Sulfur makes the difference: synthesis and mesomorphic properties of novel thioether-functionalized imidazolium ionic liquid crystals

Novel thioether-linked imidazolium ionic liquid crystals were synthesized starting from methyl 2-mercaptoacetate. The mesomorphic properties were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. All mesogens displayed smectic A mesophase geometries with strongly interdigitated bilayer structures. Comparison of the thioether-linked imidazolium salts with the corresponding amine- and amide-linked imidazolium salts as well as simple N-alkyl-imidazolium salts showed that both mesophase width and stability increased with increasing softness of the linking unit, thus indicating the beneficial effect of sulfur. Additionally, an increase of the length of the linking unit decreased the interdigitation of the alkyl chains.     

Front Cover: Creating Hydrophobic Foils From Biopolymer Blends Using Mechanical Microimprinting (ChemPhysChem 20/2023)

The surface topography of biodegradable polymer foils is modified by mechanical imprinting on a submillimeter length scale. The created patterns strongly influence the wetting behavior and allow the preparation of hydrophobic surfaces with controlled solid-liquid interaction. A detailed analysis of anisotropic surface patterns reveals that the observed effect arises from a combination of topographical and compositional changes that are introduced to the surface. As a main result it is found that an individual combination of material and structure is required for the production of water-repellent biopolymer foils that are highly attractive for packaging applications.     

Low-temperature thermolysis behavior of tetramethyl- and tetraethyldistibines

The thermolysis behavior of tetramethyl- and tetraethyldistibine (Sb(2)Me(4) and Sb(2)Et(4)) was investigated using a mass spectrometer coupled to a tubular flow reactor under near-chemical vapor deposition (CVD) conditions. Sb(2)Me(4) undergoes a gas-phase disproportionation with an estimated activation energy of 163 kJ/mol. This reaction leads to the formation of methylstibinidine, SbMe, that reacts on the surface to produce antimony film and SbMe(3). Unfortunately, this clean decomposition pathway is limited to a narrow temperature range of 300-350 degrees C. At temperatures exceeding 400 degrees C, SbMe(3) decomposes following a radical route with a consequent risk of carbon contamination. In contrast, Sb(2)Et(4) disproportionates at the hot wall of the reactor. According to mass-spectrometric data, this reaction is significant starting at a temperature of 100 degrees C, with an apparent activation energy of 104 kJ/mol. Within the temperature range of 100-250 degrees C, the precursor decomposition leads to the formation of antimony films and SbEt(3), whereas different molecular reaction pathways are significantly activated above 250 degrees C. The use of Sb(2)Et(4) lowers the risk of carbon contamination compared to Sb(2)Me(4) at high temperature. Therefore, Sb(2)Et(4) is a promising CVD precursor for the growth of antimony films in the absence of hydrogen atmosphere in a wide temperature range.     

Cut points in metric spaces

In this note, we will define topological and virtual cut points of finite metric spaces and show that, though their definitions seem to look rather distinct, they actually coincide. More specifically, let X denote a finite set, and let denote a metric defined on X. The tight span T(D) of D consists of all maps for which f(x)=sup_yX(xy−f(x)) holds for all xX. Define a map fT(D) to be a topological cut point of D if T(D)−{f} is disconnected, and define it to be a virtual cut point of D if there exists a bipartition (or split) of the support of f into two non-empty sets A and B such that ab=f(a)+f(b) holds for all points aA and bB. It will be shown that, for any given metric D, topological and virtual cut points actually coincide, i.e., a map fT(D) is a topological cut point of D if and only if it is a virtual cut point of D.     

A generalized Fourier–Hermite method for the Vlasov–Poisson system

BIT Numerical Mathematics - A generalized Fourier–Hermite semi-discretization for the Vlasov–Poisson equation is introduced. The formulation of the method includes as special cases the...     

β-Sheet Core of Tau Paired Helical Filaments Revealed by Solid-State NMR

One of the hallmarks of Alzheimer's disease is the self-assembly of the microtubule-associated protein tau into fibers termed "paired helical filaments" (PHFs). However, the structural basis of PHF assembly at atomic detail is largely unknown. Here, we applied solid-state nuclear magnetic resonance (ssNMR) spectroscopy to investigate in vitro assembled PHFs from a truncated three-repeat tau isoform (K19) that represents the core of PHFs. We found that the rigid core of the fibrils is formed by amino acids V306 to S324, only 18 out of 99 residues, and comprises three β-strands connected by two short kinks. The first β-strand is formed by the well-studied hexapeptide motif VQIVYK that is known to self-aggregate in a steric zipper arrangement. Results on mixed [(15)N:(13)C]-labeled K19 fibrils show that β-strands are stacked in a parallel, in-register manner. Disulfide bridges formed between C322 residues of different molecules lead to a disturbance of the β-sheet structure, and polymorphism in ssNMR spectra is observed. In particular, residues K321-S324 exhibit two sets of resonances. Experiments on K19 C322A PHFs further confirm the influence of disulfide bond formation on the core structure. Our structural data are supported by H/D exchange NMR measurements on K19 as well as a truncated four-repeat isoform of tau (K18). Site-directed mutagenesis studies show that single-point mutations within the three different β-strands result in a significant loss of PHF aggregation efficiency, highlighting the importance of the β-structure-rich regions for tau aggregation.