Decolorization mechanism

Both purified laccase as well as the crude enzyme from the WRF Cerrena unicolor were used to convert the dyes in aqueous solution. Biotransformation of the dyes was followed spectrophotometrically and confirmed by high performance liquid chromatography. The results indicate that the decolorization mechanism follows MichaeliseMenten kinetic and that the initial rate of decolorization depends both on the structure of the dye and on the concentration of the dye. Surprisingly, one recalcitrant azo dye (AR 27) was decolorized merely by purified laccase in the absence of any redox mediator [46],... 

Polyene structures formed during the thermal- and/or photo-oxidative degradation of poly(vinyl chloride) react easily with a number of different solvents, which cause their discoloration (Table 3.16). This process is accelerated by irradiation with light (Fig. 3.39) or heating in the presence of various radical sources (Fig. 3.40 and Fig. 3.41). The decoloration mechanism depends upon the type of solvent used [1426, 1673] ... 

To 40 g. of dry chitin in a 500-ml. beaker is added 200 ml. of concentrated hydrochloric acid (c.p., sp. gr. 1.18), and the mixture is heated on a boiling water bath for 2.5 hours with continuous mechanical agitation. At the end of this time solution is complete, and 200 ml. of water and 4 g. of Norite are added. The beaker is transferred to a hot plate, and the solution is maintained at a temperature of about 60° and is stirred continuously during the process of decolorization. After an hour the solution is filtered through a layer of a filter aid such as Filter-Cel. The filtrate is usually a pale straw color however, if an excessive color persists, the decolorization may be repeated until the solution becomes almost colorless. The filtrate is concentrated under diminished pressure at 50° until the volume of the solution is 10-15 ml. The white crystals of glucosamine hydrochloride are... 

The crude 2-(p-nitrobenzenesulfonamido)-pyrimidine from the preceding step was suspended in 130 parts alcohol and 1.5 parts of concentrated hydrochloric acid were added. The suspension was then heated to reflux and 30 parts of iron powder were added with mechanical stirring. The mixture was refluxed and stirred for 24 hours with r"-asional addition of concentrated hydrochloric acid. The reaction mixture was then made slightly basic and filtered hot and the residues were extracted with several portions of boiling alcohol. The filtrate and wash solutions were combined and evaporated. The 2-(sulfanilamido)-pyr-imidine was recrystallized from boiling water with decolorizing charcoal added, according to U.S. Patent 2,410,793. 

In a 5-I. round-bottom flask fitted with a mechanical stirrer is placed a solution of 330 g. (8 moles) of stick sodium hydroxide (u.s.p.) in 2.8 1. of water and the solution is cooled to o° in an ice-salt bath. To the well-stirred solution 480 g. (3 moles) of bromine is added from a separatory funnel at such a rate as to keep the temperature below io° (Note 1) (fifteen to twenty minutes). The solution is cooled again to o° and 100 g. (1 mole) of pinacolone (Org. Syn. 5, 91) is added from a separatory funnel, keeping the temperature below io°. After the solution is decolorized (about an hour) it is stirred for three hours at room temperature. 

Yoo ES, Libra J, Adrian L (2001) Mechanism of decolorization of azo dyes in anaerobic mixed culture. J Env Engin 127 844—849... 

As discussed earlier, Azo biological decolorization are mainly reduced in a direct reduction or mediated/indirect reduction with nonspecial azo reductase or reduced enzyme cofactors (Figs. 1 and 3). According to the direct enzymatic reduction mechanism, nonspecial azo reductase can catalyze the transfer of reducing equivalents originating from the oxidation of original electron donor in the azo dyes. In... 

Theoretically, according to the mechanism of biological azo dye reduction, the processes of biological decolorization are oxidation-reduction reactions, in which transfer of electrons match with the proton flow by the help of coenzymes, such as NADPH/NADP+ and NADH/NAD+. The oxidation-reduction potentials of the couples of NADPH/NADP+ and NADH/NAD+ are -324 and -320 mV, respectively [25, 46]. The least AGo value of the conversion NADPH/NADP+ and NADH/NAD+ is 44 kJ [47]. Therefore, —93 mV, which is obtained from (1), could be considered as a rough limited ORP value for ordinary primary electron donors of the third mechanism of biological azo dye reduction. This was demonstrated by the results of many researches (Table 1). Hence, the observed failure of cyanocobala-min [30] and ethyl viologen [48] to act as a mediator is most probably due to their too low Ed values 530 and —480 mV, respectively. 

Combined Anaerobic-Aerobic Treatment Processes 4.1 Mechanism of Decolorization... 

Mechanisms of Yeast-Mediated Azo Dyes Decolorization 2.1 Yeast Definition... 

The few reports on bioremediation of colored effluents by yeasts usually mention nonenzymatic processes as the major mechanism for azo dye decolorization [5-10]. In a first approximation based on the cellular viability status, these processes can be divided into two different types bioaccumulation and biosorption. Bioaccumulation usually refers to an active uptake mechanism carried out by living microorganisms (actively growing yeasts). The possibility of further dye biotransformation by redox reactions may also occur due to the involvement of... 

In view of the present state of the art, we think that it is important to test other yeast species, either from Ascomycota or Basidiomycota phylum, to know the real diversity of yeasts capable of removing azo dyes, their main mechanisms of decolorization, and biotechnological potential. 

Tang, WZ Chen, RZ. Decolorization kinetics and mechanism of commercial dyes by H202/iron powder system. Chemosphere, 1996 32 (5), 947-958. 

Mohey El-Dein, A Libra, JA Wiesmann U. Mechanism and kinetic model for the decolorization of the azo dye Reactive Black 5 by hydrogen peroxide andUV radiation. Chemosphere, 2003 52, 1069-1077. 

Tetrahydrofuran (36 g., 0.5 mole) (Note 1) is added to a mixture of potassium iodide (332 g., 2 moles), 85% orthophosphoric acid (231 g., 135 ml., 2 moles), and phosphoric anhydride (65 g.) (Notes 2, 3, and 4) in a 1-1. three-necked flask equipped with a sealed mechanical stirrer, a reflux condenser, and a thermometer. The mixture is stirred and heated at its reflux temperature for 3 hours, during which time a dense oil separates from the acid layer. The stirred mixture is cooled to room temperature, and 150 ml. of water and 250 ml. of diethyl ether are added (Note 5). The ether layer is separated, decolorized with dilute aqueous sodium thiosulfate solution, washed with cold saturated sodium chloride solution, and dried over anhydrous sodium sulfate. The ether is removed by distillation on a steam bath, and the residue is distilled under reduced pressure from a modified Claisen flask. The portion boiling at 108-110°/10 mm. is collected. The yield of colorless 1,4-diiodobutane ( o 1-615 df 2.300) (Note 6) is 143-149 g. (92-96%). 

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