Abstract
Cyclodextrins (CDs) are cyclic oligosaccharides used in many fields. Grafting polymers onto CDs enables new structures and applications to be obtained. Polylactide (PLA) is a biobased, biocompatible aliphatic polyester that can be grafted onto CDs by -OH-initiated ring-opening polymerization. Using 4-dimethylaminopyridine (DMAP) as an organocatalyst, a quantitative functionalization is reached on native α-, β-, γ- and 2,3-dimethyl- β-cyclodextrins. Narrow molecular weight distributions are obtained with the native CDs (dispersity < 1.1). The DMAP/β-CD combination is used as a case study, and the formation of an inclusion complex (1/1) is shown for the first time in the literature, which is fully characterized by NMR. The inclusion of DMAP into the cavity occurs via the secondary rim of the β-CD and the association constant (Ka) is estimated to be 88.2 M−1. Its use as an initiator for ring-opening polymerization leads to a partial functionalization efficiency, and thus a more hydrophilic β-CD-PLA conjugate than that obtained starting from native β-CD. Polymerization results including also the use of the adamantane/β-CD inclusion complex as an initiator suggest that inclusion of the DMAP catalyst into the CD may not occur during polymerization reactions. Rac-lactide does not form an inclusion complex with β-CD.
Highlights
Cyclodextrins (CDs) are cyclic oligosaccharides produced from starch by enzymatic degradation
Complex, in contrast to the native carbohydrate. This may be ascribed to the interaction of hydroxyl groups with the included DMAP or a steric hindrance induced by the proximity of the DMAP
We have shown using 2D Rotating-frame Overhauser Effect Spectroscopy (ROESY) Nuclear Magnetic Resonance (NMR) that the inclusion of DMAP into the cavity takes place through the secondary side of the β-CD
Summary
Cyclodextrins (CDs) are cyclic oligosaccharides produced from starch by enzymatic degradation. The hydrophobic, size-selective toroidal cavity with C-6 primary hydroxyl groups on the narrow rim and C-2 and C-3 secondary hydroxyl groups on the wider rim is well known to incorporate a large range of hydrophobic molecules. Due to this capacity to form inclusion complexes and the properties of amphiphilic structures, CDs are very interesting for many industrial applications such as Molecules 2022, 27, 1083 of amphiphilic structures, CDs are very interesting for many industrial applications2soufc1h3 as in chemistry, pharmaceutical science and chromatography, and in food, cosmetic, textile and environmental fields [1,2,3,4,5,6,7]. Dopifefnerinengtpsoylnytmheetriiczsattriaotneg(RieOs aPr)eoafvcayiclalibcleesttoerascc[e1s6s,1t7h]e.sTehmisaccaronmboeledcounlearwoibthjecotrs,wsuitchhoaust dthireeuctsecooufpalcinagta,loyrstt.hReeugsaerdofinthgethheyldartotexry,lHgaroraudpas eotfacly. crleopdoerxtetrdinthaes cinyictlioadtoerxstrfoinr itnhietiraitnegdpotagotpagoohhvvfrpfforoeeooeelttletyhyuhhurrubnmaaemepepLusiggnesgsalbegeeek.g.clruorluTTuitiddpflpzizchkhcdeeaoaaoooeeggetlptplcpiyiyrrrroooa(yeeymeemLntlnreessryaaAessuuaeolomnrynrll)foofitotisozeiiflczflstnnaarasoa.pepicegctgutzRiototuioaoulooooleldnnytnynnllngiiiimeomegigtaaot(.snsrolo.fReesLdieieLεroroOnnaissii-anfzztttcbPbbteeegεaaaeeuu)rrr-ttpr,tciilloaao,hooirkkatfrroipennptmmiiwclennralwyuunaossacttcptpealtshhwwtlaodseieestctcneerohost,baarreeohoeHb1eyb1sniow0sst0nffaewβeeoeoniwrrwn-ntuiuancisntcceandneyhiee[trtdtrdac1aheeieoola6tdaeottfof,toootttd1eahbbaba7tdbbenytenhtl]axeeya.y.ebpwitirccnTryonropeooieeethnetprwtvvhsdhdieosaβaseie,es,unrllrrsw-tcetewrCuceancβedniodnroiDtt-ticte-hlmCl-hayctybc[hcaDnua2eeullaettiti0painpnadnh[n]cl2l.kktyoyycyit0oneelnroscs]feddtclt1.eooa1r[/[rtt1weds/1moo33ea8e8is,ttxai,tti1hh1ennhhtm99reeiiet]tiot]hi.niiCC.adraaNecN22etitwtniiauinnucc(vicimDaatggmttiihrritaMbvbbyOOboteiooeeuFtoHHrdnnyrtf-)withoLuatctaidceo(-LcaAta)lcyosut,ldleaadlsiongbetoopaennuedmbbyerβ-a-cvyecralogdeedxterginreienodfimpoeltyhmylefroirzmataiomnidaero(uDnMdF2) wanidthaoudteagrceoe-coaftsaulybsstt,itlueatidoinngoft1o.5a, nthuemobliegro-alavcetriadgeeadrmegsrbeeeinofgpgoralyftmederoiznatthioenCa6rocuarnbdon aonf dthae dceygclroedeeoxftrsiunb[s2ti1t]u.tIinonthoef 1sa.5m, tehferaomligeo, lPaecptitdueeatrmal.s rbeepinorgtegdratfhteedgorenetnhesyCn6thceasribsoonf oofligthoelaccyticdloeddeexrtirvianti[v2e1s].bIansethdeosnamnaetifvreamα-e,, βP-eapntud eγt-aCl.Dr,eipnowrtehdichthCe Dgrsepenlaysytnhtehreoslies ooff obloitgholiancittiiadteodr earnivdactaivtaelsybstasinedbounlknfaotriv7e2αh-,[β22- ]a.nMdaγs-s CspDe,citnrowmheitcrhy,CNDMs pRlasypetchterorsocloepoyf banotdhrienviteirasteodr-apnhdasceatlaiqlyusitdinchbruolmk afotorg7r2aphh[2y2w].eMreausssesdpeinctroormdeertrtyo, dNeMteRrmsipneecttrhoescsotrpuyctaunrde roefvtehresefdin-palhapsreodliuqcutisd, cchormopmoasteodgroafpuhnyrweaecrteedusLeAd imn oorndoemr etor, dfreeteermCDinseatnhde sptroulyctlaucrteidoef t(hPeLAfin) ahlopmroodpuoclytsm, ceorminpaodsedditioofnutnoreCaDct-ePdLLAAcmonojungoamtee.r,MfroereeCovDesr,atnhde preoalycltaiocntidwea(sPcLaAr-) hrioemd oouptolsyemlecetrivinelaydodnittihoenptorimCDar-yPLriAmcoofnCjuDgsa.tCe.DMs oarreeolvinekr,etdhewriethacmtioornewthaasncaornreieodlioguotslaecletactteivcehlyaionnptehreCpDrimmaorlyecruimle.oTfhCeDasu.thCoDrss ashreowlinekdetdhawtitthhemroearecttihviatny oonf ethoeligCoDlascwtaates cdhifafienrepnetrfCorDthmeoRleOcuPloe.f TLhAe, awuitthhotrhseshhiogwheedsttrheaatctthiveitryeafcotrivthiteyβo-fCtDheaCnDdsawloaws edrifrfeearecntitvfiotyr tfhoer tRhOePγ-oCf DLA. , with the highest reactivity for the β-CD and a lower reactivity for the γ-CD
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