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.     

Use of whole‐body cryosectioning and desorption electrospray ionization mass spectrometry imaging to visualize alkaloid distribution in poison frogs

Ambient mass spectrometry is useful for analyzing compounds that would be affected by other chemical procedures. Poison frogs are known to sequester alkaloids from their diet, but the sequestration pathway is unknown. Here, we describe methods for whole‐body cryosectioning of frogs and use desorption electrospray ionization mass spectrometry imaging (DESI‐MSI) to map the orally administered alkaloid histrionicotoxin 235A in a whole‐body section of the poison frog Dendrobates tinctorius. Our results show that whole‐body cryosectioning coupled with histochemical staining and DESI‐MSI is an effective technique to visualize alkaloid distribution and help elucidate the mechanisms involved in alkaloid sequestration in poison frogs.     

Formation of plasma dust structures at atmospheric pressure

The formation of strongly coupled stable dust structures in the plasma produced by an electron beam at atmospheric pressure was detected experimentally. Analytical expressions were derived for the ionization rate of a gas by an electron beam in an axially symmetric geometry by comparing experimental data with Monte Carlo calculations. Self-consistent one-dimensional simulations of the beam plasma were performed in the diffusion drift approximation of charged plasma particle transport with electron diffusion to determine the dust particle levitation conditions. Since almost all of the applied voltage drops on the cathode layer in the Thomson glow regime of a non-self-sustained gas discharge, a distribution of the electric field that grows toward the cathode is produced in it; this field together with the gravity produces a potential well in which the dust particles levitate to form a stable disk-shaped structure. The nonideality parameters of the dust component in the formation region of a highly ordered quasi-crystalline structure calculated using computational data for the dust particle charging problem were found to be higher than the critical value after exceeding which an ensemble of particles with a Yukawa interaction should pass to the crystalline state.     

Infrared absorption in dense sodium vapor

The absorption spectra of a dense resonance medium were experimentally studied for the example of thermally heated dense sodium vapor. Several mechanisms that might cause substantial absorption and enhanced intensity of emission in the IR spectral region, λ τ; 0.9 μm, were considered. For the first time, a detailed study of the structure of the absorption spectra of sodium vapor in the specified wavelength range was performed to determine the influence of the kind and pressure of the buffer gas. It was found that buffer gas characteristics had a substantial effect on the absorption coefficient of vapor. The presence of the molecular component (dimers and trimers) in sodium vapor could not explain the experimental dependences of absorption in the infrared region. Possible influence of microparticles formed in condensation of convective sodium vapor flows in heated cells on the optical properties of vapor was considered. Microparticles could contribute to the observed absorption, but were incapable of explaining the substantial intensity of vapor radiation reported earlier. Possible many-particle effects on the absorption in the far spectral line wing were discussed. For the first time, the method of molecular dynamics was used to show for the example of the distribution function of ionic microfields in a dense plasma that such effects were in principle capable of substantially raising the profile of the line and increasing absorption in the region of large detunings from the resonance compared with the simple quasi-static model in the nearest-neighbor approximation.     

Ceramic high pressure cell with profiled anvils for neutron diffraction investigations (up to 7 GPa)

Abstract

A high pressure cell with profiled anvils for neutron diffraction investigations has been designed and tested. The matrices of the cell are made of alloyed aluminium oxide ceramic. The reliable working pressure range of the cell is up to 7 GPa at a sample volume of 64 mm³. The cell attenuates the neutron flux not more than four times, with the transmission of the cell very slightly depending on neutron wavelength.     

Click and Release Chemistry for Activity-Based Purification of β-Lactam Targets

β-Lactams, the cornerstone of antibiotherapy, inhibit multiple and partially redundant targets referred to as transpeptidases or penicillin-binding proteins. These enzymes catalyze the essential cross-linking step of the polymerization of cell wall peptidoglycan. The understanding of the mechanisms of action of β-lactams and of resistance to these drugs requires the development of reliable methods to characterize their targets. Here, we describe an activity-based purification method of β-lactam targets based on click and release chemistry. We synthesized alkyne-carbapenems with suitable properties with respect to the kinetics of acylation of a model target, the Ldt_fm L,D-transpeptidase, the stability of the resulting acylenzyme, and the reactivity of the alkyne for the cycloaddition of an azido probe containing a biotin moiety for affinity purification and a bioorthogonal cleavable linker. The probe provided access to the fluorescent target in a single click and release step.     

13C nuclear magnetic resonance spectra of several hydroxy diterpene derivatives

¹³C NMR spectra of several hydroxy diterpene derivatives having a pimarane, isopimarane and (13S, 8α)rosane skeleton have been recorded. The most significant effects caused by the introduction of hydroxyl groups in such a skeleton are demonstrated. The magnitudes of the γ- and δ-effects are large enough to allow their use in sterochemical assignments.