Electron transfer, 151. Decomposition of peroxynitrite as catalyzed by copper(II)

The decomposition of peroxynitrite in aqueous solution at pH 9.8-11.1 is catalyzed by copper(II) at the 10(-7)10(-6) m level. In the presence of added ammonia (0.03 m) or imidazole (0.005 M), reaction rates were as much as 160 times as great as those in copper-free systems. Catalysis was strongly inhibited by glycine, 2,2-bipyridyl, and EDTA. The yield of nitrite from the decomposition, [NO2-]/[O=NOO-](taken) = 0.26, did not vary significantly with pH or [Cu-II]. Variation of reaction rates with [H+] and [Cu-II] is consistent with partition of the catalyst into an acidic form, (cat)(HA) (pK(A) 10.2-10.5), a dimer, (cat(HA))(2), and a basic form (cat)(A); only the first of these is active. Both transformations are taken to be initiated by Cull-induced homolysis of the O-O bond in peroxynitrite, yielding the reactive intermediate, a species of the type Cu-III (OH). The latter may react further with peroxynitrite (ultimately yielding NO2- and O-2) or with nitrite (yielding NO3-). It is further suggested that catalytic activity of the type observed requires a substitution-labile Cu-II(OH2) function.