Nitric oxide kinetics with

At the high temperatures found in MHD combustors, nitrogen oxides, NO, are formed primarily by gas-phase reactions, rather than from fuel-bound nitrogen. The principal constituent is nitric oxide [10102-43-9] NO, and the amount formed is generally limited by kinetics. Equilibrium values are reached only at very high temperatures. NO decomposes as the gas cools, at a rate which decreases with temperature. If the combustion gas cools too rapidly after the MHD channel the NO has insufficient time to decompose and excessive amounts can be released to the atmosphere. Below about 1800 K there is essentially no thermal decomposition of NO. 

A sophisticated quantitative analysis of experimental data was performed by Voltz et al. (96). Their experiment was performed over commercially available platinum catalysts on pellets and monoliths, with temperatures and gaseous compositions simulating exhaust gases. They found that carbon monoxide, propylene, and nitric oxide all exhibit strong poisoning effects on all kinetic rates. Their data can be fitted by equations of the form ... 

The associative reaction of oxygen atoms with nitric oxide produces the yellow-green chemiluminescence in the air afterglow, easily seen by the naked eye. The reaction has long been used to measure the concentrations of O atoms in kinetics experiments [49-51] and is so bright that it has been used to visualize... 

Ru(edta)(H20)] reacts very rapidly with nitric oxide (171). Reaction is much more rapid at pH 5 than at low and high pHs. The pH/rate profile for this reaction is very similar to those established earlier for reaction of this ruthenium(III) complex with azide and with dimethylthiourea. Such behavior may be interpreted in terms of the protonation equilibria between [Ru(edtaH)(H20)], [Ru(edta)(H20)], and [Ru(edta)(OH)]2- the [Ru(edta)(H20)] species is always the most reactive. The apparent relative slowness of the reaction of [Ru(edta)(H20)] with nitric oxide in acetate buffer is attributable to rapid formation of less reactive [Ru(edta)(OAc)] [Ru(edta)(H20)] also reacts relatively slowly with nitrite. Laser flash photolysis studies of [Ru(edta)(NO)]-show a complicated kinetic pattern, from which it is possible to extract activation parameters both for dissociation of this complex and for its formation from [Ru(edta)(H20)] . Values of AS = —76 J K-1 mol-1 and A V = —12.8 cm3 mol-1 for the latter are compatible with AS values between —76 and —107 J K-1mol-1 and AV values between —7 and —12 cm3 mol-1 for other complex-formation reactions of [Ru(edta) (H20)]- (168) and with an associative mechanism. In contrast, activation parameters for dissociation of [Ru(edta)(NO)] (AS = —4JK-1mol-1 A V = +10 cm3 mol-1) suggest a dissociative interchange mechanism (172). 

The NO/NO+ and NO/NO- self-exchange rates are quite slow (42). Therefore, the kinetics of nitric oxide electron transfer reactions are strongly affected by transition metal complexes, particularly by those that are labile and redox active which can serve to promote these reactions. Although iron is the most important metal target for nitric oxide in mammalian biology, other metal centers might also react with NO. For example, both cobalt (in the form of cobalamin) (43,44) and copper (in the form of different types of copper proteins) (45) have been identified as potential NO targets. In addition, a substantial fraction of the bacterial nitrite reductases (which catalyze reduction of NO2 to NO) are copper enzymes (46). The interactions of NO with such metal centers continue to be rich for further exploration. 

N-diazeniumdiolates spontaneously dissociate at physiological pH to release nitric oxide (NO) by stable first order kinetics with half-lives ranging from 2 s to 20 h [209, 210]. They are blessed with many attributes that make them an especially attractive starting point for designing solutions to important clinical problems, namely they are stable as solids, have structural diversity, a controlled rate of release of NO on hydrolysis, and a rich derivatization chemistry that facilitates targeting of NO to specific sites of need, a critical goal for therapeutic uses of a molecule with natural bioeffector roles in virtually every organ [208]. 

The formation of S-nitroso thiols (R -S-N=0) is partly understood. A hypothetical mechanism is the reduction of A-oxosulfinamide derivatives (9.21, Fig. 9.4), but nothing appears to be known about such a possibility. What has been demonstrated is that nitric oxide by itself does not react with thiols to form 5-nitroso thiols, but does so in the presence of 02. Detailed kinetic analyses led to the mechanism summarized by Eqns. 9.1-9.3 [44] [45], In these and the following reactions, thiols are written as R -SH in consistency with Figs. 9.4 and 9.5. 

Y. Shiro, M. Fujii, T. Iizuka, S. Adachi, K. Tsukamoto, K. Nakahara, H. Shoun, Spectroscopic and Kinetic Studies on Reaction of Cytochrome P450 nor with Nitric Oxide , J. Biol. Chem. 1995, 270, 1617-1623. 

O DormeU, V. B., Chumley, P. H., Hogg, N., Bloodsworth, A., Darley-Usmar, V. M., and Freeman, B. A., 1997, Nitric oxide inhibition of Upid peroxidation kinetics of reaction with lipid peroxyl radicals and comparison with alpha-tocopherol, Biochemistry 36 15216-15223. 

A kinetic study of nitrous acid-catalyzed nitration of naphthalene with an excess of nitric acid in aqueous mixture of sulfuric and acetic acids (Leis et al. 1988) shows a transition from first-order to second-order kinetics with respect to naphthalene. (At this acidity, the rate of reaction through the nitronium ion is too slow to be significant the amount of nitrous acid is sufficient to make one-electron oxidation of naphthalene as the main reaction path.) The reaction that initially had the first-order in respect to naphthalene becomes the second-order reaction. The electron transfer from naphthalene to NO+ has an equilibrium (reversible) character. In excess of the substrate, the equilibrium shifts to the right. A cause of the shift is the stabilization of cation-radical by uncharged naphthalene. The stabilized cation-radical dimer (NaphH)2 is just involved in nitration ... 

Lewis, R. S., and W. M. Deen, Kinetics of the Reaction of Nitric Oxide with Oxygen in Aqueous Solutions, Chem. Res. Toxicol., 7, 568-574 (1994). 

Comparison of the observed pseudo-first-order decay of biological activity with a half-life of 30 sec at normal oxygen tensions versus decomposition via nitrogen dioxide by pseudo-second-order kinetics predicted by Reaction 4. The loss of nitric oxide through formation of nitrogen oxide is twice as fast as calculated by Reaction 4 because each nitrogen dioxide formed rapidly attacks a second nitric oxide to form nitrite. 

Hyman, M. R., and Arp, D. J. (1991). Kinetic analysis of the interaction of nitric oxide with the membrane-associated, nickel and iron-sulfur-containing hydrogenase from Azotobacter vinelandii. Biochim. Biophys. Acta 1076, 165-172. 

From the thermodynamic data of Appendix C, show that the product of the reaction of ammonia gas with oxygen would be nitrogen, rather than nitric oxide, under standard conditions and in the absence of kinetic control by, for example, specific catalysis of NO formation by platinum. (Assume the other product to be water vapor.)... 

Bodenstein has, however, shown that the combination of nitric oxide and oxygen 2N0 + 02 = 2N02 is a homogeneous change which is kinetically of the third order, and the same appears to apply to the combination of nitric oxide with chlorine and with bromine f and to the reaction between nitric oxide and hydrogen. J 2NO + C12 = 2NOC1 2NO + Br2 = 2NOBr 2NO + H2 = N20+H20... 

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