Thermophysical Analysis of Sulfamerazine Sodium and Sulfadiazine Sodium in Water and Aqueous Glyceline: Concentration- and Temperature-Dependent Molecular Interactions

A systematic thermophysical investigation of sulfamerazine sodium (SMR-Na) and sulfadiazine sodium (SDZ-Na) in water and aqueous glyceline (choline chloride: glycerol, 1:2) was carried out over the temperature range 293.15–318.15 K. Experimental measurements of density, ultrasonic velocity, and viscosity were used to evaluate apparent molar volume (Vϕ), apparent molar isentropic compressibility (Kϕ,s), viscosity B-coefficients, hydration number (nH), and Hepler’s constant. The results reveal strong solute–solvent interactions and significant modification of the hydration environment in aqueous glyceline media. Positive transfer properties and decreasing hydration numbers suggest preferential solvation of the drug molecules by glyceline components, leading to partial replacement of water molecules in the hydration shell and alteration of the electrostrictive hydration around the solute species. The negative temperature coefficient of the viscosity B-coefficient (dB/dT) along with positive Hepler’s constants suggests structure-making behavior of the drugs in aqueous glyceline media. The observed transfer properties were interpreted using the cosphere overlap model, suggesting possible modification of the local solvent environment. Overall, the study provides molecular-level insights into drug–DES interactions and establishes a thermophysical basis for future investigations of DES-assisted pharmaceutical formulations.