Tritium distribution

If one assumes, however, that tritium is scavenged in a similar manner as other radioactivity, then immediately following the detonation most of the tritium observed in the present ejecta profiles would have been in the missile ejecta stratum. This supposition is supported by the consistent pattern of tritium distribution with depth on the crater lip and at more distant stations where ejecta was deposited as a thin layer on undisturbed soil materials. 

Figure 3 shows the pattern of tritium distribution on the 18A (southeastern) transect. The concentrations of tritium increase sharply with depth at all stations on the transect, and the peak tritium concentration occurs at a depth of 3 to 5 feet at all stations regardless of ejecta depth. In another transect of the ejecta field on the west side of the crater at 20A, shown in Figure 4, the tritium depth profiles show a similar pattern, and maximum tritium concentrations occur in the same zone, 2-5 feet. At a distance of 2000 feet from the crater lip, the depth of ejecta was 2-3 inches. The maximum concentration of tritium in soil water was at 3 feet at that site. 

Fallback presents a different condition from the bulk ejecta because it is that portion of the ejecta which falls through the fireball or cloud as it drops back into the crater. The tritium distribution in fallback in... 

Tritium Distribution. The present distribution of tritium in the Sedan ejecta field has therefore been produced by rainfall and attendant environmental factors of the desert ecosystem. The initial distribution of tritium was primarily in the missile ejecta layer which had the greatest... 

Kumar, Sh., Koganti, S.B. 2001. Modelling of tritium distribution coefficients in 30 vol% TBP/ -dodecane/U02(N03)2/nitric acid system. Indian J. Chem. Technol. 8 (1) 51-53. 

Preliminary results99 indicated that 11-demethyltomaymycin (118) had a similar genesis to anthramycin (116) from tryptophan and tyrosine, and these results have now been published in full.100 Tryptophan has been shown to provide ring A, presumably by catabolism through anthranilic acid. The results99,100 are summarized in Scheme 12. It is to be noted that methionine provides only the aromatic O-methyl group [in anthramycin there is an extra carbon present in the unit related to (119) which derives from methionine see above]. Further evidence from incorporation of labelled tyrosine indicates that the C7 unit (119) derives from seven tyrosine carbon atoms. The incorporation of L-[l-14C,2,3-3H2]tyrosine (tritium distribution H-2, 50% H-3-pro-S, 41.5% H-3-pro-R, 8.5%) with loss of half the tritium label was interpreted reasonably as involving loss only of the C-2... 

PLP-aminoacrylate, revealed the tritium distribution shown in Scheme XVI. The methyl group has S configuration, indicating hydride attack at the Re face of the intermediate PLP-aminoacrylate, the same side as the Si face at C-4. L configuration at C-a has not yet been proven but seems extremely likely. The results provide... 

Scheme XVI. Tritium distribution in pyridoxylalanine derived from sodium [3H]borohydride reduction of tryptophan synthase in the presence of (3/ )-[3-2H]serine and indolepropanol phosphate.

The mechanism of the Wilzbach method applied to the labeling of aromatic compounds was also the subject of a number of investigations, usually involving the measurement of the intramolecular tritium distribution within the labeled aromatic substance. Whilst toluene was the most frequently employed aromatic substrate (Aliprandi et al., 1960 Cacace andPossagno, 1960 Cacace, 1961a Ache etal., 1961, 1962 Ache and Herr, 1962 Ache, 1967), chlorobenzene, nitrobenzene and anisole (Cacace et al., 1960) and anthranilic acid (Crawford and Garnett, 1965 Garnett et al., 1965) have also been studied. 

Heterogeneous catalysis (Pd) in tritiation of l,4-dien-3-ones leads mainly to l) -tritiation (ca. 76%). Tritium distribution studies indicate that the reaction is probably a 1,4-addition of tritium onto the more exposed p-face of the dienone, which is tilted downwards with respect to ring b (211). Homogeneous catalysis with tris(triphenylphosphine)rhodium chloride, however, is known to favour la-tritiation. Similarly, homogeneous hydrogenation of the less reactive... 

Demtis F, Andrews JN, Parker A, Poole J, Wolf M (1997) Isotopic and noble gas study of Chalk ground water in the London Basin, England. Appl Geochem 12 763-773 Doney SC, Glover DM, Jenkins WJ (1992) A model function of the global bomb tritium distribution in precipitation, 1960-1986. J Geophys Res 97 5481-5492 Dunkle SA, Plummer LN, Busenberg E, Phillips PJ, Denver JM, Hamilton PA, Michel RL, Coplen TB... 

The use of gaseous tritiated radical scavengers to determine the secondary free radical distribution in y-irradiated lyo-philized macromolecules has been explored. For proteins the similarity of the tritium distributions obtained with tritiated H2S and HI as well as studies with H235S, support the assumption that these distributions are an approximate measure of the secondary radical distribution. Radical distributions of several native proteins were characteristically different, those of denatured proteins approximately the same, thus demonstrating a pronounced effect of conformation. In contrast to proteins, the reaction of irradiated dry DNA with tritiated H2S or HI gave approximately 100 times more tritium label on the DNA than expected from the initial concentration of free radicals in the DNA. 

Reaction of HS- radicals, produced by Reaction 3, with the carbon radicals formed by radiolysis, may lead to distorted tritium distributions if the carbon radicals located on a particular amino acid residue react more slowly with HST than those located on other amino acid residues, but rapidly with HS- radicals. 

Figure 3. Effect of ammonia on tritium distributions of (3-la-beled ribonuclease and lysozyme and on y-labeled ribonuclease.

The same tritium distribution is obtained when ribonuclease is dried for a week in an evacuated drying pistol over P2O5 at 100 °C. before /3-labeling with TI. This experiment indicates that the mechanism does not involve exchange with TI dissolved in small amounts of protein-bound water. 

Figure 4. (y + ft)-, /3-, and y-labeled tritium distributions in ribonuclease with TI... 

Figure 6. y-Labeled tritium distribution of ribonuclease and chymotrypsinogen with HST and TI as radical interceptors... 

It appears that almost all of the HS radicals formed in the labeling reaction react with the protein and do not recombine in the gas phase. In native RNase about 70% of the HS- radicals react with disulfide bridges (Reaction 8), while 30% add to carbon radicals (Reaction 6). The latter process could, under conditions previously discussed, cause a distortion of the tritium distribution. The reactions of HS- radicals in reduced proteins remain to be investigated. 

Tritium Distribution of Native Ribonuclease. In a standard y-label-ing experiment 20 mg. of protein were irradiated at 10 3 torr to about 5 Mrads at room temperature and subsequently exposed to HST at a pressure of about 150 torr for 4 hours (Experiment A, Figure 8). A portion of the unfractionated protein was then hydrolyzed, after exchange, to determine the tritium distribution. The results in Figure 8 demonstrate that essentially the same tritium distribution is obtained under a variety of experimental conditions (B-F). In Experiment B, ribonuclease was irradiated at 77°K. and then allowed to warm to 298°K. before adding HST. The comparison of distributions from Experiments A and B (Figure 7) shows that the radicals formed by radiolysis at 298°K. are identical with the secondary radicals produced from the primary radicals, formed by radiolysis at 77 °K. and subsequent heating to 298 °K. The same conclusion was previously reached (11, 22) from interpretation of ESR spectra. 

Figure 8. Effect of experimental conditions on the tritium distribution of...

Normalized Specific Activities Among Native Proteins. Figure 9 shows a comparison of tritium distributions for native proteins irradiated to about 6 Mrads (except for myoglobin which was irradiated to 23 Mrads). Each bar represents the average normalized specific activity of five separate labeling experiments for ribonuclease and of two for each of the other proteins. The tritium distributions have many similarities. The activities of proline and methionine are generally high. Lysine and histidine are heavily labeled in most proteins, while threonine and serine... 

Each protein has, within this general pattern, its own characteristic radical distribution. In ribonuclease, lysine exhibits a much higher activity than do the remaining amino acids. Lysine and methionine are the most heavily labeled residues in lysozyme. In myoglobin, histidine has the highest activity. Methionine is the most heavily labeled amino acid in chymotrypsinogen, as is proline in insulin. Despite the similarities, therefore, each native protein exhibits a characteristic tritium distribution. 

Figure 9. Comparison of tritium distributions in native proteins...

Denatured Proteins. Gelatin as well as carboxymethylated reduced proteins is included in this group. It can be seen from Figure 10 and shown by analysis of the product-moment correlation coefficients (32) that the tritium distributions of the CM-reduced proteins are more similar... 

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