Preferential Solvation of Ketoprofen in Some Co-solvent Binary Mixtures

The preferential solvation parameters of ketoprofen (KTP) in ethanol (EtOH) + water and propylene glycol (PG) + water binary solvent mixtures were obtained from their thermodynamic properties by means of the inverse Kirkwood–Buff integrals (IKBI) and quasi-lattice quasi-chemical methods. According to the IKBI method, it is found that KTP is very sensitive to specific solvation effects, so the preferential solvation parameter by co-solvents, δx _1,3, is negative in the water-rich mixtures of both binary systems but positive in the other compositions at temperatures of 293.15, 303.15 and 313.15 K. From this it can be assumed that, in water-rich mixtures, hydrophobic hydration around the aromatic rings and the methyl group, present in the drug, plays a relevant role in the solvation. The bigger amount of drug solvation by the co-solvent in mixtures of similar solvent proportions and in co-solvent-rich mixtures could be due mainly to polarity effects. Moreover, in these mixtures the solute will be acting as a Lewis acid with the co-solvent molecules, because they are more basic than water.