title: N-demethylation of methylene blue by lignin peroxidase from Phanerochaete chrysosporium. Stoichiometric relation for H2O2 consumption.
abstract: Phanerochaete chrysosporium lignin peroxidase (LiP) can degrade synthetic dyes such as heterocyclic, azo, and triphenylmethane on its activation by H2O2. Analysis of the reaction products indicated that N-demethylation reactions are involved in the degradation of crystal violet and methylene blue (MB). We studied LiP oxidation of methylene blue and azure B (AB) in reaction mixtures containing different dye:H2O2 stoichiometric relations aiming at the selective formation of N-demethylated derivatives. High yields, about 70%, of the mono- and didemethylated derivatives, azure B and azure A, were obtained with the use of 1:1 and 1:2 MB:H2O2, respectively. Using azure B as substrate in reaction mixtures containing 1:1 AB:H2O2, a yield of 70% was also observed in azure A. Reaction mixtures containing 1:3 MB:H2O2 and 1:2 AB:H2O2, originated several oxidation products in similar proportions. These results indicated that the process of enzymatic degradation of methylene blue and azure B initiates via N(CH3)2 oxidation. According to the yields that were obtained for azure B and azure A, this enzymatic route can be used for the synthesis of these dyes since these data compare favorably to the chemical route that has a yield of 35%. The use of a dye:H2O2 relation of 1:10 resulted in a decoloration level of about 85%, showing the usefulness of this procedure for wastewater treatment. The reaction products were followed by spectrophotometric analysis within the wavelength of 500-700 nm. The product identifications were performed using a reverse-phase high-performance liquid chromatography (HPLC) C-18 column and thin-layer chromatography.
authors.affiliation: Instituto de Química, Universidade Federal do Rio de Janeiro, Brazil.
authors.forename: V S
authors.initials: VS
authors.lastname: Ferreira
authors.forename: D B
authors.initials: DB
authors.lastname: Magalhães
authors.forename: S H
authors.initials: SH
authors.lastname: Kling
authors.forename: J G
authors.initials: JG
authors.lastname: da Silva Júnior
authors.forename: E P
authors.initials: EP
authors.lastname: Bon
mesh_terms: D001673:Biodegradation, Environmental; D002851:Chromatography, High Pressure Liquid; D005840:Gentian Violet / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D008751:Methylene Blue / Q000378:metabolism*; D010544:Peroxidases / Q000378:metabolism*; D020075:Phanerochaete / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D006861:Hydrogen Peroxide; D010544:Peroxidases; C042858:lignin peroxidase; D005840:Gentian Violet; D008751:Methylene Blue