Isotopenaustauschvorgänge bei homogen katalysierten reaktionen—II: H/D-Austausch bei der deuterierung von cycloalkenen in gegenwart von tris-(triphenylphosphin-)rhodium(I)-chlorid

The homogeneous deuteration of cycloalkenes in benzene solution at 22±1° under normal pressure using tris(triphenylphosphine)rhodium(I)chloride (1) is reported. In all cases isotopic scrambling accompanies deuteration, the extent of this scrambling depends very much on the ring size. Simultaneously a H/D-exchange takes place in the cycloalkenes. These results are discussed on the base of a mechanistic scheme containing reversible formation of rhodiumalkyl species.     

The cell-penetrating peptide TAT(48-60) induces a non-lamellar phase in DMPC membranes.

Cell-penetrating peptides (CPPs) are short polycationic sequences that can translocate into cells without disintegrating the plasma membrane. CPPs are useful tools for delivering cargo, but their molecular mechanism of crossing the lipid bilayer remains unclear. Here we study the interaction of the HIV-derived CPP TAT (48-60) with model membranes by solid-state NMR spectroscopy and electron microscopy. The peptide induces a pronounced isotropic (31)P NMR signal in zwitterionic DMPC, but not in anionic DMPG bilayers. Octaarginine and to a lesser extent octalysine have the same effect, in contrast to other cationic amphiphilic membrane-active peptides. The observed non-lamellar lipid morphology is attributed to specific interactions of polycationic peptides with phosphocholine head groups, rather than to electrostatic interactions. Freeze-fracture electron microscopy indicates that TAT(48-60) induces the formation of rodlike, presumably inverted micelles in DMPC, which may represent intermediates during the translocation across eukaryotic membranes.     

Role and Perspective of Molecular Simulation-Based Investigation of RNA–Ligand Interaction: From Small Molecules and Peptides to Photoswitchable RNA Binding

Aberrant RNA–protein complexes are formed in a variety of diseases. Identifying the ligands that interfere with their formation is a valuable therapeutic strategy. Molecular simulation, validated against experimental data, has recently emerged as a powerful tool to predict both the pose and energetics of such ligands. Thus, the use of molecular simulation may provide insight into aberrant molecular interactions in diseases and, from a drug design perspective, may allow for the employment of less wet lab resources than traditional in vitro compound screening approaches. With regard to basic research questions, molecular simulation can support the understanding of the exact molecular interaction and binding mode. Here, we focus on examples targeting RNA–protein complexes in neurodegenerative diseases and viral infections. These examples illustrate that the strategy is rather general and could be applied to different pharmacologically relevant approaches. We close this study by outlining one of these approaches, namely the light-controllable association of small molecules with RNA, as an emerging approach in RNA-targeting therapy.     

Untersuchungen zur Katalyse der Ammoniaksynthese und des Stickstoffisotopenaustausches durch Schichtverbindungen von Graphit mit Eisen,Ruthenium und Osmium

Investigations on the Catalysis of Ammonia Synthesis and Nitrogen Isotope Exchange by Lamellar Compounds of Graphite with Iron, Ruthenium, and Osmium The catalytic activity of transition metal potassium-graphite lamellar compounds for the synthesis of ammonia from the elements and the catalysis of the equilibration by isotope exchange of the isotopic nitrogen molecules are shown to correlate. Connections between the state of metal in the catalyst exist with iron as metal which is shown by Mössbauer spectroscopy and the catalytic activity in relation to the potassium content.     

Microscopic identification of the origin of generation-recombination noise in hydrogenated amorphous silicon with noise-detected magnetic resonance

Spin-dependent changes in the noise power of undoped amorphous hydrogenated silicon ( a-Si:H) are observed under electron spin resonance conditions. The noise-detected magnetic resonance (NDMR) signal has the g value of holes in the valence band tail of a-Si:H. Both the sign of the NDMR signal and the frequency dependence of its intensity can be quantitatively accounted for by a resonant reduction of the generation-recombination noise time constant tau. This identifies hopping in the valence-band tail as the dominant spin-dependent step governing noise in this material.     

Photo- and electroluminescence of nitrogen isoelectronic traps in GaAs1–xPx

The variation with temperature of the charge on the surface of NaCl single crystals has been measured directly by means of vibrating capacitor probe. The charge is negative at room temperature, in agreement with theory based on values of the free energy of vacancy formation, decreases with increase of temperature in two stages to a zero value at the isoelectric temperature, and then becomes positive. Values of isoelectric temperature obtained on surfaces are consistent with those obtained by experiments on charged dislocations, which suggests that surfaces could be used to obtain accurate values of the free energy of formation of cation and anion vacancies.     

Magnetic microstructure of nanocrystalline FeCuNbSiB soft magnets

The soft magnetic properties and the domain patterns of optimized nanocrystalline FeCuNbSiB-alloys are typically comparable to those of highly permeable Co-based amorphous alloys. Yet the nanocrystalline alloys show some specific peculiarities absent in the amorphous case. The most prominent example is patchy magnetization patterns which reflect the residual contribution of the averaged random magneto-crystalline anisotropy to the magnetization process. The article surveys the typical characteristics and the consequences for the magnetization process.     

Organic semiconductors for solution-processable field-effect transistors (OFETs)

The cost-effective production of flexible electronic components will profit considerably from the development of solution-processable, organic semiconductor materials. Particular attention is focused on soluble semiconductors for organic field-effect transistors (OFETs). The hitherto differentiation between "small molecules" and polymeric materials no longer plays a role, rather more the ability to process materials from solution to homogeneous semiconducting films with optimal electronic properties (high charge-carrier mobility, low threshold voltage, high on/off ratio) is pivotal. Key classes of materials for this purpose are soluble oligoacenes, soluble oligo- and polythiophenes and their respective copolymers, and oligo- and polytriarylamines. In this context, micro- or nanocrystalline materials have the general advantage of somewhat higher charge-carrier mobilities, which, however, could be offset in the case of amorphous, glassy materials by simpler and more reproducible processing.     

Online monitoring of thermoset post-curing by dynamic mechanical thermal analysis DMTA

Thermosetting moulding compounds are synthetic materials which can be easily formed in the molten state and achieve high temperature stability due to a cross-linking process which takes place during manufacture. To ensure thermal and mechanical properties, post-curing of moulded phenolic resin components is necessary for high quality applications. In the industrial practice, post-curing time–temperature-programs are heuristically acquired. In this paper, dynamical mechanical thermal analysis is employed to determine optimal post-curing conditions for injection moulded parts from phenolic resin.