When water and water don’t mix
On the role of ionic liquids in Aqueous Biphasic Systems
A typical experiment in elementary science classes is separating oil from water, something we are told cannot be done with two water-like liquids. But in fact, some specific, water-based liquid mixtures may separate into two-immiscible, incompatible phases. These so-called Aqueous Biphasic Systems can, for example, be formed with the aid of ionic liquids, a subject which is thoroughly and critically reviewed by both the Molecular Thermodynamics Lab and CICECO in their most recent paper just published in Chemical Society Reviews.
Aqueous Biphasic Systems, or ABS for short, consist of two immiscible aqueous solutions containing polymers or salts and have typically been used for separating biological molecules. While certain polymers or salts are water soluble, when they are present above a given total concentration, they may promote phase splitting into two coexisting liquid phases, one of them enriched in one of these solutes, thus generating two liquid phases with distinct solvent quality.
Ionic liquids, which are essentially salts in a liquid form, have contributed to the ABS theme for some time, expanding the number and potential of possible systems. With a comprehensive review of publications describing ionic liquid-based ABS, most of which led by Portuguese laboratories, researchers discuss the effect of the ionic liquids' structure and the influence of secondary parameters such as temperature and pH on the behaviour of ABS.
Researchers point out that ionic liquid-based ABS will be important in the extraction of biomolecules and other added-value compounds and also as alternative approaches for removing and recovering ionic liquids from aqueous media after different applications.
Aqueous biphasic systems: a boost brought about by using ionic liquids
Mara G. Freire, Ana Filipa M. Cláudio, João M., M. Araújo, João A. P. Coutinho, Isabel M. Marrucho, José N. Canongia Lopes and Luís Paulo N. Rebelo