Novel Acetylcholine Chloride Based Water Immiscible Deep Eutectic Solvent: Formulation, Characterization and Application in Drug Solubilization

Deep eutectic solvents (DESs) are the emerging class of new and inexpensive solvents composed of two or three safe components capable of self-association through hydrogen bond interaction. The depression in the melting point characterizes DESs compared to those of the individual components. These solvents have properties like the traditionally used ionic liquids (ILs), but they can offset the significant drawbacks of ILs, such as biodegradability, toxicity, and complex synthesis. Due to these remarkable advantages, the research in DESs is increasing exponentially. However, current deep eutectic solvents still have limitations to apply to the real chemical industries due to hydrophilicity and the solid-state nature at room temperature of most solvents. Thus, this study focuses on the formulation of novel water-immiscible DES. The formulation of new DESs using novel hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) and their unique combinations will broaden the scope of green solvent selection for diverse applications. The first objective of this dissertation is to formulate new water immiscible DESs, pairing acetylcholine chloride (AcChCl) as HBA and fatty acids as HBDs at different molar ratios. Fourier-transform infrared spectroscopy (FTIR) and proton nuclear resonance spectroscopy (NMR) confirmed the interaction between HBA and HBDs. The freezing point was determined using differential scanning calorimetry (DSC). All synthesized DESs exhibited a lower freezing point than the individual components, thereby confirming the formation of the eutectic mixture. The in-depth characterization of the prepared DESs was performed. First, the physical properties of DESs, including viscosity, density, conductivity, refractive index, surface tension, and pH, were investigated. These properties were highly dependent on the composition, and the molar ratio of the HBA and HBDs used for DESs preparation. Second, the thermal stabilities of the DESs were determined using thermogravimetric analysis (TGA). DESs showed higher thermal stability than HBDs due to strong intermolecular forces occurring within the solvents. The electronic and molecular properties of the DESs were studied using Solvatochromic parameters, including polarity and Kamlet-Taft parameters. Changes in the composition of HBDs and the molar ratio of HBA to HBDs change the polarity of the solvents. Increasing the carbon chain length of the organic acid increases the hamlet-Taft parameter α, β. However, with an increase in the chain length of organic acid, the decrease in П* parameter was observed. The Kamlet-Taft parameters α, β, П* of formulated DESs were compared with organic solvents and ionic liquids using solvent selectivity triangles. The polarity of some DESs was very close to the polarity of organic solvents, whereas others had polarity comparable to those of ionic liquids. Lastly, the application of the DESs for solubilizing the poorly water-soluble drugs, such as aspirin, paracetamol, acetanilide, and phenacetin, was evaluated. All selected drugs show higher solubility in formulated DESs than in an aqueous medium. For example, the xx solubility of aspirin is 2- to 11- times higher, paracetamol is 1.5- to 5.4 times higher, acetanilide is 7- to 15- times higher, and phenacetin is 15- to 64- times higher in prepared DESs than in water. The overall result obtained showed that the synthesized solvents could replace traditional solvents and would be suitable for diverse engineering and industrial applications