The role of choline-based ionic liquids in modulating the thermophysical properties of d-fructose solutions.

In order to better understand how choline-based ionic liquids can improve the process of converting sugar to bioethanol, our study examined how d-fructose interacted with aqueous solutions of choline salicylate ([Ch][Sal]), choline formate ([Ch][For]), and choline acetate ([Ch][Ace]). A series of measurements including density, speed of sound, viscosity, and electrical conductivity were performed across varying temperatures and concentrations to assess the physicochemical performance of d-fructose in the studied solutions. The obtained properties including apparent molar volume (V_φ), apparent molar isentropic compressibility (κ_φ), viscosity B-coefficients, and molar conductivity (Λ) were analyzed to gain insights into the nature of intermolecular interactions. The calculated standard partial molar volume (V_φ⁰) of d-fructose indicated enhanced interactions between d-fructose and the ionic liquids. Hepler's constant values pointed to a structure-making tendency of d-fructose, particularly in aqueous [Ch][Sal] solutions. To further probe these interactions, DFT-COSMO calculation was employed, revealing that [Ch][Sal] exhibits preferentially the most energetically favorable interactions. Additionally, values of apparent specific volume (ASV) and apparent specific isentropic compressibility (ASIC) suggested that the ILs have a negligible influence on the inherent physical characteristics of d-fructose. As the temprature increased, the hydration number of d-fructose decreased, which can be due to the weakening of hydrogen bonding with water. These results highlight [Ch][Sal] ionic liquid as a promising medium for potentially promoting sugar-to-bioethanol conversion.