Charlène Esmieu
Structure-activity relationships in copper complexes bio-inspired from nitrous oxide reductase
Published on 13 November 2014
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Thesis presented November 13, 2014
Abstract :
N2O is a powerful greenhouse gas and is involved in the ozone layer destruction, which makes it degradation very interesting. N2O is an intermediate of the catalytic cycle of bacterial nitrification. Indeed, in biology a metalloenzyme can reduce N2O with two electrons to N2 and H2O. The active site of nitrous oxide reductase, the CuZ center, contains a unique combination of four copper ions bridged by a sulfide ion.
In order to obtain complexes able to activate N2O and deepen the understanding of the catalytic mechanism of the enzyme we have developed models based on the CuZ center. Binuclear copper containing the {Cu2(µ-S)} pattern that is supposed essential to N2O activation have been synthetized. Mixed valent complexes described in this work were fully characterized and their activity toward N2O was evaluated. These complexes are the first model like this capable of N2O reduction. Spectroscopic, electrochemical and theoretical studies have also allowed us to propose a reaction mechanism, which passes through the formation of an adduct complex-N2O. We were also able to highlight the crucial role of the exogenous water molecule in this mechanism.
In parallel, the solution stability of different disulfide bonds present in tetranucleating ligands in the presence of CuII was evaluated. The reactivity of the disulfide bond is dependent upon the binding of copper ions near sulfur atoms. Three ligands with different amino groups were tested, each having a specific reactivity. We have shown for one of them that the oxidation of the disulfide bond could be carried out in the absence of strong oxidizer, water acting as the nucleophile.
Keywords:
Nitrous oxide, Bio-inspired complexes, Copper, Spectroscopy, Coordination chemistry, Metalloenzyme
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