Characterization of interactions between β-lactoglobulin with surface active ionic liquids in aqueous medium

The interaction of beta-lactoglobulin (beta LG) with surface active ionic liquids (ILs), 1-dodecyl-3-methylimidazolium bromide [C(12)mim][Br] and 1-hexyl-3-methylimidazolium dodecylsulfate [C(6)mim][C12OSO3] has been investigated employing tensiometry, conductivity, fluorescence, dynamic light scattering (DLS), zeta potential and circular dichroism (CD) methods. A significant difference was observed in the nature of interactions present in the beta LG-[C(12)mim][Br] system as compared to beta LG-[C(6)mim][C12OSO3]. The IL, [C(12)mim][Br] interacted strongly with beta LG to form complexes at the interface as compared to weaker interactions observed in case of beta LG-[C(6)mim] [C12OSO3] system. The results of intrinsic fluorescence measurements along with CD measurements have provided insights into the unfolding of beta LG due to binding of ILs. Turbidity measurements have shown the coacervate formation in case of beta LG-[C(12)mim][Br] which was also supported from DLS and zeta potential measurements. An excellent correlation of results obtained from multiple techniques has been used to characterize the interactional behavior of ILs and beta LG in a wide concentration regime. The results of the present studies are expected to contribute in understanding the interactional behavior of beta LG with surface active ILs and its effect on functionality of protein. (C) 2018 Elsevier B.V. All rights reserved.