Selective Labeling Schemes

The target amino acids are usually chosen based on an a priori knowledge of some of the relevant structural details [162]. These methods require a carefijUy selected labeling scheme to counteract the effects of isotope scram-bhng and amino acid conversion, which might randomize the isotopic label within the protein [162,163]. 

Recently, numerous studies reported the application of homonuclear and heteronuclear selective recoupling schemes on uniformly labelled ligand interacting with membrane receptors. The polarization exchange curves were fitted with the two-spin model and showed that it is possible to determine intemuclear distances up to 4.5 A.118... 

Figure 4 Solid-state structure, partial labeling scheme and selected bond lengths of dimeric ZnPh2 10.

The observation of biological macromolecules in cellular systems is based on labeling schemes that enable the selective identification of these macro-... 

Selective labelling of the two diastereotopic methyl groups of i-leucine (144) has enabled their fates during secondary metabolic reactions to be elucidated [66]. Moreover, in the context of protein interactions, differentiation of the leucine pro-R and pro-S methyl groups in protein NMR spectra allows molecular recognition phenomena to be studied [67]. Recently, efficient routes to both forms of Relabeled leucine, based on application of an auxiliary-controlled stereoselective conjugate addition reaction (Scheme 6.27) have been described [68]. Thus, starting... 

Fluoroimmunoassays comprise a subclass of extrinsic labehng methods where various selective antigen (Ag)- antibody (Ab) immunoassay fluorescent labeling schemes yield a emission signal. One common scheme involves an enzyme-linked immunosorbent assay (ELISA) depicted in Figure 11.2 where the free Ab is tagged with a fluorophore. Numerous analytes can be detected via these types of selective lock-and-key methods. ... 

An isotopic labeling scheme based on pseudo-enantiomers that enabled the diastereomeric receptors to be individually addressed (by LC-MS) was also examined. This methodology enabled the direct identification of the amplified diastereomer and the measurement of its selectivity over the competing stereoisomers (Fig. 5.12). 

Figure 3. Single crystal X-ray structure of the mono-HCI salt of sapphyrin 3. This X-ray structural figure was generated using unpublished data provided by Sessler et al., but corresponds to a structure originally reported in ref. 10a. Atom labeling scheme carbon 0 nitrogen chlorine hydrogen o. Selected hydrogen atoms have been omitted for clarity.

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