Osmotic Coefficients of Gabapentin Drug in Aqueous Solutions of Deep Eutectic Solvents: Experimental Measurements and Thermodynamic Modeling

Abstract

Most of the applications for aqueous deep eutectic solvent (DES) solutions are directly related to molecular interactions, which can be studied using thermodynamic properties. In this regard, the activity coefficient and osmotic coefficient studies have provided evidence for understanding the depth of ion pair formation, ion solvent, and ion–ion interactions in solutions. In this study, the osmotic coefficients for binary gabapentin (GBP)/water and ternary GBP/DES (ChCl/EG and ChCl/U) aqueous solutions were calculated using vapor pressure osmometry measurements at T = 298.15 K and pressure 872 hPa. Water activities, osmotic coefficients, and vapor pressure depressions were all calculated for binary solutions. The Pitzer equation was used to correlate the osmotic coefficient values. Activity coefficients for GBP in the binary systems were determined by the obtained parameters of this equation. The standard deviation for the osmotic coefficient value in the binary system with the Pitzer equation is 0.0059. In ternary solutions, two different DES concentrations (about molality 1 and 3) were used to investigate the effect of concentration on osmotic coefficients. For ternary solutions, it was also possible to obtain quantities like water activity and osmotic coefficient data. Finally, the predicted values of water activity using the Lin and ECA models were applied to compare the results of water activity in the studied systems. The results showed that the ECA and Lin models have 0.00045 and 0.0011 average standard deviation, respectively.