Quantum Molecular Dynamics Approach to Understanding Interactions in Betaine Chloride and Amino Acid Natural Deep Eutectic Solvents.

The unique properties and versatile applications of natural deep eutectic solvents (NaDES) have sparked significant interest in the field of green chemistry. Comprised of natural components that form liquids at room temperature through strong noncovalent electrostatic interaction, these solvents are cost-effective, nontoxic, and versatile. Betaine chloride-based NaDES, in particular, have shown promise in biocatalysis and sugar extraction due to their excellent properties. Despite their potential, the complex nature of these solvents, characterized by intense hydrogen bonding and proton transfer processes, poses significant challenges. This study employs quantum molecular dynamics (ab initio MD-AIMD) to explore the intricate NaDES-microstructure formed from betaine chloride and amino acids (arginine, histidine, lysine). Our findings highlight the dynamic nature of proton transfers within these solvents, demonstrating rapid and extensive hydrogen bonding interactions. The Van Hove correlation functions reveal that proton transfers are highly mobile, facilitating the formation and breaking of covalent hydrogen bonds. This dynamic behavior is further corroborated by the radial distribution functions, which indicate significant proton exchange between amino acids and betaine cations. Chloride anions play a crucial role in maintaining the structural integrity of NaDES through strong interactions with proton donors. These findings advance our understanding of these eutectic solvents and their potential applications in sustainable chemical processes.