Computational studies of [NiFe] and [FeFe] hydrogenases

From protein engineering to artificial enzymes - biological and biomimetic approaches towards sustainable hydrogen production

Hydrogen gas is used extensively in industry today and is often put forward as a suitable energy carrier due its high energy density. Currently, the main source of molecular hydrogen is fossil fuels via steam reforming. Consequently, novel production methods are required to improve the sustainability of hydrogen gas for industrial processes, as well as paving the way for its implementation as a future solar fuel. Nature has already developed an elaborate hydrogen economy, where the production and consumption of hydrogen gas is catalysed by hydrogenase enzymes. In this review we summarize efforts on engineering and optimizing these enzymes for biological hydrogen gas production, with an emphasis on their inorganic cofactors. Moreover, we will describe how our understanding of these enzymes has been applied for the preparation of bio-inspired/-mimetic systems for efficient and sustainable hydrogen production.

Hydrogen bonding effect between active site and protein environment on catalysis performance in H2-producing [NiFe] hydrogenases

The interaction between the active site and the surrounding protein environment plays a fundamental role in the hydrogen evolution reaction (HER) in [NiFe] hydrogenases. Our density functional theory (DFT) findings demonstrate that the reaction Gibbs free energy required for the rate determining step decreases by 7.1 kcal mol^-1 when the surrounding protein environment is taken into account, which is chiefly due to free energy decreases for the two H⁺/e^- addition steps (the so-called Ni-SIa to I1, and Ni-C to Ni-R), being the largest thermodynamic impediments of the whole reaction. The variety of hydrogen bonds (H-bonds) between the amino acids and the active site is hypothesised to be the main reason for such stability: H-bonds not only work as electrostatic attractive forces that influence the charge redistribution, but more importantly, they act as an electron 'pull' taking electrons from the active site towards the amino acids. Moreover, the electron 'pull' effect through H-bonds via the S^- in cysteine residues shows a larger influence on the energy profile than that via the CN^- ligands on Fe.

A Major Structural Change of the Homocitrate Ligand of Probable Importance for the Nitrogenase Mechanism

Mo-containing nitrogenase is the main enzyme that is able to take N₂ from the air and form ammonia. The active-site cofactor of the enzyme, termed FeMoco, is unique in nature. It has seven Fe and one Mo atoms connected by S bridges, with a C atom in the center of the cofactor. Another unusual feature is that it has a large homocitrate ligand known to be of importance for catalysis. In the present computational study, the role of the homocitrate ligand is investigated. It is found that a large structural change, which makes Mo^III five-coordinated, is energetically favorable in the more reduced states. This is of probable importance for the nitrogenase mechanism.

The oxygen reduction reaction on [NiFe] hydrogenases

Oxygen tolerance capacity is critical for hydrogen oxidation/evolution catalysts.

Deciphering the chemoselectivity of nickel-dependent quercetin 2,4-dioxygenase

QM/MM calculations were performed to elucidate the reaction mechanism and chemoselectivity of 2,4-QueD. The protonation state of the first-shell ligand Glu74 plays an important role in dictating the selectivity.

Jensen HJ, Hedegård ED. Exploration of H2 binding to the [NiFe]-hydrogenase active site with multiconfigurational density functional theory

The combination of density functional theory (DFT) with a multiconfigurational wave function is an efficient way to include dynamical correlation in calculations with multiconfiguration self-consistent field wave functions.

Photochemical Dynamics of a Trimethyl-Phosphine Derivatized [FeFe]-Hydrogenase Model Compound

Though there have been many studies on photosensitizers coupled to model complexes of the [FeFe]-hydrogenases, few have looked at how the models react upon exposure to light. To extract photoreaction information, ultrafast time-resolved UV/visible pump, IR probe spectroscopy was performed on Fe₂(μ-S₂C₂H₄)(CO)₄(PMe₃)₂ (2b) dissolved in heptane and acetonitrile and the photochemical dynamics were determined. Excitation with 532 and 355 nm light produces bleaches and new absorptions that decay to half their original intensity with time constants of 300 ± 120 ps and 380 ± 210 ps in heptane and acetonitrile, respectively. These features persist to the microsecond timescale. The dynamics of 2b are assigned to formation of an initial set of photoproducts, which were a mixture of excited-state tricarbonyl isomers. These isomers decay into another set of long-lived photoproducts in which approximately half the excited-state tricarbonyl isomers recombine with CO to form another complex mixture of tricarbonyl and tetracarbonyl isomers.

Theoretical investigation of aerobic and anaerobic oxidative inactivation of the [NiFe]-hydrogenase active site

The extraordinary capability of [NiFe]-hydrogenases to catalyse the reversible interconversion of protons and electrons into dihydrogen (H₂) has stimulated numerous experimental and theoretical studies addressing the direct utilization of these enzymes in H₂ production processes.

Reaction Coordinate Leading to H2 Production in [FeFe]-Hydrogenase Identified by Nuclear Resonance Vibrational Spectroscopy and Density Functional Theory

[FeFe]-hydrogenases are metalloenzymes that reversibly reduce protons to molecular hydrogen at exceptionally high rates. We have characterized the catalytically competent hydride state (Hhyd) in the [FeFe]-hydrogenases from both Chlamydomonas reinhardtii and Desulfovibrio desulfuricans using 57Fe nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT). H/D exchange identified two Fe-H bending modes originating from the binuclear iron cofactor. DFT calculations show that these spectral features result from an iron-bound terminal hydride, and the Fe-H vibrational frequencies being highly dependent on interactions between the amine base of the catalytic cofactor with both hydride and the conserved cysteine terminating the proton transfer chain to the active site. The results indicate that Hhyd is the catalytic state one step prior to H2 formation. The observed vibrational spectrum, therefore, provides mechanistic insight into the reaction coordinate for H2 bond formation by [FeFe]-hydrogenases.

Interplay of hemilability and redox activity in models of hydrogenase active sites

The hydrogen evolution reaction, as catalyzed by two electrocatalysts [M(N₂S₂)·Fe(NO)₂]⁺, [Fe-Fe]⁺ (M = Fe(NO)) and [Ni-Fe]⁺ (M = Ni) was investigated by computational chemistry. As nominal models of hydrogenase active sites, these bimetallics feature two kinds of actor ligands: Hemilabile, MN₂S₂ ligands and redox-active, nitrosyl ligands, whose interplay guides the H₂ production mechanism. The requisite base and metal open site are masked in the resting state but revealed within the catalytic cycle by cleavage of the MS-Fe(NO)₂ bond from the hemilabile metallodithiolate ligand. Introducing two electrons and two protons to [Ni-Fe]⁺ produces H₂ from coupling a hydride temporarily stored on Fe(NO)₂ (Lewis acid) and a proton accommodated on the exposed sulfur of the MN₂S₂ thiolate (Lewis base). This Lewis acid-base pair is initiated and preserved by disrupting the dative donation through protonation on the thiolate or reduction on the thiolate-bound metal. Either manipulation modulates the electron density of the pair to prevent it from reestablishing the dative bond. The electron-buffering nitrosyl's role is subtler as a bifunctional electron reservoir. With more nitrosyls as in [Fe-Fe]⁺, accumulated electronic space in the nitrosyls' π*-orbitals makes reductions easier, but redirects the protonation and reduction to sites that postpone the actuation of the hemilability. Additionally, two electrons donated from two nitrosyl-buffered irons, along with two external electrons, reduce two protons into two hydrides, from which reductive elimination generates H₂.

Electronic and molecular structure relations in diiron compounds mimicking the [FeFe]-hydrogenase active site studied by X-ray spectroscopy and quantum chemistry

Synthetic diiron compounds of the general formula Fe₂(μ-S₂R)(CO)_n(L)_6-n (R = alkyl or aromatic groups; L = CN^- or phosphines) are versatile models for the active-site cofactor of hydrogen turnover in [FeFe]-hydrogenases. A series of 18 diiron compounds, containing mostly a dithiolate bridge and terminal ligands of increasing complexity, was characterized by X-ray absorption and emission spectroscopy in combination with density functional theory. Fe K-edge absorption and Kβ main-line emission spectra revealed the varying geometry and the low-spin state of the Fe(i) centers. Good agreement between experimental and calculated core-to-valence-excitation absorption and radiative valence-to-core-decay emission spectra revealed correlations between spectroscopic and structural features and provided access to the electronic configuration. Four main effects on the diiron core were identified, which were preferentially related to variation either of the dithiolate or of the terminal ligands. Alteration of the dithiolate bridge affected mainly the Fe-Fe bond strength, while more potent donor substitution and ligand field asymmetrization changed the metal charge and valence level localization. In contrast, cyanide ligation altered all relevant properties and, in particular, the frontier molecular orbital energies of the diiron core. Mutual benchmarking of experimental and theoretical parameters provides guidelines to verify the electronic properties of related diiron compounds.

Understanding the CO Dissociation in [Fe(CN)2(CO)2(dithiolate)]2- Complexes with Quantum Chemical Topology Tools

The active site of the [NiFe]-hydrogenase contains a pentacoordinated iron atom; therefore, a vacant coordination site is available for substrate binding. Nonetheless, most organometallic models of the [NiFe]-hydrogenase failed to reproduce this key feature of the active site. In order to rationalize such behavior, quantum chemical calculations were carried out on a series of [Fe(CN)₂(CO)_n(dithiolate)]^2- n = 1,2 complexes, where dithiolate denotes the ligands (CF₃)₂C₂S₂^2-, (CO₂Me)₂C₂S₂^2-, Ph₂C₂S₂^2-, C₆Cl₂H₂S₂^2-, C₆H₄S₂^2-, C₂H₄S₂^2-, and C₃H₆S₂^2-. Structural and energetic features are discussed, and a topological analysis based on two scalar fields, the one-electron density and the electron localization function (ELF), has been attempted to describe the nature of the metal-ligand bonds. The present approach contributes to better understand the ability of noninnocent dithiolene to strongly labilize one CO whereas innocent dithiolate cannot. The methodology developed throughout the paper could be useful in the field of the CO-releasing molecules.

Cooperative Catalysis at Metal-Sulfur Bonds

Cooperative catalysis has attracted tremendous attention in recent years, emerging as a key strategy for the development of novel atom-economic and environmentally more benign catalytic processes. In particular, Noyori-type complexes with metal-nitrogen bonds have been extensively studied and evolved as privileged catalysts in hydrogenation chemistry. In contrast, catalysts containing metal-sulfur bonds as the reactive site are out of the ordinary, despite their abundance in living systems, where they are assumed to play a key role in biologically relevant processes. For instance, the heterolysis of dihydrogen catalyzed by [NiFe] hydrogenase is likely to proceed through cooperative H-H bond splitting at a polar nickel-sulfur bond. This Account provides an overview of reported metal-sulfur complexes that allow for cooperative E-H bond (E = H, Si, and B) activation and highlights the potential of this motif in catalytic applications. In recent years, our contributions to this research field have led to the development of a broad spectrum of synthetically useful transformations catalyzed by cationic ruthenium(II) thiolate complexes of type [(DmpS)Ru(PR₃)]⁺BAr^F₄^- (DmpS = 2,6-dimesitylphenyl thiolate, Ar^F = 3,5-bis(trifluoromethyl)phenyl). The tethered coordination mode of the bulky 2,6-dimesitylphenyl thiolate ligand is crucial, stabilizing the coordinatively unsaturated ruthenium atom and also preventing formation of binuclear sulfur-bridged complexes. The ruthenium-sulfur bond of these complexes combines Lewis acidity at the metal center and Lewis basicity at the adjacent sulfur atom. This structural motif allows for reversible heterolytic splitting of E-H bonds (E = H, Si, and B) across the polar ruthenium-sulfur bond, generating a metal hydride and a sulfur-stabilized E⁺ cation. Hence, this activation mode provides a new strategy to catalytically generate silicon and boron electrophiles. After transfer of the electrophile to a Lewis-basic substrate, the resulting neutral ruthenium(II) hydride can either act as a hydride donor (reductant) or as a proton acceptor (Brønsted base); the latter scenario is followed by dihydrogen release. On the basis of this concept, the tethered ruthenium(II) thiolate complexes emerged as widely applicable catalysts for various transformations, which can be categorized into (i) dehydrogenative couplings [Si-C(sp²), Si-O, Si-N, and B-C(sp²)], (ii) chemoselective reductions (hydrogenation and hydrosilylation), and (iii) hydrodefluorination reactions. All reactions are promoted by a single catalyst motif through synergistic metal-sulfur interplay. The most prominent examples of these transformations are the first catalytic protocols for the regioselective C-H silylation and borylation of electron-rich heterocycles following a Friedel-Crafts mechanism.

Quantum chemical approaches to [NiFe] hydrogenase

The mechanism by which [NiFe] hydrogenase catalyses the oxidation of molecular hydrogen is a significant yet challenging topic in bioinorganic chemistry. With far-reaching applications in renewable energy and carbon mitigation, significant effort has been invested in the study of these complexes. In particular, computational approaches offer a unique perspective on how this enzyme functions at an electronic and atomistic level. In this article, we discuss state-of-the art quantum chemical methods and how they have helped deepen our comprehension of [NiFe] hydrogenase. We outline the key strategies that can be used to compute the (i) geometry, (ii) electronic structure, (iii) thermodynamics and (iv) kinetic properties associated with the enzymatic activity of [NiFe] hydrogenase and other bioinorganic complexes.

Proton Transfer in the Catalytic Cycle of [NiFe] Hydrogenases: Insight from Vibrational Spectroscopy

Catalysis of H₂ production and oxidation reactions is critical in renewable energy systems based around H₂ as a clean fuel, but the present reliance on platinum-based catalysts is not sustainable. In nature, H₂ is oxidized at minimal overpotential and high turnover frequencies at [NiFe] catalytic sites in hydrogenase enzymes. Although an outline mechanism has been established for the [NiFe] hydrogenases involving heterolytic cleavage of H₂ followed by a first and then second transfer of a proton and electron away from the active site, details remain vague concerning how the proton transfers are facilitated by the protein environment close to the active site. Furthermore, although [NiFe] hydrogenases from different organisms or cellular environments share a common active site, they exhibit a broad range of catalytic characteristics indicating the importance of subtle changes in the surrounding protein in controlling their behavior. Here we review recent time-resolved infrared (IR) spectroscopic studies and IR spectroelectrochemical studies carried out in situ during electrocatalytic turnover. Additionally, we re-evaluate the significant body of IR spectroscopic data on hydrogenase active site states determined through more conventional solution studies, in order to highlight mechanistic steps that seem to apply generally across the [NiFe] hydrogenases, as well as steps which so far seem limited to specific groups of these enzymes. This analysis is intended to help focus attention on the key open questions where further work is needed to assess important aspects of proton and electron transfer in the mechanism of [NiFe] hydrogenases.

Direct Observation of an Iron-Bound Terminal Hydride in [FeFe]-Hydrogenase by Nuclear Resonance Vibrational Spectroscopy

[FeFe]-hydrogenases catalyze the reversible reduction of protons to molecular hydrogen with extremely high efficiency. The active site ("H-cluster") consists of a [4Fe-4S]H cluster linked through a bridging cysteine to a [2Fe]H subsite coordinated by CN- and CO ligands featuring a dithiol-amine moiety that serves as proton shuttle between the protein proton channel and the catalytic distal iron site (Fed). Although there is broad consensus that an iron-bound terminal hydride species must occur in the catalytic mechanism, such a species has never been directly observed experimentally. Here, we present FTIR and nuclear resonance vibrational spectroscopy (NRVS) experiments in conjunction with density functional theory (DFT) calculations on an [FeFe]-hydrogenase variant lacking the amine proton shuttle which is stabilizing a putative hydride state. The NRVS spectra unequivocally show the bending modes of the terminal Fe-H species fully consistent with widely accepted models of the catalytic cycle.

Catalytic Activity of Thiolate-Bridged Diruthenium Complexes Bearing Pendent Ether Moieties in the Oxidation of Molecular Dihydrogen

Thiolate-bridged diruthenium complexes bearing pendent ethers have been found to work as effective catalysts toward the oxidation of molecular dihydrogen into protons and electrons in water. The pendent ether moiety in the complex plays an important role to facilitate the proton transfer between the metal center and the external proton acceptor.

H2binding to the active site of [NiFe] hydrogenase studied by multiconfigurational and coupled-cluster methods

CCSD(T) and DMRG-CASPT2 calculations show that H₂prefers to bind to Ni rather than to Fe in [NiFe] hydrogenase.

Following [FeFe] Hydrogenase Active Site Intermediates by Time-Resolved Mid-IR Spectroscopy

Time-resolved nanosecond mid-infrared spectroscopy is for the first time employed to study the [FeFe] hydrogenase from Chlamydomonas reinhardtii and to investigate relevant intermediates of the enzyme active site. An actinic 355 nm, 10 ns laser flash triggered photodissociation of a carbonyl group from the CO-inhibited state Hox-CO to form the state Hox, which is an intermediate of the catalytic proton reduction cycle. Time-resolved infrared spectroscopy allowed us to directly follow the subsequent rebinding of the carbonyl, re-forming Hox-CO, and determine the reaction half-life to be t1/2 ≈ 13 ± 5 ms at room temperature. This gives direct information on the dynamics of CO inhibition of the enzyme.

Hydrogenase Enzymes and Their Synthetic Models: The Role of Metal Hydrides

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.

Mechanism of H2 Production by Models for the [NiFe]-Hydrogenases: Role of Reduced Hydrides

The intermediacy of a reduced nickel-iron hydride in hydrogen evolution catalyzed by Ni-Fe complexes was verified experimentally and computationally. In addition to catalyzing hydrogen evolution, the highly basic and bulky (dppv)Ni(μ-pdt)Fe(CO)(dppv) ([1](0); dppv = cis-C2H2(PPh2)2) and its hydride derivatives have yielded to detailed characterization in terms of spectroscopy, bonding, and reactivity. The protonation of [1](0) initially produces unsym-[H1](+), which converts by a first-order pathway to sym-[H1](+). These species have C1 (unsym) and Cs (sym) symmetries, respectively, depending on the stereochemistry of the octahedral Fe site. Both experimental and computational studies show that [H1](+) protonates at sulfur. The S = 1/2 hydride [H1](0) was generated by reduction of [H1](+) with Cp*2Co. Density functional theory (DFT) calculations indicate that [H1](0) is best described as a Ni(I)-Fe(II) derivative with significant spin density on Ni and some delocalization on S and Fe. EPR spectroscopy reveals both kinetic and thermodynamic isomers of [H1](0). Whereas [H1](+) does not evolve H2 upon protonation, treatment of [H1](0) with acids gives H2. The redox state of the "remote" metal (Ni) modulates the hydridic character of the Fe(II)-H center. As supported by DFT calculations, H2 evolution proceeds either directly from [H1](0) and external acid or from protonation of the Fe-H bond in [H1](0) to give a labile dihydrogen complex. Stoichiometric tests indicate that protonation-induced hydrogen evolution from [H1](0) initially produces [1](+), which is reduced by [H1](0). Our results reconcile the required reductive activation of a metal hydride and the resistance of metal hydrides toward reduction. This dichotomy is resolved by reduction of the remote (non-hydride) metal of the bimetallic unit.

Preparation and Protonation of Fe2(pdt)(CNR)6, Electron-Rich Analogues of Fe2(pdt)(CO)6

The complexes Fe2(pdt)(CNR)6 (pdt(2-) = CH2(CH2S(-))2) were prepared by thermal substitution of the hexacarbonyl complex with the isocyanides RNC for R = C6H4-4-OMe (1), C6H4-4-Cl (2), Me (3). These complexes represent electron-rich analogues of the parent Fe2(pdt)(CO)6. Unlike most substituted derivatives of Fe2(pdt)(CO)6, these isocyanide complexes are sterically unencumbered and have the same idealized symmetry as the parent hexacarbonyl derivatives. Like the hexacarbonyls, the stereodynamics of 1-3 involve both turnstile rotation of the Fe(CNR)3 as well as the inversion of the chair conformation of the pdt ligand. Structural studies indicate that the basal isocyanide has nonlinear CNC bonds and short Fe-C distances, indicating that they engage in stronger Fe-C π-backbonding than the apical ligands. Cyclic voltammetry reveals that these new complexes are far more reducing than the hexacarbonyls, although the redox behavior is complex. Estimated reduction potentials are E1/2 ≈ -0.6 ([2](+/0)), -0.7 ([1](+/0)), and -1.25 ([3](+/0)). According to DFT calculations, the rotated isomer of 3 is only 2.2 kcal/mol higher in energy than the crystallographically observed unrotated structure. The effects of rotated versus unrotated structure and of solvent coordination (THF, MeCN) on redox potentials were assessed computationally. These factors shift the redox couple by as much as 0.25 V, usually less. Compounds 1 and 2 protonate with strong acids to give the expected μ-hydrides [H1](+) and [H2](+). In contrast, 3 protonates with [HNEt3]BAr(F)4 (pKa(MeCN) = 18.7) to give the aminocarbyne [Fe2(pdt)(CNMe)5(μ-CN(H)Me)](+) ([3H](+)). According to NMR measurements and DFT calculations, this species adopts an unsymmetrical, rotated structure. DFT calculations further indicate that the previously described carbyne complex [Fe2(SMe)2(CO)3(PMe3)2(CCF3)](+) also adopts a rotated structure with a bridging carbyne ligand. Complex [3H](+) reversibly adds MeNC to give [Fe2(pdt)(CNR)6(μ-CN(H)Me)](+) ([3H(CNMe)](+)). Near room temperature, [3H](+) isomerizes to the hydride [(μ-H)Fe2(pdt)(CNMe)6](+) ([H3](+)) via a first-order pathway.

Models of the Ni-L and Ni-SIa States of the [NiFe]-Hydrogenase Active Site

A new class of synthetic models for the active site of [NiFe]-hydrogenases are described. The Ni(I/II)(SCys)2 and Fe(II)(CN)2CO sites are represented with (RC5H4)Ni(I/II) and Fe(II)(diphos)(CO) modules, where diphos = 1,2-C2H4(PPh2)2(dppe) or cis-1,2-C2H2(PPh2)2(dppv). The two bridging thiolate ligands are represented by CH2(CH2S)2(2-) (pdt(2-)), Me2C(CH2S)2(2-) (Me2pdt(2-)), and (C6H5S)2(2-). The reaction of Fe(pdt)(CO)2(dppe) and [(C5H5)3Ni2]BF4 affords [(C5H5)Ni(pdt)Fe(dppe)(CO)]BF4 ([1a]BF4). Monocarbonyl [1a]BF4 features an S = 0 Ni(II)Fe(II) center with five-coordinated iron, as proposed for the Ni-SIa state of the enzyme. One-electron reduction of [1a](+) affords the S = 1/2 derivative [1a](0), which, according to density functional theory (DFT) calculations and electron paramagnetic resonance and Mössbauer spectroscopies, is best described as a Ni(I)Fe(II) compound. The Ni(I)Fe(II) assignment matches that for the Ni-L state in [NiFe]-hydrogenase, unlike recently reported Ni(II)Fe(I)-based models. Compound [1a](0) reacts with strong acids to liberate 0.5 equiv of H2 and regenerate [1a](+), indicating that H2 evolution is catalyzed by [1a](0). DFT calculations were used to investigate the pathway for H2 evolution and revealed that the mechanism can proceed through two isomers of [1a](0) that differ in the stereochemistry of the Fe(dppe)CO center. Calculations suggest that protonation of [1a](0) (both isomers) affords Ni(III)-H-Fe(II) intermediates, which represent mimics of the Ni-C state of the enzyme.

Metal organic frameworks mimicking natural enzymes: a structural and functional analogy

In this review, we have portrayed the structure, synthesis and applications of a variety of biomimetic MOFs from an unprecedented angle.

Noncovalent interactions between the second coordination sphere and the active site of [NiFeSe] hydrogenase

QM/MM studies on seven truncated models of the oxidized as-isolated state of the [NiFeSe] Hases reveal the influence of the residues in the second coordination sphere on the active site.

DFT study of the mechanism of hydrogen evolution catalysed by molecular Ni, Co and Fe catalysts containing a diamine–tripyridine ligand

Electrolysis of water to obtain hydrogen is a practical way to transform surplus electrical power into clean and sustainable hydrogen fuels.

Why is a proton transformed into a hydride by [NiFe] hydrogenases? An intrinsic reactivity analysis based on conceptual DFT

The hydrogen evolution reaction (HER) catalysed by [NiFe] hydrogenases entails a series of chemical events involving great mechanistic interest.

Hydrogen evolution in [NiFe] hydrogenases and related biomimetic systems: similarities and differences

Schematic overview of the orbitals that play a role in the cycle of reversible hydrogen oxidation in [NiFe] hydrogenases.