Nitric oxide reduction— products

Besides the photochemical dissociation, ozone decays in oxidation-reduction reactions with different species. The stratospheric 03 reacts rapidly with nitric oxide and products of photodissociation of halogenated hydrocarbons (Figure 9.5). 

Nitrous oxide (N20, also known as dinitrogen oxide) is one of the main products of nitric oxide reduction. It is regarded as an undesirable and harmful component of automotive exhaust gases,40 and it is a more harmful greenhouse gas than carbon dioxide, possibly contributing to ozone depletion in the upper atmosphere.6 13 In spite of this, there are still only a few papers... 

Nitric oxide reduction by hydrocarbons over oxidized copper samples has been studied by multiplexed mass-spectrometry in an all quartz reactor operated in static mode. At 600°C the reaction proceeds exclusively via consumption of HC and NO. NO is not consumed in the presence of dioxygen but preoxidation of the copper sample is necessary to facilitate high conversion rates. Infrared spectra obtained in situ at 45- incidence angle verify the conversion and show that the bulk of the active catalyst consists of cuprous oxide. A combination of IR-and mass-spectroscopy has proven to be a successful way to identify additional products and intermediates in the gasphase. 

Again, nitric acid readily dissolves lead but is unable to oxidise lead beyond the oxidation state -P 2. The reduction products of the nitric acid vary with the concentration of acid used, and a number of nitrogen oxides are usually obtained. Warm dilute nitric acid gives mainly nitrogen oxide, NO. 

Nitric oxide and NjO are direct intermediates in the denitrification pathway, the reduction of NO3 to Nj. Reduction to Nj is often incomplete, so that both NjO and Nj are equally important end products of denitrification, the ratio of NjO/Nj production being determined by soil physical properties. For example, NjO is the main end-product in acid soils, whereas low redox potentials and high organic matter content favour the further reduction to Nitric... 

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

Nitroxides are iV, iV-disubsdnited nitric oxide radicals, the unpaired electron being delocalized between the nitrogen and oxygen The reduction of 2-methyl-2-nitropropane with sodium or electrochemically yields di-r-butyl nitroxide as the final product " Such nitroxide radicals are important for the snidy of a organic ferromagnet... 

Copper metal is comparatively inactive, but it reacts with concentrated nitric acid. The brown fumes are I l02(g), a reduction product of HN03. The copper is oxidized to Cuz+ ions, which impart their color to the solution. (The penny is an old one made of solid copper. Newer pennies have a coating of copper over a zinc core.)... 

Dilute nitric acid (6 M) gives a wide variety of reduction products, depending on the nature of the reducing agent. With inactive metals such as copper (E = —0.339 V), the major product is usually NO (oxid. no. N = +2) ... 

A relationship between polyol pathway activity and reduction in endothelium-dependent relaxation in aorta from chronic STZ-diabetic rats has recently been reported (Cameron and Cotter, 1992). In agreement with several previous studies (Oyama et al., 1986 Kamata et al., 1989), endothelial-dependent relaxation was defective in the diabetic rats but the deficit was prevented by prior treatment with an AR inhibitor. The mechanism underlying the defect has been speculated to be due to decreased production of endothelium-derived relaxing factor (EDRF) or nitric oxide, NO (Hattori et al., 1991). It has been speculated that these vascular abnormalities may lead to diminished blood flow in susceptible tissues and contribute to the development of some diabetic complications. NO is synthesized from the amino-acid L-arginine by a calcium-dependent NO synthase, which requires NADPH as a cofactor. Competition for NADPH from the polyol pathway would take place during times of sustained hyperglycaemia and... 

Water soluble iron porphyrins [Fem(TPPS)(H20) ]3-330 and [Fem(TMPy)(H20)2]5+ 331 332 (TPPS = maso-tetrakis(/ -sulfonatophenyl)porphyrin, TMPyP = / /e.vo-tetrakis(7V-methyl-4-pyridi-nium)porphyrin331 or maso-tetrakis (A -methyl-2-pyridinium)porphyrin332 dications) act as effective electrocatalysts for the reduction of nitrite to ammonia in aqueous electrolytes (Equation (64) Ei/2= 0.103 V vs. SCE at pH 7), with NH2OH or N20 also appearing as products depending on the reaction conditions. Nitric oxide then ligates to the iron(III) porphyrin to form a nitrosyl complex [Fen(P)(NO+)] (P = porphyrin) as intermediate. 

However, aluminum forms an oxide layer on the surface, and it becomes passive to further action. Sulfur is oxidized to sulfuric acid, with the reduction product being nitric oxide. 

However, at high rates of nitric oxide flux, the formation of nitrated and oxidized products became insensitive to the presence of catalase or MPO inhibitors but increasingly inhibited by SOD, suggesting the participation of peroxynitrite. (It is interesting that Reaction (30) might be a one-electron reduction of hydrogen peroxide by nitrite ion. If such a process really takes... 

The capacity of furoxan derivatives to behave as NO-donors was first demonstrated by Feelisch et al. [19], who showed that furoxan derivatives produce nitric oxide when dissolved in physiological solution in the presence of thiols. Among the reaction products, they isolated nitrite and, in lesser amounts, nitrate, which are the final oxidation products of nitric oxide in aerobic water solution, as well as dioxime derivatives, which are the reduction products of the furoxans. They also evidenced a marked p H -dependent production of S-nitrosothiols. Working with N, AF-diisopropylfuroxan-3,4-dicarboxamide (29, Ipramidil) and an excess of glutathione (GSH), the amount of S-nitrosoglutathione formed increased with increasing pH until pH 9, above which it... 

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