2-2--azino-di-(3-ethylbenzothiazoline)-6-sulfonic-acid and 1-hydroxybenzotriazole

Laccases (EC 1.10.3.2) catalyze oxidation of phenolic groups in lignin to phenoxyl radicals during reduction of O

Topics: Benzothiazoles; Catalysis; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Fungal Proteins; Laccase; Lignin; Oxidation-Reduction; Phenols; Phthalimides; Sordariales; Sulfonic Acids; Trametes; Triazoles

Laccase from basidiomycete fungus Cyathus bulleri was evaluated for its ability to decolorize a number of reactive and acidic dyes in the presence of natural and synthetic mediators. The extent of decolorization was monitored at different mediator/dye concentrations and incubation time. Among the synthetic mediators, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) was effective at low mediator/dye ratios and resulted in 80-95% decolorization at rates that varied from 226 +/- 4 nmol min(-1) mg(-1) for Reactive Orange 1 to 1,333 +/- 15 nmol min(-1) mg(-1) for Reactive Red 198. Other synthetic mediators like 1-hydroxybenzotriazole and violuric acid showed both concentration- and time-dependent increases in percent decolorization. Natural mediators like vanillin, on the other hand, were found to be less effective on all the dyes except Reactive Orange 1. Computed rates of decolorization were about twofold lower than that with ABTS. The laccase-ABTS system also led to nearly 80% decolorization for the simulated dye mixture. No clear correlation between laccase activity on the mediator and its ability to decolorize dyes was found, but pH had a significant effect: Optimum pH for decolorization coincided with the optimum pH for mediator oxidation. The treated samples were also evaluated for toxicity in model microbial systems. The laccase-mediator system appears promising for treatment of textile wastewaters.

Topics: Azo Compounds; Barbiturates; Benzaldehydes; Benzothiazoles; Color; Coloring Agents; Cyathus; Hydrogen-Ion Concentration; Industrial Waste; Laccase; Mutagenicity Tests; Naphthalenesulfonates; Oxidation-Reduction; Oxygen Consumption; Pseudomonas putida; Sulfonic Acids; Sulfuric Acid Esters; Textile Industry; Triazines; Triazoles; Water Pollutants, Chemical

Efficient transformation of several polycyclic aromatic hydrocarbons (PAHs) was obtained using a fungal laccase in the presence of phenolic compounds related to those formed in nature during the turnover of lignin and humus. The effect of these natural mediators, namely vanillin, acetovanillone, acetosyringone, syringaldehyde, 2,4,6-trimethylphenol, p-coumaric acid, ferulic acid, and sinapic acid, was compared with that of synthetic mediators such as 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and 1-hydroxybenzotriazole (HBT). Anthracene was significantly degraded by laccase in the absence of mediators, whereas benzo[a]pyrene and pyrene were weakly transformed (less than 15% after 24 h). Vanillin, acetovanillone, 2,4,6-trimethylphenol, and, above all, p-coumaric acid strongly promoted the removal of PAHs by laccase. 9,10-Anthraquinone was the main product detected from anthracene oxidation by all the laccase-mediator systems. The yield of anthraquinone formed was directly correlated with the amount of p-coumaric acid used. This compound resulted in a better laccase mediator than ABTS and close similarity to HBT, attaining 95% removal of anthracene and benzo[a]pyrene and around 50% of pyrene within 24 h. Benzo[a]pyrene 1,6-, 3,6-, and 6,12-quinones were produced during benzo[a]pyrene oxidation with laccase and p-coumaric acid, HBT, or ABTS as mediators, although use of the latter mediator gave further oxidation products that were not produced by the two other systems.

Topics: Basidiomycota; Benzothiazoles; Coumaric Acids; Laccase; Molecular Structure; Phenols; Polycyclic Aromatic Hydrocarbons; Propionates; Soil; Sulfonic Acids; Time Factors; Triazoles

Phenanthrene is a three-ring polycyclic aromatic hydrocarbon and commonly found as a pollutant in various environments. Degradation of phenanthrene by white rot fungus Trametes versicolor 951022 and its laccase, isolated in Korea, was investigated. After 36 h of incubation, about 46% and 65% of 100 mg/l of phenanthrene added in shaken and static fungal cultures were removed, respectively. Phenanthrene degradation was maximal at pH 6 and the optimal temperature for phenanthrene removal was 30 degrees C. Although the removal percentage of phenanthrene was highest (76.7%) at 10 mg/l of phenanthrene concentration, the transformation rate was maximal (0.82 mg/h) at 100 mg/L of phenanthrene concentration in the fungal culture. When the purified laccase of T versicolor 951022 reacted with phenanthrene, phenanthrene was not transformed. The addition of redox mediator, 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) or 1-hydroxybenzotriazole (HBT) to the reaction mixture increased oxidation of phenanthrene by laccase about 40% and 30%, respectively.

Topics: Benzothiazoles; Biodegradation, Environmental; Culture Media; Hydrogen-Ion Concentration; Kinetics; Laccase; Oxidation-Reduction; Phenanthrenes; Polyporales; Sulfonic Acids; Temperature; Time Factors; Triazoles

The mechanism of oxidation of lignin by laccase and mediator has been investigated by cyclic voltammetry and bulk electrolysis. Electrochemical properties and reactivities of the two mediators 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) and 1-hydroxybenzotriazole (HBT) were studied and their intermediates responsible for lignin oxidation were characterized. ABTS was oxidized first to the cation radical (ABTS+.) and then to the dication (ABTS2+). The two oxidized species are relatively stable and electrochemically reversible, with formal redox potentials (E0' vs Ag/AgCl) of 472 mV for ABTS/ABTS+. and 885 mV for ABTS+./ABTS2+. The dication was shown to be the intermediate responsible for the oxidation of the non-phenolic lignin model compound veratryl alcohol, whereas the cation radical reacted only with phenolic structures in lignin. Cyclic voltammetry of HBT shows only one oxidation peak at 878 mV, but unlike ABTS, the oxidized intermediate was not stable and decayed rapidly. The radical intermediate of HBT was shown to catalyze the oxidation of veratryl alcohol to veratraldehyde. The kinetics of homogeneous redox catalysis of mediators and veratryl alcohol were estimated. ABTS-mediated lignin oxidation at the redox potential of laccase (585 mV) was shown to be possible, but at a very slow rate, as previously reported for laccase and mediator.

Topics: Benzothiazoles; Benzyl Alcohols; Catalysis; Electrochemistry; Indicators and Reagents; Laccase; Lignin; Models, Chemical; Oxidation-Reduction; Oxidoreductases; Sulfonic Acids; Triazoles

Laccase of Trametes versicolor was generally able to oxidize anthracene in vitro. After 72 h incubation about 35% of the anthracene was transformed stoichiometrically to 9,10-anthraquinone. Transformation of anthracene increased rapidly in the presence of different mediators that readily generate stable radicals: 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 1-hydroxybenzotriazole. For the reaction, the presence of both the laccase and the mediator was necessary. In the presence of 0.005 mM 1-hydroxybenzotriazole this conversion had removed 47% of the anthracene after 72 h; 75% of the substrate was oxidized during this period when ABTS (1 mM) was used as mediator. In contrast to reactions without or with only low concentrations of a mediator, there was a discrepancy between the disappearance of anthracene and the formation of 9,10-anthraquinone in mediator-forced reactions. Coupling-products of mediators with anthracene degradation products were found. Anthracene disappeared nearly completely after incubation for 72 h with laccase in a 0.1 mM solution of 1-hydroxybenzotriazole and was transformed to 9,10-anthraquinone in about 80% yield; 90% of the substrate was transformed in the presence of ABTS (2.0 mM) resulting again in 80% quinone. Phenothiazine was not effective in this system.

Topics: Anthracenes; Anthraquinones; Benzothiazoles; Biodegradation, Environmental; Biotechnology; Free Radicals; Laccase; Oxidation-Reduction; Oxidoreductases; Polyporaceae; Sulfonic Acids; Triazoles