Cooperative Demolition: Water's Disruption of Structures in Deep Eutectic Solvents

We report a study of cooperativity in the transition from a nonaqueous deep eutectic solvent (DES) to an aqueous solution. In some systems, a nonequilibrium region prevails at low water contents, while cooperativity is always observed at high water contents. Catechol-based mixtures exhibit a Hill constant (n(H)) of similar to 3 and an overall Delta G degrees of ca. -3-5 kJ/mol for the transition from DES to aqueous solution. In contrast, o-phenylenediamine-based mixtures exhibit a shift from n(H) = 0 at low water contents to n(H) similar to 12 at high water contents with an overall Delta G degrees of ca. -13-15 kJ/mol. To the best of our knowledge, this is the first evidence for a shift from nonequilibrium to cooperative binding in a transition from nonaqueous to aqueous solutions.