Computational Studies of [NiFe] and [FeFe] Hydrogenases

Siegbahn, Per E. M.; Tye, Jesse W.; Hall, Michael B.

doi:10.1021/cr050185y

Cited by 382 publications

(397 citation statements)

References 148 publications

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“…[13][14][15] In an eclipsed geometry, the bridging, as opposed to terminal, position is most reactive, facilitating formation of stable but unreactive bridging hydrides. [16][17][18] Thus the models tend to be poor catalysts for proton reduction and require substantial overpotentials for the catalysis. Development of mononuclear iron complexes with an open coordination site can, in principle, overcome this difficulty and mimic the reactivity of the distal iron site of the enzyme if an appropriate ligand set can be found to simulate the electronic environment of the second missing metal.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

et al. 2014

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Abstract:Two pentacoordinate mononuclear iron carbonyls of the form (bdt)Fe(CO)P 2 [bdt = benzene-1,2-dithiolate; P 2 = 1,1'-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal iron (Fe d ) of the active site of [FeFe]-hydrogenase. Xray crystal structures of the complexes reveal that, despite similar ν(CO) stretching band frequencies, the two complexes have different coordination geometries. In X-ray crystal structures, the iron center of 1 is in a distorted trigonal bipyramidal arrangement, and that of 2 is in a distorted square pyramidal geometry. Electrochemical investigation shows that both complexes catalyze electrochemical proton reduction from acetic acid at mild overpotential, 0.17 and 0.38 V for 1 and 2, respectively. Although coordinatively unsaturated, the complexes display only weak, reversible binding affinity towards CO(1 bar). However, ligand centered protonation by the strong acid, HBF 4 .OEt 2 , triggers quantitative CO uptake by 1 to form a dicarbonyl analogue [1(H)-CO] + that can be reversibly converted back to 1 by deprotonation using NEt 3 . Both crystallographically determined distances within the bdt ligand and DFT calculations suggest that the iron centers in both 1 and 2 are partially reduced at the expense of partial oxidation of the bdt ligand. Ligand protonation interrupts this extensive electronic delocalization between the Fe and bdt making 1(H) + susceptible to external CO binding.3

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Section: Introductionmentioning

confidence: 99%

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

et al. 2014

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“…In this way, two base metals in a single unit can share the required redox changes and perform two-electron catalytic functions as do single noble metals such as Pt 0 or Pd 0 , currently used in hydrogen technology. The search for mechanistic understanding of the electrocatalysis by the active site models has inspired informative computational studies 7 that intimate the roles of each component of the deceptively simple active site. Biochemical studies have shown that the redox active 4Fe4S cluster that is directly attached to the 2Fe subsite is required for the extraordinary activity of the enzyme.…”

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confidence: 99%

Redox active iron nitrosyl units in proton reduction electrocatalysis

et al. 2014

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Base metal, molecular catalysts for the fundamental process of conversion of protons and electrons to dihydrogen, remain a substantial synthetic goal related to a sustainable energy future. Here we report a diiron complex with bridging thiolates in the butterfly shape of the 2Fe2S core of the [FeFe]-hydrogenase active site but with nitrosyl rather than carbonyl or cyanide ligands. This binuclear [(NO)Fe(N 2 S 2 )Fe(NO) 2 ] þ complex maintains structural integrity in two redox levels; it consists of a (N 2 S 2 )Fe(NO) complex (N 2 S 2 ¼ N,N 0 -bis(2-mercaptoethyl)-1,4-diazacycloheptane) that serves as redox active metallodithiolato bidentate ligand to a redox active dinitrosyl iron unit, Fe(NO) 2 . Experimental and theoretical methods demonstrate the accommodation of redox levels in both components of the complex, each involving electronically versatile nitrosyl ligands. An interplay of orbital mixing between the Fe(NO) and Fe(NO) 2 sites and within the iron nitrosyl bonds in each moiety is revealed, accounting for the interactions that facilitate electron uptake, storage and proton reduction.

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“…The [FeFe] hydrogenases from Clostridium pasteurianum (CpI) 1 and Desulfovibrio desulfuricans (DdH) have been intensively studied by various spectroscopic methods as well as X-ray crystallography (1,(10)(11)(12) (1,16). The two iron atoms are connected via a dithiolate bridge.…”

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Spectroelectrochemical Characterization of the Active Site of the [FeFe] Hydrogenase HydA1 from Chlamydomonas reinhardtii

et al. 2009

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Hydrogenases catalyze the reversible oxidation of molecular hydrogen. The active site of the [FeFe] hydrogenases (H-cluster) contains a catalytically active binuclear subcluster ([2Fe] H ) connected to a "cubane" [4Fe4S] H subcluster. Here we present an IR spectroelectrochemical study of the [FeFe] hydrogenase HydA1 isolated from the green alga Chlamydomonas reinhardtii. The enzyme shows IR bands similar to those observed for bacterial [FeFe] hydrogenases. They are assigned to the stretching vibrations of the CN -and CO ligands on both irons of the [2Fe] H subcluster. By following changes in frequencies of the IR bands during electrochemical titrations, two one-electron redox processes of the active enzyme could be distinguished. The reduction of the oxidized state (H ox ) occurred at a midpoint potential of -400 mV vs NHE (H ox /H red transition) and relates to a change of the formal oxidation state of the binuclear subcluster. A subsequent reduction (H red /H sred transition) was determined to have a midpoint potential of -460 mV vs NHE. On the basis of the IR spectra, it is suggested that the oxidation state of the binuclear subcluster does not change in this transition. Tentatively, a reduction of the [4Fe4S] H cluster has been proposed. In contrast to the bacterial [FeFe] hydrogenases, where the bridging CO ligand becomes terminal when going from H ox to H red , in HydA1 the bridging CO is present in both the H ox and H red state. The removal of the bridging CO moiety has been observed in the H red to H sred transition. The significance of this result for the hydrogen conversion mechanism of this class of enzymes is discussed.

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Computational Studies of [NiFe] and [FeFe] Hydrogenases

Cited by 382 publications

References 148 publications

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

Redox active iron nitrosyl units in proton reduction electrocatalysis

Spectroelectrochemical Characterization of the Active Site of the [FeFe] Hydrogenase HydA1 from Chlamydomonas reinhardtii

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