Light-Driven Hydrogen Evolution Reaction Catalyzed by a Molybdenum-Copper Artificial Hydrogenase

Orange protein (Orp) is a small bacterialmetalloprotein of unknownfunction that harbors a unique molybdenum/copper (Mo/Cu) heterometalliccluster, [S2MoS2CuS2MoS2](3-). In this paper, the performance of Orp as acatalyst for the photocatalytic reduction of protons into H-2 has been investigated under visible light irradiation. We reportthe complete biochemical and spectroscopic characterization of holo-Orp containing the [S2MoS2CuS2MoS2](3-) cluster, with dockingand molecular dynamics simulations suggesting a positively chargedArg, Lys-containing pocket as the binding site. Holo-Orp exhibits excellent photocatalytic activity, in the presenceof ascorbate as the sacrificial electron donor and [Ru(bpy)(3)]Cl-2 as the photosensitizer, for hydrogen evolution witha maximum turnover number of 890 after 4 h irradiation. Density functionaltheory (DFT) calculations were used to propose a consistent reactionmechanism in which the terminal sulfur atoms are playing a key rolein promoting H-2 formation. A series of dinuclear [S2MS2M ' S2MS2]((4n)-) clusters, with M = Mo-VI, W-VI and M '((n+)) = Cu-I, Fe-I, Ni-I, Co-I,Co- Zn-II, Cd-II were assembled in Orp, leading to different M/M '-Orpversions which are shown to display catalytic activity, with the Mo/Fe-Orpcatalyst giving a remarkable turnover number (TON) of 1150 after 2.5h reaction and an initial turnover frequency (TOF degrees) of 800 h(-1) establishing a record among previously reported artificialhydrogenases.

Automated summary

In this study, the performance of the orange protein (Orp) as a catalyst for photocatalytic reduction of protons into H-2 under visible light irradiation was investigated. It was found that Orp exhibited excellent photocatalytic activity in the presence of ascorbate as the sacrificial electron donor and [Ru(bpy)(3)]Cl-2 as the photosensitizer. Density functional theory (DFT) calculations were used to propose a consistent reaction mechanism.