DETERMINATION OF NONBONDED POTENTIAL PARAMETERS FOR PEPTIDES

The repulsive Lennard-Jones nonbonded parameters for the conformationa l study of neutral peptide molecules are developed. This repulsive non bonded potential energy is consistent with the electrostatic interacti on energy calculated with modified-PEOE charges, the attractive Lennar d-Jones nonbonded potential energy, and the hydrogen-bond potential en ergy, which were developed previously. Both equilibrium conditions of molecules in molecular crystals and lattice energies of molecular crys tals were used as constraints during the determination of the repulsiv e nonbonded potential parameters. The reliability of the optimized par ameters was tested by crystal packing studies. The crystals used as co nstraints are paraffins, conjugated ring compounds, sulfur containing hydrocarbons, carboxylic acids, and amides. The calculated properties of the molecular crystals, lattice energies and lattice cell parameter s, agree well with experimental values. A complete set of intermolecul ar potential functions for neutral peptides was prepared in a self-con sistent manner.