Ionic Liquid Modification Optimizes the Interface between Lipase and Magnetic GO for Enhancing Biocatalysis

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Characterization of a recombinant Aspergillus niger GZUF36 lipase immobilized by ionic liquid modification strategy

Enzyme immobilized on magnetic nanomaterials is a promising biocatalyst with efficient recovery under applied magnets. In this study, a recombinant extracellular lipase from Aspergillus niger GZUF36 (PEXANL1) expressed in Pichia pastoris GS115 was immobilized on ionic liquid-modified magnetic nano ferric oxide (Fe3O4@SiO2@ILs) via electrostatic and hydrophobic interaction. The morphology, structure, and properties of Fe3O4@SiO2@ILs and immobilized PEXANL1 were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction, vibration sample magnetometer, and zeta potential analysis. Under optimized conditions, the immobilization efficiency and activity recovery of immobilized PEXANL1 were 52 ± 2% and 122 ± 2%, respectively. The enzymatic properties of immobilized PEXANL1 were also investigated. The results showed that immobilized PEXANL1 achieved the maximum activity at pH 5.0 and 45 °C, and the lipolytic activity of immobilized PEXANL1 was more than twice that of PEXANL1. Compared to PEXANL1, immobilized PEXANL1 exhibited enhanced tolerance to temperature, metal ions, surfactants, and organic solvents. The operation stability experiments revealed that immobilized PEXANL1 maintained 86 ± 3% of its activity after 6 reaction cycles. The enhanced catalytic performance in enzyme immobilization on Fe3O4@SiO2@ILs made nanobiocatalysts a compelling choice for bio-industrial applications. Furthermore, Fe3O4@SiO2@ILs could also benefit various industrial enzymes and their practical uses. KEY POINTS: • Immobilized PEXANL1 was confirmed by SEM, FT-IR, and XRD. • The specific activity of immobilized PEXANL1 was more than twice that of PEXANL1. • Immobilized PEXANL1 had improved properties with good operational stability.

Covalent immobilization of lipase on an ionic liquid-functionalized magnetic Cu-based metal-organic framework with boosted catalytic performance in flavor ester synthesis

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.

Preparation and Characterization of Magnetic Metal–Organic Frameworks Functionalized by Ionic Liquid as Supports for Immobilization of Pancreatic Lipase

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.