Urine steroid profiles of hirsute women (author's transl)]

Steroid profiles of women suffering from idiopathic hirsutism show in more than 50% of the cases of 10--100 fold increase in the excretion of dehydroepiandrosterone (DHEA) compared with normal values. The excretion of DHEA was reduced much more than that of other 17-ketosteroids if the adrenals (NNR) were suppressed by dexamethasone (DXM). Within one week they reached values at the compound noise level of the gas chromatograms. If the ovaries were stimulated with human chorionic gonadotropin during continued suppression of the NNR with DXM no increase of DHEA could be detected.     

Measurement of balmer and lyman X-rays in antiprotonic hydrogen isotopes at pressures below 300 hPa

X-Rays of Balmer and Lyman transitions in antiprotonic hydrogen and of Balmer transitions in antiprotonic deuterium were observed at pressures below 300 hPa using Si(Li) semiconductor detectors. The measurement was performed at the LEAR-facility at a beam momentum of 202 MeV/c. In order to stop antiprotons in a low pressure gaseous target with high efficiency, a novel technique, the cyclotron trap has been used. Absolute yields were determined and compared with cascade calculations. A distinct difference in the cascade of antiprotonic hydrogen and deuterium is found. The parameters of strong interaction in antiprotonic hydrogen are determined to be? _1s=?(620±100) eV,Γ _1s=(1130±170) eV andΓ _2p=(32±10) meV.     

Magnetic confinement of massless Dirac fermions in graphene

Because of Klein tunneling, electrostatic potentials are unable to confine Dirac electrons. We show that it is possible to confine massless Dirac fermions in a monolayer graphene sheet by inhomogeneous magnetic fields. This allows one to design mesoscopic structures in graphene by magnetic barriers, e.g., quantum dots or quantum point contacts.     

Preparation and x-ray structure analysis of [Rh2Cl2(μ-CO)(μ-vdpp)2] [vdpp=H2C=C(PPh2)2]

Summary The complex [Rh₂Cl₂(-CO)(-vdpp)₂] (1) (vdpp=H₂C=C(PPh₂)₂) was prepared by reaction of [Rh₂(CO)₄-(-Cl)₂] with vdpp. When (1) is allowed to stand overnight under an atmosphere of CO without stirringtrans-[Rh₂Cl₂(CO)₂(-vdpp)₂] is formed as a red precipitate in low yields. On rapid addition of CO the tricarbonyl complex [Rh₂(CO)₂(-CO)(-Cl)(-vdpp)₂]-Cl is formed instead. The chemical behaviour of the vdpp-substituted complex (1) is very similar to that of the corresponding dppm-substituted complex [Rh₂(Cl₂-(-CO)(-dppm)₂] (dppm=H₂C(PPh₂)₂). this similarity also extends to the molecular structures of both compounds. Unit cell parameters of (1): space group Pben (Z=8),a=2344.7(5),b=1506.9(7),c=3021.6(9)pm. Rh-Rh 267.4(1) pm.     

Quantum Monte Carlo simulation of the dynamics of the spin-boson model

This paper presents the results of stationary-phase Monte Carlo simulations for the dynamics of the spin-boson problem. The problem of alternating weights ubiquitous in dynamical simulations has been solved using discretized path-integral simulations in conjunction with stationary-phase filtering techniques. Our computation covers the bulk of the parameter space, including non-zero bias and frequency-dependent dissipation. Besides a comparison with analytic predictions, we present some new results. For sub-Ohmic dissipation, the dynamics at low temperatures depends significantly on the initial preparation. In the Ohmic regime 1/2<K<1, whereK is Kondo's dimensionless coupling strength, we find significant deviations from the predictions of the non-interacting blip approximation at long times and low temperatures.     

Screening and interaction of magnetic impurities in Luttinger liquids

The spin and charge correlations induced in the conduction electron sea by the presence of a spin-1=2 magnetic impurity are investigated for one-dimensional electrons. For correlated conduction electrons, the RKKY interaction between magnetic impurities exhibits only a slow algebraic decay with distance. Increasing the exchange coupling between conduction electrons and magnetic impurity leads to a competition between the RKKY interaction and the Kondo effect. For a two-impurity model, we study the influence of the electronic correlations on this competition. Furthermore, the Kondo screening cloud and the local spin susceptibility far away from a magnetic impurity are discussed.     

Experimental observation of excited state muon transfer in mixtures of hydrogen isotopes

Molecular dynamic (MD) computer simulations are used to investigate the stopping of heavy ions in strongly coupled electron plasmas. Our results show, that in this regime collisions between the electrons as well as non-linear screening effects yield at low ion velocities a dependence of the stopping power on the ion chargeZ which scales like Z^1.43 instead of the usual Z² ln(const/Z)-scaling for weak coupling. This is connected with an enhanced local density of electrons around a highly charged, slow ion.Supported by the Bundesministerium für Bildung und Forschung (BMBF), the Gesellschaft für Schwerionenforschung Darmstadt (GSI) and the European Community.     

1,2,3-Triazolidine durch Cycloaddition von Aziminen an Olefine

1,2,3-Triazolidines by Cycloaddition of Azimines to Olefines Azimines A can undergo [3+2]-cycloadditions with olefines B to give 1,2,3-triazolidines C , a class of hitherto unknown heterocycles. The three examples of this reaction realized here involved the azimine 1 with electron-withdrawing substituents and the olefines 2, 3 and 4 with an electron-donating substituent, yielding the cycloadducts 5,6 and 7 . The triazolidine structure of 5 was established by an X-ray diffraction analysis. Characteristic for 5 are also: (a) that the three N-atoms are pyramidal (and thus centers of chirality), (b) that the five-membered heterocycle takes on a twist (half-chair) form, and (c) that the regioselectivity of the cycloaddition places the (E)-substituent of the olefine 2 vicinal to the terminal (Z)-substituent of the azimine 1 . On this basis the constitutions of 6 and 7 are assigned. The spectral properties of the triazolidines 5, 6 and 7 , including the ¹⁵N-NMR signals of one example, are compared with those of the related triazane 12 .     

Verwendung eines ortsauflösenden proportionalzählrohres zur messung von dünnschichtchromatogrammen C-markierter substanzen

Use of a position-sensitive proportional counter system for measurements of thin-layer chromatograms of ¹⁴C-labelled substancesA position-sensitive proportional counter system has been developed for the quantitative determination of thin-layer chromatograms of ¹⁴C-labelled substances. The described system allows simultaneous measurements of the whole chromatogram. Data interpretation (integration of peajs) is very simple with a modern multichannel analyzer.The specific properties of the system are compared with a normally used chromatogram scanner. The usefulness of the system is demonstrated on ¹⁴C-labelled chromatograms.

Zusammenfassung

Mit Hilfe eines Proportionalzählrohres wurde ein ortsempfindliches Detektorsystem für die quantitative Auswertung von Dünnschichtchromatogrammen ¹⁴C-markierter Substanzen entwickelt. Das vorgeschlagene Messsystem bietet gegenüber herkömmlichen Scannern den Vorteil, dass das gesamte Chromatogramm gleichzeitig gemessen wird und die Auswertung der Messung mit einem modernen Vielkanalsystem rasch und einfach vorgenommen werden kann. Die praktische Anwendung der Anlage sowie der Vergleich mit einem herkömmlichen Radiochromatogramm-Scanner wird anhand von ¹⁴C-markierten Testmischungen demonstriert.     

Synthesis and cannabinoid receptor activity of ketoalkenes from Echinacea pallida and nonnatural analogues

Despite its popularity and widespread use, the efficacy of Echinacea products remains unclear and controversial. Among the various compounds isolated from Echinacea, ketoalkenes and ketoalkenynes exclusively found in the pale purple coneflower (E. pallida) are major components of the extracts. In contrast to E. purpurea alkamides, these compounds have not been synthesized and studied for immunostimulatory effects. We present a practical and useful synthetic approach to the ketoalkenes using palladium-catalyzed cross-coupling reactions and the pharmaceutical results at the human cannabinoid receptors. The synthetic route developed provides overall good yields for the ketoalkenes and is applicable to other natural products with similar 1,4-diene motifs. No significant activity was observed at either receptor, indicating that the ketoalkenes from E. pallida are not responsible for immunomodulatory effects mediated via the cannabinergic system. However, newly synthesized non-natural analogues showed micro-molar potency at both cannabinoid receptors.