Development of reversible and temperature-driven phase transition of ionic liquid/water mixtures

Ionic liquids (ILs) composed entirely of ions are a kinds of salt with very low melting temperature, negligible vapor pressure, less-flammability, and high ion conductivity. One of research topics is controlling phase behavior of these ILs and water mixture, especially temperature-driven phase control of IL/water mixture. We have designed a lot of ILs and studied phase behavior of these IL/water mixture. The data suggested that some IL/water mixture show lower critical solution temperature (LCST)-type phase transition (Fig. 1), when total hydrophobicity of cation and anion fixed within a certain range(Fig. 2). In the LCST-type phase transition, the homogeneous mixture underwent phase separation upon heating, and the mixture became homogeneous again upon cooling. These phase change could be controlled by small temperature change. By effective utilization of LCST-type phase transition of IL/water mixture, separation of a target protein from their mixtures was successfully carried out using the LCST behaviour of the IL/water mixtures (Fig. 3). In the future,enzymatic reaction will occur in a homogeneous solution, and then product and enzyme will be easily separated by small temperature change (Fig. 4).