NO Switching Sides on Copper

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Science  13 Sep 2013:
Vol. 341, Issue 6151, pp. 1153
DOI: 10.1126/science.341.6151.1153-c

For eons, microbes have been shuttling electrons back and forth through nitrogen compounds; some break up N2 using nitrogenase enzymes, whereas others put it back together via nitrite reductases. In the past century or so, humans have gotten in on the act as well: The Haber process takes N2 to ammonia (NH3), whereas at the other end of the cycle, copper catalysts keep noxious nitric oxide (NO) out of exhaust streams by turning it back into N2. Kwak et al. have now uncovered a somewhat unanticipated symmetry between the biochemical and synthetic processes. By using 15N nuclear magnetic resonance and infrared absorption spectroscopy, they gathered compelling evidence for a side-on bonding motif between NO+ and Cu(I) centers in zeolite catalysts for selective NO reduction. This intermediate resembles the similarly side-bound copper nitrosyl previously observed in a nitrite reductase active site. The authors go on to propose a detailed mechanism for the zeolite reaction by merging their spectroscopic characterization with published kinetic data.

Angew. Chem. Int. Ed. 52, 10.1002/anie.201303498 (2013).

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