Isotopically labelled compounds

Isotopically Labeled Compounds. The hydrogen isotopes are given special names H (protium), H or D (deuterium), and H or T (tritium). The superscript designation is preferred because D and T disturb the alphabetical ordering in formulas. 

Isotopically labeled compounds may be described by inserting the italic symbol of the isotope in brackets into the name of the compound for example, H C1 is hydrogen chloride[ CZ] or hydrogen chloride-36, and H C1 is hydrogen H chloride[ CZ] or hydrogen-2 chloride-38. 

Before sample preparation, surrogate compounds must be added to the matrix. These are used to evaluate the efficiency of recovery of sample for any analytical method. Surrogate standards are often brominated, fluorinated, or isotopically labeled compounds that are not expected to be present in environmental media. If the surrogates are detected by GC/MS within the specified range, it is... 

John Wiley Sons, Cornell University ms 125,000 CD-ROM, tape isotopic labeled compound QuaUty Index algorithm... 

Another widely used approach to the elucidation of metabolic sequences is to feed cells a substrate or metabolic intermediate labeled with a particular isotopic form of an element that can be traced. Two sorts of isotopes are useful in this regard radioactive isotopes, such as and stable heavy isotopes, such as or (Table 18.3). Because the chemical behavior of isotopically labeled compounds is rarely distinguishable from that of their unlabeled counterparts, isotopes provide reliable tags for observing metabolic changes. The metabolic fate of a radioactively labeled substance can be traced by determining the presence and position of the radioactive atoms in intermediates derived from the labeled compound (Figure 18.13). 

One of the possibilities is to study experimentally the coupled system as a whole, at a time when all the reactions concerned are taking place. On the basis of the data obtained it is possible to solve the system of differential equations (1) simultaneously and to determine numerical values of all the parameters unknown (constants). This approach can be refined in that the equations for the stoichiometrically simple reactions can be specified in view of the presumed mechanism and the elementary steps so that one obtains a very complex set of different reaction paths with many unidentifiable intermediates. A number of procedures have been suggested to solve such complicated systems. Some of them start from the assumption of steady-state rates of the individual steps and they were worked out also for stoichiometrically not simple reactions [see, e.g. (8, 9, 5a)]. A concise treatment of the properties of the systems of consecutive processes has been written by Noyes (10). The simplification of the treatment of some complex systems can be achieved by using isotopically labeled compounds (8, 11, 12, 12a, 12b). Even very complicated systems which involve non-... 

Chapters were planned on Structural chemistry of solids NMR and ESR Carbon acidity Syntheses and uses of isotopically labelled compounds and on Pyrolysis in this volume, but did not materialize. We will try to fill these gaps in a future supplementary volume. 

Trager, W.F. (1988). Isotope effects as mechanistic probes of cytochrome P450-catalysed reactions. In Synthesis and Application of Isotopically Labelled Compounds Proceedings of the Third International Symposium T.A. Baillie and J.R. Jones (Eds.) Amsterdam Elsevier 333-340. 

An important breakthrough in HTS ee assays came from the group of Reetz in late 1990, with the introduction of mass spectroscopy (MS)-based procedures [90]. These methods use special asymmetrically isotope-labeled compounds. Enzymatic transformations of these compounds usually lead to two pseudoenantiomeric compounds whose relative concentration can be estimated using MS techniques. 

Many mechanistic aspects of the hydrolysis of phosphate esters in protic media remain uncertain. In spite of predictions that racemization at phosphorus should be the final outcome if indeed the (hypothetical) metaphosphate intermediate is involved in the solvolysis of monoesters, the results of several studies on the methanolysis of appropriately O-isotopically labelled compounds are consistent with reactions proceeding with inversion of configuration, as observed for all enzymic and non-enzymic systems so far examined this has resulted in the suggestion that if metaphosphate is actually formed, then it must be in a masked form. 

The synthesis, analysis and applications of labeled compounds is an area in which basic and applied research go hand-in-hand. Over the last quarter of a century the field has seen considerable expansion as reflected in the emergence of a specific journal (Journal of Labeled Compounds and Radiopharmaceuticals) and the publication of the proceedings of international conferences held at three-yearly intervals. The formation of the International Isotope Society is also an indication of the increasing importance of isotopes and isotopically labeled compounds. 

R. N. Hanson, in Proceedings of the Third International Symposium on the Synthesis and Applications of Isotopically Labelled Compounds (Eds. T. A. Bailie and J. R. Jones), Elsevier, Amsterdam, 1989, pp. 275-281. 

Analysis by competitive antibody binding of isotopically labelled compounds... 

ANALYSIS BY COMPETITIVE ANTIBODY BINDING OR ISOTOPICALLY LABELLED COMPOUNDS... 

Part—VI has been solely devoted to Miscellaneous Assay Methods wherein radioimmunoassay (RIA) (Chapter 32) has been discussed extensively. Various arms of theoretical aspects viz., hapten determinants and purity importance of antigenic determinants and analysis of competitive antibody binding of isotopically labeled compounds. The applications of RIA in pharmaceutical analysis, such as morphine, hydromorphone and hydrocordone in human plasma clonazepam, flurazepam in human plasma chlordiazepoxide in plasma barbiturates, flunisolide in human plasma have been described elaborately. Lastly, the novel applications of RIA-techniques, combined RIA-technique-isotope dilution and stereospecificity have also been included to highlight the importance of RIA in the analytical armamentarium. 

---