Wiring Photosystem I for Direct Solar Hydrogen Production

The generation of H-2 by the use of solar energy is a promising way to supply humankind's energy needs while simultaneously mitigating environmental concerns that arise due to climate change. The challenge is to find a way to connect a photochemical module that harnesses the sun's energy to a catalytic module that generates H-2 with high quantum yields and rates. In this review, we describe a technology that employs a.,molecular wire" to connect a terminal [4Fe-4S] cluster of Photosystem I directly to a catalyst, which call be either a Pt nanoparticle or the distal [4Fe-4S] cluster of all [FeFe]- or [NiFe]-hydrogenase enzyme. The keys to connecting these two moieties are surface-located cysteine residues, which serve as ligands to Fe-S clusters and which call be changed through site-specific mutagenesis to glycine residues, and the use of a molecular wire terminated ill sulfhydryl groups to connect the two modules. The sulfhydryl groups at the end of the molecular wire form a direct chemical linkage to a Suitable catalyst or can chemically rescue a [4Fe-4S] cluster, thereby generating a strong coordination bond. Specifically, the molecular Wire call connect the F-B iron-sulfur Cluster of Photosystem I either to a Pt nanoparticle or, by using the same type of genetic modification, to the differentiated iron atom of the distal [4Fe-4S]center dot(Cys)(3)(Gly) cluster of hydrogenase. When electrons are Supplied by a sacrificial donor, this technology forms the cathode of a photochemical half-cell that evolves H-2 when illuminated. If such a device were connected to the anode of a photochemical half-cell that oxidizes water, an in vitro solar energy converter could be realized that generates Only O-2 and H-2 in the light. A similar methodology can be used to connect Photosystem I to other redox proteins that have surface-located [4Fe-4S] clusters. The controlled light-driven production of strong reductants by such systems can be used to produce other biofuels or to provide mechanistic insights into enzymes catalyzing multielectron, proton-coupled reactions.