Synthesis and Analysis of Model Complexes of the Active Site of Nitrous Oxide Reductase

Nitrous Oxide (N2O) is a leading cause for global warming and ozone layer depletion. The environmental impact of N2O could be mitigated by controlling its emission, accumulation and understanding its metabolism. The anaerobic denitrification pathway involves converting the harmful N2O to N2 and H2O by an enzyme called Nitrous Oxide Reductase (N2OR). The 2e-, 2H+ catalytic reduction of N2O to N2 and H2O is carried out at the tetracopper sulfur [Cu4(μ4-S)] active site (CuZ) of N2OR. The synthetic model complexes of CuZ could be an excellent tool to investigate the structural and the mechanistic features, which could otherwise be hindered by the complexity of the enzyme system. Herein, we report the synthesis, characterization, reactivity and mechanistic studies of several CuZ synthetic model complexes that are supported by rationally designed small organic ligand systems. The desired structure, nuclearity and redox activity are achieved by fine tuning the steric and electronics of the ligand framework. To date, two of our model complexes remain as the only examples that closely resemble both structure and function of the active site of N2OR. Altogether, the experimental, crystallographic, spectroscopic and theoretical studies of our model complexes have enlightened and broaden the field of synthetic model systems of CuZ.