Preferential solvation of dehydroepiandrosterone acetate in (co-solvent plus ethyl acetate) mixtures according to the inverse Kirkwood-Buff integrals method

The preferential solvation parameters (delta x(1,3))of dehydroepiandrosterone acetate (DHEA acetate) in three co-solvent mixtures of methanol (1) + ethyl acetate (2), ethanol (1) + ethyl acetate (2), and isopropanol (1) + ethyl acetate (2) were derived from their available solubility data by means of the inverse Kirkwood-Buff integrals method. The values of delta x(1,3) vary non-linearly with the co-solvent (1) proportion in all the co-solvent mixtures. For the studied systems, the values of delta x(1,3) are negative in alcohol-rich mixtures, but positive in ethyl acetate-rich mixtures. The preferential solvation magnitude of DHEA acetate by the ethyl acetate is highest in {methanol (1) + ethyl acetate (2)} mixtures at 293.15 K and 303.15 K. While at 313.15 K, it is highest in {isopropanol (1) + ethyl acetate (2)} mixtures. The delta x(1,3) values are positive indicating that DHEA acetate is preferentially solvated by ethyl acetate. The co-solvent action may be related to the disordered structure of ethyl acetate molecules around the non-polar moieties of DHEA acetate which increases the solvation having maximum values near to x(1)= 0.25-0.35 for the three co-solvent mixtures. (C) 2017 Elsevier Ltd.