Molecular orbital calculations on polypeptides and proteins. Part 5.—Stable conformations of oxygen-containing peptides

Abstract

EHT and CNDO molecular orbital methods have been used to determine the torsional angles which may be present in stable conformations of seryl and threonyl residues. The results have been compared with a previous calculation based on PCILO framework. There is a general agreement on the regions of stability as predicted by the three techniques. However, there are some differences in the relative stabilities of the various minima on the conformational map. The side chain hydroxyl group stabilizes some of the conformations by forming hydrogen bonds with the backbone carbonyl group. The seven membered hydrogen bonded (H′-7) structure is predicted to be one of the stable structures for dipeptides. However, for polypeptides where intra- and inter-chain hydrogen bonds are possible, the right handed α-helix, collagen and β-structures are favoured.