Immobilization of lipase in a mesoporous reactor based on MCM-41

An immobilized enzyme has been prepared by incorporation of porcine pancreatic lipase (PPL) in the channels of MCM-41 by virtue of the hydrogen bonding interactions between the abundant weakly acidic hydroxyl groups of the support and the enzyme. The activity of the immobilized enzyme falls off rapidly when reused, however, because the weakly held enzyme is leached out from the pores. When the immobilized enzyme is treated with vinyltrimethoxysilane, the N2 adsorption–desorption plot of the product shows a type I isotherm with a steep region in the desorption branch of the hysteresis loop, suggesting that most of the organic groups have been coupled to the walls at the pore openings, which partly shrink the pore opening. The 29Si MAS-NMR spectrum shows three peaks between −60 and −80 ppm consistent with the presence of siloxane groups grafted at the pore openings, resulting in a decrease in their size. After the grafting process is complete, pores with narrow necks and wide bodies (so-called ‘ink bottle’ pores) are formed. When the modified immobilized enzyme was used to hydrolyze triacetylglycerol in a batch process, the activity remained constant over five cycles of reuse. This confirms that reaction with vinyltrimethoxysilane has led to the enzyme being immobilized inside a ‘mesoporous reactor’ from which leaching of the enzyme is prevented without inhibiting access to the substrate and release of the products.