Polarized IR-microscope spectra of guanidinium hydrogenselenate single crystal

The polarized IR-microscope spectra of C(NH2)3.HSeO4 small single crystal samples were measured at room temperature. The spectra are discussed with the framework of oriented gas model approximation and group theory. The stretching nuOH vibration of the hydrogen bond with the O...O distance of 2.616 A gives characteristic broad AB-type absorption in the IR spectra. The changes of intensity of the AB bands in function of polarizer angle are described. Detailed assignment for bands derived from stretching and bending modes of selenate anions and guanidinium cations were performed. The observed intensities of these bands in polarized infrared spectra were correlated with theoretical calculation of directional cosines of selected transition dipole moments for investigated crystal. The vibrational studies seem to be helpful in understanding of physical and chemical properties of described compound and also in design of new complexes with exactly defined behaviors.     

A Combined Experimental and Theoretical Study of Nitrofuran Antibiotics: Crystal Structures,DFT Computations,Sublimation and Solution Thermodynamics

Single crystal of furazolidone (FZL) has been successfully obtained, and its crystal structure has been determined. Common and distinctive features of furazolidone and nitrofurantoin (NFT) crystal packing have been discussed. Combined use of QTAIMC and Hirshfeld surface analysis allowed characterizing the non-covalent interactions in both crystals. Thermophysical characteristics and decomposition of NFT and FZL have been studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and mass-spectrometry. The saturated vapor pressures of the compounds have been measured using the transpiration method, and the standard thermodynamic functions of sublimation were calculated. It was revealed that the sublimation enthalpy and Gibbs energy of NFT are both higher than those for FZL, but a gain in the crystal lattice energy of NFT is leveled by an entropy increase. The solubility processes of the studied compounds in buffer solutions with pH 2.0, 7.4 and in 1-octanol was investigated at four temperatures from 298.15 to 313.15 K by the saturation shake-flask method. The thermodynamic functions of the dissolution and solvation processes of the studied compounds have been calculated based on the experimental data. Due to the fact that NFT is unstable in buffer solutions and undergoes a solution-mediated transformation from an anhydrate form to monohydrate in the solid state, the thermophysical characteristics and dissolution thermodynamics of the monohydrate were also investigated. It was demonstrated that a combination of experimental and theoretical methods allows performing an in-depth study of the relationships between the molecular and crystal structure and pharmaceutically relevant properties of nitrofuran antibiotics.     

Generators and relations for wreath products

Generators and defining relations for wreath products of groups are given. Under a certain condition (conormality of generators), they are minimal. Published in Ukrains'kyi Matematychnyi Zhurnal, Vol. 60, No. 7, pp. 997–999, July, 2008.     

Structure formation and its influence on thermodynamic and optical properties of montmorillonite organoclay-5CB liquid crystal nanocomposites

Montmorillonite (MMT) clay modified with octadecylbenzyldimethylammonium chloride (OBDM), B2, and its composites with nematic liquid crystal (LC) 4-pentyl-4'-cyanobiphenyl (5CB), 5CB-B2, with different concentration of the clay (3-8 wt %) were investigated by X-ray diffraction, polarizing optical microscopy, differential scanning calorimetry, FTIR spectroscopy and atomic force microscopy. Modification of Na-MMT with OBDM surfactant results in an increase of the chemical affinity of the clay for 5CB. This results in considerable increase of the basal spacings of the clay, giving a possibility for 5CB dimers to penetrate into the interlayer space. Better affinity of the clay for LC allows clay nanoparticles to disperse homogeneously in the LC, and affects thermodynamic and optical properties of the nanocomposites. For 5CB-B2 composites, the structure formation and the strength of the interface interactions were practically independent on B2 concentration. A comparison with 5CB-B3 composites (B3 is MMT modified with dioctadecyldimethylammonium chloride) revealed that the ability of the clay to form homogeneous structures in the LC and thermodynamic and optical properties of the composites are highly dependent on the chemical nature of the surfactant. Varying the type of the clay mineral modifier, it is possible to develop novel heterogeneous LC nanocomposites with desirable electro-optical properties.     

Magnetocaloric effect in nano- and polycrystalline La0.8Sr0.2MnO3 manganites

The sol–gel method is applied to prepare the polycrystalline La_0.8Sr_0.2MnO₃ manganite and to reduce grain sizes of nanocrystalline sample down to 23 nm. The magnetocaloric effect was determined from isothermal magnetization measurements. Transition from the polycrystalline to nanocrystalline structure reduces the size of magnetocaloric effect and markedly broadens the temperature interval over which it occurs. The relative cooling power RCP(S) = 35 J/kg in polycrystalline manganite remains almost the same in the nanocrystalline case.     

Van der Waals Gaps in Sm1+x Ba2−x Cu3O y and Their Effect on Superconductivity

We have used electron–positron annihilation to study superconducting cuprates Sm_1+x Ba_2–x Cu₃O _y . We have determined the average radii for oxygen ions in Sm_1+x Ba_2–x Cu₃O _y . Taking into account the ion coordinates and their radii, we have constructed a geometric model for the arrangement of copper and oxygen ions in CuO₂ layers in the [b, c] plane, responsible for the superconductivity. From these data, we have determined the length of the ionic/covalent bonds and the width of the interionic gaps. We have established the effect of the features of the atomic structure of Sm_1+x Ba_2–x Cu₃O _y on the superconducting transition temperature T _c and we have shown that T _c increases as X inceases.     

Representations ofD-forms

A criterion for module boundedness of a certain class of semihereditary rings — tensor algebras ofD-form — is given.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 4, pp. 572–574, April, 1992.