SOLVENT EFFECT ON THE POTENTIAL SURFACE OF THE PROTON-TRANSFER IN [H3N-H-NH3](+)

Statistical mechanics Monte Carlo simulations of the proton transfer in [H3N-H-NH3](+) in aqueous solution have been carried out using the combined quantum mechanical and molecular mechanical AM1/TIP3P potential. As in the gas phase, squeezing and stretching motions of the donor-acceptor distance have profound effects on the proton transfer. Solvation increases the activation free energy of the proton transfer by 3 kcal/mol over that in the gas phase. The results suggest that the combined QM/MM potential may be used in models that treat the proton motion quantum mechanically and the solvent dynamics classically. (C) 1993 John Wiley & Sons, Inc.