Paweł Góralski

Interactions between cholesterol and triacylglycerols in carbon tetrachloride: calorimetric and spectroscopic studies

Abstract The equilibrium constant (Kf) and enthalpy (ΔfH) of hydrogen bond complex formation (1:1) between cholesterol and triacylglycerols have been determined by means of spectroscopic (IR) and calorimetric methods. The triacylglycerols used (triacetin, tributyrin, trilaurin, tripalmitin and triolein) form weak hydrogen bonds with cholesterol which are shown by the low values of Kf (from 2.4 to 3.3 M−1) and ΔfH (from −9.6 to −11.8 kJ mol−1). The basicity of triacylglycerols expressed by pKHB has a predominant effect on the enthalpy of complex formation with cholesterol.

Heat of solution of cholesterol and its interactions with different solvents: a calorimetric study

Abstract The values of the standard enthalpy of solution of cholesterol (Δ H s XXX ) in twelve solvents of various polarities and with different proton-acceptor and proton-donor properties were measured by calorimetry. The enthalpies of the cholesterol interaction and solvation in these media relative to cyclohexane were evaluated. Among the discussed factors affecting the solute-solvent interaction (dispersion, dipole and donor-acceptor interactions), the dispersion forces characterised by the Hildebrand solubility parameter was found to play a considerable role.

Interaction site enthalpies of the phenol–tetrahydrofuran hydrogen-bond complex in various solvents

Enthalpies of solution of several solutes in cyclohexane, benzene, toluene, p-xylene, carbon tetrachloride and 1,1,2,2-tetrachloroethane have been measured. They permitted a determination of the interaction site enthalpies of phenol (Ph) and tetrahydrofuran (THF) molecules with the solvents mentioned above. Spencers additive model of solute–solvent interaction was used. These interaction site enthalpies were used to calculate the enthalpies of PH–THF complex formation [ΔH(complex)] and transfer enthalpies [ΔHtr(complex)] of this complex from cyclohexane to other solvents used. A good agreement between the calculated and experimental values of ΔH(complex) and ΔHtr(complex) shows the correctness of the simple model of molecular interactions being used.

Hydrogen bonds between cholesterol and nitrogen bases : a thermodynamic study

Abstract Values of the equilibrium constant and of the enthalpy of hydrogen bond complex formation (Δ H f ) between cholesterol and some nitrogen bases (1-butylamine, di-1-butylamine, tri-1-butylamine, triethylamine, pyridine, acetonitrile, and benzonitrile) have been determined by calorimetry and IR spectroscopy. The enthalpies found for nitriles satisfy the linear correlation of Δ H f and Gutmanns donor number, determined previously for oxygen bases. Values of Δ H f for amines do not satisfy this relationship. The effect of steric hindrance in the amines on the thermodynamic data of the cholesterol—amine complex formation is discussed.

Volumetric manifestation of van der Waals interactions between cholesterol and organic solvents of linear structure

Abstract The densities of solution of cholesterol in several selected n-alkanes, alkan-1-ols and tertiary amines have been measured at 298.15 K. The values of standard partial molar volume of cholesterol have been calculated and the effect of solute–solvent and solvent–solvent interactions on the partial molar volume of cholesterol have been discussed. The increase in the alkyl chain length (Ri) of solvents such as alkanes and amines enhances the dispersion solvent–solvent interactions (per –CH2–) and weakens the contribution of dispersion forces in the cholesterol-solvent interactions. Both these effects bring about an increase in the partial molar volume of cholesterol with increasing the alkyl chain length of solvent molecules. In alcohols, the cholesterol–solvent dispersion interactions increase with Ri. This effect may be accounted for by the self-association of the solvent. In consequence, there is no distinct dependence of partial molar volume of cholesterol on the alkyl chain length of alcohol.

Thermodynamic studies on the hydrogen bonding of cholesterol with proton-acceptor solvents

Abstract The standard enthalpies of solution (ΔH?s of cholesterol and cholesteryl methyl ether in carbon tetrachloride and some basic solvents were measured by calorimetery. The obtained ΔH?s values were used for the determination of the enthalpy of the hydrogen-bond complex formation between cholesterol and proton acceptors using the Arnett “pure base” method. The enthalpy of hydrogen-bond complex formation ranges from −10.4 (diethylcarbonate) to −24.6 kJ mol−1 (hexamethylphosphortriamide), being a linear function of the solvent basicity.

Calorimetric investigations of association in ternary systems. Part 4.—The influence of solvation on enthalpy of complex formation in phenol-tetrahydrofuran and 2,6-dimethylphenol–tetrahydrofuran systems

The enthalpies of solution of tetrahydrofuran (THF), phenol (Ph) and 2,6-dimethylphenol (DMPh) have been determined in benzene, toluene, p-xylene and 1,1,2,2-tetrachloroethane. The equilibrium constants and enthalpies of hydrogen-bond complex formation (1:1) of Ph–THF and DMPh–THF have been determined calorimetrically in the abovementioned solvents. The solvent effect on the solution enthalpy of pure compounds and enthalpy of complex formation are discussed.

Calorimetric investigations on association in ternary systems. Part 3.—Hydrogen-bonded complexes in phenol–tetrahydrofuran systems in CCl4

The thermodynamic functions of hydrogen-bond complex formation for a number of phenols with tetrahydrofuran in carbon tetrachloride have been determined by a calorimetric method. The phenols studied included phenol, pentafluorophenol, pentachlorophenol, pentabromophenol and 2,6-dimethylphenol. The heats of solution in CCl4 were determined in the range of low concentrations only for the substituted phenols. The equilibrium constants and enthalpies of complex formation are compared with the corresponding data obtained by infrared spectroscopy. The effect of acidity, steric hindrance and ability to form intramolecular hydrogen bonds is discussed in terms of the ability of phenols to form intermolecular hydrogen-bond complexes.

Calorimetric investigations of association in ternary systems. Part 1.—Enthalpy of complex formation of benzoic acid with proton acceptors

The procedure for determining the enthalpy of donor–acceptor complex formation in systems in which one of the components is strongly dimerized is presented.The proposed method makes use of the values of equilibrium constants (K1) of dimerization and of complex formation (K2) obtained by spectroscopy as well as calorimetric measurements of the heat of solution. The values of complex formation enthalpy of benzoic acid with proton acceptors have been determined.

Calorimetric investigations on association in ternary systems. Part 2.—Thermodynamic functions of complex formation of pentahalogenobenzoic acids and 1,1-dinitroethane with proton acceptors

Enthalpies of complex formation (ΔH) by hydrogen bonding of pentachlorobenzoic (PClHBz) and pentafluorobenzoic (PFHBz) acids with a number of proton acceptors in CCl4 have been determined.A calorimetric method of determining equilibrium constants and enthalpies of formation of hydrogen-bonded complexes which are in equilibrium with proton transfer complexes is described. The K and ΔH values of complex formation of a C—H acid (1,1-dinitroethane) with a number of proton acceptors are determined. The results obtained both by the calorimetric method and by infrared spectroscopy are compared with those obtained by the use of the i.r. method only. The ΔH values of complex formation are discussed as a function of their acidity, dipole moments and the Gutmanns donor numbers of the investigated substances.