Probing the Interactions of 1-Alkyl-3-methylimidazolium Tetrafluoroborate (Alkyl = Octyl, Hexyl, Butyl, and Ethyl) Ionic Liquids with Bovine Serum Albumin: An Alkyl Chain Length-Dependent Study.

Herein, we have investigated the binding interaction of bovine serum albumin (BSA) with a series of 1-alkyl-3-methylimidazolium tetrafluoroborate (alkyl = ethyl, butyl, hexyl, and octyl) ionic liquids (ILs) in physiological buffer medium. The ILs are chosen basically to understand the effect of alkyl chain length on IL-protein interaction. Experiments have shown that the quenching of fluorescence of BSA is induced by relatively longer alkyl chain-containing ILs, [OMIM][BF4] and [HMIM][BF4]. The enthalpy-driven spontaneous binding (-ve Δ G) of hexyl and octyl chain-containing ILs with the protein is mediated by both hydrogen-bonding and van der Waals interactions. The experimental data have categorically explained the denaturation of protein conformation upon interaction with both [OMIM][BF4] and [HMIM][BF4]. The molecular docking calculation nicely corroborates the experimentally obtained results. The present study reveals that neither a smaller alkyl group-containing IL nor a very large alkyl group-containing IL is necessary to have effective protein-IL interactions. The study also reveals the influence of hydrophobic interaction over and above the hydrogen-bonding interaction on protein-IL binding events and essentially gives an idea about the optimum hydrophobic character of the ILs that is necessary to induce protein-IL interaction and consequently the denaturation of the protein structure.