High-temperature synthesis of magnesium silicates from solid mixtures of SiO2 and various magnesium compounds

For many years, the high-temperature synthesis of magnesium silicates from a magnesite-quartz sand mixture has been the basis for the production of enstatite and the subsequent manufacture of steatites for the ceramics industry of the G.D.R. It is now shown that, in principle, mixtures of other magnesium compounds with SiO₂ can also be transformed to magnesium silicate phases.Depending on the mechanical and thermal conditions chosen, different reactive intermediates are formed which, after ceramic firing, are responsible for the differences within the phase composition.Thermoanalytical methods are well suited to compare the solid-state reactivities of various mixtures.

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Zusammenfassung Über lange Zeit war die Hochtemperatursynthese von Magnesiumsilicaten aus einer Mischung von Magnesit und Quarzsand die Grundlage für die Produktion von Enstatit und die nachfolgende Herstellung von Steatiten in der Keramik-Industrie der DDR. Hier wird gezeigt, dass grundsätzlich auch andere Magnesiumverbindungen mit SiO₂ zu Magnesiumsilicaten umgesetzt werden können. Abhängig von den gewählten mechanischen und thermischen Bedingungen werden unterschiedliche Zwischenprodukte gebildet, die nach dem Brennen Unterschiede in der Phasenzusammensetzung zur Folge haben können. Thermoanalytische Methoden sind gut geeignet, die Reaktivität verschiedener Gemische in fester Phase zu vergleichen.

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Polymer coated cation exchanger in ion chromatography: preparation, properties and applications

Summary Stationary phases synthesized by polymer-coating of silica gel were investigated for the separation of cations by ion chromatography. Two kinds of polymer coating (polystyrene, polyglycidylmethacrylate) with sulphonic acid cation-exchange groups on various silica gels were prepared. These low capacity strong acid cation-exchangers were applied to determine alkali and alkaline earth metal ions in tap and mineral water, and grape juice samples. The IC-results were compared with those of AAS-measurement and of EDTA-titration of alkali metals and of alkaline earth metals, respectively.     

Study of ethylene oligomerization

A study was made of the oligomerization of ethylene, initiated by the thermal decomposition of azoethane and azo-isopropane at low temperatures, where the polymerization equilibria are shifted somewhat in the direction of the formation of products with longer carbon chains. The findings supported the picture acquired from a study of the propionaldehyde–ethylene system. Also under these conditions the oligomerization proceeds via addition between the ethylene and radicals, followed by isomerization and decomposition of the longer radicals, with a tendency to yield propylene and longer olefins. At the lower temperatures the decomposition of radicals with shorter carbon chain becomes less important in comparison with their addition reactions and, in spite of the otherwise identical mechanism, this leads to a different product distribution.     

Synthesis of pyrazolo[1,5-alpha]pyrimidinone regioisomers

This work describes two distinct routes to prepare pyrazolo[1,5-alpha]pyrimidin-7-ones and two distinct routes to prepare pyrazolo[1,5-alpha]pyrimidin-5-ones. Use of 1,3-dimethyluracil as the electrophile in the preparation of the pyrimidin-5-one regioisomer represents a correction of previously reported results. Also, a novel reaction to prepare this isomer was identified and the reaction mechanism elucidated. This work provides the experimentalist with complimentary synthetic pathways that afford either the pyrimidin-7-one or the pyrimidin-5-one regioisomer.     

Formation of smooth, conformal molecular layers on ZnO surfaces via photochemical grafting

We have investigated the photochemical grafting of organic alkenes to atomically flat ZnO(10 ?10) single crystals and ZnO nanorods as a way to produce functional molecule-semiconductor interfaces. Atomic force microscopy shows that photochemical grafting produces highly conformal, smooth molecular layers with no detectable changes in the underlying structure of the ZnO terraces or steps. X-ray photoelectron spectroscopy measurements show that grafting of a methyl ester-terminated alkene terminates near one monolayer, while alkenes bearing a trifluoroacetamide-protected amine form very smooth multilayers. Even with multilayers, it is possible to deprotect the amines and to link a second molecule to the surface with excellent efficiency and without significant loss of molecules from the surface. This demonstrates that the use of photochemical grafting, even in the case of multilayer formation, enables multistep chemical processes to be conducted on the ZnO surface. Photoresponse measurements demonstrate that functionalization of the surface does not affect the ability to induce field effects in the underlying ZnO, thereby suggesting that this approach to functionalization may be useful for applications in sensing and in hybrid organic-inorganic transistors and related devices.     

Alignment of laser-induced fluorescence and mass spectrometric detection traces using electrophoretic mobility scaling in CE-LIF-MS of labeled N-glycans

The combination of optical detection techniques like photometry (UV) or laser-induced fluorescence (LIF) with mass spectrometry for capillary electrophoresis offers advantages, both for later use of stand-alone CE-UV or CE-LIF systems and for combined CE-UV-MS or CE-LIF-MS analysis. Faster method development is enabled, the identification of analytes is facilitated, and it allows christian the optical detection scheme to be used for more precise quantification. However, shortcomings of current methodology and equipment hindered the broader use of such detection combinations mainly due to the long distance between the detection points (at least 20 cm). Large shifts in migration times and changes in resolution are visible between the detection traces hindering their straightforward comparison. We present here novel equipment for a robust coupling of CE-LIF-MS with the shortest possible distance between detection points (12 cm) determined by the length of the electrospray needle. In addition, we encourage the use of a normalization of detection traces using a scale of effective electrophoretic mobility to obtain the same x-scale for both detection traces. As an example, the proposed methodology is applied to a mixture of labeled as well as non-labeled N-glycans.