From nitrites

Table 3. Synthesis of ort/io-Substituted Fluoroaromatics from Nitrite Esters, Boron Trifluoride, and Hydrogen Fluoride [26]...

Apart from nitrite and molybdate, silicate is commonly employed in anodic inhibitor programs, although seldom as the primary inhibitor. Both silicates and molybdates provide benefits of synergistic inhibition and also help to reduce corrosion risks through softer waters and multimetal systems. 

NMOR is a potent hepatocarcinogen in the rat and induces tracheal and nasal cavity tumors in the Syrian golden hamster (43, 44, 45). It is formed readily from nitrite and morpholine in vitro and administration of these precursors to rodents causes tumors indicative of NMOR formation in vivo (44, 55, 56), NMOR has been detected in crankcase emissions of diesel engines and in factories engaged in rubber and tire manufacturing (57, 58). 

Recently nitrosamines have attracted attention because of their marked carcinogenic activity in a wide variety of animal species Q, ). Nitrosamines are likely to be carcinogens in man as well human exposure to these compounds is by ingestion, inhalation, dermal contact and vivo formation from nitrite and amines Nitrite and amines react most rapidly at an acidic pH A variety of factors, however, make nitrosation a potentially important reaction above pH 7 these include the presence of microorganisms, and the possibilities of catalysis by thiocyanate, metals and phenols, and of transnitrosation by other nitroso compounds. 

We have proposed that gastric cancer may be the end result of a series of mutations (or similar cell transformations) begun many years before cancer becomes clinically apparent. The mutagens could be nitroso compounds synthesized situ from nitrite and naturally-occurring nitrogen-containing compounds. 

The principal source of nitrite for formation of N-nitroso compounds in the stomach is cured meats, since the concentration of nitrite will be highest because of the rapidity of ingestion of them. The rate of formation of N-nitroso compounds is proportional to the square of the nitrite concentration, so that the extent of formation of these compounds will be greater from the nitrite supplied by cured meats than from nitrite in saliva, even... 

In their paper in 1987, Hibbs et al. (1987a) proposed that the characteristic pattern of metabolic dysfunction inflicted by CAMs is due to iron loss from aconitase and other iron-sulfur-containing enzymes resulting from nitrite or oxygenated nitrogen intermediates in the pathway of nitrite and nitrate synthesis. Much data have since been published to support this proposal, although as described below the chemical details of this process are still not clear. 

Based on the incomplete inhibition of iron-sulfur proteins by nitrite, and the observation that low-spin Fe—NO EPR signals were observed by C. sporogenes cultures that recovered from nitrite treatment, Payne et al. (1990a) concluded that the antimicrobial effect of nitrite or NO cannot be explained by direct inhibition of preformed pyruvate—ferredoxin oxidoreductase or hydrogenase. 

Zubillaga, M. P., and Maerker, G. (1987). Antioxidant activity of polar lipids from nitrite-treated cooked and processed meats. J. Am. Oil Chem. Soc. 64, 757-760. 

As will be discussed further in this chapter, there is now much evidence to suggest that NO is an obligatory intermediate in the denitrification pathway. Furthermore, there is evidence that NH3 nitrifiers can synthesize the denitrification apparatus in addition to the nitrification apparatus and that the former system can produce NO and N2O (also N2 in at least one case) from nitrite under low partial pressures of O2. It is possible therefore that NO may be an intermediate in the denitrification activity of nitrifiers and so arise as a secondary consequence of NH3 oxidation. NO can also be ptoduced by nondenitrifying organisms under certain conditions. For example, NO can be slowly produced by the anaerobic reduction of nitrite, but only in absence of nitrate, by a variety of enteric bacteria. Some of the NO can be further reduced to N2O. 

The second means of inducing nitrite reductase to produce NjO also applied principally but not exclusively to the Cu-type enzyme and involves the use of hydroxylamine (NH2OH) as reducing agent (Denariaz et al., 1991 Iwasaki and Matsubara, 1972 Iwasaki and Mori, 1958 Kim and Hollocher, 1984 Liu etal., 1986 Masuko et al., 1984 Matsubara, 1970 Zumft et al., 1987). The reaction catalyzed [Eq. (4)] is one in which one atom of N in N2O arises from nitrite and the other from NHjOH. 

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