Synthesis and Biological Activity of New Aminophosphabetaines

Russian Journal of General Chemistry - Aminophosphabetaines, i.e., isobutyl {[alkyl(dimethyl)ammonio]methyl}phosphonates with higher alkyl substituents at the nitrogen atom, were obtained by a...     

Estimation of output beam characteristics of laser with unstable resonator and turbulent active medium

In this paper we present calculations of the three-dimensional mode structure and output beam characteristics of unstable resonator with turbulent active medium. The calculations of the output beam are carried out in the Fresnel approximation using the well-known iterative method [1]. The active medium is modeled as a series of phase screens with Kolmogorov statistics. The dependence of output radiation parameters of the gas flow laser with unstable resonator on the strength of turbulence in active medium and parameters of resonator is under consideration.     

Vibrational characteristics of the niobium dichalcogenide. Bulk samples and nanofilms

A model of the niobium diselenide crystal lattice has been proposed. This model sufficiently describes the vibrational characteristics of both bulk samples and nanofilms with a thickness beyond one three-layered structural element. Calculation of the local Green functions and mean-squared atom amplitudes have been performed using the Jacobi-matrix method.Phonon density of states features stipulated by acoustic branches and low-frequency low-dispersion optical modes cross-over have been analyzed.     

Pseudo-CSA restraints for NMR refinement of nucleic acid structure

Upon alignment of oligonucleotides in a magnetic field, the downfield TROSY component of the 13C-{1H} doublet changes its resonance frequency as a result of residual 13C-1H dipolar coupling (RDC) and residual 13C chemical shift anisotropy (RCSA), and the sum of these two second rank tensors is referred to as the pseudo-CSA. The experimentally measured difference in the resonance frequency of the 13C TROSY component in the aligned and isotropic samples is referred to as residual pseudo-CSA (RPCSA), and it can be used directly as a restraint during structure calculation. Because measurement of the RPCSA involves detection of the narrow TROSY 13C doublet component, it is applicable to systems with larger rotational correlation times than RDC measurement. The method is demonstrated for structure refinement of the helical region of a 24-nt stem-loop segment or ribosomal helix-35, uniformly enriched in 13C and 15N, with RPCSA values measured at 5 and 25 degrees C. Substantial cross-validated improvements in structural accuracy are obtained upon incorporation of RPCSA restraints.     

Local vibrations in fcc crystals with two-parametric substitutional impurities

The threshold parameters of defects (the mass defect and the relative change in the force constants) are determined at which local vibrations start to occur in an fcc crystal with substitutional impurities. The characteristics of local vibrations are investigated, and the influence of the defect parameters on the frequency of local vibrations and their decay rate with distance from the impurity atom is analyzed. The frequencies and the intensities of local vibrations are calculated for the nearest neighboring atoms of an impurity, which, combined with the impurity atom, form a defect cluster.     

Numerical investigation of the microstructure of a clad layer produced via laser cladding with coaxial metal powder injection

The microstructure of a clad layer produced via selective laser cladding with coaxial metal powder injection is studied numerically. The Johnson–Mehl–Avrami–Kolmogorov equation for condensed systems with inhomogeneous rates of nucleation is used to model the phase change kinetics. The impact of the substrate boundary along with interconnected heat transfer and phase change processes on the final microstructure of a built-up layer is demonstrated. The qualitative difference between the behavior of the temperature on the built-up layer’s surface and at the depth of the substrate is established, revealing the inhomogeneous microstructure of the final layer.     

Improved fitting of solution X-ray scattering data to macromolecular structures and structural ensembles by explicit water modeling

A new procedure, AXES, is introduced for fitting small-angle X-ray scattering (SAXS) data to macromolecular structures and ensembles of structures. By using explicit water models to account for the effect of solvent, and by restricting the adjustable fitting parameters to those that dominate experimental uncertainties, including sample/buffer rescaling, detector dark current, and, within a narrow range, hydration layer density, superior fits between experimental high resolution structures and SAXS data are obtained. AXES results are found to be more discriminating than standard Crysol fitting of SAXS data when evaluating poorly or incorrectly modeled protein structures. AXES results for ensembles of structures previously generated for ubiquitin show improved fits over fitting of the individual members of these ensembles, indicating these ensembles capture the dynamic behavior of proteins in solution.