Degradation routes

Nicotinamide is incorporated into NAD and nicotinamide is the primary ckculating form of the vitamin. NAD has two degradative routes by pyrophosphatase to form AMP and nicotinamide mononucleotide and by hydrolysis to yield nicotinamide adenosine diphosphate ribose. 

Because of the complexity of the polyether antibiotics tittle progress has been made in stmcture determination by the chemical degradation route. X-ray methods were the techniques most successfully applied for the early stmcture elucidations. Monensin, X206, lasalocid, lysocellin, and salinomycin were included in nineteen distinct polyether x-ray analyses reported in 1983 (190). Use of mass spectrometry (191), and H (192) and nmr (141) are also reviewed. More recently, innovative developments in these latter techniques have resulted in increased applications for stmcture determinations. Eor example, heteronuclear multiple bond connectivity (hmbc) and homonuclear Hartmann-Hahn spectroscopy were used to solve the stmcture of portimicin (14) (193). East atom bombardment mass spectrometry was used in solving the stmctures of maduramicin alpha and co-factors (58). 

Conley showed that die primary degradation route for resole networks is oxidation regardless of the atmosphere.6 By contrast, Morterra and Low found tiiat... 

Disruption of the native structure of a protein can also contribute to chemical instability by accelerating the rates of a variety of degradation routes, including deamidation, hydrolysis, oxidation, disulfide exchange, /1-elimination, and racemization. 

During catabolic and anabolic processes, a renovation of the molecular cellular components takes place. It should be emphasized that the catabolic and anabolic pathways are independent of each other. Be these pathways coincident and differing in the cycle direction only, the metabolism would have been side-tracked to the so-called useless, or futile, cycles. Such cycles arise in pathology, where a useless turnover of metabolites may occur. To avoid this undesirable contingency, the synthetic and degradative routes in the cell are most commonly separated in space. For example, the oxidation of fatty acids occurs in the mitochondria, while the synthesis thereof proceeds extramitochondrially, in the microsomes. 

Dorn et al. have studied the fate of epifenonane in polluted water (24). When Glatt River water was fortified with epifenonane at 10 ppm and exposed to open air for four weeks, 61% of the applied dose was recovered as intact epifenonane. Volatility losses amounted to 18% of the applied 3H while metabolites contributed a mere 21%. The characterized metabolites are listed in Table VI. The two major degradation routes involved epoxide modification and benzylic oxidation. 

Chlorination products of glyphosate, one of the most widely used herbicide in the world, and glycine, one of the intermediates in glyphosate chlorination, were investigated by Mehrsheikh et al. [111]. Both compounds followed a similar degradation route, with the final glyphosate chlorination products identified as methanediol and other small molecules, such as phosphoric acid, nitrate, CO2, and N2. 

Fe(II) goethite and Fe(II) with no mineral phase added. The degradation kinetics of CgCl NO in reactions and the change in sorbed Fe(II), [Fe(II)] as a function of pH are shown in Fig. 16.8. The primary degradation route for C Cl NO occurs through a surface-mediated reaction with Fe(II) the final product is C Cl NH, with an intermediate product believed to be phenylhydroxylamine (Cp NHOH). 

PLA is a compostable plastic material. Chemical hydrolysis is considered to be the main degradation route for PLA [14]. This hydrolysis process takes place at high humidity and at elevated temperatures (for example in industrial composting facilities). The fragments that result from the hydrolysis process, i.e., short oligomers and monomers, then can be metabolized by microorganisms. Therefore,... 

Figure 5.2 Production of 5-methylpyranozoic acid (5-MPA) by P. putida ATCC 33015. The upper part shows the degradation route for p-xylene, the lower part the production of 5-MPA, which is not attacked by benzoic acid dioxygenase.

Figure 5.5 Degradation routes for nitriles. The first route is a two-step reaction involving a nitrile hydratase, which converts the nitrile to the amide, and an amidase, which converts the amide to the corresponding acid. The second pathway involves direct hydrolysis of the nitrile to the carboxylic acid and ammonia by a nitrilase.

Ring and aryl methyl group oxidation were the initial toluene-degradation routes speculated on for the nitrate-reducing enrichment obtained by Kuhn etal. (1988) and the metabolically diverse iron-reducing bacterium Geobacter metallireducens (Lovley Lonergan, 1990). The speculation was consistent with the fact that both of these cultures could metabolize the appropriate suite of putative intermediates. However, conclusive evidence as to which pathway was actually involved was not obtained. 

The degradation reactions of polymers have been widely reviewed 525). In the absence of air, thermal reactions are the important degradation route. They may involve reactions of functional groups on the chain without chain scission, typified for example by the dehydrochlorination of PVC, or reactions involving chain scission, often followed by depropagation and chain-transfer reactions to yield complex mixtures of products. This latter route would be typical of the degradation of poly(methyl methacrylate), which depolymerizes smoothly to its monomer, and of polystyrene, which produces a wide range of tarry products. 

Hydrolysis and oxidation are the two primary degradation routes to which liposomal phospholipids are susceptible. Hydrolytic attack at the fatty acyl carbonyl will produce free fatty acids and lysophosphatides [e.g., lyso-phosphatidyl choline (LPC)]. Hydrolysis generally follows Lrst-order... 

More recently, studies have demonstrated that UV irradiation (220-460 nm) of aqueous PFOA solutions at room temperature in the presence of oxygen resulted in the formation of shorter-chain perfluoroalkyl carboxylates, CO2, and F" [30]. The environmental significance for this photolytic pathway was not discussed, but it is not likely to be an important degradation route for PFOA in natural surface waters. PFOA absorbs UV mostly at wavelengths below 220 nm [30], and these energetic wavelengths are not present at the earth s surface. 

The resistance of adamantane derivatives toward metabolic degradation is apparently due to three factors. First, adamantane is an unnatural biological substrate. For this reason, enzymes have not been developed in man to specifically attack it. Second, common degradative routes such as elimination are blocked in the adamantane nucleus. Adamantene or the enol of adamanta-... 

For both polyethylene and its many copolymeric variants and polypropylene, the main thermal degradative routes follow initial random chain scission. These reactions are only slightly affected by the differences in the physical structure such as crystallinity, but are influenced by the presence of impurities. However, it is largely true that while these may influence the proces-sibility and long-term stability of respective polyolefins, they may have little or no effect on the flammability. 

A number of drug substances and excipients employed in pharmaceutical products have a variety of chemical structures, which may be broken down under certain environmental conditions. Major degradation routes are hydrolysis, oxidation, and photolysis. 

Soil. In laboratory soil, DT50 6 days (aerobic), 28 days (anaerobic). Degradation routes include hydroxylation (at the 4 -phenoxyphenyl position), ring opening (with formation of a glycolic acid derivative), and is primarily microbial... 

Soil/environment. In laboratory soil (40% MHC, pH 5.3-7 7), DT50 2-9 days (20°C). Field DT50 <4 week. Koc 39-84. For degradation route, see fluazifop-P-butyl... 

The main degradation routes of the primarily produced molecular ion are those which require the lowest amount of energy. Therefore the weakest bonds are cleaved and the most stable degradation products are formed preferentially, because in these cases the energy... 

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