Water-modulated structure and dynamics in aqueous choline chloride-polyol deep eutectic solvents: Insights from molecular dynamic simulations

Understanding how water modulates the structure and dynamics of deep eutectic solvents (DESs) is essential for their rational design, yet their complex structuring in aqueous environment remains poorly understood. Here, we have performed molecular dynamic simulations to investigate structural organization, hydrogen-bond (H-bond) network, and water dynamics of aqueous DESs (ADESs) composed of choline chloride and three polyols, erythritol, xylitol, and sorbitol, at 0, 25, 50, and 75 wt. % of water, respectively. These polyols are deliberately chosen as H-bond donors because they possess an increasing number of hydroxyl groups. Radial distribution functions and cluster size distributions reveal various micro-structures formed inside ADESs. Their dependence on water content and on alcohol identity reflects a complex interplay of interactions. Alcohol-alcohol clustering decreases with increasing water content; however, water-water clustering shows a non-monotonic dependence. The normalized H-bond counts with varying water wt. % can explain the underlying alcohol dependency. The water dynamics is further investigated through tetrahedral order parameter, H-bond relaxation times, self-diffusion coefficients, and rotational time correlation functions. These reveal a progressive recovery of bulk-like water structure and dynamics from a confined environment with increasing water content, a well-known transition of "water in DESs" to "DESs in water." Such effects directly influence solvent behavior, viscosity, and hydration properties, which are critical for biocatalysis. The results highlight the importance of tuning DES composition to control water-mediated structuring for chemical and biological applications.