Synthesis?Side-chain Regulation And Responsiveness Of Cationic Polypeptides With UCST

Stimuli-responsive polymers have recently received much attention for their interesting conformational or chemical changes in response to external triggers,such as temperature,pH,light,and other stimuli.They have shown great potential in various applications,including sensors,drug delivery,and tissue engineering.Among all external triggers,temperature and pH are the most studied because they are the most common environment stimulators.Herein,we design and synthesize a series of stimuli-responsive cationic polypeptides.The molecular structures were characterized by ¹H NMR,FTIR,GPC and CD and the stimuli-responsiveness was investigated by UV-vis and DLS.Our results not only enrich the types of stimuli-responsive polypeptides,but also provide guidance for subsequent studies.The specific content of this article is as follows:In the second chapter,we synthesized a kind of sulfonium-based UCST-type thermoresponsive or thermo and pH dual responsive polymers by single-side esterification,cyclization,ring-opening polymerization,click chemistry,and ion exchange reactions.With the pH increases,the polymer changes from clear to turbid,and sharp solution phase separation of PPLG-MSEA-BF₄ occurred in a very small pH range??pH = 0.05?when the pH increased from 7.37 to 7.42 as suggested by dynamic light scattering?DLS?.The UCST-type phase transition temperature?Tpt?of PPLG-MSEA-BF₄ increased by 20? as the pH increased from 7.42 to 7.50 as revealed by variable-temperature UV-vis spectroscopy.We speculate that the mechanism of this transition is electrostatic interaction.Increasing polymer or NaBF₄ concentrations or decreasing NaCl concentration can further increase the Tpt.In the third chapter,we report a kind of UCST-type thermoresponsive polypeptides with Y-shaped and N-butylimidazolium pendants through bromination,azidation,click chemistry and ion exchange reactions.The molecular structures were confirmed by a combination of spectroscopic and chromatographic techniques,such as ¹H NMR,13C NMR,FTIR,and GPC.The solid-state and solution conformations of the resulting polypeptides were analyzed by FTIR and CD,respectively.PPLG-?ImI?₂ showed a reversible UCST-type phase behavior in ethanol,whereas PPLG-?ImBF₄?₂ showed reversible UCST-type phase behaviors in both methanol and water.In order to compare the effect of the Y-shaped pendant on the UCST-type phase behavior and transition temperature?Tpt?,PPLG-ImX?X = Br,I or BF₄?with a single IL group per repeating unit was prepared by coppermediated 1,3-dipolar cycloaddition and ion-exchange reaction from PCPLG.PPLG-?ImX?₂?X = I or BF₄?with a Y-shaped pendant and PPLG-ImX?X = I or BF₄?with a traditional pendant showed similar polymer concentration and salt concentration dependence of the Tpt,namely the Tpt increased with increasing of the polymer concentration or NaBF₄ concentration,whereas it decreased with increasing of NaI or NaCl concentrations.Finally,we conclude that the difference in the thermoresponsive of polymers in alcohols is mainly attributed to the effect of hydrogen bonding,whereas the difference in thermoresponsive in deionized water is mainly due to electrostatic interactions.We then conducted a preliminary exploration of the application of cationic polypeptides.In the fourth chapter,we report a kind of PVA hydrogel blended with cationic polypeptide.The effect of the nature of cation groups?imidazolium and pyridinium?,degree of polymerization?DP = 24,67?,main-chain conformation?a-helix and random coil?,and polypeptide weight content?x = 0.01-0.12?on the mechanical properties of PVA hydrogels has been studied.We observed the surface morphology of hydrogels and studied the mechanism of hydrogel formation.In this chapter,we provide a method for the modification of traditional PVA hydrogels,which can further improve the mechanical properties,thereby better interpreting the structure-property relationship of cationic polypeptides.