Cobinamide production of hydrogen in a homogeneous aqueous photochemical system, and assembly and photoreduction in a (βα)8 protein

• Type of Material: Article
• Authors: Wesley D. Robertson, Emory University; Adonis M. Bovell, Emory University; Kurt Warncke, Emory University
• Language: English
• Date: 2013-08
• Publisher: Springer Verlag (Germany)
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2013, SBIC
• Final Published Version (URL): http://link.springer.com/article/10.1007%2Fs00775-013-1015-3
• Title of Journal or Parent Work: Journal of Biological Inorganic Chemistry
• ISSN: 0949-8257
• Volume: 18
• Issue: 6
• Start Page: 701
• End Page: 713
• Grant/Funding Information: The purchase of the Bruker E500 EPR spectrometer was supported by the National Center for Research Resources of the National Institutes of Health under award number RR17767 and by Emory University.; The research reported in this publication was supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under award number R01 DK054514.
• Keywords: Green energy; Cobalt complex; Cobinamide; Hydrogen; Homogeneous catalysis
• Research Categories: Chemistry, Inorganic; Environmental Sciences; Physics, Atmospheric Science

Abstract

Components of a protein-integrated, earth-abundant metal-macrocycle catalyst, purposed for hydrogen (H2) production from aqueous protons under green conditions, are characterized. The cobalt (Co) -corrin complex, cobinamide, is demonstrated to produce H2 (4.4±1.8×10−3 turnover number per hour) in a homogeneous, photosensitizer/sacrificial electron donor system, in pure water at neutral pH. Turnover is proposed to be limited by the relatively low population of the gateway Co(III) hydride species. A heterolytic mechanism for H2 production from the Co(II) hydride is proposed. Two essential requirements for assembly of a functional protein catalyst complex are demonstrated, for interaction of cobinamide with the (βα)8, TIM-barrel protein, EutB, from the adenosylcobalamin-dependent ethanolamine ammonia-lyase from Salmonella typhimurium: (1) High affinity equilibrium binding of the cobinamide (dissociation constant, 2.1×10−7 M), and (2) in situ photoreduction of the cobinamide-protein complex to the Co(I) state. Molecular modeling of the cobinamide-EutB interaction shows that these features arise from specific hydrogen bond and apolar interactions of the protein with the alkylamide substituents and ring of the corrin, and accessibility of the binding site to solution. The results establish cobinamide-EutB as a platform for design and engineering of a robust H2 production metallo-catalyst, that operates under green conditions, and utilizes advantages of protein as a tunable medium and material support.