Enzymatic esterification plays an important role in the fields of chemistry and biotechnology. In this study, lipase was immobilized on an ionic liquid (IL)-modified magnetic metal–organic framework (MOF) and used to synthesize isoamyl acetate. The immobilized lipase (PPL-ILs/Fe₃O₄@MOF) showed 2.1-fold and 1.8-fold higher activity compared to the free and immobilized lipase without ILs (PPL-Fe₃O₄@MOF), respectively. In addition, the anti-denaturant ability and reusability of the PPL-ILs/Fe₃O₄@MOF were also higher than those of other samples. The ester yield reached 75.1% when the biocatalyst was used to synthesize isoamyl acetate in hexane. The synthesized supports supplied a good microenvironment for the immobilized lipase through multiple interactions. Results of the structural analysis showed that the conformation state of lipase molecules changed after immobilization. The magnetism of the prepared biocatalyst makes it easy to recycle so that PPL-ILs/Fe₃O₄@MOF maintained 70.2% of the initial activity after eight cycles. The prepared composite materials exhibited good potential in lipase immobilization with enhanced catalytic ability and stability.

Enzymes are difficult to recycle, which limits their large-scale industrial applications. In this work, an ionic liquid-modified magnetic metal–organic framework composite, IL-Fe₃O₄@UiO-66-NH₂, was prepared and used as a support for enzyme immobilization. The properties of the support were characterized with X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectra, transmission electron microscopy (TEM), scanning electronic microscopy (SEM), and so on. The catalytic performance of the immobilized enzyme was also investigated in the hydrolysis reaction of glyceryl triacetate. Compared with soluble porcine pancreatic lipase (PPL), immobilized lipase (PPL-IL-Fe₃O₄@UiO-66-NH₂) had greater catalytic activity under reaction conditions. It also showed better thermal stability and anti-denaturant properties. The specific activity of PPL-IL-Fe₃O₄@UiO-66-NH₂ was 2.3 times higher than that of soluble PPL. After 10 repeated catalytic cycles, the residual activity of PPL-IL-Fe₃O₄@UiO-66-NH₂ reached 74.4%, which was higher than that of PPL-Fe₃O₄@UiO-66-NH₂ (62.3%). In addition, kinetic parameter tests revealed that PPL-IL-Fe₃O₄@UiO-66-NH₂ had a stronger affinity to the substrate and, thus, exhibited higher catalytic efficiency. The results demonstrated that Fe₃O₄@UiO-66-NH₂ modified by ionic liquids has great potential for immobilized enzymes.

Recently, ionic liquids (ILs) have shown potential in enzyme activation and stabilization. In this work, ILs consisting of imidazolium-based cations coupled with [Tf₂N]⁻ anions were grafted onto a magnetic Ca²⁺-based metal–organic framework (CaBDC), and the composites were then employed to immobilize lipase. The support of ILs/MCaBDC and immobilized porcine pancreatic lipase (PPL) of PPL-ILs/MCaBDC were thoroughly characterized and fully investigated. Compared with a wild enzyme, PPL-ILs/MCaBDC showed 2.16 times higher activity. After introducing the ILs into the supports, PPL-ILs/MCaBDC showed enhanced thermal, storage, and stability properties compared with PPL–MCaBDC. After 10 cycles, PPL-ILs/MCaBDC retained a higher (83.2%) fraction of its initial activity than PPL–MCaBDC (73.4%). Furthermore, the relationship between the support–enzyme interactions and the structural changes of immobilized lipase was also analyzed in detail. Application of circular dichroism (CD) spectroscopy analysis helped us understand the changes of the enzyme secondary structure. Therefore, this work further confirmed the effectiveness of ILs for enzyme immobilization.