The Abiotic Nitrite Oxidation by Ligand-Bound Manganese (III): The Chemical Mechanism
| Autor: | Scott D. Wankel, Kevin M. Sutherland, George W. Luther, Jennifer S. Karolewski, Colleen M. Hansel |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
chemistry.chemical_classification
Nitrous acid 010504 meteorology & atmospheric sciences Inorganic chemistry chemistry.chemical_element Manganese 010501 environmental sciences Electron acceptor Inner sphere electron transfer 01 natural sciences Nitrogen chemistry.chemical_compound Geophysics chemistry Geochemistry and Petrology Nitronium ion Nitrification Nitrite 0105 earth and related environmental sciences |
| Zdroj: | Aquatic Geochemistry. |
| ISSN: | 1573-1421 1380-6165 |
| DOI: | 10.1007/s10498-021-09396-0 |
| Popis: | Given their environmental abundances, it has been long hypothesized that geochemical interactions between reactive forms of manganese and nitrogen may play important roles in the cycling of these elements. Indeed, recent studies have begun shedding light on the possible role of soluble, ligand-bound Mn(III) in promoting abiotic transformations under environmentally relevant conditions. Here, using the kinetic data of Karolewski et al. (Geochim Cosmochim Acta 293:365–378, 2021), we provide the chemical mechanism for the abiotic oxidation of nitrite (NO2−) by Mn(III)-pyrophosphate, MnIIIPP, to form nitrate (NO3−). Nitrous acid (HNO2), not NO2−, is the reductant in the reaction, based on thermodynamic and kinetic considerations. As soluble Mn(III) complexes react in a one-electron transfer reaction, two one-electron transfer steps must occur. In step one, HNO2 is first oxidized to nitrogen dioxide, ·NO2, a free radical via a hydrogen atom transfer (HAT) reaction. We show that this inner sphere reaction process is the rate-limiting step in the reaction sequence. In step two, ·NO2 reacts with a second MnIIIPP complex to form the nitronium ion (NO2+), which is isoelectronic with CO2. Unlike the poor electron-accepting capability of CO2, NO2+ is an excellent electron acceptor for both OH− and H2O, so NO2+ reacts quickly with water to form the end-product NO3− (step 3 in the reaction sequence). Thus, water provides the O atom in this nitrification reaction in accordance with the O-isotope data. This work provides mechanistic perspective on a potentially important interaction between Mn and nitrogen species, thereby offering a framework in which to interpret kinetic and isotopic data and to further investigate the relevance of this reaction under environmental conditions. |
| Databáze: | OpenAIRE |
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