In‐Situ and Ex‐Situ Microscopic Study of Gas Phase Propylene Polymerization over a High Activity TiCl4‐MgCl2 Heterogeneous Ziegler‐Natta Catalyst

In‐situ gas phase poly(propylene) (PP) formation over a high activity TiCl₄‐MgCl₂‐supported Ziegler‐Natta catalyst has been studied by video microscopy combined with ex‐situ light microscopy, SEM, high‐resolution TEM, and STEM/PEELS/EDX for the first time. In‐situ observation revealed rapid formation of poly(propylene) beads 9–10 μm in size (< 1/30 s) as well as growth of significant amounts of polymer within local regions. Catalyst particles containing 2–5 nm‐sized MgCl₂ crystalline domains are subjected to transformations during catalysis that form PP/catalyst aggregated structures of 30–50 μm in size.     

Simultaneous determination of various cardiac glycosides by liquid chromatography–hybrid mass spectrometry for the purity assessment of the therapeutic monitored drug digoxin

A high performance liquid chromatography–hybrid tandem mass spectrometry (LC–MSⁿ) method utilising electrospray ionisation has been developed and implemented for the simultaneous determination of several cardiac glycosides (CGs) as well as their corresponding aglycones formed by and extracted from herbaceous plants of the genus Digitalis. The method has been validated in-house and its performance characteristics (linearity, repeatability, limits of detection, etc.) were assessed for use in the quantification of CGs and their corresponding aglycones. LODs from 38 to 936 pg g⁻¹ in solution, corresponding to mass fraction impurity levels from 0.0009 (or 0.00008%) to 0.019 mg g⁻¹ (or 0.0019%) detectable in the pure materials have been realized. Moreover, the method was used to characterize and to determine the inherent CG impurities in batches of the therapeutic monitored drug digoxin which served as candidate reference material for an organic purity assessment inter-laboratory study (CCQM-P20.f) organised by the BIPM Chemistry Section and carried out within the framework of the Organic Analysis Working Group (OAWG) of the Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM). Digoxin was selected from materials required for the establishment of reference measurement systems for clinical chemistry and laboratory medicine.     

ALDH2 Mediates 5-Nitrofuran Activity in Multiple Species

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Highlights? Zebrafish provide a viable assay for the biological toxicity of 5-nitrofurans ? ALDH2 inhibitors prevent 5-nitrofuran toxicity in zebrafish and yeast ? Genetic dependence on ALDH2 for 5-nitrofuran toxicity in zebrafish and yeast systems ? 5-Nitrofurans bind to and are substrates of human ALDH2     

Macrobicyclic aminals

The synthesis of Schiff base macrocycles in the absence of templating cations and in non-protic and non-coordinating solvent media is reported. The reaction of pyridine-2,6-dicarboxaldehyde with the diamines 1,2-bis(2-aminophenoxy) ethane and 1,4-bis(2-aminophenoxy) butane has been found to give the corresponding macrobicyclic aminals. The chemical properties of the aminals are reported together with a preliminary study of their metal complexation reactions. The X-ray crystal structure of the aminal derived from pyridine-2,6-dicarboxaldehyde and 1,2-bis(2-aminophenoxy) ethane has been determined and verifies the macrobicyclic nature of the product.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

An Example of <Emphasis Type="Italic">k</Emphasis>-Elliptic Optimization in Distribution Modelling

A particular type of distribution problem (bulk transfer of finished product linked with collection of raw materials) is described. A multistage model is proposed, part of which is a special case of k-elliptic optimization. The coordinate geometry necessary to carry out the analysis of a distribution network is described in detail. This is used in a heuristic to identify feasible regions in two-dimensional Euclidean space. A further heuristic is then developed to optimally locate variable points with respect to those regions.     

The effect of the earth's magnetic field on auger analysis

Semi-quantitative analyses of thin films or surfaces are commonly obtained from the peak intensities in the differentiated Auger spectrum. To reduce effects of surface roughness, beam focus and electron current, ratios of peak heights are used rather than absolute values. In performing analysis of CdSe single crystal and thin film samples in a commercial Auger analyzer fitted with a cylindrical mirror analyzer (CMA), the ratio of the Cd(376 eV) to Se(1315 eV) peaks was found to vary by as much as 15% when the diameter of the incident electron beam was increased from 5 to 60 μm. The effect was found to be due to an energy-dependent shift of the electron beam caused by the earth's magnetic field. The electron transmission of the CMA was measured as a function of the primary electron beam spot position on the sample. The transmission decreases rapidly once the spot falls outside an area with a radius ～25 μm. Due to this response, the relative shift in position caused by the magnetic field produces variations in peak ratios when the spot size is changed. This effect will produce inaccurate analysis if the Auger peaks differ significantly in energy and the primary electron beam spot size is large, and accounts for the observed 15% variation in $\text{Cd}\text{Se}$ ratio.     

Rapid catalytic oxidation of CO to CO(2) - On the development of a new approach to on-line oxygen isotope analysis of organic matter

A new approach to on-line oxygen isotope analysis has been developed which utilises existing elemental analyser and mass spectrometry technology to produce a sample of carbon dioxide gas for oxygen isotople analysis. The method relies on on-line high temperature pyrolysis of the sample over a carbon source followed by a rapid, non-contributive partial catalytic oxidation over nickel powder at between 550 and 600 degrees C. Initial results demonstrate both good precision (better than 0.2 per thousand) and accuracy for both cellulose and silver nitrate samples. Copyright 1999 John Wiley & Sons, Ltd.