Ein synthetisches Analogon für [2Fe‐2S]‐Cluster des Rieske‐Typs

Ballmann, Joachim; Albers, Antonia; Demeshko, Serhiy; Dechert, Sebastian; Bill, Eckhard; Bothe, Eberhard; Ryde, Ulf; Meyer, Franc

doi:10.1002/ange.200803418

Cited by 17 publications

(16 citation statements)

References 46 publications

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“…Diferric (NEt 4 ) 2 5 was synthesized via a stepwise ligand exchange reaction starting from the tetrachloro-coordinated [2Fe-2S] cluster (NEt 4 ) 2 [Cl 2 FeS 2 FeCl 2 ], in close analogy to the synthesis of the first structural Rieske model (NEt 4 ) 2 1 . 11 To this end, phenylbis(benzimidazolyl)methane was first deprotonated with KH and then added to a solution of (NEt 4 ) 2 [Cl 2 FeS 2 FeCl 2 ] in MeCN at −30°C to furnish the {N 2 } cap. 1,1′-biphenyl-2,2′-dithiolate, after deprotonation with KH, was subsequently attached as the {S 2 } capping ligand.…”

Section: Resultsmentioning

confidence: 99%

“…24 Therefore the value g av = 1.935 reflects increased valence localization in 5 3 − compared to the synthetic homoleptic {N 2 /N 2 } analogues 2 3 − ( g av = 1.940 in DMF/0.25 M n BuNClO 4 , 77 K) 12 and 4 3 − ( g av = 1.951 in DMF, 6 K), 13 but electron localization is less pronounced than in 1 3 − ( g av = 1.918). 11 …”

Section: Resultsmentioning

confidence: 99%

“…The present new model system is only the second synthetic analogue emulating the heteroleptic ligation of the Rieske cofactor, 11 and the first that features a biomimetic {His 2 Cys 2 }-like ligation amenable to PCET at the N-coordinated subsite of the [2Fe-2S] cluster. It thus represents an excellent structural, spectroscopic and functional analogue, and it is the highest fidelity Rieske model known so far.…”

Section: Discussionmentioning

confidence: 99%

“…In 2008 we reported the first (and so far only) synthetic [2Fe-2S] cluster that emulates the heteroleptic {S 2 /N 2 } ligation characteristic for the biological site, (NEt 4 ) 2 1 (Figure 1, left). 11 While (NEt 4 ) 2 1 is an excellent structural and spectroscopic Rieske model in both the diferric as well as mixed-valent states (Mössbauer and EPR, respectively), the reduced mixed-valence species proved quite unstable and the lack of peripheral N atoms at the bis(indol) ligand in (NEt 4 ) 2 1 precluded any functional studies towards proton-coupled electron transfer (PCET).…”

Section: Introductionmentioning

confidence: 99%

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Fast Proton-Coupled Electron Transfer Observed for a High-Fidelity Structural and Functional [2Fe–2S] Rieske Model

et al. 2014

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Rieske cofactors have a [2Fe–2S] cluster with unique {His2Cys2} ligation and distinct Fe subsites. The histidine ligands are functionally relevant, since they allow for coupling of electron and proton transfer (PCET) during quinol oxidation in respiratory and photosynthetic ET chains. Here we present the highest fidelity synthetic analogue for the Rieske [2Fe–2S] cluster reported so far. This synthetic analogue 5x– emulates the heteroleptic {His2Cys2} ligation of the [2Fe–2S] core, and it also serves as a functional model that undergoes fast concerted proton and electron transfer (CPET) upon reaction of the mixed-valent (ferrous/ferric) protonated 5H2– with TEMPO. The thermodynamics of the PCET square scheme for 5x– have been determined, and three species (diferric 52–, protonated diferric 5H–, and mixed-valent 53–) have been characterized by X-ray diffraction. pKa values for 5H– and 5H2– differ by about 4 units, and the reduction potential of 5H– is shifted anodically by about +230 mV compared to that of 52–. While the N–H bond dissociation free energy of 5H2– (60.2 ± 0.5 kcal mol–1) and the free energy, ΔG°CPET, of its reaction with TEMPO (−6.3 kcal mol–1) are similar to values recently reported for a homoleptic {N2/N2}-coordinated [2Fe–2S] cluster, CPET is significantly faster for 5H2– with biomimetic {N2/S2} ligation (k = (9.5 ± 1.2) × 104 M–1 s–1, ΔH‡ = 8.7 ± 1.0 kJ mol–1, ΔS‡ = −120 ± 40 J mol–1 K–1, and ΔG‡ = 43.8 ± 0.3 kJ mol–1 at 293 K). These parameters, and the comparison with homoleptic analogues, provide important information and new perspectives for the mechanistic understanding of the biological Rieske cofactor.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fast Proton-Coupled Electron Transfer Observed for a High-Fidelity Structural and Functional [2Fe–2S] Rieske Model

et al. 2014

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“…The QM calculations were performed using the BP86 functional [24, 25] and the def2-SV(P) basis sets [26], which have given reasonable results for [2Fe–2S] clusters in previous calculations [18, 27]. For the MM calculations, we used the Amber-99 force field [28, 29].…”

Section: Methodsmentioning

confidence: 99%

A combined computational and experimental investigation of the [2Fe–2S] cluster in biotin synthase

2009

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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···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···Fe distance found in the crystal structure could not be reproduced.

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Die vollständige Charakterisierung eines reduzierten biomimetischen [2 Fe‐2 S]‐Clusters

Albers¹,

Demeshko²,

Dechert³

et al. 2011

Angewandte Chemie

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Den Zuständen auf den Grund gegangen: Ein biomimetischer [2 Fe‐2 S]‐Cluster wurde im [Fe3+Fe3+]‐ und [Fe2+Fe3+]‐ Zustand strukturell charakterisiert. Der [2 Fe‐2 S]‐Kerns bleibt bei der Reduktion nahezu unverändert. Die gemischtvalente Form hat einen S=1/2‐Grundzustand, wobei das ungepaarte Elektron teilweise über den Clusterkern delokalisiert ist. Die experimentell bestimmte effektive Kopplungskonstante ermöglicht die Vorhersage der Lage der Intervalenzbande im IR‐Bereich.

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Ein synthetisches Analogon für [2Fe‐2S]‐Cluster des Rieske‐Typs

Cited by 17 publications

References 46 publications

Fast Proton-Coupled Electron Transfer Observed for a High-Fidelity Structural and Functional [2Fe–2S] Rieske Model

Fast Proton-Coupled Electron Transfer Observed for a High-Fidelity Structural and Functional [2Fe–2S] Rieske Model

A combined computational and experimental investigation of the [2Fe–2S] cluster in biotin synthase

Die vollständige Charakterisierung eines reduzierten biomimetischen [2 Fe‐2 S]‐Clusters

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