13C NMR chemical shift and conformation of β-benzyl l-aspartate residues in copolymers of β-benzyl l-aspartate and l-alanine in solution

Abstract

High resolution 13C NMR spectra of copolymers of β-benzyl l-aspartate and l-alanine residues have been recorded, in order to obtain detailed information about the conformational behaviour of the main-chain and side-chains of the β-benzyl l-aspartate residues in solution. The observed results in solution show that the main-chain takes both the right- and left-handed α-helical forms, which is identical with the α-helix conformation in the solid state. The inner side-chains in the right-handed α-helical form have different characteristic conformations in solution and in the solid state. Such chemical shift behaviour of the side-chains suggests that inter-side-chain interactions make the inner side-chains take a conformation with higher energy than the isolated side-chain. Such interactions may account for the fact that in solution the main-chain takes the left-handed α-helix rather than the right-handed one.