Molecular and Spectroscopic Insights of a Choline Chloride Based Therapeutic Deep Eutectic Solvent

In this study, atomic level interactions of a 1:1 choline chloride (ChCl)/acetylsalicylic acid (ASA) therapeutic deep eutectic solvent (THDES) has been investigated by combining the molecular dynamics (MD), density functional theory (DFT), and spectroscopic (Raman and IR) techniques. Atom-atom radial distribution functions (RDFs) based on MD simulation reveal that hydrogen bonds are formed between Cl^-···HO_Ch⁺ and Cl^-···HO_COOH of the THDES, where Cl^- works as a bridge between ASA and Ch⁺. Cation-anion electrostatic attractions are disrupted by highly interconnected hydrogen bonds. Cluster conformers of the THDES are isolated from MD simulation and optimized using ωB97XD/6-311++G(d,p) level of theory, in which the strongest H bonds are found among OH_Ch⁺···Cl^- (2.37 Å) and Cl^-···HO_COOH(2.40 Å). Charge transfer calculations, using CHEPLG and NBO analysis, disclose that the charge of Cl^- is reduced in the cluster structures and transferred to Ch⁺ and ASA. Further analyses are conducted using experimental and computed spectroscopic data. These confirm the formation of the THDES as peaks for -COOH, -COOR, and -OH functional groups of ASA and ChCl are either get broadened or disappeared in the spectra of the cluster conformers. Moreover, principal component analysis (PCA) assists to understand the feature of the simulated data and confirms the formation of the THDES. Solvent selectivity triangle (SST) of solvatochromic parameters also demonstrate that this THDES has some important properties similar to ionic liquids and common deep eutectic solvent.