Noise-induced precursors of tonic-to-bursting transitions in hypothalamic neurons and in a conductance-based model

The dynamics of neurons is characterized by a variety of different spiking patterns in response to external stimuli. One of the most important transitions in neuronal response patterns is the transition from tonic firing to burst discharges, i.e., when the neuronal activity changes from single spikes to the grouping of spikes. An increased number of interspike-interval sequences of specific temporal correlations was detected in anticipation of temperature induced tonic-to-bursting transitions in both, experimental impulse recordings from hypothalamic brain slices and numerical simulations of a stochastic model. Analysis of the modelling data elucidates that the appearance of such patterns can be related to particular system dynamics in the vicinity of the period-doubling bifurcation. It leads to a nonlinear response on de- and hyperpolarizing perturbations introduced by noise. This explains why such particular patterns can be found as reliable precursors of the neurons' transition to burst discharges.     

Engineering Multifunctional Capsules through the Assembly of Metal–Phenolic Networks

Metal–organic coordination materials are of widespread interest because of the coupled benefits of inorganic and organic building blocks. These materials can be assembled into hollow capsules with a range of properties, which include selective permeability, enhanced mechanical/thermal stability, and stimuli‐responsiveness. Previous studies have primarily focused on the assembly aspects of metal‐coordination capsules; however, the engineering of metal‐specific functionality for capsule design has not been explored. A library of functional metal–phenolic network (MPN) capsules prepared from a phenolic ligand (tannic acid) and a range of metals is reported. The properties of the MPN capsules are determined by the coordinated metals, allowing for control over film thickness, disassembly characteristics, and fluorescence behavior. Furthermore, the functional properties of the MPN capsules were tailored for drug delivery, positron emission tomography (PET), magnetic resonance imaging (MRI), and catalysis. The ability to incorporate multiple metals into MPN capsules demonstrates that a diverse range of functional materials can be generated.     

Synthesis and conformational analysis of efrapeptins

The efrapeptin family of peptide antibiotics produced by the fungus Tolypocladium niveum, and the neo‐efrapeptins from the fungus Geotrichum candidumare inhibitors of F₁‐ATPase with promising antitumor, antimalaria, and insecticidal activity. They are rich in C^α‐dialkyl amino acids (Aib, Iva, Acc) and contain one β‐alanine and several pipecolic acid residues. The C‐terminus bears an unusual heterocyclic cationic cap. The efrapeptins C–G and three analogues of efrapeptin C were synthesized using α‐azido carboxylic acids as masked amino acid derivatives. All compounds display inhibitory activity toward F₁‐ATPase. The conformation in solution of the peptides was investigated with electronic CD spectroscopy, FT‐IR spectroscopy, and VCD spectroscopy. All efrapeptins and most efrapeptin analogues were shown to adopt helical conformations in solution. In the case of efrapeptin C, VCD spectra proved that a 3₁₀‐helix prevails. In addition, efrapeptin C was conformationally studied in detail with NMR and molecular modeling. Besides NOE distance restraints, residual dipolar couplings (RDC) observed upon partial alignment with stretched PDMS gels were used for the conformational analysis and confirmed the 3₁₀‐helical conformation.     

Microstructures by solvent drop evaporation on polymer surfaces: dependence on molar mass

When a solvent drop evaporates from a polymer surface, it leaves behind a characteristic structure, typically a crater. We deposited toluene drops with a microsyringe onto planar polystyrene (PS) surfaces and analyzed the surface topography after drying. For low molar mass PS (Mw = 20.9-24.3 kDa) dotlike protrusions with a ridge at the periphery formed on the polymer surface. With increasing molar mass the central region decreased in height. At Mw = 29.6-643 kDa a craterlike structure with a depression in the center and a ridge was observed. At even higher molar mass, irregular structures without rotational symmetry occurred. We explain the observed dependence on the molar mass with a different degree of entanglement, leading to different dissolution rates and different diffusion constants.     

Investigation of the Crystalline State of Identical Sample Domains by Means of Divergent X-ray Beam Technique in the Direction of Transmission and Reflection in the Scanning Electron Microscope (SEM)

A supplementary device to a scanning electron microscope allows the simultaneous taking of wide-angle interferences in the directions of transmission and back reflection of identical specimen areas. A developed computer program simulates the complete reflex system so that the identity with the pattern is obtained. This results, on the one hand, in qualitative and quantitative statements concerning the real structure of the specimen and, on the other hand, shadings of reflexes caused by the target holder tube can be distinguished from interruptions of reflexes caused by the grain size effects. The efficiency of the supplementary device for the characterizing of mono- and polycrystalline specimens is demonstrated by several examples.     

ChemInform Abstract: Structure and Properties of NaCl and the Suzuki Phase Na6CdCl8

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.