Degradation tritium

A radioactivity detector is used to measure radioactivity in the HPLC eluent, using a flow cell. The detection principle is based on liquid scintillation technology to detect phosphors caused by radiation, though a solid-state scintillator is often used around the flow cell [17,31]. This detector is very specific and can be extremely sensitive. It is often used for conducting experiments using tritium or C-14 radiolabeled compounds in toxicological, metabolic, or degradation studies. 

J.C. Sutherland and Griffin incorporated tritium-labelled thymine into DNA and irradiated it with 313 nm light in buffered saline in the presence of p-aminobenzoic acid for up to 12 min. After separation of the products by TLC, the radioactivity was associated with a fraction which had the characteristic RF of dimers. When the hydrolysate from a 313 nm irradiated sample was re-irradiated at 254 nm and then chromatographed, the radioactivity had the mobility of thymine monomer. This is characteristic of pyrimidine cyclobutyl dimers which were known to be photosynthesized at 313 nm and photodegrad-ed to monomers at 254 nm. Although not degraded itself, the p-aminobenzoic acid clearly acted as a photosensitizer for the DNA-damaging thymine dimerization [40]. 

Investigations of the mechanism of decarboxylation of hexuronic acids have largely involved kinetic and tracer studies. When either D-xylo-5-hexulosonic acid or D-glucuronic acid is converted into 27 in acidified, tritiated water, the resulting 27 contains 18% and 15%, respectively, of the activity of the solvent as carbon-bound tritium.21 Further degradation studies showed that the isotope is situated on the furan ring at either position 3 or 4, or both these atoms correspond to C-3 or C-4 of the starting uronic acid. 

Abeles and associates showed that when dioldehydratase (Table 16-1) catalyzes the conversion of l,2-[l-3H]propanediol to propionaldehyde, tritium appears in the coenzyme as well as in the final product. When 3H-containing coenzyme is incubated with unlabeled propanediol, the product also contains 3H, which was shown by chemical degradation to be exclusively on C-5 . Synthetic 5 -deoxyadenosyl coenzyme containing 3H in the 5 position transferred 3H to product. Most important, using a mixture of propanediol and ethylene glycol, a small amount of inter-molecular transfer was demonstrated that is, 3H was transferred into acetaldehyde, the product of dehydration of ethylene glycol. Similar results were also obtained with ethanolamine ammonia-lyase 399... 

In many situations, the experimenter will prefer to buy labeled compounds from commercial suppliers rather than attempt to synthesize them. The radiochemical purity of such purchased compounds cannot be assumed. Radiation-induced selfdecomposition (radiolysis) can result in the formation of a variety of labeled degradation products, which must be removed before experimental use of the compounds. The extent of radiolysis depends on the nature of the labeled compound, how long it has been stored, and the manner of storage. Radiolysis is most significant with low-energy (3 emitters (especially tritium) since the decay energy is dissipated almost entirely with the compound itself. Furthermore, impurities involving other radionuclides may be present. 

In the first the mode of incorporation of the amino phenol O-methyl-norbelladine 343 into 10 was examined. Thus, tritium labels were inserted ortho and para to the phenolic hydroxy groups of 343 by base-catalyzed exchange with tritiated water under conditions ensuring equal labeling in all exchangeable positions. Norpluviine biosynthetized from multiply labeled 343 in Texas daffodil was selectively degraded to locate the tritium labels. 

Traditional methods of C-terminal end determination55 were hydrazine degradation, carboxypeptidase digestion, and tritium labeling. Unfortunately, no chemical methods analyzing amino acid sequence sequentially from the C-terminal end is available with reliability similar to that of Edman degradation. Carboxypeptidase digests a protein and... 

The degradation of tritium is described as a 1st order kinetic reaction as follows (see also Table 14) ... 

Remodel the degradation of tritium in the unsaturated zone with this new input function. Compare your results with the results obtained from the assumption of an impulse-like tritium input in Fig. 42. 

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