Polycondensation of low-active monomers in mesomorphic-like reaction mixtures and in presence of polymeric matrix

The study results of the synthesis of polyheterocycles based on dianhydrides, obtained by photochemical reaction of aromatic compounds with maleic anhydride, have been presented. In comparison with aromatic analogues the low reactivity of anhydride cycles is characteristic for tricyclodecenetetracarboxylic dianhydrides. This fact made unsuitable the traditional two-stage method to synthesize high-molecular polyheterocycles on the basis of these monomers. There has been estimated a possibility of chain growth of oligomeric polyamic acids (PAMA) in mesomorphic-like state of its solutions in mixed solvents. In this conditions the PAMA polymerization degree changed from 7 up to 60. These peculiarities have given the opportunity to synthesize polyheterocycles in mild conditions. The features of polycondensation of tricyclodecenetetracarboxylic dianhydrides with bis(4-aminophenyl) ether in the presence of poly-4-vinylpyridine, polyacrylic and polymethacrylic acids have been studied. There have been synthesized high-molecular-weight polyimides and polyamidoimides, possessing good physicomechanical and thermal properties.     

Polyacrylic Acid Modifies Local and Lateral Mobilities in Lipid Membranes

Polyacrylic acid (PAA) is a promising polymer for engineering lipid-based drug-delivery vesicles. Its unique properties allow lowering drug dose and delivery the drug close to the site of its release. To design a successful delivery scheme, however, it is important to understand on the molecular scale how the polymer interacts with lipids under various conditions in the human body. Some aspects of the PAA-lipid interaction can be revealed using physical methods, such as differential scanning microscopy, nuclear magnetic resonance spectroscopy, NMR-diffusometry, and infrared spectroscopy. This work discusses the use of these techniques as well as the peculiarities of preparing vesicular and microscopically aligned PAA-lipid systems.      

Phosphorylated amino derivatives of thiacalix[4]arene as membrane carriers: synthesis and host–guest molecular recognition of amino,hydroxy and dicarboxylic acids

Promising membrane transport and separation systems for selected dicarboxylic, α‐hydroxy‐ and α‐amino acids based on thiacalixarene platform have been developed. For the first time, p‐tert‐butyl thiacalix[4]arenes functionalized at the lower rim with aminophosphonate fragments have been obtained and characterized. As was established by UV–vis spectroscopy, membrane extraction and HPLC, the substitution of amino groups by α‐aminophosphonate units significantly enhances the selectivity of host molecules that bind to aspartic and glycolic acids. The aminophosphonate compounds synthesized can be used in the development of sensors and systems employed in the purification and separation of organic acids. Copyright © 2013 John Wiley & Sons, Ltd.     

Three-dimensional problems of wall-rock stability in the vicinity of a cleaned working with control exercised over the stress-strain state of the mass

S. P. Timoshenko Institute of Mechanics, Academy of Sciences of the Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 30, No. 8, pp. 42–48, August, 1994.     

Problems of stability of the wall rock in the working of deep coal seams

Institure of Mechanics, Ukrainian Academy of Sciences, Kiev. Translated from Prikladnaya Mekhanika, Vol. 28, No. 12, pp. 64–71, December, 1992.     

Energy filtration of charge carriers in a nanostructured material based on bismuth telluride

The dependences of the electrical conductivity and thermopower on the size of grains in a nanocrystalline material based on Bi₂Te₃-Sb₂Te₃ solid solutions of the p type have been investigated theoretically and experimentally. The relaxation time in the case of hole scattering by nanograin boundaries in an isotropic polycrystal has been calculated taking into account the energy dependence of the probability of tunneling of charge carriers and the dependence of the scattering intensity on the nanograin size L _n . A decrease in the probability of boundary scattering with an increase in the energy of charge carriers leads to an increase in the thermopower. The dependences of the thermopower and electrical conductivity on the nanograin size, which have been obtained taking into account the boundary scattering and scattering by acoustic phonons, are in good agreement with experimental data. For the material under consideration, the thermopower coefficient increases by 10–20% compared to the initial solid solution at L _n = 20–30 nm. This can lead to an increase in the thermoelectric figure of merit by 20–40%, provided that the decrease in the electrical conductivity and the decrease in the lattice thermal conductivity compensate each other. Despite the absence of a complete compensation, it has been possible to increase the thermoelectric figure of merit for the samples under investigation to ZT = 1.10–1.12.     

New bifunctional compounds obtained by selective hydrolysis of tetrathiacalix[4]arene tetraethyl esters with Cs2CO3

A new strategy for the synthesis of bifunctional compounds, based on 1,3-alternate tetrathiacalix[4]arene precursors functionalized by pairs of carboxylic acid and ester groups located on opposite sides of the macrocycle platform is described. These building blocks were prepared by the Cs₂CO₃ induced selective hydrolysis of tetrathiacalix[4]arene tetraester derivatives. A mechanism for the selective hydrolysis is suggested. The structures of the compounds are elucidated by NMR spectroscopic analysis and X-ray single crystal diffraction.     

Nickel Fluorocarbene Metathesis with Fluoroalkenes

Alkene metathesis with directly fluorinated alkenes is challenging, limiting its application in the burgeoning field of fluoro‐organic chemistry. A new nickel tris(phosphite) fluoro(trifluoromethyl)carbene complex ([P₃Ni]=CFCF₃) reacts with CF₂=CF₂ (TFE) or CF₂=CH₂ (VDF) to yield both metallacyclobutane and perfluorocarbene metathesis products, [P₃Ni]=CF₂ and CR₂=CFCF₃ (R=F, H). The reaction of [P₃Ni]=CFCF₃ with trifluoroethylene also yields metathesis products, [P₃Ni]=CF₂ and cis/trans‐CFCF₃=CFH. However, unlike reactions with TFE and VDF, this reaction forms metallacyclopropanes and fluoronickel alkenyl species, resulting presumably from instability of the expected metallacyclobutanes. DFT calculations and experimental evidence established that the observed metallacyclobutanes are not intermediates in the formation of the observed metathesis products, thus highlighting a novel variant of the Chauvin mechanism enabled by the disparate four‐coordinate transition states.     

Amplitudes and phases of electron scattering in polyatomic systems for the structural analysis of disordered,amorphous, and nanosized materials via EXAFS spectroscopy

The results from developing and testing a software package for calculating the amplitudes and phases of electron scattering in polyatomic systems are presented. The potential with which an excited electron moves in a medium is constructed using the muffin-tin approximation with Hartree–Fock exchange interaction. Tests of the package for metals, oxides, and iron-bearing water sulphate solutions show that structural parameters can be derived with high degrees of accuracy (the error for interatomic distances is ~0.01 Å; for coordination numbers, it is ~7%). Using the developed approach and software, analysis of the Ag K-EXAFS spectra of silver nanoparticles in silica glass allow us to determine the average structural parameters of Ag–O and Ag–Ag bonds.