Electromagnetic field distributions in waveguide-based axial-type microwave plasma source

We present results from simulations of 2D distributions of the electromagnetic field inside a waveguide-based axial-type microwave plasma source (MPS) used for hydrogen production via methane reforming. The studies are aimed at optimization of discharge processes and hydrogen production. We derive equations for determining electromagnetic field distributions and next determine the electromagnetic field distributions for two cases – without and with plasma inside the MPS. For the first case, we examine the influence of the length of the inner conductor of the coaxial line on electromagnetic field distributions. We have obtained standing wave patterns along the coaxial line and found resonances for certain positions of the coaxial line inner conductor. For the case with plasma inside the MPS, we perform calculations assuming that distributions of plasma parameters are known. Simulations are done for several values of maximum electron density. We have found that for values of electron density greater than strong skin effect in the plasma is observed. Consequently, plasma may be treated as an extension of the inner conductor of the coaxial line. We have used FlexPDE software for the calculations.     

Organocatalyzed Tsuji-Trost reaction: a new method for the closure of five- and six-membered rings

A combination of organotransition metal catalysis and organocatalysis allows for Tsuji-Trost 5-exo- and 6-exo-cyclizations of aldehydes. This transformation can also be accomplished as a catalytic asymmetric reaction, which affords vinylcyclopentane derivatives with up to 98%ee.     

THE EFFECT OF NORFLURAZON ON PHOTOTROPIC REACTION IN Phaseolus aureus Roxb. SEEDLINGS

Abstract. The phototropic response of norflurazon-treated mung bean seedlings has been studied to evaluate the possible role of carotenoids, carotenoid-derived growth substances, or other factors in the perception/reaction system. Phototropism was slowed significantly in plants grown in white and blue light in the presence of norflurazon. This effect was evident in norflurazon-bleached seedlings, as well as in those whose pigment system was not affected, due to a shorter period of herbicide action. The possible modes of norflurazon action are discussed.     

Polypyrrole-coated capillaries for capillary zone electrophoresis

Fused-silica capillaries are permanently coated by silanization with 3-{[3-(N-pyrrole)-2-hydroxypropyl]amino}propyltriethoxysilane followed by oxidative polymerization of the pyrrole moieties with iron (III) or peroxodisulfate in the presence of chloride, perchlorate, or dextransulfate as anions. This approach allows to modulate the EOF in its magnitude as well as in its direction. With the small anions chloride and perchlorate, the EOF is reversed below pH 5 while with the large dextransulfate polyanions (DS) the EOF is relatively constant over the pH range from 2.5 to 9.4. This can be of advantage at low pH, at which the EOF of uncoated capillaries is close to zero. Application for separation of some herbicides is shown. The lifetime of PP-modified capillaries is satisfactory: the decrease in EOF is less than 3% during 80 analyses (160 min) and less than 5% over three months of storage. The reproducibility of capillary modification is about 5% (RSD of EOF).     

Positron lifetimes at the initial stage of pore formation in Vycor glass

The formation of narrow pores during leaching of Vycor glass by sulphuric acid was investigated using the positron lifetime technique. During the leaching process the pore diameter remained roughly constant (except for the case of cold leaching). The time of processing changed the total length of capillaries, but not their number; at the temperature 50°C during 20 min of leaching the average leaching depth was 24 μm.     

Mixed-ligand chromium(III)-oxalate-pirydinedicarboxylate complexes: potential biochromium sources: kinetic studies in NaOH solutions and effect on 3T3 fibroblasts proliferation

Base hydrolysis of [Cr(ox)₂(pda)]³⁻ (where pda is N,O-bonded 2,4- and 2,5- pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The main reaction path proceeds through [Cr(ox)(pda)(OH)₂]³⁻ and [Cr(pda)(OH)₄]³⁻ complexes. The kinetics of the first oxalate dissociation was studied spectrophotometrically, within the lower energy d–d band region, at 0.4–1.0 M NaOH. The character of spectroscopic changes was consistent with a consecutive reaction model, where the chelate-ring opening and the one-end bonded oxalato liberation are the first and the second reaction stages. The pseudo-first order rate constants (k _obs0 and k _obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)₃]³⁻ were studied. The calculated rate constants were independent of [OH ⁻ ]. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined. Effect of the [Cr(ox)₂(pda)]³⁻ and [Cr(2,4-pda)₃]³⁻ complexes on 3T3 fibroblasts proliferation was studied. The results manifested low cytotoxicity of these complexes, which makes them promising candidates for dietary supplements.     

Synthesis, biology, and modeling of a C-4 carbonyl C,D-seco-taxoid

A C,D-seco-paclitaxel derivative 26 was prepared from taxine and tested for biological activity. Chemical reactivity of the seco-compounds proved to be substantially modified, with respects to taxoids. The corresponding C,D-seco-taxoid does not show tubulin stabilizing activity or cytotoxicity. Explanation of these observations based on molecular modeling is provided.