Synthesis And Thermoresponsive Polypeptide With Y-Shaped And Charged Side-Chains

Thermoresponsive polypeptides are of excellent biocompatibility,biodegradability,and solution phase trasition with temperature variation,which is similar to the response of the human body when the disease occurs.Thus,they are expected to be useful in biomedical field.The grafting of oligoethylene glycol?OEG?to the polymer side chain enhances the water solubility and biocompatibility of the polymer.Changing polymer structure can effectively control the nature of thermoresponsive polypeptides.However,thermoresponsive polymers with Y-shaped side chain are rarely reported.Water-soluble thermoresponsive poly??-4-methylbenzyl-L-glutamate?bearing Y-shaped?i.e.,oligo-ethylene-glycol and alkyl groups,such as 1-butyl,1-hexyl,or1-dodecyl?and triazolium tetrafluoroborate sidechains?PMBLG-OEG₇/C_m-BF4,m =4,6,and 12?have been prepared by nucleophilic substitution of poly??-4-methylbenzyl-L-glutamate?-oligo-ethylene-glycol conjugates?PMBLG-OEG7?and various 1-alkyl bromide and ion-exchange reactions of triazolium bromide and NaBF4.A series of ionic polypeptides bearing p-tolyl pendants and3-methyl-1,2,3-triazolium linkages [PPLG-MBP/CH₃-X?X = Cl,I,BF4?] is synthesized by N-alkylation and subsequent ion-exchange reaction.The polymers have been characterized using a combination of spectroscopic and chromatographic techniques,such as 1H NMR,FTIR,and GPC.The effects of alkyl side chain,counter ion type and salt concentration on the thermoresponsive properties of PMBLG-OEG₇/C_m-X in lower critical solution temperature?LCST?in aqueous solution were investigated by variable-temperature UV-vis spectroscopy.The solution phase transition temperature of LCST type decreases with increasing polymer concentration and salt concentration,and increasing the alkyl side chain length will further reduce the solution phase separation temperature.PPLG-MBP/CH₃-I has a thermoresponsive nature of a upper critical solution temperature?UCST?type phase behaviors in ethanol/water mixed solvent.