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The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands

Conversion from superoxide (O(2)(−)) to hydroperoxide (OOH(−)) on the metal center of oxygenases and oxidases is recognized to be a key step to generating an active species for substrate oxidation. In this study, reactivity of cobalt(III)-superoxido complexes supported by facially-capping tridentate...

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Autores principales: Nishiura, Toshiki, Ohta, Takehiro, Ogura, Takashi, Nakazawa, Jun, Okamura, Masaya, Hikichi, Shiro
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2022
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Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9571172/
https://www.ncbi.nlm.nih.gov/pubmed/36234952
http://dx.doi.org/10.3390/molecules27196416
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author Nishiura, Toshiki
Ohta, Takehiro
Ogura, Takashi
Nakazawa, Jun
Okamura, Masaya
Hikichi, Shiro
author_facet Nishiura, Toshiki
Ohta, Takehiro
Ogura, Takashi
Nakazawa, Jun
Okamura, Masaya
Hikichi, Shiro
author_sort Nishiura, Toshiki
collection PubMed
description Conversion from superoxide (O(2)(−)) to hydroperoxide (OOH(−)) on the metal center of oxygenases and oxidases is recognized to be a key step to generating an active species for substrate oxidation. In this study, reactivity of cobalt(III)-superoxido complexes supported by facially-capping tridentate tris(3,5-dimethyl-4-X-pyrazolyl)hydroborate ([HB(pz(Me2,X))(3)](−); Tp(Me2,X)) and bidentate bis(1-methyl-imidazolyl)methylborate ([B(Im(N)(-Me))(2)Me(Y)](−); L(Y)) ligands toward H-atom donating reagent (2-hydroxy-2-azaadamantane; AZADOL) has been explored. The oxygenation of the cobalt(II) precursors give the corresponding cobalt(III)-superoxido complexes, and the following reaction with AZADOL yield the hydroperoxido species as has been characterized by spectroscopy (UV-vis, resonance Raman, EPR). The reaction of the cobalt(III)-superoxido species and a reducing reagent ([Co(II)(C(5)H(5))(2)]; cobaltocene) with proton (trifluoroacetic acid; TFA) also yields the corresponding cobalt(III)-hydroperoxido species. Kinetic analyses of the formation rates of the cobalt(III)-hydroperoxido complexes reveal that second-order rate constants depend on the structural and electronic properties of the cobalt-supporting chelating ligands. An electron-withdrawing ligand opposite to the superoxide accelerates the hydrogen atom transfer (HAT) reaction from AZADOL due to an increase in the electrophilicity of the superoxide ligand. Shielding the cobalt center by the alkyl group on the boron center of bis(imidazolyl)borate ligands hinders the approaching of AZADOL to the superoxide, although the steric effect is insignificant.
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spelling pubmed-95711722022-10-17 The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands Nishiura, Toshiki Ohta, Takehiro Ogura, Takashi Nakazawa, Jun Okamura, Masaya Hikichi, Shiro Molecules Article Conversion from superoxide (O(2)(−)) to hydroperoxide (OOH(−)) on the metal center of oxygenases and oxidases is recognized to be a key step to generating an active species for substrate oxidation. In this study, reactivity of cobalt(III)-superoxido complexes supported by facially-capping tridentate tris(3,5-dimethyl-4-X-pyrazolyl)hydroborate ([HB(pz(Me2,X))(3)](−); Tp(Me2,X)) and bidentate bis(1-methyl-imidazolyl)methylborate ([B(Im(N)(-Me))(2)Me(Y)](−); L(Y)) ligands toward H-atom donating reagent (2-hydroxy-2-azaadamantane; AZADOL) has been explored. The oxygenation of the cobalt(II) precursors give the corresponding cobalt(III)-superoxido complexes, and the following reaction with AZADOL yield the hydroperoxido species as has been characterized by spectroscopy (UV-vis, resonance Raman, EPR). The reaction of the cobalt(III)-superoxido species and a reducing reagent ([Co(II)(C(5)H(5))(2)]; cobaltocene) with proton (trifluoroacetic acid; TFA) also yields the corresponding cobalt(III)-hydroperoxido species. Kinetic analyses of the formation rates of the cobalt(III)-hydroperoxido complexes reveal that second-order rate constants depend on the structural and electronic properties of the cobalt-supporting chelating ligands. An electron-withdrawing ligand opposite to the superoxide accelerates the hydrogen atom transfer (HAT) reaction from AZADOL due to an increase in the electrophilicity of the superoxide ligand. Shielding the cobalt center by the alkyl group on the boron center of bis(imidazolyl)borate ligands hinders the approaching of AZADOL to the superoxide, although the steric effect is insignificant. MDPI 2022-09-28 /pmc/articles/PMC9571172/ /pubmed/36234952 http://dx.doi.org/10.3390/molecules27196416 Text en © 2022 by the authors. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Nishiura, Toshiki
Ohta, Takehiro
Ogura, Takashi
Nakazawa, Jun
Okamura, Masaya
Hikichi, Shiro
The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands
title The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands
title_full The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands
title_fullStr The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands
title_full_unstemmed The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands
title_short The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands
title_sort conversion of superoxide to hydroperoxide on cobalt(iii) depends on the structural and electronic properties of azole-based chelating ligands
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9571172/
https://www.ncbi.nlm.nih.gov/pubmed/36234952
http://dx.doi.org/10.3390/molecules27196416
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