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High level theoretical calculations were employed to study the structural and conformational equilibrium of the Oxacalix[4]arenes. We have proposed that the replacement of methylene bridges with the oxygen atoms stabilizes 1,3-Alternate conformer predominantly. Furthermore, assessment of conformational equilibrium was explored in gaseous as well as solvation phases. The role of dispersion forces, possibility of complexation, distribution of electrostatic-potential, population analysis, substitution effects that are crucial for the analyte recognition were also discussed. [ABSTRACT FROM AUTHOR]

The thermodynamic extended real associated solution (ERAS) model is reviewed and modified to accommodate weakly associating components. ERAS is a theoretical scheme applied to binary liquid mixtures whereby certain physically meaningful parameters such as the association equilibrium constants, species reduced volume and energy terms may be determined by optimization against the experimental excess molar volumes and enthalpies. The implicit assumption used for any non-associating molecule B is to routinely set the hydrogen-bonding energy Δ h B * , reaction volume Δ v B * and association constants K B to zero. It is proven here that such assignments lead to singularities in the ERAS parameters that are featured in the excess state functions used. A series of optimizations using the results of conductor-like screening model for real solvents (COSMO-RS) on the excess enthalpy H E of dimethoxymethane in binary mixtures with a series of alcohols are determined, and the parameters Δ h B * , Δ h AB * (mixed enthalpy of reaction) and X AB (interaction parameter) are determined. It is shown that the stipulated range of X AB values from ERAS theory requires minor modification if the above assumptions are not made. The magnitude of the computed variables are shown to be physically reasonable. The Bondi group averaged estimates for s i , the ratio of the van der Waals (vdW) surface area to the vdW volume for molecule i , are contrasted against the more specific and reliable derivations from quantum calculations when calculating the excess functions. The degree of correlation is improved using the latter s i values. We conclude that the results of the optimizations indicate that the ERAS model can be extended even to weakly self-associating components previously considered impossible in especially engineering thermodynamical applications, with the above modifications and refinements. [ABSTRACT FROM AUTHOR]

Anomeric proportions of d -glucopyranose, defined as the ratio of the amount of substance of α- d -glucopyranose to the sum of that of α- and β- d -glucopyranoses, in aqueous solution were determined from 1 H NMR spectra in the concentration range between 0.1 wt% and 10 wt% at 25.0 °C. First of all, experimental conditions were investigated in terms of a time required to equilibrate anomerization and an irradiation power and a target frequency of the presaturation pulse in 1 H NMR measurement. Using the optimal condition determined by us, we were able to obtain spectra whose resonant peaks of anomeric protons of d -glucopyranoses were symmetric and baseline were non-distorted. These spectra allowed us to determine the anomeric proportions within experimental error of 0.005. Anomeric proportions of α-glucopyranose in the concentration range from 0.1 wt% to 10 wt% were determined from peak areas corresponding to anomeric hydrogens of α- and β- d -glucopyranose in 1 H NMR spectra. The anomeric proportion increased with increasing glucose concentration, though the degree of its increment was not uniform. The steep increase of the proportion was observed in the range between 0.1 wt% and 1 wt% and the increase was gentle between 1 wt% and 6 wt%. The proportion at infinite dilution determined by the least square method using a quadratic curve for the proportions was 0.3598 with a standard error of ± 0.0003, which lead that the Gibbs energy of anomerization of − 1.43 kJ mol − 1 . The concentration dependence of the ratio of the activity coefficient for α-glucopyranose to that for β-glucopyranose was estimated from the anomeric proportions and equilibrium constant of the anomerization. The ratio increased with increasing concentration, which shows that the activity coefficient for β-glucopyranose was slightly greater than those for α-glucopyranose at this concentration range. [ABSTRACT FROM AUTHOR]

The paper presents some data on physico-chemical study of the fullerenol-70 water solutions. The data on temperature dependence of solubility in water, concentration dependence of density, concentration dependence of the hydrogen ion concentration, specific conductivity, molar conductivity, dissociation constant, and dynamic light scattering are presented and characterized; composition of equilibrium solid phase in the fullerenol-70 + water binary system is determined. [ABSTRACT FROM AUTHOR]

Abstract: We present a molecular thermodynamic approach to model the chemical equilibria of biodiesel compounds, i.e., long-chain fatty acid monohydric alcohol esters. Molecules in the reactive system are modeled as chains of spherical segments; van der Waals forces between segments are described by monomer–monomer square-well potentials (SW) whereas associating behavior is introduced via short-ranged attractive anisotropic SW sites. The theoretical framework is based on a non-stoichiometric treatment of the reactive system that uses the minimization of the Helmholtz free energy and a mass balance equation as a restriction. The thermodynamics of the fluid system is obtained from the Statistical Associating Fluid Theory for chain molecules with attractive potentials of variable range (SAFT-VR; A. Gil-Villegas, A. Galindo, P. J. Whitehead, S.J. Mills, G. Jackson, A. N. Burgess, J. Chem. Phys. 106 (1997) 4168–4186). In order to test the accuracy of the theoretical predictions, experimental results were obtained for the esterification of lauric acid with methanol to produce methyl laurate. [Copyright &y& Elsevier]

Abstract: Extraction constants (K ex±) for complex ions (ML z+) of L=15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6), benzo-18C6, dibenzo-18C6, or dibenzo-24-crown-8 ether (DB24C8) with A− =picrate ion (Pic−) into nitrobenzene (NB) were evaluated at z =1 and 2. Here, the following thermodynamic relation was used for their evaluation: K ex± =[ML z+]NB([A−]NB) z /([M z+][L]NB[A−] z )= K D,M(K D,A) z β 1 NB; K D, j and β 1 NB denote an individual distribution constant of species j (=M z+, A−) into the NB phases and a stability constant for ML z+ in the phases. Using these results and the number of water (w) molecules co-extracted with M+, L, and ML+ into the NB phases, an effect of the w molecules released with the ML+ formation in the NB phases on K ex± was discussed. The above results were also applied for the prediction of an actual separation of Ba2+ from Sr2+ or Ca2+, using DB24C8 or 18C6 as L, Pic− as A−, and NB as diluent. Then, it was predicted that DB24C8 is more effective as L for the separation of Ba2+ from Ca2+ than 18C6. No effective L for the separation of Cs+ from Na+ was found out, using A− =I− and NB as the diluent. [Copyright &y& Elsevier]

Abstract: Polyamidoamine dendrimer (PAMAM-NH2 G4) complex with 5-fluorouracil, an oncological drug, was investigated by the technique of equilibrium dialysis at temperatures of 20°C and 45°C. The results obtained were worked out by means of the modified model of two sets of active sites proposed by Bobrovnik. Based on the analysis of the results obtained, it was calculated that at a temperature of 20°C the dendrimer molecule can bind about 12 molecules of the ligand with equilibrium constant K 1 ≅5600 and about 37 molecules with equilibrium constant K 2 ≅150. At a temperature of 45°C the number of the dendrimer binding sites is similar but the equilibrium constants of binding 5-fluorouracil with both sets of active sites are clearly lower (K 1 ≅1820, K 2 ≅70). The saturation of both the sets of active sites is of an exothermic character. [Copyright &y& Elsevier]