And isotopic labelling

Isotopic substitution and isotopic labelling 2-Carb-17. Unsaturated monosaccharides... 

Fischer projection of acyclic form, 56-57 glycosides, 132-135 C-glycosyl compounds, 139-140 N-glycosyl derivatives, 137-139 glycosyl halides, 136-137 glycosyl residues, 125 isotopic substitution and isotopic labelling, 91 me so forms, 59 optical rotation, 59 parent structure choice, 53... 

Despite the broad medical potentials reported so far, the total synthesis of triterpene QMs is yet to be reported. On the contrary, the biosynthesis of triterpene QMs has recently been validated as from the oxidosqualene 88 (Scheme 8.16) in the plants including Maytenus aquifolium and Salacia campestris.10S With the assistance of HPLC analysis and isotopic labeling, it was found that triterpene QMs 90 were formed only in the root of these plants from friedelin 89 and similar cyclized intermediates, which were synthesized in the leaves from oxidosqualene by cyclase. 

Investigation of Methanol Adsorbate by On-Line Mass Spectroscopy and Isotope Labeling... 

Exchange reactions between bulk and adsorbed substances can be studied by on-line mass spectroscopy and isotope labeling. In this section the results on the interaction of methanol and carbon monoxide in solution with adsorbed methanol and carbon monoxide on platinum are reported [72], A flow cell for on-line MS measurements (Fig. 1.2) was used. 13C-labeled methanol was absorbed until the Pt surface became saturated. After solution exchange with base electrolyte a potential scan was applied. Parallel to the current-potential curve the mass intensity-potential for 13C02 was monitored. Both curves are given in Fig. 3.1a,b. A second scan was always taken to check the absence of bulk substances. 

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. 

If all CO molecules have the same identity it is impossible to tell one from another. What is needed is some way to distinguish the CO groups from each other, and isotopic labeling constitutes such a technique. 

ESI represents a powerful method by which to transfer organometallic ions from catalytically active solutions into the gas phase. ESI-MS systems allow the characterization of the gas-phase ions using CID, reactivity, and isotope-labeling studies. The application of ESI-tandem-MS systems allows gas-phase preparations and isolation of desired organometallic ions in the first ESI-octopole-quad-rupole, followed by characterization or reactivity studies in the second octopole-quadrupole. 

Table 65 Impact of H20 and isotope label on the forward decomposition rate of the pseudo-stabilized formate (/.< ., to H2 and C02) by infrared spectroscopy361... 

It can be concluded that further work is necessary to improve method reproducibility. The lack of reference materials and isotope-labelled standards to control the quality assurance of analytical methods is a... 

Obviously, mass spectrometry is ideally suited for distinguishing between isotopic species, and isotopic labeling is used for mechanistic as well as analytical applications (Chap. 3.2.9). However, the effect of isotopic substitution is not only an effect on ionic mass, but isotopic substitution can have several simultaneous effects, and this complication sometimes produces results which are at first sight curious. [65]... 

A reaction that has been much investigated is the hydrolysis of esters, e.g. (164), by aqueous base, i.e. OH. It is found to be kinetically second order, and isotopic labelling experiments on (164) have... 

In this review, we will discuss the use of in situ spectroscopic techniques, in combination with kinetic and isotopic labeling studies, to obtain a detailed mechanistic insight of the rhodium catalyzed hydroformylation. 

As a result of metabolic reactions an isotope may appear at more than one position in a product, yielding two or more isotope isomers or isotopomers. These are seen individually by NMR spectroscopy and the concentration and isotope labeling patterns of the labeled compounds can be followed over a period of time. The use of this isotopomer analysis in studies of the citric acid cycle is illustrated in Box 17-C and its use in studies of glucose metabolism is considered in Chapter 17, Section L. 

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