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| 2. |
- Ballmann, Joachim, et al.
(författare)
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Secondary bonding interactions in biomimetic [2Fe-2S] clusters
- 2008
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 47:5, s. 1586-1596
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Tidskriftsartikel (refereegranskat)abstract
- A series of synthetic [2Fe-2S] complexes with terminal thiophenolate ligands and tethered ether or thioether moieties has been prepared and investigated in order to provide models for the potential interaction of additional donor atoms with the Fe atoms in biological [2Fe-2S] clusters. X-ray crystal structures have been determined for six new complexes that feature appended Et (1(C)), OMe (1(O)), or SMe (1(S)) groups, or with a methylene group (2(C)), an ether-O (2(O)), or an thioether-S (2(S)) linking two aryl group. The latter two systems provide a constrained chelate arrangement that induces secondary bonding interactions with the ether-O and thioether-S, which is confirmed by density functional theory (DFT) calculations that also reveal significant spin density on those fifth donor atoms. Structural consequences of the secondary bonding interactions are analyzed in detail, and effects on the spectroscopic and electronic properties are probed by UV-vis, Mossbauer, and H-1 NMR spectroscopy, as well by SQUID measurements and cyclic voltammetry. The potential relevance of the findings for biological [2Fe-2S] sites is considered.
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| 3. |
- Fuchs, Michael G. G., et al.
(författare)
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A combined computational and experimental investigation of the [2Fe-2S] cluster in biotin synthase
- 2010
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Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 1432-1327 .- 0949-8257. ; 15:2, s. 203-212
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Tidskriftsartikel (refereegranskat)abstract
- Biotin synthase was the first example of what is now regarded as a distinctive enzyme class within the radical S-adenosylmethionine superfamily, the members of which use Fe/S Clusters as the sulphur source in radical sulphur insertion reactions. The crystal structure showed that this enzyme contains a [2Fe-2S] cluster with a highly unusual arginine ligand, besides three normal cysteine ligands. However, the crystal structure is at such a low resolution that neither the exact coordination mode nor the role of this exceptional ligand has been elucidated yet, although it has been shown that it is not essential for enzyme activity. We have used quantum refinement of the crystal structure and combined quantum mechanical and molecular mechanical calculations to explore possible coordination modes and their influences on Cluster properties. The investigations show that the protonation state of the arginine ligand has little influence on cluster geometry, so even a positively charged guanidinium moiety would be in close proximity to the iron atom. Nevertheless, the crystallised enzyme most probably contains a deprotonated (neutral) arginine coordinating via the NH group. Furthermore, the Fe center dot center dot center dot Fe distance seems to be independent of the coordination mode and is in perfect agreement with distances in other structurally characterised [2Fe-2S] clusters. The exceptionally large Fe center dot center dot center dot Fe distance found in the crystal structure could not be reproduced.
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| 4. |
- Fuchs, Michael G G, et al.
(författare)
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A five-coordinate [2Fe-2S] cluster.
- 2010
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 49:13, s. 5853-5858
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Tidskriftsartikel (refereegranskat)abstract
- A unique [2Fe-2S] cluster (1) with genuinely five-coordinate ferric ions has been synthesized and investigated both structurally and spectroscopically. The crystal structure of 1 as well as (1)H NMR data reveal that 2,6-bis(imidazol-2-yl)pyridine binds to the [2Fe-2S] core as a tridentate capping ligand. DFT calculations showing spin density on all coordinating atoms support this finding. Cluster 1 has also been characterized by Mössbauer and UV/vis spectroscopy, mass spectrometry, cyclic voltammetry, and magnetic susceptibility measurements. Significant spectroscopic properties that make 1 distinct from conventional [2Fe-2S] clusters include a rather small quadrupole splitting of 0.43 mm/s.
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