Role of solvation structure in the shuttling of the hydrated excess proton

Abstract

The classic Marcus electron transfer reaction model demonstrated that a barrierless electron transfer reaction can occur when both the reactant and product have almost similar solvation environment. In our recently developed proton model, we have incorporated the pre-solvation concept and showed that it indeed facilitates the proton diffusion in aqueous solution. In this work, we further quantify the degree of pre-solvation using different structural parameters, e.g., tetrahedral order parameter, average numbers of hydrogen bonds. All the above said parameters exhibit a very strong correlation with the proton share parameter. The more Zundel-like configurations have almost identical solvation environment for both the water molecules and support the pre-solvation concept. However, in the case of Eigen-like configurations, the central hydronium and “special pair” water have distinctly different solvation structures. Synopsis Hydrated excess proton transfer events in liquid water are highly coupled with local solvent orientations than previously thought. The weak hydrogen bond accepting nature of the hydronium helps to create water-like solvation environment around hydronium. This pre-solvated configuration facilitates the proton transfer process in liquid water. Proton sharing parameter-dependent radial distribution function shows the tiny intensity at 2.0 Å, which arises from the $$4^{\mathrm{th}}$$ water molecule solvating the hydronium moiety.