Studies of the photooxidation mechanism of polymers. III. Role of tetrahydrofuran in the photooxidative degradation of poly(vinyl chloride)

The influence of tetrahydrofuran (THF) on photooxidative degradation of poly(vinyl chloride) in films cast from THF solution was studied. THF is partially retained in the polymer matrix in amounts of 6–8% after casting and drying the film. The last 2–3% is very difficult to remove. By use of thermogravimetric analysis, density measurements, and gas permeability measurements, it was shown that THF residues can be removed by preheating the PVC samples to 80°C. THF forms a charge-transfer complex with oxygen which is easily photolyzed. During this reaction hydroperoxide radicals are formed. Molecular weight distribution curves by gel-permeation chromatography (GPC) show that THF in the presence of air promotes the photodegradation of PVC. Attention has been given to the correct interpretation of the infrared absorption spectra of PVC films containing THF residues and ultraviolet-irradiated in air.     

Interaction of carbon dioxide with zirconocene and hafnocene dihydrides

Zirconocene and hafnocene dihydrides Cp₂MH₂ (M = Zr, Hf) are capable of rapid absorbing carbon dioxide at room temperature and atmospheric pressure in a THF medium. In the case of Cp₂ZrH₂, the reaction results in the cleavage of the C=O bond of a CO₂ molecule to form cyclic trimeric zirconocene oxide [Cp₂ZrO]₃, whose structure was confirmed by analytical and spectral methods as well as by X-ray diffraction study. Small amounts of formaldehyde and methyl formate are found in the organic products of the reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2366–2368, September, 1996.     

Lamellar graphite compounds with metallic potassium as catalysts for deuterium-hydrogen exchange in hydrocarbons

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1935–1936, August, 1991. March 13, 1991.     

Perfluorinated polymercuramacrocycles as anticrowns. Applications in catalysis

The catalytic and complexing properties of two perfluorinated polymercuramacrocycles, viz., cyclic trimeric perfluoro-o-phenylenemercury (o-C₆F₄Hg)₃ and cyclic pentameric perfluoroisopropylidenemercury [(CF₃)₂CHg]₅, are analyzed. These macrocycles contain several Lewis acidic centers in the ring and can be considered as peculiar antipodes of crown ethers and their thia and aza analogs. Both macrocycles can efficiently bind various anions to form unique complexes, in which the anionic species is simultaneously coordinated to all Lewis acidic atoms of the ring. For the (o-C₆F₄Hg)₃ macrocycle, unusual complexes with various neutral Lewis bases, such as nitriles, carbonyl compounds, aromatic hydrocarbons, etc., were also described. Data on the activity of polymercury-containing macrocycles in phase transfer catalysis of electrophilic reactions and proton transfer from an aqueous to an organic phase are surveyed and discussed.     

Fractal-cluster kinetics in phase transformations in the relaxor ceramic PLZT

Fractal formalism has been used to study the evolution of a heterophase state (consisting of polar nanoregions in a nonpolar matrix) subjected to polarization in an electric field within the diffuse phase transition in the transparent relaxor ferroelectric ceramic PLZT 8/65/35. The time dependences of the fractal dimensions of polar clusters under polarization switching and spontaneous backswitching at different temperatures have been derived from measurements of the elastic scattering of transmitted light. Various scenarios for the evolution of the heterophase and nanodomain states in relaxors with variation of the temperature and electric field are proposed. Fiz. Tverd. Tela (St. Petersburg) 41, 505–509 (March 1999)     

Fluorescence properties of Nd3+ doped stoichiometric LiNbO3 fiber single crystals by micro‐pulling down method

Using the micro‐pulling down (μ‐PD) method, 1 and 3 mol% Nd₂O₃ doped near stoichiometric lithium niobate (LiNbO₃) single crystal fibers were grown in 1 mm diameter and 35∼40 mm length. The grown crystal fibers were free of cracks and the homogeneous distribution of Nd³⁺ ion concentrations were confirmed by the electron probe micro analysis. The changes of fluorescence spectra were measured with respect to the Nd³⁺ ion doping concentration. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase Matched Wavelength Dependent on Atomic Displacement in Potassium Lithium Niobate Crystals Grown by Micro Pulling Down Method

Phase-matched wavelength in potassium lithium niobate (KLN) crystals grown by the micro pulling down (μ-PD) method dependent on the atomic displacement changed by melt composition was investigated. It has been found that the polar components of the atomic displacement of the metal atoms Nb(1) and Nb(2) increase with increasing Nb content of melt. Also, phase matched wavelength for second harmonic generation (SHG) properties was determined from ultra-violet to green region by increasing Nb content of melt.     

Alternative Targets for Modulators of Mitochondrial Potassium Channels

Mitochondrial potassium channels control potassium influx into the mitochondrial matrix and thus regulate mitochondrial membrane potential, volume, respiration, and synthesis of reactive oxygen species (ROS). It has been found that pharmacological activation of mitochondrial potassium channels during ischemia/reperfusion (I/R) injury activates cytoprotective mechanisms resulting in increased cell survival. In cancer cells, the inhibition of these channels leads to increased cell death. Therefore, mitochondrial potassium channels are intriguing targets for the development of new pharmacological strategies. In most cases, however, the substances that modulate the mitochondrial potassium channels have a few alternative targets in the cell. This may result in unexpected or unwanted effects induced by these compounds. In our review, we briefly present the various classes of mitochondrial potassium (mitoK) channels and describe the chemical compounds that modulate their activity. We also describe examples of the multidirectional activity of the activators and inhibitors of mitochondrial potassium channels.     

Phase transformation kinetics induced in thin sol-gel PZT films under thermal annealing

The surface morphology evolution and phase transformation kinetics in thin lead zirconate-titanate (PZT) sol-gel films during rapid thermal annealing were studied by in situ measurement of scattered light intensity and by recording successive instantaneous optical microscope images. We also studied the variation of the texture perfection, the fraction of the growing phase, and the angular dependence of the scattered intensity in partially annealed samples. The parameters characterizing the kinetics of the pyrochlore-perovskite phase transformation were derived by a mathematical treatment of the experimental data. The phase transformation kinetics and the film crystalline texture are shown to depend substantially on the pyrolysis temperature. The texture formation mechanism is considered.     

Ammonia synthesis from dinitrogen and dihydrogen over the catalysts based on supported mononuclear potassium carbonyl ruthenate. Promoting effect of alkyllithium compounds

New catalysts for the ammonia synthesis from dinitrogen and dihydrogen based on supported mononuclear potassium carbonyl ruthenate K₂Ru[(CO)₄] as a precursor of catalytically active particles have been developed. Magnesium oxide and graphite-like active carbon Sibunit were used as supports, while aliphatic organolithium compounds (BuⁿLi and Bu^tLi) were employed as electron promoters in these catalysts. The systems with MgO as a support are the most efficient. The introduction of RLi into these systems allows one to considerably increase the ammonia synthesis rate. When using carbon Sibunit, the promoting effect of organolithium compounds is much weaker but the activity of such catalysts can be essentially increased by the introduction of an additional electron promoter, viz., metallic potassium, into the system. All the catalysts tested are active in the ammonia synthesis at atmospheric pressure and temperatures ??250 °C.