(513ej) Functionalized Core-Shell Structured Covalent Organic Framework for Immobilized Lipase

Background: Currently, humans have a special preference for environmentally friendly enzyme catalysts. However, enzymes have problems of operational stability and reusability in practical applications. Covalent organic frameworks (COFs) has the characteristics of high surface area, chemical and thermal stability, adjustable porous structure and modifiable chemical structure, which can be used as an ideal material for immobilized enzymes.

Methods: The 3,3′-dihydroxybenzidine and 1,3,5-tri (4-formylbiphenyl) benzene were selected as ligands to prepare COFs with hydroxyl groups. Then, we introduced Fe₃O₄ with magnetic separation function to prepare the core-shell structure Fe₃O₄@COF and modified Fe₃O₄@COF with succinic acid. As the model Candida antarctica lipase B (CALB), CALB was immobilized onto the Fe₃O₄@COF-SA composites by covalent bonding method (Fe₃O₄@COF-SA@CALB). Subsequently, the enzymatic properties of Fe₃O₄@COF-SA@CALB and free CALB were investigated. In addition, the esterification reaction between lauric acid (LA) and n-lauryl alcohol that was catalyzed by Fe₃O₄@COF-SA@CALB was also studied.

Results: The morphology and properties of Fe₃O₄, Fe₃O₄@COF and Fe₃O₄@COF-SA@CALB were analyzed by SEM, TEM, TGA, FT-IR and XRD, which proved that CALB was successfully immobilized to the Fe₃O₄@COF-SA. The enzymatic properties of Fe₃O₄@COF-SA@CALB and free CALB were investigated. The results showed that Fe₃O₄@COF-SA@CALB exhibited better pH, thermal stability, organic solvents tolerance and storage stability than free CALB. The Fe₃O₄@COF-SA@CALB was used to catalyze the esterification reaction of LA and n-lauryl alcohol, and the maximum LA conversion of the esterification reaction was 90.3%. After the 10th cycle of the reaction, the esterifying enzyme activity of Fe₃O₄@COF-SA@CALB remained 78.9% of the initial enzyme activity.

Conclusions: We reported for the first time that the enzyme was covalently bound to the core-shell structure of Fe₃O₄@COF. Fe₃O₄@COF-SA@CALB showed desirable pH stability, thermal stability, organic solvent tolerance and storage stability. This research showed that the COFs possessed a wide range of applications as a host material for the immobilization enzyme.