Publication 683

J. Am. Chem. Soc., 133 (17), 6668-6674, 2011 DOI:10.1021/ja110935c
Water (in water) as an intrinsically efficient proton acceptor in concerted proton electron transfers

Laboratoire d’Electrochimie Moléculaire, UMR CNRS 7591, Université Paris Diderot, 15 rue Jean-Antoine de Baïf, 75205 Paris Cedex 13, France

The oxidation of PhOH in water by photochemically generated Ru^III(bpy)₃ is taken as prototypal example disclosing the special character of water, in the solvent water, as proton acceptor in concerted proton−electron transfer reactions. The variation of the rate constant with temperature and driving force, as well as the variation of the H/D kinetic isotope effect with temperature, allowed the determination of the reaction mechanism characterized by three intrinsic parameters, the reorganization energy, a pre-exponential factor measuring the vibronic coupling of electronic states at equilibrium distance, and a distance-sensitivity parameter. Analysis of these characteristics and comparison with a standard base, hydrogen phosphate, revealed that electron transfer is concerted with a Grotthus-type proton translocation, leading to a charge delocalized over a cluster involving several water molecules. A mechanism is thus uncovered that may help in understanding how protons could be transported along water chains over large distances in concert with electron transfer in biological systems.