Reaktion von Hydroperoxiden mit Radikalen

2,4,6-Tri-tert.-butyl-phenoxyl was reacted with tert.-butyl hydroperoxide (BHPO), cumene hydroperoxide (CHPO) and tri-phenylmethyl hydroperoxide (TPMHPO). Main reaction products are 2,4,6-tri-tert.-butyl phenol and substituted 4-cyclo-hexadienoneperoxides. Only by reacting TPMHPO a 2-cyclohexadienoneperoxide was isolated but by reacting BHPO and CHPO 3,5-di-tert.-butyl-o-quinone, isobutene and tert.-butanol or dimethylphenylcarbinole, resp., were formed. The products show the phenoxyradical attacking the peroxidic H-atom and a combination of formed peroxyradicals with phenoxyradicals. ESR-measurements demonstrate a first order radical decay, the reaction rate varies linear with hydroperoxide concentration. Hexaphenylethane (triphenylmethyl) reacts with BHPO under formation of triphenylmethylcarbinole, benzophenone, p-tert.-butoxy-triphenyl methane and little triphenylmethane. From these reaction products is to conclude that this radical attacks predominantly the peroxidic oxygen-oxygen bond.     

Three generations of cyclosporine a formulations: an in vitro comparison

When the microemulsion formulation of the critical dose drug cyclosporine A (CsA) (Sandimmun Optoral) was introduced in the mid-1990s, it became clear that this new formulation improves the oral bioavailability of CsA and has a positive influence on its pharmacokinetic variability. Previous studies with the original CsA formulation (Sandimmun) showed that the size of the emulsion droplets and concomitant food intake has an effect on the absorption of CsA from the small intestine when orally administered. It was suggested that these effects might have an influence on the drugs' pharmacokinetic parameters.In this study, we focused on the two above-mentioned aspects and compared the first and second generations of CsA products (Sandimmun, Sandimmun Optoral) to generic CsA formulations by analyzing the contents of cyclosporine A gel capsules with respect to their emulsion droplet and micelle sizes using photon correlation spectroscopy (PCS). We tried to discern any differences in droplet size between different generations of CsA formulations, primarily the second and third generation, through simple physical tests. Because a high fat content food may influence the absorption of CsA, we also determined the distribution of CsA between hydrophilic and lipophilic phases using high-performance liquid chromatography analysis.It became clear that when compared under simple physical conditions, established cyclosporine formulations and new generic products show significant differences in droplet size and distribution between an aqueous phase and a high fat content food. Whether these differences are of clinical relevance remains to be investigated.     

Novel catalysts, room temperature, and the importance of oxygen for the synthesis of single-walled carbon nanotubes

In this letter, we show for the first time the use of metal oxides as catalysts in the synthesis of single-walled carbon nanotubes (SWCNTs) using laser ablation. Further, SWCNTs have been synthesized at low temperature (down to room temperature), where their nucleation cannot be explained via fullerene nucleation. The data point to a nucleation mechanism previously not identified, that places a stable oxidized ring as the root cause for the growth of SWCNTs.     

Comparative measurements of suspended particulates using several gravimetric methods and the British smoke sampler

Comparative measurements by gravimetric methods and the British black-smoke method show that the black-smoke method is less precise than the gravimetric methods. The present studies reveal that the black-smoke device only separates fractions of suspended particulates up to a particle size of 1μm. Separate evaluations of data sets measured over a period of a year and, during the winter, in accordance with the “Council Directive of the EC on air quality limit values and guide values for sulphur dioxide and suspended particulates” showed different correlations and relations to values established gravimetrically. The black-smoke method proved to be unsuitable for the evaluation of ambient air concentrations of suspended particulates by comparison with limit values.     

Review: geometric and dimensional tolerance modeling for sheet metal forming and integration with CAPP

The focus of this publication is a review of the state of the art in tolerance analysis, synthesis, and transfer for geometric and dimensional tolerances in sheet metal forming and the integration solutions with computer-aided process planning systems. In this context, the general tolerance methods are first described. Then, the mathematical models for sheet metal tolerance analysis and synthesis are examined in detail. To address the CAPP modeling concerns, the paper is then followed up with a brief review of past research works related to feature-based process planning. Finally, those imperative future research areas are identified.     

Kinetics of the thermal dissociation of ZnO exposed to concentrated solar irradiation using a solar‐driven thermogravimeter in the 1800–2100 K range

The two‐step H₂O‐splitting thermochemical cycle based on the Zn/ZnO redox reactions is considered for solar H₂ production, comprising the endothermal dissociation of ZnO followed by the exothermal hydrolysis of Zn. A solar‐driven thermogravimeter, in which a packed‐bed of ZnO particles is directly exposed to concentrated solar radiation at a peak solar concentration ratio of 2400 suns while its weight loss is continuously monitored, was applied to measure the thermal dissociation rate in a set‐up closely approximating the heat and mass transfer characteristics of solar reactors. Isothermal thermogravimetric runs were performed in the range 1834–2109 K and fitted to a zero‐order Arrhenius rate law with apparent activation energy 361 ± 53 kJ mol^?1 K^?1 and frequency factor 14.03 × 10⁶ ± 2.73 × 10⁶ kg m^?2 s^?1. Application of L‘vov’s kinetic expression for solid decomposition along with a convective mass transport correlation yielded kinetic parameters in close agreement with those derived from experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009