INFORMATIVE THERMODYNAMIC PROPERTIES OF THE EFFECT OF STEREOCHEMISTRY ON CARBOHYDRATE HYDRATION

Partial molar heat capacities of aqueous solutions of pentoses, hexoses, methyl aldoglycopyranosides, and some disaccharides as well as partial molar expansibilities and isothermal compressibilities of methyl aldoglycopyranosides in aqueous solution are reported. A comparison is made with partial molar volumes and partial molar isentropic compressibilities. It is shown that stereochemical aspects of carbohydrate hydration are revealed properly only by properties such as partial molar isentropic and isothermal compressibilities and partial molar expansibilities for which the intrinsic value is negligible. In addition, the success of the measurements depends on the accuracy of the technique. Thermodynamic properties such as partial molar volumes and partial molar heat capacities have a considerable intrinsic contribution that obscures the effect of stereochemistry on the hydration layer. They are valuable thermodynamic properties for a comparison of carbohydrate hydration with the hydration of other solutes. However, they cannot be applied to obtain information on the dependence of hydration on the stereochemistry of a carbohydrate. It appears that the analysis of stereochemical aspects of carbohydrate hydration hinges heavily on an appropriate choice of the thermodynamic property used to characterize the interaction between the carbohydrate and water.