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<p>Control over copper nuclearity is a key issue in bioinspired oxidation chemistry, yet its mechanistic consequences in sulfur-donor environments remain insufficiently understood. Here, remote tert-butyl substitution on a flexible dithioether-dithiolate ligand scaffold switches the preferred copper(II) assembly from binuclear [CuS<sub>4</sub>]<sub>2</sub> to mononuclear [CutBuS<sub>4</sub>], enabling a direct assessment of nuclearity effects within a common sulfur-ligated framework. Combined spectroscopic, electrochemical, stopped-flow kinetic, and DFT studies show that this steric perturbation modifies complex stability, productive substrate binding, and the extent to which catalytic turnover benefits from metal-metal cooperativity. In the aerobic oxidation of 3,5-di-tert-butylcatechol, both complexes follow a two-step sequence of rapid reversible substrate binding and slower oxidation, and both reach similar maximum turnover frequencies under saturating conditions, ca. 1700–1750&#xa0;h<sup>− 1</sup>. The binuclear [CuS<sub>4</sub>]<sub>2</sub> nevertheless shows stronger productive substrate binding, with <i>K</i><sub><i>M</i></sub> values of 3.4 vs. 5.0 mM for the mononuclear <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\:\left[CutBu{S}_{4}\right]\)</EquationSource> </InlineEquation>, respectively. In contrast, oxidation of o-aminophenol to aminophenoxazinone is strongly nuclearity-dependent, with [CuS<sub>4</sub>]<sub>2</sub> displaying substantially higher activity than <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\:\left[CutBu{S}_{4}\right]\)</EquationSource> </InlineEquation> (2772 vs. 684&#xa0;h<sup>− 1</sup>), consistent with a decisive role for dicopper cooperativity in oxidative coupling. Detection of H<sub>2</sub>O<sub>2</sub> and the lack of 4-nitrocatechol oxidation support an oxidase-type pathway in which catalytic competence depends on substrate reducing power and access to productive oxygen-dependent redox chemistry.</p>

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Steric control of copper nuclearity in sulfur ligated oxidase mimics alters catechol and phenoxazinone oxidation

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月9日

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  • Eman I. Khalaf,
  • Fawzya I. Elshami,
  • Shaimaa F. Gad,
  • Amr M. Beltagi,
  • Ali M. Nassar,
  • Shaban Y. Shaban

摘要

Control over copper nuclearity is a key issue in bioinspired oxidation chemistry, yet its mechanistic consequences in sulfur-donor environments remain insufficiently understood. Here, remote tert-butyl substitution on a flexible dithioether-dithiolate ligand scaffold switches the preferred copper(II) assembly from binuclear [CuS4]2 to mononuclear [CutBuS4], enabling a direct assessment of nuclearity effects within a common sulfur-ligated framework. Combined spectroscopic, electrochemical, stopped-flow kinetic, and DFT studies show that this steric perturbation modifies complex stability, productive substrate binding, and the extent to which catalytic turnover benefits from metal-metal cooperativity. In the aerobic oxidation of 3,5-di-tert-butylcatechol, both complexes follow a two-step sequence of rapid reversible substrate binding and slower oxidation, and both reach similar maximum turnover frequencies under saturating conditions, ca. 1700–1750 h− 1. The binuclear [CuS4]2 nevertheless shows stronger productive substrate binding, with KM values of 3.4 vs. 5.0 mM for the mononuclear \(\:\left[CutBu{S}_{4}\right]\) , respectively. In contrast, oxidation of o-aminophenol to aminophenoxazinone is strongly nuclearity-dependent, with [CuS4]2 displaying substantially higher activity than \(\:\left[CutBu{S}_{4}\right]\) (2772 vs. 684 h− 1), consistent with a decisive role for dicopper cooperativity in oxidative coupling. Detection of H2O2 and the lack of 4-nitrocatechol oxidation support an oxidase-type pathway in which catalytic competence depends on substrate reducing power and access to productive oxygen-dependent redox chemistry.