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Institutes/ Institute of life sciences research and technologies (iRTSV)/ Laboratoire Chimie et Biologie des Métaux (LCBM)/ Biocatalysis/ Hydrogenases modelisation

Hydrogenases modelisation



Project leader
 
Dr. Vincent Artero
CEA research scientist
iRTSV/LCBM
CEA Grenoble
17 rue des martyrs
38 054 Grenoble cedex 09
Phone: (33) 4 38 78 91 06
Fax: (33) 4 38 78 91 24

Biography
 
Hydrogen Economy
 
Molecular hydrogen is widely considered as a convenient energy vector. Its combustion in a fuel-cell generates electricity with high yield and without any pollutant exhaust, water being the sole reaction product. However although hydrogen is one of the most abundant elements on the Earth, molecular hydrogen exists only as traces in the atmosphere and should thus be produced through processes that require an energy input.

In the perspective of a hydrogen economy, one major issue concerns the availability of economically viable methods for production of H2 from renewable sources.
Reduction of protons is apparently a very simple reaction but in fact requires multi-step catalysis. As a consequence, except on platinum metal electrodes, this reaction does not proceed at appreciable rates which is at the origin of overvoltages and significantly lowers the energetic yield of devices. In the long term replacement of platinum with inexpensive materials is critical to large-scale utilisation of hydrogen as a clean energy vector. An alternative to the use of platinum-loaded carbon as electrode material for this reaction is the combination of a common electrode material with a coordination complex able to catalyse the reaction at a reasonable potential, ie lower the overvoltage.
Another great challenge would consist in exploiting solar energy, mimicking in a way photosynthesis in plants, for the production of fuels such as hydrogen.

This research project is part of the BioHydrogen program of the CEA.
 
Hydrogenases and Biocatalysis
 

Nature widely utilises first-row transition metals in enzymes to catalyse difficult chemistry under ambient conditions. To date, no molecular system but hydrogenases proved to be effective catalysts for proton reduction or hydrogen oxidation.

H2 2H+ + 2e-

These enzymes are divided into two classes depending on the metal content at the active site. The structures of both classes have been recently published by Juan Fontecilla-Camps (figures below). [Fontecilla-Camps et al., Chem. Rev., 2007]



Figure 1: X-ray structure of the NiFe hydrogenase of the oxidised unready form of Desulfibrio fructosovorans (resolution: 1.83 Å, PDB code 1YQW). The iron atoms are depicted in purple, the nickel atom, in green, the sulfur atoms in yellow, the carbon atoms of the diatomic ligands in grey, the nitrogen atoms of cyanide ions in blue and the oxygen atom of the carbonyl and peroxo ligand in red.

Figure 2: Molecular structure of the active site of NiFe hydrogenases in the inactive oxidised (Ni-A and Ni-B) and active reduced (Ni-SI) forms.

In addition to classical Fe/S clusters, FeFe hydrogenases (figure 2) display an hexanuclear active site (H-cluster) constituted by a [4Fe-4S] cluster bound through a cystein-derived sulfur bridge to the [Fe2(µ2ν4-SRS)(CO)3(CN)2L] (R is proposed to be -CH2NHCH2-, L = H2O, H2 or H-) subsite. By contrast, NiFe hydrogenases enclose a dinuclear NiFe active centre (figure 2). In the reduced active state the nickel ion is only coordinated by four cysteinate residues, two of them also bridging an organometallic {Fe(CO)(CN)2} moiety. Both are electrochemically characterized by a quasi-nernstian behaviour [Jones AK et al., Chem. Comm., 2002; Parkin A et al., J. Am. Chem. Soc., 2007] making the enzymes themselves or chemical mimicks very attractive for biotechnological applications.
 
Chemical mimicks
 
This has prompted in the past decade the synthesis of a great variety of biomimetic complexes. Based on structural information of the enzyme metal centers, the synthetic analogue strategy, as defined by Holm [Ibers JA and Holm RH, Science, 1980], indeed allows defining the minimal structure required for a catalyst to achieve the biological function. The aim is both to better understand at the molecular level the catalytic mechanism of native hydrogenases and to develop new electrocatalysts to be used in fuel-cells for hydrogen uptake or in electrolytic/photosynthetic cells for hydrogen production. Significant synthetic achievements were achieved and the new biomimics of FeFe and NiFe hydrogenases show proton reduction activity: In our group, we focuss on NiFe hydrogenase modelisation. We have recently reported on the catalytic activity of a series of bio-inspired dinuclear nickel-ruthenium complexes (Figure 3) in which various electron-rich organometallic ruthenium moieties were introduced as subrogates for the {Fe(CO)(CN)2} fragment. DFT calculations on these systems are done in collaboration with the Modeling and Simulation group of Martin Field (IBS).





Figure 3: Top: cristallographic structure of the active site of NiFe hydrogenase and the model complex [Ni(xbsms)Ru(CO)2Cl2]. Bottom: electrocatalytic properties for H2 evolution in the presence of Et3NHCl in DMF on a glassy carbon electrode.
A purely structural approach may not be the most adequate one for the elaboration of highly active catalysts. It could be worth taking the problem from another angle, starting from an active or potentially active non-biomimetic system (different ligands, different metals) and introducing new structural or electronic properties inspired from the structure of the active sites of the enzymes.
 
   
Figure 2: [Co(dmgBF2)2L2] (L=H2O, CH3CN, left) and [Co(DO)(DOH)pn Br2] (right)

Cobaloxime is a class of such catalysts. We have reported on the activity of various cobaloximes as electrocatalysts for the reduction of protons in organic solvents and demonstrated that the active species is a CoIII–hydride formed by protonation of the CoI complex. The water-soluble {BF2}-bridged cobaloxime [Co(dmgBF2)2L] (L = CH3CN or DMF) (figure 4) which is quite stable under acidic conditions was shown to be the most efficient catalysts for hydrogen evolution in non-aqueous solvent in term of potential and turnover frequency. We recently discovered that diimine-dioxime complexes of cobalt (Figure 4, right) catalyze hydrogen evolution with similar performances. These new catalysts are significantly more stable against hydrolysis.This non-biomimetic approach will be deepened in the futur and widened to other families of catalysts.
Cobaloxime-Based Photocatalytic Devices for Hydrogen Production
 

Homogeneous light-driven catalytic systems for hydrogen production and, more generally, efficient photo-activated synthetic multi-electron catalysts remain relatively scarce. Such systems generally consist of
(i) a photosensitizer, often based on the ruthenium tris(diimine) moiety,
(ii) a metal-based catalytic center and in some cases
(iii) an additional redox mediator. However their efficiency remains to be improved in terms of both turnover numbers (stability) and turnover frequencies and these systems should use inexpensive first-row transition metal catalysts rather than unsustainable noble metals. We and others recently reported that cobaloximes are very efficient and cheap electrocatalysts for hydrogen evolution.

 We thus decided to couple cobaloximes with ruthenium tris(diimine) moieties in order to make a supramolecular variant of the system previously studied by Lehn et al for hydrogen photo-production [Lehn, Nouv. J. Chim., 1983, 7: 271]. In such a molecular device, the intramolecular electron-transfer from the photoactivated center to the catalytic center can potentially be controlled and the charge recombination processes limited, to an extent larger than in intermolecular systems, by a fine tuning of both the distance between metal centers and the nature of the bridge. Such an organized assembly is found in hydrogen-evolving green-algae where the photosystem I is tightly coupled to hydrogenase enzymes.
We have recently reported the synthesis and activity of a series of novel heterodinuclear ruthenium-cobaloxime photocatalysts able to achieve hydrogen photo-production with the highest turnover numbers so far reported for such devices. The influence of the stability, CoII/CoI redox potential and nucleophilicity of the cobaloxime moiety on the photocatalytic properties has been studiedd. Preliminary photophysical studies were carried out in collaboration with Winfried Leibl (Laboratoire de Photocatalyse et Biohydrogène, iBiTec-S/SB2SM, Saclay).



Figure 5: Structure of a Ruthenium-Cobalt supramolecular photocatalyst for H2 evolution.
 
Grafting Catalysts for Hydrogen production/Uptake on nanostructured electrodes
 
Incorporating the new synthetic catalysts in devices for hydrogen production/uptake is the final goal of this project. As stated in the introduction, the covalent grafting onto an electrode material such as carbon or the incorporation of catalyst into a polymer coating an electrode would lead to new electrocatalytic materials for hydrogen production or uptake.  We have developed an original strategy, combining the above biomimetic molecular approach with nanochemical tools and shown that the covalent attachment of a nickel-bisdiphosphine mimic of the active site of hydrogenase enzymes on carbon nanotubes results in a nickel-based cathode nanomaterial with remarkable performances under the strongly acidic conditions required in the expanding proton exchange membrane (PEM) technology. Hydrogen indeed evolves from aqueous sulphuric acid solution with very low overvoltages (20 mV) and exceptional stability (> 100,000 turnovers). Interestingly, this Pt-free catalyst is also very efficient for hydrogen oxidation under the same conditions with current densities similar to those observed for hydrogenase-based materials. These results have been accepted for publication in Science.
 
This research project has been initiated through the NanoSciences transversal program of the CEA and was carried out in collaboration with the Laboratory of Chemistry of Surfaces and Interfaces (Serge Palacin and Bruno Jousselme, Matter Science Division of the CEA, IRAMIS, SPCSI) and the Laboratory for Innovation in Energetic Technologies and Nanomaterials (Nicolas Guillet and Nicolas Bardi, LITEN/DTH/LCPEM).
 
Towards Artificial Hydrogenases
 
Hydrogen production catalyzed by bio-inspired catalysts is still associated with high overvoltages so that optimization need to be achieved. For that, it is crucial to better understand how the interactions with peptidic residues stabilize and beyond control the reactivity and catalytic activity of soft organometallic centers in aqueous solutions. In this perspective, a bio-synthetic approach, i.e using peptides or proteins as coordinates instead of synthetic ligands, is very attractive but remains to be investigated regarding the design of artificial hydrogenases.

In a first study, in collaboration with Christine Cavazza (IBS), we have investigated the reactivity of a variety of water-soluble iron, ruthenium and manganese carbonyl complexes towards lysozyme. This protein was selected on the basis of its reported ability to incorporate a {Ru(Ρ-cymene)}2+ center [McNae IW et al., Chem. Comm., 2004]. In most cases however, binding to lysozyme was not specific and no defined adduct could be isolated but we could purify and characterize, at the spectroscopic and structural level, a {Mn(CO)3}+ derivative of lysozyme. Furthermore, we have found that this compound is able to transfer the {Mn(CO)3}+ group to a nickel complex, thus forming a structural mimic of [NiFe] hydrogenases active site similar to the functional nickel-ruthenium electrocatalyst described above.



Figure 6: Structure of the covalent adduct [lysozyme-{MnI(CO)3}] and recativity with the nickel complex [Ni(xbsms)].
 
Publications
 

• Le Goff A, Moggia F, Debou N, Jegou P, Artero V, Fontecave M, Jousselme B and Palacin S
Facile and tunable functionalization of carbon nanotube electrodes with ferrocene by covalent coupling and [pi]-stacking interactions and their relevance to glucose bio-sensing.
Journal of Electroanalytical Chemistry, 2010, 641(1-2): 57-63

• Vaccaro L, Artero V, Canaguier S, Fontecave M and Field MJ
Mechanism of hydrogen evolution catalyzed by NiFe hydrogenases: Insights from a Ni-Ru model compound.
Dalton Transactions, 2010, 39(12): 3043-3049

• Jacques PA, Artero V, Pécaut J and Fontecave M
Cobalt and nickel diimine-dioxime complexes as molecular electrocatalysts for hydrogen evolution with low overvoltages.
Proceedings of the National Academy of Sciences USA, 2009, 106(49): 20627–20632

• Le Goff A, Artero V, Jousselme B, Dinh Tran P, Guillet N, Métayé R, Fihri A, Palacin S and Fontecave M
From hydrogenases to noble metal-free catalytic nanomaterials for H2 production and uptake.
Science, 2009, 326(5958): 1384-1387

• Canaguier S, Vaccaro L, Artero V, Ostermann R, Pecaut J, Field MJ and Fontecave M
Cyclopentadienyl ruthenium-nickel catalysts for biomimetic hydrogen evolution: Electrocatalytic properties and mechanistic DFT studies.
Chemistry A European Journal, 2009, 15(37): 9350-9364

• Oudart Y, Artero V, Norel L, Train C, Pécaut J and Fontecave M
Synthesis, crystal structure, magnetic properties and reactivity of a Ni-Ru model of NiFe hydrogenases with a pentacoordinated triplet (S = 1) NiII center.
Journal of Organometallic Chemistry, 2009, 694(17): 2866-2869

• Fihri A, Artero V, Pereira A and Fontecave M
Efficient H2-producing photocatalytic systems based on cyclometalated iridium- and tricarbonylrhenium-diimine photosensitizers and cobaloxime catalysts.
Dalton Transactions, 2008, (41): 5567-5569

• Canaguier S, Artero V and Fontecave M
Modelling NiFe hydrogenases: Nickel-based electrocatalysts for hydrogen evolution.
Dalton Transactions, 2008, 315-325

• Fihri A, Artero V, Razavet M, Baffert C, Leibl W and Fontecave M
Cobaloxime-based photocatalytic devices for hydrogen production.
Angewandte Chemie International Edition, 2008, 47(3): 564-567

• Razavet M, Artero V, Cavazza C, Oudart Y, Lebrun C, Fontecilla-Camps JC and Fontecave M
Tricarbonylmanganese(I)-lysosyme complex: A structurally characterized organometallic protein.
Chemical Communications, 2007, 2007(27): 2805-2807

• Oudart Y, Artero V, Pécaut J, Lebrun C and Fontecave M
Dinuclear nickel-ruthenium complexes as functional bio-inspired models of [NiFe] hydrogenases.
European Journal of Inorganic Chemistry, 2007, 18: 2613-2626
Cet article a fait la page de couverture d’une édition spéciale du European Journal of Inorganic Chemistry, « celebrating 10 years of excellence »

• Baffert C, Artero V and Fontecave M
Cobaloximes as functional models for hydrogenases. 2. Proton electroreduction catalyzed by difluoroborylbis(dimethylglyoximato)cobalt(II) complexes in organic media.
Inorganic Chemistry, 2007, 46: 1817-1824

• Oudart Y, Artero V, Pecaut J and Fontecave M
[Ni(xbsms)Ru(CO)2Cl2]: A bioinspired nickel-ruthenium functional model of [NiFe] hydrogenase.
Inorganic Chemistry, 2006, 45(11): 4334-4336

• Artero V and Fontecave M
Some general principles for designing electrocatalysts with hydrogenase activity.
Coordination Chemistry Review, 2005, 249(15-16): 1518-1535

• Razavet M, Artero V and Fontecave M
Proton electro-reduction catalyzed by cobaloximes: Functional models for hydrogenases
Inorganic Chemistry, 2005, 44(13): 4786-4795
 
PhD theses
 
• Sigolène Canaguier.
Modelling the active site of NiFe hydrogenases: new catalysts for the electro-production of H2 and mechanistic studies. (24 septembre 2009, Université Joseph Fourier)
[Abstract] - [Thesis on line]

• Yohan Oudart.
Modèles structuraux et fonctionnel du site actif des hydrogénases [NiFe] : de nouveaux catalyseurs bio-inspirés pour la production d'hydrogène. (28 septembre 2006, Université Joseph Fourier)
[Abstract] - [Thesis on line]