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Nitrite Reduction in Aqueous Solution Mediated by Amavadin Homologues: N 2 O Formation and Water Oxidation
Author(s) -
Dias Lúcia,
Bekhti Nihel,
Kuznetsov Maxim L.,
Ferreira José A. B.,
Bacariza Maria C.,
da Silva José Armando L.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201705385
Subject(s) - chemistry , nitrite , aqueous solution , protonation , vanadium , inorganic chemistry , redox , molecule , ligand (biochemistry) , nitrate , photochemistry , ion , organic chemistry , biochemistry , receptor
Reactions of two vanadium(IV) complex anions that are homologues of amavadin, [V(HIDPA) 2 ] 2− and [V(HIDA) 2 ] 2− (HIDPA= N ‐oxyiminodipropionate, HIDA= N ‐oxyiminodiacetate), with the nitrite ion (NO 2 − ) in aqueous solution were investigated by experimental (absorption spectroscopy in the visible range, through measurements of dioxygen formed in solution from water oxidation and identification of nitrogen oxide species of a gaseous atmosphere from nitrite reduction by using an IR analyser) and theoretical methods. Two reactions, mediated by the vanadium complexes, with environmental and biological significance, were observed in this system, namely, reduction of nitrite to N 2 O and oxidation of water to molecular oxygen. The reduction of nitrite, as studied by DFT calculations, occurs through the formation of NO (Δ G ≠ =14.3 kcal mol −1 ), which is strongly dependent on pH and slightly endergonic, and is then easily converted into N 2 O, with an overall activation barrier of Δ G ≠ =11.8 kcal mol −1 . The later process includes dimerisation 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 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 nitrogen metabolism of Amanita muscaria and other fungi containing this vanadium complex.