Microwave-assisted saccharide coupling with n-pentenyl glycosyl donors

n-Pentenyl glycosides, armed and disarmed, and n-pentenyl orthoesters couple with acceptors, hindered and unhindered, within 25 min under microwave activation. The reaction takes place in acetonitrile under neutral conditions with N-iodosuccinimide as promotor, which are therefore ideal for use with reactants bearing acid-labile protecting groups.     

Metallic contact formation for molecular electronics: interactions between vapor-deposited metals and self-assembled monolayers of conjugated mono- and dithiols

We present grazing-incidence Fourier transform infrared and AFM data of Au, Al, and Ti vapor-deposited onto self-assembled monolayers (SAMs) of conjugated mono- and dithiols. SAMs of 4,4'-dimercapto-p-quaterphenyl, 4,4"-dimercapto-p-terphenyl, and 4,4'-dimercapto-p-biphenyl have reactive thiols at the SAM/vacuum interface that interact with vapor-deposited Au or Al atoms, preventing metal penetration. Conjugated monothiols lack such metal blocking groups, and metals (Au, Al) can penetrate into their SAMs. Vapor deposition of Ti onto conjugated mono- and dithiol SAMs and onto hexadecanethiol SAMs destroys the monolayers.     

TG study on the reduction kinetics of hematite and iron oxide-containing wastes

The reduction kinetics of a pure and a Ca-added hematite, as well as of two iron oxide-containing metallurgical wastes, were studied by means of isothermal TG measurements, using H₂ or CO as reducing agents.Below 900 K, the wastes were far less reactive than the pure or Ca-added hematite. This phenomenon was attributed to retardation of the hematite-magnetite transformation by surface Na and Si. Above 1000 K, however, the reaction rates for the wastes and for the Caadded hematite were higher than that of the pure hematite. The higher reactivities were attributed to the effects of the Ca on the microstructure of the product layer.The models of nucleation and growth processes were applied to describe the isothermal TG curves at low temperatures and in the vicinity of the rate minimum, while the model for gas-film diffusion control could be used in the case of high reaction rates.

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Zusammenfassung Die Kinetik der Reduktion von reinem sowie Ca-angereichertem Hämatit als auch von zwei eisenoxidhaltigen metallurgischen Nebenprodukten wurde mittels isothermen TG-Messungen untersucht. Dabei wurde CO und H₂ als Reduktionsmittel verwendet.Unterhalb 900 K waren die Abfallprodukte weitaus weniger reaktiv als reines oder Ca-angereichertes Hämatit. Dies wurde der verzögerten Transformation Hämatit-Magnetit durch Na und Si an der Oberfläche zugeschrieben. Oberhalb 1000 K waren die Reaktionsgeschwindigkeiten für die Nebenprodukte und für Ca-angereichertes Hämatit höher als die für reines Hämatit. Die grössere Reaktivität wurde dem Einwirken von Ca auf die Mikrostruktur der Reaktionsprodukteschicht zugeschrieben.Zur Erklärung der isothermen TG-Kurven bei niedrigeren Reaktionsgeschwindigkeiten und niedrigeren Temperaturen konnten Kristallkernbildungs- und Kristallkernwachstumsmodelle, für höhere Reaktionsgeschwindigkeiten gasschichtdiffusionskontrollierte Modelle erfolgreich angewendet werden.

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Internal conversion in energy dispersive X-ray analysis of actinide-containing materials.

The use of X-ray elemental analysis tools like energy dispersive X-ray (EDS) is described in the context of the investigation of nuclear materials. These materials contain radioactive elements, particularly alpha-decaying actinides that affect the quantitative EDS measurement by producing interferences in the X-ray spectra. These interferences originating from X-ray emission are the result of internal conversion by the daughter atoms from the alpha-decaying actinides. The strong interferences affect primarily the L X-ray lines from the actinides (in the typical energy range used for EDS analysis) and would require the use of the M lines. However, it is typically at the energy of the actinide's M lines that the interferences are dominant. The artifacts produced in the X-ray analysis are described and illustrated by some typical examples of analysis of actinide-bearing material.     

Advances in capillary electrophoresis: the challenges to liquid chromatography and conventional electrophoresis

In the 1980s, capillary electrophoresis (CE) developed rapidly into a first-class analytical separation technique. Its advances in instrumentation and method development will not only enhance or complement existing mature separation techniques such as liquid chromatography and conventional slab gel electrophoresis, but will also severely challenge these separation methods. A brief overview of the most striking achievements of CE in the 1980s is given. which illustrates the challenges to liquid chromatography and conventional slab gel electrophoresis, and some detailed discussions are presented to highlight the advantages of CE. New developments in CE that can be expected for the 1990s include especially column technology, separation chemistry and instrumentation, which will serve further to diversify and improve the applicability of this technique in areas which are poorly addressed by other separation methods. This paper considers and speculates on the technological advancements that can be expected to emerge for CE in the 1990s.     

Relevance of the glycosyl donor to the regioselectivity of glycosidation of primary-secondary diol acceptors and application of these ideas to in situ three-component double differential glycosidation

[reaction: see text] Three pairs of primary-secondary diol acceptors have been exposed to armed, disarmed, and n-pentenyl ortho ester glycosyl donors in glycosidation reactions. It is shown that the regioselectivity of those glycosylations is greatly influenced by the armed, disarmed, or ortho ester nature of the glycosyl donors. The selectivities observed have been used to devise efficient in situ three-component glycosylations involving two donors and one acceptor.     

Kinetics of γ-alumina chlorination by phosgene

The kinetics of the reaction between γ-Al₂O₃ and COCl₂ have been studied by isothermal TG measurements in the temperature range 585–1085 K. The influence of the partial pressure of COCl₂ on the reaction rate was investigated at 648, 673 and 698 K in the 10⁴–10⁵ Pa range, using N₂ as a diluting gas. The reaction seems to proceed in the chemical control region below 675 K. Above this temperature, however, diffusional processes and decomposition of COCl₂ are considered to affect the reaction rate. In the chemical control region an apparent order of reaction of 0.75 in respect of COCl₂ and an apparent activation energy of 128–135 kJ mole^?1 were found for the chlorination process.