The research on structural and functional biomimics of the active site of [FeFe]-hydrogenases is in an attempt to elucidate the mechanisms of H(2)-evolution and uptake at the [FeFe]-hydrogenase active site, and to learn from Nature how to create highly efficient H(2)-production catalyst systems. Undoubtedly, it is a challenging, arduous, and long-term work. In this perspective, the progresses in approaches to photochemical H(2) production using mimics of the [FeFe]-hydrogenase active site as catalysts in the last three years are reviewed, with emphasis on adjustment of the redox potentials and hydrophilicity of the [FeFe]-hydrogenase active site mimics to make them efficient catalysts for H(2) production. With gradually increasing understanding of the chemistry of the [FeFe]-hydrogenases and their mimics, more bio-inspired proton reduction catalysts with significantly improved efficiency of H(2) production will be realized in the future.
"On the basis of such data organometallic mimic structures of [NiFe]-and [FeFe]cofactors are designed in growing number and diversity that again inspire and enrich basic research on architecture and catalytic function of both cofactors . But only a small number of these chemical compounds exhibit significant proton reduction activity over a time range exceeding a few hours . Their restricted catalytic activity indicates that the role of the polypeptide environment for the catalytic process has been underestimated. "
[Show abstract][Hide abstract] ABSTRACT: The precise electrochemical features of metal cofactors that convey the functions of redox enzymes are essentially determined by the specific interaction pattern between cofactor and enclosing protein environment. However, while biophysical techniques allow a detailed understanding of the features characterizing the cofactor itself, knowledge about the contribution of the protein part is much harder to obtain. [FeFe]-hydrogenases are an interesting class of enzymes that catalyze both, H2 oxidation and the reduction of protons to molecular hydrogen with significant efficiency. The active site of these proteins consists of an unusual prosthetic group (H-cluster) with six iron and six sulfur atoms. While H-cluster architecture and catalytic states during the different steps of H2 turnover have been thoroughly investigated during the last 20years, possible functional contributions from the polypeptide framework were only assumed according to the level of conservancy and X-ray structure analyses. Due to the recent development of simpler and more efficient expression systems the role of single amino acids can now be experimentally investigated. This article summarizes, compares and categorizes the results of recent investigations based on site directed and random mutagenesis according to their informative value about structure function relationships in [FeFe]-hydrogenases.
"Precise delivery and removal of protons or H 2 to the active site is accomplished by structured channels formed by the protein tertiary structure. Numerous structural models of the [FeFe]-hydrogenases have been synthesized       , and many are functional in that they perform some of the same reactions as the natural hydrogenases. For example, the Pickett, Rauchfuss, Darensbourg, Gloaguen and Lichtenberger groups have all reported functional models of the hydrogenase enzyme that Biochimica et Biophysica Acta 1827 (2013) 1123–1139 ☆ This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems. "
[Show abstract][Hide abstract] ABSTRACT: This review discusses the development of molecular electrocatalysts for H(2) production and oxidation based on nickel. A modular approach is used in which the structure of the catalyst is divided into first, second, and outer coordination spheres. The first coordination sphere consists of the ligands bound directly to the metal center, and this coordination sphere can be used to control such factors as the presence or absence of vacant coordination sites, redox potentials, hydride donor abilities and other important thermodynamic parameters. The second coordination sphere includes functional groups such as pendent acids or bases that can interact with bound substrates such as H(2) molecules and hydride ligands, but that do not form strong bonds with the metal center. These functional groups can play diverse roles such as assisting the heterolytic cleavage of H(2), controlling intra- and intermolecular proton transfer reactions, and providing a physical pathway for coupling proton and electron transfer reactions. By controlling both the hydride donor ability of the catalysts using the first coordination sphere and the proton donor abilities of the functional groups in the second coordination sphere, catalysts can be designed that are biased toward H(2) production, oxidation, or bidirectional (catalyzing both H(2) oxidation and production). The outer coordination sphere is defined as that portion of the catalytic system that is beyond the second coordination sphere. This coordination sphere can assist in the delivery of protons and electrons to and from the catalytically active site, thereby adding another important avenue for controlling catalytic activity. Many features of these simple catalytic systems are good models for enzymes, and these simple systems provide insights into enzyme function and reactivity that may be difficult to probe in enzymes. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
[Show abstract][Hide abstract] ABSTRACT: A membrane electrode assembled with electrospun-fibers derived from a composite of cellulose acetate (CA) functionalised with carboxylated multiwall carbon nanotubes (cMWCNTs), polyvinyl pyrrolidone (PVP), and diiron model ([Fe2(edt)(CO)6], edt = ethanedithiolate) catalyses proton reduction in water with the presence of acetic acid.
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