Radioactive degradation

If the former, only two carbons would be radioactive. Degradation, however, showed that radioactivity was equally distributed between all four C-atoms—2, 6, 10, and 11. Consequently, in this case at least, cadaverine is a metabolic intermediate. 

Norman ef al. (SO) showed that purified nucleoside diphosphate kinase from the Jerusalem artichoke was phosphorylated during incubation with P-ATP, and from an alkaline hydrolysate of the labeled enzyme 3-phosphohistidine was isolated. In similar experiments, nucleoside diphosphate kinases from human erythrocytes and bovine hver were phosphorylated with P-ATP and upon hydrolysis, the radioactive degradation products from the two enzymes were found to be the same and to include two phosphorylated derivatives of histidine and one of lysine, indicating that the nucleoside diphosphate kinases have similar structures at their active sites. 

There are only a few studies concerning the degradation and elimination of thiamin in animals. Most excess thiamin is eliminated as such by the kidneys. In a couple of older studies (Neal and Pearson 1964 Pearson et al. 1966), radioactive thiamin was administered in rats and the urines were analysed. Several radioactive degradation products of thiamin (2-methyl-4-amino-5-pyrimidine carboxylic acid and 4-methyl-thiazole-5-acetic acid), resulting from the cleavage between the thiazole and the pyrimidine moieties, were excreted in the urine. Other products were also detected but not identified. No enzymes specifically involved in thiamin degradation in mammals have been identified. 

Although temperature is the most common method of ageing materials, it is inappropriate when the issue is the radioactive degradation of any material. However, in practice temperature is a key parameter affecting chemical kinetics, and its use is normally based on the application of Arrhenius kinetics. In the absence of mechanistic information, the normal practice is to use the rule of thumb (the rate of reaction doubles per 10 °C rise) to identify a simulated age. However in practice, this is rarely true for many materials and multi-material assemblies and questions the validity of accelerated ageing trials based upon this rule of thumb. Therefore great caution is required in the use of Arrhenius kinetics in life prediction [2]. 

Another of the elements that has a crucial impact on the total dose is the Ra226, arisen with radioactive degradation of uranium matrix—with a short half-life (1600 years) the released quantity is increasing with natural degradation of safety barriers and a large mass of U238 concentrated in a small volume of the DGR. 

The metabohc rate of poly(ester—amide) where x = Q has been studied in rats using carbon-14 labeled polymer. This study indicates that polymer degradation occurs as a result of hydrolysis of the ester linkages whereas the amide linkages remain relatively stable in vivo. Most of the radioactivity is excreted by urine in the form of unchanged amidediol monomer, the polymer hydrolysis product (51). 

A related mechanism of degradation involves the direct interaction of the radioactive emission with other tracer molecules in the preparation. This phenomenon is likely to occur in high specific activity compounds stored at high radiochemical concentrations in the absence of free-radical scavengers. 

The analyses of system failures which could challenge the containment or lead to the release of radioactivity form the licensing process. The design basis analyses are deterministic, and degraded core accidents are not considered. PSA determines the probabilities of the numerous sequences that could lead to core degradation and how the core behaves. 

The formed acrolein was photochemically degraded to ethylene and carhon monoxide. It has been found that radioactivity was exclusively associated with ethylene when propylene tagged with at C2 was used. Also, carhon monoxide was found to he free from radioactivity ... 

When propylene tagged with at either Ci or C3 was oxidized to acrolein and then degraded, both CH2=CH2 and CO were radioactive, and the ratio of radioactivity was 1. 

Scheme 27.—A degradation of D-ribose, which allows the localization of radioactivity in each carbon atom.

The experiments with (U-l3C)AIRs showed that this nucleoside supplied all of the carbon atoms of pyramine. Because out of 6 carbon atoms of pyramine, only three may come from the imidazole part of AIRs, it can be concluded that the three other carbon atoms come from the ribose part of this nucleoside. In complete agreement with these results, radioactivity from AIRs, labeled mainly with, 4C in its ribose part, was found to incorporate into the three carbon atoms of pyramine, the origin of which was, at the time, unknown. Owing to the minute amount of AIRs supplied (as compared with that of glucose) in both experiments, the incorporation of label from AIRs after metabolic degradation is ruled out. 

Nick translation A technique for labeling DNA based on the ability of the DNA polymerase from E colt to degrade a strand of DNA that has been nicked and then to resynthesize the strand if a radioactive nucleoside triphosphate is employed, the rebuilt strand becomes labeled and can be used as a radioactive probe. 

The application of substrates isotopically labeled in specific positions makes it possible to follow the fate of individual atoms during the microbial degradation of xenobiotics. Under optimal conditions, both the kinetics of the degradation, and the formation of metabolites may be followed— ideally when samples of the labeled metabolites are available. Many of the classical studies on the microbial metabolism of carbohydrates, carboxylic acids, and amino acids used radioactive... 

Validation of true extraction efficiency normally requires the identification and quantitation of field-applied radiolabeled analyte(s), including resulting metabolites and all other degradation products. The manufacturer of a new pesticide has to perform such experiments and is able to determine the extraction efficiency of aged residues. Without any identification of residue components the calculation of the ratio between extracted radioactivity and total radioactivity inside the sample before extraction gives a first impression of the extraction efficiency of solvents. At best, this ratio is nearly 1 (i.e., a traceability of about 100%) and no further information is required. Such an efficient extraction solvent may serve as a reference solvent for any comparison with other extraction procedures. 

The fundamental issue is to describe how much of the residue can be characterized accurately and whether an accounting of the applied mass of pesticide can be maintained throughout the course of the experiment. A series of environmental fate studies is required for pesticide registration in order to characterize the degradation pathways and formation and decline patterns of each major degradate. These studies are typically conducted in the laboratory under controlled conditions, applying radiolabeled pesticides to evaluate the extraction efficiency of various procedures. When standard extraction methods fail to release a significant amount of the applied radioactivity, more efficient and exhaustive extraction procedures are tried in a stepwise fashion... 

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