Enhancing effects of amino acid residue model compounds on catalytic activity of an artificial oxygen evolving center

Electrocatalytic water oxidation was studied for an artificial oxygen evolving center (OEC) model using Nafion (Nf) membrane-coated electrode incorporating Ru-red ([(NH3)(5)Ru-O-Ru(NH3)(4)-O-RU(NH3)(5)](6+)) and an amino acid residue model compound. On the cyclic voltammogram (CV) of Ru-red in the presence of a Tyr residue model, p-cresol (p-Cre) or a His residue model, 4-methylimidazole (MIm), the anodic current in an oxidative scan is much higher than that without the model compounds. The amount of O-2 evolved in the potentiostatic electrolysis increased remarkably in the presence of p-Cre or MIm. The enhancing effect of the model compounds on the catalytic activity was analyzed in terms of the intrinsic activity, charge-transfer distance between the complexes, and their critical decomposition distance based on the intermolecular distance distribution. The charge-transfer distance was remarkably prolonged from 1.28 to 2.25 nm by the presence of p-Cre and to 1.60 nm by Mim, which strongly suggests that p-Cre and MIm work as mediators for charge transfer in an artificial OEC model.