AB-INITIO FORCE-FIELD FOR THE CARBOXYL GROUP OF GLUTATHIONE DERIVED FROM HYDROGEN-BONDED GLYCINE

To derive a suitable starting force field to refine empirical force co nstants for the hydrogen-bended glycyl COOH group of glutathione, we h ave obtained scaled ab initio force fields for a non-global-minimum co nformer of glycine with two H2O molecules associated with the COOH gro up. Scale factors were derived from a revised vibrational analysis of the isolated glycine global-minimum structure, with particular attenti on to reproducing infrared intensities as well as frequencies of four matrix-isolated isotopic species and making use of the dipole derivati ve distribution in assigning bands. The force constants for the glycin e molecule are not found to be significantly affected by the torsional state of the H2O molecules if the structure is optimized. This proced ure may have general applicability for deriving force fields of struct ural components that can be related to non-global-minima conformers of model molecules.