Thermal-stress induced phenomena in two-component material:Part Ⅱ

The paper deals with analytical models of the elastic energy gradient Wsq representing an energy barrier. The energy barrier is a surface integral of the elastic energy density Wq. The elastic energy density is induced by thermal stresses acting in an isotropic spherical particle （q = p） with the radius R and in a cubic cell of an isotropic matrix （q = m）. The spherical particle and the matrix are components of a multi-particle-matrix system representing a model system applicable to a real two-component material of a precipitation-matrix type. The multi-particle-matrix system thus consists of periodically distributed isotropic spherical particles and an isotropic infinite matrix. The infinite matrix is imaginarily divided into identical cubic cells with a central spherical particle in each of the cubic cells. The dimension d of the cubic cell then corresponds to an inter-particle distance. The parameters R, d along with the particle volume fraction v = v（R, d） as a function of R, d represent micro- structural characteristics of a real two-component material. The thermal stresses are investigated within the cubic cell, and accordingly are functions of the microstructural charac- teristics. The thermal stresses originate during a cooling pro- cess as a consequence of the difference am - ap in thermal expansion coefficients between the matrix and the particle, am and ap, respectively. The energy barrier Wsq is used for the determination of the thermal-stress induced strengthening aq. The strengthening represents resistance against com- pressive or tensile mechanical loading for am - ap 〉 0 or am - ap 〈 0. respectively.     

Stereospecific Synthesis of D-Glycero-D-ido-oct-2-ulose

Summary.  D-Glycero-D-gulo-heptose reacted with 2,2-dimethoxypropane to give its 2,3:6,7-di-O-isopropylidene derivative. Its base-catalyzed addition to formaldehyde resulted in the formation of 2,3:6,7-di-O-isopropylidene-2-C-(hydroxymethyl)-D-glycero-D-gulo-heptofuranose. After acid hydrolysis of this aldolization product, a new branched-chain aldose, 2-C-(hydroxymethyl)-D-glycero-D-gulo-heptose, was obtained, which was stereospecifically rearranged under the catalytic action of molybdic acid to D-glycero-D-ido-oct-2-ulose. Received October 17, 2000. Accepted December 4, 2000     

Self-Associating Polymers Chitosan and Hyaluronan for Constructing Composite Membranes as Skin-Wound Dressings Carrying Therapeutics

Chitosan, industrially acquired by the alkaline N-deacetylation of chitin, belongs to β-N-acetyl-glucosamine polymers. Another β-polymer is hyaluronan. Chitosan, a biodegradable, non-toxic, bacteriostatic, and fungistatic biopolymer, has numerous applications in medicine. Hyaluronan, one of the major structural components of the extracellular matrix in vertebrate tissues, is broadly exploited in medicine as well. This review summarizes that these two biopolymers have a mutual impact on skin wound healing as skin wound dressings and carriers of remedies.     

Reagents for Detection of Carboxylate Anion Ligands after Chromatographic Separation of Zinc Carboxylato Complexes

JPC – Journal of Planar Chromatography – Modern TLC - Reagents for detection of carboxylate anions as components of zinc carboxylato mixed-ligand complexes, after chromatographic...     

The structural transitions in ferronematics and ferronematic droplets

The paper presents an overview of the observations of structural transitions in ferronematic based on thermotropic nematic 6CHBT (4-trans-4′-n-hexyl-cyclohexyl-isothiocyanato-benzene) and in ferronematic droplets. The type of anchoring was determined using the results of the capacitance measurements. The ferronematic droplets were observed in solutions of nematogenic 6CHBT with fine magnetic particles and phenyl isocyanate. The phase diagram of the transitions between isotropic and nematic phases was found. The magneto-dielectric measurements of various structural transitions in this new system enabled to estimate the type of anchoring of nematic molecules on magnetic particles surfaces in droplets.     

Monitoring enzymic peroxidation of NAD by capillary electrophoresis

NAD⁺ is degraded by horse liver alcohol dehydrogenase in a reaction with p-methylbenzyl hydroperoxide, which acts as a pseudo-substrate. An unstable intermediate product (called compound I) is formed, and this is converted into the final product NADX. The reaction can be monitored by capillary electrophoresis. NADX migrates as two well resolved peaks (NADX₁ and NADX₂), which belong probably to the tautomers of the same substance. The intermediate product, compound I, has the same effective mobility as the conformer NADX₂ and it was impossible to separate compound I from NADX₂. The spectra taken during the separation show clearly that the “9-min” peak contains different compounds during the course of the reaction and the NADX₂ is not identical with compound I.     

REVIEW: metal complexes as urease inhibitors

Urease plays a significant role in the pathogenesis of several diseases and also has practical implications in other fields, such as agriculture or chemical analysis. Among the multitude of chemical species known to inhibit urease, metal complexes stand out as a special category due to their specific mechanism of action, distinct from purely organic substances. Their inhibitory activity seems to depend on the type of metal and its oxidation state as well as on the coordination environment of the central atom. Furthermore, the study of the interaction between metal ions and their complexes with urease renders valuable insights into detailed catalytic mechanisms of this enzyme. This brief survey attempts to provide an overview of the published research on urease inhibition by metal complexes.     

Structure and properties of titanium-zinc borophosphate glasses

The structure of 50ZnO-10B₂O₃-40P₂O₅+xTiO₂ glasses prepared by slow cooling (for x=0-24 mol% TiO₂) or by quenching (for x=28-64 mol% TiO₂) was studied by Raman, ³¹P and ¹¹B MAS NMR spectroscopy. TiO₂ incorporates into the glass structure, which results in a decrease in the molar volume and an increase in the glass transition temperature. According to Raman spectra Ti atoms form distorted TiO₆ octahedra and their incorporation into the structural network results in the depolymerization of phosphate chains. ¹¹B NMR spectra of the glasses with increasing TiO₂ content show gradual changes from one symmetrical signal of B(OP)₄ units to a broad complex signal which was separated into five signals ascribed to four different types of BO₄ units and one BO₃ unit. With increasing TiO₂ content a part of boron atoms changes from tetrahedral BO₄ to trigonal BO₃ units, which is ascribed to the formation of TiO₆ units in the glass structure.