Experimental and theoretical electron density study of a highly twisted polycyclic aromatic hydrocarbon: 4-methyl-[4]helicene

Helicenes are molecules of considerable interest in view of their aromaticity which persists despite a marked departure from planarity and because of the extreme potency of some of their metabolites as tumor and mutation promoters. In this study, the electron density of 4-methyl-[4]helicene (or 4-methylbenzo[c]phenanthrene) is studied topologically with an emphasis on the fjord region since this region is where metabolic activation is initiated. The molecule consists of four fused aromatic rings that assume a twisted geometry. This geometry brings two hydrogen atoms into close proximity in the fjord region of the molecule accompanied by the appearance of an intramolecular C-Hdelta+...delta+H-C bond path (an interaction termed hydrogen-hydrogen or H- H bonding to distinguish it from dihydrogen bonding from which it is qualitatively distinct). In addition to the intramolecular H-H interaction, a number of intermolecular interactions are shown to be involved in the packing of this molecule in the crystalline state. The effect of the nonplanarity of the molecule on the local aromaticity of each ring is also discussed.     

Electron-density studies on hydrogen bonding in chromone derivatives. Part II: comparative study

The experimental electron density of a chromone derivative was determined from a multipole refinement of 100 K X-ray synchrotron data and complemented by theoretical calculations with experimental and optimized geometry. Atomic and topological properties were obtained using the Quantum Theory of Atoms in Molecules approach. The examination of topological parameters unambiguously showed π-delocalization within the H-bonded ring. The application of source function analysis confirmed the intramolecular N–H···O hydrogen bond to be a resonance-assisted hydrogen bond. The topological study confirmed the covalent nature of N–H···O interaction and the electrostatic nature of weak C–H···O interactions.     

Oligomerization of higher olefins and alkylation of toluene catalyzed by 2-[hydroxy(diaryl)methyl]-8-hydroxyquinoline oxovanadium(v) complexes

Russian Chemical Bulletin - New oxovanadium(V) complexes with 2-[hydroxy(diaryl)methyl]-8-hydroxyquinoline ligands were synthesized. These compounds were found to be efficient tandem catalysts of...     

Titanium(4+) and zirconium(4+) dichloride complexes with pyridinedicarboxylic acid derivatives as ethylene polymerization catalysts

Titanium(4+) and zirconium(4+) complexes with pyridinedicarboxylic acid derivatives have been synthesized. The composition and structure of the synthesized 2,6-bis(diphenylhydroxymethyl)pyridine complexes have been corroborated by NMR and IR spectroscopy, and elemental analysis. The complexes activated with methylaluminoxane (MAO) are catalytically active in ethylene polymerization, Depending on the Ti/Al_MAO ratio, the catalytic activity of the complexes varies between 90 and 420 kg PE/mol Ti h atm.     

Synthesis and transport properties of proton-conducting membranes based on polyvinylidene fluoride films with introduced and sulfonated polystyrene

Thermal polymerization of styrene sorbed into a polyvinylidene fluoride (PVdF) film from a toluene solution followed by sulfonation of the resulting material was performed. The kinetics of polystyrene (PS) accumulation in the PVdF film during thermal polymerization was studied. Samples with 6–30 wt % PS and ∼100% PS sulfonation were obtained. Proton-exchange membranes wsith an ion-exchange capacity of up to 2 mg-eq/g and proton conductivity of up to 0.008 S/cm at 75% relative humidity were prepared. The permeability coefficients of water, methanol, and hydrogen and their dependences on the amount of introduced PS, ion-exchange capacity, and water uptake of membranes were measured. The synthesized materials proved similar to MF-4SK membranes in their basic transport characteristics and can be used as proton-exchange membranes in hydrogen-air and alcohol fuel cells.     

Petroleum luminophores of pyrolytic origin and energy transfer between their components

Photoexcitation of luminophores prepared from heavy oil pyrolysis tar was studied, and properties of these compounds, determining the variation of the luminescence color and intensity depending on the solution concentration, were evaluated.     

Casimir effect within (3 + 1)<Emphasis Type=Italic>D</Emphasis> Maxwell-Chern-Simons electrodynamics

Within the framework of the Lorentz-violating (3 + 1)-dimensional extended electrodynamics including the Lorentz-violating CPT-odd Chern-Simons term, we consider the electromagnetic field between two parallel perfectly conducting plates. We find the one-particle eigenstates of such a field, as well as the implicit expression for the photon energy spectrum. In order to find the leading Chern-Simons correction to the vacuum energy, we renormalize and evaluate the sum over all one-particle eigenstate energies using the residue theorem. The resulting correction to the Casimir force, which is attractive and quadratic in the Chern-Simons term, disagrees with the one calculated in [1] and based on wrong equations of motion. Compared with the experimental data, our result places a constraint on the absolute value of the Chern-Simons term.     

Generalization of dual-energy method for material identification with X-ray introscopy

X-ray nondestructive testing was used for flaw location, for examination of the content of a package, and for fault detection. However, a monoenergetic beam can determine only the density variations of the analyzed object, not its structure. Study of the structure of an object was carried out by dual-energy X-ray beams. It is established that materials have different dependences of the X-ray extinction coefficient on its energy. The possibility of determination the composition of the material using two polychromatic X-ray beams with different energy spectra is shown. A variant of the algorithm for determination of the atomic number Z in the case of a weakly absorbing material is proposed.