V. P. Korolev

Temperature and length scale dependence of tetraalkylammonium ion-amide interaction.

We have studied the temperature and length scale dependence of the energetics of the pair interaction of well-established hydrophobic solutes tetraalkylammonium bromides with hydrophilic formamide (FA) and hydrophobic hexamethylphosphoric triamide (HMPT). Our results do indicate the anomalous length scale dependence of the tetraalkylammonium cation-amide interaction in water. As the cation size is increased, the unfavorable enthalpy of interaction is increased rather linearly until the maximum is reached, after which there appears to be a reversal of the trend. We believe that this phenomenon arises from the impossibility of water to maintain its H-bond network near large tetraalkylammonium cations that leads to the formation of a somewhat disordered solute hydration shell. The energetic cost for overlapping this shell with the amide hydration shell in water is noticeably smaller than that for tetraalkylammonium cations of a moderated size.

Enthalpies of 1,4-Dioxane, 1,2-Dimethoxyethane, and Ethylacetate Solvation in the Water–1-Propanol and Water–Glycerol Binary Mixtures

The enthalpies of 1,4-dioxane, 1,2-dimethoxyethane, and ethylacetate solution in binarymixtures of water with 1-propanol and glycerol were measured at 25°C using a precise isoperibol calorimeter. The enthalpies of the solute solvation were calculated and compared with the experimental data for other solutes. The results obtained were interpreted in terms of universal and specific solute solvation using parameters of a solvent polarity. It was found that the extreme shape of the curve ΔsolvH° vs. X for ethylacetate in the mixtures of water with 1-propanol results from peculiarities of carbotylate-group solvation and appears to be not connected with the influence of alcohol microaggregates in the mixed solvent.

Thermochemistry of Benzene Solution in Alcohols, Aprotic Solvents, and Mixtures of Aprotic Solvents with Methanol

The standard enthalpies of solution of benzene at 25°C in alcohols (methanol, 1-propanol, 1-pentanol, 1-decanol), aprotic solvents (1,4-dioxane, acetone, acetonitrile, dimethyl sulfoxide, dimethylformamide, propylene carbonate), and mixtures of methanol with these aprotic solvents were determined. Multiple regression analysis revealed the role of specific and nonspecific interactions in solvation of benzene in these solvents.

Enthalpies of mixing and state of components in aqueous-organic mixtures with nets of hydrogen bonds

The enthalpies of mixing of water with glycerol over the entire composition range were determined at 298.15 K. The partial excess enthalpies of the components of mixtures of water with glycerol, ethylene glycol, 1,2- and 1,3-propylene glycol, and formamide were estimated and used for examining solvation and the state of water and the organic components in the solutions. The composition of the solvation shells of the components of the mixtures were shown to depend on the nature and structure of the organic solvent.

Hydration numbers of Na+ and Cl− ions in an aqueous urea solution

The relations for the calculation of the partial molar volumes of NaCl, NaBPh4, and Ph4AsCl in an aqueous urea solution are obtained. The salt characteristics are divided into ionic components. Different methods of the division are discussed. It is shown that the hydration numbers of Na+ and Cl− ions decrease with increasing urea concentration; therewith, the dehydration of Cl− ion occurs relatively faster.

Thermodynamics of aqueous L-proline solutions at 273–323 K

Enthalpies of dissolution of L-proline in water were measured calorimetrically at 283–313 K. The experimental temperature of dissolution of proline in water at the studied temperatures was shown to be almost independent of its concentration over the range 0.01–0.11 mol/kg. Standard enthalpies of dissolution and standard heat capacities of dissolution were calculated over this temperature range. The heat capacity of dissolution was ascertained to increase in the row glycine, proline, and alanine. The partial molar heat capacity of proline in water was determined and compared with the values obtained by extrapolation of the apparent heat capacities. The changes in entropy and reduced enthalpy and the Gibbs energy over the temperature range from 273 to 323 K were determined using familiar thermodynamic relations. The data for glycine and alanine were compared.

The thermodynamic characteristics of solution of L-α-histidine and L-α-phenylalanine in water at 273–373 K

The solubility of L-phenylalanine and L-histidine in water at 298.15 and 318.15 K and the heat effects of solution of the amino acids at 328.15 K were determined. These results and the data obtained earlier were used to calculate all the standard thermodynamic functions of solution of the amino acids and the solubilities of L-phenylalanine and L-histidine over the temperature range 273–373 K. The selection of the form of the ΔsolHo = f(T) dependence had a negligible effect on the free energies of solution and solubilities of the amino acids. This selection primarily influenced the entropy and heat capacity characteristics of the process.

Hydration numbers of glycine in an aqueous urea solution

An analysis of the literature data on the partial molar volume of glycine in an aqueous urea solution at 298 K is performed. The mentioned value linearly increases with the increase in the urea concentration (wt.%). The hydration number of glycine decreases by a factor of 2 when passing from water to the saturated (20m) urea solution.

Thermochemistry of Aniline Solution in Binary Mixtures Water-Aprotic Solvent

Enthalpies of aniline solution in mixed solvents water-1,4-dioxane, water-acetone, and waterdimethyl sulfoxide at 25°C were determined within entire ranges of their compositions. The enthalpies of its solvation and transfer from water into mixed solvents, and also contributions of hydrocarbon radicals and functional groups to these quantities were calculated. Effects of composition and properties of the mixtures on the aniline thermochemical characteristics in solutions were considered.

Dehydration of glycine in mixed solvents

The analysis of changes in the partial volume of glycine