Labeling Experimental Materials

This mechanism of a -elimination reaction is supported by experimental findings with " S- and C-labeled starting materials." The Chugaev reaction is analogous to the ester pyrolysis, but allows for milder reaction conditions—i.e. it occurs at lower temperatures. It is less prone to side reactions, e.g. the formation of rearranged products, and is therefore the preferred method. 

Labeling of all containers of experimental chemical materials is prudent. Because the properties of an experimental material are generally not completely known, its label cannot be expected to provide all necessary... 

The most important information on the label of an experimental material is the name of the researcher responsible, as well as any other information, such as a laboratory notebook reference, that can readily lead to what is known about the material. For items that are to be stored and retained within a laboratory where the properties of materials are likely to be well understood, only the sample identification and/or name may... 

All containers of R D-exempt material or of mixtures containing the material should have an experimental material label and a TSCA R D label. While EPA does not specify the language, the following is an example of a TSCA R D label ... 

Direct quantitation of receptor concentrations and dmg—receptor interactions is possible by a variety of techniques, including fluorescence, nmr, and radioligand binding. The last is particularly versatile and has been appHed both to sophisticated receptor quantitation and to dmg screening and discovery protocols (50,51). The use of high specific activity, frequendy pH]- or p lj-labeled, dmgs bound to cmde or purified cellular materials, to whole cells, or to tissue shces, permits the determination not only of dmg—receptor saturation curves, but also of the receptor number, dmg affinity, and association and dissociation kinetics either direcdy or by competition. Complete theoretical and experimental details are available (50,51). 

Re-evaluation of pulse delay times used to record fullerene 13C NMR spectra revealed that a 16 s pulse delay, twice the value for a standard detection, allowed the observation of a weak resonance in the sp3 region at 90.4 ppm in the 13C NMR spectrum of the unlabeled heterofullerene 114. Attempts were made to optimize the NMR experimental parameters for a long 7 i, i.e. the variation of delay times and pulse angles. Various conditions were tried on the labeled material without success. This is probably due to the mixture of the labeled and unlabeled 114 which give too low S/N for signal detection. Table 49 summarizes the NMR results obtained and illustrates a distinct pattern of the azafullerenes. 

The isotope effects for transfer of hydrogen were 1.79 for transfer from OH to N and 2.86 for transfer from CH to ruthenium. The isotope effect for transfer of the doubly labelled material d% 2-propanol) was 4.88, within the experimental error. If the hydrogen atoms would be transferred in separate... 

Comparison of the results allows calculation of kj6/ki8. Obviously there are drawbacks to this procedure. The major one is the necessity of a costly and tedious isotopic synthesis of labeled materials. Optimally those compounds should be as close as possible to 100% enriched. This can seldom be achieved and using partially enriched samples requires substantial corrections to the raw data and increases experimental uncertainty. A rule of thumb used in remote labeling experiments is that the remote (reporting) position should be reasonably far from the reaction center (the phenolic oxygen in the present example). For the case where there is no isotope effect at the reporting site (e.g. no 15N-KIE), the double-label experiment leads directly to the isotope effect of interest. This is more probable when the reporting site is remote, (i.e. well isolated from the reaction coordinate). 

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