Murexide, interaction with

Interaction with murexide. The murexide method depends on the formation of a complex between Ca2+ and ammonium purpurate (murexide, M) ... 

Theobromine (3,7-dimethylxanthine, 3,7-dihydro-3,7-dimethyl-lW-purine-2,6-dione). C7H,N402, Mr 180.17 formula, see under theophylline. Monoclinic, bitter tasting needles, mp. 357 °C, sublimes at 290-295 °C, soluble in hot water, alkali hydroxides, concentrated acids, moderately soluble in ammonia, poorly soluble in cold water and alcohol. With acids T. forms salts which decompose in water detection by the murexid reaction. T. is the main alkaloid of cocoa (Theobroma cacao, 1.5-3 wt.-%), from which it is obtained - especially from the husks in which it accumulates during fermentation. The typical bitter taste of cocoa is the result of interactions between T. and the pip-erazinediones formed in the roasting process. T. has diuretic, vasodilatory, and stimulating effects on cardiac muscle. The activities are weaker than those of the structurally related caffeine (a methylation product of T.) with which it co-occurs in cola nuts. For further pharmacological properties, see table under theophylline. 

These effects are noted especially in region D of the plot in Fig. 11.12a the results for three samples of NaDS are shown in Fig. 11.12b. In this work the nickel concentration at the micellar surface was estimated by titration with murexide, a chromophoric anion. This interaction has been studied in more detail the reaction between Ni " and murexide (below) results in a pronounced colour change making the reaction easy to follow. Murexide being hydrophilic is not solubilized by the micellar species and thus can be used as an indicator of the appearance of micellar surface . 

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