Preferential Solvation of Some Sulfonamides in Propylene Glycol plus Water Solvent Mixtures According to the IKBI and QLQC Methods

The preferential solvation parameters, which represent differences between the local and bulk mole fractions of the solvents near to the solute, in solutions of some sulfonamides in propylene glycol + water binary mixtures are derived from their thermodynamic properties by means of the inverse Kirkwood-Buff integrals (IKBI) and the Quasi-Lattice Quasi-Chemical (QLQC) method. From solvent effect studies, it is found that sulfonamides are sensitive to solvation effects; the preferential solvation parameter, delta X-PG,X-S, is negative in water-rich mixtures but positive in compositions from 0.20 to 1.00 in mole fraction of propylene glycol according to IKBI method and positive in all co-solvent compositions if the QLQC method is considered. It is conjecturable that in water-rich mixtures, hydrophobic hydration around the aromatic ring and/or other non-polar groups plays a relevant role in the solvation. The greater solvation by propylene glycol mixtures of similar solvent compositions and in co-solvent-rich mixtures could be due mainly to polarity effects and acidic behavior of the sulfonamides, in contrast to the more basic solvent propylene glycol.