Enthalpies and heat capacities of transfer of some sugars from water to aqueous urea solutions

Abstract

Integral enthalpies of solution at 298.15 and 308.15 K for glucose, sucrose, cellobiose and maltose monohydrate were measured in 2,4 and 6 mol kg-1 aqueous urea solutions using an isoperibol calorimeter. These data were used to determine enthalpies and heat capacities of transfer from water to aqueous urea solutions. The observed exothermic enthalpies of transfer and positive heat capacities of transfer are explained in terms of hydrogen-bonding interactions between the sugars and urea molecules. An attempt is made to explain the differences in enthalpies of transfer of the sugars in terms of the compatibility of the disaccharide aqueous conformation with the tetrahedral structural order existing in water.