Synthesis, Characterization, and Thermoresponsive Properties of Helical Polypeptides Derivatized from Poly(γ-4-(3-chloropropoxycarbonyl)benzyl-L-glutamate)

A series of side-chain-functionalized alpha-helical polypeptides, i.e., poly(gamma-4-(3-chloropropoxycarbonyl)benzyl-L-glutamate) (6) have been prepared from n-butylamine initiated ring-opening polymerization (ROP) of gamma-4-(3-chloropropoxycarbonyl)benzyl-L-glutamic acid-based N-carboxyanhydride. Polypeptides bearing oligo-ethylene-glycol (OEG) groups or 1-butylimidazolium salts were prepared from 6 via coppermediated [2+3] alkyne-azide 1,3-dipolar cycloaddition or nuleophilic substitution, respectively. CD and FTIR analysis revealed that the polymers adopt alpha-helical conformations both in solution and the solid state. Polymers bearing OEG (m = 3) side-chains showed reversible LCST-type phase transition behaviors in water while polymers bearing 1-butylimidazolium and I- counter-anions exhibited reversible UCST-type transitions in water. Variable-temperature UV-vis analysis revealed that the phase transition temperatures (T(pt)s) were dependent on the main-chain length and polymeric concentration. (C) 2015 Wiley Periodicals, Inc.