Molecular orbital calculations on polypeptides and proteins. Part IV. Studies by EHT and CNDO on the influence of hydrogen bond and chain length on certain structures

Abstract

The effect of intra- and inter-chain hydrogen bonding and chain length on some selected polypeptide structures has been examined by extended Hückel (EHT) and Complete Neglect of Differential Overlap (CNDO) methods. The EHT method does not predict the expected hydrogen-bonding behaviour. It is shown that the dipeptides serve as fairly good models in conformational studies. For glycine-rich polypeptides fully extended β-structures and collagen are predicted to be most stable forms. On the other hand, polypeptides rich in bulkier side chains may exist only in the right-handed α-helix and collagen forms. A seven-membered folded form is predicted to be the most stable monomeric structure by CNDO for dipeptides.