgP=-3.42.Itisseenthattheneutralformofligandismorelipophilicthanitsprotonatedform.Theligandexhibitsconsiderableantibacterialactivity25.Itwasreportedthatthethiosemicarbazoneseriesexhibiteda

53、specificandconsistentstructureactivityrelationship33.Lipinskietal.34describedthedesiredrangesforcertainpropertiesthoughttobeimportantforpharmacokineticsanddrugdevelopment.Theyare:lgPOCT5(thelogarithmofpartitioncoefficientbetweenwaterandoctanol),numberofhydrogenbonddonors5,numberofhydrogenbondaccepto

54、rs10,andmolecularweight500.ThemolecularweightofHLis256.33g·mol-1.HbonddonatingsoluteshavelgPDCElowerthanthelgPOCTvalues.Thepartitioncoefficientwascalculatedusinginternetsoftwareproducts(AlgPS,IAlgP,ClgP,lgPKowin,andxlgP)35.TheaveragelgPOCTvalueforHLwasobtainedas2.40±0.41.3ConclusionsDespit

55、ethewideresearchofthiosemicarbazonesandtheincreasinginterestinchemistryandbiology,wearenotawareofanypreviousinvestigationofthefacilitatediontransferbythiosemicarbazonesattheITIESabouttheirlipophilicityexceptourgroup.Inthisstudy,thecharacterizationoftheiontransferreactionandthelipophilicityscaleof2be

56、nzoylpyridinethiosemicarbazoneatthewater/1,2DCEinterfacewascharac-terized.Thestudiedligandhashighantibacterialactivity;therefore,electrochemically,thedeterminationoflipophilicityattheinterfacesbetweenwaterand1,2DCEasmembranemodelcanbeexpectedtocontributethepharmaceuticalpropertiesofthestudiedligand.

57、Theligandpossessesthreeindependentspecies:thecationic(H2L+),theanionic(L-),andtheneutral(HL)forms.TransferofH2L+atmacroITIESwasobtainedbetweenpH1and5,andwasanalyzedbycyclicvoltammetry.Ontheotherhand,theobtainedtransferofL-abovepH12couldnotbeanalyzedowingtoitsnature.References1Kong,Y.T.;Kakiuchi,T.J.

58、Electroanal.Chem.,2000,483:222Takahashi,K.;Sakano,H.;Rytting,J.H.;Numata,N.;Kuroda,S.;Mizuno,N.DrugDev.Ind.Pharm.,2001,27:1593Reymond,F.;Steyaert,G.;Carrupt,P.A.;Testa,B.;Girault,H.H.Helv.Chim.Acta,1996,79:1014Bouchard,G.;Carrupt,P.A.;Testa,B.;Gobry,V.;Girault,H.H.Chem.Eur.J.,2002,8:3478Jing,P.;Zhang,M.;Hu,H.;Xu,X.;Liang,Z