Volume-related interaction parameters for dilute solutions of tetramethylurea in normal and heavy water between 278.15Â K and 318.15Â K

Density measurements were carried out on dilute solutions of tetramethylurea (TMU) in normal and heavy water in the aquamolality ranges 0.058-1.74 and 0.052-1.72, respectively, at 278.15 K, 288.15 K, 298.15 K, 308.15 K, and 318.15 K. The excess partial molar volumes of TMU (V¯E,∞) and volume second virial coefficient (vxx), calculated from the densities of the H/D isotopically distinguishable solutions, are negative, which indicate that the solute has a predominantly structure-making effect on aqueous surroundings. With decreasing temperature and on going from protiated solvent to deuterated one the values of V¯E,∞ and vxx become more negative, suggesting that the hydration sphere around a TMU molecule is more structured in the specified cases. The obtained results were discussed allowing for enthalpic and some other characteristics of TMU solutions in normal and heavy water.