Structural and dynamic microheterogeneity of rubber powder

Spin probe EPR spectroscopy was used to study the local dynamics of vulcanizates of an ethylenepropylene-diene elastomer and rubber powders prepared from them. It was revealed that the preparation of rubber powders is accompanied by the formation of a polymer network with an essentially nonuniform local structure.     

Density functional and spectroscopic studies of nitrogen inversion in substituted dizocilpines

While developing a synthesis towards tagged dizocilpine (MK‐801) analogues, we observed highly restricted inversion of a nitrogen centre in a number hydroxylamines obtained as key intermediates. These compounds are shown to possess some of the structural elements which are expected to significantly hinder the nitrogen inversion, potentially leading to hydroxylamines with a chiral nitrogen centre. Free energy barriers (ΔG^≠) of the nitrogen inversion were estimated to be ca. 22 kcal mol^?1 at temperatures near 420 K using variable temperature NMR measurements in DMSO‐d₆. Further density functional studies of a number model systems were undertaken in order to better rationalize the measured inversion barriers and follow the role of various structural factors in raising the barrier height of the nitrogen inversion process. Copyright © 2008 John Wiley & Sons, Ltd.     

Strong coupling constants of light pseudoscalar mesons with heavy baryons in QCD

We calculate the strong coupling constants of light pseudoscalar mesons with heavy baryons within the light cone QCD sum rules method. It is shown that sextet–sextet, sextet–antitriplet and antitriplet–antitriplet transitions are described by one universal invariant function for each class. A comparison of our results on the coupling constants with the predictions existing in literature is also presented.     

Interactions of benzoxazolin(benzothiazolin)ones and-thiones with α-bromopropionyl chloride

At interaction of benzoxazolin(benzothiazolin)ones with -bromopropionyl chloride N-acylation takes place, while in the case of benzoxazoline(benzothiazoline)thiones, the reaction is accompanied by S-alkylation.Plant Substance Chemistry Institute, Academy of Sciences of the Uzbekistan Republic, Tashkent 700170. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 270–273, February, 1999.     

A new liquid membrane electrode for determination of vitamin B1 in multivitamin preparations

Summary A new liquid membrane electrode was developed which is highly selective and sensitive for vitamin B₁. It is based on the thiamine-picrolonate ion-pair complex as an electroactive material in nitrobenzene solvent. The electrode has a remarkable selectivity for vitamin B₁ in the presence of vitamins B₂, B₆, B₁₂ and nicotinamide. The results obtained for the determination of vitamin B₁ in various multivitamin preparations at levels as low as 1 g/ml show an average recovery of 98% (mean standard deviation 1.8%) and are favourably compared with those obtained by the official methods.

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Neue Flüssig-Membranelektrode zur Bestimmung von Vitamin B₁ in Multivitaminpräparaten

Zusammenfassung Eine neue, für Vitamin B₁ hochselektive Flüssig-Membranelektrode wurde entwickelt. Sie beruht auf dem Thiamin-Picrolonat-Ionenpaarkomplex als elektroaktives Material im Lösungsmittel Nitrobenzol. Die Elektrode besitzt eine beachtliche Selektivität für Vitamin B₁ in Gegenwart der Vitamine B₂, B₆, B₁₂ und Nicotinamid. Bei Bestimmungen in verschiedenen Multivitaminpräparaten mit Konzentrationen bis herab zu 1 g/ml erhielt man eine durchschnittliche Wiederfindung von 98% (mittlere Standardabweichung 1,8%). Die erhaltenen Resultate zeigen gute Übereinstimmung mit den nach amtlichen Methoden erhaltenen Werten.

     

Use of gas-liquid chromatography for analyzing products of carbonylation of certain pyridine bases

A method has been elaborated for the quantitative gas-chromatographic analysis of a mixture of piperidine, N-formylpiperidine, and pyridine on polyethylene glycol-4400 applied onto a chromosorb and NaCl, and apezon L, applied onto NaCl. The relative retentive volumes and heats of solution of the components of the mixture were calculated.     

Step structures on III-V phosphide (001) surfaces: how do steps and Sb affect CuPt ordering of GaInP2?

The observation of III-V phosphide (001)-(2 x 2) surfaces makes it possible to solve a long standing mystery of step structures. First-principles calculations show that a bulklike type-B step on a hydrogenated 2 x 2 surface is more stable than a rebonded one by 1.1 eV/unit step. In contrast, this energy difference for a H-free beta(2 x 4) surface is only 0.5 eV/unit step. The large difference explains why the CuPt ordering of GaInP is stronger in metal-organic chemical vapor deposition than in molecular beam epitaxy. However, a minute amount of Sb will preferentially attach to the 2 x 2 surface steps and induce additional step structures that cause ordering disruption.     

Growth model for atomic ordering: the case for quadruple-period ordering in GaAsSb alloys

Quadruple-period ordering in GaAsSb alloys is studied both theoretically and experimentally. A growth model is proposed to account for the observed three-dimensional (3D) ordered structure. The model is qualitatively different from the widely accepted surface reconstruction and dimerization-induced ordering models that strictly speaking explain only the in-plane 2D patterns. Here, we show that the already ordered substrate will affect the reconstruction of the growth front with respect to the substrate to ensure a correct stacking of the individual 2D ordered layers into the observed 3D lattice.     

<Emphasis Type="Italic">N</Emphasis>-shaped voltage-current characteristic and current oscillations in Sm<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> manganite

The voltage-current characteristics (VCC) of Sm_1?xSr_x MnO₃ samples with x=0.425 and x=0.450 were experimentally studied at a temperature of 77 K in pulsed and constant electric (E) and magnetic (H) fields up to 10 kOe for the H‖E and H⊥E orientations. N-shaped VCCs and high-frequency (up to 3 MHz) current oscillations were observed. It was found that the effect of colossal magnetoresistance had a threshold character and was smoothly reduced to zero with E→0.