Thermodynamics of H/D isotope effects of hydration of urea and structural features of its aqueous solutions at various temperatures: I. Volume properties of water-urea and heavy water-deuterated urea systems

At T > 300 K the effect of urea as an agent distorting the structure of wat er drastically weakens, and the ordering effects of the solvent structure i n the hydration shell become dominant; at T > 320 K associates of urea with water have equal rights with (are complementary to) the other components o f the system. Bonds in the crystal structure of urea are stronger than in u rea hydrate complexes.