Tracking Light-Induced Electron Transfer Toward O-2 In A Hybrid Photoredox-Laccase System

Photobiocatalysis uses light to perform specific chemical transformations in a selective and efficient way. The intention is to couple a photoredox cycle with an enzyme performing multielectronic catalytic activities. Laccase, a robust multi-copper oxidase, can be envisioned to use dioxygen as a clean electron sink when coupled to an oxidation photocatalyst. Here, we provide a detailed study of the coupling of a [Ru(bpy)(3)](2+) photosensitizer to laccase. We demonstrate that efficient laccase reduction requires an electron relay like methyl viologen. In the presence of dioxygen, electrons transiently stored in superoxide ions are scavenged by laccase to form water instead of H2O2. The net result is the photo accumulation of highly oxidizing [Ru(bpy)(3)](3+). This study provides ground for the use of laccase in tandem with a light-driven oxidative process and O-2 as one-electron transfer relay and as four-electron substrate to be a sustainable final electron acceptor in a photocatalytic process.