Preferential solvation of sulfadiazine, sulfamerazine and sulfamethazine in ethanol plus water solvent mixtures according to the IKBI method

The preferential salvation parameters of sulfadiazine, sulfamerazine and sulfamethazine in ethanol + water binary mixtures were derived from their thermodynamic properties by means of the inverse Kirkwood-Buff integrals (IKBI) method. From solvent effect studies, it is found that these sulfonamides are sensitive to solvation effects, so the preferential salvation parameter by ethanol delta X-E,X-S, is negative in water-rich and ethanol-rich mixtures but positive in compositions from 024 to 0.54-058 in mole fraction of ethanol according to the sulfonamide. It is conjecturable that in water-rich mixtures the hydrophobic hydration around aromatic rings and/or methyl groups plays a relevant role in the solvation. The more salvation by ethanol in mixtures of similar co-solvent compositions could be due mainly to polarity effects. Finally, the preference of these drugs for water in ethanol-rich mixtures could be explained in terms of the bigger acidic behavior of water interacting with hydrogen-acceptor groups in the sulfonamides. (C) 2013 Elsevier B.V. All rights reserved.