No abstract

In this study, imidazolium-based ionic liquids (ILs) were used to modify carboxymethyl cellulose-coated Fe 3 O 4 nanoparticles with graphene oxide deposition (ILs-MCMC/GO). The prepared composites were characterized and used to immobilize lipase. The prepared biocatalyst (PPL-ILs-MCMC/GO) exhibited higher activity, which was 3.55-fold that of free lipase and 1.41-fold that of immobilized lipase without IL (PPL-MCMC/GO). After reusing 10 times, the residual activity of PPL-ILs-MCMC/GO was 91.3%, which was higher than those of PPL-MCMC/GO (83.6%) and PPL-MCMC (73.6%). In addition, using kinetic analysis, we showed that the affinity between PPL-ILs-MCMC/GO and the substrate was improved. The secondary structures of free and immobilized lipase were analyzed to explain the mechanism by which the performance of PPL-ILs-MCMC/GO was improved. The introduction of imidazole-based IL was useful in improving the microenvironment of immobilized lipase. Furthermore, magnetic supports loaded with lipase could be recovered easily.

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.