Molecular-Level Insights into the Microstructure of a Hydrated and Nanoconfined Deep Eutectic Solvent

Despite the recent advancements in the field of deep eutectic solvents (DESs), their high viscosity often prevents practical applications. A versatile strategy to overcome this problem is either to add a co-solvent or to confine the DES inside a nanoscaled self-organized system. This work assesses the microstructures of a hydrated and nanoconfined DES comprising benzyltripropylammonium chloride [BTPA]Cl and ethylene glycol (EG). They act as a hydrogen-bond acceptor and a donor, respectively. The hydrogen bonding between [BTPA]Cl and EG in the DES (i.e., BTEG) and the molecular states of water in the hydrated BTEG were studied by Raman spectroscopy. The results show different hydrogen-bonding associations between water-water and water-BTEG or EG molecules. In addition, we investigated the confinement effects of BTEG in a Polysorbate 80 (Tween-80)/cyclohexane reverse micellar (RM) system. The results are compared with those of an ionic liquid-encapsulated RM system. The formation, bonding characteristics, and thermal stability of the RM droplets were studied by solubilization, dynamic light scattering, rheology, and Raman spectroscopy experiments. Furthermore, it is shown that hydrogen bonding between the DES and the surfactant leads to a stable RM system. Interestingly, the viscosity of the RM system is significantly lower than that of the neat DES suggesting that DESs have a much wider practical applicability in the form of RMs.

Zwitterions as novel phase forming components of aqueous biphasic systems

A novel class of aqueous biphasic systems (ABS) formed by zwitterions (ZI) has been investigated in the present work. A series of water soluble ZIs have been synthesized using triethylamine, N-Methylimidazole, N-Vinylimidazole, pyridine, N-Methylpyrrolidine, N-Ethylpiperidine and 1,4 butane sultone. The synthesized ZIs were explored for their ability to form biphasic systems in combination with aqueous inorganic salt solutions of K3PO4, K2HPO4 and K2CO3. The phase diagrams for all systems have been constructed through cloud point titration method at 298.15 K and atmospheric pressure. The phase behavior of ZI based ABS have been analyzed to understand the structural effects of ZIs as well as the effect of nature of salt used on the overall phase formation. Further the temperature dependence of the ZI based ABS was also explored by studying the phase behavior at variable temperatures of 298.15, 308.15 and 318.15 K. In order to estimate the applicability of proposed ZI based ABS, extraction experiments have been performed for an alkaloid i.e. caffeine for all synthesized ZIs with K3PO4 and at 298.15 K. ZI based ABS have been found to be capable of single step extraction of caffeine similar to IL based ABS thus providing the possibilities to explore these ZI based ABS as efficient extraction and separation systems.

Aggregation behaviour of biocompatible choline carboxylate ionic liquids and their interactions with biomolecules through experimental and theoretical investigations

The self-assembly of long-chain choline carboxylates accompanied by their interaction with BSA protein were investigated with focus on environmental sustainability.

How water manifests the structural regimes in ionic liquids

Ionic liquids (ILs) are being considered as greener alternatives to the conventional organic solvents. However, highly viscous nature of ILs often limits their applications. Hence studies on IL/water binary mixtures have received tremendous attention. These mixtures exhibit much lower viscosity, but almost similar density, compressibility and other properties as that of the neat ILs, up to certain water content. Hence, determining the IL-water ratio till which the solution behaves like IL and subsequently changes to a state of solute IL dissolved in continuous water phase is of paramount importance. Noting the very different and characteristic behaviours of neat ILs and pure water over a temperature range, herein, we measured the various thermophysical properties of the binary mixtures of tetramethylguanidinium benzoate/water and tetramethylguanidinium salicylate/water with water content varying from 20 wt% to 95 wt% for a temperature range of 298 K to 343 K. The results show that similar to neat ILs, the measured densities and compressibility of these mixtures display a linear change, and viscosity decreases rapidly as temperature is increased for water content up to 50 wt%. At higher water concentrations, the measured density and compressibility exhibit nonlinear behaviour and the decrease in viscosity with increased temperature is minute, mimicking the behaviour of bulk water. MD simulations were carried out to explain the experimental observations. Simulation results show a greater temperature-induced disintegration of IL ion-water interactions in dense systems, explaining the rapid decay of the properties with temperature. The results also exhibit the presence of a neat, IL-like, H-bond mediated expanded structure in concentrated solution versus a collapsed IL structure in dilute solution.