Synthesis of macrolide antibiotics Communication 2. Synthesis of the C9-C13 fragment of erythronolides A and C and megalonolide

Conclusions The synthesis of the C⁹-C¹³ fragment of erythromycin A has been accomplished, starting from levoglusan (18 steps, 3.4%).For previous communications, see [1, 2].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2561–2568, November, 1982.     

Measuring the solubilities of ionic liquids in water using ion-selective electrodes

Polyvinyl chloride-plasticized membrane ion-selective electrodes (ISE) based on conventional ion-exchangers have been proposed as a cheap universal tool to measure the solubilities of ionic liquids (ILs) in water. They are applicable for ILs with a wide range of solubilities in water, since the linear range of a potentiometric response spans several orders of magnitude. As an example, we have fabricated and tested ISEs for widely used alkylimidazolium ionic liquids. The aqueous solubilities of four typical ILs have been determined at 21 °C: 0.075±0.001 mol l^–1 (1-butyl-3-methylimidazolium, BMIm, hexafluorophosphate); 0.018±0.001 mol l^–1 (BMIm bis(triflylimide)); 0.054±0.007 mol l^–1 (1-butyl-2,3-dimethylimidazolium, BDMIm, hexafluorophosphate); 0.014±0.001 mol l^–1 (BDMIm bis(triflylimide)).     

Piezo-thermoelectromotive force in strained p-GaAs samples

Experimental data are given on the thermo-emf in strained samples of p-type gallium arsenide with hole densities of 10¹⁷ to 10¹⁹ cm^?3 in the temperature range from 77 to 400°K. It is shown that the thermo-emf in the strained samples depends on the degree of doping and orientation of the original crystals. Phonon drag is observed in strained p-GaAs samples at a temperature of about 100°K. A maximum of the dependence α=f(T) is observed in the <111> direction, and a minimum of the thermo-emf in the <100> direction. The indicated behavior of the thermo-emf can be explained by anisotropy of the hole effective masses. It is postulated that scattering of holes by acoustic lattice vibrations and by impurity ions takes place in the case of p-GaAs samples with a hole concentration of 10¹⁷ cm^?3, whereas only scattering by impurity ions takes place for samples with p=10¹⁹ cm^?3. The temperature dependence is calculated for m _p ^* =0.7 m₀ on the basis of these assumptions. The experimental dependences α₀=f(T) are used to determine the anisotropy of the hole effective masses. The maximum variation of (m _p ^* )_ε is observed in the <111> direction, and the minimum variation in the <100> direction.     

Cross sections of large-angle hadron production in proton– and pion–nucleus interactions III: tantalum nuclei and beam momenta from ±3 GeV/c to ±15 GeV/c

We report on double-differential inclusive cross sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% λ _abs thick stationary tantalum target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20°<θ<125°. They are of particular relevance for the optimization of the design parameters of the proton driver of a neutrino factory.     

Photoinduced charge redistribution and its influence on excitonic states in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures

The photoinduced charge redistribution in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures under different conditions of optical excitation has been investigated using scanning probe microscopy and optical spectroscopy in the temperature range from 5 to 300 K. Excitation of the samples by radiation with a photon energy greater than the band gap of Zn(Cd)Se leads to the accumulation of electrons in quantum wells, which is detected using scanning spreading resistance microscopy. For moderate excitation densities (up to 25 W/cm²) and at temperatures ranging from 80 to 100 K, the density of a quasi-two-dimensional electron gas formed in quantum wells is several orders of magnitude higher than the density of electron-hole pairs generated by the excitation radiation. The excess electron concentration in the quantum well leads to a broadening of the exciton resonances and to an increase in the relative intensity of the donor-bound exciton emission line and also determines the increase in the luminescence quantum yield with increasing excitation intensity. An additional illumination with a photon energy less than the band gap of Zn(Cd)Se decreases the concentration of excess electrons in quantum wells. The influence of the additional illumination is observed at a temperature of approximately 100 K and almost completely suppressed at 5 K. The obtained results are explained in terms of the formation of a potential barrier for electrons at the ZnMgSSe/GaAs interface and by the specific features of recombination processes in the electron-hole system containing impurity centers with different charge states.