Masanobu Janado

Effect of sugars on the solubility of hydrophobic solutes in water

It was found that the cosolvent effect of sugars on the solubilities of n-octanol, n-heptanol, and sodium dodecyl sulfate monomer in water depended on a set of factors that included molecular weight and concentration ofthe sugars, the kind of monosaccharides, the type of glycosidic linkages involved, and the temperature. All hexoses examined, D-glucose, D-galactose, and D-mannose, caused solubility depression of the hydrophobic solutes at low concentrations but to widely different extents. As the molecular weight of the sugar increased, the solubility depression was considerably lessened and further, as the concentration of the sugars increased, the solubility-increasing effect predominated leading to increased solubilities of the hydrophobic solutes relative of their solubility in pure water. The solubility-increasing effect was markedly enhanced at high temperatures. The free energy of the spontaneous transfer of octanol from water to the sugar solutions is entropic in nature and is attributed primarily to hydrophobic bond formation between the solute molecule and the hydrophobic surfaces of the sugar molecules.