Visible Light-Driven O2 Reduction by a Porphyrin–Laccase SystemLatest updated: May 29, 2020
Authors: Theodore Lazarides, Igor V. Sazanovich A. Jalila Simaan , Maria Chrisanthi Kafentzi Milan Delor, Yasmina Mekmouche , Bruno Faure , Marius Réglier , Julia A. Weinstein, Athanassios G. Coutsolelos, and Thierry Tron
Ref: J. Am. Chem. Soc., 2013, 135 (8), pp 3095–3103
Several recent studies have shown that the combination of photosensitizers with metalloenzymes can support a light-driven multielectron reduction of molecules such as CO2 or HCN. Here we show that the association of the zinc tetramethylpyridinium porphyrin (ZnTMPyP4+) photosensitizer with the multicopper oxidase (MCO) laccase allows to link the oxidation of an organic molecule to the four electrons reduction of dioxygen into water. The enzyme is photoreduced within minutes with porphyrin/enzyme ratio as low as 1:40. With a 1:1 ratio, the dioxygen consumption rate is 1.7 μmol L–1 s–1. Flash photolysis experiments support the formation of the triplet excited state of ZnTMPyP4+ which reduces the enzyme to form a radical cation of the porphyrin with a kET ≈ 107 s–1 M–1. The long-lived triplet excited state of the ZnTMPyP4+ (τ0 = 0.72 ms) accounts for a substantial electron-transfer quantum yield, ϕET = 0.35. Consequently, the enzyme-dependent photo-oxidation of the electron donor occurs with a turnover of 8 min–1 for the one-electron oxidation process, thereby supporting the suitability of such enzyme/sensitizer hybrid systems for aerobic photodriven transformations on substrates. This study is the first example of a phorphyrin-sensitized four-electron reduction of an enzyme of the MCO family, leading to photoreduction of dioxygen into water.
stopped-flow fluorescence enzymology