Spontaneous activation of [FeFe]-hydrogenases by an inorganic [2Fe] active site mimic
TL;DR: It is shown that a chemical mimic of the [2Fe] subcluster can reconstitute apo-hydrogenase to full activity, independent of helper proteins, and will be a powerful tool for developing new artificial H₂-producing catalysts.
Abstract: Hydrogenases catalyze the formation of hydrogen. The cofactor ('H-cluster') of [FeFe]-hydrogenases consists of a [4Fe-4S] cluster bridged to a unique [2Fe] subcluster whose biosynthesis in vivo requires hydrogenase-specific maturases. Here we show that a chemical mimic of the [2Fe] subcluster can reconstitute apo-hydrogenase to full activity, independent of helper proteins. The assembled H-cluster is virtually indistinguishable from the native cofactor. This procedure will be a powerful tool for developing new artificial H₂-producing catalysts.
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TL;DR: In this paper, a review of the literature on 3D metal-based molecular catalysts is presented, focusing on their immobilization on heterogeneous solid-state supports for the synthesis of renewable fuels from abundant water or greenhouse gas CO2.
Abstract: The synthesis of renewable fuels from abundant water or the greenhouse gas CO2 is a major step toward creating sustainable and scalable energy storage technologies. In the last few decades, much attention has focused on the development of nonprecious metal-based catalysts and, in more recent years, their integration in solid-state support materials and devices that operate in water. This review surveys the literature on 3d metal-based molecular catalysts and focuses on their immobilization on heterogeneous solid-state supports for electro-, photo-, and photoelectrocatalytic synthesis of fuels in aqueous media. The first sections highlight benchmark homogeneous systems using proton and CO2 reducing 3d transition metal catalysts as well as commonly employed methods for catalyst immobilization, including a discussion of supporting materials and anchoring groups. The subsequent sections elaborate on productive associations between molecular catalysts and a wide range of substrates based on carbon, quantum dot...
511 citations
TL;DR: The intent is to provide a comprehensive overview of all work in the field up to December 2016, organized according to reaction class, which allows for comparison of similar reactions catalyzed by ArMs constructed using different metallocofactor anchoring strategies, cofactors, protein scaffolds, and mutagenesis strategies.
Abstract: The incorporation of a synthetic, catalytically competent metallocofactor into a protein scaffold to generate an artificial metalloenzyme (ArM) has been explored since the late 1970’s. Progress in the ensuing years was limited by the tools available for both organometallic synthesis and protein engineering. Advances in both of these areas, combined with increased appreciation of the potential benefits of combining attractive features of both homogeneous catalysis and enzymatic catalysis, led to a resurgence of interest in ArMs starting in the early 2000’s. Perhaps the most intriguing of potential ArM properties is their ability to endow homogeneous catalysts with a genetic memory. Indeed, incorporating a homogeneous catalyst into a genetically encoded scaffold offers the opportunity to improve ArM performance by directed evolution. This capability could, in turn, lead to improvements in ArM efficiency similar to those obtained for natural enzymes, providing systems suitable for practical applications and ...
504 citations
Additional excerpts
...Building on these results, Happe and Fontecave demonstrated that the use of HydF could even be avoided, that is, a direct loading of a synthetic complex into apo-HydA is possible (Scheme 20, path b).(193) Building upon this strategy, Hu and coworkers reported the direct reconstitution of an [Fe]-hydrogenase by loading its apo-form with a synthetic complex (Scheme 20, path c)....
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TL;DR: Advances in physical and theoretical characterization of H2ase enzymes and synthetic models have proven key to the study of hydrides in particular, and will guide modeling efforts toward more robust and active species optimized for practical applications.
Abstract: Hydrogenase enzymes efficiently process H2 and protons at organometallic FeFe, NiFe, or Fe active sites. Synthetic modeling of the many H2ase states has provided insight into H2ase structure and mechanism, as well as afforded catalysts for the H2 energy vector. Particularly important are hydride-bearing states, with synthetic hydride analogues now known for each hydrogenase class. These hydrides are typically prepared by protonation of low-valent cores. Examples of FeFe and NiFe hydrides derived from H2 have also been prepared. Such chemistry is more developed than mimicry of the redox-inactive monoFe enzyme, although functional models of the latter are now emerging. Advances in physical and theoretical characterization of H2ase enzymes and synthetic models have proven key to the study of hydrides in particular, and will guide modeling efforts toward more robust and active species optimized for practical applications.
433 citations
TL;DR: The more recent systems constructed as models for the hydrogenase enzymes are reviewed, with a specific focus on the various strategies employed for incorporating of synthetic models into supramolecular frameworks and polypeptidic/protein scaffolds.
412 citations
TL;DR: These ADMSs incorporated in pristine MOFs and MOF-derived carbon materials possess unique advantages over molecular or bulk metal-based catalysts and bridge the gap between homogeneous and heterogeneous catalysts for energy-conversion applications.
Abstract: Metal sites play an essential role in both electrocatalytic and photocatalytic energy conversion. The highly ordered arrangements of the organic linkers and metal nodes as well as the well-defined pore structures of metal-organic frameworks (MOFs) make them ideal substrates to support atomically dispersed metal sites (ADMSs) located in their metal nodes, linkers, and pores. Porous carbon materials doped with ADMSs can be derived from these ADMS-incorporating MOF precursors through controlled treatments. These ADMSs incorporated in pristine MOFs and MOF-derived carbon materials possess unique advantages over molecular or bulk metal-based catalysts and bridge the gap between homogeneous and heterogeneous catalysts for energy-conversion applications. This Review presents recent progress in the design and incorporation of ADMSs in MOFs and MOF-derived materials for energy-conversion applications.
411 citations
References
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TL;DR: A three-dimensional structure for the monomeric iron-containing hydrogenase (CpI) from Clostridium pasteurianum was determined, providing insights into the mechanism of biological hydrogen activation and has broader implications for [Fe-S] cluster structure and function in biological systems.
Abstract: A three-dimensional structure for the monomeric iron-containing hydrogenase (CpI) from Clostridium pasteurianum was determined to 1.8 angstrom resolution by x-ray crystallography using multiwavelength anomalous dispersion (MAD) phasing. CpI, an enzyme that catalyzes the two-electron reduction of two protons to yield dihydrogen, was found to contain 20 gram atoms of iron per mole of protein, arranged into five distinct [Fe-S] clusters. The probable active-site cluster, previously termed the H-cluster, was found to be an unexpected arrangement of six iron atoms existing as a [4Fe-4S] cubane subcluster covalently bridged by a cysteinate thiol to a [2Fe] subcluster. The iron atoms of the [2Fe] subcluster both exist with an octahedral coordination geometry and are bridged to each other by three non-protein atoms, assigned as two sulfide atoms and one carbonyl or cyanide molecule. This structure provides insights into the mechanism of biological hydrogen activation and has broader implications for [Fe-S] cluster structure and function in biological systems.
1,719 citations
TL;DR: The structure of the heterodimeric Fe-only hydrogenase from Desulfovibrio desulfuricans is reported - the first for this class of enzymes and it is suggested that it was imported from the inorganic world as an already functional unit.
1,279 citations
TL;DR: This article sets out to review the chemistry relating to the synthesis of structural and functional analogues of the three classes of hydrogenases, including the di-iron system.
Abstract: This article sets out to review the chemistry relating to the synthesis of structural and functional analogues of the three classes of hydrogenases. This chemistry has grown explosively over the last 10 or so years since the first X-ray structures of [NiFe]- and [FeFe]-hydrogenase systems were published. There are now some 400 papers covering structural and functional aspects, with the majority of these associated with the di-iron system. As much emphasized in earlier papers
1,135 citations
TL;DR: These results represent a considerable impetus to research the catalytic mechanism of hydrogenases and the design of organometallic compounds which mimic their structural or functional properties, or both.
Abstract: Many microorganisms, such as methanogenic, acetogenic, nitrogen-fixing, photosynthetic, or sulfate-reducing bacteria, metabolize hydrogen. 2a] Hydrogen activation is mediated by a family of enzymes, termed hydrogenases, which either provide these organisms with reducing power from hydrogen oxidation or act as TMelectron sinks∫, following the reaction: H2 2H 2e . Not surprisingly, hydrogenases are mostly studied with a view to designing chemical or biochemical processes to produce molecular hydrogen more abundantly and cheaply than with platinum catalysts ; molecular hydrogen is an ideally clean fuel. 5] Hydrogenases (cytochrome c3 oxidoreductase, EC 1.18.99.1) are classified into two major families in the present paper on the basis of the metal content of their respective dinuclear catalytic centers, that is nickel ± iron (NiFe) hydrogenases and TMiron only∫ (FeFe) hydrogenases. Some NiFe hydrogenases also contain selenium at their catalytic center in the form of selenocysteine (Table 1). The two hydrogenases families differ functionally from each other in that NiFe hydrogenases tend to be more involved in hydrogen oxidation and FeFe hydrogenases in hydrogen production. Moreover, NiFe hydrogenases are approximately 10 1 ± 10 2 times less active, show 10 times more affinity for hydrogen, and are less sensitive to inhibition by oxygen and carbon monoxide than FeFe hydrogenases (Table 2). A TMmetalfree∫ hydrogenase, found in methanogenic bacteria, catalyzes the reversible reduction of a methenyltetrahydromethanopterin (methenyl-H4MPT) methanogenic cofactor with H2 to form methylene-H4MPTand a proton during methane formation from CO2 and 4H2. The three-dimensional atomic models of four NiFe, one NiFeSe, and, more recently, two FeFe 14] hydrogenases (Table 3) have been elucidated by X-ray crystallography on the basis of gene sequencing and a wealth of biochemical and spectroscopic studies, in some cases coupled with isotopic labeling. 2, 16] These results represent a considerable impetus to research the catalytic mechanism of hydrogenases and the design of organometallic compounds which mimic their structural or functional properties, or both. The aim of this short review is to highlight some recent works and trends in hydrogenase research.
732 citations
TL;DR: It is shown that three synthetic mimics (containing different bridging dithiolate ligands) can be loaded onto bacterial Thermotoga maritima HydF and then transferred to apo-HydA1, one of the hydrogenases of Chlamydomonas reinhardtii algae, providing new mechanistic and structural insight into hydrogenase maturation.
Abstract: Hydrogenases are the most active molecular catalysts for hydrogen production and uptake1, 2, and could therefore facilitate the development of new types of fuel cell3, 4, 5. In [FeFe]-hydrogenases, catalysis takes place at a unique di-iron centre (the [2Fe] subsite), which contains a bridging dithiolate ligand, three CO ligands and two CN- ligands6, 7. Through a complex multienzymatic biosynthetic process, this [2Fe] subsite is first assembled on a maturation enzyme, HydF, and then delivered to the apo-hydrogenase for activation8. Synthetic chemistry has been used to prepare remarkably similar mimics of that subsite1, but it has failed to reproduce the natural enzymatic activities thus far. Here we show that three synthetic mimics (containing different bridging dithiolate ligands) can be loaded onto bacterial Thermotoga maritima HydF and then transferred to apo-HydA1, one of the hydrogenases of Chlamydomonas reinhardtii algae. Full activation of HydA1 was achieved only when using the HydF hybrid protein containing the mimic with an azadithiolate bridge, confirming the presence of this ligand in the active site of native [FeFe]-hydrogenases9, 10. This is an example of controlled metalloenzyme activation using the combination of a specific protein scaffold and active-site synthetic analogues. This simple methodology provides both new mechanistic and structural insight into hydrogenase maturation and a unique tool for producing recombinant wild-type and variant [FeFe]-hydrogenases, with no requirement for the complete maturation machinery
557 citations