Temperature effect on the volume properties of a bisurea aqueous solutions

The densities of aqueous solutions of bisurea (2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione) were measured using a vibrating-tube densimeter at 288.15, 298.15, 308.15, and 318.15 K in the concentration range up to ∼3·10−3 moles of solute (1000 g of H2O)−1 with the error at most ±5· 10−6 g cm−3 (reproducibility up to 2·10−6 g cm−3). The limiting partial molar volume and expansibility of bisurea in water were calculated. The bicyclic molecules under study form in aqueous solution H-bonded hydrate complexes with rather high structure-packing density. These complexes are more subjected to the destroying effect of temperature than the corresponding urea complexes. The hydration of bisurea weakens with the temperature increase.