Xanthine dyes

Xanthine Dyes, Photochemistry of the (Neckers and Valdes-Aguilera).. ... 

In pharmacy, the dyes used are azo dyes, quinoline dyes, tri-phenylmethane and xanthine dyes. They are not recommended in children because many colouring agents, mainly synthetic dyes, have been associated with hypersensitivity and other adverse reactions (gastrointestinal intolerance, dermatological reactions and carcinogenic concerns). Approximately 2-20% of people with asthma are sensitive to aspirin. Cross-reactions to azo dyes such as tartrazine produce similar effects. They have occurred in patients both with and without a history... 

Paucescu, S. D. lonescu-Ioan, C. Microscopy xanthine dyes. II. Fluorescein bromination to tetrabromo compounds. Rev. Chim. 1980, 31,339—341 Chem Abstr. 1980,93, 96775. 

The xanthine dyes, phloxine B and uranine, are used as pesticides. These dyes were extracted from guava fruit and separated on a Cjg column (2 = 493 nm for uranine and 546 nm for phloxine B) using a 15-min 80/20 —> 20/80 water (0.5 M ammonium acetate)/acetonitrile gradient [983]. Separation and peaks shapes were excellent. Samples were spiked with 0.05-5 pg/g with limits of detection reported as... 

Krapp-farbe, /. madder color, madder dye. -filrbcn, n. madder dyeing, -farbstoff, -farbc-atoff, m. alizarin, -gelb, n. madder yellow, xanthin. -lack, m. madder lake. -rot n. madder red, alizarin, -stoff, m. alizarin, -wurzel, /. madder root. 

Classes Of Sensitization, a. Photoreducible Dye Sensitization. In 1954 Oster (7) reported the first documentation of a dye-sensitized photoredox system. During the course of his work, Oster identified several classes of effective dyes, termed by him "photoreducible." These included examples of the classes of acridine, xanthine, and thiazine dyes. Figure 3 illustrates an example of each class, chosen in such a manner that the entire visible spectrum is covered by their absorption spectra. In Oster s work, identification of suitable activators (reduc-tants) to use in conjunction with the dyes was empirically determined. 

The base readily penetrates the hair and promotes bleaching. The addition of stabilizers such as sodium pyrophosphate or sodium oxalate [16,17] retards the decomposition of hydrogen peroxide in the alkaline preparation and thus enhances the bleaching action. The same holds for complexing agents (seques-trants) such as ethylenediaminetetraacetic acid, which hinder decomposition due to traces of heavy metals. Thickening additives include carboxymethyl celluloses, xanthine derivatives, and synthetic polymers. Certain dyes can also be added. 

The potentials of the redox centers of xanthine oxidase have been investigated by titrations in the presence of redox mediator dyes. An early study (245) used dithionite to generate reducing equivalents and quantified the reduced species by EPR measurements at low temperature. Subsequent studies as a function of pH showed that the potential of the molybdenum center was sensitive to pH (246). Concern over the effect of temperature on the observed potentials led to redox titrations monitored by room temperature CD and EPR spectroscopy (247). These experiments indicated that the redox potentials of all of the prosthetic... 

The respective mixed-mode phase with cation-exchange properties is suitable for the analysis of a number of compound classes. The most important ones include alkaloids, water-soluble vitamins, sulfonamides, cephalosporins, catecholamines, diuretics, and xanthines, as well as a number of basic dyes. Figure 6.71 shows the separation of 10 different alkaloids, of which theophylline, theobromine, and caffeine are genuine constituents in beverages such as coffee and tea. In comparison to the classical separation on ODS phases, potentially interfering matrix components are better separated on a mixed-mode phase. 

The organization of xanthine oxidase appears to be quite complex. There is evidence that various substrates are not bound at the same site, and that the primary reaction of different substrates may occur with various ones of the cofactors. The oxidation of purines and aldehydes is inhibited by pteridyl aldehyde and by cyanide, but these reagents do not affect the oxidation of DPNH. It is possible that these inhibitors influence substrate binding sites and primary electron transport, respectively, and that the oxidation of DPNH involves a different binding site and avoids the cyanide-sensitive electron transport mechanism, which may well involve iron. Xanthine oxidase, and probably all flavoproteins, require —SH groups, but a definite function for these groups cannot be ascribed at this time. Similarly, various factors influence the reactions with oxidants differentially. Cyanide inhibits cytochrome reduction, but not the reactions with 0 or dyes. Reduction of either cytochrome c or nitrate depends upon the presence of molybdenum. These observations... 

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