Bulky aluminum alkyl scavengers in olefin polymerization with group 4 catalysts

The binding of H2O to MeAl(OAr)2 (1: Ar = 2,6-di-tert-butyl-4-methylphenyl) in THF-d8 at -40 degrees C provides aquo complex 2, the structure of which was determined by X-ray crystallography. Complex 2 is unstable above 0 degrees C in THF-d8 and decomposes to form ArOH (major), CH4 (minor), and a methyl aluminoxane of undetermined structure. Decomposition of 2 follows first-order kinetics with k = 3.0 x 10-4 s-1 at 5 degrees C. The hindered phenol ArOH slowly reacts with [Cp2ZrMe][MeB(C6F5)3] (4) in bromobenzene-d5 solution at 25 degrees C to furnish CH4 and [Cp2ZrOAr][MeB(C6F5)3] (5), the structure of which was confirmed by X-ray crystallography. This reaction follows second-order kinetics for [ArOH] = [4] = 0.045 M and with k = 2.8 x 10-3 M-1 s-1 at 25 degrees C. This corresponds to a rate that is >107 x slower than the apparent rate of ethylene insertion for 4 at 25 degrees C at typical concentrations encountered in olefin polymerization. The kinetic data, as well as control experiments involving the addition of ArOH to active catalyst producing poly(ethylene), demonstrate that ArOH has essentially no effect on polymerization kinetics involving 4.     

Rapid separations of corrosion and fission products

A separation scheme of a complex mixture of radiohygienically important radionuclides of corrosion and fission products has been worked out. Rapid separation by means of solvent extractions with metal (sodium, antimony, zinc) diethyldithiocarbamates has been achieved. Chloroform containing metal diethyldithiocarbamates has been used as the organic phase. The procedure permits to separate selectively the representative radionuclides. The selectivity of separation was verified by gamma spectrometry.     

Excitation conditions in a mixed-gas low-pressure microwave induced plasma

Double probe measurements and optical measurements have been carried out to determine the variation of electron temperature, electron density and emission intensities in low-pressure (0.1–0.5 torr) microwave induced plasmas (MIP's) in dependence of the composition of the binary gas mixture used to carry the discharge.For low concentrations of an added component the excitation parameters maintain values typical for the dominant species and the line intensities of the added component vary linearly with its concentration. When the percentage of the added component reaches 1% the excitation conditions start to change and the line intensities are no longer proportional to the concentration. Detailed analysis shows that the variations in line intensities observed in different mixed-gas discharges are closely related to the variations in electron temperature and density, with the former parameter exerting the major influence.     

The gas temperature inside graphite furnaces used for atomic absorption spectrometry

A simplified model for heat transfer is used to calculate the gas temperature inside graphite furnaces used for atomic absorption spectrometry. In the absence of a convective flow through the furnace, the gas temperature follows the wall temperature of the heated furnace to within a few degrees. When a significant flow of protective cold gas is forced through the furnace, the gas temperature varies greatly along the furnace and its average value can be several hundred degrees lower than the wall temperature. These predictions are confirmed by the vapour temperatures which were measured experimentally by means of the two-line absorption technique. The results also demonstrate that analyte species volatilized in the furnace have the same temperature as the inert gas. The advantages of preheating the protective gas are indicated.     

A Physicochemical Study of the Effects of Acidity on the Distribution and Antioxidant Efficiency of Trolox in Olive Oil‐in‐Water Emulsions

The efficiency of antioxidants to inhibit the oxidation of lipid‐based emulsions depends on several factors including their nature and their concentration at the reaction site. Here, we have analyzed the effects of acidity and of surfactant concentration on the distribution and efficiency of the vitamin E analog Trolox (TR) in stripped olive oil‐in‐water emulsions stabilized with Tween 20. The distribution was assessed in the intact emulsions by employing a kinetic method that exploits the reaction between the hydrophobic 4‐hexadecylbenzenediazonium ions and TR. Kinetic results are interpreted on the grounds of the pseudophase model. The effects of TR on the oxidative stability of the emulsion were determined at different pH values by monitoring the formation of conjugated dienes over time. The results show that the efficiency of TR increases upon increasing pH even though its concentration in the interfacial region decreases.     

Intermittent compression of N-alkyl-N,N-dimethylamine N-oxides encapsulated in a container with bis[2]catenane topology

Abstract

We report the encapsulation of a homologous series of N-alkyl-N,N-dimethylamine N-oxides in a molecular container with bis[2]catenane topology. N-oxides with short alkyl chains are co-encapsulated with one solvent molecule. Elongation of the alkyl chain from R = methyl to pentyl produced the progressive compression of the guest. The hexyl N-oxide reduces its compression by being singly encapsulated. Longer N-oxides (R = octyl to decyl) had to fold to adapt to the capsule’s dimensions and also experience a progressive compression. The mechanically interlocked nature of the container and the polar functionalisation of its cavity are responsible for the assembly of encapsulation complexes in solution displaying high packing coefficients (0.65–0.70). The high energy conformations adopted by the alkyl chains of the bound N-oxides are deduced from NMR experiments and molecular modelling studies.     

Method development and validation study for quantitative determination of nifedipine and related substances by ultra‐high‐performance liquid chromatography

A novel stability‐indicating reversed phase ultra‐high performance liquid chromatography (UPLC) coupled photodiode array gradient method was developed for determination of the nifedipine and related compounds. Furthermore, based on the chromatographic conditions and forced degradation studies performed through the development of the related substances method a UPLC isocratic method was validated for the determination of the assay of this active substance. An Acquity Shield RP₁₈ (50 × 3.0 mm 1.7 µm) column was used for separation of nifedipine and its five potential impurities within 11 min, which is 5‐fold less than the official method. A mobile phase consisting of 10 mm ammonium formate (pH 4.5) and methanol, delivered at a flow rate 0.5 mL/min, was employed to achieve a minimum resolution of 2.0 for all consecutive pairs of compounds. The precision value expressed as percentage relative standard deviation for method repeatability and reproducibility was <5.0%. The recoveries for all the related compounds were in the range of 99–105.0%. Linearity was found to be acceptable over the concentration range of 0.25–1.5 µg/mL for nifedipine and its impurities. The limit of quantification for nifedipine was 0.05 µg/mL, which is much less than the European Pharmacopoeia method. Copyright © 2014 John Wiley & Sons, Ltd.