Experimental and Theoretical Study of the Synthesis of a Deep Eutectic Solvent Based on Protonated Caffeine, Ethylene Glycol, and ZnCl.

In this study, a deep eutectic solvent (DES) incorporating protonated caffeine (CafCl), ethylene glycol (EG), and zinc chloride (ZnCl2) was synthesized and characterized for the first time. Caffeine was protonated using an optimized procedure in an anhydrous medium to enhance its interaction with the system, and its structure was confirmed by FTIR spectroscopy, NMR, and thermogravimetric analysis (TGA), evidencing the formation of the N-H bond in the imidazole ring. A eutectic mixture with a molar ratio of ETG:ZnCl2:CafCl of 1:2:0.1 was synthesized, and its characterization confirmed the formation of hydrogen bonds and the coordinative interaction between the components. Additionally, computational simulations based on COSMO-RS and ab initio molecular dynamics (AIMD) were conducted to analyze the charge distribution and the stability of the hydrogen bond network in the eutectic mixture. Sigma profiles revealed that protonated caffeine possesses highly polar regions capable of establishing strong interactions with EG and ZnCl2, enhancing the system's stability. Furthermore, radial distribution functions (RDFs) showed a decrease in the interaction distance between key atoms after incorporating protonated caffeine. The results suggest that this novel DES has promising potential for industrial applications, especially in the extraction of sulfur compounds from fossil fuels due to the activation of the imidazole ring of caffeine. However, further studies are needed to optimize its operating conditions and evaluate its performance on an industrial scale.