Nonenzymatic anaerobic ammonium oxidation through a hydrazine intermediate

Abstract

Anaerobic ammonium oxidation (anammox) − the biological process that activates ammonium with nitrite − is responsible for a significant fraction of N2 production in marine environments. Despite decades of biochemical research, however, no synthetic models capable of anammox have been identified. Here, we report that a copper sulfide mineral replicates the entire biological anammox pathway catalyzed by three metalloenzymes. A copper-nitrosonium (Cu+−NO+) complex formed by nitrite reduction was identified as the oxidant for ammonium oxidation, leading to heterolytic N−N bond formation from nitrite and ammonium. Similar to the biological process, N2 production was mediated by the highly reactive intermediate hydrazine, one of the most potent reductants in nature. Another pathway involving N−N bond heterocoupling for the formation of hybrid N2O, a potent greenhouse gas with a unique isotope composition, was also identified. Our study represents the first nonenzymatic anammox reaction that interconnects six redox states in the abiotic nitrogen cycle.