Molecular Complexes of Crown Ethers in Crystals and Solutions

A review of the experimental and theoretical studies of the crown ether complexes with polar molecules in their crystals, solutions, and in a gas phase is given. The type of the molecular bonds in the complexes, their stoichiometry, and the change in the macrocycle conformation during complex formation are considered, as well as the effect of the macrocycle structure and the nature of the medium on the efficiency of the molecular bonding. New data are given on the enthalpies of transfer of the crown ethers from tetrachloromethane into solvents capable of forming hydrogen bonds. The enthalpies of specific interactions of macrocycles with the molecules of the solvents in the medium of the same solvents are characterized. The conformations of the crown ethers in the media under study are discussed.     

Thermal dissociation of supramolecular complexes on the basis of 18-crown-6 and amino acids

The possibility of isolation of crystalline supramolecular complexes of 18-crown-6 with glycine, L-alanine, L-valine, L-leucine, L-phenylalanine, L-proline, L-hystidine, and L-threonine from aqueous solutions was studied. Comparative analysis of thermal decomposition of the complexes and their individual components and mechanical mixture was studied by means of thermogravimetry, differential thermal analysis, and differential scanning calorimetry. Crystaline complexes of 18-crown-6 with glycine, L-alanine, and L-hystidine were isolated and shown to be stable up to 140°C, which was additionally confirmed by IR spectroscopy.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 8, 2004, pp. 1313–1317.Original Russian Text Copyright © 2004 by Terekhova, Kulikov, Barannikov.This revised version was published online in April 2005 with a corrected cover date.     

Dissociation constants of protolytic dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solution at 298 K

Protolytic dissociation constants of stepwise dissociation of glutamyl-glutamic and glycyl-glutamic acids in aqueous solutions at 298.15 K at ionic strengths of 0.1, 0.5, and 1.0 M on the NaCl background were measured by potentiometric titration. The thermodynamic dissociation constants were calculated. Using the obtained and published data, we discuss the effect of additional carboxy groups in the side chains of the molecule on the protolytic dissociation constants of peptides.     

Thermal stability of porphyrins with chemicaly active NH bond and their associates with electron-donor solvents

The composition and stability of the crystalline H associates of NH active tetrapyrroles with electron-donor solvents were investigated by thermogravimetry. It was found that common porphyrins and their analogs can form 1: 1 and 1: 2 macrocycle solvent H associates whose energy of formation depends on their composition and ranges from 20 to 115 kJ/mol. Based on the results from an analysis of the Stokes shifts, we concluded that the formation of H associates in a solution is accompanied by variations in the degree of macrocycle nonplanarity. The stability of a series of tetrapyrroles with regard to thermal destruction in argon atmosphere and in the presence of atmospheric oxygen was shown to drastically vary.     

Supersymmetry and cohomology of graph complexes

Letters in Mathematical Physics - I describe a combinatorial construction of the cohomology classes in compactified moduli spaces of curves $$\widehat{Z}_{I}\in H^{*}\left( \bar{\mathcal...     

Noncommutative Batalin–Vilkovisky geometry and matrix integrals

I study the new type of supersymmetric matrix models associated with any solution to the quantum master equation of the noncommutative Batalin–Vilkovisky geometry. The asymptotic expansion of the matrix integrals gives homology classes in the Kontsevich compactification of the moduli spaces, which I associated with the solutions to the quantum master equation in my previous paper. I associate with the Bernstein–Leites matrix superalgebra equipped with an odd differentiation, whose square is nonzero, the family of cohomology classes of the compactification. This family is the generating function for the products of the tautological classes. The simplest example of my matrix integrals in the case of dimension zero is a supersymmetric extension of the Kontsevich model of 2-dimensional gravity.     

Melting of polyolefins in presence of liquids

The existence of a section with a constant melting point in the curve of melting polyolefins in presence of a liquid was confirmed experimentally by the method of differential scanning calorimetry.     

Thermodynamic functions of solvation of 1,4-dioxane in various solvents at 298.15 K

The standard changes in enthalpy during the solvation of 1,4-dioxane in methanol, ethyl acetate, DMF, and acetonitrile were determined from calorimetric data and compared with the literature data for a series of solvents with different polarities. The standard changes in the Gibbs energy during the solvation of 1,4-dioxane in a wide series of solvents were calculated from the activity coefficients reported in the literature. The variation of the solvation functions of low-polar 1,4-dioxane in the series of solvents was found to be consistent with the enthalpy-entropy compensation rule. The results for 1,4-dioxane were compared with those for its open-chain analog and related large cyclic molecules. The electrostatic interactions of the solute with the solvents did not markedly affect the thermodynamic characteristics of ether in media with different polarities, but affected the interaction of the solute with the solvent more significantly. The solvation of the small ring of 1,4-dioxane in aprotic solvents was accompanied by a more significant exothermal effect than in the case of its open-chain analog. The conclusion was drawn that the enthalpies of the formation of hydrogen bonds between 1,4-dioxane and the associated water and chloroform molecules in solution were smaller in magnitude than the bonds of the similar open-chain polyether.