Water-Soluble Copolypeptides with Oligo-Ethylene-Glycol and Benzyl Pendants: Synthesis, Characterization, and Thermoresponsive Properties.

A series of random copolypeptides, i.e. poly(-propyl-l-glutamate)-graft-(oligo-ethylene-glycol)-random-poly(γ-benzyl-l-glutamate)s (PPLG-g-OEG3-ran-PBLG) with similar main chain lengths and various compositions of OEG and benzyl pendants were synthesized in three steps, including ring-opening polymerization of γ-chloropropyl-l-glutamic acid-based N-carboxyanhydride (CPLG-NCA) and γ-benzyl-l-glutamic acid-based N-carboxyanhydride (BLG-NCA), nucleophilic substitution in the presence of NaN₃, and copper-mediated alkyne-azide 1,3-dipolar cycloaddition. ¹H NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography results confirmed the molecular structures of the resulting copolypeptides and characterized their molar masses, molar mass distributions, and the OEG/benzyl compositions. Fourier transform infrared spectroscopy and circular dichroism analysis revealed that PPLG-g-OEG₃-ran-PBLG samples adopted a-helical conformations both in aqueous solution and solid state. Variable-temperature UV-visible spectroscopy revealed that PPLG-g-OEG3-ran-PBLG samples with high OEG molar content (x ≥ 0.57) possessed lower critical solution temperature-type phase transitions in water. The cloud point temperature, in the range of 22-53°C, can be readily obtained by controlling the OEG/benzyl composition. [ABSTRACT FROM AUTHOR]