Solubility and preferential solvation of sulfadiazine, sulfamerazine and sulfamethazine in propylene glycol plus water mixtures at 298.15 K

The equilibrium solubility of sulfadiazine, sulfamerazine and sulfamethazine in propylene glycol (PG) + water binary mixtures was determined at 298.15 K and the preferential solvation parameters were derived from their thermodynamic solution properties by means of the inverse Kirkwood-Buff integrals method. It is found that these sulfonamides are sensitive to specific solvation effects. The preferential solvation parameters by PG (delta x(1,3)) are negative in water-rich mixtures but positive in mixtures with compositions from 0.20 in mole fraction of PG to pure PG. It is conjecturable that in the former case the hydrophobic hydration around aromatic rings and/ or methyl groups plays a relevant role in the solvation. The more solvation by PG in mixtures of similar co-solvent compositions and in PG-rich mixtures could be explained in terms of the bigger basic behavior of this co-solvent interacting with hydrogen-donor groups of the drugs. (C) 2015 Elsevier B.V. All rights reserved.