Volume-related interaction parameters for dilute solutions of 1,3-dimethylpropyleneurea in normal and heavy water between 278.15 K and 318.15 K

Density measurements were carried out on dilute solutions of 1,3-dimethylpropyleneurea (DMPU) in normal (H2O) and heavy (D2O) water in the aquamolality range from 0.04 to 1.0 at 278.15, 288.15, 298.15, 308.15, 313.15 and 318.15 K. The excess partial molar volumes of DMPU (image) and volume second virial coefficients (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 H2O to D2O, values of image and vxx become more negative, suggesting that the hydration sphere around a DMPU molecule is more structured in the specified cases. Comparing the obtained results with earlier those for the analogues of DMPU such as acyclic 1,1,3,3-tetramethylurea (TMU) and cyclic 1,3-dimethylpropyleneurea (DMEU) corroborates the previously made conclusion that the DMPU molecule, being a stronger hydrated, has a more pronounced structure-making effect on water (H2O or D2O) than the TMU or DMEU molecule.