Labeled, preparation chemical methods

A chemical method for determining number-average molecular weights involves an analysis of end groups. If the polymer was prepared in such a way that each chain has either one or two labelled ends, then analysis for these ends is equivalent to counting the chains. For example, the ends could be hydroxyl groups or radioactive initiator fragments, and the analysis could involve titration, spectroscopy, or measurements of radioactivity. Chains formed in condensation polymerizations, from A-B monomers... 

Isotopically-labeled GAs and GA precursors are required for metabolic studies and as internal standards for quantitation by mass spectrometry. Numerous chemical methods have been used for the synthesis of labeled GAs from readily-available GAs. Labeled GAs have also been prepared biochemically using either fungal cultures or cell-free preparations from higher plants. 

The formation of an amide bond by organic chemical methods Is usually accomplished by reacting the acid halogenlde and the amino acid unless the acid substrate contains other reactive groups. The acid chloride Is prepared directly with thlonyl chloride (244) or Indirectly via the formation of a mixed anhydride by use of another acid halogenlde (245,246). Isotoplcally labeled [(2,4-Dlchlorophenoxy)acetyl]valine was synthesized by a DCC catalyzed reaction between the acid and valine (247). A few examples of synthetic amino acid conjugates of xenobiotics are shown In Table X. Several taurine conjugates of both alkanolc and benzylic acids have been synthesized and their physical properties determined by Idle et al. (2 ). 

Deuterium-labeled compounds1 are prepared almost exclusively by chemical methods. There is no physical method for deuterium-labeling similar to that... 

Synthetic chemical methods for the preparation of carbon-14-labeled chemicals utilize a number of basic building components that are prepared from barium carbonate ( " C). These are versions of carbon dioxide, acetylene, benzene, sodium acetate (1- and 2- " C), methyl iodide, methanol, sodium cyanide, and urea. Many complicated labeled compounds may be synthesized from these materials. 

Under the original standard, the label preparer provided the identity of the chemical and the appropriate hazard warnings. The preparer determined the method to convey the information. The revised standard specifies what information to provide for each hazard class and category (Table 7.9). 

The free-radical reactions in solid polymers in the presence of NO are of particular significance for the preparation of spin-labelled polymers. This method has become particularly important for chemically inert, rigid and insoluble polymers, for instance, polytetrafluoroethylene (PTFE), because of the difficult problem of introducing spin labels by chemical reactions of nitroso compounds, nitrons or nitroxyl biradicals [31], Oriented PTFE films y-irradiated at room temperature in air after prolonged NO exposure contain nitroxyl radicals whose ESR spectra are displayed in Figure 3 [32],... 

Most radioactive drugs are prepared by chemical methods because many of them are unobtainable by biosynthetic procedures. It is also easier using methods to increase production of the drug simply by scaling up the procedure. The isotopic label is introduced as late as possible in the synthetic route to minimise labour and cost, and to achieve a greater specificity in positioning of the label. A late introduction of the isotope also facilitates the isolation and purification of the desired product in that interference by unwanted products of the synthetic route is minimised. 

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