Bionanodevice Beats Photosynthesis

A hydrogen-producing nanodevice based on photosynthetic proteins has higher electron-transfer throughput than natural photosynthesis, scientists report (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1114660108). John H. Golbeck of Pennsylvania State University and coworkers tethered an electron donor and an electron acceptor directly to photosystem I (PSI) from cyanobacteria. They connected the electron donor cytochrome c₆ (Cyt c₆) via a zero-length diimide-based cross-linking agent and the electron acceptor—the [4Fe-4S] cluster of a cyanobacterial hydrogenase (H₂ase)—via molecular wires containing three to 10 methylene groups or one or two phenyl groups. With a 1,8-octane­dithiol wire, the researchers achieved light-induced H₂ evolution of 2,200 μmol H₂ per mg chlorophyll per hour. The equivalent electron-transfer rate through the system was more than twice that of natural cyanobacterial photosynthesis. The nanodevice generated H₂ for the four hours of each experiment, declining only when the sacrificial electron donor, sodium ascorbate, became depleted. The system retained its H₂-evolving ability for 100 days at room temperature under anoxic conditions. Golbeck and coworkers suggest that tethering the proteins to the redox cofactors increases the electron-transfer rate by overcoming diffusion-based limitations.