Photo-Induced Switchable Binding Behavior of Bridged Bis(β-cyclodextrin) with an Azobenzene Dicarbo

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Photo-InducedSwitchableBindingBehaviorofBridgedBis(b-cyclodextrin)withanAzobenzeneDicarboxylateLinker

YULIU1,*,SHUKANG1,YONGCHEN1,YING-WEIYANG1JURRIAANHUSKENS21DepartmentofChemistry,StateKeyLaboratoryofElemento-OrganicChemistry,NankaiUniversity,Tianjin300071,P.R.China;2LaboratoryofSupramolecularChemistryandTechnologyandStrategicResearchOrientation‘‘Nano-fabrication’’,MESA+InstituteforNanotechnology,UniversityofTwente,217,Enschede7500AE,TheNetherlands

Keywords:azobenzene,bridgedbis(cyclodextrin),photoisomerization,switchablebindingbehavior

AbstractAbridgedbis(b-cyclodextrin)(1)withanazobenzenedicarboxylatelinkerwassynthesized,anditsbindingbehaviorwithafluorescentdye,acridinered(AR),wasinvestigatedbymeansoffluorescencespectroscopy.Duetothephoto-inducedconversionoftheazobenzenedicarboxylatelinkerfromthetrans-conformertothecis-conformer,1exhibitsadifferentbindingbehaviorbeforeandafterUVlightirradiation,givingastrongerbindingabilitytowardsARinthecisform.Thisswitchablebindingbehaviorof1mayopenanewchanneltothedesignofazobenzene-linkeddimericreceptorsasphoto-inducedmoleculardevices.

Introduction

Azobenzenederivativesareexpectedtoprovideusefulapplicationsforopticalswitching[1]andimagestorage[2]devices,becausetheirphotoisomerizationcaninducechangesofvariouschemicalandphysicalpropertiessuchastheabsorptionspectrum,dielectricconstant,andrefractiveindex.Amongthem,cyclodextrin(CD)/azo-benzenederivativesystemsattractextensiveinterestbecauseCDscanforminclusioncomplexeswithazo-benzenederivativesviahost–guestrecognition,andthephotoisomerizationofazobenzenegroupscancontroltheinclusionandexclusionofguestmolecules[3].Thesemachinelikeswitchingmotionshavebeenwidelyappliedtomolecularshuttles,motors,andinformationstorageinvariousmatrices[4–6].Asearlyas1979,Uenoetal.preparedtheazobenzene-cappedb-CDtoregulatethebindingabilityofb-CDbylight[7].At1998,theyfur-thersynthesizedtheazobenzene-bridgedbis(b-CD)andinvestigateditsphotoisomerizationinaqueoussolution[8].Recently,Matsuietal.reportedthattheazoben-zene-coatednanotubescouldbeimmobilizedontoa-CDSAMsonapatternedAusubstrateviahost–guestrec-ognitionanddetachedviaUVirradiationduetothephotoisomerizationofazobenzenegroups[9].Tianetal.reportedalight-drivenrotaxanemolecularshuttlecon-taininganazobenzeneorastilbeneunit,andthecis–transphotoisomerizationofthephotoswitchableunitresultedinthemotionoftheCDmacrocycleonthetrack[10,11].Morerecently,wereportedtheinclusioncomplexationbehaviorofazobenzene-modifiedCDswithaliphaticalcohols[12]aswellastheself-assemblyofCD/azobenzenecomplexes[13].Comparedwithmono-modifiedCDs,bridgedbis(CD)sarewelldocu-mentedtogreatlyenhancetheoriginalbindingabilityofnativeCDsthroughthecooperativebindingofdualhydrophobiccavitieslocatedinclosevicinitywithaguestmolecule.Therefore,weherereporttheprepara-tionofanewbis(b-CD)withanazobenzenedicarb-oxylatelinker(Chart1)andtheinvestigationofthephotoisomerizationoftheazobenzenelinkeranditsef-fectontheconformationandbindingbehaviorofazo-benzene-bridgedbis(b-CD).Thesestudieswillbeusefulforthedesignofphoto-drivenmoleculardevicesandmachines.

Experimental

Material

b-CDofreagentgrade(ShanghaiReagentWorks)wasrecrystallizedtwicefromwateranddriedinvacuoat95°Cfor24hpriortouse.N,N-Dimethylformamide(DMF)wasdriedovercalciumhydridefor2daysandthendistilledunderareducedpressurepriortouse.Dicyclohexylcarbodiimide(DCC)wascommerciallyavailable(ShanghaiReagentFactory)andusedwithoutfurtherpurification.Disodiumhydrogenphosphateandsodiumdihydrogenphosphateweredissolvedindis-tilled,deionizedwatertomakea0.1MphosphatebuffersolutionofpH7.20forspectralmeasurements.*Authorforcorrespondence.E-mail:yuliu@nankai.edu.cnJournalofInclusionPhenomenaandMacrocyclicChemistry(2006)56:197–201ÓSpringer2006DOI10.1007/s10847-006-9083-4Synthesisofbis(b-cyclodextrin-6-yl)-3,3¢-dicarboxyl-azobenzene(1)

ToasolutionofDMF(40ml)containing2.6gb-CDand0.4gofDCCwasadded0.278g3,3¢-azodibenzoicacid(3)inthepresenceofasmallamountof4AmolecularsievesScheme1.Thereactionmixturewasstirredfor2daysinanicebathandanother2daysatroomtemperature,andthenallowedtostandforseveralhoursuntiltheprecipitatenotincreasinganymore.Theprecipitatewasremovedbyfiltrationandthefiltratewaspouredinto300mlofacetone.TheprecipitatewascollectedandsubsequentlypurifiedonaSephadexG-25columnwithwateraseluent.Aftertheresiduewasdriedinvacuo,apuresamplewasobtainedin25%yield.UV/Viskmax(H2O)/nm(log󰀂)323nm(4.4);1HNMR(D2O,TMS)d3.27–3.82(m,84H),4.91(m,14H),7.22(m,2H),7.67(m,2H),8.06(m,2H),8.46(m,2H);FT-IR(KBr)m/cm)13852,3746,3335,2927,2152,1719,1652,1604,1558,1455,1435,1364,1292,1206,1154,1079,1031,943,859,758,704,582,534;Anal.CalcdforC98H146O72N2Æ6H2O:C,45.06;H,6.10;N,1.07.Found:C,45.46;H,6.20;N,1.00.