Zur Verträglichkeit von Polyamid-6 und Hochdruckpolyethylen in Abhängigkeit von Temperatur und Mischungsverhältnis

Zusammenfassung Verschiedene Mischungen von Polyamid-6 (PA-6) und Polyethylen mit niedriger Dichte (LDPE) wurden von Raumtemperatur bis 373 K auf ihre Verträglichkeit mittels Analyse des Freien Induktionsabfalls untersucht. Das Mischungsverhältnis wurde im Bereich 0 Gew.-% bis 100 Gew.-% des PA-6 variiert.Der Vergleich der Relaxationszeiten der Mischungen mit denen des reinen LDPE zeigt, daß die Mischungskomponenten im gesamten untersuchten Temperatur- und Konzentrationsbereich unverträglich im Sinne einer behinderten Durchdringung von Segmenten sind. Dieses Ergebnis wird durch den Temperaturverlauf der Spindichte der frei beweglichen Protonen bestätigt.Der Temperaturverlauf der Spindichte der frei beweglichen Protonen des LDPE zeigt für das reine Material sowie für die Mischungen einen deutlichen Knick im Bereich 330 K bis 340 K. Dies wird als Folge eines bei dieser Temperatur aktivierten Bewegungsmechanismus in den Polyethylenbereichen interpretiert.Herrn Prof. Dr. F. H. Müller gewidmet.     

π-Interactions between Cyclic Carbocations and Aromatics Cause Zeolite Deactivation in Methanol-to-Hydrocarbon Conversion

The understanding of catalyst deactivation represents one of the major challenges for the methanol-to-hydrocarbon (MTH) reaction over acidic zeolites. Here we report the critical role of intermolecular π-interactions in catalyst deactivation in the MTH reaction on zeolites H-SSZ-13 and H-ZSM-5. π-interaction-induced spatial proximities between cyclopentenyl cations and aromatics in the confined channels and/or cages of zeolites are revealed by two-dimensional solid-state NMR spectroscopy. The formation of naphtalene as a precursor to coke species is favored due to the reaction of aromatics with the nearby cyclopentenyl cations and correlates with both acid density and zeolite topology.     

High Accuracy Protein Structures from Minimal Sparse Paramagnetic Solid‐State NMR Restraints

There is a pressing need for new computational tools to integrate data from diverse experimental approaches in structural biology. We present a strategy that combines sparse paramagnetic solid‐state NMR restraints with physics‐based atomistic simulations. Our approach explicitly accounts for uncertainty in the interpretation of experimental data through the use of a semi‐quantitative mapping between the data and the restraint energy that is calibrated by extensive simulations. We apply our approach to solid‐state NMR data for the model protein GB1 labeled with Cu²⁺‐EDTA at six different sites. We are able to determine the structure to 0.9 Å accuracy within a single day of computation on a GPU cluster. We further show that in some cases, the data from only a single paramagnetic tag are sufficient for accurate folding.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

Electrostatic Complementarity Drives Amyloid/Nucleic Acid Co-Assembly

Proteinaceous plaques associated with neurodegenerative diseases contain many biopolymers including the polyanions glycosaminoglycans and nucleic acids. Polyanion-induced amyloid fibrillation has been implicated in disease etiology, but structural models for amyloid/nucleic acid co-assemblies remain limited. Here we constrain nucleic acid/peptide interactions with model peptides that exploit electrostatic complementarity and define a novel amyloid/nucleic acid co-assembly. The structure provides a model for nucleic acid/amyloid co-assembly as well as insight into the energetic determinants involved in templating amyloid assembly.