Indistinguishability of the models of molecular self-assembly

Numerous applications dealing with molecular aggregation at the interface of biology, physics and chemistry use either the dimer or the indefinite equilibrium constant models even though there is the well-known property of indistinguishability of the models with respect to fitting experimental data by various experimental techniques. The problem of indistinguishability is uncovered in the present work and the way in which the existing paradigm of how these models should be applied to analysis of molecular self-association is suggested.     

Synthesis and phase behaviour of poly(propylene imine) dendromesogens of lowest generations

Liquid crystal poly(propylene imine) dendrimers of the zero (D₀) and the first (D₁) generations were synthesised and structurally characterised by elemental analysis, FT-IR and nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MALDI-ToF). The phase behaviour of all the compounds was studied using polarisation microscopy and differential scanning calorimetry. Their structures were investigated by X-ray diffraction method by direct magnetic field influence. Analysis of diffraction patterns was carried out using the paracrystal model of Hosemann and the Fonk cluster model. Structural simulation and diffraction calculations on the models were used for determining the layer structure parameters of the dendrimers. Temperature behaviour of the structural parameters was considered in the interval from room temperature to isotropic melting temperature. It was determined that only the dendrimer of zero generation can be oriented by magnetic field. The schemes of phase transformations of the dendrimers look like: Cr→159^°С→Sm-C→274^°С→I for D₀ and G→55–66^°С→Sm-F→108^°С→Sm-C→274^°С→I for D₁.     

Synthesis and magnetic properties of solid solutions In<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sb〈Mn〉

Manganese-doped solid solutions In_1–x Ga _x Sb (x = 0.05, 0.1, 0.5, 0.9, 0.95) were synthesized. It was found that, in samples of the compositions In_0.95Ga_0.05Sb〈Mn〉 and In_0.05Ga_0.95Sb〈Mn〉, a homogeneous substitutional solid solution forms, into which manganese-containing clusters are incorporated. The clusters are mainly located at crystal lattice defects—grain boundaries and dislocations. The ferromagnetic properties of the obtained samples at room temperature and higher are caused by clusters Mn_1+x Sb, the effective size of which is about 180–300 nm.     

A Review of Application of Total Reflection X-ray Fluorescence Spectrometry to Water Analysis

Abstract

The aim of this article is to review the literature on the application of the total reflection X-ray fluorescence (TXRF) spectrometry for the determination of the chemical composition of aqueous samples. Details of the main stages of the analytical procedures are described. Special attention is given to the sample preparation procedure, current instrumentation, and potential error sources when analyzing the water samples of varying compositions. The examples of matrix effects and spectral interferences as well as the analytical figures of merit are also presented.     

Effect of preparation conditions on fractal structure and phase transformations in the synthesis of nanoscale M-type barium hexaferrite

The conditions of the synthesis of carbonate-hydroxide precursors (pH of FeOOH precipitation and heat treatment regimes) were studied in terms of their effect on the fractal structure and physical-chemical properties of precursors. Phase transformations which occur during the synthesis of nanosize M-type barium hexaferrite (BHF) were studied as well.The first structural level of precursors' aggregation for mass fractals, the correlation between fractal dimension and precursors' activity during the synthesis of BHF were determined.Synthesis parameters for the precursors with the optimal fractal structure were determined. These data permit an enhancement of the filtration coefficient of the precipitates by a factor of 4-5, obtaining substantial decrease in the temperature required for synthesis of a single-phase BHF, and monodispersed plate-like nanoparticles (60 nm diameter) with the shape anisotropy and good magnetic characteristics (saturation magnetization (M_s)=68,7 emu/g and coercitivity (H_c)=5440 Oe).     

Solid electrolytes based on lithium-containing lanthanum metaniobates and metatantalates with defect-perovskite structure

The structure and transport properties of lithium-containing lanthanum metaniobates and metatantalates with defect-perovskite structure, La_2/3−xLi_3x□_4/3−2xNb[Ta]₂O₆, have been studied. It has been shown that the materials under investigation possess a high lithium ion-conductivity Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002.     

Effect of synthesis conditions on the fractal structure of yttrium-stabilized zirconium dioxide

The effect of synthesis conditions (sequential precipitation, coprecipitation, and sol–gel method) on the fractal structure of yttrium-stabilized zirconium dioxide has been investigated. It has been shown that the difference between methods manifests itself clearly in xerogel nanostructures, viz. by the number of fractal aggregation levels (three levels in hydroxide precipitates and two in sol–gel) and the absence of mass-fractal aggregation in sol–gel. It is been determined that the mass-fractal aggregation of precursors contributes to good filtration of hydroxide precipitates and allows preparation of oxides with soft, readily destructible aggregates, and that surface-fractal aggregation makes for good pressability of oxides.     

Study of a composition of officinal herb mixtures using gas-liquid chromatography with mass-spectrometric detection

A composition of the volatile fraction of acetonitrile extracts of officinal herbs, used in the therapy of respiratory diseases, has been investigated. For each of the plant species we offered a set of markers, which made it possible to standardize a raw plant material and herb mixtures using a gas-liquid chromatography with mass-spectrometric detection.     

Cluster magnetism in doped InSb

Magnetic properties of indium antimonide doped by Mn and by, simultaneously, Mn and Zn, and Mn and Cd have been analyzed. It has been established that the basic contribution to the formation of the magnetic properties of these materials comes from clusters, whose composition and Curie temperature change depending on the content of manganese, zinc, and cadmium.     

Mössbauer study and magnetic properties of M-type barium hexaferrite doped with Co + Ti and Bi + Ti ions

Using X-ray powder diffractions, M?ssbauer spectroscopy, and magnetic measurements, the effect of complex dopants (Co2+ + Ti4+) and (Bi3+ + Ti4+) on the fine structure and magnetic properties of M-type barium hexaferrite prepared by hydroxide and carbonate precipitations has been studied. The distribution of cations over five nonequivalent positions of barium hexaferrite with magnetoplumbite structure is discussed. It has been shown that doped barium hexaferrite can be used for high-coercitivity data storage media.