| 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. |
- Eilers, Gerriet, et al.
(författare)
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Ligand versus metal protonation of an iron hydrogenase active site mimic
- 2007
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 13:25, s. 7075-7084
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Tidskriftsartikel (refereegranskat)abstract
- The protonation behavior of the iron hydrogenase active-site mimic [Fe2(u-adt)(CO)4(PMe3)2] (1; adt=N-benzyl-azadithiolate) has been investigated by spectroscopic, electrochemical, and computational methods. The combination of an adt bridge and electron-donating phosphine ligands allows protonation of either the adt nitrogen to give [Fe2(μ-Hadt)(CO)4(PMe3)2]+ ([1H]+), the Fe-Fe bond to give [Fe2-(μ-adt)(μ-H)(CO)4(PMe3)2]+ ([1Hy]+), or both sites simultaneously to give [Fe2(μ-Hadt)(μ-H)(CO)4(PMe3)2]2+ ([1HHy]2+). Complex 1 and its protonation products have been characterized in acetonitrile solution by IR, 1H, and 31PNMR spectroscopy. The solution structures of all protonation states feature a basal/basal orientation of the phosphine ligands, which contrasts with the basal/apical structure of 1 in the solid state. Density functional calculations have been performed on all protonation states and a comparison between calculated and experimental spectra confirms the structural assignments. The ligand protonated complex [1H]+ (pKa =12) is the initial, metastable protonation product while the hydride [1Hy]+ (pKa=15) is the thermodynamically stable singly protonated form. Tautomerization of cation [1H]+ to [1Hy]+ does not occur spontaneously. However, it can be catalyzed by HCl (k=2.2M-1s-1), which results in the selective formation of cation [1Hy]+. The protonations of the two basic sites have strong mutual effects on their basicities such that the hydride (pKa=8) and the ammonium proton (pKa=5) of the doubly protonated cationic complex [1HHy]2+ are considerably more acidic than in the singly protonated analogues. The formation of dication [1HHy]2+ from cation [1H]+ is exceptionally slow with perchloric or trifluoromethanesulfonic acid (k= 0.15 M-1s-1), while the dication is formed substantially faster (k > 102 M-1 s-1) with hydrobromic acid. Electrochemically, 1 undergoes irreversible reduction at -2.2V versus ferrocene, and this potential shifts to -1.6, - 1.1, and -1.0 V for the cationic complexes [1H]+, [1Hy]+, and [1HHy]2+, respectively, upon protonation. The doubly protonated form [1HHy]2+ is reduced at less negative potential than all previously reported hydrogenase models, although catalytic proton reduction at this potential is characterized by slow turnover.
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