Copolymerisation von Itaconsäuredialkylestern mit Styrol

Zusammenfassung Die radikalische Copolymerisation von sechs verschiedenen Itaconsäuredialkylestern mit Styrol bei 60 °C wird untersucht. Aus den UV-spektroskopisch ermittelten Zusammensetzungen der Copolymeren werden die Copolymerisationsparameter und dieQ- unde-Werte nachAlfrey undPrice berechnet und diskutiert.

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Summary The radical initiated copolymerization of six different dialkyl esters of itaconic acid with styrene was investigated at 60 °C. The composition of the copolymers was determined by UV-spectroscopy; theQ- ande-values according toAlfrey andPrice were calculated and discussed.

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Die Arbeit wurde vom Fonds der chemischen Industrie durch die Überlassung von Mitteln zur Gerätebeschaffung unterstützt, wofür wir verbindlichst danken.     

Muon diffusion and trapping by defects in electron-irradiated Nb and Ta

The transverse spin relaxation of positive muons ( ⁺) has been measured on Nb and Ta after irradiation with 3 MeV electrons. In high-purity Nb the ⁺ diffusivity derived from the trapping at irradiation-induced defects above 100 K is explained in terms of adiabatic hopping. At lower temperatures there is evidence for the dominating processes to be fewphonon incoherent tunnelling and coherent hopping. Annealing results in the formation of new defects capable of trapping the ⁺. In Ta at least two types of irradiation-induced defects capable of trapping ⁺ survive up to annealing temperatures of 400 K.     

Initial or thermally controlled impurity trapping of muons in niobium?

We have studied muon depolarization in some very well characterized samples of niobium (pure Nb with <1 ppm impurities and Nb doped with 15 at.ppm N and 53 at.ppm Ta, respectively). This has allowed us to separate the influence of substitutional and interstitial impurities on theSR linewidth. The purest sample shows a low but non-zero linewidth from 0.1 to 70 K. Ta-doping increases the width strongly below 20 K. while N-doping gives a broad maximum between 30–70 Kand a considerable width below 20 K.Conventional two-trap models cannot explain the occurrence of a linewidth significantly lower that that predicted for static ⁺ and constant over a wide temperature range. A consistent explanation of these three observations can however be obtained from the following model: In pure Nb only a fraction of the muons is self-trapped thermally; the other muons do not form small polarons but remain in a propagating metastable nonlocalized state. Impurities can catalyse further initial polaron formation, decreasing the metastable fraction. This process causes temperature-independent plateaus in up to the detrapping temperature. The muons localized at shallow traps (Ta induced) can diffuse at higher temperatures and be trapped again at deeper traps (associated with the N-impurities).     

Insertion of chloral into linear and cyclic acetals

Contrary to the known difficulties of synthesizing dialkyl-acetals of chloral, it was found that the latter can be quantitatively inserted into the C? O? C bonds of cyclic, linear, substituted, or unsubstituted acetals at low temperatures in substantially anhydrous, acidic media, providing a variety of novel co-acetals, including a 1,3,5,8-tetraoxecane. The reaction was not applicable to ketals, where an aldol condensation was observed, nor to aldehydes other than chloral. A mechanism which avoids unstable chloral carbonium ion intermediates is discussed. In cases of substituted cyclic acetals or when two chloral units were added, often pure structural isomers were isolated, selectively formed by different Lewis acid catalysts.     

Das Goldschlägerhäutchen

Zusammenfassung Es werden natürliche und künstliche Goldschl?gerhaut sowie Ochsenblinddarm elektronenmikroskopisch untersucht. Die echte Goldschl?gerhaut, die etwa 100mal so dick wie dünnstes technisches Blattgold ist, besteht aus Bündeln von Fibrillen, deren Querstreifung eine Periode von 180 mμ ergab. Die sehr gro?e Elastizit?t und die Freiheit von harten Einschlüssen lassen es verst?ndlich erscheinen, da? bisher kein brauchbarer Ersatzstoff gefunden wurde. Es wird auf die M?glichkeit aufmerksam gemacht, da? vielleicht halbkünstliche Erzeugnisse aus tierischem Bindegewebe (z. B. Naturin) zu künstlicher Goldschl?gerhaut zu entwickeln sind. Wie weit solche Folien wirklich brauchbar w?ren, bedarf der Prüfung. Angeschlossen der Arbeitsgemeinschaft Industrieller Forschungsvereinigungen.     

The size dependent shift of the surface plasmon absorption band of small spherical metal particles

It has been previously established that the surface plasmon of small spherical silver particles, which are embedded in a noble gas matrix, shifts to higher energies (blue shift) as the mean diameterD of the particles decreases (100 Å>D>20 Å). This blue shift has also been found for supported silver particles, and quite recently we observed it by elastic light scattering in the gas phase. This latter experiment proves unambiguously that the blue shift in small silver particles is not induced by interactions with the environment, the presence of which is clearly recognized in less inert matrices such as O₂ or CO. From self-consistent calculations of the surface response of planar jellium surfaces one would expect a red shift, which is also directly confirmed by a few calculations for selected jellium spheres. The contradiction between the observed blue shift for small particles and the predicted red shift for jellium spheres disappears, if one accounts for thed-electrons of silver in a very simple approximation.     

Studies on azaspiracid biotoxins. II. Mass spectral behavior and structural elucidation of azaspiracid analogs

In this report, the mass spectral analysis of azaspiracid biotoxins is described. Specifically, the collision-induced dissociation (CID) behavior and differences between CID spectra obtained on a triple-quadrupole, a quadrupole time-of-flight, and an ion-trap mass spectrometer are addressed here. The CID spectra obtained on the triple-quadrupole mass spectrometer allowed the classification of the major product ions of the five investigated compounds (AZA 1-5) into five distinct fragment ion groups, according to the backbone cleavage positions. Although the identification of unknown azaspiracids was difficult based on CID alone, the spectra provided sufficient structural information to allow confirmation of known azaspiracids in marine samples. Furthermore, we were able to detect two new azaspiracid analogs (AZA 1b and 6) in our samples and provide a preliminary structural analysis. The proposed dissociation pathways under tandem mass spectrometry (MS/MS) conditions were confirmed by a comparison with accurate mass data from electrospray quadrupole time-of-flight MS/MS experiments. Regular sequential MS(n) analysis on an ion-trap mass spectrometer was more restricted in comparison to the triple-quadrupole mass spectrometer, because the azaspiracids underwent multiple [M + H - nH(2)O](+) (n = 1-6) losses from the precursor ion under CID. Thus, the structural information obtained from MS(n) experiments was somewhat limited. To overcome this limitation, we developed a wide-range excitation technique using a 180-u window that provided results comparable to the triple-quadrupole instrument. To demonstrate the potential of the method, we applied it to the analysis of degraded azaspiracids from mussel tissue extracts.     

Three Bromides of Lanthanum: LaBr2, La2Br5, and LaBr3

Colourless LaBr₃ was obtained via the ammonium-bromide route and in singlecrystalline form by chemical vapour-phase transport with aluminium tribromide. Black single crystals of LaBr₂ and La₂Br₅ have been grown from the melts that are obtained by lithium reduction of lanthanum tribromide in sealed tantalum ampoules at 850°C. The crystal structures of the three bromides of lanthanum were refined: LaBr ₂. 2H₂–MoS₂ type, hexagonal (P6₃/mmc), a = 409.88(4) pm, c = 1390.0(1) pm, R = R_w = 0.092; La ₂ Br ₅. Pr₂I₅ type, monoclinic (P2₁/m), a = 789.09(6) pm, b = 424.89(4) pm, c = 1342.3(1) pm, β = 91.60(1)º, R = 0.067, R_w = 0.055; LaBr₃ . UCl₃ type, hexagonal (P6₃/m), a = 797.13(4) pm, c = 452.16(4) pm, R = 0.036, R_w = 0.032.