Urea Water Solutions Research Articles

Urea and urea–water solutions—an infrared study

Infrared studies of urea both in crystal and in water solution are presented. On the basis of temperature and concentration measurements of urea–water solutions, as well as from the spectra of crystalline urea films of hydrogenated and partially deuterated molecules, we have assigned the main bands in urea spectrum. It is shown that the series of spectra recorded at various concentrations in water can be decomposed into four basic spectra: the first one is the same as the spectrum of liquid water, the second one has features only due H 2O but is slightly disturbed as compared with the first one and the other two display in addition features due to vibrations in urea. The relative intensities of these components show a strong concentration dependence, particularly for what concerns the ratio of the last two components. We ascribe one of these two components to a structure where urea–urea interaction is predominant in the solution while the other one is ascribed to a structure where spectral features are mainly due to urea–water interactions. The first component with urea–urea features can be observed only at urea concentrations higher than 1 M. Concentration dependence of the population of these two components shows that at higher urea concentrations the interaction between urea molecules can be observed presumably as a consequence of aggregation of urea molecules. Such aggregation of urea molecules in dimers and/or oligomers may explain some peculiarities connected with the unusual behaviour of urea solutions in water as predicted by the Shellman, Kreschek, Scheraga and Stokes model. Concentration measurements also show that urea molecules only slightly alter the structure of bulk water, and hence cannot be described as ‘structure breakers’.

Modeling of transfer properties using revised HKF theory: thermodynamics of transfer of an amino acid and small peptides from water to urea–water solutions at 298.15 K

Relative densities, [Formula: see text] and heat capacity ratios, [Formula: see text] have been measured for aqueous solutions of glycine, glycylglycine, and glycylglycylglycine in aqueous urea solutions containing 1–13 mol kg−1 urea. These data have been used to calculate apparent molar volumes, [Formula: see text] and apparent molar heat capacities, [Formula: see text] which in turn have been used to obtain standard state volumes, [Formula: see text] and standard state heat capacities, [Formula: see text].Volumes and heat capacities of transfer from water to urea have been calculated from our reported standard state data. Heat capacities of transfer of the investigated systems have been modeled using a procedure developed from the semiempirical calculation procedures proposed by Helgeson, Kirkham, and Flowers. Keywords: amino acids, peptides, calorimetry, transfer thermodynamics, HKF theory.

Thermodynamics of bolaform electrolytes. V. Enthalpies and heat capacities in aqueous urea solutions

The partial molal heats of solution at infinite dilution of 1,4-bis(triethylammonium)butane dibromide and 1,10-bis(triethylammonium)decane dibromide in aqueous urea (up to 8m urea) have been determined calorimetrically in the temperature range 18–33°C. These data have been used to derive the partial molal heat capacities at infinite dilution, the enthalpies of transfer, and heat capacities of transfer at infinite dilution from water to urea-water solutions. The results show that the enthalpies of transfer are negative and decrease with increasing urea concentrations. The heat capacities of transfer are negative at low urea concentrations and increase in magnitude at higher urea concentrations. In the case of the smaller cation the partial molal heat capacity in 8m aqueous urea solution is greater than in pure water. The results are discussed in terms of structural changes in the solvents on dissolution.

Ionic mobilities of the potassium ion in urea-water solutions at 25�C

Determination of potassium ion conductances directly from measurements of boundary velocities and solution potential gradients are reported for water, urea-water, methanol, and urea-methanol solutions. The results are interpreted in terms of the structure-breaking role generally assigned to urea in aqueous solutions.

Dielectric Constants: Ethanol—Diethyl Ether and Urea—Water Solutions between 0 and 50°

Dielectric Constants: Ethanol—Diethyl Ether and Urea—Water Solutions between 0 and 50°