Chapter 17: Wired Reaction Centers

New methods to generate alternative fuels, specifically through light driven reactions, are of major contemporary interest. Dihydrogen is a particularly attractive alternative fuel since it contains no carbon and thus does not contribute to increased levels of greenhouse gases. This chapter highlights progress in the utilization and exploitation of naturally-occurring reaction centers to generate dihydrogen. Photosynthetic reaction centers carry out the conversion of solar energy into chemical bond energy with high efficiencies and high quantum yields. In addition, the standard biochemical midpoint potential of the final product of Photosystem I is poised at an appropriate Gibbs free energy to carry out the reaction: 2H⁺+2e⁻ → H₂(g). Due to these properties, Photosystem I is an appropriate photochemical module that, when coupled to a catalytic module, shows promise in reducing protons to dihydrogen. Various light-to-hydrogen systems will be discussed, from the use of whole organisms to purified protein constructs. A major challenge is the transfer of the electrons between the photochemical module and the catalytic module. To address this problem, several unique attachment strategies have been employed, including a novel technology that directly wires together the electron transfer chains of the photochemical and catalytic modules. We conclude with a section on the attachment of these systems to electrode surfaces, which is ultimately a necessity for incorporation of these modules into a useable bio-inspired device, as well as future prospects and applications for these technologies.