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Ariafard A, Longhurst M, Swiegers G, Stranger R. Mechanisms of Mn(V)-oxo to Mn(IV)-oxyl Conversion: From Closed-Cubane Photosystem II to Mn(V) Catalysts and the Role of the Entering Ligands. Chemistry 2024:e202400396. [PMID: 38659321 DOI: 10.1002/chem.202400396] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 04/02/2024] [Accepted: 04/20/2024] [Indexed: 04/26/2024]
Abstract
The low activation barrier for O-O coupling in the closed-cubane Oxygen-Evolving Centre (OEC) of Photosystem II (PSII) requires water coordination with the Mn4 'dangler' ion in the Mn(V)-oxo fragment. This coordination transforms the Mn(V)-oxo into a more reactive Mn4(IV)-oxyl species, enhancing O-O coupling. This study explains the mechanism behind this and indicates that in the most stable form of the OEC, the Mn4 fragment adopts a trigonal bipyramidal geometry but needs to transition to a square pyramidal form to be activated for O-O coupling. This transition stabilizes the Mn4 dxy orbital, enabling electron transfer from the oxo ligand to the dxy orbital, converting the oxo ligand into an oxyl species. The role of the water is to coordinate with the square pyramidal structure, reducing the energy gap between the oxo and oxyl forms, thereby lowering the activation energy for O-O coupling. This mechanism applies not only to the OEC system but also to other Mn(V)-based catalysts. For other catalysts, ligands like OH- stabilize the Mn(IV)-oxyl species better than water, improving catalyst activation for reactions like C-H bond activation. This study is the first to explain the Mn(V)-oxo to Mn(IV)-oxyl conversion, providing new foundation for Mn-based catalyst design.
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Affiliation(s)
- Alireza Ariafard
- Australian National University, Chemistry, 2601, Canberra, AUSTRALIA
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Somasundaram JD, Ebrahimi A, Nandan SP, Cherevan A, Eder D, Šupolíková M, Nováková E, Gyepes R, Krivosudský L. Functionalization of decavanadate anion by coordination to cobalt(II): Binding to proteins, cytotoxicity, and water oxidation catalysis. J Inorg Biochem 2023; 239:112067. [PMID: 36423394 DOI: 10.1016/j.jinorgbio.2022.112067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 11/01/2022] [Accepted: 11/08/2022] [Indexed: 11/18/2022]
Abstract
A series of five decavanadates (V10) using a simple, one-pot synthesis, adhering to the model template: transition metal ion - decavanadate - ligands:(Hnicotinamide)2{[Co(H2O)3(nicotinamide)2]2[μ-V10O28]}.6H2O (1), {[Co(H2O)4(isonicotinamide)2]3}V10O28·4H2O (2), {[Co(H2O)4]2[Co(H2O)2(μ-pyrazinamide)2][μ-V10O28]}·4H2O (3) {[Co(H2O)4(μ-pyrazinamide)]3.V10O28}·4H2O (4), and (NH4)2{[Ni(H2O)4(2-hydroxyethylpyridine)]2}V10O28·2H2O (5) was synthesized. X-ray analysis reveals that 1 and 3 are decavanadato complexes, while 2, 4 and 5 are decavanadate complex salts. Moreover, 3 is the first example of a polymeric decavanadato complex, employing direct coordination with the metal center and the organic ligand, in toto. From the solution studies using 51V NMR spectroscopy, it was decoded that 1 and 3 stay stable in the model buffer solution and aqueous media. Binding to model proteins, cytotoxicity and water oxidation catalysis (WOC) was studied primarily for 1 and 3 and concluded that neither 1 nor 3 have an interaction with the model proteins thaumatin, lysozyme and proteinase K, because of the presence of the organic ligands in the Co(II) center, any further interplay with the proteins was blocked. Cytotoxicity studies reveal that 1 is 40% less toxic (0.05 mM) and 26% less toxic (0.1 mM) than the uncoordinated V10 with human cell lines A549 and HeLa respectively. In WOC, 1 performed superior activity, by evolving 143.37 nmol of O2 which is 700% (9-fold) increase than the uncoordinated V10.
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Affiliation(s)
- Janaki Devi Somasundaram
- Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, Mlynská dolina, 842 15 Bratislava, Slovakia
| | - Arash Ebrahimi
- Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, Mlynská dolina, 842 15 Bratislava, Slovakia
| | - Sreejith P Nandan
- Institute of Materials Chemistry, Technische Universität Wien, 1060 Vienna, Austria
| | - Alexey Cherevan
- Institute of Materials Chemistry, Technische Universität Wien, 1060 Vienna, Austria.
| | - Dominik Eder
- Institute of Materials Chemistry, Technische Universität Wien, 1060 Vienna, Austria
| | - Miroslava Šupolíková
- Department of Microbiology and Virology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, Mlynská dolina, 842 15 Bratislava, Slovakia
| | - Eva Nováková
- Department of Microbiology and Virology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, Mlynská dolina, 842 15 Bratislava, Slovakia
| | - Róbert Gyepes
- Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, Prague 128 00, Czech Republic
| | - Lukáš Krivosudský
- Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, Mlynská dolina, 842 15 Bratislava, Slovakia.
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