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51.
[reaction: see text] A formal total synthesis of the sex attractant of male dried bean beetle, methyl (R,E)-(-)-tetradeca-2,4,5-trienoate, was achieved by a new efficient route utilizing the Pd-catalyzed asymmetric allene synthesis reaction. It was found that the atropisomeric biaryl bisphosphine (R)-segphos showed better enantioselectivity than (R)-binap in the Pd-catalyzed reaction for preparing alkyl-substituted axially chiral allenes. 相似文献
52.
A supersonic jet instrument for fluorescence spectrometry is described. It consists of a high-temperature free expansion nozzle for continuous sample introduction and a vacuum chamber equipped with a high-speed pumping system. Rotationally cooled spectra obtained with the supersonic jet are compared with gas-phase spectra measured at high temperature for perylene and benzo[a]pyrene molecules. Each component of the unresolved band structure in the high-temperature spectra was found to be composed of a rotational congestion of several vibrational bands. For a 1:1 mixture of perylene and benzo[a]pyrene, selective detection is possible by using supersonic jet spectrometry. The detection limit for perylene is 100 ng. The advantage of this technique over other low-temperature spectrometric methods based on Shpol'skii and matrix isolation effects are discussed. 相似文献
53.
M Shimizu S Horie S Terashima H Ueno T Hayashi M Arisawa S Suzuki M Yoshizaki N Morita 《Chemical & pharmaceutical bulletin》1989,37(9):2531-2532
Aldose reductase (AR) inhibitory activity-directed fractionation of the 70% ethanolic extract of Para-parai mí, Phyllanthus niruri, has led to the isolation of three active components, ellagic acid (1), brevifolin carboxylic acid (4) and ethyl brevifolin carboxylate (5). Among them, 1 showed the highest inhibitory activity, being about 6 times more potent than quercitrin, which is a known natural inhibitor of AR. 相似文献
54.
Stephanie L. Brock Tomoko Shimojo Steven L. Suib Yuji Hayashi Hiroshige Matsumoto 《Research on Chemical Intermediates》2002,28(1):13-24
Methane conversions of 11.9%, yields of hydrogen as high as 23.3% and energy yields of 1.0 mol H2/kWh have been achieved from CO2 reforming of CH4 in non-thermal, atmospheric pressure plasma reactors with Pt coated electrodes. Two reactors have been studied. A novel fan type reactor consisting of a movable rotor and immobile stator produced the highest yields in contrast to a tube type (silent discharge) reactor with a glass dielectric barrier. Conversions, yields of hydrogen and energy yields (expressed as mol H2/kWh) were studied for CO2/CH4 concentrations of 1.1% and 5.0% in He as a function of flow rate and input voltage. Hydrogen yields are observed to increase as the input voltage is increased from 411 V to 911 V and the flow rate is decreased from 100 cc/min to 30 cc/min. Energy yields vary only slightly with input voltage and flow rate. Hydrogen yields show little dependence on CO2/CH4 concentrations, but energy yields are approximately five times greater for the 5.0% mixture than the 1.1% mixture. Selectivities to H2, CO, coke, and low molecular weight hydrocarbons were also evaluated and compared to data obtained without CO2 in the feed. Hydrogen selectivities of nearly 100% were obtained, with small amounts of ethane and propane as the only observed side products and the selectivites were approximately the same whether CO2 was present or absent in the mixture. However, the reaction proceeds much more cleanly when CO2 is present, producing CO. The syngas product has an H2 : CO ratio of 1.5 with the fan type reactor and 0.67 with the tubular reactor. In the absence of CO2, coke is the main carbonaceous product. Under all conditions studied the fan type reactor demonstrated higher methane conversions (up to 11.9%) and selectivities to hydrogen. 相似文献
55.
Sadao Hayashi Toshihiro Hirai Sonoko Shimomichi Nobumasa Hojo 《Journal of polymer science. Part A, Polymer chemistry》1982,20(3):839-846
Polyiodide formed by complexation of poly(vinyl acetate) (PVAc) with iodine in the presence of iodide has been investigated by chemical analysis and resonance Raman spectrophotometry. When PVAc films were immersed in iodide-iodine aqueous solutions which had different ratios of iodide to iodine concentration [I?]/[I2], the complex films exhibited tremendous variations of swelling degree, despite the relatively small change in the amount of bound iodine. From a quantitative chemical analysis, the composition of polyiodide bound to PVAc was found to be 1.01 ± 0.035 in the molar ratio of iodide to iodine irrespective of the composition of the iodide-iodine aqueous solution ([I?]/[I2] = 2–500). The polyiodide formed in PVAc-iodine-iodide complex was therefore inferred to be (I3?)n. Resonance Raman spectra obtained on PVAc-iodine-iodide complexes were also identical to those of the benzamide-iodine complex, in which the polyiodide consists of (I3?)n, consistent with the result from chemical analysis. 相似文献
56.
Pimenta AM Rates B Bloch C Gomes PC Santoro MM de Lima ME Richardson M Cordeiro Mdo N 《Rapid communications in mass spectrometry : RCM》2005,19(1):31-37
Previous studies of the fractionated venom of the Brazilian armed spider Phoneutria nigriventer, obtained by gel filtration, have demonstrated the presence of a fraction PhM, a pool of small peptides (up to 2000 Da) that provoke contractions in smooth muscle of guinea pig ileum. Initial attempts to sequence these peptides were largely unsuccessful because of the low purification yield and the fact that the majority seemed to be blocked at their N-termini. In the present work, analysis of this venom fraction by mass spectrometry has revealed the existence of a highly complex mixture of peptides with molecular weights corresponding to those observed for the muscle-active peptides previously described (800-1800 Da). These peptides appear to be a family of isoforms with some particular features. The amino acid sequences of 15 isoforms have been determined by tandem mass spectrometry (MS/MS) using both electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-Q/ToFMS) and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-ToF/ToFMS). These molecules contain post-translational modifications such as proteolysis and C-terminal amidation, which combine to generate additional isoforms. All the isoforms sequenced in this study possess an N-terminal pyroglutamic acid residue. A search for sequence similarities with other peptides in databanks revealed that these peptides are structurally related to the tachykinins, a family of neuro-hormone peptides. The data obtained in this study will be essential for the subsequent steps of this research, the synthesis of these peptides and pharmacological characterization of their biological activity. 相似文献
57.
In this work, the phenomenon of double retrograde vaporization (DRV) is simulated using the Peng–Robinson equation of state with the classical mixing rules and several combining rules for the cross-energy and cross-co-volume parameters. The binary interaction parameters are set equal to zero in all cases, i.e., the calculations are entirely predictive. An interesting conclusion is that the predictions using the classical combining rules (geometric mean rule for aij and arithmetic mean rule for bij) provide the best agreement with the experimental data for all the systems tested: methane + n-butane, methane + n-pentane, ethane + limonene, and ethane + linalool. Another interesting observation is that several combining rules for bij, other than the arithmetic mean rule, predict the existence of three phases in equilibrium in a very narrow temperature range close to the critical temperature of methane in the methane + n-pentane system, even though, literature data indicates that n-hexane is the first n-alkane to present partial liquid phase immiscibility with methane. 相似文献
58.
T. Takeuchi S. Uehara T. Hayashi 《Journal of Radioanalytical and Nuclear Chemistry》1980,56(1-2):25-35
Several dead time correction methods were compared experimentally with the exact correction method and their limits were discussed.
These correction methods were applied to neutron activation analysis of a biological sample. A special electronic circuit
and an additional counting equipment were used to obtain the fractional dead time with a suficiently high frequency. 相似文献
59.
Pyruvate oxidase (E.C. 1.2.3.3.) is immobilized by adsorption on a wet PVC membrane. Glutamate-pyruvate transaminase activity (5–1600 IU l?1) in serum is determined by a pyruvate oxidase sensor consisting of the immobilized pyruvate oxidase coupled to a platinum electrode for measuring hydrogen peroxide, after an l-alanine—α-ketoglutarate reaction. The assay requires ?60 s, and has a precision of 2–3%. Endogenous pyruvate should not interfere if measurements are made > 30 s after starting the reaction. 相似文献
60.
A new application of atomic absorption is reported for the determination of pentachlorophenol. The method is based on solvent extraction into nitrobenzene of the ion-pair formed between tris(1,10-phenanthroline) iron(II) and the anion of pentachlorophenol, and the subsequent determination of the iron concentration m the extract by atomic absorption at the 2483 A iron line. 相似文献