AM1/TIP3P molecular dynamics simulation of imidazole proton-relay processes in aqueous solution

Molecular dynamics simulations using combined AM1 and TIP3P potentials have been carried out to analyze the mechanism of a double proton transfer in aqueous solution for the model system NH4+–imidazole–NH3 with fixed N–N distances (2.5 Å). The mechanism is shown to be stepwise involving a few system configurations in which the protons are more or less delocalised. The characteristic time for the proton relay reaction is of the order of 1–2 ps.