Volumetric Studies of Theophylline-PEGylated Deep Eutectic Solvents in Aqueous Solution

Deep eutectic solvents (DESs) have garnered significant attention as eco-friendly alternatives to conventional solvents. Understanding the solution chemistry of DES is crucial for green chemistry processes in pharmaceutical formulations. This study presents a comprehensive volumetric investigation to elucidate the molecular interactions and thermodynamic properties of theophylline in aqueous DES environments. A DES composed of PEG-400 and citric acid/ascorbic acid was tailored to study the theophylline–DES interactions. Measurements of density and speed of sound were conducted within the range of 293.15–318.15 K and 0.1 MPa. Analysis of apparent molar volumes, infinite dilution partial molar volumes, and volumetric transfer parameters provided the plausible theophylline–DES–water interactions. The findings indicate a complex interplay of interactions among DES components and theophylline, with notable observations on the dimerization of theophylline leading to a reduction in the transfer volume. This study sheds light on DES-mediated drug–water interactions, which offer valuable implications for pharmaceutical applications.