Volume-related solvation and pair interaction parameters for dilute solutions of urea and tetramethylurea in ethylene glycol between 288.15 K and 328.15 K: A comparative analysis

Solutions of Urea and Tetramethylurea in Formamide and Water: A Comparative Analysis of Volume Characteristics and Solute–Solute Interaction Parameters at Temperatures from 288.15 to 328.15 K and Ambient Pressure

“…The same error in measuring ρ s ( m ) could be brought in by trace impurities in the samples of solution components. Additionally, to check the device operability, the densities of U aqueous solutions (up to m = 0.5 mol kg –1 ) were compared with the reliable literature ρ s ( m ) values (approximated by the least-squares method at T = 298.15 K). ,− ,,,− The discovered differences between densities under comparison did not exceed 0.01 kg m –3 (as was in our previous cases). , …”

“…The temperature of the measuring cell was kept constant to 0.01 K. All densimetric experiments were carried out at the ambient pressure to be p = 99.6 ± 0.8 kPa. The apparatus design together with the experimental and calibration procedures has been detailed elsewhere. ,,− Here, we just want to highlight that the quality of water applied in the experiments was systematically checked by way of comparing its density with the “ultrapure water” density standard (from Anton Paar). During the experiments, fivefold measurements of ρ s ( m ) were reproducible to within 0.01 kg m –3 .…”

“…Due to the uniqueness of water structure, the above-specified peculiarities of molecular interactions in hydration process are studied most fully by now. In turn, there are only several such investigations for nonaqueous media possessing a similar hydrogen-bonding network. − ,− …”

“…Recently, using precision densimetry, we have studied the volume-related pairwise interaction and solvation characteristics for tetramethylurea (TMU) and urea (U) as solutes in ethylene glycol (EG). The latter, being the simplest diol, is one of the organic solvents where a spatial network of hydrogen bonds is tended to the “waterlike” structure transformations around a predominantly hydrophobic solute (such as TMU), a phenomenon defined as the solvophobic solvation. ,,− As it was concluded in ref increasing structure compactness in the “solvation complex” of both TMU and hydrophilic U on going from EG to water can be serving as a corroboration of the fact that the intermolecular hydrogen bonding in aqueous solutions is more stable. ,, At the same time, the structure-making effect in aqueous TMU, being in terms of the solvophobic solvation and pairwise solvophobic interaction, is much more pronounced than it does in the (EG + TMU) system while the structure-breaking effects in the compared solutions of U are differed not as significant. These inferences are in agreement with the results drawn from the calorimetry study performed previously by one of us (A.V.…”

“…Along with the fact that FA is one of the key solvents in organic chemistry, this amide, like the ureas considered (U and TMU), is the convenient model system for investigation of peptide and protein interactions in biological systems. − , These interactions are often associated with the competition between the influences of hydrophilic and hydrophobic moieties of a system component, ,,, which is manifested in the structure-packing effects, too. , For this reason, temperature-dependent volumetric properties of TMU and U solutions in FA have a remarkable interest. On studying such properties, it would be important to compare volume-related solvation effects as well as solute–solute interaction characteristics in {FA + TMU­(U)} to those in the similar aqueous solutions, being derived under the same experimental conditions.…”