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41.
J. Maier C. S. Kischkel M. Baumann 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,21(2):145-151
Using laser induced fluorescence spectroscopy the hyperfine structure of the even parity levels 4f 146s6d 3 D 1, 4f 14 6s8s 3 S 1 and 4f 13 5d6s6p (7/2, 5/2)J=1,2,3 as well as of the odd parity level 4f 14 6s6p 3 P 2 in neutral ytterbium has been investigated. The isotope shift of the transitions 4f 146s6p 3 P 0 → 4f 14 6s6p 3 D 1 and 4f 14 6s6p 3 P 2 → 4f 14 6s8s 3 S 1, 4f 13 5d6s6p (7/2, 5/2)J=1,2,3 could be measured with high accuracy. The results for the 4f 14 6s6p 3 D 1 level show a considerable influence of second order effects of the hyperfine interaction. The isotope shifts of the 4f 14 6s8s 3 S 1 and 4f 13 5d6s6p (7/2, 5/2)J=1 levels indicate a possible configuration mixing for these levels. 相似文献
42.
Summary In the manufacture of aero-engine components, auxiliary materials are used which impair mechanical properties if they are not completely removed afterwards. Taking the manufacture of turbine blades and vanes as an example, this investigation shows how the inclusion of an analysis stage in the fully-automatic production cycle makes it possible to monitor the thoroughness of the cleaning process. As indicator, the element Bi is used; the matrix consists of concentrated nitric acid with a high nickel content. Because of the imposition of a limiting value, it must be possible to determine differences in the Bi-content of 20 g/l. The main part of the paper concerns the selection of the most optimum process. The results using two types of AAS coupled with hydride generation are presented. The success of the complete system is illustrated by the summarized results. 相似文献
43.
44.
Mass spectrometry as an analytical tool to study protein folding and structure by hydrogen/deuterium exchange is a relatively new approach. In this study, site-specific amide deuterium content was measured in oxidized and reduced E. coli thioredoxins by using the b(n) ions in electrospray ionization CID MS/MS experiments after 20-s incubation in D(2)O phosphate-buffered solution (pH 5.7). The deuterium levels correlated well with reported NMR-determined H/D exchange rate constants. The deuterium measured by y(n) ions, however, showed much less reliable correlation with rate exchange data. In general, residues in alpha helices and beta sheets, when measured by b(n) ions, showed low incorporation of deuterium while loops and turns had high deuterium levels. Most amide sites in the two protein forms showed similar deuterium levels consistent with the expected similarity of their structures, but there were some differences. The turn consisting of residues 18-22 in particular showed more variability in deuterium content consistent with reported structural differences in the two forms. The deuterium uptake by thioredoxins alkylated at Cys-32 by S-(2-chloroethyl)glutathione and S-(2-chloroethyl)cysteine, in peptides 1-24 and 45-58, was similar to that observed for oxidized and reduced thioredoxins, but several residues, particularly Leu-53 and Thr-54, showed slightly elevated deuterium levels, suggesting that structural changes had occurred from alkylation of the protein at Cys-32. It is concluded that b(n) ions are reliable for determining the extent of site-specific amide hydrogen isotope exchange and that mass spectrometry is useful as a complementary technique to NMR and other analytical methods for probing regional structural characteristics of proteins. 相似文献
45.
The clean-up presented here includes a free flow field step electrophoresis followed by ultrafiltration. Thus, organic acids can be separated from non-acidic and high-molecular compounds in roasted and instant coffee. The acids are identified by gas chromatography/mass spectrometry after freeze-drying and trimethylsilylation. With the method presented, 31 acids could be identified in commercial roasted coffee blends and in instant coffee, among them for the first time in coffee: 3-hydroxypropionic, 2-oxobutyric, glyceric, 2,4-dihydroxybutyric, 5-hydroxymethylfuran-2-carboxylic and 2-hydroxyglutaric acid. 相似文献
46.
Ulrike Paap Vera Seidl Karsten Meyer Florian Maier Hans-Peter Steinrück 《Molecules (Basel, Switzerland)》2022,27(23)
We investigated the surface tension and surface composition of various mixtures of the two ionic liquids (ILs) 1-methyl-3-octyl-imidazolium hexafluorophosphate [C8C1Im][PF6] and 1,3-bis(polyethylene glycol)imidazolium iodide [(mPEG2)2Im]I in the temperature range from 230 to 370 K under ultraclean vacuum conditions. The surface tension was measured using a newly developed apparatus, and the surface composition was determined by angle-resolved X-ray photoelectron spectroscopy (ARXPS). In the pure ILs, the alkyl chains of [C8C1Im][PF6] and the PEG chains of [(mPEG2)2Im]I are enriched at the IL/vacuum interface. In the mixtures, a strong selective surface enrichment of the alkyl chains occurs, which is most pronounced at low [C8C1Im][PF6] contents. For the surface tension, strong deviations from an ideal mixing behaviour take place. By applying a simple approach based on the surface composition of the mixtures as deduced from ARXPS, we are able to predict and reproduce the experimentally measured temperature-dependent surface tension values with astonishingly high accuracy. 相似文献
47.
Steffen Maier Nikolai Hippchen Dr. Frank Rominger Dr. Jan Freudenberg Prof. Uwe H. F. Bunz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(66):16320-16324
The synthesis of novel (N−)acene-based cyclooligomers is reported. Glaser-Hay coupling of the bisethynylated monomers results in cyclodimers and cyclotrimers that are separable by column and gel-permeation chromatographies. For the diazatetracene, the use of sec-butyl-silylethynyl groups is necessary to achieve solubility. Diazatetracene-based cyclodimers and cyclotrimers were used as semiconductors in thin-film transistors. Although their optoelectronic properties are quite similar, their electron mobilities in proof-of-concept thin-film transistors differ by an order of magnitude. 相似文献
48.
H. Schmalfuß H. Werner G. Curli T. P. Hilditch H. E. Longenecker Fr. Kiermeier Fr. X. Maier C. I. Kruisheer P. C. den Herder G. Roeder B. Segal A. Romeo V. Crupi G. Dorta G. Lunde H. Kringstad E. Mathiesen A. Olsen F. N. Woodward S. R. Hoover S. Schmidt-Nielsen und J. Stone 《Fresenius' Journal of Analytical Chemistry》1941,121(1-2):55-59
Ohne Zusammenfassung 相似文献
49.