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21.
Kovácik V Bekesová S Tvaroska I Hirsch J Chmelík J 《Journal of mass spectrometry : JMS》2004,39(12):1554-1561
Fragmentation mechanisms of electrospray ionization (ESI) mass spectrometry of aldobiuronic and pseudoaldobiuronic acid derivatives were elucidated by multistage mass spectrometric (MS(n), n = 2-5) measurements of selected ions. Characteristic under the conditions of ESI-MS analysis is the production of alkali metal (Na and K) cationized adducts. The probability the of locations of Na cations in per-O-methylated compounds was proved by quantum chemical calculations, using the Jaguar program. The most probably position of alkali metal attachment is the carboxy group of the methoxycarbonyl C-5 group of the uronic acid unit. Characteristic cleavages vary according the kind of O-derivatization. In most cases they take place on the acidic part of the dimer and at the interglycosidic oxygen atom. As a result, the criteria for the differentiation of aldobiouronic and pseudoaldobiouronic acids derivatives were elucidated. 相似文献
22.
Summary The [Rh(acac){P(OPh)3)}2] complex (Hacac = 2,4-pentadione) reacts in solution with gaseous HCN in the presence of P(OPh)3 to give [Rh{P(OPh)3}3CN]. Structural investigations of this complex including its31P n.m.r. spectra are reported. 相似文献
23.
Hubert Fadrus und Josef Malý 《Fresenius' Journal of Analytical Chemistry》1969,246(4):239-241
Zusammenfassung Bei der Wahl einer geeigneten analytischen Methode für die Nitrat- und Nitritbestimmung in konzentrierter Schwefelsäure sind die bisher bekannten Verfahren [1,3–12] wegen ihrer ungenügenden Empfindlichkeit oder wegen Schwierigkeiten bei der Probeaufbereitung auszuschließen. Wir haben daher für diesen Zweck eine einfache und zuverlässige Modifikation unserer Brucinmethode [2] ausgearbeitet, wobei eine noch größere Empfindlichkeit der Nitratbestimmung erreicht wurde. Bei geeigneter Acidität kann die Brucin-methode auch für die selektive Nitritbestimmung verwendet werden. Das hier beschriebene Verfahren ersetzt eine analoge Modifikation [5], die wegen ihrer methodischen Unrichtigkeit unzureichend ist.
Photometric determination of nitrate and nitrite in sulphuric acid using brucine
A modified brucine method is recommended as a result of a detailed study of the reaction conditions. By suitable selection of acidity and tempering period two ranges of sensitivity have been obtained for the nitrate determination (0–5 and 0.1 bis 0.5 g NO3 –-N/g H2SO4, resp.). At low concentrations of sulphuric acid nitrite may be determined in presence of nitrate by the same brucine method. Maximum errors are ±0.02 resp. ±0.05 g NO3 –-N and ±0.05 NO2 –-N.相似文献
24.
Helmut Quast Josef Christ Yvonne Görlach Wolfgang von der Saal 《Tetrahedron letters》1982,23(36):3653-3656
The 2,6-dicyano-1,5-dimethylsemibullvalene (2d) synthesized via the bicyclo[3.3.0]octanedione 7 exists as a classical ground state which is lower in energy by less than 5 kcal/mole than the homoaromatic transition of the Cope rearrangement of 2d. 相似文献
25.
Zwickl H Traxler E Staettner S Parzefall W Grasl-Kraupp B Karner J Schulte-Hermann R Gerner C 《Electrophoresis》2005,26(14):2779-2785
The secretome of cells and tissues may reflect a broad variety of pathological conditions and thus represents a rich source of biomarkers. The identity of secreted proteins, usually isolated from cell supernatants or body fluids, is hardly accessible by direct proteome analysis, because these proteins are often masked by high amounts of proteins actually not secreted by the investigated cells. Here, we present a novel method for the specific detection of proteins secreted by human tissue specimen as well as cultured cells and chose liver as a model. The method is based on the metabolic labelling of proteins synthesized during a limited incubation period. Then, the cell supernatant is filtered, precipitated, and subjected to two-dimensional gel electrophoresis. Whereas fluorography detected a large number of proteins derived from residual plasma and dead cells, the autoradiographs selectively displayed genuinely secreted proteins. We demonstrate the feasibility of this approach by means of the secretomes of the hepatocellular carcinoma-derived cell line HepG2 and human liver slices. The selective identification of cell- and tissue-specific protein secretion profiles may help to identify novel sets of biomarkers for wide clinical applications. 相似文献
26.
Josef Ischtwan Peter Schwerdtfeger Sigrid D. Peyerimhoff Michael A. Collins Trygve Helgaker Poul Jørgensen Hans Jørgen Aa. Jensen 《Theoretical chemistry accounts》1994,89(2-3):157-168
Summary The intrinsic reaction-path, reactants, transition state and products for the reaction of NH (3–)+H2 (1
g
+
) NH2 (2B1)+H (2S) involving the lowest triplet electronic state of NH3 were calculated using multi-configuration (MC) SCF methods. The calculated change of internal energy for the reaction of 11.0 kcal mol–1 agrees with the experimental value within 2 kcal mol–1. The barrier to reaction is 23.4 kcal mol–1 high. The harmonic MCSCF reaction-path potential was calculated and canonical variational transition state theory calculations of the rate constants performed over a temperature range from 400 to 2500 K. The computed rate constants are generally two orders of magnitude smaller than those of the comparable reaction of OH with H2, whereas those of the reverse reaction are by a factor of 20 larger than those of OH2 with H. 相似文献
27.
Christian Grugel Manfred Lehnig Wilhelm P. Neumann Josef Sauer 《Tetrahedron letters》1980,21(3):273-276
Tristannanes used as photochemical precursors for the synthesis of organic compounds react via triplet states followed by homolytic CSn and SnSn bond scission. 相似文献
28.
Zusammenfassung Aus potentiometrischen Daten wurde die Konstante der Entstehungsgeschwindigkeit des Zinktartrates bei 18° berechnet. Ihr durchschnittlicher Wert beträgt 1,3·102 mol·min–1 und der Wert der Zerfallsgeschwindigkeitskonstante beläuft sich im Durchschnitt auf 7,5·10–2 mol·min–1. 相似文献
29.
Gaston Bocaz-BeneventiRosa Latorre Marta FarkováJosef Havel 《Analytica chimica acta》2002,452(1):47-63
The application of the combination of experimental design (ED) and artificial neural networks (ANNs) for the quantification of overlapped peaks in capillary zone electrophoresis is described. When the total separation cannot be achieved by separation techniques, the use of ED-ANN can be a suitable approach. The unstability of EOF causes peak shift that has to be corrected in order to apply ED-ANN methods. In this work, normalization procedure of electropherograms with consequent application of ANNs for quantification purpose was developed. Both, spectra and electropherograms can be used as multivariate data. In general, both kinds of data were found to be suitable for unresolved peaks quantification by ED-ANN approach. 相似文献
30.
Josef Edinger Heinz Falk Norbert Müller 《Monatshefte für Chemie / Chemical Monthly》1984,115(6-7):837-852
The diastereomeric 2,3-Dihydrobilatrienes-abc derivatives (4Z, 9Z, 15Z)-7 and (4Z, 9Z, 15E)-7 bearing a cholesterylacetate moiety in position 3 of the chromophore are prepared. The reaction sequence contains an isomerisation step providing quantitative enantioselective formation of the chiral center in position 3. Configurations and conformations of the diastereomers are elucidated using1H- and13C-NMR spectra, NOE-difference spectra, 2D-NMR experiments (NOESY) and arguments from UV-VIS and CD data. It is concluded that the hydrophobic interactions between chromophore and cholesteryl-fragment yield a compact conformation where the two substructures are in close contact with each other. On the other hand these interactions seem to be too weak to induce significant changes in the chemistry, absorption spectra and conformational characterics of the bile pigment chromophore. Therefore hydrophobic interactions between chromophor and apolar amino acid residues of the protein in phytochrome should be of minor relevance for determining spectroscopic shifts. 相似文献