Triphenylphosphine as an effective catalyst for ketoximes addition to acylacetylenes: regio- and stereospecific synthesis of (E)-(O)-2-(acyl)vinylketoximes

Triphenylphosphine catalyzes the regio- and stereospecific addition of ketoximes to acylacetylenes, whereas classical conditions using acetylene (KOH/DMSO, 70 °C) are unsuitable for this purpose. The reaction proceeds under mild conditions (CH₂Cl₂, rt, 7 h) to afford (E)-(O)-2-(acyl)vinylketoximes (92-98% stereoselectivity) in a yield of up to 85%. The (E)-adducts obtained are energetically less favorable than the corresponding (Z)-isomers and are gradually enriched with (Z)-isomers, thus indicating the kinetic control of (E)-stereoselectivity of the reaction.     

Stockage de l’hydrogène dans les nanotubes de carbone à paroi unique : nouvelle méthode de préparation par excitation laser

A new mode for hydrogen adsorption and storage in single-wall carbon nanotubes is used, on the basis of laser excitation. Remember that this method has been useful to obtain, in the case of the fullerene C₆₀, many complex C₆₀-atoms or C₆₀-molecules, where atoms or molecular particles are trapped inside the C₆₀-molecules. We think this method might be important to store many hydrogen molecules inside carbon nanotubes.     

Intramolecular S···O chalcogen bond in thioindirubin

Results of X-ray diffraction study and quantum-chemical calculations revealed that molecular conformation of thioindirubin molecule creates suitable conditions for formation of intramolecular C–H···O and S···O interactions. Analysis of molecular electrostatic potential (MEP) demonstrates existence of two areas of positive MEP (σ-holes) in the outermost part of the sulfur atom on the continuation of the lines of the C–S bonds. One of these σ-holes is oriented toward region of negative MEP around the oxygen atom of carbonyl group. Such situation corresponds to formation of σ-hole or chalcogen bond. Existence of both types of bonding interactions is confirmed by topological analysis of electron density distribution using “Atoms in Molecules” (AIM) theory. Energies of the C–H···O hydrogen bond and the S···O σ-hole bond derived from AIM and NBO theories are very close.     

Reactions of terminal polyynes with benzyl azide

Terminal di-, tri-, tetra-, and pentaynes substituted with a variety of functional groups react with benzyl azide in the presence of CuSO(4)·5H(2)O and ascorbic acid to give derivatives of 4-ethynyl-, 4-butadiynyl-, 4-hexatriynyl-, and 4-octatetraynyl-1,2,3-triazoles in moderate to good yields. These reactions appear to proceed regioselectively, and functionalization occurs exclusively at the terminal alkyne moiety. As well, no evidence of multiple azide additions to the polyyne framework is observed. X-ray crystallographic analysis of nine derivatives is used to document the regioselectivity of the reaction as well as outline structural characteristics of the 1,2,3-triazole products.     

On a class of nonlocal elliptic operators for compact Lie groups. Uniformization and finiteness theorem

We consider a class of nonlocal operators associated with an action of a compact Lie group G on a smooth closed manifold. Ellipticity condition and Fredholm property for elliptic operators are obtained. This class of operators is studied using pseudodifferential uniformization, which reduces the problem to a pseudodifferential operator acting in sections of infinite-dimensional bundles.     

Effects of coupled vibrations on the parameters of tangentially polarized stripe-electroded piezoelectric cylinders (L)

The effects of coupled vibrations on the piezoelectric properties and electroacoustic transducer performance of radially polarized hollow cylindrical elements as a function of the choice of height-to-diameter ratio have been well documented [J. Acoust. Soc. Am. 120(3), 1374-1380 (2006); J. Acoust. Soc. Am. 122(6), 3419-3427 (2007)]. This letter presents experimental work on the effects of coupled (circumferential, axial, and flexural) vibrations on the resonance frequencies, effective electromechanical coupling coefficient, and acoustical performance of tangentially polarized piezoceramic cylindrical elements. Comparisons are made with analytical predictions of the properties of uniformly circumferentially polarized cylinders.     

Observation of the chaotic spin-wave soliton trains in magnetic films

The transition from stationary to chaotic spin-wave soliton trains has been observed. The experiment utilized cw excitation of envelope solitons through self-modulation instability of spin waves. By increasing the spin-wave power, the secondary self-modulation instability succeeded the primary modulation instability, resulting in after-modulation of the soliton train amplitude. Further increase of the spin-wave power led to development of the higher-order instabilities, resulting in formation of the chaotic soliton train.     

Role of disorder and anharmonicity in the thermal conductivity of silicon-germanium alloys: a first-principles study

The thermal conductivity of disordered silicon-germanium alloys is computed from density-functional perturbation theory and with relaxation times that include both harmonic and anharmonic scattering terms. We show that this approach yields an excellent agreement at all compositions with experimental results and provides clear design rules for the engineering of nanostructured thermoelectrics. For Si(x)Ge(1-x), more than 50% of the heat is carried at room temperature by phonons of mean free path greater than 1 μm, and an addition of as little as 12% Ge is sufficient to reduce the thermal conductivity to the minimum value achievable through alloying. Intriguingly, mass disorder is found to increase the anharmonic scattering of phonons through a modification of their vibration eigenmodes, resulting in an increase of 15% in thermal resistivity.     

Towards a full reference library of MS(n) spectra. II: A perspective from the library of pesticide spectra extracted from the literature/Internet

To gain perspective on building full transferable libraries of MS(n) spectra from their diverse/numerous collections, a new library was built from 1723 MS(>1) spectra (mainly MS2 spectra) of 490 pesticides and related compounds. Spectra acquired on different types of tandem instruments in various experimental conditions were extracted from 168 literature articles and Internet sites. Testing of the library was based on searches where 'unknown' and reference spectra originated from different sources (mainly from different laboratories) were cross-compared. The NIST 05 MS2 library was added to the reference spectra. The library searches were performed with all the test spectra or were divided into different subsamples containing (a) various numbers of replicate spectra of test compounds or (b) spectra acquired from different instrument types. Thus, the dependence of true/false search (identification) result rates on different factors was explored. The percentage of 1st rank correct identifications (true positives) for the only 'unknown' mass spectrum and two and more reference spectra and matching precursor ion m/z values was 89%. For qualified matches, above the cut-off match factor, that rate decreased to 80%. The corresponding rates based on the best match for two and more 'unknown' and reference spectral replicates were 89-94%. For quadrupole instruments, the rates were even higher: 91-95% (one 'unknown' spectrum) and 90-100% (two and more such spectra). This study shows that MS2 spectral libraries generated from the numerous literature/Internet sources are not less efficient for the goal of identification of unknown compounds including pesticides than very common EI-MS1 libraries and are almost as efficient as the most productive from current MS2 spectral databases. Such libraries may be used as individual reference databases or supplements to large experimental spectral collections covering many groups of abundant compounds and different types of tandem mass spectrometers.