Double-label experiment

Scheme 12. Double-labelling experiments demonstrating concurrent alkylation and dealkylation in...

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). 

The most frequently used combination of radioisotopes in double labeling experiments is tritium and 14C. Ideally the ratio of the activities in the corresponding channels (Fig. 7.16) should to be high enough to insure the carbon counts in the tritium channel are negligible compared to tritium counts. Usually this is not achieved and a correction must be applied. 

Finally, an ABC assay system is nice to have available for detecting more than one antibody on an individual specimen. In double-labeling experiments, having two completely different assay systems reduces the chances of crossover reactivity. The first antigen can be detected with the standard ABC procedure, and the second antigen is then detected using the PAP system (see... 

The close agreement between the 36/34 m/e ratios observed in the oxygen derived from recovered acetyl peroxide in the double-labeling experiment and that calculated for Mechanism B suggests that no more than 1% of the reaction can proceed by Mechanism A. 

The biosynthesis of molybdopterin has been investigated using double labeling experiments using labeled... 

Reaction of Atomic Carbon with Pyrroie. Cocondensation of arc generated C with pyrrole 71 gives pyridine 72. This clean reaction is useful to insure that the system is functioning properly when setting up a new carbon arc reactor. Double labeling experiments with atoms and produce 72 with both the... 

After chromatographic removal of 3, the cleavage of the catenane, 4, to 3 and 1 was critical evidence of the structure. Numerous blank experiments excluded other possibilities. Figure 1 essentially describes a double-labeling experiment deuterium for one ring and the acyloin function for the other, the labels detected by their infrared absorption [6], The few milligrams of purified 3 could not be crystallized. The name catenane was based on the Latin catena for chain . 

The main evidence for the associative mechanism consists in double-labeling experiments conducted by Farnham and Sogah [33, 34]. At -90 °C in THF a mixture of PMMA with a dimethyltolylsilyl ketene acetal end group and PBMA with a dimethylphenylsilyl ketene acetal end group was treated with a small amount of BMA and TASF catalyst (Scheme 20). After 5 min the polymerization was quenched and the polymers separated by solubility. NMR showed a small PBMA block on the PMMA polymer but the end group was only tolyldimethylsilyl. 

In double-labeling experiments using PMMA of two different molecular weights Quirk obtained partial exchange in 2 h [37]. Since the dissociate mechanism demands complete exchange, these experiments support an associative pathway. 

D. B. Collum, Solution Structures of Lithium Dialkylamides and Related JV-lithiated Species Results from 6Li-15N Double Labeling Experiments , Acc. Chetn. Res. 1993, 26, 227-234. 

Fig. 2.4 Double labeling experiments to assign the Met carbonyl carbon resonances of SSI. A) [M]SSI ...

It should be emphasized that the foregoing experiments were not designed to study the mechanisms of heat-induced protein interactions in milk. They merely serve to illustrate the utility of radiolabeled milk proteins in studying this very complex phenomenon. The radiolabeling of other milk proteins along with double-labeling experiments should prove very instructive in future research on the heat stability of milk. 

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