Zum Verhalten von Trimethylalkoxysilanen bei Elektronenstoss

The mass spectra of trimethylalkoxy silanes (CH₃)₃Si? O? (CH₂)_n? CH₃ (n = 0-8) and (CH₃)₃Si? O? (CH₂)_n? CH(CH₃)₂ (n = 0-3) have been investigated and most of the fragmentations, induced by electron-impact, have been identified by metastable ions. The fragmentation mechanisms of trimethylpentoxysilane, established by Diekman, Thomson and Djerassi, are also observed in the mass spectra of these trimethylalkoxy silanes. Characteristic features of these reactions in the mass spectra of compounds with smaller and longer alkoxy groups, together with some additional fragmentations, are discussed.     

Die Elektronenstoßfragmentierung von substituierten Dimethylalkoxysilanen

Electron Impact Fragmentation of Substituted Dimethylalkoxysilanes The mass spectra of substitued dimethylalkoxysilanes (H₃C)₂SiOCH₃R (R ? ? F, ? Cl, ? H, ? OCH₃, ? C₆H₅, ? CH₃, ? C₂H₅, ? n-C₃H₇), and (H₃C)₂SiOC₂H₅R (R ? ? Cl, ? C₆H₅, ? CH₃, ? C₂H₅) have been recorded and the fragmentation patterns are presented. The yield of the electron impact induced reaction (M-15)⁺→(M-45)⁺+ H₂CO occuring upon fragmentation of substituted dimethylmethoxysilanes depends on the substituent R. A quantum chemical calculation was carried out by CNDO/2 method to determine the electron density distribution in the ion at mass number (M-15). It is shown that a correlation exists between the Si? O? π bond order in this ion and the yield as well as the activation energy of this reaction.     

Dielectric behavior of spin-deposited nanocrystalline nickel-zinc ferrite thin films processed by citrate-route

Nanocrystalline nickel-zinc ferrite thin films with the general formula Ni_1−xZn_xFe₂O₄, where x=0.0, 0.2, 0.4 and 0.6 were fabricated via a chemical route known as the citrate precursor route. These films were spin-deposited on indium-tin oxide coated glass, fused quartz and amorphous Si-wafer substrates, and annealed at various temperatures up to 650 °C. The films annealed below 400 °C were found to be X-ray amorphous, while the films annealed at and above 400 °C were polycrystalline exhibiting a single-phase spinel structure. The average grain size of the films evaluated by transmission electron microscopy, is found to be in the range 4-8.5 nm. The room temperature DC resistivity of the films is in the range 10³-10⁷ Ω m. Dielectric constant and dielectric loss were measured in the frequency range 100 Hz-1 MHz. Dielectric constant of the films is found to lie between 25 and 44, while the loss factor is if the order of 10⁻². The higher values of the dielectric constant for films having higher zinc concentration are attributable to the enhanced hopping between Fe²⁺ and Fe³⁺ ions in these samples. The M-H hysteresis measurement of the nickel ferrite thin films annealed at 650 °C showed narrow hysteresis loop—a characteristic of soft ferromagnetic material.     

Cryogenic 35 GHz pulse ENDOR probehead accommodating large sample sizes: Performance and applications

The construction and performance of a cryogenic 35 GHz pulse electron nuclear double resonance (ENDOR) probehead for large samples is presented. The resonator is based on a rectangular TE₁₀₂ cavity in which the radio frequency (rf) B₂-field is generated by a two turn saddle ENDOR coil crossing the resonator along the sample axis with minimal distance to the sample tube. An rf power efficiency factor is used to define the B₂-field strength per square-root of the transmitted rf power over the frequency range 2–180 MHz. The distributions of the microwave B₁- and E₁-field, and the rf B₂-field are investigated by electromagnetic field calculations. All dielectrics, the sample tube, and coupling elements are included in the calculations. The application range of the probehead and the advantages of using large sample sizes are demonstrated and discussed on a number of paramagnetic samples containing transition metal ions.     

Triazolotriazines as potential chemotherapeutic agents. VI

Several new 1,2,4-triazolo[4,3-b]triazino[7,6-b]indoles were prepared in anticipation that they would have better chemotherapeutic activities, but in the Screening test none of the Compounds was found to be active.     

Unsteady flow of a dusty viscous liquid in a rotating channel

Acta physica Academiae Scientiarum Hungaricae - The unsteady flow of a dusty viscous liquid in a parallel plate channel rotating with an angular velocity Ω is analysed. Analytical expressions...     

Direct determination of cadmium in urine using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction

A procedure is described for the direct determination of cadmium in human urine using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction. Except for a straightforward 1 + 1 V/V dilution of samples with 1.5% nitric acid, no matrix modifier or sample pre-treatment was necessary, thus reducing the risk of contamination. The concentration of cadmium in urine was evaluated directly from a calibration graph prepared using a metal-spiked human urine pool. In this way the time-consuming method of standard additions was avoided, permitting an increased sample throughput (120-150 samples per day; 90 s per analysis) with minimal attention of the analyst. In routine use, the precision (both within day and day to day) and limit of detection were of the order of less than 10% and 0.05 micrograms l-1 of Cd, respectively. The method is suitable for the biological monitoring of cadmium in the general population or in occupationally exposed persons.     

Microstructural,dielectric and magnetic behavior of spin-deposited nanocrystalline nickel–zinc ferrite thin films for microwave applications

Nanocrystalline nickel ferrite and zinc doped nickel ferrite thin films with general composition Ni_1−xZn_xFe₂O₄; x=0.0, 0.2 and 0.5 were fabricated by the spin-deposition technique. Citrate precursor method was adopted to prepare coating solution used for film deposition. This method resulted in single phase, transparent, homogeneous and crack-free nanocrystalline ferrite thin films at annealing temperature as low as 400 °C. The substrates used for film deposition were ITO-coated 7059 glass, fused quartz and Si (1 0 0). The thickness of films was found to be in the range ∼1000–5500 Å. The surface microstructure and morphology investigated by atomic force microscopy (AFM) confirmed the grain size of nickel–zinc ferrite films to be in nanometer range indicating nanocrystalline nature of the films. Dielectric properties such as the real (∈′) and imaginary parts (∈″) of complex permittivity were measured in the X-band microwave frequency region (8–12 GHz) by employing extended cavity perturbation technique. The M–H hysteresis measurements on the films annealed at 650 °C revealed narrow hysteresis curves with H_c and M_s varying for different compositions.     

Synthesis of the acylphloroglucinols rhodomyrtone and rhodomyrtosone B

In a sequential three-component coupling syncarpic acid, 3-methylbutanal and an acylated phloroglucinol were combined to the hydroxy ketone 3. Acid catalysis converted 3 directly to the natural product rhodomyrtosone B (2). The other isomer, the antibiotic rhodomyrtone (1) was obtained from 3 in a sequence of acid-catalyzed cyclization, retro Friedel–Crafts reaction, and reacylation. In preliminary assays both compounds showed potent antibiotic activity.