| 1. |
- Bruschi, Maurizio, et al.
(författare)
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A DFT investigation on structural and redox properties of a synthetic Fe6S6 assembly closely related to the [FeFe]-hydrogenases active site
- 2008
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Ingår i: Comptes Rendus. Chimie. - : Elsevier BV. - 1631-0748. ; 11:8, s. 834-841
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Tidskriftsartikel (refereegranskat)abstract
- In the present contribution, a density functional theory (DFT) investigation is described regarding a recently synthesized Fe6S6 complex - see C. Tard, X. Liu, S.K. Ibrahim, M. Bruschi, L. De Gioia, S.C. Davies, X. Yang, L.-S. Wang, G. Sawers, C.J. Pickett, Nature 433 (2005) 610 - that is structurally and functionally related to the [FeFe]-hydrogenases active site (the so-called H-cluster, which includes a binuclear subsite directly involved in catalysis and an Fe4S4 cubane). The analysis of relative stabilities and atomic charges of different isomers evidenced that the structural and redox properties of the synthetic assembly are significantly different from those of the enzyme active site. A comparison between the hexanuclear cluster and simpler synthetic diiron models is also described; the results of such a comparison indicated that the cubane moiety can favour the stabilization of the cluster in a structure closely resembling the H-cluster geometry when the synthetic Fe6S6 complex is in its dianionic state. However, the opposite effect is observed when the synthetic cluster is in its monoanionic form.
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| 2. |
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| 3. |
- Greco, Claudio, et al.
(författare)
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A QM/MM investigation of the activation and catalytic mechanism of Fe-only hydrogenases
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 46:15, s. 5911-5921
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Tidskriftsartikel (refereegranskat)abstract
- Fe-only hydrogenases are enzymes that catalyze dihydrogen production or oxidation, due to the presence of an unusual Fe6S6 cluster (the so-called H-cluster) in their active site, which is composed of a Fe2S2 subsite, directly involved in catalysis, and a classical Fe4S4 cubane cluster. Here, we present a hybrid quantum mechanical and molecular mechanical (QM/MM) investigation of the Fe-only hydrogenase from Desulfovibrio desulfuricans, in order to unravel key issues regarding the activation of the enzyme from its completely oxidized inactive state (H-ox(inac)) and the influence of the protein environment on the structural and catalytic properties of the H-cluster. Our results show that the Fe2S2 subcluster in the (FeFeII)-Fe-II redox statewhich is experimentally observed for the completely oxidized form of the enzymebinds a water molecule to one of its metal centers. The computed QM/MM energy values for water binding to the diferrous subsite are in fact over 70 kJ mol(-1); however, the affinity toward water decreases by 1 order of magnitude after a one-electron reduction of H-ox(inact), thus leading to the release of coordinated water from the H-cluster. The investigation of a catalytic cycle of the Fe-only hydrogenase that implies formation of a terminal hydride ion and a di(thiomethyl)amine (DTMA) molecule acting as an acid/base catalyst indicates that all steps have reasonable reaction energies and that the influence of the protein on the thermodynamic profile of H-2 production catalysis is not negligible. QM/MM results show that the interactions between the Fe2S2 subsite and the protein environment could give place to structural rearrangements of the H-cluster functional for catalysis, provided that the bidentate ligand that bridges the iron atoms in the binuclear subsite is actually a DTMA residue.
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| 4. |
- Greco, Claudio, et al.
(författare)
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Structural insights into the active-ready form of [FeFe]-Hydrogenase and mechanistic details of its inhibition by carbon monoxide
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 46:18, s. 7256-7258
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe]-Hydrogenases harbor a {2Fe3S} assembly bearing two CO and two CN- groups, a mu-CO ligand, and a vacant coordination site trans to the mu-CO group. Recent theoretical results obtained studying the isolated {2Fe3S} subsite indicated that one of the CN- ligands can easily move from the crystallographic position to the coordination site trans to the mu-CO group; such an isomerization would have a major impact on substrates and inhibitors binding regiochemistry and, consequently, on the catalytic mechanism. To shed light on this crucial issue, we have carried out hybrid QM/MM and free energy perturbation calculations on the whole enzyme, which demonstrate that the protein environment plays a crucial role and maintains the CN- group fixed in the position observed in the crystal structure; these results strongly support the hypothesis that the vacant coordination site trans to the mu-CO group has a crucial functional relevance both in the context of CO-mediated inhibition of the enzyme and in dihydrogen oxidation/evolution catalysis.
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