Weiterentwicklung des Analysenganges für Milligrammengen isolierter Gefügebestandteile

Zusammenfassung Der ständig zunehmende Umfang chemisch-metallkundlicher Untersuchungen an Stählen für Forschung und Betriebskontrolle machte eine Erweiterung und Rationalisierung der Isolatanalyse erforderlich. Der bisherige Analysengang beruhte vorwiegend auf Ionenaustauschertrennungen und photometrischen Bestimmungen.Ersetzt man die photometrischen Verfahren durch eine Kombination hochempfindlicher Verfahren der Atomabsorption, Röntgenfluoreszenz und Photometrie, so kann man ohne Trennungen und daher wesentlich schneller analysieren und zahlreiche zusätzliche Elemente mit erfassen. Ein Analysengang für 29 Elemente wird angegeben. Die Variationskoeffizienten betragen im jeweils optimalen Meßbereich etwa 2%.

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Further development of the analytical process for milligram amounts of isolated structural components

Summary The constantly increasing extent of chemical-metallographic studies of steels for research and plant control purposes made it necessary to extend and rationalize the isolation analysis. The analytical procedure employed up till the present has been based primarily on ion exchange separations and photometric determinations.If the photometric method is supplanted by a combination of highly sensitive procedures of atom absorptions, röntgen fluorescence and photometry, it becomes possible to conduct analyses without separations and hence fundamentally more quickly and also to include numerous additionale elements. An analytical procedure is given for 29 elements. The variation coefficients in the optimal measuring range are approximately 2%.

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Den HerrenK. Lohau undH. Grygiel sei für ihre sorgfältige und wertvolle Mitarbeit herzlieh gedankt.     

Capillary column gas chromatographic identification of sugars in honey as trimethylsilyl derivatives

A method for identifying carbohydrates (mono-, di- and trisaccharides) in honey is presented. It is based on the separate preparation of both trimethylsilyl ethers and oxime trimethylsilyl ethers of the sugars followed by their gas chromatographic separation on a fused-silica capillary column coated with OV-101 using temperature programming. From the two chromatograms, the number of peaks given by each derivatized sugar, their relative retention times and peak-area ratios are used for identification. The identities of two unidentified trisaccharide peaks are considered. Quantitative applications to honey sugar analysis are discussed.     

Enantioselective formal synthesis of uleine alkaloids from phenylglycinol-derived bicyclic lactams

A two-step route for the enantioselective construction of the tetracyclic ring system of uleine alkaloids, involving the stereoselective conjugate addition of an appropriate indole-containing nucleophile to a chiral bicyclic delta-lactam and the subsequent cyclization on the indole 3-position of the resulting 4,5-disubstituted 2-piperidone, has culminated in the formal total synthesis of several alkaloids of this group.     

Ionic equilibria in neutral amphiprotic solvents of low dielectric constant: Titration curves

Titration curves have been simulated for the titration of acids, bases and salts in neutral amphiprotic solvents such as isopropyl and tert-butyl alcohols. Ranges of pK values and acid concentrations have been examined. The incomplete dissociation of salts, which increases the acid or basic strength, has been found to be the major factor modifying the shape of the curve and the pH break. The theoretical predictions have been checked by titrating several series of acids and good agreement has been obtained between computed and experimental results.     

Enantioselective synthesis of cis- and trans-3,5-disubstituted piperidines. Synthesis of 20S- and 20R-dihydrocleavamine

[reaction: see text] Diastereoselective alkylation at the carbonyl alpha-position of chiral nonracemic lactams 2 and 3, the former prepared by cyclocondensation of (R)-phenylglycinol with a racemic gamma-substituted delta-oxoester in a process that involves a dynamic kinetic resolution and the latter by a subsequent equilibration, provides access to enantiopure cis- and trans-3,5-disubstituted piperidines. The usefulness of the approach is illustrated with the synthesis of the alkaloids 20S- and 20R-15,20-dihydrocleavamine.     

Application of XRF,XRD, thermal analysis,and voltammetric techniques to the study of ancient ceramics

An in-depth chemical-analytical study has been performed on biscuit and mortar from 17th-18th century tiles from a mediaeval hermitage in the province of Valencia (Spain). Representative samples were chosen from the tile fragments available, using appearance, essentially color and consistency, as the criterion. The chemical composition was analyzed by X-ray fluorescence of the samples in the form of glass disks after a previous qualitative study to choose the standard materials for calibration and the experimental conditions used in the analysis. X-ray diffraction of the samples provided information about the mineralogical composition which was consistent with the firing of the original materials; it also gave information about the range of temperatures used in the firing. From thermal gravimetric analysis of the limestone, and from historical considerations, it was possible to deduce the raw materials used and their approximate composition in the tiles. In the same way it was possible to determine the nature of the mortars used to fix the tiles. Cyclic voltammetric study of the iron(II) and iron(III) system in the biscuit showed the simultaneous presence of both oxidation states, corroborating the results.     

Evidence for a resonance in positron-electron scattering at 810 keV centre-of-mass Energy

A monoenergetic positron (e ⁺) beam (ΔT/T<5·10^?4) from the Stuttgart pelletron accelerator and a 4.6 mg/cm² Be target has been employed to investigatee ⁺ e ^?scattering in the MeV region in a large solid angle with high statistics by means of a novel positionsensitive detector system. Superimposed on the Bhabha scattering, a structure has been found at ane ⁺ kinetic energy of 2263 keV (810 keV excitation energy in thee ⁺ e ^?rest frame). From the energy-integrated resonance cross-section of \(\sigma _{res} \cdot \Gamma _{res}^{e^ + e^ - } \) ?30 b·eV (c.m.) and the standard resonance cross-section we estimate partial resonance widths \(\Gamma _{res}^{e^ + e^ - } \) ?72 meV or 24 meV for total angular momenta J=0 or J=1, respectively. The structure, which has not been predicted within the framework of quantum electrodynamics, coincides with one of the sum energies of the correlatede ⁺ e ^?lines observed in heavy-ion collisions.     

Conjugate additions to phenylglycinol-derived unsaturated delta-lactams. Enantioselective synthesis of uleine alkaloids

The stereochemical outcome of the conjugate addition of a variety of stabilized nucleophiles (2-indoleacetic enolates and sulfur-stabilized anions) to the phenylglycinol-derived unsaturated lactams trans-2, cis-2, and its 8-ethyl-substituted analogue 10 is studied. The factors governing the exo or endo facial stereoselectivity are discussed. This methodology provides short synthetic routes to either cis- or trans-3,4-disubstituted enantiopure piperidines as well as efficient routes for the enantioselective construction of the tetracyclic ring system of uleine alkaloids, both in the normal and 20-epi series. The formal total synthesis of several alkaloids of this group is reported.     

Measurement of the ground-state lambshift of hydrogenlike uranium at the electron cooler of the ESR

X-rays are emitted with the radiative recombination of free electrons in an electron cooler of a heavyion storage ring. Due to a small width of the X-ray lines, an observation angle close to 0° and an accurate determination of the ion velocity, the ground-state Lambshift of hydrogenlike uranium (470 ± 16) eV could be measured to an accuracy of 3.4%. A re-evaluation of a measurement of the 1s _1/2 Lambshift in hydrogenlike gold gave a new value of (202.3 ± 7.9) eV as compared to the former value of (212 ± 15) eV. The results are in excellent agreement with QED calculations and are more precise than any other measurements previously reported for a high-Z, hydrogenlike ion.