Alkali discrimination between

Simple allyl alkali metal compounds have only a small capability for discriminating between diastereotopic faces of carbonyl compounds. Although a matter of simple diastereoselectivity, this can be concluded from the reaction of conformationally locked 4-/erf-butylcyclohexanone... 

UV spectroscopy has been of little value in discriminating between positional isomers of the phenolic species. However, the UV spectra of the corresponding methine bases have been shown to behave differently on addition of alkali (770). 

Figure 6 shows the proposed subunit assembly structure of the nicotinic acetylcholine receptor channel." The inner wall of the lower half part is surrounded by hydroxyl side chains from Ser and Thr, and by carboxylates or amides from Asp, Glu, and Gin at the mouth. Furthermore, a Lys residue seems to offer ion pairing with the carboxylate at the mouth. Considering the possibly similar stabilizing effect of ether and hydroxyl groups to cations, the proposed artificial supramolecular channel could be regarded as a good model of the acetylcholine receptor channel, which selects cations over anions, but does not discriminate between alkali metals. 

A more precise cavity control is found with the three-dimensional cryptands and Figure 26 shows the variation of Ks with alkali and alkaline earth metal cations for a range of cryptands.29 Two types of selectivity are displayed. Peak selectivity occurs when there is an excellent correlation between cavity and cation radius (Table 8) and so a sharp discrimination can occur (Figure 26). Plateau selectivity occurs when there is little discrimination between cations of higher radius but discrimination against cations of small radius which are not well accommodated (Figure 26). 

Pyrolysis of food samples provides a large number of products, which, after detection by MS and analysis by advanced statistical treatment, can be used to compare different samples. The method is very rapid and does not require chromatographic separation or MS identification of the pyrolysis products. Pyrolysis MS, coupled with multivariate data analysis procedures, has been used to discriminate between cocoa butters of three different continental areas (Radovic et al., 1998). The technique could in some cases separate deodorized from non-deodorized cocoa butters and also show those that have had alkali treatment. The presence of non-cocoa fats did not affect the assay. 

Although acetylation appears to minimize or prevent lysinoalanine formation, our findings indicate that acylation does not significantly change the extent of racemization after 3 hr at 65°C (Table IV). These results show that it is possible in principle to discriminate between the alkali-induced effects of racemization and lysinoalanine formation. Additional studies in progress are designed to further delineate this principle. 

Catecholamines (epinephrine and norepinephrine) can be converted to fluorescent compounds (called lutines) by oxidation and treatment with alkali. The concentration of total catecholamine can then be determined by excitation at 405 nm and fluorescence intensity measurements at 495 nm. (These two wavelengths do not discriminate between epinephrine and norepinephrine.) The following data were recorded ... 

The M+ ions have only weak complexing tendencies, but these can be enhanced by suitably sized macrocyclic ligands (see Topic E3). Ligands with different cavity sizes can be used to discriminate between alkali ions. 

Lecolle (1989) This diagram has not yet been widely tested but offers another means of discriminating between different types of MORB. Elemental concentrations are plotted in ppm as La/10, YV15 and Nb/8 and the three main fields are further subdivided (Figure S.ll). Volcanic-arc basalts plot in field 1 and are subdivided into calc—alkali basalts (lA) and island-arc tholeiites (IQ. Field IB is where the two plot together. Field 2 characterizes continental basalts and field 2B may define continental back-arc tholeiites, although this subdivision is based upon a single... 

Diagrajm which discriminate between the alkali basalt and tholeiitic magma series... 

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