Interactions between a surface active imidazolium ionic liquid and BSA

Abstract

The interactions between a surface active imidazolium ionic liquid (IL), 1-tetradecyl-3-methylimidazolium bromide (C14mimBr) and bovine serum albumin (BSA) were studied. To investigate the structure changes of BSA induced by addition of C14mimBr, this system was studied by surface tension, isothermal titration microcalorimetry, far-UV circular dichroism (CD) and fluorescence spectra. The surface tension measurement shows the formation of C14mimBr/BSA complex and the effect of the complex on surface tension. Furthermore, it reveals the interaction type. The enthalpy change in the whole interaction process between C14mimBr and BSA was obtained by isothermal titration microcalorimetry, and the results prove the alteration of the BSA structure. To realize the structure alteration position more definitely, far-UV CD was used to obtain the contents of α-helix and random coil. Changes of these contents reveal that the secondary structure of BSA changes with addition of C14mimBr. Fluorescence spectra are used to prove that the alteration of the secondary structure is due to the interactions of C14mimBr molecules and amino acid residues. They show that tryptophan (Trp) residues, one of the intrinsic fluorophores in BSA, are exposed to a hydrophobic microenvironment with the addition of C14mimBr.