Nitrification, the oxidation of ammonia to nitrite and nitrate, is a key entry point for fixed nitrogen to return to the atmosphere as dinitrogen. Nitrification is the root of tremendous economic loss in agriculture as well as a major ecological hazard via nitrogenous eutrophication. Molecular details concerning the elementary, multi-electron chemical steps whereby ammonia is oxidized to hydroxylamine and ultimately to nitrite remain elusive. This may be attributable in part to the difficulty associated with accessing sufficient quantities of relevant enzymes for biophysical characterization. Nevertheless, such insights are attractive because they hold the promise of inspiring novel, green chemical methods for difficult bond activations and multi-electron transformations. This talk will describe our investigation of the crucial molecular steps of nitrification revealed through the application of rapid kinetics, spectroscopy, and electronic structure calculations. Key insights include the establishment of a direct link between nitrification and nitrous oxide pollution, the identification of important intermediates in hydroxylamine oxidation by both Fe, and a revision of the enzymatic steps involved in hydroxylamine oxidation. The seminar will conclude with reinterpretation of the electronic structure of high-valent copper–oxygen species toward rationalizing competence of these species for challenging E–H bond activations.
Kyle Lancaster (Cornell University)