Thermodynamic study of three pharmacologically significant drugs: Density, viscosity, and refractive index measurements at different temperatures

Measurements of density, viscosity, and refractive index of three pharmacologically significant drugs, i.e. diclofenac sodium, cetrizine, and doxycycline have been carried in aqueous medium at T = (293.15 to 313.15) K. An automated vibrating-tube densimeter, viscometer, and refractometer are used in a concentration range from (7.5) · 10−3 to 25 · 10−3) mol · kg−1. The precise density results are used to evaluate the apparent molar volume, partial molar volume, thermal expansion coefficient, partial molar expansivity, and the Hepler’s constant. Viscosity results are used to calculate the Jones–Dole viscosity B-coefficient, free energy of activation of the solute and solvent, activation enthalpy, and activation entropy. The molar refractive indices of the drug solutions can be employed to calculate molar refraction. It is inferred from these results that the above mentioned drugs act as structure-making compounds due to hydrophobic hydration of the molecules in the drugs.