Orientation of Polypeptide Side Chains in Solution

Abstract

THE conformational behaviour of polymers of L-aspartate esters has been of interest since it was first shown that poly(β-benzyl-L-aspartate) in chloroform takes up the anomalous left-handed helical form^1,2. Since then it has been shown that para-substitution of the benzene rings with nitro³ or methyl⁴ groups induces a transition to the right-handed form. In some of these derivations the helix sense can be changed by altering the solvent⁵, and poly (β-benzyl-L-aspartate) itself can be induced to take up the right-handed form when in contact with water⁶. When the aliphatic esters of poly(L-aspartic acid) are dissolved in chloroform at room temperature, they take up a helix sense dependent on the nature of the ester group: thus methyl, like benzyl, takes up the left-handed form^7,8, while ethyl, n-propyl and isopropyl take up the right-handed form⁸.