Carbon compounds isotopic tracers

TRACER. A chemical entity (almost invariably radioactive and usually an isotope) added to the reacting elements or compounds in a chemical process, which can be traced through the process by appropriate detection methods, e.g.. Geiger counter. Compounds containing tracers are often said to be tagged" or labeled." Carbon-14 is a commonly used... 

Isotopic Tools Tracers. Carbon has three stable or long-lived isotopes 98.9% of earth s C is 12C, -1.1% is 13C (a stable isotope), and about one in a trillion (1 in 1012) carbon atoms is 14C. By enriching or depleting the ratios of the rare isotopes in plants, plant litter, or other organic material put in soil, it is possible to follow the pulse of altered isotopic ratios (and the carbon compounds they were associated with) as they move through the system. 

Further reports have appeared on the reaction of trivalent phosphorus compounds with acetylene dicarboxylates. In the first, alkyl diphenylphosphinites (e.g.57) are shown to react with dialkylacetylene dicarboxylates (e.g.58) in the presence of carbon dioxide to form 1,2-oxaphosphol-3-enes (e.g.59) which in the presence of excess phosphinite decompose via (60) to give di-ylids (e.g.61). On the other hand, the phosphoranes (62) from phosphonites and phosphites react with a further phosphorus component to give the ylids (63) which are readily converted by treatment with alcohol into phosphonates (65) apparently via ketene intermediates (64) as evidenced by and isotopic tracer studies. ... 

New information on this problem has come from enzyme studies and isotope tracer studies. The work discussed in the preceding section disclosed that a great many different products were synthesized from carbon dioxide during photosynthesis. The nearest approach to a first product of photosynthesis is n-glyceric acid 3-phosphate. From this compound, through a whole series of enzyme-catalyzed reactions, the plant carries out the synthesis of the carbohydrates. 

Fortunately, my graduate research in biochemistry at Baylor College of Medicine, in Houston, involved studies on the mechanism of formic acid oxidation in animal tissues and on the incorporation of this one-carbon compound into nucleic acid components and their precursors. This provided me with experience in the use of isotopic tracers and the background in biochemical research which proved crucial, in later years, for unraveUng the intermediates and mechanisms of synthesis of purines and other compounds, when I discovered the prebiotic synthesis of adenine and other building blocks of nucleic acids, and a general pathway or method for the prebiotic formation of oligodeoxynucleotides and peptides. 

Solvent effects on, and products from, reaction of styrene with ethylene in the presence of di-)ti-chloro-dichlorobis(styrene)dipalladium(n), [Pd-(Ph CH—CH2)Cl2]2, indicate a mechanism similar to (i)->(iv) above, with the addition of a preliminary equilibrium between the dimer and solvated monomers. The mechanism of reaction of styrene with vinyl compounds, catalysed by the same chloride-bridged dipalladium complex, has been studied using isotopic tracer (H, D) experiments. Palladium-acetate-catalysed reaction of styrene with benzene, also investigated using deuterium tracer experiments, involves no hydride shift, in contrast to the rather closely related Wacker process. The importance of intermediates with palladium-carbon n-bonds in palladium(ii)-catalysed alkylation and arylation of alkenes has been demonstrated. 

Any radioactive nucUde or isotope of an element can be used as a radioactive tracer, eg, chromium-51 [14392-02-0] cobalt-60 [10198-40-0] tin-110 [15700-33-1] and mercury-203 [13982-78-0],hut the preponderance ofuse has been for carbon-14 [14762-75-5],hydj ogen-3 [10028-17-8] (tritium), sulfur-35 [15117-53-0], phosphoms-32, and iodine-125 [14158-31 -7]. More recendy phosphoms-33 has become available and is used to replace sulfur-35 and phosphoms-32 in many appUcations. By far the greater number of radioactive tracers produced are based on carbon-14 and hydrogen-3 because carbon and hydrogen exist in a large majority of the known natural and synthetic chemical compounds. 

Heavy isotopes endow the compounds in which they appear with slightly greater masses than their unlabeled counterparts. These compounds can be separated and quantitated by mass spectrometry (or density gradient centrifugation, if they are macromolecules). For example, O was used in separate experiments as a tracer of the fate of the oxygen atoms in water and carbon dioxide to determine whether the atmospheric oxygen produced in photosynthesis arose from HgO, COg, or both ... 

Isotopic studies relating to nutrition and diet have originated from two diverse fields bio-medical research and archaeology Numerous studies have been reported by researchers in the areas of biochemistry and medicine using either isotopically enriched compounds or the natural variations in isotopic abundances Such studies usually involve a specific chemical as a tracer of biochemical pathways, and in these studies soft tissues or body fluids are analyzed Recent work in nutrition has begun to examine the isotopic composition of carbon in macronutrients in diets and their disposition in body tissues (1 2) The isotopic composition of hard tissue (i e bone) however has been largely ignored in biochemical studies ... 

In Section 13.5 we learned that the isotope was used to determine the source of O2. The radioactive isotope helped to determine the path of carbon in photosynthesis. Starting with " C02, it was possible to isolate the intermediate products during photosynthesis and measure the amount of radioactivity of each carbon-containing compound. In this manner the path from CO2 through various intermediate compounds to carbohydrate could be clearly charted. Isotopes, especially radioactive isotopes that are used to trace the path of the atoms of an element in a chemical or biological process, are called tracers. 

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