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

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Solution Chemistry

Background:

• Deep eutectic solvents (DES) are gaining attention as sustainable alternatives to traditional solvents.
• Understanding the transition of DES from nonaqueous to aqueous environments is crucial for their application.
• Cooperativity plays a significant role in molecular interactions and binding phenomena.

Purpose of the Study:

• To investigate the cooperativity in the transition of deep eutectic solvents (DES) to aqueous solutions.
• To characterize the binding behavior of different DES systems across varying water concentrations.
• To provide the first evidence of a shift from nonequilibrium to cooperative binding during this transition.

Main Methods:

• Studied the transition of DES to aqueous solutions by varying water content.
• Quantified cooperativity using the Hill constant (nH).
• Determined the overall Gibbs free energy change (ΔG°) for the transition.

Main Results:

• Observed a nonequilibrium region at low water content in some DES systems.
• Demonstrated consistent cooperativity at high water content for all studied systems.
• Catechol-based DES showed a Hill constant (nH) of ~3 and ΔG° of -3-5 kJ/mol.
• o-Phenylenediamine-based DES exhibited a shift from nH = 0 (low water) to nH ~ 12 (high water) with ΔG° of -13-15 kJ/mol.

Conclusions:

• The study provides the first evidence of a shift from nonequilibrium to cooperative binding in DES upon transition to aqueous solutions.
• The binding behavior is dependent on the chemical structure of the DES components.
• These findings offer insights into the fundamental interactions governing DES behavior in mixed aqueous systems.