Why Is There Such a Small Overpotential for O[sub 2] Electroreduction by Copper Laccase?

Quantum chemical predictions are made of reversible potentials for intermediates formed during the four-electron reduction of by copper laccase, using three loosely associated partially ligated centers as models for the active site. Two mechanisms are studied, the platinum surface mechanism in acid electrolyte, and the proposed laccase mechanism for basic electrolyte. Both are found viable. The reduction to step has the lowest potential, making it responsible for the predicted low overpotential. Compared to laccase, the overpotential is somewhat high but completing the ligand coordination would be expected to lead to smaller predicted overpotentials.