A hydrogenase mimic or bio-mimetic is an enzyme mimic of hydrogenases.

Bio-mimetic compounds inspired in hydrogenases

One of the more interesting applications of hydrogenases is to produce hydrogen, due its capacity to catalyze its redox reaction:

2H+ + 2e− ----> H2

In the field of hydrogen production, the incorporation of chemical compounds in electrochemical devices to produce molecular hydrogen has been a topic of huge interest in the recent years due to the possibility of using hydrogen as a replacement of the fossil fuels as an energetic carrier. This approach of using materials inspired by natural models to do the same function as their natural counterparts is called bio-mimetic approach. Nowadays this approach has received a big impulse due to the availability of high-resolution crystal structures of several hydrogenases obtained with different techniques. The technical details of these hydrogenases are stored in electronic databases at disposition to who may be interested.

This information has allowed to determine the important parts of the enzyme necessary to catalyze the reaction and determine the pathway of the reaction in a very detailed way. Which allow to have a very good comprehension of what is necessary to catalyze the same reaction using artificial components.

Examples of bio-mimetic compounds inspired in hydrogenase

Several studies have demonstrated the possibility to develop chemical cells inspired by biological models to produce molecular hydrogen, for example: Selvaggi et al.[1] explored the possibility to use energy captured by the PSII, developing for that goal, an organic-inorganic hybrid system replacing the PSII protein complex by microspheres of TiO2 a photo-inducible compound. In order to get the hydrogen production, the TiO2 microspheres were covered with hydrogenases extracted from the marine thermophile Pyrococcus furiosus, in that way the energy of the light was captured by the TiO2 microspheres and used to generate protons and electrons from water with the subsequent production of 29 µmol de H2 hour−1.

The obtained results from immobilization of hydrogenases on the surface of electrodes have demonstrated the viability of incorporating these enzymes in electrochemical cells, due to their ability to produce gaseous hydrogen through a redox reaction. (Hallenbeck and Benemann[2]). This opens the possibility of using biomimetic compounds in electrodes to generate hydrogen.

Until the present day several bio-mimetic compounds have been developed: Collman et al.[3] produced ruthenium porphyrins, furthermore of the bio-mimetic compounds published by the research teams of Rauchfuss, Darensbourg and Pickett (in Artero and Fontecave[4]) who developed bio-mimetic compounds of the [Fe] hydrogenase. More recently Manor and Rauchfuss[5] presented a very interesting mimic compound based in the [NiFe] hydrogenase with bidirectional properties, this compound has the characteristic that it carries two borane protected cyanide ligands at the iron atom. Some works about bio-mimetic compounds of hydrogenases are summarized in table 1.

Biomimetic compound Hydrogen production Electron donor Reference
Bis(thiolate)-bridged diiron ([2Fe2S]) 0.22 (30%) Kluwer et al.[6]
2-aza-1,3-dithiol

Bridged Fe-dimer

complexes

 Sun et al.[7]
[MnRe(CO)6(m-S2CPR3)] Zhao et al.[8]
Polymer (Poly-{Fe2}) functionalized with {Fe2(CO)6} Liu et al.[9]
Diiron dithiolate complexes with 3,7-diacetyl-1,3,7-triaza-5 phosphabicyclo[3.3.1]nonane ligand(s) Na et al.[10]
Enzyme electrodes, [NiFe] hydrogenases 9-30 (nmol min−1) methyl viologen or water Morozov et al.[11]
Hydrogenase in a two-compartment proton-exchange-membrane (PEM) Sodium dithionite (SD) Oh et al.[12]
Pt-clusters deposited on the interior of a heat shock protein cage architecture 268 H2/Pt/min, methyl viologen Varpness. et al.[13]
Hydrogenase immobilization, on porous pyrolytic carbon paper (PCP) and packed graphite

columns (PGC)

 Johnston et al.[14]
Fe2(CO)6(l-ADT) (ADT = azadithiolate) Constable et al.[15]
[Fe2(CO)6(H3COCH(CH2S)2)] and [Fe2(CO)6(HOC(CH3)(CH2S)2)]. Apfel et al.[16]
Dithiolate-bridged hexacarbonyldiiron complex Goff et al.[17]
m-(SCH(CH3)CH2S)eFe2(CO)6,

m-(SCH(CH3)CH(CH3)S)eFe2(CO)6, m-(SCH2CH(CH2OH)S)eFe2(CO)6,

 Donovan et al.[18]
A series of mononuclear NiII and binuclear NiIINiII macrocyclic complexes: [NiLi(H2O)] 2H2O Martin et al.[19]
[Fe2(CO)3(l-pdt){l,g2-Ph2PCH2CH2P(Ph)CH2CH2PPh2}] Hogarth and Richards[20]
Di-iron model complexes (l-pdt)Fe2(CO)5L with L = pyridine ligands, e.g. py (A), etpy (B), btpy (C), Zhang et al.[21]

Table 1. Bio-mimetic compounds of hydrogenases

However, obtaining bio-mimetic compounds able to hydrogen production on an industrial scale still is elusive. For that reason, the research of this topic is a hot spot in science which has taken the efforts of researchers around the world. Recently a review of the works done in bio-mimetic compounds was published by Schilter et al..[22] Showing that some studies have got promising results in bio-mimetic compounds synthesized in laboratory.

Molecular modeling of bio-mimetic compounds of hydrogenases assisted with software

Recently the possibility of study such compounds using molecular modeling assisted by informatic software has opened new possibilities in the study of the redox reaction of biomimetic compounds. For example, using "Density Functional Theory" (DFT) computer modeling made it possible to propose a catalytic pathway of H2 binding on the catalytic center of hydrogenase (Greco[23]). Other example of the application of computational modeling in the study of hydrogenases is the work done by Breglia et al.,[24] whose results shows the chemical pathway of how oxygen inhibited the redox reaction of [NiFe] hydrogenases.

Bio-mimetic compounds inspired in [Fe] hydrogenases

The Fe-only hydrogenases are particularly common enzymes for synthetic organometallic chemists to mimic. This interest is motivated by the inclusion of high field ligands like cyano and CO (metal carbonyl) in the first coordination sphere of the pertinent di-iron cluster. Free cyano and carbonyl ligands are toxic to many biological systems. So, their inclusion in this system suggests they play pivotal roles. These high field ligands may ensure the iron centers at the active site remain in a low spin state throughout the catalytic cycle. In addition, there is bridging dithiolate between the two iron centers. This dithiolate has a three atom backbone in which the identity of the central atom is still undetermined; it models crystallographically as a CH2, NH or O group. There is reason to believe that this central atom is an amine which functions as a Lewis base. This amine combined with Lewis acidic iron centers makes the enzyme a bifunctional catalyst which can split hydrogen between a proton acceptor and a hydride acceptor or produce hydrogen from a proton and hydride.

Since none of the ligands on the iron centers are part of the enzyme's amino acid backbone, they can not be investigated through site-directed mutagenesis, but enzyme mimicry is a feasible approach.

Breadth

Many elegant structural mimics have been synthesized reproducing the atomic content and connectivity of the active site.[25] The work by Pickett is a prime example of this field.[26] The catalytic activity of these mimics do not however compare to the native enzyme. In contrast, functional mimics, also known as bio-inspired catalysts, aim to reproduce only the functional features of an enzyme often through the use of different atomic content and connectivity from that found in the native enzymes. Functional mimics have made advances in the reactive chemistry and have implications on the mechanistic activity of the enzyme as well as acting as catalysts in their own right.[27][28][29]

References

  1. ↑ Selvaggi, A; Barberini, U; Franchi, E; Rodriguez, F; Pedroni, P (1999). "In vitro hydrogen photoproduction using Pyrococcus furiosus sulfhydrogenase and TiO2". Journal of Photochemistry and Photobiology. 125 (1–3): 107–112. doi:10.1016/S1010-6030(99)00088-X.
  2. ↑ Hallenbeck, P; Benemann, J (2002). "Biological hydrogen production; fundamentals and limiting processes". Hydrogen Energy: 1185–1193.
  3. ↑ Collman, J; Wagenknecht, P; Lewis, N (1992). "Hydride transfer and dihydrogen elimination from osmium and ruthenium metalloporphyrin hydrides: model processes for hydrogenase enzymes and the hydrogen electrode reaction". Journal of the American Chemical Society. 14 (114): 5665–5674.
  4. ↑ Artero, V; Fontecave, S (2005). "Some general principles for designing electrocatalysts with hydrogenase activity". Coordination Chemistry Reviews. 249 (15–16): 1518–1535. doi:10.1016/j.ccr.2005.01.014.
  5. ↑ Manor, B; Rauchfuss, T (2013). "Hydrogen Activation by Biomimetic [NiFe]-Hydrogenase Model Containing Protected Cyanide Cofactors". Journal of the American Chemical Society. 135 (32): 11895–11900. doi:10.1021/ja404580r. PMC 3843950. PMID 23899049.
  6. ↑ Kluwer, A; Kaprea, F; Hartla, M; Lutzb, A; Spekb, A; Brouwera, P; Van Leeuwena, L; Reek, J (2008). "Self-assembled biomimetic [2Fe2S]-hydrogenasebased photocatalyst for molecular hydrogen evolution". Proceedings of the National Academy of Sciences of the United States of America. 26: 10460–10465.
  7. ↑ Sun, L; Ott, S; Kritikos, M; Akermark, B; Lomoth, R (2004). "A Novel Biomimetic Catalyst for Electrochemical Hydrogen Production". Preprints of Papers- American Chemical Society, Division of Fuel Chemistry. 1: 109–111.
  8. ↑ Zhao, J; Ma, Y; Bai, Z; Chang, W; Li, J (2012). "A new reactivity pattern of heterodinuclear complexes [MnRe(CO)6(m-S2CPR3)] with nBuLi/protonation and its electrochemistry properties investigation as structure and function models for the Fe only hydrogenase active site". Journal of Organometallic Chemistry. 716: 230–236. doi:10.1016/j.jorganchem.2012.07.003.
  9. ↑ Liu, X; Ru, X; Li, Y; Zhang, K; Chen, D (2011). "A polyene-based polymer functionalized with a model of [FeFe]-hydrogenase and film electrodes assembled from the polymer via spin-coating". International Journal of Hydrogen Energy. 36 (16): 9612–9619. doi:10.1016/j.ijhydene.2011.05.095.
  10. ↑ Na, Y; Wang, M; Jin, K; Zhang, R; Sun, L (2006). "An approach to water-soluble hydrogenase active site models: Synthesis and electrochemistry of diiron dithiolate complexes with 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1] nonane ligand(s)". Journal of Organometallic Chemistry. 691 (23): 5045–5051. doi:10.1016/j.jorganchem.2006.08.082.
  11. ↑ Morozov, S; Vignais, P; Cournac, L; Zorin, N; Karyakina, A; Cosnier, S (2002). "Bioelectrocatalytic hydrogen production by hydrogenase electrodes". International Journal of Hydrogen Energy. 27 (11–12): 1501–1505. doi:10.1016/S0360-3199(02)00091-5.
  12. ↑ Oh, Y; Lee, Y; Choi, E; Kim, M (2008). "Bioelectrocatalytic hydrogen production using Thiocapsa roseopersicina hydrogenase in two-compartment fuel cells". International Journal of Hydrogen Energy. 33 (19): 5218–5223. doi:10.1016/j.ijhydene.2008.05.015.
  13. ↑ Varpness, Z; Peters, J; Young, M; Douglas, T (2005). "Biomimetic Synthesis of a H2 Catalyst Using a Protein Cage Architecture". Nano Letters. 11: 2306–2309.
  14. ↑ Johnston, W; Cooney, M; Liaw, B; Sapra, R; Adams, M (2005). "Design and characterization of redox enzyme electrodes: new perspectives on established techniques with application to an extremeophilic hydrogenase". Enzyme and Microbial Technology. 36 (4): 540–549. doi:10.1016/j.enzmictec.2004.11.016.
  15. ↑ Constable, C; Housecroft, C; Kokatam, S; Medlycott, A; Zampese, J (2010). "Fe-only hydrogenase active site mimics: Fe2(CO)6(l-ADT) (ADT = azadithiolate) clusters bearing pendant 2,20:60,200-terpyridine domains and containing alkynylthienylene or alkynylphenylene spacers". Inorganic Chemistry Communications. 13: 457–460. doi:10.1016/j.inoche.2009.06.003.
  16. ↑ Apfel, U; Kowol, C; Kloss, F; Gorls, H; Keppler, B; Weigand, W (2011). "Hydroxy and ether functionalized dithiolanes: Models for the active site of the [FeFe] hydrogenase". Journal of Organometallic Chemistry. 696 (5): 1084–1088. doi:10.1016/j.jorganchem.2010.09.048.
  17. ↑ Goff, A; Artero, V; Metaye, R; Moggia, F; Jousselme, B; Razavet, M; Tran, P; Palacin, S; Fontecave, M (2010). "Immobilization of FeFe hydrogenase mimics onto carbon and gold electrodes by controlled aryldiazonium salt reduction: An electrochemical, XPS and ATR-IR study". International Journal of Hydrogen Energy. 35 (19): 10790–10796. doi:10.1016/j.ijhydene.2010.02.112.
  18. ↑ Donovan, E; Nichol, G; Felton, G (2013). "Structural effects upon the durability of hydrogenase-inspired hydrogen-producing electrocatalysts: Variations in the (m-edt) [Fe2(CO)6] system". Journal of Organometallic Chemistry. 726: 9–13. doi:10.1016/j.jorganchem.2012.12.006.
  19. ↑ Martin, M; Vidotti, M; Souza, F (2012). "Synthesis, characterization and electrocatalysis of mono- and di-nickel tetraiminodiphenolate macrocyclic complexes as active site models of [NiFe]-hydrogenases". International Journal of Hydrogen Energy. 37 (19): 14094–14102. doi:10.1016/j.ijhydene.2012.06.118.
  20. ↑ Hogarth, G; Richards, I (2006). "Synthesis, crystal structure and protonation of the asymmetric iron-only hydrogenase model [Fe2(CO)3(l-pdt){l,g2-Ph2PCH2CH2P(Ph) CH2CH2PPh2}] (pdt = SCH2CH2CH2S)". Inorganic Chemistry Communications. 10: 66–70. doi:10.1016/j.inoche.2006.09.005.
  21. ↑ Zhang, Y; Hu, M; Wen, H; Si, T; Ma, C; Chen, C; Liu, Q (2009). "Terminal pyridine-N ligation at [FeFe] hydrogenase active-site mimic". Journal of Organometallic Chemistry. 694 (16): 2576–2580. doi:10.1016/j.jorganchem.2009.03.050.
  22. ↑ Schilter, D; Camara, J; Huynh, M; Hammes-Schiffer, S; Rauchfuss, T (2016). "Hydrogenase Enzymes and Their Synthetic Models: The Role of Metal Hydrides". Chemical Reviews. 116 (15): 8693–8749. doi:10.1021/acs.chemrev.6b00180. PMC 5026416. PMID 27353631.
  23. ↑ Geco, C (2013). "H2 Binding and Splitting on a New-Generation [FeFe]-Hydrogenase Model Featuring a Redox-Active Decamethylferrocenyl Phosphine Ligand: A Theoretical Investigation". Inorganic Chemistry. 52 (4): 1901–1908. doi:10.1021/ic302118h. PMID 23374093.
  24. ↑ Breglia, R; Ruiz‑Rodriguez, M; Vitriolo, A; Gonzàlez‑Laredo, R; De Gioia, L; Greco, C; Bruschi, M (2017). "Theoretical insights into [NiFe]‑hydrogenases oxidation resulting in a slowly reactivating inactive state". Journal of Biological Inorganic Chemistry. 22 (1): 137–151. doi:10.1007/s00775-016-1416-1. PMID 27873068.
  25. ↑ L Schwartz, G Eilers, L Eriksson, A Gogoll, R Lomoth and S Ott, Chem. Commun., 2006 doi:10.1039/b514280f
  26. ↑ Cédric Tard, Xiaoming Liu, Saad K. Ibrahim, Maurizio Bruschi, Luca De Gioia, Siân C. Davies, Xin Yang, Lai-Sheng Wang, Gary Sawers and Christopher J. Pickett Nature (10 Feb 2005) 433, 610 - 613.
  27. ↑ Wilson, A. D.; Newell, R. H.; McNevin, M. J.; Muckerman, J. T.; Rakowski DuBois, M.; DuBois, D. L. J. Am. Chem. Soc. 2006 128(1) 358-366.
  28. ↑ Hu, Xile; Cossairt, Brandi M.; Brunschwig, Bruce S.; Lewis, Nathan S.; Peters, Jonas C. Chem. Commun., 2005 37, 4723-4725.
  29. ↑ Baffert, Carole; Artero, Vincent; Fontecave, Marc. Inorganic Chemistry 2007 46(5), 1817-1824.
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