Ein Thiolato‐Zink‐Komplex mit einem Zn4O4‐Bicyclooctan‐Gerüst

A Thiolate‐Zinc Complex with a Zn₄O₄ Bicyclooctane Framework The reaction of diethyl zinc with 2,4,6‐triisopropyl thiophenol (HSR*) and N‐methyl‐2‐hydroxymethyl imidazole (ImCH₂OH) in methanol yields the complex Zn₄(SR*)₄ (ImCH₂O)₃(OMe) with terminal SR* and bridging ImCH₂O and MeO ligands. The structure of its Zn₄O₄ framework is that of a bicyclo[2.2.2]octane with Zn and O at the two apices.     

The deviating behavior of thiols in nucleophilic trapping reactions of chromiumcarbonyl phenyl complex substituted propargyl cation

The (phenyl)Cr(CO)₃-complex substituted propargyl cation 4 significantly deviates in the chemoselectivity of the nucleophilic attack of thiols from the previously reported planar chiral ortho-substituted arene complexes and furnishes allenyl thioethers 5. This peculiar behavior can be rationalized assuming a subsequent base catalyzed propargyl–allenyl isomerization in acidic medium (!). An X-ray structure analysis of allenyl thioether 5c recrystallized from acetonitrile over weeks reveals that the [2+2] cyclodimer 10 has been formed. Thiolate adds to 5c to give a single diastereomer of the allyl compound 15 in good yield.     

Influence of the particle size of the MgCl2 support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties

A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl₂ support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 µm, leads to a pronounced impact on the activity in ultra‐high molecular weight polyethylene (UHMWPE) polymerization, while the M_w capabilities are only affected to a limited extend. In addition, it is observed that both the M_ws as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the M_w and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2679–2690     

Self‐Assembled Cyclic d,l‐α‐Peptides as Generic Conformational Inhibitors of the α‐Synuclein Aggregation and Toxicity: In Vitro and Mechanistic Studies

Many peptides and proteins with large sequences and structural differences self‐assemble into disease‐causing amyloids that share very similar biochemical and biophysical characteristics, which may contribute to their cross‐interaction. Here, we demonstrate how the self‐assembled, cyclic d,l ‐α‐peptide CP‐2 , which has similar structural and functional properties to those of amyloids, acts as a generic inhibitor of the Parkinson′s disease associated α‐synuclein (α‐syn) aggregation to toxic oligomers by an ?off‐pathway“ mechanism. We show that CP‐2 interacts with the N‐terminal and the non‐amyloid‐β component region of α‐syn, which are responsible for α‐syn′s membrane intercalation and self‐assembly, thus changing the overall conformation of α‐syn. CP‐2 also remodels α‐syn fibrils to nontoxic amorphous species and permeates cells through endosomes/lysosomes to reduce the accumulation and toxicity of intracellular α‐syn in neuronal cells overexpressing α‐syn. Our studies suggest that targeting the common structural conformation of amyloids may be a promising approach for developing new therapeutics for amyloidogenic diseases.     

Temporal pitch mechanisms in acoustic and electric hearing

Two experiments investigated pitch perception for stimuli where the place of excitation was held constant. Experiment 1 used pulse trains in which the interpulse interval alternated between 4 and 6 ms. In experiment 1a these "4-6" pulse trains were bandpass filtered between 3900 and 5300 Hz and presented acoustically against a noise background to normal listeners. The rate of an isochronous pulse train (in which all the interpulse intervals were equal) was adjusted so that its pitch matched that of the "4-6" stimulus. The pitch matches were distributed unimodally, had a mean of 5.7 ms, and never corresponded to either 4 or to 10 ms (the period of the stimulus). In experiment 1b the pulse trains were presented both acoustically to normal listeners and electrically to users of the LAURA cochlear implant, via a single channel of their device. A forced-choice procedure was used to measure psychometric functions, in which subjects judged whether the 4-6 stimulus was higher or lower in pitch than isochronous pulse trains having periods of 3, 4, 5, 6, or 7 ms. For both groups of listeners, the point of subjective equality corresponded to a period of 5.6 to 5.7 ms. Experiment 1c confirmed that these psychometric functions were monotonic over the range 4-12 ms. In experiment 2, normal listeners adjusted the rate of an isochronous filtered pulse train to match the pitch of mixtures of pulse trains having rates of F1 and F2 Hz, passed through the same bandpass filter (3900-5400 Hz). The ratio F2/F1 was 1.29 and F1 was either 70, 92, 109, or 124 Hz. Matches were always close to F2 Hz. It is concluded that the results of both experiments are inconsistent with models of pitch perception which rely on higher-order intervals. Together with those of other published data on purely temporal pitch perception, the data are consistent with a model in which only first-order interpulse intervals contribute to pitch, and in which, over the range 0-12 ms, longer intervals receive higher weights than short intervals.     

Nickel-induced magnetic behaviour of nano-structured α-Fe2O3, synthesised by facile wet chemical route

We report the synthesis of pristine and nickel containing iron oxide (α-Fe₂O₃) nanocrystallites by facile environmentally benign wet chemical process. The magnetic behaviour of the samples has been found to change progressively with nickel content. The Mössbauer spectra revealed the precipitation of secondary phase of nickel ferrite (NiFe₂O₄) at ～2?wt% nickel contents. The transmission electron micrographs together with asymmetric magnetic hysteresis loop have confirmed the formation of core–shell structure. The Morin temperature of nanostructured α-Fe₂O₃ as estimated by superconducting quantum interference device has been found to be 257, 245, 247 and 242?K at nickel content of 0, 1, 2 and 4?wt%, respectively. The similar trends of increase/decrease in Morin temperature have been noticed by Mössbauer analysis. Furthermore, below Morin temperature, the temperature range of coexisted antiferromagnetic and ferromagnetic states has been found to increase with increase in nickel content.     

Influence of roughness and capillary size on the zeta potential values obtained by streaming potential measurements

Streaming potential measurements are performed to determine the zeta potential of flat surfaces, particles, or fibers. Although the zeta potential is a well-defined property of solid surfaces in a liquid, there are indications that the absolute values of the zeta potential calculated using the Helmholtz-Smoluchowski equation are affected by surface roughness and—in case of particle or fiber assemblies—their packing density. The study at hand investigates these influences using flat polymer surfaces with different roughness and topography and assemblies of basalt spheres. It was found that increasing roughness of the flat surface and larger size or smaller number of particles in particle assemblies result in flatter slopes of the streaming potential versus pressure and thus lower apparent absolute values of the zeta potential. The interpretation of streaming potential measurements should therefore not focus on absolute zeta potential values but on trends in pH- and concentration-dependent measurements.     

Improving solid-state NMR dipolar recoupling by optimal control

We present the first solid-state NMR experiments developed using optimal control theory. Taking heteronuclear dipolar recoupling in magic-angle-spinning NMR as an example, it proves possible to significantly improve the efficiency of the experiments while introducing robustness toward instrumental imperfections such as radio frequency inhomogeneity. The improvements are demonstrated by numerical simulations as well as practical experiments on a 13Calpha,15N-labeled powder of glycine. The experiments demonstrate a gain of 53% in the efficiency for 15N to 13Calpha coherence transfer relative to the typically double-cross-polarization experiments.     

Recent developments in isotachophoresis

This paper is summarizing the contributions to the analytical capillary isotachophoresis published during the period 1981-1984. It characterizes the present state of the method and covers theory, fundamental analytical aspects, instrumentation and applications. Special attention was payed to the fundamental analytical aspects, and a detailed discussion is given of the selection of electrolyte systems, stability of zones and separability of substances. The present commercial instrumentation is also briefly described.