Monte Carlo computer simulation of the aqueous hydration of the glycine zwitterion at 25 degree C.

Monte Carlo computer simulation on a dilute aqueous solution of the glycine zwitterion are reported. The results are presented in terms of the Quasi-Component Distribution Functions (QCDF) of Ben Naim and partitioned into atomic and functional group contributions using the Proximity Criterion. The Proximity Criterion analysis has been extended to orientational properties and a new normalization procedure has been introduced for the radial distribution functions obtained by the Proximity Criterion. The solvation environment of the glycine zwitterion is found to contain, on the average, 14.4 water molecules out of which 3.2 belong to the ammonium group, 6.1 to the methylene group and 5.1 to the carboxyl group. The importance of the many-body statistical mechanical approach to hydration is emphasized by our finding that the configuration corresponding to the absolute minimum of the glycine zwitterion-water potential surface was found to have negligible statistical weight in the aqueous simulation.