排序方式: 共有60条查询结果,搜索用时 15 毫秒
51.
Arinir U Klein W Rohde G Stemmler S Epplen JT Schultze-Werninghaus G 《Electrophoresis》2005,26(15):2888-2891
Airway inflammation is the main pathophysiological feature of patients with chronic obstructive pulmonary disease (COPD). Interleukin-8 (IL-8) is a potent chemoattractant for neutrophils and eosinophils. Increased IL-8 levels were observed in bronchoalveolar lavage (BAL) and induced sputum in patients with COPD. To evaluate the role of the IL-8 gene, we genotyped blood samples of 122 COPD-patients and 385 healthy controls for a known polymorphism in the promoter region (-251 A/T) of the IL-8 gene. Additionally, we screened the coding region for further polymorphisms by SSCP analyses. Comparison of the allele and genotype frequencies among each group revealed no significant differences between patients and controls. Although IL-8 plays an important role in the chemotaxis of inflammatory cells, the polymorphisms investigated here do not seem to be involved in the genetic predisposition to COPD. 相似文献
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E. A. Stemmler J. L. Diener J. A. Swift 《Journal of the American Society for Mass Spectrometry》1994,5(11):990-1000
The reactions of O 2 ?. with alkyl and aryl esters of benzenedicarboxylic acids have been studied under negative-ion chemical ionization (NICI) conditions via a conventional chemical ionization source. Reaction mechanisms have been elucidated by using ion isolation techniques on a Fourier transform ion cyclotron resonance mass spectrometer. In addition, 18O 2 ?. has been used as the reagent and the products of competitive reactions that involve the mixed esters of benzenedicarboxylic acids have been studied. O 2 ?. reactions with the alkyl esters of 1,2- and l,3-benzenedicarboxylic acids are attributed to SN2 displacement at the O-alkyl carbon. The spectra of mixed alkyl esters show that O 2 ?. attack is reduced at sterically hindered alkyl groups. In contrast with the spectra of 1,2- and l,3-benzenedicarboxylic acids, the spectra of 1,4-benzenedicarboxylic acids are dominated by M?. production. Reactions of O 2 ?. with phenyl benzoates and the aryl esters of benzenedicarboxylic acids proceed via addition-elimination pathways. Experiments with mixed alkyl-aryl benzenedicarboxylic acid esters show that the addition-elimination reaction pathway is preferred over O-alkyl SN2 displacement. The O2/ Ar-NICI mass spectra show features that can be used to distinguish 1,2-, 1,3-, and 1/4-benzenedicarboxylic acid esters. Molecular and fragment ions provide structural information complementary to that generated under electron ionization and chemical ionization conditions. 相似文献
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Polycyclic aromatic hydrocarbons (PAH) undergo wall-catalyzed oxidation reactions, in conjunction with electron-and ion-molecule reactions, when oxygen is present in the chemical ionization source. Under conditions that promote these wall-catalyzed oxidation reactions (addition of oxygen, elevated ion source temperature) oxidized products are easily detected by measurement of the negative ion chemical ionization (NICI) mass spectra. The NICI mass spectra are dominated by ions that result from electron-capture ionization of oxidation products such as ketones, quinones and anhydrides. In this study the NICI mass spectra of 30 PAH and 46 methyl-substituted PAH were measured. These spectra can be used to differentiate certain isomeric PAH based upon differences in molecular structure. Of particular interest are ions that appear in the spectra of methyl-substituted PAH, which can provide information regarding the position of methyl substituents. 相似文献
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Molecular beam depletion spectroscopy has been employed to study the dissociation of small methanol clusters in the spectral region between 1000 and 1100 cm?1 which covers thev 8 CO stretch (1033.5 cm?1) and thev 7 CH3 rock (1074.5 cm?1) monomer vibrations. Size selection has been achieved by dispersing the (CH3OH) n cluster beam by a secondary He beam. Aside from the recently published CH3OH dimer absorption bands at 1026.5 and 1051.6 cm?1 which are assigned to the excitation of the CO stretching vibrations in the non-equivalent subunits of the hydrogen-bonded complex, a previously unobserved band was found at 1071.3 cm?1. This absorption band is attributed to the excitation of the CH3 rocking vibration in the dimer. It appears that this transition which is very weak in the free methanol monomer receives substantial oscillator strength due to the intermolecular interaction in the complex. A splitting of this band could not be observed. The trimer and tetramer spectra feature single peaks for the CO stretching vibration being centered at 1042.2 cm?1 and 1044.0 cm?1, respectively. This observation is consistent with the cyclic structures of these species. The trimer and tetramer rocking vibrations are observed near 1060.5 cm?1 but cannot be localized exactly, due to a gap in the CO2 laser tuning range. 相似文献
55.
B. Arbogast W. L. Budde M. Deinzer R. C. Dougherty J. Eichelberger R. D. Foltz C. C. Grimm R. A. Hites C. Sakashita E. Stemmler 《Journal of mass spectrometry : JMS》1990,25(4):191-196
Data are presented on the limits of detection for a series of nine compounds in negative chemical ionization (NCI) mass spectra obtained in five different mass spectrometers: Finnigan 4000 with a 4500 ion source, Kratos MS-80, Hewlett-Packard 5985 and two Finnigan 4500s. The nine compounds undergo either resonance capture or dissociative capture of an electron at optimum energies ranging from 0.0 to 1.1 eV. The limits of detection generally increased with increasing optimum electron energy. The limit of detection as a function of optimum electron capture energy is expected to provide information about the electron energy distribution in the ion sources. The data showed scatter within and between instruments. The scatter is believed to be due primarily to reactions with low levels of adventitious gases such as oxygen in the ion source. The data also suggested wide variations in electron energies between the instruments. The variation in the electron energy distribution is thought to have been caused by variations in the ion optical fields within the instruments. These results suggest that the requirements for reproducibility in NCI mass spectra at the limit of detection are rigorous control of trace gases in the ion source, control of the electric fields within the source including ion optical fields that penetrate the source aperture control of pressure, temperature and other factors that influence NCI mass spectra. 相似文献
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Hakemian AS Tinberg CE Kondapalli KC Telser J Hoffman BM Stemmler TL Rosenzweig AC 《Journal of the American Chemical Society》2005,127(49):17142-17143
The oxidation state of copper bound to methanobactin, a small siderophore-like molecule from the methanotroph Methylosinus trichosporium OB3b, was investigated. Purified methanobactin loaded with Cu(II) exhibits a weak EPR signal probably due to adventitious Cu(II). The EPR signal intensity increases significantly upon addition of the strong oxidant nitric acid. Features of the X-ray absorption near edge spectrum, including a 1s --> 4p transition at 8985 eV, further indicate the presence of Cu(I). EXAFS data were best fit using a multiple scattering model generated from previously reported crystallographic parameters. These results establish definitively that M. trichosporium OB3b methanobactin binds Cu(I) and suggest that methanobactin itself reduces Cu(II) to Cu(I). 相似文献
59.
Joël Wellauer Dragan Miladinov Thomas Buchholz Dr. Jan Schütz Dr. René T. Stemmler Dr. Jonathan A. Medlock Dr. Werner Bonrath Prof. Dr. Christof Sparr 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(38):9748-9752
A mild photocatalytic phenol oxygenation enabled by a continuous-flow photoreactor using visible light and pressurized air is described herein. Products for wide-ranging applications, including the synthesis of vitamins, were obtained in high yields by precisely controlling principal process parameters. The reactor design permits low organophotocatalyst loadings to generate singlet oxygen. It is anticipated that the efficient aerobic phenol oxygenation to benzoquinones and p-quinols contributes to sustainable synthesis. 相似文献
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