Coordination chemistry of the Cu site in nitrous oxide reductase and its synthetic mimics.

Atmospheric nitrous oxide (NO) has garnered significant attention recently due to its dual roles as an ozone depletion agent and a potent greenhouse gas. Anthropogenic NO emissions occur primarily through agricultural disruption of nitrogen homeostasis causing NO to build up in the atmosphere. The enzyme responsible for NO fixation within the geochemical nitrogen cycle is nitrous oxide reductase (NOR), which catalyzes 2H/2e reduction of NO to N and HO at a tetranuclear active site, Cu. In this review, the coordination chemistry of Cu is reviewed. Recent advances in the understanding of biological Cu coordination chemistry is discussed, as are significant breakthroughs in synthetic modeling of Cu that have emerged in recent years. The latter topic includes both structurally faithful, synthetic [Cu(µ-S)] clusters that are able to reduce NO, as well as dicopper motifs that shed light on reaction pathways available to the critical Cu-Cu cluster edge of Cu. Collectively, these advances in metalloenzyme studies and synthetic model systems provide meaningful knowledge about the physiologically relevant coordination chemistry of Cu but also open new questions that will pose challenges in the near future.