A direct-dynamics study of proton transfer through water bridges in guanine and 7-azaindole

To evaluate the efficiency of bridges of water molecules as proton conduits , multidimensional ab initio proton transfer rate constants are reported fo r complexes of guanine and 7-azaindole with one and two water molecules. Th ese water molecules form hydrogen-bonded bridges between functional groups involved in tautomerization via proton transfer and catalyze this transfer. Structures and energies of the relevant stationary configurations are opti mized at the second-order Moller-Plesset level and vibrational force fields are evaluated at the Hartree-Fock level. The proton transfer rate constant s, calculated with the instanton method, show the effect of the structure a nd strength of the hydrogen bonds, reflected in couplings between the tunne ling mode and the other vibrations of the complexes. The results indicate t hat strongly hydrogen-bonded, strain-free water bridges can serve as very e fficient proton conduits. (C) 2000 American Institute of Physics. [S0021-96 06(00)52202-8].