Spectroscopic studies on the interactions between imidazolium chloride ionic liquids and bovine serum albumin

The binding of three imidazolium chloride ionic liquids (ILs) with bovine serum albumin (BSA) were investigated by UV absorption spectra, fluorescence spectra and synchronous fluorescence spectra. The results showed that the UV absorption of the BSA was red-shift, and intensity of UV absorption declined with the increase in concentration of ILs. According to fluorescence spectra, fluorescence quenching of the BSA was happened with ILs added, and the main reason is static quenching. The study of synchronous fluorescence spectra indicated that ILs interacted with tryptophan (Trp) and tyrosine (Tyr) residues, changed the structure and the internal hydrophobic conformation of BSA. The binding constant K and the numbers of binding sites n were obtained by Stern–Volmer equation. For [Bmim]Cl, K = 16.12 L mol−1, n was 0.64; for [Hmim]Cl, K = 31.48 L mol−1, n was 0.70; for [Omim]Cl, K = 355.22 L mol−1, n was 0.99. The binding strength of ILs with BSA is expected to show the trend with the length of carbon chain, [Bmim]Cl < [Hmim]Cl < [Omim]Cl.

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► The study reveal the mechanism of ionic liquids interaction with bovine serum albumin.
► The UV absorption intensity of BSA decreased and red shifted with ILs.
► The fluorescence intensity of BSA static quenched with ILs.
► ILs interaction with the protein close the area of Tyr residues.
► The binding strength with BSA show the trend with the length of carbon chain of ILs.