Laccase behavior in the microenvironment of water core within a biosurfactant-based reversed micelles system rhamnolipid/n-hexanol/isooctane/water

Abstract

Compared with synthetic surfactants (cetyltrimethyl ammonium bromide, sodium bis(2-ethylhexyl) sulfosuccinate and Tween-80), the properties of the aqueous core as well as the microenvironment behavior were investigated in water-in-oil microemulsions, which are formed by water and biosurfactant rhamnolipid (RL) in the solvent of isooctane/n-hexanol (1:1, v/v). Besides, as a typical substrate of lignocellulose, guaiacol was used to detect the laccase activity in reversed micelles (RMs). The results were eventually confirmed that RL-based RM system has higher solubilization ability, more friendly environmental compatibility and milder reaction microenvironment than the others. In this study, triangle phase diagram of surfactant/n-hexanol/isooctane/water was constructed to analyze the variation of phase behavior between each RM system. For the RL-based RM system, the effect of the molar ratio of water to surfactant (ω0) on enzyme hydrolytic activity was also determined to be shown as a bell-shaped curve and presented a maximum at ω0 = 19; the O - H stretching vibrations of water in aqueous core was also studied by analyzing the IR spectrum over the region of 3050-3750 cm-1. Moreover, kinetic studies showed that the catalytic efficiency of the laccase in RL-based RM system was lower than in aqueous solution. Nevertheless, the RM system obtained the highest hydrolysis rate at RL concentration of 1.0CMC, which is 0.055 mM.