Deciphering the mechanism of interaction of an ester-functionalized cationic gemini surfactant with bovine serum albumin: A biophysical and molecular modeling study

Protein–surfactant interactions have relevance in the fields of pharmaceuticals, detergency formulation, pharmacology, personal hygiene products, etc. Accordingly, we have analyzed the biomolecular interaction between a recently synthesized C16-E2O2-C16 gemini surfactant with the transport protein, bovine serum albumin (BSA), utilizing surface tension, fluorescence (intrinsic/extrinsic, synchronous, 3-D and resonance Rayleigh scattering (RRS)), circular dichroism (CD), UV–visible, Fourier transform infrared (FT-IR) and computational methods. The critical micelle concentration (CMC) and surface parameters of the gemini surfactant get modified in the presence of BSA. The interaction of the concerned surfactant with BSA occurred via a static quenching mechanism forming a less stable complex at the higher temperature. Based on calculated thermodynamic parameters, the interaction process was found to be spontaneous (∆Gb0 is negative) and that hydrogen bond (HB) and van der Waals (VDW) forces were predominant forces in stabilizing the complex (both ∆Hb0 and ∆Sb0 are negative). FT-IR and CD measurements demonstrated that the secondary structure conformation of BSA was perturbed because of the BSA-C16-E2O2-C16 complexation. The 3-D and RRS fluorescence studies demonstrated that the BSA size enlarged in presence of the gemini and ensued in the increment of scattering effect and suggested some conformational and micro-environmental alterations of Trp/Tyr residues of BSA (the same results were obtained for pyrene extrinsic fluorescence). Molecular docking and site marker displacement investigations recognized that the surfactant C16-E2O2-C16 predominantly binds within BSA’s site I (sub-domain IIA).