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1.
S. Wohlfahrt M. Fischer M. Saraji-Bozorgzad G. Matuschek T. Streibel E. Post T. Denner R. Zimmermann 《Analytical and bioanalytical chemistry》2013,405(22):7107-7116
Comprehensive multi-dimensional hyphenation of a thermogravimetry device (i.e. a thermobalance) to gas chromatography and single photon ionization–time-of-flight mass spectrometry (TG–GC×SPI–MS) has been used to investigate two crude oil samples of different geographical origin. The source of the applied vacuum ultraviolet radiation is an electron beam pumped rare gas excimer lamp (EBEL). The soft photoionization favors the formation of molecular ions. Introduction of a fast, rapidly modulated gas chromatographic separation step in comparison with solely TG–SPI–MS enables strongly enhanced detection especially with such highly complex organic matrices as crude oil. In contrast with former TG–SPI–MS measurements, separation and identification of overlying substances is possible because of different GC retention times. The specific contribution of isobaric compounds to one mass signal is determined for alkanes, naphthalenes, alkylated benzenes, and other compounds. Figure
Specific characteristics of a two-dimensional TG–GC×SPI–MS contour plot obtained from Turkish crude oil. The complete m/z and TG temperature ranges are displayed in a. The magnified region from m/z 50–250 and 140–170 °C reveals the “pixilated” structure (b). Parts c and d reveal the system’s ability to investigate compounds in a broad m/z range with limitations for very-high and very-low boiling compounds as shown for m/z 260 and m/z 70, respectively 相似文献
2.
Emission of volatile sesquiterpenes and monoterpenes in grapevine genotypes following Plasmopara viticola inoculation in vitro
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Alberto Algarra Alarcon Valentina Lazazzara Luca Cappellin Pier Luigi Bianchedi Rainer Schuhmacher Georg Wohlfahrt Ilaria Pertot Franco Biasioli Michele Perazzolli 《Journal of mass spectrometry : JMS》2015,50(8):1013-1022
The grapevine (Vitis vinifera) is one of the most widely cultivated fruit crops globally, and one of its most important diseases in terms of economic losses is downy mildew, caused by Plasmopara viticola. Several wild Vitis species have been found to be resistant to this pathogen and have been used in breeding programs to introduce resistance traits to susceptible cultivars. Plant defense is based on different mechanisms, and volatile organic compounds (VOCs) play a major role in the response to insects and pathogens. Although grapevine resistance mechanisms and the production of secondary metabolites have been widely characterized in resistant genotypes, the emission of VOCs has not yet been investigated following P. viticola inoculation. A Proton Transfer Reaction‐Time of Flight‐Mass Spectrometer (PTR‐ToF‐MS) was used to analyze the VOCs emitted by in vitro‐grown plants of grapevine genotypes with different levels of resistance. Downy mildew inoculation significantly increased the emission of monoterpenes and sesquiterpenes by the resistant SO4 and Kober 5BB genotypes, but not by the susceptible V. vinifera Pinot noir. Volatile terpenes were implicated in plant defense responses against pathogens, suggesting that they could play a major role in the resistance against downy mildew by direct toxicity or by inducing grapevine resistance. The grapevine genotypes differed in terms of the VOC emission pattern of both inoculated and uninoculated plants, indicating that PTR‐ToF‐MS could be used to screen hybrids with different levels of downy mildew resistance. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
Michael Meyer Gerd Wohlfahrt Jörg Knäblein Dietmar Schomburg 《Journal of computer-aided molecular design》1998,12(5):425-440
The complex structure of glucose oxidase (GOX) with the substrate glucose was determined using a docking algorithm and subsequent molecular dynamics simulations. Semiempirical quantum chemical calculations were used to investigate the role of the enzyme and FAD co-enzyme in the catalytic oxidation of glucose. On the basis of a small active site model, substrate binding residues were determined and heats of formation were computed for the enzyme substrate complex and different potential products of the reductive half reaction. The influence of the protein environment on the active site model was estimated with a point charge model using a mixed QM/MM method. Solvent effects were estimated with a continuum model. Possible modes of action are presented in relation to experimental data and discussed with respect to related enzymes. The calculations indicate that the redox reaction of GOX differs from the corresponding reaction of free flavins as a consequence of the protein environment. One of the active site histidines is involved in substrate binding and stabilization of potential intermediates, whereas the second histidine is a proton acceptor. The former one, being conserved in a series of oxidoreductases, is also involved in the stabilization of a C4a-hydroperoxy dihydroflavin in the course of the oxidative half reaction. 相似文献
4.
K. Wohlfahrt 《Archiv der Mathematik》1977,29(1):455-457
Ohne Zusammenfassung 相似文献
5.
We report the measurement of the strong interaction shifts and widths of the 3d → 2p transitions in pionic 40,42,43,44,48Ca and 46,48,50Ti. Using these new data in combination with earlier low-Z pionic data (6 ≦ Z ≦ 16), we have studied, in a purely phenomenological way, the pion-nuclear optical potential. Employing nuclear-structure information from Hartree-Fock calculations and measured charge densities, we have fitted the pion-nuclear potential parameters to the pionic atom data. The effect of adding an isovector dependence to the s- and p-wave two-nucleon terms has been investigated. We have also explored the sensitivity of these data to the value of the Lorentz-Lorenz parameter ξ. A small but definite sensitivity to the latter parameter has been observed with the best fit value of ξ being significantly greater than 1. We have used the phenomenological potentials to determine the neutron radii of the Ca and Ti isotopes and, in fact, find reasonable agreement with Hartree-Fock predictions and with the results of other hadronic probes. 相似文献
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7.
To the core: An efficient total synthesis of (+)-awajanomycin was achieved starting with an asymmetric allylboration of a vic-tricarbonyl compound (see scheme; TES=triethylsilyl). A stereoselective alkene dihydroxylation followed by a differentiation of diastereotopic ester groups and a subsequent lactamization gave the bicyclic core structure. 相似文献
8.
Y. Tanaka D.B. Laubacher R.M. Steffen E.B. Shera H.D. Wohlfahrt M.V. Hoehn 《Physics letters. [Part B]》1982,108(1):8-10
The ground-state quadrupole moments of 155Gd and 157Gd were determined by measuring the quadrupole hyperfine-splitting energies of the M X-rays of muonic Gd atoms. The results are for 157Gd. 相似文献
9.
Klaus Wohlfahrt 《Numerische Mathematik》1962,4(1):393-397
Ohne Zusammenfassung
Hans Petersson zum 60. Geburtstag gewidmet. 相似文献
10.
Jasper Hölzer Michael Fischer Thomas Gröger Thorsten Streibel Mohammad Saraji-Bozorgzad Sebastian Wohlfahrt Georg Matuschek Ralf Zimmermann 《Journal of Thermal Analysis and Calorimetry》2014,116(3):1471-1479
Thermal processes are part of many industrial treatments; therefore, it is of great interest to gain more insight of these processes. Evolved gas analysis (EGA) is the most straightforward way to make chemical reactions in thermal processes accessible for on-line investigations. The sample matrix of evolved off gas e.g., from coffee roasting is a permanently changing and complex mixture of a multitude of substances that have to be analyzed simultaneously for real on-line investigations without any sample trapping or separation device. Therefore, a measurement system as an ion trap mass spectrometer (ITMS) with soft ionization is required with its tandem mass spectrometry capability to provide distinct substance identification unperturbed by the remaining matrix. The presented novel system setup is based on a thermogravimetric device (TG) to simulate the thermal treatment as in industrial processes combined with an ITMS with soft single photon ionization (SPI) to achieve the required substance information. Hence it is possible to gain single mass spectrometric information of expected substances for process control. More comprehensive than that are the two-dimensional MS data which are required for research and process development purposes though. The conducted analyses show that this novel setup is able to provide distinct substance identification in evolved gas of roast and ground coffee powder. To our knowledge, this is the first TG–SPI–ITMS setup with successful application in verifying the identity of different mass traces within a single run. 相似文献