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61.
Omar Deeb Prof. Monika Leibscher Dr. Jörn Manz Prof. Wulf von Muellern Tamar Seideman Prof. 《Chemphyschem》2007,8(2):322-328
We propose an approach for separating nuclear spin isomers with coherent light and illustrate it by numerical calculations using fulvene as a model system. The scheme employs the equivalence of torsion and interchange of equivalent H-atoms in a class of molecules of which fulvene is a simple example. The exchange symmetry couples with the rotational symmetry to produce a spatial distinction between the two photo-excited nuclear spin isomers, and wavepacket interferometry is applied to separate the species. 相似文献
62.
Summary A fully integrated chromatographic system was developed for the determination of leukotrienes in biological samples using
photodiode-array detection (PDAD), which eliminates time consuming manual sample handling steps. A special solid phase extraction,
(SPE) methodology for leucotriene metabolite stability was developed which increased the recoveries and eliminates the contamination
risk of biological samples. The inherent instability (autooxidation) of many of the leukotriene mediators, and the adsorption
effects onto exposed surfaces in vials and in the chromatographic system were found to be very important parameters to control
in order to circumvent high loss of sample analytes. By binding the cell supernatants to the functionalities of the SPE support
stabilised these mediators. Cell culture samples were eluted through a disposable C18 SPE column. The SPE columns were allowed to thaw and deposited in an automated sample handling unit (ASPEC XL). Desorption
of the analytes was followed by a second on-line SPE step, to eliminate remaining interfering matrix compounds. Typical recoveries
when stored at −70°C were in-between 55–97% except for (LTE4) which was found to be around 40% after 72 days of storage. Seven reversed-phase packings were studied. Selectivity factors,
as well as the separation efficiencies, were found to differ for the various C18 bonded silica stationary phases. This integrated on-line column liquid chromatographic system was applied to the determination
of leukotriene B4, leukotriene C4, leukotriene D4, leukotriene and E4 in human cell extracts using prostaglandin B2 as the internal standard. More than 1500 biological samples were analysed. Some validation data are presented for unattended
operations. 相似文献
63.
64.
Compton scattering normalization method is described for the analysis of uranium bearing ore respect to the usage of K X-rays of uranium. Minimum backscatter energy is obtained at a scatter angle of 180° with fixed point source geometry and collimation in appropriate conclusions. By normalizing the intensities of uranium K-lines to the Compton profile in the measured spectra, the results do not depend on several measuring parameters such as primary radiation intensity, matrix, composition, mass of the sample and measuring time. The method presented in this study indicates the convenience of uranium K-lines analysis for thick targets with an adequate measuring geometry. 相似文献
65.
Hofmann C Boll R Heitmann B Hauser G Dürr C Frerich A Weitnauer G Glaser SJ Bechthold A 《Chemistry & biology》2005,12(10):1137-1143
The oligosaccharide antibiotic avilamycin A is composed of a polyketide-derived dichloroisoeverninic acid moiety attached to a heptasaccharide chain consisting of six hexoses and one unusual pentose moiety. We describe the generation of mutant strains of the avilamycin producer defective in different sugar biosynthetic genes. Inactivation of two genes (aviD and aviE2) resulted in the breakdown of the avilamycin biosynthesis. In contrast, avilamycin production was not influenced in an aviP mutant. Inactivation of aviGT4 resulted in a mutant that accumulated a novel avilamycin derivative lacking the terminal eurekanate residue. Finally, AviE2 was expressed in Escherichia coli and the gene product was characterized biochemically. AviE2 was shown to convert UDP-D-glucuronic acid to UDP-D-xylose, indicating that the pentose residue of avilamycin A is derived from D-glucose and not from D-ribose. Here we report a UDP-D-glucuronic acid decarboxylase in actinomycetes. 相似文献
66.
Süleyman Özçeli Hakan Sezgin 《Journal of inclusion phenomena and macrocyclic chemistry》2003,45(3-4):185-190
New Hofmann-diaminohexane(dahxn)-type clathrates of the form M(1,6-dahxn)Ni(CN)4.G (M = Co, Ni or Cd; G = chlorobenzene, 1,2-, 1,3 or 1,4-dichlorobenzene) were prepared inpowder form and their infrared spectra are reported. The spectral data suggest that these compounds are similar in structure to those of the Hofmann-diam-type clathrates. Their structure consists of planar polymeric layers, {M–Ni(CN)4}, formedfrom Ni(CN)4 anions coordinated to the bridging 1,6-diaminohexane molecules bound directly to the metal (M). The M atoms are bound to four N atoms of the CN ions and, the Ni atoms are surrounded by four C atoms of the CN groups in a square-planar layer. 相似文献
67.
Remedios González-Luque Manuela Merchán Piotr Borowski Björn O. Roos 《Theoretical chemistry accounts》1993,86(6):467-476
Summary Multiconfigurational electron correlation methods have been analyzed in order to theoretically compute the electron affinity (EA) of ozone. The near-degeneracy correlation effects, which are so important in O3 and O
3
–
, have been described using complete active space (CAS) SCF wave functions. Remaining dynamic correlation effects are computed using second-order perturbation theory (the CASPT2 method). The best calculated adiabatic value (including zero-point energy corrections), 2.19 eV, is about 0.09 eV larger than the experimental value. Comparative studies using size-consistent coupled pair functional approaches (CPF and ACPF) have also been performed. The harmonic frequencies in O
3
–
have been determined to be: 1=992, 2=572, and 3=879 cm–1, which gives a zero-point energy of 0.151 eV. 相似文献
68.
Labeling conditions of synkavit (2-methyl-1,4-naphthoquinol disodium phosphate) with iodine-125 have been studied. In this study, labeling temperature, reaction time, successive using of iodogen coated tubes, iodogen amount and synkavit concentrations have been determined to get optimum conditions for maximum labeling. Final results showed that when the labeling temperature, reaction time, synkavit concentration, and iodogen amount were, at room temperature, 15 min (in the case of successive using of three iodogen coated tubes), 2 mg ml–1 and 5 mg, respectively; labeling yield was 90% and specific activities of the order of 555 GBq mmol–1 (15 Ci mmol–1) have been obtained. 相似文献
69.
Fluoride ions and, in about 0.005M concentration, tungstate ions form gelatinous precipitates, poorly soluble in water, with calcium ions. The radiometric determinations
of the above ions are based on these reactions. Accurate radiometric determination can be carried out only if the gelatinous
precipitate formed during titration can be properly separated from the solution. It has been found that in the case of fluoride
ions the application of crystalline, easily filtrable Ca(COO)2·H2O or CaCO3, and in the case of tungstate ions the application of CaWO4 precipitate improves the filtration properties of45CaF2 and45CaWO4, respectively, formed during titration, whereby the radiometric determinations of the above ions become possible. Titrations
were carried out with 0.05M and 0.005M CaCl2 solutions, labelled with45Ca. 相似文献
70.
Novel prostaglandin F(2)(alpha) derivatives, functionalized at C13 and C14, have been prepared. 17-Phenyl-18,19,20-trinorprostaglandin F(2)(alpha) isopropyl ester [(15S)-1] and its epimer [(15R)-1] were stereoselectively epoxidized, using Sharpless conditions, to produce each of the four diastereomeric epoxides (15S)-2, (15S)-3, (15R)-2, and (15R)-3. Treatment of the four epoxides with LiOH stereospecifically-produced the pentahydroxy substituted analogues 12 and 13. Alternatively, epoxides 2 and 3were allowed to react with thiophenolate ion. The attack of the sulfur nucleophile on the epoxide occurred at either C13 or C14 depending on the stereochemistry of the epoxide and of C15. 相似文献