Free Energy Changes by Mixing of the D-Glucose?Calcium Chloride?Water and the D-Glucose?Guanidinium Bromide?Water Systems

Abstract

Free energy changes by mixing aqueous solutions of D-glucose with aqueous solutions of calcium chloride or guanidinium bromide were measured at 25°C by the isopiestic comparison method. As shown in Figs.5 and 6, excess free energy changes of mixing (°G_m^ex) were positive for the D-glucose-calcium chloride-water systems. The signs of °G_m^ex of both solutes were positive at the total molality (M) of 1 mol·kg^-1 (Fig.5), but the sign of °G_m^ex of CaCl2 turned to be negative in the high mole fraction region of CaCl₂ at the total molality of 2 ·kg^-1 (Fig.6). These results were interpreted in terms of structural incompatibility of the hydration cospheres around these two kinds of the solutes and the ion-dipole intractions. As shown in Figs.8 and 9, °G_m^ex Gex for the D-glucose-guanidinium bromide-water system was in negative values, indicating mutual salting-in. This result is attributed to the structure breaking effect of the guanidinium ion.