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141.
Gensch T Rönnefahrt M Czerwonka R Jäger A Kataeva O Bauer I Knölker HJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(3):770-776
Pd(II) caught in the act: The diaryl Pd(II) intermediate of a Pd(II)-catalyzed oxidative biaryl bond formation proceeding via a double C-H bond activation has been isolated and fully characterized, including an X-ray crystal structure analysis. Stabilization due to chelation by adjacent pivaloyloxy and acetyl groups has allowed the isolation of this long-sought crucial intermediate. On gentle warming, the complex is transformed into a carbazole product, and the catalytically active Pd(II) species is regenerated by oxidation with Cu(II). 相似文献
142.
Saini R Boland S Kataeva O Schmidt AW Kurzchalia TV Knölker HJ 《Organic & biomolecular chemistry》2012,10(21):4159-4163
A stereoselective synthesis of (25S)-Δ(1)-, (25S)-Δ(1,4)-, (25S)-Δ(1,7)-, (25S)-Δ(8(14))-, (25S)-Δ(4,6,8(14))-dafachronic acid, methyl (25S)-Δ(1,4)-dafachronate and (25S)-5α-hydroxy-3,6-dioxocholest-7-en-26-oic acid is described. (25S)-Δ(1,4)-Dafachronic acid and its methyl ester are natural products isolated from corals and have been obtained by synthesis for the first time. (25S)-5α-Hydroxy-3,6-dioxocholest-7-en-26-oic acid represents a promising synthetic precursor for cytotoxic marine steroids. 相似文献
143.
144.
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used as a powerful multielement analytical method
for trace analysis of geological glasses which are useful as reference materials for geochemical in-situ microanalytical work.
The quantification of the analytical results was carried out using the BCR-2G and NIST 612 glass standard reference material
(SRM). The experimentally determined relative sensitivity coefficients (RSC) for both SRMs vary between 0.2 and 3 for most
of the elements, with increasing mass an increasing of relative sensitivity coefficients was observed. The relative standard
deviation (RSD) for determination of trace element concentration of most elements (N=3) are between 2 and 10%. The determination
of trace elements in various geological glasses by LA-ICP-MS yielded a good agreement with the reference values and those
results of other trace analytical methods.
Received October 15, 1999. Revision April 14, 2000. 相似文献
145.
Sergei F. Boulyga J. Sabine Becker Alexander F. Malenchenko Hans-Joachim Dietze 《Mikrochimica acta》2000,134(3-4):215-222
As a result of the Chernobyl nuclear power plant accident in 1986, thyroid pathologies occurred among children in some regions
of Belarus. Besides the irradiation of children’s thyroids by radioactive iodine and caesium nuclides, toxic elements from
fallout are a direct risk to health. Inductively coupled plasma quadrupole-based mass spectrometry was used for multielement
determination in small amounts (1–10 mg) of thyroid tissue samples obtained during thyroid operations in Minsk hospitals.
The accuracy of the applied analytical technique for small biological sample amounts was checked using NIST Standard Reference
Material oyster tissue (SRM 1566b) and by comparison with independent analytical methods, such as neutron activation analysis.
Almost all essential elements as well as a number of toxic elements such as Cd, Pb, Hg, U etc. were determined in a multitude
of human and animal thyroid tissues (up to 1 mg sample material) by quadrupole-based ICP-MS using micronebulization. In general,
the thyroid tissue affected by pathology is characterized by higher calcium content. Some other elements, among them Fe, Mn,
V, As, Cr, Ni, Pb, U, Ba, Sb, were also accumulated in such tissue. The results obtained will be used as initial material
for further specific studies of the role of particular elements in thyroid pathology development.
Received November 15, 1999. Revision March 15, 2000. 相似文献
146.
Karsten Haas J. Feldmann Rainer Wennrich Hans-Joachim Stärk 《Analytical and bioanalytical chemistry》2001,370(5):587-596
The analytical performance of an axial inductively-coupled-plasma time-of-flight mass spectrometer (ICP–TOFMS) as a detector
for fast transient chromatographic signals resulting from the coupling to capillary gas chromatography (CGC) was investigated.
A cryotrapping GC–ICP–TOFMS method for the determination of volatile metal(loid) compounds (VOMs) in gases was used and the
suitability of the TOF mass analyzer for multi-elemental speciation analysis and multi-isotope ratio determinations was studied
in terms of accuracy and precision. Isotope ratios 118Sn/120Sn and 121Sb/123Sb have been determined in in-house gas standard atmospheres in Tedlar bags at two different levels (100 pg and 1 ng) for
different elemental species (SnH4, MeSnH3, Me2SnH2, Me3SnH, BuSnH3, SbH3, and MeSbH2). A limitation arising from counting statistics in both detection modes could be shown. A solution containing rhodium (10
ng mL–1) and cadmium (40 ng mL–1) was introduced simultaneously to the GC outlet. Rhodium acts as a continuous internal standard and Cd is used for mass-bias
correction (by measuring the 111Cd/113Cd ratio). The detection system in both pulse counting and analog mode was examined. The best attainable precision was established
for Me2SnH2 (analog mode, 12 replicates, 1 ng, RSD 0.34%, accuracy 0.31%) whereas most other species ranged between 0.4 and 0.5% RSD
if higher concentrations were used. The limitations of the pulse counting system are clearly seen, with peak heights of more
than 2000 counts reaching saturation (for an integration time of 100 ms), which reduces the accuracy of isotope ratio determinations.
A dozen VOM could be detected in an aged landfill gas sample; several unidentified Sn compounds were present. Although their
isotope ratios are within the confidence value of the standards, it is not yet clear if the acquired precision is good enough
to identify isotopic fractionation of metal(loid)s through biovolatilization processes. With the precision achieved, the combination
of cryotrapping GC and ICP–TOFMS is a powerful tool for monitoring volatile multi-element species in multi-tracer experiments
and isotope dilution methodology.
Received: 23 November 2000 / Revised: 19 February 2001 / Accepted: 24 February 2001 相似文献
147.
148.
149.
Hans-Joachim Kroll 《Geometriae Dedicata》1984,16(1):79-83
Ohne ZusammenfassungHerrn Professor Adriano Barlotti zum 60. Geburtstag 相似文献
150.
(Ph3P)4Pd - or (RO)3P/Ni(COD)2 - catalysed [3+2]-cycloaddition of methylenecyclopropanes 1a – 1e with the ketenimines 2a, 2b leads selectively to pyrrols, α -methylene- Δ3 -pyrrolines or iminocyclopentenes depending on the substituents of the imino group and the methylenecyclopropanes. 相似文献