Inhibitory effects of ionic liquids on the lactic dehydrogenase activity

• The interaction of lactic dehydrogenase with ionic liquids was investigated.
• The activity of LDH decrease in the presence of ILs.
• Fluorescence quenching of LDH by six ILs is dynamic mechanism.
• Hydrophobicity is the main driven force underlying IL-enzyme interaction.

Ionic liquids (ILs) were widely used in scientific and industrial application and have been reported to possess potential toxicity to the environment and human health. The effects of six typical N-methylimidazolium-based ILs ([Cnmim]X, n = 4, 6, 8; X = Br−, Cl−, BF4−, CF3SO3−) on the lactic dehydrogenase (LDH) activity and the molecular interaction mechanism of ILs and the LDH were investigated with the aid of spectroscopic techniques. Experimental results showed that the LDH activity was inhibited in the presence of ILs. For the ILs with the same anion but different cations, their inhibitory ability on the LDH activity increased with increasing the alkyl chain length on the IL cation. Thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) were obtained by analyzing the fluorescence behavior of LDH with the addition of ILs. Both positive ΔH and ΔS suggested that hydrophobicity was the major driven force in the interaction process as expected.