Immobilization of chloroperoxidase on silica-based materials for 4,6-dimethyl dibenzothiophene oxidation

Silica-based materials have been used as effective supports for the immobilization of enzymes. Moreover, the understanding on the oxidation of sulfur compounds by immobilized chloroperoxidase represents a step further in the development of a biocatalytic desulfurization process of fossil fuels. Here, chloroperoxidase from Caldariomyces fumago was immobilized on amorphous and structured silica-based materials either physically or covalently using an organosilane derivative for the oxidation of a recalcitrant organosulfur compound currently found in gas oil and diesel, such as 4,6-dimethyldibenzothiophene (4,6-DMDBT). Such materials were characterized by FTIR, N2-adsorption, XRD, SEM and TEM. We have found that the chemical differences on the silanol/siloxane groups of SG/67 and SBA15 mesoporous materials deeply modify the enzymatic load, activity, thermal stability and reusability. The physical immobilization of CPO was characterized by a high adsorption capacity (qm) and affinity constants (Km) when compared to the covalent approach, but it resulted more sensitive to temperature than free, the silanized and covalently immobilized enzyme. The thermal residual activity as well as reusability of CPO were first improved by silanization, then by covalent immobilization in a support with a large pore size and high silanol/siloxane ratio.