Source and reduction of nitrous oxide

Abstract

Nitrous oxide is a potent greenhouse gas with a global warming impact 300-fold higher than carbon dioxide. Due to its exponential increase in the atmosphere and its implications in climate change there is the need to develop strategies to mitigate its emissions and to reduce it to the inert dinitrogen gas. Only three enzymes have been reported to be able to reduce nitrous oxide, namely nitrogenase, one multicopper oxidase and nitrous oxide reductase, with the latter being the only one with a relevant physiological activity. In this enzyme, reduction of nitrous oxide occurs in a unique catalytic tetranuclear sulfide center, named “CuZ” center, a complex center required to overcome the high activation barrier of this reaction. Nitrous oxide reductase can be isolated with “CuZ” center in two forms, CuZ*(4Cu1S) and CuZ(4Cu2S), that differ in their catalytic and spectroscopic properties. Recently, another step towards a better understanding of the catalytic and activation mechanism of this enzyme was taken by identifying and spectroscopically characterizing an intermediate species of its catalytic cycle, CuZ0.A different approach for N2O reduction can be attained using model compounds. The unique structural motif present in “CuZ” center, a Cu4(µ4-S), has been a challenge for inorganic synthesis but several synthetic clusters that mimic different forms of “CuZ” center have been reported. Model compounds for the oxidation states involved in N2O reduction are also available. The advances in this area will be discussed in light of the recent data, with structural and functional model compounds of N2OR active site.