Displacement, competitive

Although peroxide initiated reactions can produce preparative yields of organomercury salts, a mixture of products was usually obtained due to chain mechanism/radical displacement competition and to the prevalence of side reactions [Eqs. (24), (25), and (109)]. An alternative to the... 

Thallium is a highly toxic metal, being readily absorbed by any route including the skin. Once in the body, approximately 70% of thallium binds to the red blood cells. It behaves in a similar manner to potassium, which it displaces competitively. 

An alternative format for a chromatographic immunoassay is the displacement competitive binding immunoassay. In this format, the lAC column is first saturated with the labeled analogue, followed by application of sample to the column. As the analyte travels through the column, it is able to bind to any antibody sites that are momentarily unoccupied by the label as the analyte and antibodies undergo local dissociation and reassociation. This situation results in competition between the analyte and the label... 

This same experimental approach can be used to determine the appHcabiUty of the aDAS—AP to a competitive assay for DAS. As shown in Eigure 6, increasing amounts of free DAS were used to define the 50% inhibition level (ID q) of DAS for binding of two aDAS—AP conjugates to immobilized DAS. This approach was also used to determine the sensitivity of an EIA, as well as the specificity of the assay, as shown in Table 2. Increasing amounts of trichothecene mycotoxins closely related to DAS were added to microtiter plate wells containing a constant amount of prereacted DAS—aDAS—AP. After 30 min, excess toxin and any free toxin—aDAS—AP were washed out, and substrate was added. Quantification of the color produced was directly related to the abihty of the added toxin to displace aDAS—AP from the immobilized DAS, which is an indication that the aDAS also has an avidity for that toxin. 

Fig. 9. Immunosensor approaches where A is the analyte, is the labeled analyte, and Y is the antibody, (a) Direct immunosensors where the actual antigen—antibody interaction is measured (b) indirect immunosensors 1 and 2 which utilize formats similar to competitive and displacement...

The extent of displacement depends on the relative stabiUties of the complexes and the mass action effect of an excess of M For equivalent total amounts of M and M, K must be on the order of 10 for 99% complete displacement to occur. Similar considerations apply for the displacement of L from ML by U. The situation is quite analogous to the familiar competition of two bases for the hydrogen ion. 

The petroleum industry is now the principal suppHer of ben2ene, toluene, the xylenes, and naphthalene (see BTX processing Feedstocks). Petroleum displaced coal tar as the primary source for these aromatic compounds after World War II because it was relatively cheap and abundantly available. However, the re-emergence of king coal is predicted for the twenty-first century, when oil suppHes are expected to dwindle and the cost of producing chemicals from coal (including new processes based on synthesis gas) will gradually become more competitive (3). 

Displacement Development A complete prediction of displacement chromatography accounting for rate factors requires a numerical solution since the adsorption equilibrium is nonlinear and intrinsically competitive. When the column efficiency is high, however, useful predictious can be obtained with the local equilibrium theoiy (see Fixed Bed Transitions ). 

The ease of reaction of halopyridazines is indicated by the exothermic nature of the reaction of 3,6-dichloropyridazine with sodium methoxide at room temperature to yield 3-chloro-6-methoxy-pyridazine. Displacement of the deactivated chloro group in the latter required heating (66°, < 8 hr) the reaction mixture. Competitive methoxy-dechlorination (20°, 12 hr) of 3,4,6-trichloropyridazine shows the superior reactivity of the 4-position the 3,6-dichloro-4-methoxy analog (296) was isolated in high yield. The greater reactivity of the... 

Evaluating relative reactivity at different positions by competitive displacement in polychloroazines requires the unjustified assumption that the chloro groups have a negligible or equal effect on each other. In a polychloro compound bearing a different kind of substituent, the activation or deactivation of the chloro groups is generally neither equal nor negligible, as already demonstrated. 

As noted previously, in all cases these various functions describe an inverse sigmoidal curve between the displacing ligand and the signal. Therefore, the mechanism of interaction cannot be determined from a single displacement curve. However, observation of a pattern of such curves obtained at different tracer ligand concentrations (range of [A ] values) may indicate whether the displacements are due to a competitive, noncompetitive, or allosteric mechanism. 

Competitive displacement for a range of [A ] values (Equation 4.8) yields the pattern of curves shown in Figure 4.6a. A useful way to quantify the displacement is to determine the concentration of displacing ligand that produces a diminution of the signal to 50% of the... 

Competitive, noncompetitive, and allosteric antagonism can be discerned from the pattern of multiple displacement curves. 

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