Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The equilibrium solubility of 6-chloroguanine in four co-solvent mixtures of dimethyl sulfoxide (DMSO) (1) + water (2), N,N-dimethylformamide (DMF) + water (2), isopropanol (1) + water (2) and 1,4-dioxane (1) + water (2) over the temperature range from (278.15 to 333.15) K were reported. At the same temperature and composition of DMSO, DMF, isopropanol or 1,4-dioxane, the mole fraction solubility of 6-chloroguanine was highest in DMSO (1) + water (2) mixtures, and lowest in 1,4-dioxane (1) + water (2) mixtures. By using the Jouyban-Acree, van't Hoff-Jouyban-Acree and Apelblat-Jouyban-Acree models, 6-chloroguanine solubility was well correlated obtaining RAD lower than 5.83% and RMSD lower than 4.82 * 10-4. Quantitative values for the local mole fraction of DMSO (DMF, isopropanol or 1,4-dioxane) and water around the 6-chloroguanine were computed by using the Inverse Kirkwood-Buff integrals method applied to the determined solubility data. For the DMF (1) + water (2) mixture with composition 0.20 less than x1 less than 0.69, DMSO (1) + water (2) mixture with composition 0.20 less than x1 less than 1 and 1,4-dioxane (1) + water (2) mixture with composition 0.18 less than x1 less than 0.35, 6-chloroguanine is preferentially solvated by the co-solvent. For the isopropanol (1) + water (2) mixture with composition 0.25 less than x1 less than 0.70, 6-chloroguanine is preferentially solvated neither by isopropanol nor by water. However, in the other regions for the four co-solvent mixtures, 6-chloroguanine is preferentially solvated by water. The dissolution process of 6-chloroguanine in solvent solutions was endothermic. Furthermore, transfer Gibbs energy (deltatrG.deg.), enthalpy (deltatrH.deg.), and entropy (deltatrS.deg.) were calculated, demonstrating that the solubilization capacity was more favorable with the increase in the co-solvent concentration.