The role of ionic association of choline amino acid ionic liquids on the two-phase formation and extraction of bovine serum albumin in ATPSs containing PEGDME250 and choline histidine or choline arginine at different temperatures

Abstract

The choline amino acid ionic liquids, [Ch][AA]-ILs, as atoxic task-specific solvents are used for inducing an aqueous two-phase systems, ATPSs, in the presence of polymers such as polyethylene glycol di-methyl ether 250, PEGDME250. In these ILs, depending on anions structure the varied and strong interactions are existed between choline cation, [Ch]+, and amino acid anions, [AA], leading to an increase of ion association. These interactions affect ILs hydration behavior and therefore the studying of these ionic associations in some detail are useful in regard to phase formation ability. In this respect, binodal curve locations and tie-lines for ATPSs composed of PEGDME250 and choline histidine or choline arginine have been determined at three temperatures (298.15–318.15) K under atmospheric pressure (≈85 kPa) and followed by searching the effects of structure and ionic association of ILs together with temperatures on the phase diagram. The ionic association constants of the above ILs together with the previously studied ILs were calculated from ionic conductivity measurements made on the these binary aqueous IL solutions at T = (288.15–318.15) K using low concentration Chemical Model method. For correlation of equilibrium data the Othmar-Tobias, Bancraft and Setschenow equations along with osmotic virial and NRTL (e-or m-NRTL) models were utilized. Finally, influences of ionic association of ILs and temperature were investigated on the separation of bovine serum albumin. The results show that phase forming ability of different [Ch][AA]-ILs is increased by decreasing of Ka values which is parallel with decreasing of amino acid hydrophobicity.