A H-labeled

Prominent examples of successful application of contrast variation are the investigations of the single chain dynamics of polymers in melts. Here a mixture of about 10% h-polymer in a matrix of d-polymer is used. Further details are obtained by investigating d-polymers that contain only a h-labelled section, i.e. at the ends, at branching points or at its centre in a fully deuterated matrix. 

Both trapping reactions have a fourfold symmetry, hence A trap = dWtrap-Nucleation involves a cluster of five adjacent (A, H)-labelled sites, which are all converted to (A, S), which explains the factor of five appearing in equation (63). Because of the sixfold symmetry of this reaction, we have nucl — dlTnucl-... 

Abood, L.G., Lu, X., Baneijee, S., 1987. Receptor binding characteristics of a H-labelled azetidine analogue of nicotine. Biochera. Pharmacol. 36, 2337-2341. 

Cryopreserved human hepatocytes from three male and two female donors or freshly isolated male rat hepatocytes are analyzed for viabilities (75-85%) using the trypan blue exclusion methods. Incubations are performed by suspending the hepatocytes in Krebs-biocarbonate buffer followed by addition of a H-labeled compound in methanol. The specific radioactivity of the compounds is 100 Ci/ mol. The final concentration of test compound in the suspension is 10 xM in a final volume of 1 mL (1x10 cells/mL), and the final concentration of methanol does not exceed 0.2% (v/v). Incubations are allowed to proceed at 37 °C for 1 h, and are quenched with acetonitrile (5 mL). The remaining procedures are the same as described in Section 14.2.2 (the protocol for in vitro covalent protein binding in human or rat liver microsomes a test-tube method). Covalent protein binding values in pmol-equiv./mg protein are estimated based on the residual radioactivity in the protein pellets. 

The specificity of the combining site of the rabbit hepatic lectin has been explored by a competitive binding assay using a [ H]-labelled precursor blood-group I substance with terminal non-reducing /3-D-galactosyl residues and the... 

Myocardial LPL activity was estimated in post-heparin perfusate ( heparin-releasable ) and in acetone/ether-dried ground tissue powders ( residual-tissue ) by using a H-labelled triolein substrate emulsion and counting radioactivity in evolved fatty acids extracted in methanol/chloroform/heptane. ... 

The situation is illustrated in Fig. 22 for the case of a -H-labeled methylene segment of a surfactant molecule residing in a micelle. The director axis, Z , corresponds to the micellar surface normal. The field gradient tensor is cylindrically symmetrical around the C- H bond axis, with the maximum component in the bond axis direction, Zm. 

Once a H-labelled compound has been made it can be incorporated into a long-chain acid by chain extension (via the nitrile, by malonation, or by enamine synthesis) or by involvement in a Wittig or acetylenic synthesis as in the following synthesis of methyl 11-dideutero-oleate. 

One of the most important analytical techniques one should incorporate into any LC—MS method is the use of stable isotope dilution. There is no other better internal standard then the heavy labeled version of the compound of interest. The use of either [ C] and/or [ N] labels are preferred as deuterium ([ H]) incorporation alters the retention time of the internal standard. On reversed-phase columns, a [ H]-labeled analog will elute earlier than the protium form and on normal phase columns the analog will elute later. This elution order is due to slight differences in their interactions with the stationary phase. Stable isotope dilution methods provide the assurance that the internal standard experiences the same environment during sample preparation as well as during ionization in the source. This method allows for accurate and precise quantification of the analyte of interest. This technique is becoming increasingly popular however, many labeled internal standards, especially those of novel biomarkers, are not commercially available and must be synthesized. 

Reagent systems involving triphenylphosphine have been employed to activate primary hydroxyl groups for displacement with nitrogen nucleophiles. A H-labelled form (40) of an inhibitor of lipopolysaccharide biosynthesis has been synthesized from the 2-deoxy-j9-KD0 derivative (41), a redox sequence being used to introduce the H-label (Scheme 11). Hitsunobu conditions... 

Figure 5.10 (a) The structure and numbering of virginae butanolide A. (h) Labelling... 

As an additional approach in preparing a H-labeled anthraquinone, the radiochemical labeling of emodin (33) was undertaken (Groger et al., 1968). Reaction with 10 Ci tritium gas for 3 wk (Wilzbach conditions) (Wenzel and Schulze, 1962) yielded, after exchange of the labile tritium and intensive purification, crystalline emodin (33) with specific tritium radioactivity of 11.6 mCi/mmole. As usual with Wilzbach tritiations (Evans, 1974), the radioactivity was predominantly located on the aromatic nucleus, and the C-methyl radioactivity as determined by Kuhn-Roth oxidation amounted to only 8.5% of the overall radioactivity. 

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