Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.     

Vier neue Metabolite von Giberella zeae: 5-Formyl-zearalenon, 7′-Dehydrozearalenon, 8′-Hydroxy- und 8′-epi-Hydroxy-zearalenon

From cultures of Gibberella zeae ergosterol, zearalenone ( 1 ) and hitherto unknown minor metabolites, i.e.. 5-formyl-zearalenone ( 6 ), 7′-dehydrozearalenone ( 8 ), 8′-hydroxyzearalenone ( 9 ) and 8′-epi-hydroxyzearalenone ( 11 ) were isolated. The production of zearalenone and its congeners proved to be very strongly dependent on the conditions of culture. 5-Formyl-zearalenone ( 6 ) as well as 3-formylzearalenone ( 4 ) were synthesized from zearalenone ( 1 ) and characterized by the di-O-methyl derivatives 7 and 5 respectively. The structure of 7′- dehydrozearalenone ( 8 ) was deduced from spectral data. The di-O-methyl derivatives 10 and 12 respectively of the two corresponding epimeric 8′-hydroxy derivatives 9 and 11 yielded the same β-diketone 13 . The keto-enol equilibrium of 13 was studied.     

Chemistry at High Dilution: Dinuclear 99 mTc Complexes

The formation of di- or polynuclear complexes at nanomolar concentrations is generally too slow to be observed with ^99mTc. It is reported in this communication that an appropriate choice of potentially bridging ligands, herein thiols HS-R, accelerates the dimerization reaction to an extent that dinuclear complexes are formed at very high dilution. The dinuclear nature of [^99mTc₂(μ₂-SR)₃(CO)₆]⁻ is shown by chromatographic comparison, not only with its rhenium homologue as commonly done, but also with the true ⁹⁹Tc analogue.     

Quantitative Bestimmung organischer Verbindungen

Ohne Zusammenfassung