Some remarks on the energy band structure of protein

Abstract

The energy bands of protein were calculated by using the chemical model ofEvans andGergely devised to demonstrate the way in which the infinite MO-s are originated. The calculation based on the simple LCAO MO theory was performed by the method developed byKouteczkŷ andZahradnik [7]. In the first approximation the 2p z orbitals of the C, O and N atoms of the peptide (H−N−C=O) group were used, while in a second four-centre approximation also the empty 2p z orbital of the H atom was taken into consideration. A variation of the values of the integralsα H,β N,H andβ O,H has shown the results to change only to a slight extent with the values of these parameters. The first three-centre approximation resulted in 5,11 ev for the width of the forbidden band between the highest filled and the lowest unfilled band, while in the four-centre approximation this value was only 3.95 ev. These findings and the fact that the band widths obtained were larger than those given byEvans andGergely suggest the electronic conductivity of protein, found experimentally, to arise from the mobility of the π electrons on the infinite MO-s of the model considered. The results of the more realistic four-centre approximation also show in comparison with a free monopeptide group a significant increase in electron affinity and a considerable stabilization energy (≈32 kcal/mole peptide groups) in the protein molecule.