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排序方式: 共有320条查询结果,搜索用时 31 毫秒
1.
2.
A p68 reductase participating in the asymmetric reduction of the C–C double bond of 2-substituted 2-butenolides was isolated from Marchantia polymorpha. The enzyme reduced 2-substituted 2-butenolides to give (R)-butanolides, and the reduction of citraconic anhydride afforded (R)-methylsuccinic anhydride. 相似文献
3.
High-performance liquid chromatographic conditions are reported for the electrochemical detection (ED) of Gentian Violet, its demethylated metabolites, Leucogentian Violet and Methylene Blue. Gentian Violet, its demethylated metabolites and Leucogentian Violet were separated within 14 min on a cyano column eluted isocratically with methanol-buffer (60:40) as the mobile phase. ED responses for Gentian Violet, Leucogentian Violet and Methylene Blue were linear over the ranges 0.54-6.75, 0.50-25.2, and 5.7-285 ng, respectively. Under these conditions, the compounds were eluted in the following order: Leucogentian Violet, N"-2-tetra-methylparaosaniline chloride, N'-1-tetramethylpararosaniline chloride, pentamethylpararosaniline chloride and Gentian Violet. Methylene Blue and Gentian Violet had essentially the same retention time under these parameters. The detection limit for Gentian Violet, its demethylated metabolites and Leucogentian Violet was determined to be 0.1 pmol. A detection limit of 3 pmol was established for Methylene Blue. Detector response, elution, separation, linearity and sensitivity of detection are discussed. 相似文献
4.
A new method involving efficient, widely applicable, and highly selective alpha-chlorination of simple silyl enolate with Lewis acid and an alpha,alpha-dichloro-1,3-dicarbonyl controller unit was reported. Diastereoselectivity and enantioselectivity of the reaction were investigated. High reactivity and selectivity were achieved by using alpha,alpha-dichlorinated malonic ester. 相似文献
5.
Spin preference and S-T gaps of localized 1,3-diradicals were studied by an orbital phase theory and theoretical calculations. The orbital phase theory was applied to rationalize thermodynamic and kinetic stabilities of diradicals. We theoretically designed some singlet localized 1,3-diradicals, substituted trimethylenes, which are more stable than the lowest triplets. Some diradicals with the four-membered rings, 2,4-disilacyclobutane-1,3-diyls, were designed and shown to have singlet ground states and to be more stable than the sigma-bonded isomers, 2,4-disilabicyclo[1.1.0]butanes. The ab initio calculations supported predictions of the stable carbon-centered localized singlet 1,3-diradicals. 相似文献
6.
A capillary electrophoretic method for the simultaneous determination of sulfamethoxazole and trimethoprim in plasma was developed. Sulfamethoxazole and trimethoprim extracted from human plasma with ethyl acetate were analyzed at 20 kV and 25 degrees C using 15 mm phosphate buffer (pH 6.2) as the electrolyte. The detection was by UV at 220 nm. The run time was 8.0 min and the limit of quantification was 10.00 microg/mL for sulfamethoxazole and 2.00 microg/mL for trimethoprim. The recovery was >99% for both compounds. This method enabled the detection of sulfamethoxazole and trimethoprim in plasma of patients after oral ingestion of their combined formulation. The present simple and rapid method is applicable to drug monitoring in immunocompromised patients who are taking the combined formulation of these compounds for the treatment or prophylaxis of Pneumocystis carinii pneumonia. 相似文献
7.
N. Takahashi T. Shimoda Y. Fujita T. Itahashi H. Miyatake 《Zeitschrift für Physik B Condensed Matter》1995,98(3):347-351
Short-lived ions12B (beta-radioactive, T1/2=20.3 ms) sustaining nuclear spin polarization were introduced into superfluid helium at 1.7 K. It was found that the12B ions were transported as charged entities under a static electric field and that the nuclear polarization was maintained throughout the lifetime of12B nuclei. Polarization of12B was determined through beta-NMR method. Snowball, a singly charged microcluster of helium atoms formed around an impurity ion, is responsible for the behaviour and thus constitutes a suitable environment for preserving nuclear polarization of the core ions12B. In a separate experiment snowballs were produced by implanting8Li (T1/2=830 ms) into liquid helium and detected by means of alpha particles from the core ions to guarantee that the snowballs survive longer than the lifetime of12B. 相似文献
8.
Masaki Takeguchi Kazutaka Mitsuishi Miyoko Tanaka Kazuo Furuya 《Microscopy and microanalysis》2004,10(1):134-138
About 1 monolayer of palladium was deposited onto a silicon (111) 7 x 7 surface at a temperature of about 550 K inside an ultrahigh vacuum transmission electron microscope, resulting in formation of Pd2Si nanoislands and a 1 x 1 surface layer. Pd clusters created from an excess of Pd atoms on the 1 x 1 surface layer were directly observed by in situ plan view high-resolution transmission electron microscopy. When an objective aperture was introduced so that electron diffractions less than 0.20 nm were filtered out, the lattice structure of the 1 x 1 surface with 0.33 nm spacing and the Pd clusters with a trimer shape were visualized. It was found that image contrast of the 1 x 1 lattice on the specific height terraces disappeared, and thereby an atomic structure of the Pd clusters was clearly observed. The appearance and disappearance of the 1 x 1 lattice was explained by the effect of the kinematical diffraction. It was identified that a Pd cluster was composed of three Pd atoms without a centered Si atom, which is consistent with the model proposed previously. The feature of the Pd clusters stuck at the surface step was also described. 相似文献
9.
Tsuda M Izui N Shimbo K Sato M Fukushi E Kawabata J Katsumata K Horiguchi T Kobayashi J 《The Journal of organic chemistry》2003,68(13):5339-5345
A novel cytotoxic 16-membered macrodiolide, amphidinolide X (1), has been isolated from a marine dinoflagellate Amphidinium sp. (strain Y-42). The gross structure of 1 was elucidated on the basis of spectroscopic data including one-bond and long-range (13)C-(13)C correlations. The relative and absolute stereochemistries were determined by combined analyses of NOESY data and (1)H-(1)H and (1)H-(13)C coupling constants of 1 and NMR data of the degradation products. Amphidinolide X (1) is the first macrodiolide consisting of polyketide-derived diacid and diol units from natural sources. The biosynthetic origins of 1 were investigated by means of feeding experiments with (13)C-labeled acetates. 相似文献
10.
Joonho Lee Wataru Shimoda Toshihiro Tanaka 《Monatshefte für Chemie / Chemical Monthly》2005,40(10):1829-1834
Temperature dependence of the surface tension of liquid Sn–Ag and Sn–Cu base lead-free solder alloys and oxygen partial pressure
dependence of liquid Sn–Ag alloy were evaluated using the experimental data obtained, respectively, by the constrained drop
method and the sessile drop method in the previous studies [1, 2]. The temperature dependences of the surface tension have
maximum positive values when the mol fraction of Ag and Cu is about 0.7, while those for pure liquid Sn, Ag, and Cu have negative
values. The calculated values based on Butler’s equations were found to be in reasonable agreement with those of the experimental data. The oxygen partial pressure dependences
of the surface tension of liquid Sn–Ag alloys at 1253 K have a minimum value when the mol fraction of Ag is about 0.9 and
the oxygen partial pressure is less than about 10−13 atm. From this, it is considered that the oxygen adsorption increased by adding Ag to Sn when the mol fraction of Ag is less
than 0.9. 相似文献