Bioinspired Heme, Heme/Nonheme Diiron, Heme/Copper, and Inorganic NOx Chemistry: •NO(g) Oxidation, Peroxynitrite−Metal Chemistry, and •NO(g) Reductive Coupling

Abstract

The focus of this Forum Article highlights work from our own laboratories and those of others in the area of biochemical and biologically inspired inorganic chemistry dealing with nitric oxide [nitrogen monoxide, •NO_(g)] and its biological roles and reactions. The latter focus is on (i) oxidation of •NO_(g) to nitrate by nitric oxide dioxygenases (NODs) and (ii) reductive coupling of two molecules of •NO_(g) to give N₂O(g). In the former case, NODs are described, and the highlighting of possible peroxynitrite/heme intermediates and the consequences of this are given by a discussion of recent works with myoglobin and a synthetic heme model system for NOD action. Summaries of recent copper complex chemistries with •NO_(g) and O₂(g), leading to peroxynitrite species, are given. The coverage of biological reductive coupling of •NO_(g) deals with bacterial nitric oxide reductases (NORs) with heme/nonheme diiron active sites and on heme/copper oxidases such as cytochrome c oxidase, which can mediate the same chemistry. Recently designed protein and synthetic model compounds (heme/nonheme/diiron or heme/copper) as functional mimics are discussed in some detail. We also highlight examples from the chemical literature, not necessarily involving biologically relevant metal ions, that describe the oxidation of •NO_(g) to nitrate (or nitrite) and possible peroxynitrite intermediates or reductive coupling of •NO_(g) to give nitrous oxide.