STEREOCHEMICAL ASPECTS OF HYDRATION OF CARBOHYDRATES IN AQUEOUS-SOLUTIONS .3. DENSITY AND ULTRASOUND MEASUREMENTS

Density and ultrasound measurements have been performed in aqueous solutions of pentoses, hexoses, methylpyranosides, and disaccharides as a function of molality of carbohydrate (0-0.3 mol kg-1). Partial molar volumes, partial molar isentropic compressibilities, and hydration numbers have been calculated. The data reveal that the compatibility of a carbohydrate into the three-dimensional hydrogen-bonded structure of water is governed by the stereochemistry of the carbohydrate. The carbohydrates can be divided into three groups with different fit into water, dependent on the relative position of OH(4) in conjunction with OH(2). This is discussed in terms of the fit of the O2-O4 distances of the carbohydrate molecule with the O-O distances of water. The smaller hydration numbers are found for the carbohydrates which fit the water structure best. The results agree with previously obtained kinetic data.