Nitrite Reduction in Aqueous Solution Mediated by Amavadin Homologues: N₂O Formation and Water Oxidation

Abstract

Reactions of two vanadium(IV) complex anions that are homologues of amavadin, [V(HIDPA) ] and [V(HIDA) ] (HIDPA=N-oxyiminodipropionate, HIDA=N-oxyiminodiacetate), with the nitrite ion (NO ) 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 O and oxidation of water to molecular oxygen. The reduction of nitrite, as studied by DFT calculations, occurs through the formation of NO (ΔG =14.3 kcal mol ), which is strongly dependent on pH and slightly endergonic, and is then easily converted into N O, with an overall activation barrier of ΔG =11.8 kcal mol . 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.

Relativistic DFT Probe for Reaction Energies and Electronic/Bonding Properties of Polypyrrolic Hetero-Bimetallic Actinide Complexes: Effects of Uranylendo-Oxo Functionalization

“…Furthermore, the energy density H ( r ) is the sum of kinetic G ( r ) and potential V ( r ) parts and could be used as another descriptor for the characterization of the chemical bond. The interaction energy ( E int ) has been obtained by computing the 0.5* V ( r ) in previous reports. , The calculated QTAIM parameters are presented in Tables and S11.…”

“…The interaction energy (E int ) has been obtained by computing the 0.5*V(r) in previous reports. 80,81 The calculated QTAIM parameters are presented in Tables 6 and S11. Actinide sandwich complexes An(C n H n ) 2 (An = Th, Pa, U, Np, Pu; n = 5−8) prefer strong covalent interactions between actinide and carbon atoms.…”

Import and Implications of Vanadium in Live Aspects

“…Its biological function has so far not yet been established with certainty. Due to the reversible oxidation/reduction (V IV ⇆ V V + e − ), a role for amavadin as a redox catalyst is assumed: Amavadin homologues have been shown to mediate the reduction of NO2 − to N2O and the oxidation of water to O2 [19]. The fly agaric mushroom Amanita muscaria (Figure 3) accumulates vanadium at concentrations of up to several hundred mg kg −1 dry mass [18], with a maximum concentration found in the bulb.…”

“…Its biological function has so far not yet been established with certainty. Due to the reversible oxidation/reduction (V IV V V + e − ), a role for amavadin as a redox catalyst is assumed: Amavadin homologues have been shown to mediate the reduction of NO 2 − to N 2 O and the oxidation of water to O 2 [19]. Sea dwellers such as ascidians (e.g., Ascidia sydneiensis samea) and polychaeta fan worms (Pseudopotamilla [20], Perkinsiana [21]) accumulate vanadium from seawater.…”

Catalytic Applications of Vanadium: A Mechanistic Perspective

“…References for manuscripts of homogeneous vanadium catalysis published in 2018 after the preparation of this document, but prior to publishing, which were not discussed in the text. − …”