G. A. Al’per

The viscosity and density of the methanol + n-nonane, ethanol + n-nonane, and ethanol + n-decane systems

This work presents the results obtained in measurements of the kinematic viscosity and density of the methanol-n-nonane, ethanol-n-nonane, and ethanol-n-decane systems at various temperatures and low n-alkane concentrations (within the concentration range of miscibility). The dynamic viscosities of these systems at 298.15 K were calculated according to free volume theory. The results substantiated the existence of an anomaly in the behavior of viscosity of the methanol-n-nonane system (positive Δlnη values) and its absence for the ethanol-n-alkane systems.

The interaction of caffeine with substituted cyclodextrins in water

The interaction of caffeine with hydroxypropyl-and methylcyclodextrins in water was studied by the calorimetry, spectroscopy, and solubility methods at 298.15 K. The interaction of caffeine with these cyclodextrins did not result in the formation of stable inclusion complexes and was mostly accompanied by predominantly endothermic effects of particle dehydration. The introduction of substituents and changes in the size of cyclodextrin molecular cavity did not influence the ability of cyclodextrins to form complexes with caffeine. The conclusion was drawn that substituted cyclodextrins could not be used for increasing the solubility of caffeine in water.

Solubility of porphyrin macrocycles in mixed solvents

A method based on the statements of molecular association theory and a simple lattice model (ASL = Associated Solution + Lattice) is used to calculate the solubility of a series of porphyrin macrocycles (blood porphyrins) in binary solvents (tetrachloromethane-ethyl acetate, tetrachloromethane-methanol). Separate contributions to solubility are identified and the relative role of different factors determining the solubility dependence on the mixed solvent composition is analyzed. The calculated solubility values are in good agreement with the experimental data obtained for the studied systems by the isothermal saturation method with a spectrophotometric control of concentrations.

The influence of intermolecular interactions in n-pentane-alkane-1-ol systems on their physicochemical properties

The Helmholtz energy of dipole-dipole interaction (ΣΔdF) and its long-range (ΔdF°) and short-range (ΔdF*) components were calculated for n-pentane-alkane-1-ol (from methanol to dodecane-1-ol) systems at 298.15 K using the Winkelmann statistical model theory of liquid dielectrics. It was shown that the longer the alkane-1-ol hydrocarbon radical, the greater the extent to which the properties of the systems with n-pentane were determined by the structure of n-alkane.

The volume characteristics of solution of naphthalene in heptane-ethanol mixtures at 298.15 K

The solubility of naphthalene was studied by the isothermal saturation method, and the density of naphthalene-heptane-ethanol solutions at 298.15 K was measured using an oscillating tube densimeter. The results were used to calculate the volume characteristics of naphthalene in the systems specified. The solubility of naphthalene in heptane was substantially higher than in ethanol. The composition dependences of apparent partial molar volumes contained extrema. The reason for such nonlinear dependences can be a sharp change in the contribution to the entropy of mixing related to the packing of molecules of different diameters (naphthalene and heptane). Another possible mechanism of these anomalies can be related to the stabilization of the structure of alkanols in the solvation sheath of alkanes noticed earlier.

Calculations of the Solubility of Gases in Mixed Nonaqueous Solvents within the Framework of the Theory of Molecular Association

A method for calculating the solubility of gases in mixed nonaqueous solvents was suggested. The method was based on the theory of molecular association and the simple lattice model. It allowed the solubility of gases in mixed nonaqueous solvents to be calculated only using molecular association parameters and the mutual exchange energy ωAB determined from the data on phase equilibria in mixed solvents.

The viscosity of the methanol-n-decane system in the region of low n-decane concentrations

The kinematic viscosity and density of the methanol-n-decane system were measured at various temperatures at low n-decane concentrations (over the miscibility range). The theory of free volume with taking into account molecular association was used to calculate the dynamic viscosity of this system at 298.15 K. The results substantiated the presence of an anomaly in this system (positive Δlnη values).

Complexation of cyclodextrins with nicotinamide and N-(hydroxymethyl)nicotinamide in aqueous solution

Complex formation of α- and β-cyclodextrins with biologically active nicotinamide and Nhydroxymethylnicotinamide (nicodine) was studied by calorimetry and 1H NMR spectroscopy. Cyclodextrins showed a weak complexing ability toward nicotinamide and nicodine: 1: 1 enthalpy-stabilized host-guest complexes were formed in aqueous solution at 298.15 K. Nicotinamide and nicodine molecules appeared inside the macrocycle cavity of cyclodextrins, but interaction between their polar side-chain groups with the outer surface of cyclodextrins cannot be ruled out. Thermodynamic parameters of the complexation process were calculated, and a mechanism was proposed for the observed interaction. The results were compared with those obtained previously for the complexation of cyclodextrins with nicotinic acid.

Calculations of the enthalpy of solution of nonelectrolytes in mixed solvents within the framework of molecular association theory

The enthalpies of solution of nonelectrolytes in mixed solvents were calculated using the Associated Solution + Lattice thermodynamic model, whose parameters are equilibrium constants, the enthalpies of formation of associates, and the energy of mutual exchange of mixed solvent components. The method of calculations used provided close agreement between calculation results and experimental data on nonassociated solutions and systems with a complex molecular association character.

The special features of H-bonding in supercritical water close to the saturation curve

A complex study of H-bonding in supercritical water in the region close to the saturation curve was performed at constant pressures of 30 and 50 MPa and a constant temperature of 673 K. The topological H-bond characteristics were calculated by the molecular dynamics method with the use of the TIP4P-HB potential. The calculations included the number of H-bonds per water molecule, the degree of H-bonding, and the distributions of molecules according to the number of H-bonds (fractions and the gradients of fractions of molecules with n H-bonds). Changes in these characteristics as the temperature, density, and pressure varied were studied.