Improving the Stability of Immobilized Penicillin G Acylase via the Modification of Supports With Ionic Liquids

With the aim of improving the stability of penicillin G acylase (PGA), functional ionic liquids (ILs) were used to modify the surface chemistry of the supports on which they were physically adsorbed. Four kinds of ILsspecifically, 1-methyl-3-(triethoxysilylpropyl)-imidazolium salts, with Cl^–, BF₄^–, PF₆^–, and Tf₂N^– as the anions (IL-Cl^–, BF₄^–, PF₆^–, and Tf₂N^–, respectively)were used to tune the hydrophilic or hydrophobic properties of the ILs. The synthesized ILs were first immobilized on magnetic silica nanoparticles (Fe₃O₄/SiO₂), and the composite material (Fe₃O₄/SiO₂–IL) was then applied to immobilize PGA via physical adsorption. The amount of protein loading, the specific activity, the immobilization yield, and the stability of immobilized PGA were investigated to evaluate the effects of the ILs on the PGA immobilization. The results showed that PGA immobilized on Fe₃O₄/SiO₂–ILs was more stable than that immobilized on Fe₃O₄/SiO₂ with no IL modification. Among the four kinds of ILs tested, the hydrophilic ILs (IL-Cl^–, and IL-BF₄^–) were superior to the hydrophobic ones (IL-PF₆^–, and IL-Tf₂N^–) for PGA immobilization. The reusability of the immobilized PGA on Fe₃O₄/SiO₂–IL (BF₄^–) was evaluated; a high residual activity (70% of the initial activity) was observed after 9 consecutive operation cycles under the experimental conditions. This activity was 1.8 times higher than that of immobilized PGA on naked Fe₃O₄/SiO₂ (40%)