Double- and zero-quantum NMR relaxation dispersion experiments sampling millisecond time scale dynamics in proteins

TROSY-based NMR relaxation dispersion experiments that measure the decay of double- and zero-quantum (1)H-(15)N coherences as a function of applied (1)H and (15)N radio frequency (rf) fields are presented for studying millisecond dynamic processes in proteins. These experiments are complementary to existing approaches that measure dispersions of single-quantum (15)N and (1)H magnetization. When combined, data from all four coherences provide a more quantitative picture of dynamics, making it possible to distinguish, for example, between two-site and more complex exchange processes. In addition, a TROSY-based pulse scheme is described for measuring the relaxation of amide (1)H single-quantum magnetization, obtained by a simple modification of the multiple-quantum experiments. The new methodology is applied to a point mutant of the Fyn SH3 domain that exchanges between folded and unfolded states at 25 degrees C.     

Accelerated Nuclear Magnetic Resonance Spectroscopy with Deep Learning

Nuclear magnetic resonance (NMR) spectroscopy serves as an indispensable tool in chemistry and biology but often suffers from long experimental times. We present a proof-of-concept of the application of deep learning and neural networks for high-quality, reliable, and very fast NMR spectra reconstruction from limited experimental data. We show that the neural network training can be achieved using solely synthetic NMR signals, which lifts the prohibiting demand for a large volume of realistic training data usually required for a deep learning approach.     

Electrophysical characteristics and structural parameters of metamorphic HEMT nanoheterostructures In0.7Al0.3As/In0.7Ga0.3As/In0.7Al0.3As containing superlattices with different numbers of periods in the metamorphic buffer

The results of studying the electrophysical characteristics and structural parameters of metamorphic In_0.7Al_0.3As/In_0.7Ga_0.3As/In_0.7Al_0.3As HEMT nanoheterostructures epitaxially grown on GaAs (100) substrates have been presented. A linear metamorphic buffer with inserted unbalanced superlattices characterized by different numbers of periods is used. Transmission electron microscopy has shown that an increase in the number of superlattice periods from 5 to 30 promotes the improvement of the crystal structure. In this case, the electrophysical parameters of metamorphic HEMT nanoheterostructures are also significantly improved.     

Effect of nanosized titania on the structure and properties of the composites based on butadienenitrile rubber

Nanocomposites based on butadienenitrile rubber (butadiene copolymer with 28% acrylonitrile) with functional titania nanoparticles of different nature have been obtained, and their complex study by X-ray diffractometry, small-angle X-ray scattering, scanning electron microscopy, electron probe X-ray microanalysis, and X-ray energy-dispersive spectroscopy has been performed. Differences in the morphology and composition of the surface and transverse cuts of nanocomposites in dependence of nanoparticle characteristics are established. It is found that the nanocomposites with the largest crystallite sizes have the lowest viscosity. It is also revealed that the nature of titania nanoparticles barely affects the vulcanization kinetics, and that the optimal vulcanization time for the composites is 25 min. Uniaxial extension tests have shown that nanocomposites with the best properties can be fabricated by introducing amorphous titania into the polymer (butadienenitrile rubber).     

Synthesis of sodium allyl sulfonate in an aqueous medium by micellar catalysis with methoxy polyethylene glycol methacrylates

Micellar catalysis with various polyoxyethylated compounds was used to synthesize sodium allyl sulfonate by the reaction of allyl chloride with an aqueous solution of sodium sulfite. It was shown that methoxy polyethylene glycol methacrylates and water soluble polymers based on these compounds are surfactants and can be used to intensify the synthesis of sodium allyl sulfonate, which is of interest in the case of its subsequent application to obtain copolymers with methoxy polyethylene glycol methacrylates.     

Separating ultra-high molecular weight polymers on monolithic capillary columns

The chromatographic behavior of a polystyrene sample with a molecular weight of 20 × 10⁶ Da and narrow molecular weight distribution is studied on a monolithic capillary column based on polydivinylbenzene. It is found that either one symmetrical peak or two peaks that cannot be completely separated over the range of flow rates for the mobile phase can be observed in the chromatogram, depending on the flow rate of the mobile phase. The observed changes in the elution profile of polystyrene standards are attributed to the presence of dynamic equilibrium in the system (reaction chromatography), for which the apparent constants of forward and reverse reactions and the apparent equilibrium constant are obtained. It is noted that the apparent constant of direct reaction increases linearly with a rising eluent flow rate, while saturation and even a drop in the apparent rate constant of the reverse reaction is observed when the flow rate of the eluent rises. It is suggested that the observed changes are related to conformational transitions in the macromolecules of polystyrene, but a detailed explanation of the observed effect requires further investigation.     

Steady motions and integral manifolds of systems with quadratic integrals

An investigation is made of conservative systems with an additional integral of motion which is quadratic in the velocity. A method which takes into account the specific features of the mechanical problems is proposed to describe steady motions and integral surfaces in phase space. As an example, a non-holonomic problem, involving the motion of a rigid body carrying a gyroscope is considered.     

Model-Free Approach beyond the Borders of Its Applicability

Model calculations presented in this article show that commonly used methodology of¹⁵N relaxation data analysis completely fails in detecting nanosecond time scale motions if the major part of the molecule is involved in these motions. New criteria are introduced for the detection of such cases, based on the dependence of the apparent overall correlation time, derived from theT₁/T₂ratio, on the spectrometer frequency. Correctly estimating the overall rotation correlation time τ_Rwas shown to play the key role in model-free data analysis. It is found, however, that in cases of slow internal motions with characteristic times of more than 3–4 ns, the effective τ_Rprovided by theT₁/T₂ratio for individual amide nitrogens can be used for the characterization of the fast picosecond internal dynamics.     

Hyperdimensional NMR spectroscopy with nonlinear sampling

An approach is described for joint interleaved recording, real-time processing, and analysis of NMR data sets. The method employs multidimensional decomposition to find common information in a set of conventional triple-resonance spectra recorded in the nonlinear sampling mode, and builds a model of hyperdimensional (HD) spectrum. While preserving sensitivity per unit of measurement time and allowing for maximal spectral resolution, the approach reduces data collection time on average by 2 orders of magnitude compared to the conventional method. The 7-10 dimensional HD spectrum, which is represented as a set of deconvoluted 1D vectors, is easy to handle and amenable for automated analysis. The method is exemplified by automated assignment for two protein systems of low and high spectral complexity: ubiquitin (globular, 8 kDa) and zetacyt (naturally disordered, 13 kDa). The collection and backbone assignment of the data sets are achieved in real time after approximately 1 and 10 h, respectively. The approach removes the most critical time bottlenecks in data acquisition and analysis. Thus, it can significantly increase the value of NMR spectroscopy in structural biology, for example, in high-throughput structural genomics applications.