Hydrogenase mimic produces hydrogen under the light

24 Jan 2013

Researchers from the laboratory of Giovanna Ghirlanda working on Subtask 3 (Fuel Production Complex) have achieved the synthesis of a peptide-based hydrogenase mimic that is capable of photoinduced hydrogen production. Results of the study have been published in the October 11, 2012, issue of Chemical Communications and the article has been featured on the cover of that issue.

Molecular hydrogen is an efficient and clean fuel of the future. Artificial hydrogen producing catalysts are primary targets in the search for sustainable fuel production systems. Natural hydrogenases in many microorganisms catalyze the reduction of protons to molecular hydrogen reversibly under mild conditions. The active site of one kind of hydrogenase is a cluster of two iron atoms where each metal is coordinated by carbon monoxide (CO) and cyanide (CN-) ligands. One of the strategies of the design of the artificial hydrogen production complex is to mimic the active center of the natural hydrogenases that produce hydrogen from protons and electrons. Recently the lab of Giovanna Ghirlanda has achieved a synthesis of a peptide-based hydrogenase mimic that was capable of photoinduced hydrogen production.

The research team includes Anyndya Roy, a graduate student from the Ghirlanda’s lab (left in a picture), who has synthesized the components of the system and achieved successful insertion of the iron-based hydrogenase mimic into the peptide and Chris Madden, a postdoctoral student from the Gust-Moore-Moore Lab, who was involved in the characterization of the hydrogen producing properties of the complex. The team has solved several problems. First, they synthesized an artificial peptide, which is a structural scaffold for holding the catalytic site, and a diiron hexacarbonyl, which is a mimic of the active site of the natural Fe-Fe hydrogenases. Second, they achieved a novel synthesis of an unnatural amino acid that contains the thiol moiety. This aminoacid was used to covalently anchor the diiron hexacarbonyl center to the artificial protein. The study has confirmed that the diiron hexacarbonyl center successfully constitutes into the peptide and stabilizes the helical structure through hydrogen bonding of a side chain to the CO. A ruthenium-complex based photosensitizer is employed to absorb light and supply electrons for hydrogen production by the diiron hexacarbonyl catalytic site. The hydrogenase mimic catalyzes photoinduced hydrogen production in water, under mild conditions (pH 6), in presence of a photosensitizer (Ru(bpy)3.6H2O) and a sacrificial electron donor (ascorbate), with a TON of 84 in 2.30 h. Work is proceeding on the development of improved versions of this artificial hydrogenase for use in the solar water splitting system being developed by BISfuel.

 

Source: Roy, A., Madden, C., and Ghirlanda, G. (2012) Photo-induced hydrogen production in a helical peptide incorporating a [FeFe] hydrogenase active site mimic, Chemical Communications, 48, 9816–9818

 

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