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S K-edge XAS of Cu^II, Cu^I, and Zn^II oxidized Dithiolene complexes: Covalent contributions to structure and the Jahn-Teller effect.

ABSTRACT: Reduced dithiolene ligands are bound to high valent Mo centers in the active site of the oxotransferase family of enzymes. Related model complexes have been studied with great insight by Prof. Holm and his colleagues. This study focuses on the other limit of dithiolene chemistry: an investigation of the 2-electron oxidized dithiolene bound to low-valent late transition metal (TM) ions (Zn^II, Cu^I, and Cu^II). The bonding descriptions of the oxidized dithiolene [N,N-dimethyl piperazine 2,3-dithione (Me₂Dt⁰)] complexes are probed using S K-edge X-ray absorption spectroscopy (XAS) and the results are correlated to density functional theory (DFT) calculations. These experimentally supported calculations are then extended to explain the different geometric structures of the three complexes. The Zn^II(Me₂Dt⁰)₂ complex has only ligand-ligand repulsion so it is stabilized at the D_2d symmetry limit. The Cu^I(Me₂Dt⁰)₂ complex has additional weak backbonding thus distorts somewhat from D_2d toward D_2h symmetry. The Cu^II(Me₂Dt⁰)₂ complex has a strong σ donor bond that leads to both a large Jahn-Teller stabilization to D_2h and an additional covalent contribution to the geometry. The combined strong stabilization results in the square planar, D_2h structure. This study quantifies the competition between the ligand-ligand repulsion and the change in electronic structures in determining the final geometric structures of the oxidized dithiolene complexes, and provides quantitative insights into the Jahn-Teller stabilization energy and its origin.

SUBMITTER: Ha Y

PROVIDER: S-EPMC9680909 | biostudies-literature | 2022 May

REPOSITORIES: biostudies-literature

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S K-edge XAS of CuII, CuI, and ZnII oxidized Dithiolene complexes: Covalent contributions to structure and the Jahn-Teller effect.

Ha Yang Y Dille Sara A SA Braun Augustin A Colston Kyle K Hedman Britt B Hodgson Keith O KO Basu Partha P Solomon Edward I EI

Journal of inorganic biochemistry 20220208

Reduced dithiolene ligands are bound to high valent Mo centers in the active site of the oxotransferase family of enzymes. Related model complexes have been studied with great insight by Prof. Holm and his colleagues. This study focuses on the other limit of dithiolene chemistry: an investigation of the 2-electron oxidized dithiolene bound to low-valent late transition metal (TM) ions (ZnII, CuI, and CuII). The bonding descriptions of the oxidized dithiolene [N,N ...[more]

PMID: 35202982

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Project description:The treatment of malignant cells that are deficient in oxygen due to the insufficient flow of blood is often seen as a major hindrance in radiotherapy. Such cells become radio-resistant because molecular oxygen, the natural and best radio-sensitizer, is depleted. Hence, to compensate this deficiency in oxygen, there is a need for agents that enhance radiation-induced damage of cells (radio-sensitizers) in a manner that normal cells are least affected. Simultaneously, agents capable of showing activity under hypoxic conditions are known as hypoxic cytotoxins that selectively and preferably destroy cells under hypoxic environments. 5-Nitroimidazoles fit both definitions. Their efficiency is based on their ability to generate the nitro radical anion that interacts with the strands of DNA within cells, either damaging or modifying them, leading to cell death. 5-Nitroimidazoles are important radio-pharmaceuticals (radio-sensitizers) in cancer-related treatments where the nitro radical anion has an important role. Since its generation leads to neurotoxic side effects that may be controlled through metal complex formation, this study looks at the possibility of two monomeric complexes of Ornidazole [1-chloro-3-(2-methyl-5-nitro-1H-imidazole-1-yl)propan-2-ol] with CuII and ZnII to be better radio-sensitizers and/or hypoxic cytotoxins than Ornidazole. The study reveals that although there is a decrease in nitro radical anion formation by complexes, such a decrease does not hamper their radio-sensitizing ability. Nucleic acid bases (thymine, cytosine, and adenine) or calf thymus DNA used as targets were irradiated with 60Co γ rays either in the absence or presence of Ornidazole and its monomeric complexes. Radiation-induced damage of nucleic acid bases was followed by high-performance liquid chromatography (HPLC), and modification of calf thymus DNA was followed by ethidium bromide fluorescence. Studies indicate that the complexes were better in performance than Ornidazole. CuII-ornidazole was significantly better than either Ornidazole or ZnII-ornidazole, which is attributed to certain special features of the CuII complex; aspects like having a stable lower oxidation state enable it to participate in Fenton reactions that actively influence radio-sensitization and the ability of the complex to bind effectively to DNA.

Dataset Information

S K-edge XAS of Cu^II, Cu^I, and Zn^II oxidized Dithiolene complexes: Covalent contributions to structure and the Jahn-Teller effect.

Publications

S K-edge XAS of Cu<sup>II</sup>, Cu<sup>I</sup>, and Zn<sup>II</sup> oxidized Dithiolene complexes: Covalent contributions to structure and the Jahn-Teller effect.

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