Features of crystallization of chitosan with different molecular mass and its mixtures with pluronic F-127 according to atomic force microscopy and X-ray diffraction data

The structure of chitosan with different molecular mass and its mixtures with pluronic F-127 (triblock copolymer of ethylene and propylene oxide) crystallized from aqueous solutions was analyzed by atomic force microscopy and X-ray diffraction methods. It was established that the low-molecular-mass chitosan (M_w = 20000) had a highly ordered macrocrystalline structure, whereas the high-molecular-mass chitosan (M_w = 250000) was characterized by a poorly ordered quasi-crystalline structure. It was shown that, after evaporation of the aqueous solution of high-molecular-mass chitosan and pluronic F-127, chitosan formed a continuous film on the mica surface and pluronic formed dendritic structures on the chitosan surface. At the same time, the evaporation of the solution of the low-molecular-mass chitosan and pluronic F-127 mixture resulted in the formation of interpenetrating dendrites of chitosan and pluronic on the mica surface. In the low-molecular-mass chitosan-pluronic systems, a pluronic crystalline phase was formed at a lower pluronic content than in the case of high-molecular-mass chitosan-pluronic systems.     

Phase equilibria and crystal structures of complex oxides in systems La-M-Fe-O (M = Ca or Sr)

Phase equilibria in systems La-M-Fe-O (M = Ca or Sr) at 1100° in air were studied. The homogeneity ranges and structures of solid solutions La_{1 ? x} M _x FeO_{3 ? δ} (0 ≤ x ≤ 0.3 for M = Ca and 0 ≤ x ≤ 0.8 for M = Sr), Sr_{2 ? y} La _y FeO_{4 ? δ} (0.8 ≤ y ≤ 1.0), and Sr_{3 ? z} La _z Fe₂O_{7 ? δ} (0 ≤ z ≤ 0.2) were determined using X-ray powder diffraction. The structural parameters of complex oxides were refined using the full-profile Rietveld technique. Correlations between the unit cell parameters and the compositions of solid solutions were derived. Isobaric/isothermal phase diagrams were constructed for systems La-M-Fe-O (M = Ca or Sr) at 1100°C in air.     

Phase equilibria and crystal structure of the complex oxides in the Sr-Fe-Co-O system

Phase relations in the Sr-Fe-Co-O system have been investigated at 1100 °C in air by X-ray powder diffraction on quenched samples. Solid solutions of the form SrFe_1−xCo_xO_3−δ (0?x?0.7), Sr₃Fe_2−yCo_yO_7−δ (0?y?0.4) and Sr₄Fe_6−zCo_zO_13±δ (0?z?1.6) were prepared by solid-state reaction and by the sol-gel method. The structural parameters of single-phase samples were refined by the Rietveld profile method. The variation of the lattice parameters with composition has been determined for each solid solution and a cross-section of the phase diagram at 1100 °C in air for the entire Sr-Fe-Co-O system has been constructed.     

Synthesis of new functionalized 3,7-diazabicyclo[3.3.1]nonanes by aminomethylation of the Guareschi imides

The aminomethylation of 4,4-dialkyl-2,6-dioxopiperidine-3,5-dicarbonitriles (Guareschi imides) was studied for the first time. When the Guareschi imides were treated with primary aliphatic amines and an excess of formaldehyde, 2,4-dioxo-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarbonitriles were obtained in varying yields (15–67%). The structure of 9,9-dimethyl-7-(2-methylpropyl)-2,4-dioxo-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarbonitrile was studied by X-ray diffraction analysis.     

Crystal structure and physicochemical properties of doped lanthanum manganites

Substituted lanthanum-strontium manganites La_0.7Sr_0.3Mn_0.9Me_0.1O_{3 ± ??} (Me = Ti, Cr, Fe, and Cu) are obtained by standard ceramic and glycerin-nitrate techniques. High-temperature powder X-ray diffraction is employed to study the crystal structure of La_0.7Sr_0.3Mn_0.9Me_0.1O_{3 ± ??} oxides. It is shown that in the range 298?C1023 K in air, La_0.7Sr_0.3Mn_0.9Me_0.103 ± ?? manganites crystallized in an orthorhombic cell (space group R-3c). The isobaric temperature dependences of unit cell parameters are determined. Thermal expansion coefficients are calculated for La_0.7Sr_0.3Mn_0.9Me_0.10_{3 ± ??} oxides. The conductivity of La_0.7Sr_0.3Mn_0.9Me_0.10_{3 ± ??} is studied as a function of temperature in the range 500 K ?? T ?? 1200 K in air. It is shown that substituting 3d metal for manganese considerably lowers the conductivity of basic La_0.7Sr_0.3Mn_0.9O_{3 ± ??}. The chemical stability of iron-substituted manganite La_0.7Sr_0.3Mn_0.9Fe_0.1O_{3 ± ??} is studied with respect to the electrolyte material.     

Thermal behavior of a mixture of fullerenes and fullerites C60/70

The thermal behavior of a mixture of fullerites C_60/70 was studied by X-ray diffraction and IR and UV spectroscopy. The temperature range in which the molecular and crystal states degrade was determined (825?C875°C in a CO medium). In the C_60/70 mixture, fullerenes decomposed at lower temperatures than in pure C₆₀ and C₇₀; the decomposition temperature depended on the impurity (oxygen and solvent) content.     

Development of novel formulations for photodynamic therapy on the basis of amphiphilic polymers and porphyrin photosensitizers. Porphyrin-polymer complexes in model photosensitized processes

We have studied the effect of amphiphilic polymers with different structure (polyvinylpyrrolidone, polyethyleneoxide and a triblock copolymer of ethylene- and propyleneoxide—(Pluronic F127)) on the photoactivity of a hematoporphyrin derivative (dimegin). It has been shown that such polymers can cause a considerable increase in the porphyrin photosensitizer (PPS) activity both in the process of singlet oxygen photogeneration and in the reaction of a substrate photooxidation in D2O and water. Among the studied polymers, polyvinylpyrrolidone appeared to have a most significant influence onto the photoactivity of dimegin. We attribute the observed effect of the amphiphilic polymers on the photoactivity of dimegin to the presence of polymer-porphyrin interactions resulting in the porphyrin disaggregation in aqueous phase. Using 1H NMR spectroscopy, we have found that dimegin binds to the polymers via the PPS interaction mainly with the hydrophobic fragments of polymeric macromolecules. However, in the case of polyvinylpyrrolidone we observed also PPS interactions with the hydrophilic fragments of macromolecules.     

Electric field effect on refraction of light in a layer of chiral liquid crystal with large pitch

The effect of an alternating electric field on the trajectory of an extraordinary light wave in a layer of a chiral liquid crystal with a 180° turn of the director is studied. In this structure, in the absence of the field and at a large angle of incidence of the light wave on the liquid crystal layer, the light undergoes refraction inside the layer. It is shown that the deformation of the director that arises under the action of the electric field changes the character of refraction of the extraordinary wave and the layer begins to transmit the light. The threshold voltage of this effect is determined. The dynamics of the effect is studied. At large voltages, in addition to the extraordinary wave, an ordinary light wave is observed in the light passed through the cell. The ordinary wave intensity is modulated by the initial frequency of the control signal, whereas the extraordinary wave intensity is modulated by the double initial frequency.     

Coherent backscattering of light in nematic liquid crystals

Multiple light scattering by director fluctuations in nematic liquid crystals is considered. A uniform director orientation is assumed to be specified by an applied magnetic field. The coherent backscattering effect, which consists in the presence of a sharp light backscattering peak, is studied. The Bethe-Salpeter equation is used to calculate the multiple scattering intensity taking into account the contributions of ladder and cyclic diagrams. An analytical expression for the angular and polarization dependences of the coherent backscattering intensity is obtained in terms of the diffusion approximation. The calculation and experimental results are compared. The developed theory is shown to qualitatively describe the elliptical shape of the backscattering cone, to explain the absence of a coherent contribution for crossed polarizations, and to calculate the relative peak height.