Biocatalysis in ionic liquid: Degradation of phenol by laccase

Abstract

The aim of this work was to optimize the reaction conditions for the degradation of phenol in aqueous and ionic liquid (IL)-aqueous solution by biocatalysis using two commercial laccases. In order to evaluate the effect of IL on laccase-mediated reactions, the IL 1-ethyl-3-methylimidazolium ethylsulfate, [C2mim][EtSO4] was selected as reaction media for this study. Preliminary studies for phenol degradation were carried out in a lab-scale stirred batch reactor with 2 commercial laccases (from Trametes versicolor; Sigma and from Aspergillus; Novozymes). The synthetic effluent was prepared with phenol in appropriated buffer solutions, with pH varying from 3.0 to 9.0 and different enzyme mediators: 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS), N-hydroxyacetanilide (NHA) and (2,2,6,6-tetramethylpiperidin-1-yloxy) (TEMPO). For the optimization of reaction conditions, laccase concentration was varied in the range 1000-2000 U/L, pH in the range 6.0-7.0 and IL concentration in the range 10-20% v/v. For comparison, acetonitrile was used as organic solvents at the same conditions. Quantitative analysis of phenols and by-products formed were determined by HPLC (LaChrom Elite HPLC) with a column RP-18 LichroCART at 25°C. In conclusion, laccase (from the class of oxidases) was shown to possess catalytic activity for the degradation of phenol in systems containing ionic liquids. This finding opens up promising perspectives for applying these environmentally benign solvents to a broad range of important oxidative biotransformations. (c) 2012 Published by Elsevier Ltd.