Probing HSA-ionic liquid interactions by spectroscopic and molecular docking methods.

Herein, we report the interaction of synthesized pyrrolidinium based ionic liquid, N-butyl-N-methyl-2-oxopyrrolidinium bromide (BMOP) with human serum albumin (HSA). The BMOP was characterized by using (1)H NMR, (13)C NMR and FT-IR techniques. The critical micelle concentration (cmc) of BMOP was confirmed by surface tension, conductivity and contact angle measurements. The interactions between HSA and BMOP were studied by steady-state and time-resolved fluorescence, UV-visible, FT-IR spectroscopic and molecular docking methods. The steady-state fluorescence spectra showed that BMOP quenched the fluorescence of HSA through combined quenching mechanism. Corresponding thermodynamic parameters viz. Gibbs free energy change (ΔG), entropy change (ΔS) and enthalpy change (ΔH) illustrated that the binding process was spontaneous and entropy driven. It is also suggested that hydrophobic forces play a key role in the binding of BMOP to HSA. In addition, the pyrene probe analysis again suggests the involvement of hydrophobic interaction in HSA-BMOP complex formation. Surface tension profile showed that the cmc value of BMOP in the presence of HSA is higher than the cmc value of pure BMOP. The FT-IR results show a conformational change in the secondary structure of HSA upon the addition of BMOP. The molecular docking result indicated that BMOP binds with HSA at hydrophobic pocket domain IIA with hydrophobic and hydrogen bond interactions in which hydrophobic interactions are dominating.