Dyeing with congo

Dyeing with a Substantive Dye Congo (Sections 622, 625, 628). —The cotton to be used in this and the experiments which follow should be heated for 10 minutes in a boiling solution of 1 gram of sodium carbonate in 500 cc. of water. Prepare in this way seven pieces of white cotton cloth about 6 inches square. Wash the cotton three times with water and let it stand under water until needed. 

Dissolve 0.1 gram of Congo and 0.1 gram of sodium carbonate in 500 cc. of water. Heat the solution to a temperature just below boiling, and add pieces of white cotton cloth, woolen cloth, 

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Hirai et al. [18] found that /LCD forms 1 1 complexes with Methyl Orange and Congo Red in water, whereas y-CD forms 1 2 complex with Methyl Orange and 1 1 complex with Congo Red. Induced circular dichroism of the dyes was studied allowing determination of stability constants. 

Use and exposure Benzidine is a white, grayish-yellow, or slightly reddish crystalline solid or powder with extensive applications in industry. It is used for the synthesis of dyes like Congo red, dye intermediates, and as a hardener in rubber manufacturing industries. The predominant use for benzidine is in the production of dyes, especially azo dyes in the leather, textile, and paper industries. ... 

Many dyes used in the clothing industry contain sulfonic acid groups which impart water solubility and help to make the dye become fast to the fabric. The dye becomes fast by attaching itself to polar sites in the fibres of, for instance, cotton, wool or silk. Many azo dyes, like Congo Red (see Introduction, p. 5), contain one or more sulfonic acid groups. Another example is Orange II (7), synthesised by coupling p-naphthol (8) with diazotised sulfanilic acid (9) (Scheme 2). 

Colloidal dyes, with the exception of Congo red, and strongly lipid-soluble dyes do not appear in bile (H17). 

Recently, a pH sensor developed by immobilizing a direct azo dye on a porous cellulosic polymer film has been described [37]. Advantageous features of the design include a rapid equilibration time (< 1.3 s) and a large dynamic range (>4 pH units with Congo Red as dye). 

William Klunk and Chester Mathis vadiolabelled a fluorescent dye, related to Congo Red, labeled with fluorine-18, that is bound by P-amyloid protein in plaques found in the brain of patients with AD. After years of research, they developed a dye with 34 times the affinity for amyloid than Congo Red. Some think that P-amyloid is the cause of AD, whereas others think it is the result Patients with Down syndrome carry an extra copy of the amyloid gene, and they develop brain plaques and symptoms of AD when they reach middle age. 

Direct dyes. The first direct dye was Congo Red (Figure 2.26) obtained by tetrazotizing benzidine and coupling the tetrazo compound with 2 molecules of naphthionic acid (as sodium salt) in the presence of sodium acetate to act as buffer, i.e. 

Dyestuffs Protected with Colloids. — As already stated on page 197 some dyestuffs are very sensitive toward electrolytes. To this group of dyes belong Congo Red and Benzopurple, which may be easily coagulated with alkali salts even when the disperse phase is of molecular dimensions. Bayliss 1 has established the fact that such dye-... 

By definition, amyloid deposits stained with Congo red dye express green birefringence under polarized light microscopy (3). Electron microscopy... 

Certain organic compounds form reversible gels with poly(vinyl alcohol). Congo red, for example, yields a red gel that melts sharply at about 40°C. Other organic compounds that form temperature-reversible complexes with PVA include a2o dyes, resorcinol, catechol, and gaUic acid (168—170). 

Carefully scrape the separated bromophenol blue spots on to a sheet of clean smooth-surfaced paper using a narrow spatula (this is easier if two grooves are made down to the glass on either side of the spots). Pour the blue powder into a small centrifuge tube, add 2 mL of ethanol, 5 drops of 0.880 ammonia solution, and stir briskly until the dye is completely extracted. Centrifuge and remove the supernatant blue solution from the residual white powder. Repeat this procedure with the separated Congo red and phenol red spots . 

In the photometric analysis, a calibration of samples is made with the 5-30 ml of the water solutions of Congo red dye (Congo red Ind., Beijing Huagonchang) pH 5.6. This dye has the absorbance maximum 500 nm. Before the measurements, the tests are dried up on air at 50°C for 60 min. The absorbance of Congo red is also used as a blank for the absorbance measurements of AchE-biotests on the matrixes. 

The decolorization potential of immobilized P. chrysosporium MTCC 787 for azo dyes Acid Orange, Acid Red 114, triphenylmethane dye Methyl Violet, diazoic dye Congo Red, vat dye Vat Magenta, thiazine dye Methylene Blue, and anthraqui-none Acid Green was demonstrated by Radha et al. [53]. Decolorization experiments were carried out with immobilized calcium alginate (Ca-ALG) beads of different sizes (2-6 mm). 

They found the percentage decolorization decrease with increasing bead diameter for all dyes. Adsorption was determined by Ca-ALG beads (without immobilization) and it showed an initial reduction of 20% of the color. The immobilized fungus in Ca-ALG beads showed a low K,lyl. value for the Congo Red, a high K,lyl. value for Acid Orange and almost a constant value for Acid Red 114. They reported that P. chrysosporium was not able to decolorize Acid Green at a concentration... 

Certain water-soluble dyes are directly adsorbed onto cotton that has not been pretreated with a mordant (section 3.2.1). The first dye in which this phenomenon was observed was Congo red (4.57 Cl Direct Red 28), discovered in 1884 by Bottiger. The extreme pH sensitivity of this dye now restricts its use to that of an indicator, but it deserves mention as the forerunner of the direct dye class. 

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