Specific features of pathogenic mineral formation in the human body

Key relationships in pathogenic mineral formation within the human body were summarized. It was shown that pathogenic organomineral aggregates in human body are formed in complex multicomponent media containing organic and inorganic components. In the course of lithogenesis, the composition of biological fluid undergoes major changes. Phase formation in human urine and oral fluid in the initial stages leads to emergence of less thermodynamically stable phases, i.e., is kinetically controlled. Amino acids, as well as a number of inorganic impurities, are actively involved in crystallization of the main phases of renal calculi.     

Specific features of interface formation for metal-ceramic coatings on a steel base

Mechanism of pearlite formation in the base metal in melting of coatings based on self-fluxing alloys was studied. A zone in the form of a complex carboboride (Fe, Ni, Cr, Si) (BC) in the multilayer coating-steel interface was found and studied. The effect of pore space filling by needles of carboboride phases of the solid interlayer was revealed. It was shown that the coating composition and characteristics of strengthening additives (composition and dispersity) affect the structuring of the transition zone.     

Specific features of the formation of zinc and cadmium complexes with tetraphenylporphine in amphiprotic media

The kinetics of the complex formation reactions of tetraphenylporphine with zinc and cadmium acetates in mixed solvents containing alcohols and inert diluents was studied by electronic absorption spectroscopy. The dependences of the rate constant on the binary solvent composition have an extreme character, which is universal in the temperature range 298–313 K for different salts, alcohols, and weakly solvating diluents. The electric conductivity of zinc acetate solutions was measured in a wide range of compositions of alcohol-chloroform binary solvents. The electric conductivity increased with an increase in the content of alcohols.     

Specific features of the formation,catalytic activity,and corrosion stability of PdCu electrolytic co-deposit

Journal of Solid State Electrochemistry - A mixed electrolytic deposit (ED) of PdCu (~20 at.% Cu) is synthesized from a solution of 1 mМ PdSO4 + 5 mМ...     

Specific features of formation and molecular structure of polyaniline-based composite coatings deposited from active gas phase

Regular trends in formation of composite polymeric coatings based on polyaniline (emeraldine base) and thermoplastic polymers (polytetrafluoroethylene, polyurethane) from the gas phase generated by electron-beam dispersion were determined. The dependence of the molecular structure and adsorption activity of the deposited coating on its composition at various modes of support treatment was examined.     

Modelization of photocatalyzed oxidation of polyolefins. II. ZnO and TiO2 photocatalyzed decomposition of tert-butyl hydroperoxide and atactic polypropylene hydroperoxides

Direct evidence of the TiO₂ and ZnO photocatalytic decomposition of tert-butyl hydroperoxide and atactic polypropylene hydroperoxides in solution is reported. Molecular and macromolecular hydroperoxides behaved similarly. Untreated TiO₂ in the rutile form was a far more efficient photocatalyst than ZnO in solution; the photoactivities of both pigments were limited on preferential absorption sites. In the solid state no preferential reaction sites were observed. When added to preoxidized atactic polypropylene both pigments were photocatalysts of the formation of macromolecular hydroperoxides and of their decomposition. The photoreactivities of untreated TiO₂ and ZnO varied less than in solution.     

Specific features of polymer oxidation

A polymeric substance consists of long chainlike molecules forming complex non-uniform structures. Both anisotropy of macromolecules and irregularity of their packing result in a marked deviation of polymer oxidation process from that of low-molecular compounds.     

Specific features of the structural organization of composite fibrous membranes polycon and their electrotransport properties

Peculiarities of the porous structure and hydrophilic-hydrophobic properties of composite ion-exchange membranes Polycon K based on novolac phenolformaldehyde fibers are studied by the method of standard contact porosimetry. Differences are revealed in the values of maximum porosity, internal specific surface, volume of macropores, and other structural characteristics associated with different conditions of sulfonation of fibers. The formation of pores in the fibrous phase at the diffusion of monomers during the preparation of membranes is confirmed by the data of scanning electron microscopy and differential scanning calorimetry. Correlation is found between the structural characteristics and electrotransport properties of composite membranes. It is shown that the increase in the macropore volume in the modified fibers enhances the sensitivity of specific conductivity of membranes with respect to the concentration of equilibrium solution and leads to the lower selectivity.     

Peroxycarbenium-mediated C-C bond formation: applications to the synthesis of hydroperoxides and peroxides

The Lewis acid-mediated reaction of alkene nucleophiles with peroxyacetals provides an effective route for the synthesis of homologated peroxides and hydroperoxides. In the presence of Lewis acids such as TiCl(4), SnCl(4), and trimethylsilyl triflate, peroxyacetals and peroxyketals undergo reaction with allyltrimethylsilane, silyl enol ethers, and silyl ketene acetals to afford homoallyl peroxides, 3-peroxyketones, and 3-peroxyalkanoates, respectively. Reactions of peroxyacetals are Lewis acid dependent; TiCl(4) promotes formation of ethers while SnCl(4) and trimethylsilyl triflate promote formation of peroxides. Lewis acid-promoted reactions of silylated hydroperoxyacetals furnish silylated hydroperoxides, which can be deprotected to homologated hydroperoxides. Hydroperoxyketals undergo Lewis acid-mediated allylation to furnish 1,2-dioxolanes via attack of hydroperoxide on the intermediate carbocation. Lewis acid-mediated cyclization of unsaturated peroxyacetals furnishes 1,2-dioxanes, 1,2-dioxepanes, and 1,2-dioxacanes through 6-endo/exo, 7-endo/endo, and 8-endo/endo pathways. The corresponding reactions involving 6-endo/endo and 5-endo/exo pathways were unsuccessful.     

Surface properties of hydrosilylated polyolefins annealed in supercritical carbon dioxide

Two hydrosilylated polyolefin compounds are obtained by reacting polypropylene (PP) and polyethylene (PE) with di‐ and multi‐functional hydride‐terminated poly(dimethylsiloxane) (dH‐PDMS and mH‐PDMS), respectively. The PDMS‐rich surface layers on these two samples show different Si concentrations but similar thicknesses. Samples of these materials are annealed in supercritical carbon dioxide (scCO₂) at various temperatures and pressures for different periods of time. On the PP/dH‐PDMS sample, an increase in the annealing temperature does not affect the Si concentration up to 120°C. However, the Si concentration is sharply reduced at T = 150°C at which point the surface appears to be covered by SiO₂ particles. Annealing the PP/dH‐PDMS sample for short times leads to submicron scale SiO₂ particle formation on the surface. The particles form aggregated clusters that spread all over the surface uniformly when the annealing time is extended. However, Si concentration on the PE/mH‐PDMS sample surface is enhanced as the annealing temperature increases, reaching a maximum at an annealing temperature of 100°C. No particle formation is observed on the PE/mH‐PDMS sample surface. The contact angle of both samples is found to increase with annealing temperature. Increasing the scCO₂ pressure leads to a higher Si concentration on the surfaces of both samples. On the other hand, increasing the CO₂ pressure leads to opposite trends in contact angle with the PP/dH‐PDMS sample exhibiting an increasing contact angle and the PE/mH‐PDMS sample exhibiting a decreasing one. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of polyolefins with unique properties by using metallocene-type catalysts

Copolymerization of ethylene and 1,5-hexadiene (HD) by zirconocene catalysts proceeded via cyclization-addition mechanism to form 1,3-didsubstituted cyclopentane structure in the polyethylene chain. The 1,3-cyclopentane structure was found to be taken in the crystalline structure of polyethylene (isomorphism) by partially chainging the trans zigzag chain into gauche conformation, thereby, inducing a transformation of orthorhombic crystal to pseudohexagonal crystal. Copolymerization of ethylene and cyclopentene (CPE) by zirconocene catalysts yielded copolymers having 1,2-disubstituted cyclopentane structure in the polyethylene chain. The 1,2-cyclopentane structure was not taken into the crystalline structure of polyethylene. The melting point (T_m) and the crystallinity (X_c) of polyethylene decreased by copolymerization of HD or CPE, and the T_m- and X_c-decreasing effect of CPE was stronger than HD. For copolymers of propylene and HD or CPE obtained with isospecific zirconocene catalyst, the isomorphism was not ovserved.     

Specific features of chitosan-montmorillonite interaction in an aqueous acid solution and properties of related composite films

The rheological properties of chitosan solutions in a 2% aqueous solution of acetic acid with added montmorillonite nanoparticles and the mechanical properties and structural organization of chitosan-based composite films are studied. The interaction between the polymer functional groups and surface charges of nanoplatelets is confirmed by conductometric and potentiometric measurements. With the use of a X-ray diffraction analysis, it is shown that the nanoparticles in films are in the exfoliated and intercalated states. The incorporation of up to 10 wt % modified montmorillonite nanoparticles into the chitosan matrix results in a successive increase in rigidity and a decrease in the elongation at break.     

Acid-catalyzed formation of free radicals in the reaction of hydroperoxides with ketones

The kinetics of formation of free radicals in the cyclohexanone (CH)-tert-butylhydroperoxide (TBHP)-para-toluenesulfonic acid (PTSA) system in acetonitrile was studied. The stoichiometry of the reaction corresponds to the consumption of two TBHP molecules per ketone molecule, whereas the yield of free radicals is -20 % based on the TBHP reacted.     

Specific features of the formation of polymer-dye systems based on nanostructured polymer matrices prepared by solvent crazing

Specific features of the formation of polymer-dye systems based on various nanostructured polymer matrices prepared by the method of solvent crazing are discussed. In the general case, the formation of polymer-dye composites includes four main stages: sorption of dye molecules by the highly disperse fibrillar material of crazes, shrinkage of the polymer composite due to the removal of the solvent, migration of dye molecules from their localized sites on the surface of fibrils, and healing of the structure of crazes (internal interfacial boundaries) under thermal treatment. Analysis of the migration of dye molecules in the polymer matrix includes the following assumptions: first, a metastable (nonequilibrium) state of the system after solvent crazing and introduction of dye molecules into the fibrillar craze material and, second, the statement according to which both the depth and direction of the above migration processes are controlled by the free energy of mixing of components. For amorphous glassy systems (PVC, PS, PC), healing of the fibrillar craze material (after shrinkage and removal of the solvent) is observed. In the case of semicrystalline polymers (PP, vinylidene fluoride-trifluoroethylene copolymer) and amorphous crystallizable polymer matrices (PET), the intensity of healing upon thermal treatment decreases due to the presence of crystalline regions, which slow down the motion of macromolecules.     

Unusual formation of hydroperoxides in the reactions of substituted spiro[pyrazolinecyclopropanes]

3-Cyano- and 3-(alkoxycarbonyl)spiro[2-pyrazoline-5,1’-cyclopropane] and 5-phenylspiro[1-pyrazoline-3,1’-cyclopropane] undergo unusual transformations into 3(5)-substituted 5(3)-(2-hydroperoxyethyl)pyrazoles in the presence of atmospheric oxygen. The conditions for the formation of hydroperoxides (e.g., in oxygen-saturated solutions of spiro[2-pyrazoline-5,1’-cyclopropanes] in CHCl₃) and their conversion into (2-hydroxyethyl)pyrazoles or the corresponding nitrates under the action of nitrosating reagents were considered.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2160–2164, October, 2004.     

Structural aspects of the radiation modification of the dielectric properties of polyolefins

The effects of crystallization conditions and supermolecular structure on the processes of radical formation and changes in the dielectric (tan; ) and strength (E _st) properties of LDPE, HDPE, and PP under exposure to -radiation were studied. It was found that polyolefin specimens with a high crystallinity exhibited an enhanced electric strength, radiation stability, and a high yield of quasi-stable radicals at 293 K. It was assumed that a possible mechanism of the electric strengthening of PE and PP by their radiation modification (at radiation doses of 30–50 and to 5–6 Mrad, respectively) consists in a reaction of the type R^· + e^– R^–, the capture of trapped electrons by quasi-stable radicals.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 3, 2005, pp. 176–182.Original Russian Text Copyright © 2005 by Magerramov, Dashdamirov.     

Specific features of tetrahydrofuran copolymerization with lactones

Mechanistic features of the cationic copolymerization of lactones with cyclic ethers are studied for β-propiolactone (PL) with tetrahydrofuran (THF) and ?-caprolactone (CL) with THF. It is shown that, in the PL-THF system at [THF]₀ > [THF]_e, the copolymer is considerably enriched with the more basic THF whereas at [THF]₀ < [THF]_e anomalous enrichment of the copolymer with the less basic PL is observed. The mechanism of this phenomenon, which is applicable to many other cases and causes the formation of block copolymers from some heterocyclic monomers, is considered. At concentrations below equilibrium, THF is incorporated in the copolymer as pairs of units due to the effect of the penultimate unit on the thermodynamics of its addition.     

Specific features of preparing residual graphite hydrosulfate

The hydrolysis of graphite hydrosulfate prepared in the system aqueous solution of sodium dichromate-sulfuric acid was studied, and the composition of gases evolving from the solid phase during the hydrolysis was determined. The effects of the duration of the graphite hydrosulfate hydrolysis on the expansion factor and also on the morphology and particle size of the final product, residual graphite hydrosulfate, was studied.