E. P. Kharitonova

Cell attachment on poly(3-hydroxybutyrate)-poly (ethylene glycol) copolymer produced by Azotobacter chroococcum 7B

BackgroundThe improvement of biomedical properties, e.g. biocompatibility, of poly(3-hydroxyalkanoates) (PHAs) by copolymerization is a promising trend in bioengineering. We used strain Azotobacter chroococcum 7B, an effective producer of PHAs, for biosynthesis of not only poly(3-hydroxybutyrate) (PHB) and its main copolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV), but also alternative copolymer, poly(3-hydroxybutyrate)-poly(ethylene glycol) (PHB-PEG).ResultsIn biosynthesis we used sucrose as the primary carbon source and valeric acid or poly(ethylene glycol) 300 (PEG 300) as additional carbon sources. The chemical structure of PHB-PEG and PHB-HV was confirmed by 1H nuclear-magnetic resonance (1H NMR) analysis. The physico-chemical properties (molecular weight, crystallinity, hydrophilicity, surface energy) and surface morphology of films from PHB copolymers were studied. To study copolymers biocompatibility in vitro the protein adsorption and COS-1 fibroblasts growth on biopolymer films by XTT assay were analyzed. Both copolymers had changed physico-chemical properties compared to PHB homopolymer: PHB-HV and PHB-PEG had less crystallinity than PHB; PHB-HV was more hydrophobic than PHB in contrast to PHB-PEG appeared to have greater hydrophilicity than PHB; whereas the morphology of polymer films did not differ significantly. The protein adsorption to PHB-PEG was greater and more uniform than to PHB and PHB-PEG copolymer promoted better growth of COS-1 fibroblasts compared with PHB homopolymer.ConclusionsThus, despite low EG-monomers content in bacterial origin PHB-PEG copolymer, this polymer demonstrated significant improvement in biocompatibility in contrast to PHB and PHB-HV copolymers, which may be coupled with increased protein adsorption and hydrophilicity of PEG-containing copolymer.

The Terpolymer Produced by Azotobacter Chroococcum 7B: Effect of Surface Properties on Cell Attachment

The copolymerization of poly(3-hydroxybutyrate) (PHB) is a promising trend in bioengineering to improve biomedical properties, e.g. biocompatibility, of this biodegradable polymer. We used strain Azotobacter chroococcum 7B, an effective producer of PHB, for biosynthesis of not only homopolymer and its main copolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV), but also novel terpolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-poly(ethylene glycol) (PHB-HV-PEG), using sucrose as the primary carbon source and valeric acid and poly(ethylene glycol) 300 (PEG 300) as additional carbon sources. The chemical structure of PHB-HV-PEG was confirmed by 1H nuclear-magnetic resonance analysis. The physico-chemical properties (molecular weight, crystallinity, hydrophilicity, surface energy) of produced biopolymer, the protein adsorption to the terpolymer, and cell growth on biopolymer films were studied. Despite of low EG-monomers content in bacterial-origin PHB-HV-PEG polymer, the terpolymer demonstrated significant improvement in biocompatibility in vitro in contrast to PHB and PHB-HV polymers, which may be coupled with increased protein adsorption, hydrophilicity and surface roughness of PEG-containing copolymer.

Crystal structure of the oxygen conducting compound Nd5Mo3O16

Abstract Structure of the Nd5Mo3O16 single crystal grown in the Nd2O3–MoO3 system was studied using the X-rays diffraction technique at 293 K and 110 K temperatures. The unit-cell values were always cubic relating to that of CaF2 fluorite as a ≈ 2af (af = 5.5 Å). The structure was solved within the Pn-3n symmetry group. It was found that the Nd5Mo3O16 compound has a fluorite-like structure with all atoms disordered. An indirect confirmation for the violation of translational periodicity in the distribution of Mo and Nd atoms was obtained. The possible oxygen diffusion paths were analyzed using the one-particle potentials of the oxygen atoms. The ionic conductivity of Nd5Mo3O16 compound is associated with the disordering of the oxygen atoms in several positions, and their deficiency in comparison with the initial fluorite.

Specific features of phase transitions and the conduction of La2Mo2O9 oxide-ion conducting compound doped with vanadium

The X-ray powder analysis, calorimetric studies, and conductivity measurements of a series of ceramic La2Mo2−xVxOy specimens with different vanadium content are performed with the aim of following the dynamics of phase formation of the low-temperature α, high-temperature β, and metastable βms phases. At x ≥ 0.06, the cubic phase becomes stable and the monoclinic phase vanishes; therefore, the main α → β transition is suppressed. According to the data of differential thermal analyses, a weak thermal anomaly is observed in the range 450–470°C at x ≥ 0.06. This anomaly is indicative of the βms → β transition due to the conversion of the cubic phase with statically disordered oxygen atoms into the cubic phase with dynamic disorder. The conductivity of the high-temperature β phase obeys the Vogel-Tammann-Fulcher law.

Oxygen-conducting crystals of La2Mo2O9: Growth and main properties

Single crystals of the anionic conductor La2Mo2O9 are grown by crystallization from a nonstoichiometric melt. Their polymorphism and domain structure, as well as the temperature dependences of conductivity and dielectric permittivity, are studied. In the temperature range 750–600°C, the conductivity of these crystals is as high as 10−1–10−2 Ω−1 cm−1.

Synthesis and electrical properties of mixed-layer Aurivillius phases

Polycrystalline samples of the mixed-layer Aurivillius phases Bi10Ti3W3O30, Bi7Ti4NbO21, Bi7Ti4TaO21, SrBi6Ti3Nb2O21, BaBi6Ti3Nb2O21, SrBi8Ti7O27, and BaBi8Ti7O27 (ferroelectrics with high oxygen-ion conductivity) have been prepared by solid-state reactions, and their electrical properties have been studied. All of the compounds undergo a second-order ferroelectric phase transition at temperatures from 500 to 800°C and have high electrical conductivity. Of particular interest is the compound Bi10Ti3W3O30, whose conductivity exceeds that of the other mixed-layer Aurivillius phases by more than one order of magnitude and reaches 5 × 10−2 S/cm at 800°C.

Novel composite Zr/PBI-O-PhT membranes for HT-PEFC applications.

Summary Novel composite membranes for high temperature polymer-electrolyte fuel cells (HT-PEFC) based on a poly[oxy-3,3-bis(4′-benzimidazol-2″-ylphenyl)phtalide-5″(6″)-diyl] (PBI-O-PhT) polymer with small amounts of added Zr were prepared. It was shown in a model reaction between zirconium acetylacetonate (Zr(acac)4) and benzimidazole (BI) that Zr-atoms are capable to form chemical bonds with BI. Thus, Zr may be used as a crosslinking agent for PBI membranes. The obtained Zr/PBI-O-PhT composite membranes were examined by means of SAXS, thermomechanical analysis (TMA), and were tested in operating fuel cells by means of stationary voltammetry and impedance spectroscopy. The new membranes showed excellent stability in a 2000-hour fuel cell (FC) durability test. The modification of the PBI-O-PhT films with Zr facilitated an increase of the phosphoric acid (PA) uptake by the membranes, which resulted in an up to 2.5 times increased proton conductivity. The existence of an optimal amount of Zr content in the modified PBI-O-PhT film was shown. Larger amounts of Zr lead to a lower PA doping level and a reduced conductivity due to an excessively high degree of crosslinking.

Crystal growth and physical properties of Cs2Nb4O11 and Rb2Nb4O11 single crystals

The Cs 2 Nb 4 O 11 (CN) and Rb 2 Nb 4 O 11 (RN) single crystals are grown by means of flux method and their physical properties are studied. Despite the similarity of their chemical formulae the crystals are not isostructural. CN crystals undergo ferroelectric phase transition at 164 C. Both the compounds show electrical conductivity of about 10 -4 Ω -1 cm -1 at room temperature.

Phase transition peculiarities in LAMOX single crystals

The series of oxide-ion-conducting La2Mo2O9 single crystals, undoped and doped with Ca, Bi, W, Nb, Zn and V (LAMOX), was grown by the flux method in the system La2O3–MoO3, which has allowed us to use polarization microscopy for the identification of phases. Phase transition peculiarities in the LAMOX family have been studied by polarization microscopy and calorimetry. The results demonstrate that both the monoclinic phase (α), which is stable at room temperature, and the metastable cubic phase (βms), or a mixture of these phases, may exist at room temperature, depending on the post-growth cooling rate and the nature of the dopant at low doping level. On heating, all of the quenched crystals undergo (450 °C) and (500–560 °C) phase transitions (where β designates the stable cubic phase). At heavy doping levels, the high-temperature transition is suppressed and the crystals (La2Mo1.95V0.05Oy, La2Mo1.84W0.16Oy in our case) are found in the cubic state. The thermal peak near 450 °C at high doping level is not associated with a transition and may be the result of defect association/dissociation in the cubic crystals. The thermal history, nature of the dopant and doping level are shown to influence the phase transition sequence and type.

Synthesis and electrical properties of Bi2V1 − x Ge x O5 + y solid solutions

A continuous series of Bi2V1 − xGexO5 + y solid solutions has been prepared by solid-state reactions, and their polymorphism and electrical properties have been studied. The solid solutions with 0 < x ≤ 0.2 are isostructural with the monoclinic phase α-Bi2VO5.5, and those with 0.2 < x ≤ 0.3 are isostructural with the orthorhombic phase. In the range 0.6 ≤ x < 1, the solid solutions have the orthorhombic Bi2GeO5 structure. The solid solutions with 0.4 ≤ x ≤ 0.5 have a tetragonal structure. Increasing the germanium content suppresses the ferroelectric phase transition in the Bi2VO5.5-based solid solutions, without changing the transition temperature. With increasing vanadium content, the conductivity of the solid solutions gradually increases, from 3 × 10−5 (x = 1) to 3 × 10−1 S/cm (x = 0) at 550°C.