P-coumaric acid-zinc basic salt nanohybrid for controlled release and sustained antioxidant activity

P-coumaric acid (pCA) has been intercalated in zinc basic salt (ZBS) to design an organic-inorganic nanohybrid material with controlled release and sustained antioxidant activity. According to the powder X-ray diffraction patterns and FT-IR spectra, pCA molecules were intercalated into ZBS without any noticeable alterations in their structural integrity. In vitro release test showed a biphasic discharge of pCA out of the interlayer space of two-dimensional ZBS lattice consisting of an initial burst release followed by a slow and sustained release. The pCA-ZBS nanohybrid exhibited comparable antioxidant activity to that of the free pCA.     

Spectral manifestations of nonplanarity effects in Pd complexes of porphyrins

It is found on the basis of kinetic spectral studies in nonane, dodecane, and vitreous solutions at 77 K (phosphorescence spectra, polarized phosphorescence, decay kinetics, and phosphorescence excitation spectra) that symmetric and nonsymmetric Pd-porphyrins are characterized by the presence of two noninteracting spectrally different long-and short-wavelength forms in the ground state. The existence of the long-wavelength form is associated with the displacement of the central Pd ion from the macrocycle plane, which leads to the formation of the nonplanar “dome” conformation of the porphyrin ligand. In the case of a nonsymmetrically substituted Pd-tetramethyl-diethylporphyrin molecule, the nonplanar conformation of the π-conjugated macrocycle is characterized by the splitting of the triplet state into two components (T ₁ and T ₂, Δν=90 cm^?1 at 77 K). Both narrow components, which have the same decay, form a dual phosphorescence of the long-wavelength form of this compound, which is caused by efficient thermal exchange between T ₁ and T ₂ levels in the course of deactivation to the ground state.     

The influence of electronic and structural factors on the photoinduced electron transfer in sterically strained <Emphasis Type="Italic">meso</Emphasis>-nitrophenyl-substituted porphyrins

The electronic and structural factors affecting the efficiency of the photoinduced electron transfer in meso-nitrophenyl-substituted octaethylporphyrins are theoretically analyzed by semiempirical methods of quantum chemistry. It is shown that the experimental differences between the rate constants of electron transfer associated with the change in the position of the nitro group in the meso-phenyl ring (ortho, meta, or para positions) are determined by such factors as torsional vibrations of the phenyl ring around the single C₁-C_m bond, electronic properties of the phenyl group, rotations of the nitro group around the single C-N bond, and out-ofplane deformations of the porphyrin macrocycle. It is ascertained that the matrix elements of electronic interactions and the energies of excited charge-transfer states depend substantially both on the position of the nitro group in the meso-phenyl ring and on intramolecular vibrations of the phenyl and the nitro groups. In nonpolar media, the fluorescence quenching in the compounds under study occurs mainly due to the admixture of chargetransfer excitations to the lowest S ₁ state of porphyrin. Upon increasing polarity, the main channel of deactivation of excited singlet states is direct photoinduced electron transfer either through space (the ortho position) or through a bond involving the participation of orbitals of the phenyl spacer (the meta and para positions).     

X-ray study of structural features of GaSb(Si) single crystals grown using a set of diffraction methods under various heat and mass transfer conditions

Structural features of GaSb(Si) single crystals grown under various heat and mass transfer conditions were studied by x-ray topography and by double- and triple-crystal diffractometry. It was shown that a decrease in the convective flow intensity during crystal growth by the vertical Bridgman method with axisymmetric upper heat supply in comparison with the Czochralski method eliminates growth striations (caused by microsegregation) and improves the uniformity of electrical parameters of materials. According to triple-crystal x-ray diffractometry data, the increased density of structural defects observed in some crystal regions causes significant lattice distortions, which makes an additional contribution to crystal inhomogeneity. Some specific features in x-ray topography images of growth striations, caused by a high silicon concentration and a dopant state deviation from an ideal substitutional solid solution, were revealed.     

Heat effect of pulsed laser radiation on the real structure of CdTe single crystals

Real structure modification of CdTe single crystals exposed to pulsed radiation of ruby and Nd: YAG lasers is investigated using X-ray diffraction topography in the reflection configuration. The changes are mostly due to effects of heat in a thin surface layer. Depending on the incident laser energy, the following significant changes in the real structure of the crystal surface layer are observed: (1) integral improvement of the surface structure due to microstress relaxation; (2) the formation, development, and degradation of an ordered twin structure in the process of recrystallization; and (3) the formation of a fine-mesh dislocation structure. All these changes barely affect the bulk of the crystal. Mechanisms of the modifications are discussed, along with possibilities for their monitoring and control.     

Transformation of a plane wave by a periodically time modulated dielectric medium

The problem of the transformation of a plane monochromatic wave by a finite-duration sequence of periodic rectangular pulses of the dielectric permittivity and magnetic permeability is solved exactly with integral equations. The expressions for the transformed component of the electric field at any point in space at an arbitrary time are derived and analyzed.     

Alternating copolymerization of ethylene with carbon monoxide on a supported palladium catalyst

The kinetics of the alternating copolymerization of ethylene with carbon monoxide has been studied in the presence of a palladium catalyst immolized on a polymer support in various media (methanol, toluene, heptane). In the case of hydrocarbon solvents, the activity of the supported catalyst is commensurable with the activity of a homogeneous system in methanol. The melting temperature of the resulting copolymer and its molecular mass depend on the solvent nature. The IR reflectance spectra of the active palladium complex and the ethylene-carbon monoxide copolymer are measured.     

Submillimeter-wave Josephson spectroscopy

A Josephson high-temperature superconducting (HTSC) submillimeter-wave spectrometer is designed, built, and experimentally investigated. The integrated detection structure of the spectrometer includes a YBCO Josephson junction on a bicrystalline boundary, a double-slot or log-periodic antenna, and a low-inductance resistive shunt. The selective detector response and the response at an intermediate frequency of 1.4 GHz are measured under the action of a signal in the frequency range 350–1250 GHz. Three methods of spectroscopy are investigated using this setup: 1) a method of Hilbert spectroscopy with processing of the detector response is implemented; 2) it is found that for a wide Josephson line at intermediate frequency (IF) the response has the same form as the detector response, making it possible to obtain a spectrum and the width of the generation line from IF response measurements; 3) for a narrow Josephson line the IF response corresponds to the regime of conversion with self-pumping. A new method is proposed for calculating the emission spectrum. The method consists of simple shift, summation, and subtraction operations. The advantages of the method are simplicity, high sensitivity, and high resolution. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 338–343 (10 September 1999)     

Homogenization of Monotone Operators by the Method of Two-Scale Convergence

Homogenization theorems are obtained for nonlinear second-order elliptic operators occurring in some models of media with double porosity. Basic homogenization properties are proved by the method of two-scale convergence combined with the technique of p-connectedness.__________Translated from Trudy Seminara imeni I. G. Petrovskogo, No. 24, pp. 44–66, 2004.