Growth and study of single crystals of (Na,K)NbO<Subscript>3</Subscript> solid solutions

(Na, K)NbO₃ crystals with a perovskite structure and a KNbO₃ content up to 40 mol % were grown from flux with the use of the solvent NaBO₂. The dielectric measurements of the crystals grown revealed phase transitions that had never been observed before in ceramic samples.     

Regeneration of Iron(III) Chloride Etching Solutions Containing Organic Additives

The behavior of inorganic macrocomponents (Fe^{3 +}, Fe^{2 +}, Cu^{2 +}, and Cl^-) and organic additives (judged from the relative concentration of total carbon) in regeneration and reuse of spent etching solutions used in fabrication of copper type-plates was studied. The conditions of electrochemical and sorption stages of the regeneration process were discussed.     

Crystal structure and dielectric properties of aurivillius phases A 0.5Bi4.5 B 0.5Ti3.5O15 (A = Na,Ca, Sr,Pb; B = Cr,Co, Ni,Fe, Mn,Ga)

New polycrystalline Bi-containing layered perovskite-like oxides having the Aurivillius phase (AP) structure with the general formula A _0.5Bi_4.5 B _0.5Ti_3.5O₁₅ (A = Na, Ca, Sr, Pb; B = Cr, Co, Ni, Fe, Mn, Ga) have been synthesized. The unit cell parameters of the synthesized compounds have been determined by X-ray powder diffraction. All studied APs crystallize in the orthorhombic system (space group A2₁ am (36)). The degree of distortion of AP unit cells has been analyzed based on the obtained structural parameters. The temperature dependences of the permittivity have been measured and the Curie temperatures have been determined for all the samples. The significant difference in the values of the permittivity maxima for APs Sr_0.5Bi_4.5Co_0.5Ti_3.5O₁₅ and Sr_0.5Bi_4.5Ni_0.5Ti_3.5O₁₅ has been interpreted based on the electron microscopy data and explained by substantial changes in the porosity and crystal grain sizes of these ceramic samples.     

Novel bicyclic derivatives of 1,3-selenazine

Bicyclic isoselenoureas (1-selena-3-azaspiro[5.5]undec-2-en-2-ylamines and 3-selena-1-azabicyclo[3.3.1]non-2-ylideneamines) were obtained by intramolecular cyclization of selenoureas leading to 1,3-selenazine ring formation and tested for antioxidant activity.     

Modification of gamma-carbolines with N-substituted propionamides as a new approach to mitoprotective agents

An approach to the modification of biologically active gamma-carbolines with the N-substituted propionamide fragments by the reaction of N-substituted acrylamides with gamma-carbolines catalyzed by cesium fluoride has been suggested. The compounds synthesized were studied for the influence on the functional characteristics of brain mitochondria, in particular, on the membrane potential, calcium-induced “swelling” and calcium capasity of the rat brain mitochondria.     

Diffusion of Quinine with Ethanol as a Co-Solvent in Supercritical CO2

This study aims at contributing to quinine extraction using supercritical CO₂ and ethanol as a co-solvent. The diffusion coefficients of quinine in supercritical CO₂ are measured using the Taylor dispersion technique when quinine is pre-dissolved in ethanol. First, the diffusion coefficients of pure ethanol in the supercritical state of CO₂ were investigated in order to get a basis for seeing a relative change in the diffusion coefficient with the addition of quinine. We report measurements of the diffusion coefficients of ethanol in scCO₂ in the temperature range from 304.3 to 343 K and pressures of 9.5, 10 and 12 MPa. Next, the diffusion coefficients of different amounts of quinine dissolved in ethanol and injected into supercritical CO₂ were measured in the same range of temperatures at p = 12 Mpa. At the pressure p = 9.5 MPa, which is close to the critical pressure, the diffusion coefficients were measured at the temperature, T = 343 K, far from the critical value. It was found that the diffusion coefficients are significantly dependent on the amount of quinine in a small range of its content, less than 0.1%. It is quite likely that this behavior is associated with a change in the spatial structure, that is, the formation of clusters or compounds, and a subsequent increase in the molecular weight of the diffusive substance.