The use of temporary tethers in the meta photocycloaddition reaction

The use of temporary tethers in facilitating meta photocycloaddition reactions between phenol and allyl alcohol derivatives has been investigated. The merits of silicon, carbonate and methylene acetal tethers were assessed, whilst considering strategies for the preparation of the natural products gymnomitrol and gelsemine. The photoadducts were epoxidised, and then subjected to acid catalysed fragmentation with concomitant cleavage of the tether. Depending on whether water or methanol was used during the fragmentation stage of the methylene tethers, the methylene group was either removed altogether or transformed into a MOM group.     

Effect of Ga doping on magneto-transport properties in colossal magnetoresistive La0.7Ca0.3Mn1−xGaxO3 (0<x<0.1)

Samples of La_0.7Ca_0.3Mn_1−xGa_xO₃ with x=0, 0.025, 0.05 and 0.10 were prepared by standard solid-state reaction. They were first characterized chemically, including the microstructure. The magnetic properties and various transport properties, i.e. the electrical resistivity, magnetoresistivity (for a field below 8 T), thermoelectric power and thermal conductivity measured each time on the same sample, are reported. The markedly different behaviour of the x=0.1 sample from those with a smaller Ga content, is discussed. The dilution of the Mn³⁺/Mn⁴⁺ interactions with Ga doping considerably reduces the ferromagnetic double exchange interaction within the manganese lattice leading to a decrease of the Curie temperature. The polaron binding energy varies from 224 to 243 meV with increased Ga doping.     

Die Reduktion von TiIV, VV CrIII, MoVI, WVI, UVI und FeIII mit Na-Pb-Legierung

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Molecular beam infrared spectroscopy and complex-forming reactions of CH3F in argon clusters

A molecular beam of medium-large argon clusters containing CH₃F has been characterized by means of photoevaporation infrared laser spectroscopy at several stagnation pressures and CH₃F concentrations. Bolometric detection and line tunable, isotopically substituted CO₂ lasers have been used. Two spectral features have been assigned to the CH₃F monomer and the dependence of their shifts and widths on stagnation pressure has been measured. Concentration studies have allowed us to identify the features produced by the CH₃F dimer and to recognize tentatively the effect of the higher polymers. CH₃F has also been deposited on the clusters surface by means of the previously introduced pick-up technique. In contrast to the results obtained with the SF₆/Ar combination, no peaks could be associated with surface adsorbed species. The CH₃F/Ar clusters thus characterized have been made to interact with a side flux of HCl and the ensuing complex-forming reaction has been studied. Both the decrease in the CH₃F monomer absorption intensity, and the extra absorption due to the newly formed (CH₃F-HCl) complexes, have been used to monitor this dynamic process, which has been found to proceed to completion in a time shorter than 100 μs even for the large clusters (approx. 10³ argon atoms) produced by our source at the largest viable stagnation pressure.     

Method development and inter-laboratory comparison about the determination of titanium from titanium dioxide nanoparticles in tissues by inductively coupled plasma mass spectrometry

Nanosized titanium dioxide (TiO₂) is one of the most interesting and valuable nanomaterials for the construction industry but also in health care applications, food, and consumer goods, e.g., cosmetics. Therefore, the properties associated with this material are described in detail. Despite its widespread use, the analytical determination and characterization of nanosized metal oxides is not as straightforward as the comparatively easy-to-detect metallic nanoparticles (e.g., silver or gold). This study presents the method development and the results of the determination of tissue titanium (Ti) levels after treatment of rats with the nanosized TiO₂. Total Ti levels were chosen to evaluate the presence and distribution of TiO₂ nanoparticles. A procedure consisting of incubation with a mixture of nitric acid (HNO₃) and hydrofluoric acid (HF), and heating was developed to digest tissues and TiO₂ nanomaterials in order to determine the total Ti content by inductively coupled plasma mass spectrometry (ICPMS). For the inter-laboratory comparison, altogether four laboratories analyzed the same samples upon digestion using the available ICPMS equipment. A major premise for any toxicokinetic study is the possibility to detect the chemical under investigation in biological samples (tissues). So, the study has to be performed with a dose high enough to allow for subsequent tissue level measurement of the chemical under investigation. On the other hand, dose of the chemical applied should not induce over toxicity in the animal as this may affect its absorption, distribution, metabolism, and excretion. To determine a non-toxic TiO₂ dosage, an acute toxicity study in rats was performed, and the organs obtained were evaluated for the presence of Ti by ICPMS. Despite the differences in methodology and independent of the sample preparation and the ICPMS equipment used, the results obtained for samples with Ti concentrations >4 μg Ti/g tissue agreed well.

Eine neue photometrische Methode zur Bestimmung von prim?ren Aminen und Aminos?uren

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