Covalent binding of hyper-activated Rhizomucor miehei lipase (RML) on hetero-functionalized siliceous supports

• The various ratios of octyl/epoxy were used for the supports functionalization.
• The physical adsorption/covalent attachment of RML were simultaneously performed.
• The over-activated biocatalysts were obtained by physical adsorption of RML.
• Covalent attachment of physically adsorbed RML lowered the release of the enzyme.
• The stability of RML was greatly improved by physical/covalent immobilization.

Physical adsorption onto hydrophobic supports has proven to be an effective way to improve the activity of lipases. Covalent binding, on the other hand, enhances the active lifetime of the immobilized biocatalysts. To combine the benefits of adsorption and covalent binding, immobilization of RML on new hetero-functional supports are reported. For this, chemical modification of silica and silica mesoporous nanoparticles was performed by the simultaneous use of two coupling linkers; Octyltriethoxysilane (OTES) for hydrophobic interaction and glycidoxypropyltrimethoxylsilane (GPTMS) for covalent linkage of RML. Altering the GPTMS/OTES ratio makes possible to have different amount of octyl and epoxy groups on the supports. The results showed that immobilization of RML on octyl-functionalized supports produces specific activity almost 1.5–2 folds greater than the specific activity of the free enzyme. The observed hyper-activation decreased with increasing epoxy groups on the supports confirming the enhancement of covalent nature of the attachment. Leaching experiment was also confirmed positive effect of the presence of epoxy groups on the supports. Regarding the specific activity of the immobilized preparations and desorption percentages of RML from each support, the most suitable carrier obtains from the functionalization of the supports in presence of GPTMS and OTES in the ratio of 1:1.