Oxidative denitrification

P., Oxidative denitrification of N-omega-hydroxy-L-arginine by the superoxide radical anion, Biochem. J. 317 (1996), p. 17-21... 

Nitropropane exists in equilibrium with its tautomer propane-2-nitronic acid, present in physiological media as the anion propane-2-nitronate. Dayal et al. (1991) have investigated the metabolism of both 2-nitropropane and propane-2-nitronate in mouse microsomes and found that the oxidative denitrification of propane-2-nitronate was 5-10 times more extensive than that of 2-nitropropane. Acetone formed by this reaction affords the source of 002 detected when 2-nitro -C prop iiic was administered in vivo. However, neither 2-nitropropane nor propane-2-nitronate was cytotoxic to mouse hepatocytes. 

Dayal, R., Goodwin, B., Linhart, I., Mynett, K. Gescher, A. (1991) Oxidation denitrification of 2-nitropropane and propane-2-nitronate by mouse liver microsomes lack of correlation with hepatocytotoxic potential. Chem.-biol. Interact., 79, 103-114... 

The reaction and separation synthesis approach of Section 5 has been adopted to the problem of activated sludge process design (83). The conventional designs as well as all novel schemes for combined oxidation/denitrification of wastewater are explored. The process is optimized using a novel methodology for optimal reaction/separation network synthesis, supplied with a comprehensive kinetic model (84). The activated sludge process is synthesized using the systematic... 

In the Baltic-North Sea transition smdy of Thamdrup and Dalsgaard (2002), anammox contributed 33-67% of total N2 production at continental shelf sites, but just 2% of total N2 production at the site in a coastal bay (Figure 16). The difference between the bay site and the closest continental shelf site was due primarily to an increase in the denitrification rate, rather than a decrease in anaerobic oxidation. Denitrification declined in parallel with declining sediment organic carbon content from the coastal bay seaward. Absolute rates of anaerobic NH4 oxidation were in the range 30-99 p.M d and were lowest at the site where the percent contribution was highest. This pattern is consistent with evidence that anammox organisms are autotrophic, whereas denitrifiers are heterotrophic. 

Some of the important reactions catalyzed by the P450 monooxygenase system include aliphatic hydroxylation, aromatic hydroxylation, epoxidation, heteroatom (N-, 0-, and S-)dealkylation, nitrogen oxidation, oxidative deamination, oxidative dehalo-genation, oxidative denitrification, and oxidative desulfuration. Most of these reactions result from the initial oxidation of a carbon atom, another reason that P450 is so important in the oxidative biotrans-formation of lipophilic chemicals. Some P450-cataly-zed oxidation reactions are illustrated in Table 2. 

FIGURE 16.10 Soil redox zone where methane and nitrous oxide denitrification occur. (Modified from data by Yu and Patrick, 2003.)... 

The process of nitrification—denitrification can be practiced in one of two ways. In the oxidation ditch, nitrification occurs in the vicinity of the aerators. When the dissolved oxygen is depleted as the sludge—wastewater mixture passes from the aerator, denitrification occurs. 

K. A. Smith and J. R. M. Arah, Losses of Nitrogen by Denitrification and Emissions of Nitrogen Oxides from Soils, The Fertiliser Soeiety, 1990, Proeeedings No. 299. 

In soil, microbial nitrification and denitrification are the predominant sources of NO and NjO and the emission fiiixes may be regarded as leakage during the transformation processes shown in Figure 6. Nitrifiers can produce NO and NjO during the oxidation of NH4 to NO3". Both gases are by-products of the nitrification pathway and the typical yield of NO in well-aerated soil is 1-4% of the NH4 oxidized and for NjO is less than... 

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... 

W. J. Payne, in Denitrification, Nitrification and Atmospheric Nitrons Oxide, ed. C. C. Delwiche,... 

Nitrogen oxides are formed at various stages of the biological denitrification process. This process starts with nitrate as the nitrate is reduced through various steps, NO2, NO, N2O, and N2 can be formed and, depending on the conditions, released to the atmosphere. 

Acetylene-block assay Estimates denitrification by determining release of nitrous oxide (NjO) from acetylene-treated soil. 

Denitrification The reduetion of nitrates to nitrites and finally to nitrous oxide or even to moleeular nitrogen eatalyzed by faeultative aerobie soil baeteria working under anaerobie eonditions. 

Bremner, J. M. and Blackmer, A. M. (1981). Terrestrial nitrification as a source of atmospheric nitrous oxide. In Denitrification, Nitrification, and Atmospheric Nitrous Oxide" (C. C. Delwiche, ed.). Wiley, New York. 

Table 19-1 demonstrates that with the exception of water vapor, all of these cycles have been severely perturbed by human activity. Of course, all of these cycles are also linked in many ways. For example, the combustion of fossil fuel has increased the fluxes of carbon, sulfur, and nitrogen oxides to the atmosphere. Denitrification, the production of N2O, is linked with the production of CO2 during respiration and decay. And of course, other important cycles are involved which are not depicted here. Look back at Fig. 17-8, which sums up the climate forcings by the key agents. 

Hydrogenation reactions, particularly for the manufacture of fine chemicals, prevail in the research of three-phase processes. Examples are hydrogenation of citral (selectivity > 80% [86-88]) and 2-butyne-l,4-diol (conversion > 80% and selectivity > 97% [89]). Eor Pt/ACE the yield to n-sorbitol in hydrogenation of D-glucose exceeded 99.5% [90]. Water denitrification via hydrogenation of nitrites and nitrates was extensively studied using fiber-based catalysts [91-95]. An attempt to use fiber-structured catalysts for wet air oxidation of organics (4-nitrophenol as a model compound) in water was successful. TOC removal up to 90% was achieved [96]. 

Denitrification involves the sequential formation of nitrite, nitric oxide, and nitrous oxide. Two aspects of nitric oxide have attracted attention (a) chemical oxidation of biogenic nitric oxide to Nq, in the context of increased ozone formation (Stohl et al. 1996) and (b) the physiological role in mammalian systems (Feldman et al. 1993 Stuehr et al. 2004), in parasitic infections (James 1995), and in the inhibition of bacterial respiration (Nagata et al. 1998). Nitric oxide may be produced microbiologically in widely different reactions such as... 

Moir JWB, DJ Richardson, SJ Ferguson (1995) The expression of redox proteins of denitrification in Thiosphaerapantropha grown with oxygen, nitrate, and nitrous oxide. Arch Microbiol 164 43-49. 

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