Preferential solvation of some structurally related sulfonamides in 1-propanol + water co-solvent mixtures

The preferential solvation parameters by 1-propanol of sulfadiazine, sulfamerazine and sulfamethazine in 1-propanol + water mixtures were derived from their solution thermodynamic properties by means of the inverse Kirkwood-Buff integrals method. These sulfonamides are sensitive to solvation effects, so the preferential solvation parameter delta x(1,3) is negative in water-rich and 1-propanol-rich mixtures but positive in intermediate compositions. It is possible that the hydrophobic hydration around aromatic rings and/or other non-polar groups plays a relevant role in the solvation in water-rich mixtures. The more solvation by 1-propanol in mixtures of similar composition could be due mainly to polarity effects and acidic behaviour of the sulfonamides in front to the more basic solvent 1-propanol. Otherwise, the more solvation by water in 1-propanol-rich mixtures could be due to basic behaviour of the sulfonamides in front to water, which is the more acidic solvent.