Hydration Harmony in Choline Chloride/Pyruvic Acid Deep Eutectic Solvent: Insights from Molecular Dynamics

Area of Science:

• Green Chemistry and Sustainable Solvents
• Physical Chemistry of Materials
• Computational Materials Science

Background:

• Deep eutectic solvents (DESs) are tunable, eco-friendly solvents with growing applications.
• Choline chloride-based DESs often exhibit high viscosity, limiting their use.
• Water's effect on DES structure and properties is crucial for understanding their behavior.

Purpose of the Study:

• To investigate the influence of water content on the molecular structure and dynamics of a choline chloride/pyruvic acid DES.
• To elucidate the formation of water-DES nanoclusters and their impact on system properties.
• To correlate simulation findings with experimental data for validation.

Main Methods:

• Molecular dynamics (MD) simulations were employed to study DES hydration from 0 to 80 wt % water.
• Analysis included radial distribution functions (RDFs), hydrogen bond (HB) analysis, and free energy landscape (FEL) evaluations.
• Self-diffusion coefficients, shear viscosity (Green-Kubo, Einstein relation), density, and ionic conductivity were calculated and compared to experimental data.

Main Results:

• Two competing structures, H2O-in-DES and DES-in-H2O, were identified, with full solvation at 50 wt % water.
• A critical hydration level of 25 wt % was observed, below which Ch+ diffusion is highest, and above which Ch+ and Cl- diffusion converge.
• Water significantly reduces viscosity, with simulated values aligning well with experimental data.

Conclusions:

• Water content critically dictates the structural organization and dynamics of choline chloride/pyruvic acid DES.
• The identified hydration threshold (25 wt %) is key to understanding the transition in molecular mobility.
• MD simulations provide a reliable framework for predicting DES properties, aiding in the design of tailored solvent systems.