Solution Thermodynamics and Preferential Solvation of Atenolol in {Ethanol (1) + Water (2)} Cosolvent Mixtures

Abstract

: The solubility of atenolol (ATN) in some {ethanol (1) + water (2)} mixtures expressed in mole fraction at temperatures from 298.2 to 313.2 K was calculated from reported solubility values expressed in molarity scale. The van’t Hoff and Gibbs equations were used to calculate the respective apparent thermodynamic functions: Gibbs energy, enthalpy, and entropy of the dissolution processes. Non-linear enthalpy–entropy relationship was observed for this drug ATN in the plot of enthalpy vs. Gibbs energy of solution with negative slope in the composition region 0.00 ≤ w 1 ≤ 0.20 but positive slope in the region 0.20 ≤ w 1 ≤ 0.40. Beyond this composition, the behavior is more complex. Hence, the driving mechanism for ATN dissolution process is the entropy in water-rich mixtures and the enthalpy in mixtures 0.20 ≤ w 1 ≤ 0.40. Furthermore, the preferential solvation of ATN by both solvents was analyzed by using the inverse Kirkwood- Buff integrals observing that this drug is preferentially solvated by water molecules in water-rich and also in ethanol-rich mixtures but preferentially solvated by ethanol molecules in mixtures 0.24 ≤ x 1 ≤ 0.51.