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81.
Rosemarie Philipp Olaf Hanebeck Sebastian Hein Wolfram Bremser Tin Win Irene Nehls 《Accreditation and quality assurance》2010,15(3):141-146
The Federal Institute for Materials Research and Testing (BAM), Germany, has issued a series of large volume ethanol in water
certified reference materials (CRMs), primarily developed for the calibration of evidential breath alcohol analyzers in Germany.
The certified parameter is the ethanol mass concentration at 20 °C. When used in a wet bath simulator, the solutions deliver
gas samples that meet the requirements set by the Organization of Legal Metrology for calibration of breathalyzers. The materials
were prepared gravimetrically by spiking of ethanol into water in single 5 L units. A complete uncertainty budget for the
preparation process has been established. The purity of the commercial ethanol stock solution was identified to be the main
source of uncertainty. For stability and homogeneity measurements and for the verification of the gravimetric mass concentration
of the CRMs, a robust high-precision gas chromatography, with flame-ionization detection method for ethanol determination
in aqueous samples was developed and validated. The good performance of this method has been demonstrated in several international
comparisons organized by the Consultative Committee for Amount of Substance—Metrology in Chemistry at the International Bureau
of Weights and Measures. 相似文献
82.
Dr. Philipp Le Dr. Matthew B. Nodwell Dr. Jürgen Eirich Prof. Stephan A. Sieber 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12644-12651
The illudin natural product family are fungal secondary metabolites with a characteristic spirocyclopropyl-substituted fused 6,5-bicyclic ring system. They have been extensively studied for their cytotoxicity in various tumor cell types, and semisynthetic derivatives with improved therapeutic characteristics have progressed to clinical trials. Although it is believed that this potent alkylating compound class acts mainly through DNA modification, little is known about its binding to protein sites in a cellular context. To reveal putative protein targets of the illudin family in live cancer cells, we employed a semisynthetic strategy to access a series of illudin-based probes for activity-based protein profiling (ABPP). While the probes largely retained potent cytotoxicity, proteomic profiling studies unraveled multiple protein hits, suggesting that illudins exert their mode of action not from addressing a specific protein target but rather from DNA modification and unselective protein binding. 相似文献
83.
A. Janke H. Hiller R. Dworzak L. Ebert C. Mayr E. Kroupa G. Koller F. v. Wessely H. Lieb J. Schintlmeister M. Nießner G. Lock G. Ortner 《Mikrochimica acta》1942,30(1-2):181-192
Ohne Zusammenfassung 相似文献
84.
Zusammenfassung Es wird gezeigt, daß ein expliziter Zusammenhangzwischen Aktivitätskoeffizienten und Reaktionsgeschwindigkeiten im a llgemeinen nicht zu erwarten ist. Das Auftreten des Aktivitätskoeffizienten des Neutralkörpers bei der Reaktion zwischen einem Ion und einem Nichtelektrolyten wird modellmäßig verlangt. Es wird gezeigt, daß die gegenseitige Beeinflussung der Ionen eine merkliche Schwächung des elektrischen Aussalzeffektes hervorruft. 相似文献
85.
86.
Achim Häußermann Dr. Frank Rominger Prof. Dr. Bernd F. Straub 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(44):14174-14185
A sterically shielded 3‐substituted zwitterionic N,N‐dimethylisotryptammonium carboxylate has been synthesized by consecutive chemoselective double alkylation of indole. The carboxylate undergoes a quantitative and unusually facile decarboxylation in dimethyl sulfoxide (DMSO) or dimethyl formamide (DMF) at room temperature. The breaking of a nearly equidistant hydrogen bond by solvent molecules initiates heterolytic C? C cleavage. The decarboxylation rate decreases with increasing CO2 partial pressure, proving the competitiveness of protonation and re‐carboxylation of the carbanionic intermediate. Corresponding spiro compounds containing silylene and stannylene moieties show high thermal stability. Addition of an excess of methyllithium to the sodium salt triggers a reaction sequence comprising a deprotonation, carboxylate transfer, and nucleophilic trapping of the rearranged carboxylate by another equivalent of methyllithium. Hydrolytic work‐up of the geminal diolate leads to an acetyl product. The role of the sodium counterion and the mechanism of the rearrangement have been unraveled by deuteration experiments. 相似文献
87.
Carl Philipp Rosenau Dr. Benson J. Jelier Dr. Alvar D. Gossert Prof. Dr. Antonio Togni 《Angewandte Chemie (International ed. in English)》2018,57(30):9528-9533
Fluorine chemistry has taken a pivotal role in chemical reaction discovery, drug development, and chemical biology. NMR spectroscopy, arguably the most important technique for the characterization of fluorinated compounds, is rife with highly inconsistent referencing of fluorine NMR chemical shifts, producing deviations larger than 1 ppm. Herein, we provide unprecedented evidence that both spectrometer design and the current unified scale system underpinning the calibration of heteronuclear NMR spectra have unintentionally led to widespread variation in the standardization of 19F NMR spectral data. We demonstrate that internal referencing provides the most robust, practical, and reproducible method whereby chemical shifts can be consistently measured and confirmed between institutions to less than 30 ppb deviation. Finally, we provide a comprehensive table of appropriately calibrated chemical shifts of reference compounds that will serve to calibrate 19F spectra correctly. 相似文献
88.
Jaroslav Ščudla Klaus-Jochen Eichhorn Miroslav Raab Pavel Schmidt Dieter Jehnichen Liane Häußler 《Macromolecular Symposia》2002,184(1):371-387
The molecular and supermolecular orientation, morphology and structural changes observed during cold drawing of injection moulded isotactic polypropylene modified by specific α, and β nucleating agents were studied by polarised photoacoustic FTIR spectroscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Significantly lower molecular orientation was found in the core of the β-nucleated injection moulded specimens as compared to unmodified and α-nucleated materials. This has been ascribed to the fast growth of the β-crystallites which inevitably dislocates the flow-induced orientation within the crystalline regions and in their vicinity. Moreover, it was found that the presence of the developed β-crystallites distinctly diminishes the efficiency of the orientational solid-state drawing assessed on both levels of the hierarchical structure (molecular and crystalline). This structural observation is directly connected with macroscopic softening effect of the β-phase: lowering the yield stress and flattening the neck shoulder. Thus, the interrelation between the microstructural and macroscopic effects of the β-phase could be described as a feedback process. 相似文献
89.
90.