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Abstract: Mesoporous materials, especially functionalized ones, have become a promising carrier for enzyme immobilization. We synthesized room temperature ionic liquid-decorated mesoporous SBA-15 (RTIL-SBA-15) for papain immobilization. The results of powder XRD, IR and N2 adsorption–desorption isotherms have confirmed that ionic liquid [Simim+][Cl−] was successfully grafted on the surface of SBA-15. As a consequence of the electrostatic attraction between the cation [Simim+] and the negatively charged papain, RTIL-SBA-15 had an advantage over SBA-15 when papain was immobilized at pH=9.00. The kinetic study showed that the interaction between papain and the carrier was stronger after ionic liquid modification. In the casein hydrolysis, the papain immobilized on RTIL-SBA-15 showed a higher specific activity than that on SBA-15, implying that the ionic liquid [Simim+][Cl−] was beneficial to improve the activity of the immobilized papain. The optimum pH of the immobilized papain was shifted to higher than that of free enzyme. [Copyright &y& Elsevier]

Abstract: Carboxyl-modified mesoporous materials have been demonstrated as efficient carriers for immobilizing enzymes. However, little attention has been paid to the effect of H2SO4 treatment, a key in the synthesis of carboxyl-modified carriers, on the immobilization. To examine the H2SO4 treatment’s influence, we contrasted the ability of immobilizing papain between SBA-15 and the one after H2SO4 treatment (H2SO4-treated SBA-15). Meanwhile, the contribution of the as-synthesized carboxyl to the immobilization was also rechecked by comparing carboxyl-modified SBA-15 (COOH-SBA-15) and H2SO4-treated SBA-15. In relation to the experiments, the H2SO4 treatment increases the immobilizing ability of SBA-15, especially when the immobilization performs near the pI of papain. Moreover, the as-synthesized carboxyl facilitates the immobilization by means of strengthening the hydrophobic dehydration at the interface, instead of merely through electrostatic forces. Additionally, the carboxyl makes a large contribution to inducing the favorable conformation change of papain, improving the specific activity, catalytic efficiency, and binding affinity of the immobilized enzyme when combined with the substrate. [Copyright &y& Elsevier]