Thermodynamic properties of gaseous cerium molybdates and tungstates studied by Knudsen effusion mass spectrometry.

RATIONALE: CeO2 -WO3 and CeO2 -MoO3 catalysts have shown excellent performance in the selective reduction of NOx by ammonia (NH3 -selective catalytic reduction) over a wide temperature range. Strong interaction between CeO2 and WO3 or MoO3 might be the dominant reason for the high activity of these mixed oxides. Studies of ceria-containing gaseous salts involve considerable experimental difficulties, since the transition of such salts to vapor requires high temperatures. To predict the possibility of the existence of gaseous associates formed by cerium and molybdenum (tungsten) oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerium oxyacid salts were unknown. METHODS: Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species and the equilibrium constants of gas-phase reactions, as well as the formation and atomization enthalpies of gaseous cerium molybdates and tungstates. CeO2 was evaporated from molybdenum and tungsten effusion cells containing gold metal as a pressure standard. A theoretical study of gaseous cerium gaseous molybdates and tungstates was performed by several quantum chemical methods. RESULTS: In the temperature range 2050-2400 K, CeO, CeO2 , XO2 , XO3 , CeWO3 , CeXO4 , CeXO5 (X = Mo, W) and CeMo2 O7 were found to be the main vapor species over the CeO2 - Mo (W) systems. On the basis of the equilibrium constants of the gaseous reactions, the standard formation enthalpies of gaseous CeWO3 , CeXO4 , CeXO5 (X = Mo, W) and CeMo2 O7 at 298 K were determined. Energetically favorable structures of gaseous cerium salts were found and vibrational frequencies were evaluated in the harmonic approximation. CONCLUSIONS: The thermal stability of gaseous cerium oxyacid salts was confirmed by high-temperature mass spectrometry. Reaction enthalpies of the gaseous cerium molybdates and tungstates from gaseous cerium, molybdenum and tungsten oxides were evaluated theoretically and the obtained values are in reasonable agreement with the experimental one.

Thermodynamic properties of the La2 O3 -ZrO2 system by Knudsen effusion mass spectrometry at high temperature.

RATIONALE: Zirconia doped with a lanthanum oxide system is of high interest due to its exceptional thermal stability for the development of high-performance ceramics. It possesses the beneficial properties of pure zirconia, such as heat resistance, mechanical strength and inertness, but also eliminates its main disadvantage, i.e. brittleness. At high temperatures, components of such systems may vaporize selectively, leading to significant change in composition, and hence, the thermal resistance, phase stability and performance of the ceramic materials. Therefore, information on the vaporization processes and thermodynamic properties of the La2 O3 -ZrO2 system is of great importance. METHODS: Knudsen effusion mass spectrometry was used to study the vaporization processes and thermodynamic properties of solid solutions in the La2 O3 -ZrO2 system at 2110 K. Pure La2 O3 was used as a reference substance. Comprehensive characterization of the precursors and ceramics was performed via SEM, STA, XRD and PSD analysis. RESULTS: Zirconia-doped lanthania precursor powders and ceramics with La2 O3 of 33.3, 50, 70 and 90 mol.% content were manufactured by solid-state synthesis and the original cryochemical technique. La, LaO, ZrO and ZrO2 were found to be the main vapor species over the samples studied. The activities and thermodynamic properties of La2 O3 were calculated. Via XRD analysis it was shown that the phase composition of xLa2 O3 -(100-x)ZrO2 powders (x = 0.33, 0.5, 0.7 and 0.9 mol. fraction) significantly depends on the synthesis technique chosen. CONCLUSIONS: According to the XRD results combined with Rietveld refinement of the patterns, 33.3 La2 O3 -66.7 ZrO2 ceramics after solid-state synthesis are composed of well-formed cubic pyrochlore-type La2 Zr2 O7 with 5 wt.% admixture of monoclinic and cubic ZrO2 whereas 33.3 La2 O3 -66.7 ZrO2 precursor powders after cryochemical synthesis correspond to low-crystalline La(OH)3 . The components of the La2 O3 -ZrO2 system evaporate separately: there is no temperature range where lanthanum and zirconium gaseous species are present together. It was found that the activities of lanthania have low negative deviation from the ideal case.

Imaging and structural studies of DNA-protein complexes and membrane ion channels.

In bio-imaging by electron microscopy, damage of the sample and limited contrast are the two main hurdles for reaching high image quality. We extend a new preparation method based on nanofabrication and super-hydrophobicity to the imaging and structural studies of nucleic acids, nucleic acid-protein complexes (DNA/Rad51 repair protein complex) and neuronal ion channels (gap-junction, K+ and GABAA channels) as paradigms of biological significance and increasing complexity. The preparation method is based on the liquid phase and is compatible with physiological conditions. Only in the very last stage, samples are dried for TEM analysis. Conventional TEM and high-resolution TEM (HRTEM) were used to achieve a resolution of 3.3 and 1.5 Å, respectively. The EM dataset quality allows the determination of relevant structural and metrological information on the DNA structure, DNA-protein interactions and ion channels, allowing the identification of specific macromolecules and their structure.

[Comparative evaluation of antimicrobial activity of oligochitosans against Klebsiella pneumoniae].

Antibacterial activity of chitosan with different molecular weight at different pH values against gram-negative Klebsiella pneumoniae was studied. It was found that the dependence of inhibition activity of chitosan on its molecular weight was inversed when the medium pH was increased above 7.0. In acidic media higher molecular weight chitosan had the higher antibacterial activity was occured while and in weak alkaline media oligomeric forms of chitosan displayed the inhibition effect only. Our results showed that the antibacterial activity of chitosan against Klebsiella pneumoniae was closely connected with its polycationic nature, and was dependent on the degree of protonation of chitosan amino groups, which at the same time depended on the degree of polymerization and solution pH values.

Formation and thermodynamics of gaseous germanium and tin vanadates: a mass spectrometric and quantum chemical study.

The stabilities of gaseous germanium and tin vanadates were confirmed by high temperature mass spectrometry, and its structures were determined by quantum chemical calculations. A number of gas-phase reactions involving these gaseous salts were studied. On the basis of the equilibrium constants, the standard formation enthalpies of gaseous GeV2O6 (-1520 ± 42 kJ mol(-1)) and SnV2O6 (-1520 ± 43 kJ mol(-1)) were determined at a temperature of 298 K.

[The features of the establishment of zones of sanitary protection of the water source].

There are regulatory gaps in sanitary laws, which specify the procedure of approval of projects of sanitary protection zones (SPZ) of water objects. It goes without saying that natural complexes, where water intake is organized, should have a special ecological status, which plays a substantial role in the creation of favorable conditions for human health. Some recommendations are given to improve sanitary legislations. Sanitary regulations and standards (SanPin) 2.1.4.1110-02 as well as the Water Code of the Russian Federation do not fully take into account the statements of some Federal laws regarding the protection of water objects. E.g. according to the Federal law No 33- FL of 14.03.1995 "On specially protected natural reservations" there is a legal base for increasing the status of SPZ of water sources by enlarging the list of Specially Protected Natural Reservations by including SPZ therein.

High-temperature mass spectrometric study and modeling of thermodynamic properties of binary glass-forming systems containing Bi2O3.

RATIONALE: Binary glass-forming systems containing bismuth(III) oxide, especially the Bi2O3-SiO2 system, are of great importance in modern materials science: preparation of thin films, fiber optics, potential solar converters, and radiation shields in nuclear physics. Information on vaporization processes and thermodynamic properties obtained in the present study and the results of modeling of this system will be useful for optimization of the synthesis and applications of Bi2O3-containing materials at high temperatures. METHODS: High-temperature Knudsen effusion mass spectrometry was used to study the vaporization processes and to determine the partial pressures of components of the Bi2O3-SiO2 system. Measurements were performed with a MS-1301 mass spectrometer. Vaporization was carried out using two iridium-plated molybdenum effusion cells containing the sample under study and pure bismuth(III) oxide (reference substance). Modeling of the thermodynamic properties and structure of glasses and melts in the Bi2O3-SiO2 and Bi2O3-B2O3 systems was performed using a modified approach based on the generalized lattice theory of associated solutions (GLTAS). RESULTS: At a temperature of 1000 K, Bi and O2 were found to be the main vapor species over the samples studied. The Bi2O3 activity as a function of composition of the Bi2O3-SiO2 system was obtained from the measured partial pressures of the vapor species. The thermodynamic properties of mixing from oxides in this system were calculated. The advantages of GLTAS for modeling of glasses and melts in the binary systems containing Bi2O3 were demonstrated. CONCLUSIONS: The thermodynamic functions of mixing in glasses and melts of the Bi2O3-SiO2 system determined at 1000 K in the present study, as well as in the Bi2O3-B2O3 system, demonstrated negative deviations from ideality. Modeling of the obtained experimental data using GLTAS allowed a correlation to be found between the thermodynamic properties and the relative number of bonds of various types formed in the glasses and melts of these systems.

High-temperature mass spectrometric study of the vaporization processes and thermodynamic properties of melts in the PbO-B2O3-SiO2 system.

RATIONALE: The unique properties of the PbO-B2O3-SiO2 system, especially its extensive range of glass-forming compositions, make it valuable for various practical applications. The thermodynamic properties and vaporization of PbO-B2O3-SiO2 melts are not well established so far and the data obtained on these will be useful for optimization of technology and thermodynamic modeling of glasses. METHODS: High-temperature Knudsen effusion mass spectrometry was used to study vaporization processes and to determine the partial pressures of components of the PbO-B2O3-SiO2 melts. Measurements were performed with a MS-1301 mass spectrometer. Vaporization was carried out using two quartz effusion cells containing the sample under study and pure PbO (reference substance). Ions were produced by electron ionization at an energy of 25 eV. To facilitate interpretation of the mass spectra, the appearance energies of ions were also measured. RESULTS: Pb, PbO and O2 were found to be the main vapor species over the samples studied at 1100 K. The PbO activities as a function of the composition of the system were derived from the measured PbO partial pressures. The B2O3 and SiO2 activities, the Gibbs energy of formation, the excess Gibbs energy of formation and mass losses in the samples studied were calculated. CONCLUSIONS: Partial pressures of the vapor species over PbO-B2O3-SiO2 melts were measured at 1100 K in the wide range of compositions using the Knudsen mass spectrometric method. The data enabled the PbO, B2O3, and SiO2 activities in these melts to be derived and provided evidence of their negative deviations from ideal behavior.

Reconstruction of the polar interface between hexagonal LuFeO3 and intergrown Fe3O4 nanolayers.

We report the observation of an unusual phase assembly behavior during the growth of hexagonal LuFeO(3) thin films which resulted in the formation of epitaxial Fe(3)O(4) nanolayers. The magnetite layers were up to 5 nm thick and grew under the conditions at which Fe(2)O(3) is thermodynamically stable. These Fe(3)O(4) nanolayers act as buffer layers promoting a highly epitaxial growth of the hexagonal LuFeO(3) thin film up to 150 nm thick. Using scanning transmission electron microscopy, we show that the interface between (001) LuFeO(3) and (111) Fe(3)O(4) can be reconstructed in two ways depending on the sequence in which these compounds grow on each other. We suggest the polarity of the interface is the reason behind the observed interface reconstruction and epitaxial stabilization of magnetite.

Thermodynamic study of gaseous vanadium phosphates by high-temperature mass spectrometry.

Knowledge of the structures of gaseous oxyacid salts of the M(m) XO(n) type is of interest for understanding the nature of chemical bonds. Gaseous VPO(2) and VPO(3) have been identified by Knudsen effusion mass spectrometry during the vaporization of mixtures of V(2)O(3) and alkali earth phosphates from molybdenum and tungsten effusion cells. The structures and molecular parameters of the gaseous vanadium phosphates under study were determined using quantum chemical calculations. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined to be -273 ± 17 and -615 ± 16 kJ·mol(-1) for VPO(2) and VPO(3), respectively.

High-temperature mass spectrometric study of the vaporization processes of V2O3 and vanadium-containing slags.

A Knudsen effusion mass spectrometric method was used to study the vaporization processes and thermodynamic properties of pure V(2)O(3) and 14 samples of vanadium-containing slags in the CaO-MgO-Al(2)O(3)-SiO(2) system in the temperature range 1875-2625 K. The system was calibrated using gold in the liquid state as the standard. Vaporization was carried out from double tungsten effusion cells. First it was shown that, in vapor over V(2)O(3) and the vanadium-containing slags in the temperature range 1875-2100 K, the following vapor species were present: VO(2), VO, O, WO(3) and WO(2), with the latter two species being formed as a result of interaction with the tungsten crucibles. The temperature dependencies of the partial pressures of these vapor species were obtained over V(2)O(3) and the slags. The ion current comparison method was used for the determination of the V(2)O(3) activities in slags as a function of temperature with solid V(2)O(3) as a reference state. The V(2)O(3) activity coefficients in the slags under investigation indicated positive deviations from ideality at 1900 K and a tendency to ideal behavior at 2100 K. It was shown that the V(2)O(3) activity as a function of the slag basicity decreased at 1900 K and 2000 K and was practically constant in the slag melts at 2100 K. The results are expected to be valuable in the optimization of slag composition in high-alloy steelmaking processes as well as for their environmental implications.

Thermodynamic properties of the gaseous gallium molybdates and tungstates.

A number of gaseous oxyacid salts have been identified by Knudsen effusion mass spectrometry by vaporizing Ga(2)O(3) from molybdenum and tungsten cells. The stability of gaseous molecules Ga(2)MoO(4), Ga(2)WO(4), Ga(2)Mo(2)O(7), and Ga(2)W(2)O(7) was deduced from the measurements. The structures and molecular parameters of all salts investigated were obtained using quantum chemical calculations. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined to be -827 +/- 26, -843 +/- 26, -1578 +/- 32, and -1525 +/- 34 kJ.mol(-1) for Ga(2)MoO(4), Ga(2)WO(4), Ga(2)Mo(2)O(7), and Ga(2)W(2)O(7), respectively.

High-temperature mass spectrometric study of the vaporization processes in the system CaO-MgO-Al2O3-Cr2O3-FeO-SiO2.

Knudsen effusion mass spectrometry was used to study vaporization processes and thermodynamic properties of twenty samples of chromium-containing slags in the CaO-MgO-Al2O3-Cr2O3-FeO-SiO2 system in the temperature range 1850-2750 K. Tungsten cells were used and Cr2O3 solid was used as a reference material. The system was calibrated using liquid gold. As FeO was the first emanating vapor species, monitoring of the chromium-containing species could be carried out only after the complete vaporization of FeO. This, however, was found to have very little impact on the concentration of the slags investigated. During the measurements, the ion current intensities of CrO+ and CrO2+ species in the mass spectra of the vapor over the CaO-MgO-Al2O3-Cr2O3-FeO-SiO2 samples were monitored and compared with those corresponding to solid Cr2O3. Data on the partial pressures of vapor species as well as the activities of Cr2O3 as a function of temperature were obtained. The results are expected to be valuable in the optimization of slag composition in high alloy steelmaking processes.

[Prospects of application of the chitin-binding domains to isolation and purification of recombinant proteins by affinity chromatography: a review].

Properties of substrate-binding domains, some parameters of affinity sorbents, and a number of other special features that were necessary to take into account during creation of chromatographic system for isolation and purification of proteins with incorporated chitin-binding domain were discussed in this review. This method was shown to be successfully used along with metal-chelate affinity chromatography. The metal-chelate affinity chromatography with the use of polyhistidine peptides as affinity labels is successfully applied to isolation, purification, and investigation of recombinant proteins. However, this system had some disadvantages. At present, scientists attracted more and more attention to substrate-binding domains, including those chitin-binding, because they had a number of advantages being used as affinity label.

Mucoadjuvant properties of lipo- and glycoconjugated derivatives of oligochitosans.

Chitosan, (1-4)-2-amino-2-deoxy-beta-d-glucan, is a deacetylated form of chitin, an abundant biodegradable, positively charged natural polysaccharide. Chitosan is used for antigen delivery through mucosal barrier due to its ability to disrupt tight junctions. Here we produced new water-soluble low-molecular weight chitosan (LMW-Chi) lipid derivatives and compared their ability to stimulate humoral response with the effect of unmodified LMW-Chi or its oligosaccharide derivatives. LMW-Chi effectively penetrated into macrophage-like, lymphoid and epithelial cells. It also stimulated in mice IgG production to model proteins delivered either by subcutaneous or intranasal routes. Adjuvant effect of chitosan derivatives was comparable to or lower than that of unmodified LMW-Chi. Thus, it is possible that adjuvant effect is induced by unmodified glucosamine units of chitosan.

[The thermophilic bacteria hydrolyzing agar: characterization of thermostable agarase].

Three strains of anaerobic thermophilic bacteria capable of growing on agarose as a source of energy and carbon were isolated from hot springs near Lake Baikal (Barguzin National Park) and the caldera Uzon (Kamchatka). Cells of all the three strains were spore bacilli with peritrichous flagellation. These isolates grew at a temperature of 55-60 degrees C and pH 6.5-7.0 and fermented a wide range of organic substrates. Analysis of the 16S rRNA sequences allowed us to ascribe the strains B5 and K14 to the genus Thermoanaerobacter and the strain K67 to the genus Caldoanaerobacter. According to the results of DNA-DNA hybridization, B5 was determined as belonging to the species Thermoanaerobacter wiegelii. Agarase was isolated by preparative PAGE and subsequent gel chromatography from the culture liquid of strain B5 grown on the medium containing 0.5% agarose and 0.3% galactose. The molecular weight of this enzyme amounted to 67 kDa and pI, to 4.2. The T. wiegelii B5 agarase was active in the pH range of 3.5 to 7.0 (optimum, 5.2) and temperature range of 50 to 80 degrees C (optimum, 70 degrees C). The preincubation of this enzyme at 90 degrees C for 60 min did not reduce the agarase activity. This activity increased in the presence of metal ions; the maximal effect was observed in the presence of 5 mM Mg2+ and 25 mM Co2+.

[Cloning and expression of variants of the glutaryl-7-aminocephalosporic acid acylase of the bacterium Brevundimonas diminuta in Escherichia coli cells].

The gene coding for glutaryl-7-aminocephalosporic acid acylase (Gl7ACA acylase) of the bacterium Brevundimonas diminuta (BrdGl7ACA), a commercial enzyme widely used in modem biocatalytic technologies for manufacture of b-lactam antibiotics, was cloned. Efficient expression systems for producing a "native" recombinant BrdGl7ACA and its analogs modified by attaching affinity groups--the chitin-binding domain of chitinases A1 and hexahistidine sequence--were designed. It was demonstrated that both the recombinant hybrid proteins and the native Gl7ACA acylase produced in E. coli cells underwent a correct autoproteolytic processing with generation of functionally active enzymes and could be isolated with a high yield using one-step affinity chromatography.

[Effect of the molecular weight of chitosan on its antiviral activity in plants].

The effect of the molecular weight of chitosan on its ability to suppress systemic infection of bean mild mosaic virus in bean (Phasoleus vulgaris L.) plants was studied. The enzymatic hydrolysate of low-molecular-weight chitosan was successively fractionated by ultrafiltration through membranes with decreasing pore size. In total, four chitosan fractions with a weight-average molecular weight varying from 1.2 to 40.4 kDa were obtained. It was shown that the treatments of bean plants with these fractions (chitosan concentration, 10 or 100 microg/ml) inhibited virus accumulation and systemic propagation. The degree of chitosan-induced antiviral resistance increased as the molecular weight of chitosan decreased. The monomers comprising the chitosan molecule-glucosamine and N-acetylglucosamine--exhibited no antiviral activity.

[Regenerating activity and antibacterial effect of low-molecular-weight chitosan].

The antibacterial activity of two low-molecular-weight chitosans (LMWCs) was studied using two wound cultures: E. coli and St. albus. Both LMWCs exhibited antibacterial affect. The would-healing effect of methylcellulose gels comprising LMWCs (72 or 11 kDa) was studied. It was shown that wound-healing properties of gels depend on the molecular weight and concentration of LMWCs. The healing activity of LMWCs was assessed judging by the would half-closure time. The gels exhibiting the greatest healing rate contained 2% 72-kDa LMWC or 0.1% 11-kDa LMWC. The composition of the oligomeric fraction of the 11-kDa LMWC was studied by HPLC. It was shown that the oligomeric moiety of the 11-kDa LMWC represents a mixture of oligomers with a large admixture of monomers (30.82%).