Comblike poly(alpha-alkyl gamma-glutamate)s: computer simulation studies of an intermediate thermal phase.

Abstract

Monte Carlo (MC) simulations have been used to study the structure of an intermediate thermal phase of poly(alpha-octadecyl gamma,D-glutamate). This is a comblike poly(gamma-peptide) able to adopt a biphasic structure that has been described as a layered arrangement of backbone helical rods immersed in a paraffinic pool of polymethylene side chains. Simulations were performed at two different temperatures (348 and 363 K), both of them above the melting point of the paraffinic phase, using the configurational bias MC algorithm. Results indicate that layers are constituted by a side-by-side packing of 17/5 helices. The organization of the interlayer paraffinic region is described in atomistic terms by examining the torsional angles and the end-to-end distances for the octadecyl side chains. Comparison with previously reported comblike poly(beta-peptide)s revealed significant differences in the organization of the alkyl side chains.