Effect of conformational degrees of freedom on the charge transfer in model tripeptide.

An extensive conformational dependence of the intramolecular charge transfer (both hole and electron) between intermediate residues of the model tripeptide in gas phase has been studied. The charge transfer integral, spatial overlap integral and site-energy for both hole and electron transfer between the intermediate residues in the tripeptides were calculated using the fragment orbital method. The site-energies and the charge transfer integrals have been calculated for different conformation of the glycine tripeptide by varying the dihedral angles (phi and psi) along the alpha-carbon atom of amino acid subgroups. Electronic structure calculations show that the charge transfer integral between intermediate residues is strongly depending on the nature of the conformation of the peptide. The calculations indicate that the charge transfer is maximum at the particular conformation of the intermediate amino acid residues.