Molecular Recognition Of(Functionalized) Cucurbiturils And Their Applications In Polymer Self-assembly

Supramolecular chemistry is the chemistry of the intermolecular bond,covering the structures and functions of the entities formed by association of two or more chemical species.Supramolecular interactions refer to the intermolecular noncovalent interactions such as hydrogen bonding,hydrophobic interaction,?-? interaction,electrostatic interaction,metal-ligand coordination,host-guest interaction,and so forth.Host-guest interaction is based on the molecular recognition of macrocylic hosts,and it is where supramolecular chemistry originates from.Macrocylic hosts include crown ethers,cyclodextrins,calixarenes,cucurbiturils,and pillararenes.Cucurbiturils(CBs)are cyclic oligomers composed of methylene bridged glycoluril units fromed by an acid-catalyzed condensation reaction of glycoluril and formaldehyde.Cucurbit[n]urils(CB[n],n = 5-8,10,13-15)are named based on the number of glycoluril units.CBs show good thermostability and biocompatibility.The binding of guest species depend on the cavity volumes of CBs,and the binding affinity is up to 7.2 × 1017 M-1.Functionalized CBs overcome their lack of solubility in common organic solvents and expand their application fields.In this thesis,we studied the molecular recognition of functionalized CB[7]and CB[8]and conducted supramolecular assembly of polymers on this basis.We realized the transition from microcosmic molecular recognition to macroscopical materials.1.Cucurbit[7]uril terminal poly(N-isopropylacrylamide)(PNIPAM-CB[7])was synthesized via a click reaction of monopropargylated CB[7]and azido terminal PNIPAM.We found that the introduction of CB[7]and charged guest molecules raised the lower critical solution temperature(LCST)of PNIPAM significantly.And PNIPAM-CB[7]maintained high binding affinity of CB[7].2.Cucurbit[7]uril terminal methoxy polyethylene glycol(mPEG-CB[7])was synthesized via a click reaction of monopropargylated CB[7]and azido terminal mPEG.mPEG-CB[7]bound to the viologen moieties on the side-chain of styrene copolymer PSt-MV via host-guest interaction and formed supramolecular graft copolymers in DMF.The copolymers self-assembled into micelles in water,and the sizes and morphologies of micelles could be easily modulated by changing the ratio of hydrophilic polymer(mPEG-CB[7])and hydrophobic polymer(PSt-MV).With the increasing mPEG-CB[7],the sizes of micelles gradually decreased,and the micelles turned into spherical micelles with smooth surface.The polymer micelles showed good stability against dilution and biocompatibility in cell cytotoxicity studies.The anticancer drug,doxorubicin,was successfully loaded into the micelles with a drug loading capacity of 12.0%and encapsulation efficiency of 47.7%.3.A linear guest(LHV)and a tetrahedron like guest(THV)with one and four ditopic arms consisting of viologen and hexylene moieties were synthesized.This work emphasized the importance of molecular structure and steric hindrance in self sorting systems.LHV formed binary complex LHV@CB[8]with one CB[8]residing on its hexylene moiety.THV formed[5]pseudorotaxane THV@(CB[8])4 with two CB[8]residing on hexylene moieties and two CB[8]residing on viologen moieties.In this complex,the steric hindrance among the arms of the tetrahedron like guest molecule prevented CB[8]from interacting with all hexylene moieties and slowed the exchange kinetics.CB[8]moved to the viologen parts of LHV and THV and formed charge-transfer complexes with the naphthoxy moiety of stopper.Reductive LHV existed in the form of radical monomer.Homotemary complex was formed in the presence of 0.5 equivalent of CB[8],and CB[8]enhanced the dimerization of reductive LHV.Binary complex was formed in the presence of 1.0 equivalent of CB[8],and CB[8]suppressed the dimerization of reductive LHV.Different from LHV,when THV was reduced,intramolecular dimerization occurred because of its tetrahedron like molecular structure.CB[8]modulated the dynamic balance of monomer and dimer of the viologen radical units of reductive THV.Compared with reductive LHV,CB[8]had little effect on the dimerization of reductive THV.4.Naphthoxy terminal methoxy polyethylene glycol(mPEG-Np)and poly(N-isopropylacrylamide)(PNIPAM-Np)were synthesized.Supramolecular miktoarm star copolymers(SSPs)formed via cucurbit[8]uril enhanced charge-transfer interaction between the tetrahedron like guest THV and flexible ratios of mPEG-Np and PNIPAM-Np.Higher ratio of PNIPAM-Np in SSPs led to lower LCST.Aggregation of SSPs was thermal responsive,and the size of aggregates increased with increasing temperature.At the same temperature,higher ratio of PNIPAM-Np in SSPs led to larger size.The disassembly and reassembly process of supramolecular star copolymers was achieved through adding 1-adamantanamine hydrochloride and CB[8]alternately.5.Viologen terminal polyethylene glycol(MV-PEG-MV)was synthesized.It formed polypseudorotaxane MV-PEG-MV@(CB[8])2 with two CB[8]residing on viologen moieties.AB-type and ABA-type supramolecular block copolymers(SBPs)formedvia cucurbit[8]uril enhanced charge-transfer interaction between MV-PEG-MV and PNIPAM-Np with ratios equal to 1:1 and 1:2,respectively.ABA-type supramolecular triblock block copolymers had lower LCST becaues of its higher ratio of PNIPAM-Np.Aggregation of SBPs was thermal responsive,and the size of aggregates increased with increasing temperature.At the same temperature,the size of aggregates of ABA-type supramolecular triblock diblock copolymers was larger than AB-type supramolecular diblock copolymers.The disassembly and reassembly process of supramolecular block copolymers was achieved through adding 1-adamantanamine hydrochloride and CB[8]alternately.