Behavior of lysozyme within ionic liquid-in-water microemulsions

Abstract Ionic liquids (ILs) and IL-based microemulsions are of immense importance due to their broader application potential in various interdisciplinary research areas such as, synthesis, catalysis, biochemical processes, pharmaceutics, and material science. In this manuscript, we have studied the behavior of an antimicrobial enzyme lysozyme within IL-in-water (IL/W) microemulsions formed by hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6] in nonionic surfactant Brij-35 solution. It is noteworthy that the fluorophores and chromophoric responses clearly indicate significant changes in the micropolarity and microviscosity within aqueous Brij-35 micellar solution in the presence of IL [bmim][PF6] forming microemulsions. DLS shows the size of these nanostructures formed are of 6–8 nm range. IL-lysozyme interactions within the IL/W microemulsions were studied using UV–Vis, steady-state and time-resolved fluorescence and FT-IR spectral investigations. Increase in Brij-35 concentration increases the lysozyme fluorescence intensity in absence of the IL, whereas increase in IL concentration within the IL/W microemulsions results in gradual decrease in the lysozyme fluorescence intensity as a results of IL-lysozyme binding. Both steady-state and time-resolve fluorescence results suggest fluorescence quenching of lysozyme in presence of IL [bmim][PF6] within both aqueous solution and Brij-35 IL/W microemulsions. Further, electrochemical response from cyclic voltammetric studies also confirms the binding of lysozyme with IL [bmim][PF6]. FTIR spectral responses show that lysozyme remains stable within the IL/W microemulsions amid IL-lysozyme binding observed from UV–Vis and fluorescence studies.