Importance of triple soluting-out effect in the formation of aqueous three-phase systems: Thermodynamics and applications in extraction of biomolecules

A comprehensive experimental study was conducted on aqueous triphasic systems (A3PSs) to increase molecular understanding of the soluting effect phenomenon occurring in these systems. The influence of several ionic liquids, polymers and salts was studied, demonstrating that a triple soluting-out effect is a required phenomenon to formation of an A3PS. For aqueous quaternary systems 1-butyl-3methylimidazolium bromide ([Bmim][Br]) + trisodium citrate (Na(3)Cit) + polypropylene glycol 400 (PPG400) and [Bmim][Br] + disodium sulfate (Na2SO4) + PPG400 which were able to form A3PS, the respective phase diagrams were determined at 318.15 K. For aqueous [Bmim][Br] + Na2SO4 + PPG400 system, the equilibrium compositions of three coexisting phases (tie-surfaces) were determined. The results showed that, there are an aqueous polymer-rich phase with the least amount of water (top phase), an aqueous salt-rich phase with the greatest amount of water (bottom phase), and an aqueous IL/ polymer-rich phase with large amount of water (middle phase). In order to study the soluting effects occurring in these systems, deviations from the semi-ideal behavior were addressed using the isopiestic measurements. The obtained evidence showed that the triple soluting-out effect is resulted from the unfavorable IL-salt, IL-polymer, and polymer-salt, interactions and it leads to preferential hydration of solutes and thereby creation of three aqueous polymer-rich, salt-rich, and IL/polymer-rich phases in solution for entropy reason. From isopiestic data, for quaternary solutions the constant water activity lines in mono-and biphasic regions show large negative deviations from the semi-ideal hydration model and magnitude of these deviations in monophasic region are larger than those in biphasic region. In three phasic solutions, the values of deviations became positive. The distribution behavior of three amino acids including L-proline (Pro), L-phenylalanine (Phe), and L-leucine (Leu) in aqueous [Bmim] [Br] + Na2SO4 + PPG400 three-phase system was investigated. The results showed that, because of hydrophilic property of the studied amino acids and some favorable amino acid-IL interactions, these analytes are more enriched in the salt-rich or IL/polymer-rich phases than in the polymeric phase. (c) 2022 Elsevier B.V. All rights reserved.