β-Galactosidase activity in mixed micelles of imidazolium ionic liquids and sodium dodecylsulfate: A sequential injection kinetic study

Abstract

An automated methodology for the kinetic study of β-galactosidase activity in sodium dodecylsulfate (SDS)/ionic liquid (IL) mixed micelles was developed. The main objective of the work was the evaluation of mixed micelles as reaction media for the industrial synthesis of glyco-oligossacharides. Enzyme activity was evaluated by means of a model reaction with the fluorescent substrate 4-methylumbelliferyl-α-d-galactopyranoside (MUG). The assay was implemented in a sequential injection analysis (SIA) system and enzyme activity was studied in SDS/bmim [BF4] and SDS/hmim [Cl] mixed micelles with variable concentrations of both components. In order to perform a critical evaluation of the obtained results, CMC and average micellar size of SDS/hmim [Cl] mixed micelles were evaluated by fluorescence and dynamic light scattering, respectively. In the micelle characterization assays it was observed that the CMC of the mixed micelles increased with hmim [Cl] concentration up to 1molL−1. In the presence of higher IL concentrations there were no evidences of micelle formation. Regarding micellar size, it was maximum for an IL concentration of 0.09molL−1. The kinetic assays evidenced that SDS/bmim [BF4] and SDS/hmim [Cl] mixed micellar systems can led to an increase of enzyme activity. This increase is dependent on the variation of the average micellar size that occurs with the increase of IL concentration up to 0.09molL−1. It was also noticed that the most promising systems are those incorporating SDS and IL in concentrations under 50mmolL−1 and 0.5molL−1, respectively. These results evidenced that the studied ILs can modify the physico-chemical properties of the surfactant solution in a favourable way regarding β-galactosidase activity being an important achievement for the future implementation of industrial processes catalyzed by this enzyme, mainly the synthesis of glyco-oligossacharides. Indeed, surfactant/IL mixed micelles proved to be an interesting alternative to conventional organic solvents in this field enabling the implementation of the processes in a relatively hydrophobic media with enhanced enzyme activity.