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Vladivostoku, Russia

Accurate calculation of solvation free energies (SFEs) is a fundamental problem of theoretical chemistry. In this work we perform a careful validation of the theory of solutions in energy representation (ER method) developed by Matubayasi et al. [J. Chem. Phys. 2000, 113, 6070-6081] for SFE calculations in supercritical solvents. This method can be seen as a bridge between the molecular simulations and the classical (not quantum) density functional theory (DFT) formulated in energy representation. We performed extensive calculations of SFEs of organic molecules of different chemical natures in pure supercritical CO2 (sc-CO2) and in sc-CO2 with addition of 6 mol % of ethanol, acetone, and n-hexane as cosolvents. We show that the ER method reproduces SFE data calculated by a method free of theoretical approximations (the Bennett's acceptance ratio) with the mean absolute error of only 0.05 kcal/mol. However, the ER method requires by an order less computational resources. Also, we show that the quality of ER calculations should be carefully monitored since the lack of sampling can result into a considerable bias in predictions. The present calculations reproduce the trends in the cosolvent-induced solubility enhancement factors observed in experimental data. Thus, we think that molecular simulations coupled with the ER method can be used for quick calculations of the effect of variation of temperature, pressure, and cosolvent concentration on SFE and hence solubility of bioactive compounds in supercritical fluids. This should dramatically reduce the burden of experimental work on optimizing solvency of supercritical solvents. © 2015 American Chemical Society. Source

In order to answer the question: is a solute water "negatively expansible" in tetrahydrofuran or not (?), a comparative analysis of own and literature data on the temperature-dependent partial volumes at the infinite dilution of water isotopologues in tetrahydrofuran have been carried out. Used for computing the limiting partial (apparent) volumes of water isotopologues, densities of H2O and D2O solutions in the solvent studied, with the solute mole fractions ranging up to ∼0.043, were measured with an error of 1.5 · 10-5 cm3 · mol-1 at (278.15, 288.15, 298.15, 308.15, and 318.15) K and atmospheric pressure using a vibrating tube densimeter. It has been shown that the partial molar volume of H2O or D2O at infinite dilution increases with rising temperature; that is, the isotopically distinguishable solutions of water in tetrahydrofuran do not have the unusual structure-packing behavior being characteristic of the water-containing system with the so-called phenomenon of "negative partial molar expansibility". © 2010 Elsevier Ltd. All rights reserved. Source

Densities of solutions of H 2O in C 2H 5OH and D 2O in C 2H 5OD, with a water mole fraction ranging up to 0.037, were measured with an error of 1.0 · 10 -5 g · cm -3 at T = (278.15, 288.15, 298.15, 308.15, and 318.15) K and at atmospheric pressure using a precise sealed vibrating tube densimeter. Apparent molar volumes and isobaric expansibilities down to infinite dilution of a solute were calculated. The temperature-dependent behaviour of solute H/D isotope effects on the volumetric quantities studied was analysed taking account of structure-related peculiarities of the solvating media in question. © 2011 Elsevier Ltd. All rights reserved. Source

Afanas'ev V.N.,RAS Institute of Chemistry
Journal of Physical Chemistry B

A new theory of electrolyte and nonelectrolyte solutions has been developed which, unlike the Debye-Hückel method applicable for small concentrations only, makes it possible to estimate thermodynamic properties of a solution in a wide range of state parameters. One of the main novelties of the proposed theory is that it takes into account the dependence of solvation numbers upon the concentration of solution, and all changes occurring in the solution are connected with solvation of the stoichiometric mixture of electrolyte ions or molecules. The present paper proposes a rigorous thermodynamic analysis of hydration parameters of solutions. Ultrasound and densimetric measurements in combination with data on isobaric heat capacity have been used to study aqueous solutions of electrolytes NaNO3, KI, NaCl, KCl, MgCl2, and MgSO4 and of nonelectrolytes urea, urotropine, and acetonitrile. Structural characteristics of hydration complexes have been analyzed: hydration numbers h, the proper volume of the stoichiometric mixture of ions without hydration shells V2h, compressibility β1h, and the molar volume of water in hydration shells V1h, their dependencies on concentration and temperature. It has been shown that for aqueous solutions the electric field of ions and molecules of nonelectrolytes has a greater influence on the temperature dependence of the molar volume of solution in hydration shells than a simple change of pressure. The cause of this effect may be due to the change in the dielectric permeability of water in the immediate vicinity of hydrated ions or molecules. The most studied compounds (NaCl, KCl, KI, MgCl 2) have been studied in a wider range of solute concentrations of up to 4-5 mol/kg. Up to the complete solvation limit (CSL), the functions V 1h = f(T) and β1h = f(T) are linear with a high correlation factor, and the dependence YK, S = f(β 1V1*) at all investigated concentrations of electrolytes and nonelectrolytes up to the CSL enables h and βhVh to be determined on the basis of relationships obtained in the study. The behavior of nonelectrolyte solutions is no different from that of electrolyte solutions, although it is possible to trace the difference between hydrophobic and hydrophilic interactions. © 2011 American Chemical Society. Source

Rulev A.Yu.,RAS Institute of Chemistry
RSC Advances

The review discusses recent achievements in the development of more environmentally friendly and economically competitive processes for the synthesis of biologically and synthetically important phosphorus-bearing compounds by conjugate addition of hydrogen-phosphonates to different Michael acceptors. © the Partner Organisations 2014. Source

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