VIBRATIONAL STRUCTURE OF THE SOLVATED GLYCINE ZWITTERION

The vibrational frequencies of glycine in aqueous solution are calculated. The effects of the water-glycine interactions on the forces and force constants of glycine, calculated using an ab initio SCF method, are treated by means of a molecular dynamics simulation of a system consisting of a glycine molecule surrounded by 253 water molecules. These interactions cannot be ignored because the isolated glycine zwitterion is unstable and is stabilized by the solvation. The fundamental frequencies of the glycine zwitterion and three of its deuterated isotopomers were calculated from the molecular dynamics forces and force constants. The resulting frequencies, after scaling with a single factor for the four isotopomers, are in good agreement with the experimental results.