Enthalpies and heat capacities of dissolution, apparent molar heat capacities, and apparent molar volumes of some mono-, di-, tri-, and tetra-saccharides in water

Abstract

Molar enthalpies of solution at very low molalities of some mono-, di, tri, and tetra-saccharides in water have been measured at 298.15 and 308.15 K using an isoperibol calorimeter. The molar heat-capacity changes Δ_solC_p, m ^∞on dissolution at 303.15 K were derived from molar enthalpies of solution. A Picker flow microcalorimeter and an Anton Paar digital density meter were used to measure apparent molar heat capacities C_{p, 2, φ} and apparent molar volumes V_{2, φ} of solute at 298.15 K. The various compounds studied show large positive values of Δ_solC_{p, m}^∞ and C_{p, 2}^∞. The experimental C_{p, 2}^∞ values are found to be much higher than values estimated using additivity relations and heat capacities for the constituent groups derived from the heat capacities of monofunctional compounds. Results further indicate that the difference in C_{p, 2}^∞(expt) and C_{p, 2}^∞(est.) per hydroxyl group increases with an increase in the number of hydroxyl groups in a molecule. An attempt has been made to explain the C_{p, 2}^infinity values of stereoisomers in terms of the compatibility of the aqueous-solution conformation of the compound and the tetrahedral order in water.