Synthesis and Structure of N-Pyridyl-Containing Cyclic Aminomethylphosphines

N-pyridyl-containing cyclic aminomethylphosphines have been prepared via condensation of the corresponding bis(hydroxymethyl)arylphosphines with p-aminopyridine and m-aminomethylpyridine.     

Rotational Striations and Diffusion in Barium Sodium Niobate Crystals

The possibility of inducing rotational growth striae with a small period in barium sodium niobate crystals (BSN) is examined. Crystals grown had a period stability up to 1 percent and were suitable material for anisotropic light diffraction by ferroelectric domains. However intense striae were produced only for periods λ > 5 m̈m. With the help of Bragg optical diffraction by growth striae the diffusion coefficient D in solid phase responsible for striae smoothing during annealing was measured. The magnitude D ≈ 10^-11 cm² s^-1 at the melting point was obtained. Such D value leads to the vanishing of striae with λ < 5 m̈m in BSN crystals during growth.     

Synthesis and crystal structures of anhydrous lithium and ammonium hypophosphites

Conditions of synthesis (temperature, precursors) have been selected to grow crystals of anhydrous lithium and ammonium hypophosphites. The crystal structure of LiH₂PO₂ has been determined. Cell parameters and atomic positions in (NH₄)H₂PO₂ at room temperature and at 100 K have been refined. By their oxygen atoms the hypophosphite anions serve to bridge the four cations. Each oxygen atom is bonded to two cations, creating puckered layers parallel to the (001) planes. The structures show much similarity in the general arrangement, but differ in the type of the tetrahedral cation-anion bonds. In LiH₂PO₂, the Li-O bond is ionic (1.933(4) Å); in (NH₄)H₂PO₂, N-H...O is a hydrogen bond (2.846(1) Å).Original Russian Text Copyright © 2004 by M. I. Naumova, N. V. Kuratieva, D. Yu. Naumov, and N. V. PodberezskayaTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 491–496, May–June 2004.     

Kinetics of the electrocatalytic oxidation of glucose by Escherichia coli bacterial cells in the presence of exogenous mediators

Processes in the glucose-Escherichia coli cells-mediator-electrode bioelectrochemical system were studied using the kinetic model of processes on microbial mediator anodes. The model was constructed using the Michaelis-Menten equation. It takes into account the constants of substrate and mediator distribution between the inner medium of the cell and the working solution. The kinetic analysis of processes in the system under study showed that when Escherichia coli bacterial cells are used as a catalyst, methylene blue is a more effective mediator of electron transfer than gallocyanine.     

Dispersion of the dielectric function real part for Mg:LiNbO3 crystals at terahertz frequencies

We study dispersion of the dielectric function real part ε′ in the terahertz-frequency range for bulk and periodically poled congruent LiNbO₃ and Mg:LiNbO₃ crystals. The concentration of Mg in Mg:LiNbO₃ samples was close to 5 mol%, which is the photorefractive threshold. Approximate expressions for extraordinary polariton dispersion dependence were obtained in the range 0.5–6.5 THz. The influence of Mg-dopant on the optical properties of crystals in the terahertz range is revealed. Changes of the defect structure of lithium niobate crystals are discussed.     

Solution Plasma Processing as an Environmentally Friendly Method for Low-Molecular Chitosan Production

Plasma Chemistry and Plasma Processing - The use of low molecular weight chitosan in biomedicine and agriculture requires the development of new environmentally friendly technology for its...     

On the frequency spectrum of free vibrations of membranes and plates in contact with a fluid

A parallelepiped-shaped container, which is completely filled with a perfect incompressible fluid, is considered. The container is covered with an elastic lid, which is modeled by a membrane or a constant-thickness plate. The other faces of the container are nondeformable. The frequency spectrum of small free vibrations of the lid has been obtained taking into account the apparent mass of the fluid the movement of which is assumed to be potential. The main specific feature of the problem formulation is that the volume of the fluid under the cover remains unchanged in the course of vibrations. As a result, the shape of the deflection of the lid should satisfy the equation of constraint, which follows from the condition of preservation of the volume of the fluid under the lid.     

Degenerate parametric light scattering in periodically poled LiNbO3:Y:Fe

The first observation of parametric light scattering patterns (rings, lines, and dots) in bulk periodically poled nonlinear media is reported. Development of the scattering patterns proves efficient photorefractive grating recording and considerable parametric gain for seed radiation in this new nonlinear material. Several novel phase-matched parametric processes, caused by the periodicity of the domain structure, are revealed.     

Hexa­aqua­nickel(II) bis­(hypophosphite)

The structure of hexa­aqua­nickel(II) bis­(hypophosphite), [Ni(H₂O)₆](H₂PO₂)₂, has been determined. The crystals are prismatic. The packing of the Ni and P atoms (not the entire hypophosphite anions) is the same as in the structures of [Co(H₂O)₆](H₂PO₂)₂ and [Co_0.5Ni_0.5(H₂O)₆](H₂PO₂)₂. The Ni^II cations have a pseudo‐face‐centered cubic cell, with cell parameter a 10.216 Å and tetrahedral cavities occupied by P atoms. The Ni^II cation has crystallographically imposed twofold symmetry and has an octahedral coordination sphere consisting of six water O atoms, two of which also lie on the twofold axis. The planes of oppositely coordinated water mol­ecules are in a cross conformation. The geometry of the hypophosphite anion is close to point symmetry mm2. The hypophosphite anions are hydrogen bonded to the coordinated water molecules.