Aminoazo dyes

Although several N-methyl-substituted arylamines have been shown to be carcinogenic (184-186), metabolic activation pathways have been investigated primarily for the hepatocarcinogenic aminoazo dyes, N-methyl-4-aminoazobenzene (MAB) and its 3 -methyl derivative (9,21, 22,187,188). N-Hydroxy-N-methyl arylamines are generally regarded as proximate carcinogenic metabolites (22,187,189) and have been shown to be converted to electrophilic N-sulfonyloxy derivatives by hepatic sulfotransferases (9,187) or to reactive N-arylnitrones by air oxidation (21). 

Aminoazo dyes, 9 249, 250 p-Aminobenzoic acid (PABA), 25 807 cosmetic uv absorber, 7 846t Aminobenzoisothiazoles, 9 290 2-Aminobenzothiazole dyes, 9 419 Aminobenzothiazoles, 9 289 4-(p-Aminobenzyl)cyclohexylamine,... 

Figure 1.26 Tautomeric and spectral changes on protonation of aminoazo dyes.

All aminoazo dyes exist exclusively in the azo form as shown in (2.13). The various forms formed on protonation of aminoazo dyes have already been discussed in Chapter 1 (section 1.4.1.4). 

In theory, azo dyes can undergo tautomerism azo/hydrazone for hydroxyazo dyes azo/imino for aminoazo dyes, and azonium/ammonium for protonated azo dyes. A more detailed account of azo dye tautomerism can he found elsewhere. 

Tipping, E., Ketterer, B., and Christodoulides, L. (1979). Interactions of small molecules with phospholipid bilayers. Binding to egg phosphatidylcholine of some organic anions (bromosulphophthalein, oestrone sulphate, haem and bilirubin) that bind to ligandin and aminoazo-dye-binding prot [Pg.414]

In the 1940s and 1950s the pioneering studies of James and Elizabeth Miller provided early evidence for in vivo conversion of chemical carcinogens to reactive metabolites. They found that reactive metabolites of the aminoazo dye A, /V-dimcthyl-4-aminoazobenzene (DAB), a hepatocarcinogen in rats, would bind covalently to proteins and nucleic acids. The term, metabolic activation, was coined by the Millers to describe this process. Moreover they demonstrated that covalent binding of these chemicals was an essential part of the carcinogenic process. 

In the early 1960s, during investigations on the N-demethylation of aminoazo dyes, it was observed that pretreatment of mammals with the substrate or, more remarkably, with other xenobiotics, caused an increase in the ability of the animal to metabolize these dyes. It was subsequently shown that this effect was due to an increase in the microsomal enzymes involved. A symposium in 1965 and a landmark review by Conney in 1967 established the importance of induction in xenobiotic interactions. Since then, it has become clear that this phenomenon is widespread and nonspecific. Several hundred compounds of diverse chemical structure have been shown to induce monooxygenases and other enzymes. These compounds include drugs, insecticides, polycyclic hydrocarbons, and many others the only obvious common denominator... 

Whereas p -naphthylaminesulfonic acids always couple at the adjacent a position, in a-naphthylaminesulfonic acids, the coupling location is influenced by the position of the sulfonic acid group 1,6-, 1,7-, and 1,8-naphthylaminesulfonic acids couple at the 4-position 1,5-naphthylaminesulfonic acid (Laurent acid) only couples with very strong couplers (e g., 2,4-dinitroaniline), mainly at the 4-position. With diazotized aniline, chloroaniline, or diazotized aniline sulfonic acids the 2-aminoazo dyes are obtained, but with diazotized nitroaniline, mixtures of the 2-and 4-coupling products form (Scheme 2.1). 

In alkaline medium m-aminophenol couples at the position para to the hydroxyl group in an acid solution /i-hydroxy and / -aminoazo dyes are obtained. 

Aminoazo dyes undergo protonation at either the terminal nitrogen atom to give the essentially colorless ammonium tautomer (71) (kmax ca. 325 ran),... 

Direct Dyes with a Urea Bridge. By the end of the 19th century, it was discovered at BASF that the reaction of aminoazo dyes with phosgene in aqueous solution in the presence of soda resulted in valuable symmetrical urea azo dyes [11] ... 

C. I. Direct Yellow 50, 29025 [3214-47-9] (26) is obtained, for example, by phosgene treatment of two equivalents of the aminoazo dye prepared from diazo-tized 2-aminonaphthalene-4,8-disulfonic acid coupled to w-toluidine. 

The procedure that can be adopted is for intermediate products with amino groups (e g., H acid) to be condensed with cyanuric chloride and the reaction product subsequently attached to the diazo component, or aminoazo dyes are treated directly with cyanuric chloride. In the relevant commercial azo dyes, the third chlorine atom in the cyanuric chloride is usually treated with aniline or ammonia, and less frequently left unchanged. 

In general, these complexes exhibit too little stability and washfastness to be of value as dyes. Except for Co111 [2], trivalent metal salts do not form complexes with bidentate o-hydroxy- and o-aminoazo dyes. 

TABLE I. METABOLISM OF AMINOAZO DYES BY LINOLEIC ACID HYDROPEROXIDE AND HEME... 

Carcinogenic aminoazo dyes were previously found to increase the latent period of linoleate peroxidation and that DAB was a more effective antioxidant than MAB (13). Furthermore, as autoxidation of the linoleic acid proceeded, N-demethylation of DAB and MAB occurred. Demethylation of DAB also occurred in vitro when DAB is dissolved in cottonseed oil and mixed with ground brown rice (14). Our results clearly indicate that a linoleic acid hydroperoxide-hematin system readily N-demethylates DAB to MAB and MAB to AB. Previously, it was found that in this system, HCHO formation by N-demethylation of DAB was faster than that obtained with MAB (15). Similar results are now reported during the H202 peroxidase catalyzed oxidation of DAB and MAB. Peroxidase and H2O2 have previously been reported to catalyze the N-dealkylation of other arylamines (16, 17). 

If it is desired to obtain aminoazo dyes from bases which tend to form diazoamino compounds, the amines can first be converted to their (o-sulfomethyl derivatives by reaction with formaldehyde and bisulfite ... 

The sulfomethyl derivatives couple with diazo compounds to form azo compounds which yield aminoazo dyes on hydrolysis. 

Aminoazo dyes with only one amino group (aminoazobenzene type) are weak bases giving, in general, difficultly soluble salts which are readily hydrolyzed. If the dye is to be isolated as one of its salts, for example, the hydrochloride, the salt is precipitated from the reactiorr mixture by means of a considerable excess of hydrochloric acid. The precipitate is filtered off and washed with dilute hydrochloric acid, not with water. On the other hand, if the dye is to be used in coloring oils, fats, etc., it must be isolated as the free base and must contain no salts. For this purpose, the coupling reaction mixture is made alkaline and the precipitated dye is filtered off and washed thoroughly with water. The dye can be purified further by.recrystallization from an organic solvent. 

Figure 1 Induction of hepatic aminoazo dye N-demethylase and reductase activities. Rats (50 g) were injected once with 1 mg of 3-methylcholanthrene (3-MC). N-Demethylase activity was determined in fortified liver homogenates by measuring the metabolism of 3-methyl-4-monomethylaminoazobenzene to 3-methyl-4-aminoazobenzene (3-methyl-AB). Reductase activity was determined by measuring the reduction of the azo linkage of 4-dimethylaminoazobenzene (DAB). Demethylase activity is expressed as fig of 3-methyl-AB formed per 50 mg of liver per 30 min. Reductase activity is expressed as fig of DAB reduced per 30 mg of liver per 30 min. Each point is the average of the activities for two or three rats. Taken from Ref. (4).

In 1957, we reported on the use of the detergent deoxycholate for the solubilization of aminoazo dye N-demethylase, and we also reported an inhibitory effect of CO on aminoazo dye N-demethylase activity (49). In a key study in 1968, Lu Coon described the deoxycholate-dependent solubilization and resolution of a liver microsomal fatty acid >-hydroxylation system into three components by column chromatography, and they were able to reconstitute catalytic activity by combining the three fractions (50). The three fractions were identified as cytochrome P450,... 

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