Oxidation of bisphenol A catalyzed by laccase hosted in reversed micelles in organic media

The oxidation of bisphenol A [BPA: 2,2-bis(4-hydroxyphenyl)propane] catalyzed in organic solvents by laccase (polyphenoloxidase, EC 1.10.3.2) entrapped in a reversed micellar (RM) system was investigated. The laccase/RM system effectively catalyzed the oxidation reaction in isooctane, while laccase, lyophilized from an aqueous buffer solution in which its activity was optimized, exhibited no catalytic activity in nonaqueous media. To optimize the preparation and reaction conditions for the laccase/RM system, we examined the effects of pH in the water pools of RM, the concentration of laccase, and the degree of surfactant hydration (Wo) on the laccase activity in organic media. The laccase/RM system showed a strong pH-dependency in organic media. Its optimum activity was obtained when the laccase/RM was prepared at pH=5. Interestingly, native laccase in an aqueous buffer solution exhibited an optimal activity at pH=3. The effect of a cosolubilized mediator (1-hydroxybenzotriazole, HBT) on the reaction was also investigated. BPA was effectively oxidized by the laccase/RM system in the absence of a mediator. On the other hand, the addition of 1-hydroxybenzotriazole strongly enhanced the catalytic performance of the laccase/RM system against the oxidation of various chlorophenols in organic media.