Cotton binding dyes

Reactive cotton, wool, silk, and nylon reactive site on dye reacts with functional group on fiber to bind dye covalently under influence of heat and pH (alkaline) azo, anthraquinone, phthalocyanine, formazan, oxazine, and basic... 

Cotton, on the other hand, binds dyes by hydrogen bonding interactions with its many OH groups. Thus, Congo red is bound to the cellulose backbone by hydrogen bonds. 

Phthalocyanine Dyes. In addition to their use as pigments, the phthalocyanines have found widespread appHcation as dyestuffs, eg, direct and reactive dyes, water-soluble dyes with physical or chemical binding, solvent-soluble dyes with physical or chemical binding, a2o reactive dyes, a2o nonreactive dyes, sulfur dyes, and wet dyes. The first phthalocyanine dyes were used in the early 1930s to dye textiles like cotton (qv). The water-soluble forms Hke sodium salts of copper phthalocyanine disulfonic acid. Direct Blue 86 [1330-38-7] (Cl 74180), Direct Blue 87 [1330-39-8] (Cl 74200), Acid Blue 249 [36485-85-5] (Cl 74220), and their derivatives are used to dye natural and synthetic textiles (qv), paper, and leather (qv). The sodium salt of cobalt phthalocyanine, ie. Vat Blue 29 [1328-50-3] (Cl 74140) is mostly appHed to ceUulose fibers (qv). 

It is not surprising, therefore, that chitosan and its basic derivatives will complex with anionic dyes. Giles et al. [68,69] researched the use of chitosan for the removal of dyes from effluent as long ago as 1958. The binding capacity of chitosan for anionic dyes is pH-dependent, but it has been reported [65] that in effluent treatment as much as 10 g dye per kg chitosan can be complexed at pH values above about 6.5. Similarly, chitosan has been used for the aftertreatment of direct dyeings on cotton to improve their fastness. 

The 1 1 copper complex azo dyes are used both as reactive dyes for cotton and as direct dyes for paper. (For definitions of reactive dyes, which form covalent linkages with the substrate, and direct dyes, which bind more weakly, see refs. 23 and 24, respectively.) Typical monoazo dyes are Cl Reactive Violet 1 (23) and Cl Reactive Blue 13 (25), and the bis-copper-ed dye, Cl Direct Blue 80 (26). The navy blue dye, Cl Reactive Blue 82 (27), is a typical disazo dye. 

This compound is a very effective dye that renders cotton and regenerated cellulose fibers a clear blue shade on prolonged treatment in the presence of an acid-binding agent. The resulting color prove to be veiy light- and waterfast. 

Side Note 5.2 Synthesis of a Dye and Its Binding to a Cotton Fiber... 

Diazo coupling often takes place in basic solutions because deprotonation of the phenolic —OH groups and the sulfonic acid and carboxylic acid groups helps to activate the aromatic rings toward electrophilic aromatic substitution. Many of the common azo dyes have one or more sulfonate (—SO3) or carboxylate (—COO-) groups on the molecule to promote solubility in water and to help bind the dye to the polar surfaces of common fibers such as cotton and wool. 

Many commercial dyes contain one or more sulfonic acid groups to confer water solubility to the dye and assist in binding the dye to the polar fibres in the textile (cotton, nylon, silk, wool, etc.). An example is Congo Red (12) (Figure 3). This is red in alkaline solution thus, the sodium salt will dye cotton red, but it is very sensitive to acids and on acidification the colour changes from red to blue, and so this compound is also used as a type of indicator. Vat dyes, known as sulfur dyes, can be prepared by heating various organic compounds, e.g. amines, aminophenols, and nitrophenols, with sodium polysulfide. 

Binding of related symmetrical dyes (naphthalene derivatives) to apohemoglobin resulted in different CD-Cotton effects in each case. As in the case of heme (see above), a coupled oscillator interaction with Ti-Ti transition moments of aromatic side chains of the protein was suggested, but no calculations were reported (194). The binding sites of the dyes used have not been identified and may include the heme pocket in some cases (195). The induced Cotton effects appear to be very sensitive to the local protein environment of the dye chromophores (194). 

Azo dyes almost always contain one or more —SOs Na groups to confer water solubility on the dye and assist in binding the dye to the surfaces of polar fibers (wool, cotton, or nylon). Many dyes are made by coupling reactions of naphthylamines and naphthols. 

Perkin sent a sample of the new compound to a firm of dyers. Their assessment was very favourable, so at the early age of eighteen Perkin left the Royal College of Chemistry and raised sufficient capital to build a factory for the manufacture of mauve. Before mauve could be used as a dye, Perkin had to solve several technological problems connected with the dyeing process. His most significant innovation was the use of tannin as a mordant to bind the dye to the cotton. 

Textile fabric may also be treated with isolated CBMs or CBMs fused with other molecules or enzymes. Banka et al. demonstrated that a fibril-forming protein from T. reesei causes non-hydrolytic disruption of cotton fibers [150]. Lee et al. obtained images, by atomic force microscopy, of holes left in cotton fibers treated with inactivated CBH I. The holes are attributed to the penetration of fibers by the binding domain [151]. It has been shown that the surface of ramie cotton is roughened by treatments with CBM2 from C. fimi. Gilkes et al proposed that the treatment of cellulosic fibers with CBMs could be used in order to alter the dyeing characteristics of cellulose fibers [152]. Indeed, it was showed that CBM treatment increased the dye affinity of cotton fibers, especially in the case of acid dyes [153]. 

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