Synthesis of functional ionic liquid modified magnetic chitosan nanoparticles for porcine pancreatic lipase immobilization.

We developed magnetic chitosan nanoparticles (CS‑Fe3O4) with mean diameter of 15-20 nm. Subsequently, these inorganic-organic composite nanoparticles were modified using an imidazole-based functional ionic liquid (IL). The prepared support (IL‑CS‑Fe3O4), which was used to immobilize porcine pancreatic lipase (PPL), was characterized using Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM), thermogravimetry (TG), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Circular dichroism (CD) was used to analyze the secondary structure of immobilized PPL. The immobilized PPL (PPL‑IL‑CS‑Fe3O4) exhibited 1.93-fold higher specific activity than PPL‑CS-Fe3O4 when triacetin was used as the substrate, and showed 95 mg/g of lipase immobilization capacity and 382% of activity recovery. The residual activity of PPL‑IL‑CS‑Fe3O4 was above 60% of the initial activity after incubation at 50 °C for 6 h, as was higher than that of PPL‑CS‑Fe3O4 which showed 40% of the initial activity. In addition, PPL‑IL‑CS‑Fe3O4 retained 84.6% of the initial activity after 10 cycles, whereas PPL‑CS‑Fe3O4 retained only 75.5% activity. Furthermore, the kinetic parameters, apparent Km and Vmax of PPL‑IL‑CS‑Fe3O4 were 2.51 mg/mL and 1.395 U/mg respectively, these results indicated that the immobilized PPL had better affinity towards the substrate, especially when the nanoparticles were modified by functional IL. Besides, the magnetic chitosan nanoparticles loaded with PPL were easily recovered. A novel, efficient, and practical method for enzyme immobilization was developed.