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Nitric Oxide Reactivity and Unusual Redox Properties of Biomimetic Iron-Sulfur Clusters with Alternative Cluster Ligands

Christine Elisabeth Schiewer
Doctoral thesis
Date of Examination: 2018-02-23
Date of issue: 2018-05-02
Advisor: Meyer, Franc Prof. Dr.
Referee: Meyer, Franc Prof. Dr.
Referee: Tittmann, Kai Prof. Dr.
Referee: Siewert, Inke Prof. Dr.
Referee: Demir, Selvan Prof. Dr.
Referee: Thomas, Franziska Dr.
Referee: Otte, Matthias Dr.

Persistent Address: http://hdl.handle.net/11858/00-1735-0000-002E-E3D3-F

 

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Abstract

English

This work describes the nitrosylation of biomimetic [2Fe–2S] clusters with phenylbis(benzimidazol-2-yl)methane or benzimidazolthiophenol ligands in different iron oxidation states and ligand protonation states. Mixed-valent clusters are oxidized to diferric clusters in the presence of nitric oxide before they further react to form dinitrosyl iron complexes (DNICs). The reaction was monitored by UV-vis and IR spectroscopy and the reaction products were characterized by X-ray diffraction, EPR, and Mössbauer spectroscopy. Protonation studies of the DNICs supported by DFT calculations were possible due to proton-responsive ligand sites on the benzimidazole moiety and they revealed significant IR spectroscopic changes for the NO ligands. Furthermore, a cubane-type [4Fe–4S] cluster is presented in which the coordination number of one iron atom depends on the counterion according to X-ray crystallography and Mössbauer spectroscopy. Oxidation of the cluster was studied by a series of analytical techniques indicating a similar change of the coordination number. Finally, 5,6-Dithia-1,10-phenanthroline was investigated as potential ligand for [2Fe–2S] clusters. As shown in electrochemical experiments, the ligand can be employed as disulfide/dithiol switch. A proton induced shift of the reductive wave was seen in cyclic voltammetry and the S–S bond cleavage mechanism switches from EEC to ECE(C).
Keywords: bioinorganic chemistry; iron-sulfur clusters; nitric oxide; dinitrosyl iron complexes; DNIC; disulfide/dithiol switch
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