Study On The Effect Of Spacer And Pendent Group On The Thermoresponsiveness Of Cationic Polypeptides

The stimuli-responsive polymer is capable of responding to external stimuli and undergoing changes in internal structures and external states.Polypeptides have received more and more attention due to their good biocompatibility and degradability.Synthetic polypeptides with stimuli-responsiveness make them great application value in biomedical,tissue engineering,nanomaterials and so on.In this dissertation,the polymer PCPLG was firstly synthesized by concentrated sulfuric acid catalyzed esterification,cyclization in presence of triphosgene,and n-butylamine initiated NCA ring-opening polymerization.The azide group was introduced by azide reaction.Polypeptides with 3-methyl-1,2,3-triazolium salt as the spacer and mannose or p-tolyloxy as the side group were prepared by click chemistry,N-alkylation,ion-exchange reactions,and so on.The molecular structures of the obtained polymers were confirmed by 1H NMR and FTIR analysis,and their solubility and thermo-responsive properties in binary solvent mixture were tested.The results indicated that the introduction of 3-methyl-1,2,3-triazolium salt can induce the thermoresponsive of the polymer.When the spacers are the same,the thermoresponsive of the polymer are affected by the side group structure,the polymer concentration and the components of the solvent mixture.Ionic polypeptides can exhibit reversible UCST-type phase transition behavior in methanol and binary mixtures of ethanol/water by binding to appropriate counter anions.FTIR analysis showed that the polymer exhibiting UCST-type phase transition behavior interacts with solvent molecules through van der Waals forces,hydrogen bonding,or dipole interactions.Variable temperature UV-vis spectroscopy(UV-vis)reveals that the thermoresponsive of polymers with the same spacers are strongly related to the type of side groups.Glycopolypeptides bearing tetra-Oacetyl-D-(+)-mannopyranoside and 3-methyl-1,2,3-triazolium chloride linkages showed a reversible upper critical solution temperature(UCST)-type phase behavior in ethanol(EtOH).Glycopolypeptides bearing tetra-O-acetyl-D-(+)-mannopyranoside and 3-methyl-1,2,3-triazolium iodide or 3-methyl-1,2,3-triazolium tetrafluoroborate linkages showed a reversible UCST-type phase behavior in EtOH/H2O solvent mixtures.Glycopolypeptides bearing p-tolyl pendants and 3-methyl-1,2,3-triazolium iodide showed a reversible UCST-type phase behavior in MeOH and EtOH/H2O.The UCST-type phase transition temperatures(Tpt)depending on the main-chain length,polymer concentration,and the weight percentage of ethanol(fw).Poly(y-2-(2-chloroethoxy)ethyl-L-glutamate)(PCEELG)with DEG linkage and reactive chloro groups can be readily prepared from ring-opening polymerization of y-2-(2-chloroethoxy)ethyl-L-glutamic acid based N-carboxyanhydride.Homopolypeptides were conjugated with various IL pendants and counteranions by nucleophilic substitutions and subsequent ion-exchange reactions.In order to study the influence of the spacer on the temperature response property of the polymer,polymer PCPeLG with pentane spacer and similar degree of polymerization was also prepared.The results indicated that spacers have a greater influence on the polymer’s thermoresponsive.DEG spacers can effectively increase the solubility of the polymer.Regulating cationic side groups and counterions can achieve LCST<UCST(i.e.,soluble-insoluble-soluble)dual temperature-responsive polymer PEELG-TBP-I in pure water and NaI aqueous solutions,whose LCST type and UCST type phase transition temperature(Tpt)can be adjusted by polymer concentration,degree of polymerization,and NaI concentration.Homopolypeptide with DEG linkages and tributylphosphonium tetrafluoroborate showed a UCST both in DI-H2O and PBS buffer while homopolypeptide with DEG linkages and triphenylphosphonium iodide(or tetrafluoroborate)or with alkyl linkages and tributylphosphonium iodide(or tetrafluoroborate)showed a UCST in PBS buffer.The PBS buffer enhanced the solubility of the polymer and induced.the thermoresponsive properties of the polymer.The UCST-type phase transition temperature of the polypeptide can be adjusted by the concentration of the polymer,the degree of polymerization,the type of IL,the counterion,and the type of inorganic salt in the solvent.