Improving catalytic performance of Candida rugosa lipase by chemical modification with polyethylene glycol functional ionic liquids

Candida rugosa lipase was chemically modified with various polyethylene glycol functional ionic liquids to increase its catalytic performance. All tested polyethylene glycol functional ionic liquids improved lipase catalytic activity, thermostability, organic solvent tolerance, and adaptability to temperature and pH changes in olive oil hydrolysis reaction. In particular, lipase modified by [HOOCEPEG₃₅₀Im][H₂PO₄] increased the catalytic activity by 1.7-fold, thermostability by 5.0-fold at 50 °C for 2.5 h, organic solvent tolerance by 13.3-fold in 60% dimethyl sulfoxide and 3.4-fold in 5% methanol compared with the native lipase. Investigations by ultraviolet, fluorescence, and circular dichroism spectroscopy revealed microenvironment changes, the increase in β-sheet and the decrease in α-helix content of secondary structures in the modified lipases. These changes were correlated with enzymatic properties alteration, including improved activity and stability of modified lipases. Compared with the results of previous reports, the novel modification with polyethylene glycol functional ionic liquids was more effective in improving the catalytic performance of lipase.