Synthesis, physico-chemical properties of novel tropine-amino acid based ionic liquids and their effects on the lipase activity

•A new series of tropine-amino acid based ionic liquids were synthesized.•Physico-chemical properties of these ILs were measured and discussed.•The effects of novel ILs on the lipase activity were investigated.•Most of these ILs have more biocompatibility on lipase than [Bmim]Br. Despite ionic liquids (IL) have widely investigated for various applications as green solvents, their toxic effects have attracted great attention. A new series of tropine-amino acid ([BuTr][AA]) ILs were presented and characterized. Their physico-chemical properties including density, conductivity and pH, critical micelle concentrations of IL solutions were investigated in this work. Lipase activity assay was carried out to study the tolerance of [BuTr][AA] ILs to enzyme and to compare with imidazolium bromide salt ionic liquid ([Bmim]Br). It was found that the biocompatibility of most [BuTr][AA] ILs to lipase was better than [Bmim]Br. The effect of [BuTr][AA] ILs on enzyme activity was highly dependent on IL concentrations, pH and type of anion. To understand the interactions of ILs and lipase, Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectra, fluorescence, circular dichroism, isothermal titration calorimetric measurements and the molecular docking method were used to further explain the lipase activity assay.