Spectroscopic insight into the interaction of bovine serum albumin with imidazolium-based ionic liquids in aqueous solution

The study of protein-ionic liquid interactions is very important because of the widespread use of ionic liquids as protein stabilizer in the recent years. In this work, the interaction of bovine serum albumin (BSA) with different imidazolium-based ionic liquids (ILs) such as [1-ethyl-3-methyl-imidazolium ethyl sulfate (EmimESO₄ ), 1-ethyl-3-methyl-imidazolium chloride (EmimCl) and 1-butyl-3-methyl-imidazolium chloride (BmimCl)] has been investigated using different spectroscopic techniques. The intrinsic fluorescence of BSA is quenched by ILs by the dynamic mechanism. The thermodynamic analysis demonstrates that very weak interactions exist between BSA and ILs. 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence and lifetime measurements reveal the formation of the compact structure of BSA in IL medium. The conformational changes of BSA were monitored by CD analysis. Temperature-dependent ultraviolet (UV) measurements were done to study the thermal stability of BSA. The thermal stability of BSA in the presence of ILs follows the trend EmimESO₄ > EmimCl > BmimCl and in the presence of more hydrophobic IL, destabilization increases rapidly as a function of concentration.