Tritium exchange

Deuterium and Tritium Exchai e.— Thiazole is readily ionized by deuter-oxide in D2O or alkoxide in ROD, being deprotonated at C-2 and C-5 at about the same rate deprotonation at C-5 of isothiazole is slightly faster the other hydrogen atoms in either compound (H-4 in thiazole, H-3 and H-4 in isothiazole) do not exchange even under drastic conditions. The 

Measurements of the rate of detritiation in (46)—(48) have provided data concerning the base-catalysed hydrogen exchange in thiazolium salts. The results may have some bearing on the interpretation of enzymatic reactions involving thiamine.  

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An extensive series of hydrocarbons has been studied in cyclohexylamine, with the use of cesium cyclohexylamide as base. For many of the compounds studied, spectroscopic measurements were used to determine the relative extent of deprotonation of two hydrocarbons and thus establish relative acidity. For other hydrocarbons, the acidity was derived by kinetic measurements. It was shown that the rate of tritium exchange for a series of related hydrocarbons is linearly related to the equilibrium acidities of these hydrocarbons in the solvent system. This method was used to extend the scale to hydrocarbons such as toluene for which the exchange rate, but not equilibrium data, can be obtained. Representative values of some hydrocarbons withpAT values ranging from 16 to above 40 are given in Table 7.2. 

It has been shown that tritium exchange takes place readily at the 2 position of 26, despite the fact that this position is hindered by the bridge. The rates were not very... 

The tritiated version could be prepared from tritiated formic acid which we had prepared at high specific activity (2.5 Ci mmol-1) by a metal-catalyzed hydrogen-tritium exchange procedure using T2 gas. The material can be stored either as a solid or as a solution if the latter any release of tritium by back exchange can be easily monitored by 3H NMR spectroscopy. In our experience very little exchange occurs over several weeks of storage [51]. 

FIGURE 1. Relative rates of tritium exchange with cesium cyclohexylamide in cyclohexylamine31... 

Surface site densities used in the computation of the oxide site concentrations presented in this paper were determined by either rapid tritium exchange or acquired from published values (18). Reported total site densities for hydrous metal oxides show relatively little variation generally they range by less than a factor of 3. Since [M], [SOM], [H] and x are known or can be determined from experimental data, uncertainties in estimates of the total site concentration are directly translated into uncertainties in the calculated partitioning coefficient. 

G. S. Baldwin, S. G. Waley, E. P. Abraham, Identification of Histidine Residues That Act as Zinc Ligands in beta-Lactamase II by Differential Tritium Exchange , Biochem. J. 1979, 179, 459 - 463. 

A. cylindrica contains two soluble hydrogenases one of 100 kDa which exhibits MV-dependent H2 evolution and the other of 42 kDa which exhibits tritium exchange activity only. The MV-reactive enzyme is a heterodimer composed of a 50 kDa and the 42 kDa subunit form. Both proteins are required for MV reactivity (Ewart and Smith 1989). The function of this enzyme is unknown at present and the gene sequence for the tritium exchanging subunit is unrelated to any of the hydrogenases described above (Ewart et al. 1990). 

Deuterium or tritium exchange reactions with in the absence of electron donors or acceptors... 

Ewart, G. D., Reed, K. C. and Smith, G. D. (1990) Soluble hydrogenase ol Anabaena cylin-drica. Cloning and sequencing of a potential gene encoding the tritium exchange subunit. Eur. J. Biochem., 187, 215-23. 

This rate law, for example, applies to the tritium exchange from labeled dihydroxyacetone phosphate to water in the aldolase reaction or the exchange from labeled malate to water in the fumarase reaction. 

Figure 2 Rate profiles for acid-catalyzed hydrogen-tritium exchange of (a) 2,4,6-trimethylpyridine and (b) its /V-methyl salt...

Figure 3.4. Plot of the rate of tritium exchange in lithium cyclohexylamide/cyclohexylamine versus cesium ion pair acidity in cyclohexylamine. The following species are included (1) p-biphenyldiphenylmethane (2) di-p-biphenyhnethane (3) triphenyhnethane (4) diphenyl-methane (5) p-methylbiphenyl.

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