Tritium labelled compounds Water

This tritiated water can become incorporated into the normal bases of DNA and may contribute significantly to the overall apparent binding levels measured in DNA (4). Such problems are circumvented in the case of 14C labeled hydrocarbons. Tritium labeled compounds can be prepared at sufficiently high specific activities (often 20-80 Ci/mmole) that fentomole amounts of adduct may be detected. 

It is important to investigate the bioconcentration potential of natural hormones, such as 17 -estradiol, estrone (using or tritium labeled compounds) and synthetic hormones (e.g., mestranol, diethylstilbestrol etc.). However, the concentration in the water should be at environmental relevant concentrations (< 10 ng 1 ). 

Non-volatile tritium-labelled compounds have been produced, but the degree of polymerization has been found to be not very high since the intermediate carbocations participate also in other reactions which lead to shortening of the chain length (equation 132). Reaction 132c seems to be the most probable. No simple saturated aliphatic hydrocarbon has been formed in the system C H3 — CH2=CH2 . In a mixture consisting of C H3, CH2—CH2 and H2O no n-alcohols containing more than two carbon atoms have been detected. This means that the isomerization of the carbocations formed is a faster process than their reactions with water or with ethylene. The reaction... 

The values of phase contact ratio are then plotted against the water sample concentration to give a curve where problem areas are readily apparent. Obviously a phase contact ratio of 1.00 at all concentrations represents ideal performance, showing perfect phase contact and equal counting efficiency for soluble tritium-labeled compounds at all concentrations regardless of partition coefficient. 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

The assay is carried out both at 1 jaM and 1 mM substrate concentrations [162]. The enzyme preparation is incubated with tritium-labelled cyclic nucleotide in the presence of Mg, the reaction is stopped by brief heating in a water bath, the 5 -nucleotide formed is converted to the nucleoside by snake venom 5 -nucleotidase, the nucleoside is separated from the remaining cyclic nucleotide by anion exchange chromatography (Dowex 2), and the radioactivity of both compounds is counted. 

Water in a never-dried fresh-cut tree, when exchanged with a series of organic solvents, could be replaced with H- (or tritium-) labeled MMA (42). After polymerization and the use of autoradiography the H-labeled MMA was located in the cell wall and compound middle lamella. The polymer (polymethyl methacrylate) labeled with was removed from the capillaries and void spaces in the wood by solvent extraction, but the labeled polymethyl methacrylate in the wood structure remained. The same wood, after oven drying, was treated with the H-labeled monomer by using the full cell method. Again, by autoradiography, the H-labeled polymethyl methacrylate was located in the capillaries and void spaces. After solvent extraction of the poly methyl methacrylate no labeled polymer... 

The reduction of a halogen compound by a metal catalyst such as zinc in the presence of tritiated water or tritium-labelled acetic acid will obviously produce a compound with a tritium atom in place of the original halogen. Reduction of this kind, although sometimes used for labelling, requires an excess of tritium in the water, acetic acid or other solvent. 

A 98% conversion efficiency has been achieved at 1.5 atmospheric pressure of CO2 and 10% excess of water, while the yield was 85% only when stoichiometric amounts of water and carbon dioxide were used. No isotopic fractionation has been noted when 5 to 10% excess of water has been used in the reaction in equation 5. Doubly labelled methane has been used in simultaneous analysis of and both in the atmosphere and in environmental carbon dioxide as well as in analysis of and H-labelled organic compounds. Proportional counters filled with methane possess very good counting properties and there is no need to add any inactive counting gas. and tritium-labelled methanes have also been produced" by pyrolysis of sodium acetate in molten sodium hydroxide (equation 6) ... 

Compound classes labeled by heterogeneous metal-catalyzed tritium exchange from water include amino acids, peptides and proteins, sugars, polycyclic aromatic hydrocarbons, purines, pyrimidines and nucleosides, alkyl-substituted aromatics, alicyclic compounds and steroids, A-heterocycles and anilines and some O- and 5-heterocycles. The method is firmly fixed in the repertoire of methods of the commercial custom labeling industry. 

Direct Methods. The classical approach has been to prepare tritiated or carbon labeled analogs of the parent hydrocarbons which may then be used in animal or in vitro experiments. Tritiated compounds are generally easier to prepare, using exchange reactions on the parent hydrocarbon, than their 14C analogs and have higher specific activities. However, during the metabolism of such compounds, some of the tritium is released as tritiated water, either directly or... 

By Reduction of Unsaturated Precursors The method of choice for labeling with tritium is the reduction of a suitable unsaturated precursor (containing a double bond, carbonyl group, etc.) with carrier-free tritium gas or tritiated metal hydrides. The major limitation of this method is the availability of a suitable unsaturated precursor of the desired compound. It is essential to carry out the synthesis in a non-hydroxylic solvent (dioxane, ethyl acetate, etc.). Reductions carried out in alcohol or water will lead to almost complete exchange of the tritium gas with the solvent. 

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