Synthesis of functionalized polyethylenimine-grafted mesoporous silica spheres and the effect of side arms on lipase immobilization and application

• Functionalized polyethylenimine-grafted mesoporous silica spheres were synthesized.
• The prepared supports were fully characterized by various analysis methods.
• Adsorption and covalent attachment approaches applied for lipase immobilization.
• Immobilized lipase produced ethyl valerate in solvent free medium.

In the present study, silicate mesoporous materials (MCM-41), MCM-41-grafted polyethylenimine (MCM-41@PEI), and succinated PEI containing amine, amide, and acid groups were successfully synthesized and characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller analysis, and X-ray photoelectron spectroscopy. Thermomyces lanuginosa lipase (TLL) was then immobilized onto MCM-41 and polymer-grafted MCM-41 by physical adsorption. Besides, for enzyme immobilization via covalent bonding, glutaraldehyde (GLU), and hexamethylene diisocyanate (HMDI) were used as the bridges for binding the enzyme to supports. The best result was obtained with the immobilized lipase on MCM-41@PEI-GLU. In the study of the enzyme reusability, it was shown that about 83% of the initial activity could be retained after 12 cycles of uses. The immobilized lipase on the selected support was also applied for the synthesis of ethyl valerate. Following 24 h incubation in n-hexane and solvent free media, the esterification percentages were 79% and 67%, respectively.

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