Accelerated NMR Spectroscopy with Low‐Rank Reconstruction

Accelerated multi‐dimensional NMR spectroscopy is a prerequisite for high‐throughput applications, studying short‐lived molecular systems and monitoring chemical reactions in real time. Non‐uniform sampling is a common approach to reduce the measurement time. Here, a new method for high‐quality spectra reconstruction from non‐uniformly sampled data is introduced, which is based on recent developments in the field of signal processing theory and uses the so far unexploited general property of the NMR signal, its low rank. Using experimental and simulated data, we demonstrate that the low‐rank reconstruction is a viable alternative to the current state‐of‐the‐art technique compressed sensing. In particular, the low‐rank approach is good in preserving of low‐intensity broad peaks, and thus increases the effective sensitivity in the reconstructed spectra.     

Study of structural order in porphyrin-fullerene dyad ZnDHD6ee monolayers by electron diffraction and atomic force microscopy

The structure of porphyrin-fullerene dyad ZnDHD6ee monolayers formed on the surface of aqueous subphase in a Langmuir trough and transferred onto solid substrates has been studied. The data obtained are interpreted using simulation of the structure of isolated molecules and their packing in monolayer and modeling of diffraction patterns from molecular aggregates having different sizes and degrees of order. Experiments on the formation of condensed ZnDHD6ee monolayers are described. The structure of these monolayers on a water surface is analyzed using π-A isotherms. The structure of the monolayers transferred onto solid substrates is investigated by electron diffraction and atomic force microscopy. The unit-cell parameters of two-dimensional domains, which are characteristic of molecular packing in monolayers and deposited films, are determined. Domains are found to be organized into a texture (the molecular axes are oriented by the [001] direction perpendicular to the substrate). The monolayers contain a limited number of small 3D domains.     

Study of polyelectrolyte complexes of chitosan and sulfoethyl cellulose

The complexing of polycation chitosan and polyanion sulphoethyl cellulose during the formation of polyelectrolyte simplex membranes using the layer-by-layer deposition of a solution of one polyion on a gel-like film of another one has been studied. The structural characteristics of the multilayer composites and their components have been analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray microanalysis. A technique is proposed for studying the structure of surface layers of thin polymer films (15–20 μm) using a portable DIFREI-401 diffractometer. It is shown that the sequence of layer deposition during the formation of membrane films does not affect their structural characteristics. The interaction between positively charged chitosan groups (-NH ₃ ⁺ ) and negatively charged sulfoethyl cellulose groups (-SO ₃ ^? ) during the growth of polyelectrolyte complexes results in a packing of chitosan chains in the multilayer film.     

Stabilization of nanocrystalline 2D structures of silicon with perfluorophenyl ligands

Use of perfluorophenyl ligands for stabilization of silicon nanocrystals gives rise to 2D structures with an area up to 50 × 15 nm² and a thickness of about 3 nm. Their formation can be explained by specific interactions of perfluorophenyl ligands.     

High-resolution X-ray diffractometry and transmission electron microscopy as applied to the structural study of InAlAs/InGaAs/InAlAs multilayer transistor nanoheterostructures

InAlAs/InGaAs/InAlAs nanoheterostructures with different structures of metamorphic buffer layer and quantum well, which were grown by means of molecular-beam epitaxy on GaAs and InP substrates, are investigated. The laboratory technology of the growth of the given nanoheterostructures with predicted properties is perfected. The potential of an approach based on the comprehensive analysis of experimental data obtained via different techniques, namely, X-ray diffractometry, electron diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and atomic-force microscopy is studied. The metamorphic buffer layer design is improved on the basis of the results of the performed investigations. A method whereby balanced-mismatched superlattices are introduced directly inside the metamorphic buffer layer is proposed. It is established that the technological parameters of the growth of nanoheterostructures affect their structural perfection and electrophysical properties.     

Accuracy and robustness of three-way decomposition applied to NMR data

Three-way decomposition is a very versatile analysis tool with applications in a variety of protein NMR fields. It has been used to extract structural data from 3D NOESYs, to determine relaxation rates in large proteins, to identify ligand binding in screening for lead compounds, and to complement non-uniformly recorded (sparse) spectra. All applications so far concerned experimental data sets; it thus remains to address questions of accuracy and robustness of the method using simulated data where the correct answer is known. Systematic tests are presented for relaxation and NOESY data sets. Mixtures of real and synthetic data are used to allow control of various parameters and comparisons with correct reference data, while working with input that is as realistic as possible. The influence of the following parameters is evaluated: signal-to-noise, overlap of signals and the use of a regularization procedure within the algorithm. The main criteria used for the evaluation are accuracy and precision. It is shown that deterioration of accuracy is indicated by internal checks such as decrease of precision. Both with relaxation data and when interpreting NOESY spectra, three-way decomposition exhibits a robust behavior in situations with severe signal overlap and/or poor signal-to-noise, e.g., by avoiding false positives in the NOE shapes of NOESY decompositions. As a complement to this study, three-way decomposition is compared to other methods that achieve the same type of results.     

Features of the sol-gel synthesis of TiO2 nanolayers with calcium phosphate structures on titanium surface

Russian Journal of General Chemistry - A procedure for the synthesis of composite nanocoating TiO2/calcium phosphate structures on the titanium surface promising for biomedical application (bone...     

Low-Voltage Scanning Electron Microscopy and Energy-Dispersive X-Ray Microanalysis of the Interface of Multilayer Polymer Composite

The morphology of the layer of polyelectrolyte complex, which is formed in the composite based on chitosan and sulfoethyl cellulose during the contact of a solution of one of them with a gel film of the other one, has been investigated by the low-voltage (≤3 kV) scanning electron microscopy. A technique for eliminating the effects related to charge accumulation on the dielectric film surface is proposed.     

Method of Search for Hidden Photons of Cold Dark Matter Using a Multi-Cathode Counter

Physics of Atomic Nuclei - We propose a method of search for cold dark matter, which presumably consists of hidden photons, by detecting single electrons emitted from the surface of the metal...