While nitric oxide (NO) is an important signaling agent, its cellular concentrations must be tightly controlled. A significant pathway for its removal occurs at the heme-copper active site in mitochondrial cytochrome c oxidases where NO is oxidized to nitrite (NO2–) where it is held in reserve. The same heme-Cu center in a reduced state can reconvert nitrite back to nitric oxide. We will report on heme-copper assembly coordination chemistry facilitating these transformations. Progress in our attempts to model NO Reductases where two NO molecules couple at a dimetal center to give a putative hyponitrite (N2O2 dianion) intermediate, followed by release of nitrous oxide (N2O), may also be presented. A further interest is the iron or copper ion chemistry of peroxynitrite (PN; O=N-O-O–),the product of superoxide anion plus NO(g); PN is a potent biological nitrating agent or oxidizing agent, responsible for protein tyrosine phenol nitration. Metal-PN complexes may form by reaction of NO(g) with (i) copper-dioxygen adducts or (b) heme-O2 species; the latter reaction occurs in NO Dioxygenases, where the heme-PN intermediate thought to form isomerizes and releases the innocuous nitrate ion. Employing an imidazole-tailed heme, we report on the generation and characterization of a peroxynitrite heme complex, which does transform to a heme-nitrate complex. In separate chemistry, we report on a dicopper-superoxide species which reacts with NO(g) to give a peroxynitrite complex which is able to effect the nitration of a phenolic substrate, as a tyrosine surrogate.

Bioinorganic aspects of nitrogen oxide chemistry with heme and/or copper complexes

253rd National Meeting (2017)

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