Chemical names isotopic labeling

Thus, there were serotonin 1 receptors, and then there were 1 and 2 receptors, and then la and lb and 2a and 2b receptors, and on and on. These are called 5-HT receptors, since the chemical name for serotonin is 5-hy-droxytryptamine, and the scientist would never want to let the layman know just what he is talking about. DOI has been synthesized with a variety of radioactive iodine isotopes in it, and these tools have been of considerable value in mapping out its brain distribution. And by extrapolation, the possible localization of other psychedelic compounds that cannot be so easily labelled. A small neurochemical research company on the East Coast picked up on these properties of DOI, and offered it as a commercial item for research experiments. But I doubt that they are completely innocent of the fact that DOI is an extremely potent psychedelic and that it is still unrecognized by the Federal drug laws since, in their most recent catalog, the price had almost doubled and a note had been added to the effect that telephone orders cannot be accepted for this compound. 

The trimethylammonium butyrate (TMAB) isotopic tags, which are synthesized as amine-reactive AMiydroxysuccinimide derivatives, were first described by Regnier and coworkers (72). The chemical name of the TMAB-A-hydroxysuccinimide reagent (TMAB-NHS) is [3-(2,5-dioxopyrroli-din-l-yloxycarbonyl)propyl] trimethylammonium chloride. The label incorporates a quaternary amine so that the labeled peptide retains a positive charge in place of the free amine (unlike acetylation and related labels described in the next section). 

As can be concluded from the above outline, access to carotenoids isotopically labelled with and at predetermined positions is an essential part of this strategy. Labelled carotenoids can be prepared in two ways, namely by biosynthesis or by chemical synthesis. For the preparation of specifically labelled carotenoids biosynthesis is not suitable the labelled carotenoids are obtained by growing bacteria or yeasts on media containing simple isotopically labelled precursors such as sodium acetate [19]. The position of labelling can often not be predetermined and multiple labelling often occurs. Another major disadvantage is that isotopic dilution occurs for studies of carotenoid-protein complexes, carotenoids labelled at specific positions with high isotopic enrichment (preferably >99%) are needed. 

Isotopic designators in chemical names Naming conventions generally follow lUPAC rules (Pure and Applied Chemistry, 1979, 51, 353-380 www.iupac.org/publications/pac/) ( brackets preceding name of labeled unit )... 

The Boughton system, used in Chemical Abstracts, does not distinguish between labeling and substitution. The isotopic variation is shown by the symbol for the isotope (with a subscript numeral to indicate the number of isotopic atoms) placed after the name or relevant portion of the name locants are cited... 

Of all the elements, isotope effects see Isotope Effect) are greatest for hydrogen, justifying the use of distinctive names for the hydrogen isotopes protium, deuterium, and tritium. However, the chemical properties of H, D, and T are essentially identical, except in matters such as equilibrium constants. The isotopes of hydrogen are extensively used as tracers in deuterium- or tritium-labeled compounds. 

We also carried out the isotope dilution experiment with NO on soil (17). Much more NO was added because it was expected that NO would be readily consumed in reactions with soil chemicals. Nonetheless, apparent NO exchange was noted as shown in Table IV. Most of the label was trapped as NO. The sterile controls showed an order of magnitude less gas produced. It was surprising, however, that there was not a trend of more NO with decreasing pH, especially in the sterile control. The data in Table IV seem to support the interpretation of the pure culture data, namely that NO or its enzyme-boimd equilibrium species is an intermediate in denitrification. 

The flavor compounds that are labeled with stable isotopes (isotopomers) differ only slightly from the analyte in terms of mass, and their physical and chemical properties—e.g., volatility, reactivity, distribution coefficient and chromatographic behavior—are the same as those of the unlabeled flavor compounds, with the exception of minor and negligible isotope effects. They are added to foods as internal standards as early as possible, namely before the first extraction, so that they undergo virtually the same losses as the flavor compounds to be studied during the isolation method and enrichment steps that are employed. For this reason, labeled compounds satisfy nearly all of the requirements for an ideal internal standard and can also tolerate workup methods with very low recovery percentages, provided that the detection sensitivity is not too low. 

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