Solvent effect and preferential solvation of cefpiramide in cosolvent plus water mixtures

Abstract

The preferential solvation parameters (δx1,3) of cefpiramide in two cosolvent mixtures of ethanol (1) + water (2), and isopropanol (1) + water (2) were derived from their available solubility data by means of the inverse Kirkwood–Buff integrals method. For the studied systems, the values of δx1,3 were negative in the entire composition region for the isopropanol (1) + water (2) mixtures at 293.15 K and 298.15 K and for the ethanol (1) + water (2) mixtures at different temperatures studied, therefore the cefpiramide was preferentially solvated by water in the entire composition region. However in the isopropanol (1) + water (2) mixtures at 303.15 K with composition 0.45 < x1 < 0.62 and 0.85 < x1 < 1, the δx1,3 values were positive. The negative δx1,3 values indicated that cefpiramide was preferentially solvated by water. Probably the structuring of water molecules around the nonpolar aromatic group of cefpiramide (i.e. hydrophobic hydration of aromatic rings group) contributes to lowering of the net δx1,3 to negative values. Furthermore, linear solvation energy relationships concept was used to describe the variation in the solubility based on the solvent effect.