Interaction mechanisms of ionic liquids [C nmim]Br ( n=4, 6, 8, 10) with bovine serum albumin

Abstract

It is important to study the interaction of ionic liquids (ILs) with protein for the applications of ILs in biochemical process, and help the researchers to choose and design the better ILs to serve as a solvent. In this work, the interaction between 1-alkyl-3-methylimidazolium bromide [C n mim]Br ( n=4, 6, 8, 10) and bovine serum albumin (BSA) was systematically investigated for the first time by multi-spectroscopic approach (fluorescence, UV–vis and FT-IR spectroscopy) and density functional theory (DFT). [C n mim]Br ( n=4, 6, 8, 10) can bind to BSA by H-bond interaction between their cationic headgroups and Asp/Glu amino acid residue at the surface of BSA, and hydrophobic interaction between their hydrocarbon chains and the hydrophobic amino acid residues in the interior of BSA. On the basis of thermodynamic parameters and the similar structure of [C n mim]Br ( n=4, 6, 8, 10), it can be inferred that the hydrophobic interaction plays a major role in the interaction of [C 10mim]Br with BSA, while the hydrogen bond and van der Waals force play a major role in the interaction of [C n mim]Br ( n=4, 6, 8) with BSA. Synchronous fluorescence and FT-IR spectra indicate that [C 10mim]Br could markedly change the secondary structure of BSA, while [C n mim]Br ( n=4, 6, 8) could slightly change the secondary structure of BSA. The results allowed us to understand (i) the effect of the alkyl chain length of the cation on the mechanism of ILs–protein interaction and (ii) the effect of the alkyl chain length of the cation on the protein secondary structure.