A FRACTIONAL CHARGE MODEL FOR EMPIRICAL CALCULATIONS OF PEPTIDE‐WATER INTERACTIONS

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Abstract
The properties of an empirical model of interaction between a water molecule and polar groups of peptides or small peptides are explored. The H2O molecule is represented by a 4-point charges distribution. In electron donor groups, a point charge is located on the axis of the lone pairs orbitals in order to introduce some directionality in H- bonds. The effective potential is approximated by the sum of the coulombic interactions between point charges distribution and of a 6-12 atom-atom potential. The coefficients of this last potential are 1st adjusted by simulating the geometry of the water dimer. Equilibrium configurations of associated polar molecules and H2O predicted by the model are in good agreement with those resulting from more sophisticated ab initio self consistent field calculations. Interactions between H2O and the side-chains of the cyclic dipeptide C(L-Thr-L-His) are calculated. Internal bridging by water is an essential effect of the solvent. The experimental position of the H2O molecule is reproduced; the stability depends also on intermolecular interactions.