Energy Band Structures in Polypeptides

Abstract

Using the MO's for π-electrons in an isolated peptide group which are determined such that the ASMO-SCF-CI calculation reproduces the observed wavelength of the optical absorption maximum, the energy bands for both the H -bonded and the main polypeptide-chain in the case of the β-structures and of the α-helix are calculated in terms of the LCMO and the nearest-neighbor approximation. It is shown that the shifts of bands for main peptide chains are of the considerable order of -0.2∼-0.8 eV, and that in each case the band widths for main peptide chain are generally far larger than those for H -bonded polypeptide, especially those of the highest valence and the conduction band for main chain in α-helix have remarkably large values of the order of 1∼2 eV. The π-electronic structure of H -bonded di- and tri-peptide are also studied by means of the ASMO-SCF method, in comparison with those obtained by Suard et al. .