Azure A

As in the case of the leucos Azure A and B, the exocyclic acyl group is not eliminated on oxidation, resulting in a Methylene Blue-type cationic... 

Leuco Azure A or B is obtained by refluxing the dye in an acid anhydride in the presence of zinc powder wherein the dye is reduced and acylated at the same time. 

Azure A can be reduced to an air sensitive intermediate 71 and acylated in one step to produce the ballasted leuco 72 which can be isolated and capped with the dye chloroformate 69 to give the ballasted yellow dye release developer 73. 

The property of polyanions to give metachromatic reactions with basic dyes80 (see Section XI) has been widely exploited for the titration of glycosaminoglycans. Because of its high charge-density, heparin displays large shifts in the visible spectrum of the dye upon complex-formation, and can conveniently be titrated (most commonly, with Methylene Blue or Azure A), even in the presence of minor proportions of other glycosaminoglycans. It should be realized that quantitative responses with metachromatic dyes are different for different pure heparin... 

Wang and Pek [185] have described a simple titration method applicable to the analysis of cationic surfactants in sea water. Methyl orange and azure A were used as primary dye and secondary dye, respectively. The method is free from interference by high levels of inorganic salts in sea water. 

Kimerle [27] reviewed the ecotoxicology of LAS focusing on the results rather than on the method of analysis, for which the author referred to the review undertaken by Painter and Zabel [30], alluding only to two papers on biota sample preparation. Litz et al. [31] determined the concentration of LAS in rye grass by Azure A active substances (AzAAS). AzAAS is a non-specific colorimetric method, which has not been used as frequently as MBAS (see Chapter 3.1). Briefly, it consists of the formation of an ion association complex with a dyed solution of Azure A (cationic). The complex formed is solvent-extractable and is separated from unreacted dye prior to colour measurement. 

Wang, L.K. Determination of anionic surfactants with Azure A and quaternary ammonium salt. Analy. Chem. 1975, 47 (S), 1472-1475. 

Although the leucometabolite of methylene blue has been repeatedly detected (75, 76), recent research (77) cannot confirm its presence in milk various metabolites at different stages of demethylation, in addition to a methylene blue complex, are found instead. Among these metabolites, a trimethyl derivative called azure A, a dimethyl derivative called azure B, a monomethyl derivative called azure C, and completely demethylated thionin have been positively identified. Further investigation demonstrated that the methylene blue complex was a protein-thionin conjugate, whereas thionin was the residue with the longest residence time in milk (78). 

Determination of Heparin. Chemical. Modifications of the methods of Warren and Wysocki (9) and Bassiouni (I) were used. Where plasma or blood was not involved, a direct titration of the heparin with azure A, either measuring the dye removal or redissolving the precipitate, was used. 

Dyeing of Heparin on PVPyr. The transparent films of polyvinyl-pyridine permit demonstration of the presence of heparin, and some judgment of the uniformity of adsorption, by staining with a basic dye such as toluidine blue or azure A, which combine with heparin to form... 

Color additives have been reported to also either enhance drug photodegradation or protect against it. Erythrosin, eosine, role bengal, methylene blue, azure A, and azure B accelerate the photodecomposition of pyridoxine hydrochloride and pyridoxamine HCl (26). Erythrosine was found to enhance the decomposition of phenylbutazone when irradiated with unfiltered light from a 300 W projector bulb, but was stable in the absence of the dye (27). Certain dyes such as methylene blue have been found to enhance the photostability of solutions of daunorubicin (87). 

In a notable paper, Lee et al. [41] examined the dimerization and inclusion complexation equilibria of six phenothiazine dyes, including thionine (TH), azure A (AZA), methylene blue (MB), toluidine blue (TB), new methylene blue (NMB) and 1,9-dimethylmethylene blue (DMMB) (Fig. 2), with CDs (a-, (>-, and y-CDs) in aqueous medium. These phenothiazine dyes presented their structural differences in the position and number of methyl substituents located on the same phenothiazine skeleton. By means of the UV-visible absorption and fluorescence spectra, the authors studied the factors which were responsible for the dimerization of phenothiazine dyes with CDs, in terms of a multiple equilibrium system (Scheme 1). In addition, the authors also determined the JCd values and the corresponding association constants of the monomers (M) and dimers (D) with the CDs [41]. 

Fig. 5A). The emission spectra of benzo[a]phenothiazine and the three methyl derivatives exhibited generally a broad and structureless band located at 500-527 nm in water/ethanol mixture (99 1, v/v), 500-507 nm in ethanol and 512-519 nm in 11P-f>-CD (Fig. 5B). Enhancement of the Stokes shift in HP-fi-CD solutions was interpreted by a greater stabilization of the tt-tc solvated excited singlet state [21], due to the reduced rotational and conformational motions of the BPHT molecules within the HP-fi-CD cavity [82], Comparable weak excitation or emission spectral shifts upon adding CD to an aqueous medium have also been reported in the case of unsubstituted phe-nothiazine [21], azure A [83] and several types of aromatic molecules [84,85]. 

The investigation of Taniguchi et al. [137] opened new hope in the search for medicaments in Alzheimer s disease and other taupathies such as Down s syndrome. They tested 42 compounds belonging to nine different chemical classes for their ability to inhibit the heparin-induced assembly of tau protein into filaments in vitro. Some of these compounds, including phenothiazines (methylene blue, azure A, azure B and quinacrine mustard), polyphenols (myricetin, epicatechin 5-gallate, gossypetin and 2,3,4,2, 4 -pentahydroxybenzophenone) and the porphyrin ferric deuteroporphyrin IX,... 

Derivation Carbacrylic cation-exchange resin, in reversible combination with 3-amino-7-dimethy-laminophenazathionium chloride (azure A dye). 

Figure 3.1. Absorption spectra for azure A solution with heparin.

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