Study On Enzyme-responsive Linear-dendritic Block Copolymers And Super-Amphiphilic Molecules Using A Phenylalanyl-Glutamic Acid Dipeptides As Dendrons

Polymer assemblies have attracted more and more attention for their applications in biomaterials,biomedicine and biosensors.Polymer micelles and vesicles have been proved to be promising nanocarriers due to their advantages of enhancing stability,improving biocompatibility and prolonging the duration of blood circulation.In addition,stimulus responsive groups have been introduced into polymers,so that they can respond to specific triggers in the physiological environment,making them have a good application prospect in drug and gene delivery.So far,there have been many research reports on stimuli-responsive polymers such as pH,light,temperature,and redox responsive polymers,but there is little research on enzyme-responsive amphiphilic linear-dendritic block copolymers and dual-enzyme responsive super-amphiphilic molecules.In this thesis,three generations of enzyme-responsive linear-dendritic block copolymers with poly（N-vinylpyrrolidone）（PNVP）as a hydrophilic linear chain and dendritic phenylalanyl glutamic acid dipeptides with terminated ester as dendrons were synthesized by using"chain-first"and reversible addition-fragmentation chain transfer（RAFT）/xanthates（MADIX）polymerization of N-vinylpyrrolidone.The structures of these copolymers were characterized by ¹H NMR,GPC and MALDI-TOF-MS spectra.The self-assembly behavior and enzyme responsiveness of these block copolymers in aqueous solution were studied by¹H NMR,TEM and fluorescence spectra.The results showed that both the second and third generation linear-dendritic block copolymers can self-assemble into spherical micelles in aqueous solution.The micelles can disassemble and release the encapsulated hydrophobic small molecule pyrene under the action ofα-chymotrypsin.The higher the enzyme concentration,the faster the micelles disassemble.Moreover,as increase the generation of the block copolymers,the stability of micelles increased,the particle size of micelles increased,and the rate of enzymatic hydrolysis slowed.The block copolymers has a specific response toα-chymotrypsin.The ester groups of the second and third generation linear-dendritic block copolymers PNVP-b-G_n（n=2,3）dendritic periphery was removed under alkaline conditions to obtain block copolymers withd endritic periphery of carboxyl anion（PG_n^-（n=2,3））.The block copolymers and lauroylcholine chloride（LCh）with positive charge are combined by electrostatic interaction to obtain polymer super-amphiphilic molecules（LCh⁺/PG₃^-）.The self-assembly and enzyme response properties of the super-amphiphilic molecules were studied by¹H NMR,TEM and fluorescence spectra.The results showed that the super amphiphilic molecules can self-assemble into vesicles in aqueous solution.The vesicles disassemble and release the loaded hydrophobic dye Nile red under the action of ache orα-chymotrypsin.When the two enzymes（AChE andα-chymotrypsin）were present at the same time,the enzymolysisrate was greatly accelerated,and the change of vesicle morphology was more obvious,indicating that the super-amphiphilic molecules have dual enzyme responsiveness.By adding trypsin and alkaline phosphatase to LCh⁺/PG₃^-/NR（n=2,3）,the release of Nile red did not occur under the same conditions,indicating that acetylcholinesterase has enzymolysis specificity for LCh⁺/PG_n^-（n=2,3）.In addition,in the presence of donepezil,an acetylcholinesterase inhibitor,the fluorescence intensity of LCh⁺/PG₃^-/NR and acetylcholinesterase system was weakened,and the hydrolysis of lauroylcholine chloride catalyzed by acetylcholinesterase was delayed,which further indicated that the polymer super-amphiphilic molecular system had a specific response to acetylcholinesterase.