Nitric oxide, reaction mechanisms with

Studies related to the mechanisms of nitric oxide reactions with transition metal complexes in this laboratory were supported by grants from the U.S. National Science Foundation, by a Collaborative UC/Los Alamos National Laboratory Research grant, by a grant from the U.S. Japan Cooperative Research Program (Photoconversion/ Photosynthesis) (NSF INT 9116346), and by a grant from the ACS Petroleum Research Fund. We thank the students and postdoctoral fellows at UC Santa Barbara who participated in this research and acknowledge collaborative studies with Dr. David Wink (National Cancer Institute, Bethesda MD, USA), Dr. Mikio Hoshino (RIKEN, Wako-shi, Japan) and Dr. Jon Schoonover (Los Alamos National Laboratory). 

Fox, J. B., and Ackerman, S. A. (1968). Formation of nitric oxide myoglobin Mechanisms of the reaction with various reductants. J. Food Set. 33, 364-370. 

We examine here a number of reaction pathways for nitric oxide, with the emphasis on assessing their biological relevance. To date, the fastest reaction for nitric oxide with clear toxicological significance is that with superoxide to produce ONOO" (Huie and Padmaja, 1993). Thus, the chemistry and reactivity of ONOO" are discussed at length. In addition, the interaction between ONOO" and nitric oxide is examined with respect to its effects on nitric oxide half-life as well as effects on peroxynitrite reactivity toward phenol. Reaction mechanisms are proposed to account for the nitrated, hydroxylated, and nitrosated phenolic products seen. 

Analysis of products from the reaction of phenol with nitric oxide, ONOO", or both (added simultaneously) provides some insight into possible reaction mechanisms as well as products that might be formed in vivo from phenolics such as tyrosine. Based on the apparent stoichiometry of the ONOO /nitric oxide reaction (see Fig. 2), a series of reactions were carried out in which ONOO was added at three different concentrations (0.2, 0.4, and 0.8 mM) in the absence and presence of a fixed concentration of nitric oxide (0.2 mM) added simultaneously. Ratios were chosen which would allow nitric oxide to remain in excess (0.2 mM ONOO" plus 0.2 mM nitric oxide), at stoichiometric concentrations (0.4 mM ONOO" plus 0.2 mM nitric oxide), and where ONOO" was in excess (0.8 mM ONOO" plus... 

Shiro, Y., M. Fujii, T. lizuka, S.I. Adachi, K. Tsukamoto, K. Nakahara, and H. Shoun (1995). Spectroscopic and kinetic studies on reaction of cytochrome P450nor with nitric oxide. Implication for its nitric oxide reduction mechanism. J. Biol. Chem. 270, 1617-1623. 

The vanadium and manganese complexes are the least stable and least studied of the series. The compound V(NO)(CO)5, a violet solid, is made by the action of nitric oxide on vanadium carbonyl (42), while Mn(NO)-(CO)4, a red liquid freezing at -1.5° C, is best made by treating Mn2(CO)g-(PPh3)2 with nitric oxide. The mechanism of this reaction has been briefly... 

Physical properties of hexachloroethane are Hsted in Table 11. Hexachloroethane is thermally cracked in the gaseous phase at 400—500°C to give tetrachloroethylene, carbon tetrachloride, and chlorine (140). The thermal decomposition may occur by means of radical-chain mechanism involving -C,C1 -C1, or CCl radicals. The decomposition is inhibited by traces of nitric oxide. Powdered 2inc reacts violentiy with hexachloroethane in alcohoHc solutions to give the metal chloride and tetrachloroethylene aluminum gives a less violent reaction (141). Hexachloroethane is unreactive with aqueous alkali and acid at moderate temperatures. However, when heated with soHd caustic above 200°C or with alcohoHc alkaHs at 100°C, decomposition to oxaHc acid takes place. 

As the equilibrium concentration of N2O2 decreases rapidly with increase in temperature the decrease in rate is explained. However alternative mechanisms have also been suggested. ° l Nitric oxide reacts with the halogens to give XNO (p. 441). Some other facile reactions are listed below ... 

Another redox reaction leading to arenediazonium salts was described by Morkov-nik et al. (1988). They showed that the perchlorates of the cation-radicals of 4-A,A-dimethylamino- and 4-morpholinoaniline (2.63) react with gaseous nitric oxide in acetone in a closed vessel. The characteristic red coloration of these cation-radical salts (Michaelis and Granick, 1943) disappears within 20 min., and after addition of ether the diazonium perchlorate is obtained in 84% and 92% yields, respectively. This reaction (Scheme 2-39) is important in the context of the mechanism of diazotization by the classical method (see Sec. 3.1). 

This statement does not mean, however, that the mechanism of diazotization was completely elucidated with that breakthrough. More recently it was possible to test the hypothesis that, in the reaction between the nitrosyl ion and an aromatic amine, a radical cation and the nitric oxide radical (NO ) are first formed by a one-electron transfer from the amine to NO+. Stability considerations imply that such a primary step is feasible, because NO is a stable radical and an aromatic amine will form a radical cation relatively easily, especially if electron-donating substituents are present. As discussed briefly in Section 2.6, Morkovnik et al. (1988) found that the radical cations of 4-dimethylamino- and 4-7V-morpholinoaniline form the corresponding diazonium ions with the nitric oxide radical (Scheme 2-39). 

Considerable support exists for Reaction 18a (35). The application of an electrostatic field during radiolysis of ethylene-nitric oxide (I.P. 9.25 e.v.) mixtures showed no enhancement of the butene yields, consistent with an ionic mechanism. When mixtures of C2D4 and C2H4 are irradiated in the presence of nitric oxide, product butene consists almost entirely of C4H8, C4D4H4, and C4D8—evidence for a molecular association mechanism. 

Derive a rate expression that is consistent with this mechanism. Treacy and Daniels [J. Am. Chem. Soc., 11 (2033), 1955] have determined that the orders of the reaction with respect to oxygen and nitric oxide are one and two, respectively, at high pressures and less than one and greater than two at low pressures. Is the proposed mechanism consistent with this data ... 

Reaction Mechanisms of Nitric Oxide with Biologically Relevant Metal Centers Peter C. Ford, Leroy E. Laverman and Ivan M. Lorkovic... 

At present, new developments challenge previous ideas concerning the role of nitric oxide in oxidative processes. The capacity of nitric oxide to oxidize substrates by a one-electron transfer mechanism was supported by the suggestion that its reduction potential is positive and relatively high. However, recent determinations based on the combination of quantum mechanical calculations, cyclic voltammetry, and chemical experiments suggest that °(NO/ NO-) = —0.8 0.2 V [56]. This new value of the NO reduction potential apparently denies the possibility for NO to react as a one-electron oxidant with biomolecules. However, it should be noted that such reactions are described in several studies. Thus, Sharpe and Cooper [57] showed that nitric oxide oxidized ferrocytochrome c to ferricytochrome c to form nitroxyl anion. These authors also proposed that the nitroxyl anion formed subsequently reacted with dioxygen, yielding peroxynitrite. If it is true, then Reactions (24) and (25) may represent a new pathway of peroxynitrite formation in mitochondria without the participation of superoxide. 

In the last 10 to 15 years, many experimental and theoretical studies have been dedicated to the study of peroxynitrite reactions. Free radical and non-free radical mechanisms of peroxynitrite action have been proposed, which were discussed in numerous studies (see for example, Refs. [103-110]). In accord with non-radical mechanism an activated form of peroxynitrous acid is formed in the reaction of superoxide with nitric oxide, which is able to react with biomolecules without the decomposition to HO and N02 radicals. 

Thus the competition between stimulatory and inhibitory effects of NO depends on the competition between two mechanisms the direct interaction of NO with free radicals formed in lipid peroxidation and the conversion of NO into peroxynitrite or other reactive NO metabolites. Based on this suggestion, Freeman and his coworkers [42-44] concluded that the prooxidant and antioxidant properties of nitric oxide depend on the relative concentrations of NO and oxygen. It was supposed that the prooxidant effect of nitric oxide originated from its reaction with dioxygen and superoxide ... 

Peroxyl radicals are not only ones, which are able to react with ubihydroquinones. Poderoso et al. [245] showed that the short-chain ubihydroquinones Q0 and Q2 are oxidized by nitric oxide with the rate constants of 0.49 x 104 and 1.6x 1041 mol-1 s 1, respectively. The reaction apparently proceeded by one-electron transfer mechanism because the formation of intermediate semiquinone radicals has been registered. 

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