Synthesis of 4-Alkynyl-substituted 3,4-Dihydropyrimidin-2(1H)-ones

4-Alkynyl-3,4-dihydropyrimidin-2-(1H)-ones were synthesized by a one-pot reaction of propynals, ethyl acetoacetate, and urea. The yields of acetylenic dihydropyrimidinones depend significantly upon the propynal structure and catalyst type. A comparative study of the catalysts revealed an important advantage of polyphosphate ester in tetrahydrofuran in comparison with hydrochloric acid in methanol or trimethylchlorosilane in dimethylformamide, allowing the preparation of target compounds in good or moderate yields.     

Quantum corrections to the conductivity of a natural Nd<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> Ce<Subscript>x</Subscript>CuO<Subscript>4</Subscript> superlattice

Temperature and magnetic field dependences of the resistivity and Hall coefficient in layered single-crystal Nd_2?xCe_xCuO₄ (x = 0.12) films are experimentally investigated and analyzed. It is shown that this material clearly exhibits quantum effects characteristic of 2D semiconductor structures: negative magnetoresistance caused by suppression of the interference quantum correction by a magnetic field, a near-logarithmic temperature dependence of the conductivity, and a temperature dependence of the Hall coefficient related to e-e interaction. It is shown that, when analyzing experimental data, it is necessary to take interlayer transitions into account. Such an approach provides quantitative agreement between experiment and the standard theory of quantum corrections.     

1,4-Migration of Et3Ge Group in 1-Triethylgermoxypropyne

Russian Journal of Organic Chemistry -     

Selective monoallylation of β-cyclodextrin

Reaction of β-cyclodextrin with allyl bromide in dimethyl sulfoxide affords 2-О-allyl-β-cyclodextrin, while in dimethylformamide 6-О-allyl-β-cyclodextrin is formed. Optimal conditions of the reaction were found allowing to obtain the target products in quantitative yield.     

Quantum corrections to the conductivity of a two-dimensional disordered system in a strong magnetic field

A system of noninteracting electrons moving in a magnetic field and a field of randomly distributed impurities is considered. An exact expression is obtained for the sum of the series of maximally crossed diagrams; it is valid in an arbitrary magnetic field. It is shown that in the two-dimensional case the relative magnitude of the corrections to the conductivity due to this series reaches 60% in the center of the lower Landau sub-band.Physicotechnical Institute of the Urals Branch of the Russian Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 94, No. 3, pp. 486–495, March, 1993.     

Comparison between the Results of Simulating the Synchrotron Radiation from a Bending Magnet and Experimental Data

The results of using two (SPECTRA and SRW) programs for simulating synchrotron radiation (SR) are presented. Calculations are performed for coherent SR from a beam of electrons with moderately relativistic energies in a short bending magnet. Simulation is carried out for real beam parameters. A comparison between simulation and experimental data indicates their good agreement. Both general information for the given codes grouped by a number of criteria and specific data on simulating radiation from bending magnets are presented.     

Permethyl-β-Cyclodextrin Spin-Labeled with Nitronyl Nitroxide: Synthesis and EPR Study

A method for synthesis of new covalently linked spin-labeled cyclodextrin (CD) via the attachment of nitronyl nitroxide 2-(4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl to permethylated β-cyclodextrin is described. Electron spin echo envelope modulation (ESEEM) studies demonstrate that the new spin-labeled CD exhibits dynamic equilibrium between conformations with radical fragment capping the cavity of CD and radical fragment located outside the cavity. In solution, nitronyl nitroxide attached to CD retains its sensitivity to nitric oxide (NO), as reaction with NO leads to formation of iminonitroxide fragment evidenced by continuous-wave (CW) electron paramagnetic resonance (EPR). At the same time, CW EPR study of the reaction with ascorbic acid shows that the described binding of nitronyl nitroxide to CD does not provide higher stability of radical towards the reduction, and the corresponding rate constants are close to those obtained for free nitronyl nitroxide. Plausible explanations of these observations are discussed.     

Spatial-temporal dispersion of the kinetic coefficients near the Anderson transition

A generalization of the Vollhardt-Wölfle localization theory is proposed to make it possible to study the spatial-temporal dispersion of the kinetic coefficients of a d-dimensional disordered system in the low-frequency, long-wavelength range (ω?_F and q?k _F ). It is shown that the critical behavior of the generalized diffusion coefficient D(q,ω) near the Anderson transition agrees with the general Berezinskii-Gor’kov localization criterion. More precisely, on the metallic side of the transition the static diffusion coefficient D(q,0) vanishes at a mobility threshold λ _c common for all q: D(q, 0)∝t=(λ _c ?λ)/λ _c →0, where λ=1/(2π?_F τ) is a dimensionless coupling constant. On the insulator side, q≠0 D(q,ω)∝?iω as ω→0 for all finite q. Within these limits, the scale of the spatial dispersion of D(q,ω) decreases in proportion to t in the metallic phase and in proportion to ωξ ², where ξ is the localization length, in the insulator phase until it reaches its lower limit ～λ _F. The suppression of the spatial dispersion of D(q,ω) near the Anderson transition up to the atomic scale confirms the asymptotic validity of the Vollhardt-Wölfle approximation: D(q,ω)?D(ω) as |t|→0 and ω→0. By contrast, the scale of the spatial dispersion of the electrical conductivity in the insulator phase is of order of the localization length and diverges in proportion to |t|^?v as |t|→0.     

New silatranes of α,β-acetylene azomethine series

Russian Chemical Bulletin -