Isotopic labels nitrogen

Thus, upon photolyzing a mixture of two nitrites, one of which contains an isotopically labeled nitrogen, the products should show the original isotopic distribution if mechanism (a) is operative, the original isotopic distribution in unreacted nitrite but scrambling in the nitroso product if (c) is operative, and complete isotopic scrambling if (b) is operative. 

The precise nature of the reaction path is ambiguous, because the same products would be obtained regardless of whether an oxygen atom or a chlorine atom were transferred. As they pointed out in their paper, this ambiguity can be resolved by using nitryl chloride with isotopically labeled nitrogen. Pertinent to this question are the calculations of Herschbach, Johnston, Pitzer, and Powell,199 who computed pre-exponential factors based on two alternative activated complexes... 

They then studied the reaction between isotopically labeled nitrogen dioxide and ordinary SO2. The formation of labeled SO2 was taken as evidence for reaction ( — 14), and therefore for the mechanism consisting of (14) and (15). From the rate of isotopic substitution, Jaffe and Klein were able to calculate and -14-1 15 Their results were... 

Unexpectedly, reactions of some hetaryl halides with amide ion in ammonia do not follow an SnAt pathway. Although the structures of the products provide no clues that new routes are being followed, the use of isotopically labelled nitrogen atoms reveals unanticipated complexities. 

R. Zhang, D. Shuai, K. A. Guy, J. R. Shapley, T. J. Strathmann, and C. J. Werth, Elucidation of nitrate reduction mechanisms on a Pd-In bimetallic catalyst using isotope labeled nitrogen species. ChemCatChem 5,313-321 (2013). 

Notice that the negative charge is spread over two nitrogen atoms via resonance. As such, either of these nitrogen atoms can function as the nucleophilic center during the nucleophilic attack. Either the isotopically labeled nitrogen atom can attack, like this ... 

Birds and animals are tagged so that their wanderings and ultimate fate can be followed. To do the same for nitrogen fertilizer, we use the heavy isotope of nitrogen, as a tag or label . This is a safe isotope to use because it is not radioactive. The of the label is taken up by the crop, incorporated in the soil s... 

The mechanism outlined above is supported by experimental findings. An intermediate 5 has been isolated, " and has been identified by and N-nuclear magnetic resonance spectroscopy. Side-products have been isolated, which are likely to be formed from intermediate 4. N-isotope labeling experiments have shown that only the nitrogen remote from the phenyl group is eliminated as ammonia. 

Although use of radio and stable isotope labels involving the trio of covalently-bonded nitrogenous functions in 3 and in 78, provided evidence that isocyano is the precursor of the isothiocyano and formamido groups [30, 81], it remains to be shown that a biosynthetic equivalent of the in vitro chemically-proven fusion process between isocyano and free sulfur (e.g., cf. Introduction) exists in the cells of sponges. In marine biota, various ionic forms of sulfur in a number of oxidation states, as well as organo-polysulfides are known. However, any association with the isonitrile group and a sulfated species has yet to be established. 

In addition to the foregoing examples, periodate oxidation has been applied to isotopically labeled sugars (for the determination of label distribution), 226 -226 to certain branched-chain sugars,227-229 and to some nitrogenous derivatives of the simple sugars.230-236... 

Work on the molecular structure of benzonitrilio methylide 8/9 has been carried out via Fourier transform infrared (FTIR) smdies on it and five isotope-labeled variants. The nitrile ylides were generated in nitrogen matrices at 12 K either directly, by photolysis of the azirine 7, or indirectly from the azidostyrenes 6 (4). 

Acylcarnitine analysis of dried blood or bile spots is very similar to the analysis of plasma. A small disk (diameter typically 5 mm or less) is punched out of the blood spot and the acylcarnitines extracted by the addition of methanol and known concentrations of isotopically labeled acylcarnitines, which function as internal standards. The extract is dried under a stream of nitrogen, and derivatized by the addition of either n-butanol HC1 or n-methanol HC1. The acylcarnitines are measured as their butyl or methyl esters by MS-MS. The concentrations of the analytes are established by computerized comparison of ion intensities of these analytes to that of the internal standards. 

Back and Mui17 studied the reaction with isotopically labeled nitric oxide to test the proposal that active nitrogen contained vibra-tionally excited molecules capable of dissociating nitric oxide. This reaction was proposed by Winkler and his co-workers133,435... 

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