Solubility of glucose in tetrabutylammonium bromide based deep eutectic solvents: Experimental and molecular dynamic simulations

The present work attempts to measure the solid-liquid equilibrium (SLE) of glucose in three novel low cost deep eutectic solvents (DES) namely tetrabutylammonium bromide [TBAB]-Imidazole, [TBAB]-ethylene glycol, and [TBAB]-glycerol over the temperature ranging from 299.15–353.15 K. The [TBAB]-Imidazole DES gave the highest solubility of glucose in among all the DES. The experimental solubility data was correlated with the Apelblat empirical equation along with regression using local composition models namely NRTL and UNIQUAC models. The thermodynamic functions of dissolution such as enthalpy Δ_dissol^oH, Gibbs energy Δ_dissol^oG and entropy of dissolution Δ_dissol^oS were also calculated from the modified van't Hoff equation. The dissolution functions gave positive values for all the studied systems indicating that the process is endothermic in nature while being non-spontaneous and entropically favourable. In addition, classical Molecular Dynamic (MD) simulations were performed to disclose the glucose-DES interactions. From MD simulations, the anion and hydrogen bond donor (HBD) molecules is seen to overall dominate the dissolution of glucose. The anion of hydrogen bond acceptor (HBA) and the HBD molecules are primarily responsible for the dissolution of glucose. The isomerization of glucose to fructose in [TBAB]-Imidazolium DES was observed for temperatures above 313.15 K, which resulted in a lower concentration of glucose at higher temperatures.