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1.
Wolfgang Oppolzer Mark Kurth Daniel Reichlin Frank Moffatt 《Tetrahedron letters》1981,22(27):2545-2548
The chiral induction in the Diels-Alder addition → , assessed reliably by 19F-NMR-spectroscopy of the endo-esters , varied between 47 - 93% in favor of the 2-(R)-adducts depending on the auxiliary chiral group and the Lewis-acid catalyst. 相似文献
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Summary The applicability of capillary electrochromatography to the automated analysis of pesticides and phthalate esters that are
of environmental concern was assessed. Reversed phase packing materials were compared. Column to column and run to run reproducibility
was established. Peak height with an internal standard gave the best reproducibility. Faster analysis than alternative HPLC
methods was demonstrated for a mixture of the insecticide pirimicarb and related pyrimidines. The relationship between the
concentration of an analyte in a sample and at the detector was determined by the use of radio-labelled14C-pirimicarb. The volume fraction of the liquid zone was 0.64. The possibility of electroosmosis through the pores is discussed
with reference to the Rice-Whitehead model for electroosmotic flow in a capillary. A new parameter, the effective pore size
is used in equations for electroosmosis through porous packings. 相似文献
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An improved capillary electrophoresis assay for histamine in crude extracts was developed and used to determine histamine levels in a selection of tomato fruits and pastes. Performance in terms of reproducibility and sensitivity was optimized by use of a high sensitivity detector flow cell, sodium hydroxide rinses, and a voltage gradient. The method was linear down to 0.2 microgram/mL (signal-to-noise ratio = 4:1), which was below the endogenous level in all samples. 相似文献
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An insecticide, pirimicarb, and a fungicide, azoxystrobin, were analyzed by capillary electrochromatography. Nine environmental matrices derived from soil, plant and animal extracts were used. After a series of 311 consecutive injections with no washing between injections, retention times increased by ca. 0.5 min. The use of exaggerated application rates for metabolism studies enabled the detection of xenobiotic pesticide degradates by UV absorbance. A 1.2 mm path length, high-sensitivity flow cell gave a gain in sensitivity; however, a further increase in sensitivity of at least two orders of magnitude is required for pesticide residue analysis. Analyte stacking using large volume injections of aqueous samples led to a large increase in retention times. 相似文献
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Motivated by Khovanov homology and relations between the Jones polynomial and graph polynomials, we construct a homology theory for embedded graphs from which the chromatic polynomial can be recovered as the Euler characteristic. For plane graphs, we show that our chromatic homology can be recovered from the Khovanov homology of an associated link. We apply this connection with Khovanov homology to show that the torsion-free part of our chromatic homology is independent of the choice of planar embedding of a graph. We extend our construction and categorify the Bollobás-Riordan polynomial (a generalization of the Tutte polynomial to embedded graphs). We prove that both our chromatic homology and the Khovanov homology of an associated link can be recovered from this categorification. 相似文献