Nitrite reduction in aqueous solution mediated by amavadin homologues: N2O formation and water oxidation.

Reactions of two vanadium(IV) complex anions - homologues of amavadin, [V(HIDPA)2]2- and [V(HIDA)2]2- (HIDPA = N-oxyiminodiproprionate, HIDA = N-oxyiminodiacetate) with nitrite-ion (NO2-) in aqueous solution were investigated by experimental (absorption spectroscopy in the visible range, by measurements of the dioxygen formed into solution from water oxidation and identification of nitrogen oxide species of gaseous atmosphere from nitrite reduction by an infrared analyser) and theoretical methods. Two reactions, mediated by the V complexes, with environmental and biological significance were observed in this system, i.e. reduction of nitrite to N2O and water oxidation to molecular oxygen. The reduction of nitrite, studied by DFT calculations, occurs via formation of NO (G = 14.3 kcal/mol), which is strongly pH dependent and slightly endergonic, and then it is easily converted into N2O with the overall activation barrier G of 11.8 kcal/mol. This process includes dimerization of NO assisted by one molecule of the V-complex, protonation and oxidation of the formed ONNO*- ligand by another amavadin molecule or by nitrite and the NO bond cleavage/proton transfer in the ONNOH- ligand. The results indicate that amavadin exhibits an unusual nitrite reductase type activity that could be involved in the nitrogen metabolism of Amanita muscaria and other fungi bearing this V complex. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Citation

José da Silva, Lúcia Dias, Nihel Bekhti, Maxim L Kuznetsov, José A B Ferreira, Maria C Bacariza. Nitrite reduction in aqueous solution mediated by amavadin homologues: N2O formation and water oxidation. Chemistry (Weinheim an der Bergstrasse, Germany). 2017 Nov 27

PMID: 29178299

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