HYDROGEN-BONDING CAPABILITIES-BASED ON POLARIZABILITY STUDIES OF MODEL PEPTIDE SYSTEMS

The peptide bond is a fundamental unit in understanding the interactio ns between proteins and the surrounding medium. In this paper, models for the main chain and polar and nopolar side chains of amino acid res idues were carefully chosen and complexes with each other and water cl usters were calculated using a Monte Carlo/Simulated Annealing techniq ue. The dipole polarizabilities, a, of these clusters were evaluated w ithin the Coupled Perturbed Hartree-Fock (CPI-IF) method using special basis sets designed for the evaluation of electric response propertie s. The change in the interaction modified average polarizability per e lectron for each of the interacting subsystems, Delta Delta alpha, is defined in the text, evaluated for each of the interacting systems, an d used as a measure of the strength of the hydrogen bond and the ident ification of the hydrogen bond donor in each complex. The relative imp ortance of main-chain, side-chain, and solvent effects in the models u sed to describe protein folding is discussed.