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Mechanisms of NO formation

Given that hydroxylamine reacts rapidly with heme proteins and other oxidants to produce NO [53], the hydrolysis of hydroxyurea to hydroxylamine also provides an alternative mechanism of NO formation from hydroxyurea, potentially compatible with the observed clinical increases in NO metabolites during hydroxyurea therapy. Incubation of hydroxyurea with human blood in the presence of urease results in the formation of HbNO [122]. This reaction also produces metHb and the NO metabolites nitrite and nitrate and time course studies show that the HbNO forms quickly and reaches a peak after 15 min [122]. Consistent with earlier reports, the incubation ofhy-droxyurea (10 mM) and blood in the absence of urease or with heat-denatured urease fails to produce HbNO over 2 h and suggests that HbNO formation occurs through the reactions of hemoglobin and hydroxylamine, formed by the urease-mediated hydrolysis of hydroxyurea [122]. Significantly, these results confirm that the kinetics of HbNO formation from the direct reactions of hydroxyurea with any blood component occur too slowly to account for the observed in vivo increase in HbNO and focus future work on the hydrolytic metabolism of hydroxyurea. [Pg.193]

Most gaseous fuels as well as some liquid fuels contain no or only small amounts of chemically bound nitrogen. In combustion of these fuels, the important source of NO is fixation of N2 in the combustion air. Molecular nitrogen, with its triple bond, is very stable, and only very reactive radicals may succesfully attack N2. The mechanisms of NO formation from N2 is quite well understood [274], and for many applications semiquantitative predictions of NO are within reach. [Pg.604]

Laser-Fluorescence techniques for NO are of interest for studying the mechanisms of NO formation and its influence on chemical processes and pollutant formation in flames. In general, the optical fluorescence techniques provide very high detection sensitivities and good spatial resolution. [Pg.153]

One of the important hydrocarbon combustion reaction intermediates is the CH radical. Although CH chemiluminescence (.42 A — X2ir) has been observed in many hydrocarbon flames, the mechanism of CH formation and its reaction kinetics have been difficult to unravel in situ due to the low steady-state concentrations and the complex nature of combustion reactions. This project was undertaken to investigate a means of CH radical production and to study its reactions with various important species so that an overall picture of the oxidation processes, particularly with regard to the mechanism of NO formation, may be better understood. [Pg.397]

This mechanism of NO formation is believed to be basic for burning lean mixtures, when the Fenimore mechanism is already inefficient because of absence of CH radicals. Reaction (88), being termolecular, notably accelerates at high pressures and is considered to be limiting in this case. Relatively low activation energies of reactions (88) and (89) make this mechanism responsible for nitrogen oxides formation at low temperatures and pressure of several MPa, when the thermal nitrogen oxides are not virtually formed. Since coal is burnt, as a rule, at the pressure close to atmospheric, this mechanism may not be considered below. [Pg.56]

The presented brief survey of basic mechanisms of NO formation during coal combustion allows the MEIS construction with their simultaneous inclusion in the kinetic constraints. Kinetic constraints can be formulated according to the third way among those considered in Section 3.4. [Pg.56]

At the same time calculations on the modified MEIS are possible without additional kinetic models and do not require extra experimental data for calculations, which makes it possible to use less initial information and obviously reduces the time and labor spent for computing experiment. Furthermore, there arise principally new possibilities for the analysis of methods to mitigate emissions from pulverized-coal boilers, since at separate modeling of different mechanisms of NO formation the measures taken can result in different consequences for each in terms of efficiency. Consideration of kinetic constraints in MEIS will substantially expand the sphere of their application to study other methods of coal combustion (fluidized bed, fixed bed, etc.) and to model processes of forming other pollutants such as polyaromatic hydrocarbons, CO, soot, etc. [Pg.62]

England, G. C., Heap, M. P., Pershing, D.W., Nihart, R. K., and Martin, G.B., "Mechanisms of NO Formation and Control Alternative and Petroleum-Derived Liquid Fuels," 18th Symposium on Combustion, The Combustion Institute, 1981. [Pg.34]

The mechanism of NO formation has been studied in detail and can be summarized as follows (Figure 5.25) ... [Pg.125]

There is increasing attention to the biological importance of mechanisms of NO formation not involving -NO synthase. Although it has been known for decades that nitrosothiols can produce -NO, and could be important in certain... [Pg.2995]

Nitric oxide is formed in combustion engines by the interaction of oxygen and nitrogen in air at the high temperatures reached during the combustion cycle. The percentages of NO found in the exhaust gas is close to that calculated from the chemical equilibrium N2+02 = 2N0 at peak temperatures near 2500 K. Once NO is formed, its abundance seems to be effectively frozen in. The mechanism of NO formation is not precisely known. Most authors have adopted the reaction chain first proposed by Zeldovich et al. (1947) ... [Pg.179]

Figure 6. Mechanisms of NO, formation and destruction (Gibbs and Hampartsoumian, 1984)... Figure 6. Mechanisms of NO, formation and destruction (Gibbs and Hampartsoumian, 1984)...
The primary objectives of this chapter are to detail the methods by which enamines (a,/3-unsaturated amines) (I) can be synthesized and the mechanisms of enamine formation. The enamines discussed are those in which the nitrogen is tertiary and, with the exception of a few selected examples, Contain no other functional groups. The term simple enamines might be used to describe the majority of enamines noted in this chapter. [Pg.55]

There is no unanimity in regard to the exact mechanism of ECC formation under high pressure. Wunderlich et al. [11-18] suggested that when a flexible polymer molecule crystallizes from the melt under high pressure, it does not grow in the form of a stable extended chain, rather it deposits as a metastable folded chain. [Pg.296]

Mechanism of enamine formation by reaction of an aldehyde or ketone with a secondary amine, R2NH. The iminium ion intermediate has no hydrogen attached to N and so must lose H+ from the carbon two atoms away. [Pg.713]

N,4-DinitrO N-methylaniline, bright yellow needles from benz, mp 142.5° (Ref 2) CA Registry No 16698-03-6. It is prepu by the alkylation of N,p-dinitroaniline with methyl iodide in alk soln (Refs 8 9). It is one compd isolated from aged NC propints stabilized with N-methyl-p-nitroaniline. Hollingsworth at ERDE examined the reaction of nitrogen dioxide with this stabilizer in order to elucidate the mechanism of the formation of the compds isolated. He found that after 7 days at 35°,. a good yield of N,4-dinitro-N-methylaniline was obtd and postulated that it arose from the oxidn of N-nitroso-4-nitroaniline (Ref 16)... [Pg.118]

Figure 25.27 illustrates the contributions of the three mechanisms to NO formation. It can be seen from Figure 25.27 that both the fuel and prompt NO are weakly dependent on temperature. Below around 1300°C thermal NO formation is negligible. However, at the highest temperatures thermal NO is the most important. Once NO has been formed, it can then oxidize to NO2 according to ... [Pg.570]

The mechanism of H02 formation from peroxyl radicals of primary and secondary amines is clear (see the kinetic scheme). The problem of H02 formation in oxidized tertiary amines is not yet solved. The analysis of peroxides formed during amine oxidation using catalase, Ti(TV) and by water extraction gave controversial results [17], The formed hydroperoxide appeared to be labile and is hydrolyzed with H202 formation. The analysis of hydroperoxides formed in co-oxidation of cumene and 2-propaneamine, 7V-bis(ethyl methyl) showed the formation of two peroxides, namely H202 and (Me2CH)2NC(OOH)Me2 [16]. There is no doubt that the two peroxyl radicals are acting H02 and a-aminoalkylperoxyl. The difficulty is to find experimentally the real proportion between them in oxidized amine and to clarify the way of hydroperoxyl radical formation. [Pg.359]

The mechanism of NO release from N-diazeniumdiolates is depicted in Fig. 3.7. If R>, of the generic structure shown at the top is a cation, NO is generated spontaneously on protonation of the anionic portion along with the formation of dialkylamine. If R3 is covalently bound, it must be removed first to free the anion before spontaneous... [Pg.76]

The rate of NO formation in the reaction between I-Cysteine (i-Cys) and a fixed amount of Ipramidil increased as the I-Cys /furoxan ratio increased and became constant for ratios above 50 1. A reasonable mechanism to justify their findings has been proposed (Scheme 6.8). [Pg.138]

Despite intense study of the chemical reactivity of the inorganic NO donor SNP with a number of electrophiles and nucleophiles (in particular thiols), the mechanism of NO release from this drug also remains incompletely understood. In biological systems, both enzymatic and non-enzymatic pathways appear to be involved [28]. Nitric oxide release is thought to be preceded by a one-electron reduction step followed by release of cyanide, and an inner-sphere charge transfer reaction between the ni-trosonium ion (NO+) and the ferrous iron (Fe2+). Upon addition of SNP to tissues, formation of iron nitrosyl complexes, which are in equilibrium with S-nitrosothiols, has been observed. A membrane-bound enzyme may be involved in the generation of NO from SNP in vascular tissue [35], but the exact nature of this reducing activity is unknown. [Pg.293]

The solution is diluted with 200 c.c. of water and boiled until a sample, when mixed with dichromate solution, no longer smells of nitrosobenzene but of quinone (ten to fifteen minutes). To the cooled solution 2 g. of dichromate dissolved in water are added, a downward condenser is attached to the flask containing the mixture, and steam is passed through. The quinone is carried over with the steam. On the mechanism of its formation in this reaction compare p. 310. Test the residue in the flask for ammonia. [Pg.176]


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See also in sourсe #XX -- [ Pg.54 , Pg.56 ]




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