[FeFe]-Hydrogenases: recent developments and future perspectives

Wittkamp, Florian; Senger, Moritz; Stripp, Sven T.; Apfel, Ulf‐Peter

doi:10.1039/c8cc01275j

Cited by 125 publications

(124 citation statements)

References 87 publications

(144 reference statements)

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“…I have provided here a comprehensive (but not exhaustive) theoretical account of the hydrogen chemistry (H and H 2 ) of a metal sulfide cluster larger than any that have been investigated experimentally. There is substantial knowledge of the hydrogen chemistry of bimetallic sulfide systems [73], particularly the [FeFe] and [NiFe] hydrogenase enzymes [74][75][76][77][78][79]. The unusual Fe 4 S 3 (S-cysteine) 6 cluster in O 2 -tolerant [NiFe] hydrogenase [76] may have a significant SH function [80].…”

Section: Discussionmentioning

confidence: 99%

Survey of the Geometric and Electronic Structures of the Key Hydrogenated Forms of FeMo-co, the Active Site of the Enzyme Nitrogenase: Principles of the Mechanistically Significant Coordination Chemistry

Dance

2019

Inorganics

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The enzyme nitrogenase naturally hydrogenates N2 to NH3, achieved through the accumulation of H atoms on FeMo-co, the Fe7MoS9C(homocitrate) cluster that is the catalytically active site. Four intermediates, E1H1, E2H2, E3H3, and E4H4, carry these hydrogen atoms. I report density functional calculations of the numerous possibilities for the geometric and electronic structures of these poly-hydrogenated forms of FeMo-co. This survey involves more than 100 structures, including those with bound H2, and assesses their relative energies and most likely electronic states. Twelve locations for bound H atoms in the active domain of FeMo-co, including Fe–H–Fe and Fe–H–S bridges, are studied. A significant result is that transverse Fe–H–Fe bridges (transverse to the pseudo-threefold axis of FeMo-co and shared with triply-bridging S) are not possible geometrically unless the S is hydrogenated to become doubly-bridging. The favourable Fe–H–Fe bridges are shared with doubly-bridging S. ENDOR data for an E4H4 intermediate trapped at low temperature, and interpretations in terms of the geometrical and electronic structure of E4H4, are assessed in conjunction with the calculated possibilities. The results reported here yield a set of 24 principles for the mechanistically significant coordination chemistry of H and H2 on FeMo-co, in the stages prior to N2 binding.

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Section: Discussionmentioning

confidence: 99%

Survey of the Geometric and Electronic Structures of the Key Hydrogenated Forms of FeMo-co, the Active Site of the Enzyme Nitrogenase: Principles of the Mechanistically Significant Coordination Chemistry

Dance

2019

Inorganics

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“…2). [23][24][25] as proven by crystal structures. 13 Furthermore, ruthenium 26 and selenide substitutions were reported.…”

Section: Introductionmentioning

confidence: 99%

“…In the future, spectroscopy with sub-turnover time resolution will help to distinguish whether a particular intermediate is involved in the catalytic cycle. 25 Application of such approaches to [FeFe]hydrogenases is challenging due to the lack of intrinsic means to trigger and synchronize catalytic activity, but recent progress in the field is promising. [59][60][61][62] We briefly outline the key features of our model in the following.…”

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confidence: 99%

The Molecular Proceedings of Biological Hydrogen Turnover

2018

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Over the past two decades, the bioinorganic chemistry of hydrogenases has attracted much interest from basic and applied research. Hydrogenases are highly efficient metalloenzymes that catalyze the reversible reduction of protons to molecular hydrogen (H) in all domains of life. Their iron- and nickel-based cofactors represent promising blueprints for the design of biomimetic, synthetic catalysts. In this Account, we address the molecular proceedings of hydrogen turnover with [FeFe]-hydrogenases. The active site cofactor of [FeFe]-hydrogenases ("H-cluster") comprises a unique diiron complex linked to a [4Fe-4S] cluster via a single cysteine. Since it was discovered that a synthetic analogue of the diiron site can be incorporated into apoprotein in vitro to yield active enzyme, significant progress has been made toward a comprehensive understanding of hydrogenase catalysis. The diiron site carries three to four carbon monoxide (CO) and two cyanide (CN) ligands that give rise to intense infrared (IR) absorption bands. These bands are sensitive reporters of the electron density across the H-cluster, which can be addressed by infrared spectroscopy to follow redox and protonation changes at the cofactor. Synthetic variation of the metal-bridging dithiolate ligand at the diiron site, as well as site-directed mutagenesis of amino acids, provides access to the proton pathways toward the cofactor. Quantum chemical calculations are employed to specifically assign IR bands to vibrational modes of the diatomic ligands and yield refined H-cluster geometries. Here, we provide an overview of recent research on [FeFe]-hydrogenases with emphasis on experimental and computational IR studies. We describe advances in attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) and protein film electrochemistry, as well as density functional theory (DFT) calculations. Key cofactor species are discussed in terms of molecular geometry, redox state, and protonation. Isotope editing is introduced as a tool to evaluate the cofactor geometry beyond the limits of protein crystallography. In particular, the role of proton-coupled electron transfer (PCET) in the generation of catalytically relevant redox species is addressed. We propose that site-selective protonation of the H-cluster biases surplus electrons either to the [4Fe-4S] cluster or to the diiron site. Protonation of the [4Fe-4S] cluster prevents premature reduction at the diiron site and stabilizes a reactive, terminal hydride. The observed H-cluster species are assigned to rapid H conversion or to reactions possibly involved in activity regulation and cellular H sensing. In the catalytic cycle of [FeFe]-hydrogenases, an H-cluster geometry is preserved that features a bridging CO ligand. PCET levels the redox potential for two steps of sequential cofactor reduction. The concept of consecutive PCET at a geometrically inert cofactor with tight control of electron and proton localization may inspire the design of a novel generation of biomimetic catalysts for the pro...

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“…Plenty of research activities focused on the investigation of hydrogenases mimics that imitate the active‐site arrangement of the corresponding metalloenzyme, but consist of much fewer atoms than the enzyme itself . Correspondingly, more hydrogenases substitutes can be immobilized on an electrode surface to enhance the number of active sites and, hence, turnover of gaseous hydrogen.…”

Section: Acknowledgementsmentioning

confidence: 99%

Electrolyte Engineering as a Key Strategy Towards a Sustainable Energy Scenario?

Exner

2019

ChemElectroChem

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Major challenges still need to be resolved on the way towards a sustainable energy scenario. A future vision comprises the development of electrocatalysts, refraining from using scarce noble metals, for electrocatalytic key processes, such as hydrogen and oxygen evolution and reduction reactions or CO2 reduction. Hitherto, the focus was set on the investigation of electrode materials, whereas only little emphasis was put on the electrolyte solution. Recently, it was reported that, under non‐acidic pH conditions, the composition of the electrolyte solution has a non‐negligible effect on the activity of electrocatalytic processes: this outcome puts forth the idea of electrolyte engineering, a promising strategy that, besides the study of enhanced electrode materials, should be put in the focus of future research investigations in electrocatalysis.

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[FeFe]-Hydrogenases: recent developments and future perspectives

Cited by 125 publications

References 87 publications

Survey of the Geometric and Electronic Structures of the Key Hydrogenated Forms of FeMo-co, the Active Site of the Enzyme Nitrogenase: Principles of the Mechanistically Significant Coordination Chemistry

Survey of the Geometric and Electronic Structures of the Key Hydrogenated Forms of FeMo-co, the Active Site of the Enzyme Nitrogenase: Principles of the Mechanistically Significant Coordination Chemistry

The Molecular Proceedings of Biological Hydrogen Turnover

Electrolyte Engineering as a Key Strategy Towards a Sustainable Energy Scenario?

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