Immobilization of lipase on silicas. Relevance of textural and interfacial properties on activity and selectivity

Two lipases from Mucor miehei have been immobilized by adsorption in MCM-41 materials featuring different hydrophilic/hydrophobic surfaces and by encapsulation either in hydrophobic silica sol-gel or in Sponge Mesoporous Silicas (SMS), a new procedure based on the addition of a mixture of lecithin and amines to a sol-gel synthesis to provide pore-size control. The resulting biocatalysts have been evaluated for various ester hydrolysis reactions and compared with commercially available immobilized lipases in silica sol-gel (Sol-gel AK-Fluka) and in ion-exchange resin (Lipozyme-Fluka). Too hydrophilic (pure silica) or too hydrophobic (butyl-grafted silica) supports are not appropriate to develop high activity for lipases. An adequate hydrophobic/hydrophilic balance of the support, such as supported-micelle, provides the best route to enhance lipase activity. The SMS encapsulation procedure enables the highest activity for the lipases. The lecithin/amines mixture structuring the pore network leads to a suitable phospholipids bilayer-like environment, which avoids the necessity to create an interface by substrates assembly. The specificity of the lipase towards middle ester chain length is lost for immobilized lipases, but the activity of lipase towards short ester chain length is considerably increased. This typoselectivity change is more likely related to a strained configuration of the immobilized enzyme.