Molecular orbital calculations on the conformation of polypeptides and proteins: I. Preliminary investigations and simple dipeptides

Abstract

The quantum-mechanical method PCILO based on a perturbative configuration interaction using localized orbitals, particularly efficient for the calculation of ground state energies of molecules, is employed for the evaluation of potential energy surfaces and preferred conformations of two dipeptides (glycyl and alanyl residues). It represents an independent procedure for the determintion of these properties, omitting the usual partitioning of the potential energy into empirically determined components. In distinction to such empirical calculations, the computations predict as the most stable conformation of the two dipeptides a folded seven-membered hydrogen bonded ring. The prediction is in agreement with very recent experimental findings. The method is rapid enough to be applicable to large polymeric systems.