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The Reduction Potential of Nitric Oxide (NO) and Its Importance to NO Biochemistry
Michael D. Bartberger, Wei Liu, Eleonora Ford, Katrina M. Miranda, Christopher Switzer, Jon M. Fukuto, Patrick J. Farmer, David A. Wink and Kendall N. Houk
Proceedings of the National Academy of Sciences of the United States of America
Vol. 99, No. 17 (Aug. 20, 2002), pp. 10958-10963
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/3059504
Page Count: 6
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A potential of about -0.8 (±0.2) V (at 1 M versus normal hydrogen electrode) for the reduction of nitric oxide (NO) to its one-electron reduced species, nitroxyl anion (3NO -) has been determined by a combination of quantum mechanical calculations, cyclic voltammetry measurements, and chemical reduction experiments. This value is in accord with some, but not the most commonly accepted, previous electrochemical measurements involving NO. Reduction of NO to 1NO - is highly unfavorable, with a predicted reduction potential of about -1.7 (±0.2) V at 1 M versus normal hydrogen electrode. These results represent a substantial revision of the derived and widely cited values of +0.39 V and -0.35 V for the NO/3NO - and NO/1NO - couples, respectively, and provide support for previous measurements obtained by electrochemical and photoelectrochemical means. With such highly negative reduction potentials, NO is inert to reduction compared with physiological events that reduce molecular oxygen to superoxide. From these reduction potentials, the pKa of 3NO - has been reevaluated as 11.6 (±3.4). Thus, nitroxyl exists almost exclusively in its protonated form, HNO, under physiological conditions. The singlet state of nitroxyl anion, 1NO -, is physiologically inaccessible. The significance of these potentials to physiological and pathophysiological processes involving NO and O2 under reductive conditions is discussed.
Proceedings of the National Academy of Sciences of the United States of America © 2002 National Academy of Sciences