Is It Possible To Create Ternary-like Aqueous Biphasic Systems with Deep Eutectic Solvents?

The use of deep eutectic solvents (DES) as phase forming components of aqueous biphasic systems (ABS) has been proposed. However, it was shown that when dissolved in aqueous solutions, the DES complexes are destroyed and a nonstoichiometric partition of the hydrogen-bond acceptor (HBA) and the hydrogen-bond donor (HBD) between the phases of the ABS is observed. Aiming at evaluating the possibility to create ABS in which the DES integrity can be maintained, ABS composed of poly(propylene)glycol and mixtures of cholinium chloride, as HBA, and glucose, as HBD, were investigated. The results obtained suggest that a combination of factors, such as the hydrophobicity/hydrophilicity of the HBD, the nature of the ABS components, as well as the tie-line length, allows the preparation of systems in which the HBA:HBD stoichiometry used in DES preparation is maintained in the phases in equilibrium, thus behaving as de facto ternary systems. The partition of a wide range of biomolecules, namely phenolic compounds, amino-acids, and alkaloids, was studied on these systems. It was observed that besides the biomolecules and the DES nature, the HBD concentration, and the tie-line length also influence in the partition of the biomolecules studied, the partition mechanism being dominated by the hydrophobicity difference between the phases, with the exception of l-tryptophan for which specific interactions seem also to play a role.