SCALED QUANTUM-MECHANICAL FORCE-FIELD FOR CIS-GLYCINE AND TRANS-GLYCINE IN ACIDIC SOLUTION

We obtain one set of ab initio scale factors for two conformational is omers of glycine in acidic solution. Ab initio calculations are perfor med using the 4-31G basis set. Force constants from two fully optimize d glycine-H+.4H2O supermolecules are scaled using vibrational frequenc ies of glycine in water at pH 0.8. Similar calculations are shown for methylamine-H+ and acetic acid. Reasonable agreement is obtained betwe en calculated and experimental frequencies for glycine-H+, acetic acid , and methylamine-H+. Comparisons between scale factors for these mole cules show that scale factors for the same symmetry coordinates are si milar in most cases and indicate the extent to which scale factors can be transferred between these molecules. These scale factors are being used to build a scaled quantum mechanical force field for alanine, an d subsequently for peptides in aqueous solutions.