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Abstract
BackgroundPeroxidases are emerging as an important class of enzymes that can be used for the efficient degradation of organic pollutants. However, detailed studies identifying the various intermediates produced and the mechanisms involved in the enzyme-mediated pollutant degradation are not widely published.ResultsIn the present study, the enzymatic degradation of an azo dye (Crystal Ponceau 6R, CP6R) was studied using commercially available soybean peroxidase (SBP) enzyme. Several operational parameters affecting the enzymatic degradation of dye were evaluated and optimized, such as initial dye concentration, H2O2 dosage, mediator amount and pH of the solution. Under optimized conditions, 40 ppm dye solution could be completely degraded in under one minute by SBP in the presence of H2O2 and a redox mediator. Dye degradation was also confirmed using HPLC and TOC analyses, which showed that most of the dye was being mineralized to CO2 in the process.ConclusionsDetailed analysis of metabolites, based on LC/MS results, showed that the enzyme-based degradation of the CP6R dye proceeded in two different reaction pathways- via symmetric azo bond cleavage as well as asymmetric azo bond breakage in the dye molecule. In addition, various critical transformative and oxidative steps such as deamination, desulfonation, keto-oxidation are explained on an electronic level. Furthermore, LC/MS/MS analyses confirmed that the end products in both pathways were small chain aliphatic carboxylic acids.
Highlights
Peroxidases are emerging as an important class of enzymes that can be used for the efficient degradation of organic pollutants
Optimizations of other parameters are described below: Requirement of HOBT for soybean peroxidase (SBP)-mediated degradation of Crystal Ponceau 6R (CP6R) Initial experiments using only SBP and H2O2 showed that unlike other dyes, CP6R was unable to be degraded by SBP/H2O2 alone
Since CP6R could not be degraded by SBP enzyme and H2O2 alone, we decided to include HOBT in the reaction
Summary
Peroxidases are emerging as an important class of enzymes that can be used for the efficient degradation of organic pollutants. It is estimated that as much as 12% of the dyestuff amounting to about 280,000 ton/year is released to the ecosystem [2] These dyes are used in various industrial applications (total consumption is more than one million tons of dyes annually) and are engineered to be generally resistant to fading. They need to sustain alkaline or acidic environment and need to withstand washing with soaps and bleaching agents and be resistant to light and ultraviolet irradiation. A number of microorganisms including bacteria, fungi, and yeasts have been used to treat the dye contaminated wastewaters [19,20,21,22]
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