Insertion of Ethyl Isocyanate at the Tungsten–Chlorine Bond. Crystal Structure of 1,3,5-Triethyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione

The reaction of tungsten hexachloride with excess ethyl isocyanate in dichloroethane leads to the insertion of three ligand molecules at one of the tungsten–chlorine bonds. The data of elemental analysis and IR spectroscopy confirm that the thermolysis of the reaction mixture affords the WCl₄(L₃Cl) complex (I), where L = –N(Et)C(O)–. The structure of the chain of inserted molecules in I is established on the basis of IR and NMR data, and the results of X-ray diffraction analysis of crystals of an organic product (II) of the hydrolysis of I. According to the latter, compound (II) is a derivative of s-triazine—1,3,5-triethyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione.     

Recyclization of dimedone adduct with 2-(2-oxo-2-phenylethylidene)propanedinitrile in the reaction with N-nucleophiles

Three-component condensation of dimedone with phenylglyoxal hydrate and malononitrile gave a polyfunctional 5,6,7,8-tetrahydro-4H-chromene derivative, 2-amino-4-benzoyl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile, which reacted with ammonium acetate to produce pyrrolo[3,4-c]quinoline ring system. Reactions of the condensation product with primary and secondary amines and hydroxylamine hydrochloride afforded polysubstituted pyrroles, whereas the reaction with hydrazine hydrate led to 3-amino-6-phenylpyridazine-4-carbonitrile.     

Combined chemical and topographic imaging at atmospheric pressure via microprobe laser desorption/ionization mass spectrometry–atomic force microscopy

The operational characteristics and imaging performance are described for a new instrument comprising an atomic force microscope coupled with a pulsed laser and a linear ion trap mass spectrometer. The operating mode of the atomic force microscope is used to produce topographic surface images having sub‐micrometer spatial and height resolution. Spatially resolved mass spectra of ions, produced from the same surface via microprobe‐mode laser desorption/ionization at atmospheric pressure, are also used to create a 100 × 100 µm chemical image. The effective spatial resolution of the image (～2 µm) was constrained by the limit of detection (estimated to be 10⁹–10¹⁰ molecules) rather than by the diameter of the focused laser spot or the step size of the sample stage. The instrument has the potential to be particularly useful for surface analysis scenarios in which chemical analysis of targeted topographic features is desired; consequently, it should have extensive application in a number of scientific areas. Because the number density of desorbed neutral species in laser desorption/ionization is known to be orders‐of‐magnitude greater than that of ions, it is expected that improvements in imaging performance can be realized by implementation of post‐ionization methods. Published in 2009 by John Wiley & Sons, Ltd.     

The impedance-characteristic method in the study of specific temperature features of dielectric anomaly suppression in triglycine sulfate

The reflection and absorption coefficients in a waveguide loaded on ferroelectric triglycine sulfate (TGS), which has a layered domain structure near the phase transition, are calculated by the impedance-characteristic method. The calculated and experimental data do not reveal any correlations with the specific temperature features in the TGS dielectric response to microwave irradiation. The mechanism of the microwave effect is discussed.     

Resonant scattering of X-ray radiation in magnetic crystals with non-cubic local anisotropy

Features of resonant diffraction of synchrotron radiation in magnetic crystals in which the local symmetry of resonant atom positions is lower than cubic are considered. It was shown that the simultaneous presence of two anisotropic factors can cause asymmetry of the azimuthal dependence of purely resonant reflections. The observed azimuthal dependence of the 002 reflection in the HoFe₂ crystal was numerically simulated.     

Sorption of Silver and Chemiluminescent Activity of Clinoptilolite

Sorption conditions of ions and colloidal particles of silver by a zeolite (clinoptilolite) and clays, and specific features of distribution of absorbed silver in clinoptilolite grains were studied. Temperature dependences of the intensity of heterogeneous chemiluminescence from samples of natural clinoptilolite and its modified forms were obtained. The activation energies of the luminescence-active chemisorption of oxygen on electron-donor centers of the zeolite surface and relative amount of centers were determined.     

Stereoselective synthesis of dihydropyrimidinethione podand in the presence of l-proline or 4-hydroxy-l-proline and metal nitrates

The asymmetric Biginelli reaction involving a 3-oxobutanoyl-containing podand, benzaldehyde, and thiourea was studied using secondary amines as a chiral inductor, Brönsted acid as a catalyst, and metal salts (especially metal nitrates) as an additive of asymmetric catalysis (AAC) was studied. The tuberculostatically active dihydropyrimidine-thione-containing podand was synthesized with an enantiomeric excess of 57% in the presence of 4-hydroxy-l-proline. In the presence of metal nitrates, the influence of the ionic radius of the cation on the enantioselective excess of the reaction under study was observed, which made it possible to propose a possible mechanism of chiral induction controlled by the complexing ability of the initial β-ketoester-containing podand with metal ions and coordination of the reagents in the transition states.

     

Ab initio simulation of resonant forbidden reflections in Ge crystals

Forbidden reflections are observed in the case of diffraction of synchrotron radiation with wave-lengths close to the absorption edges in crystals. A new method for calculating the intensity of thermal-motion-induced (TMI) forbidden reflections is proposed in this paper. It includes two stages: simulation of instantaneous thermal atomic displacements using ab initio molecular dynamics and subsequent quantum-mechanical calculations of the resonance scattering amplitude for various configurations. This procedure is used to calculate the temperature dependence of the 600 reflection intensity for Ge. The proposed method for simulating forbidden TMI reflections is suitable for any crystal structures and can explain many results so far obtained using synchrotron.