The effect of water and ions on the energy band structure of periodic alpha-helical polypeptides.

The solvent structure around several periodic polypeptides in the alpha-helical conformation has been determined by Monte-Carlo simulations. The calculations of the water clusters have been performed in the presence and absence of Na+ ions. The resulting hydration shell has been used to calculate the band structure of the polymers in the effective field of the water molecules and ions. The results show that the maximum change of the band widths and the band gaps is about 0.7 eV in the presence of the hydration shell. The band positions are shifted by up to 4.1 eV in the presence of water molecules and ions. The results have been compared with the band structure results of periodic polypeptides in the beta-pleated sheet conformation.