Biotransformation of t-butyl phenols by micellar nanoreactors of peroxidase/ionic surfactants at mild conditions: nanobiocatalyst performance and kinetic analysis

Abstract

Recently, some bulk reaction media were substituted by micellar systems. Micellar media can be created by different types of surfactants which generate micellar nanoreactors for diverse reactions. Ionic surfactants can be used as aqueous micellar systems, providing mild conditions for the specified reactions. Ionic surfactants: sodium dodecyl sulfate, sodium decyl sulfate (SDeS), sodium octyl sulfate (SOS), n-dodecyl trimethyl ammonium bromide, and cetyltrimethylammonium bromide were used to prepare aqueous micellar and entrapped peroxidase nanoreactors as biocatalysts. Oxidative coupling reactions were investigated for a series of phenolic hydrogen donors including 2-tert-butyl phenol, 4-tert-butyl phenol, and 2,4-tert-butyl phenol catalyzed by micellar nanoreactors of horseradish peroxidase (HRP) with hydrogen peroxide and/or tert-butyl peroxide as oxidants. Higher oxidation reaction rates were obtained for 2-tert-butylphenol and 4-tert-butylphenol with hydrogen peroxide in 90 mM SDeS (SDeS90) and 150 mM SOS (SOS150) nanoreactors, respectively. Among the micellar nanoreactors studied, the SDeS90 nanoreactor showed excellent protection of the enzyme against the peroxide inactivation effect. The long-term activity of the HRP/SDeS90 nanobiocatalyst was related to the gradual diffusion of peroxide into the nanoreactor. The biocatalytic kinetic parameters: V max, k cat, catalytic efficiency, and suicide-peroxide inactivation rate constants were determined for HRP/SDeS90. Reactions were carried out successfully under mild conditions in the micellar nanoreactors. Results confirmed that substituted functional groups on the benzene ring affect the oxidative reaction routes and products. Excellent protection of the enzyme, enhanced biocatalytic parameters, higher selectivity, and yield, in the peroxidative coupling of alkylphenols, reveal the high potential of such micellar nanoreactors for diverse organic synthesis and biotransformation.