John H. Golbeck
Professor of Biochemistry and Biophysics, Professor of Chemistry
The Pennsylvania State University
This work involves the design, fabrication, characterization, and optimization of a biological/organic hybrid electrochemical half-cell that couples Photosystem I, which efficiently captures and stores energy derived from sunlight, with either a [FeFe]-H2ase or a [NiFe]-H2ase, which can generate a high rate of H2 evolution with an input of reducing power. Using a method that does not depend on inefficient solution (diffusion) chemistry, the challenge is to deliver the highly reducing electron from Photosystem I to the H2ase rapidly and efficiently in vitro. To this end, we have designed a covalently bonded molecular wire that will connect the active sites of the two enzymes. The result is that the low-potential electron can be transferred without loss and at high rates directly from PS I to the H2ase enzyme. The PS I-molecular wire-H2ase complex will be tethered to a gold electrode through a baseplate of cytochrome c6, which will additionally serve as a conduit of electrons from the gold to Photosystem I. Cytochrome c6 and the other proteins will be covalently bonded to the electrode through a self-assembling monolayer of functionalized alkanethiols The device should be capable of transferring at least 1000 electrons per second from PS I to the H2ase to carry out the reaction: 2H+ + 2e- + 2hv -> H2.