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Mechanically activated strontium titanate (SrTiO3) powders with various manganese dioxide (MnO2) doping levels (1.5, 3 and 6 wt%) were prepared by solid state method. Due to the possibility of manganese ion incorporation in SrTiO3at Ti4+and/or Sr2+sites a detailed analysis of the influence of dopants on the microstructure, morphology and optical properties of perovskite oxide was conducted. The investigation showed that manganese was incorporated into the lattice and surface layers of SrTiO3particles with the presence of manganese segregation and inhomogeneities. Optical measurements indicated a shift of the absorption edge to higher values of wavelengths where the lowest value of the band gap (3.10 eV) was for the longest activation time (120 min) and the highest weight percentage of dopant (6 wt%). In the case of lower concentration (1.5 wt%), there was a significant relative contribution of the substitution of Sr2+ions by Mn2+ions, while the substitution of Ti4+ions by Mn4+ions dominated samples with an increased concentration.

Two methods of enzyme immobilization onto silica core-shell particles were developed. The first method involved the immobilization of Candida rugosalipase inside a previously synthesized mesoporous silica layer (deposited at 80°C) surrounding a dense silica core. To prevent lipase leakage from the support, an outer mesoporous silica layer was deposited at 40°C around the first silica layer containing the immobilized lipase. The deposition of the second layer was performed at a relatively lower temperature, to prevent thermal inactivation of the immobilized enzyme. The internal silica layer was obtained by assembling primary silica nanoparticles generated from highly basic sodium silicate solution at 80°C on the surface of poly (diallyldimethylammonium chloride) (PDDA) functionalized silica core particles. The average shell thickness and pore size of the internal silica layer was ∼60nm and 24nm, respectively. The effect of process parameters on generation and aggregation of silica nanoparticles prepared from highly basic sodium silicate solution was also investigated. The aggregation of silica particles generated at 40°C and 80°C took place after 840s and 570 of reactions, respectively. The immobilization efficiency of lipase on the mesoporous silica monolayer was 80%. A decline of immobilized lipase activity was approximately 6 times after 10 reaction cycles due to lipase leakage from the monolayered shell. An outer mesoporous silica layer was deposited at 40°C onto the surface of previously PDDA-functionalized monolayered silica core-shell particles containing the immobilized lipase. The average thickness and pore size of outer mesoporous silica layer was ∼60nm and 17nm, respectively. The activity of lipase immobilized inside the bilayered shell was further reduced due to diffusion resistance within the outer silica layer and PDDA layer however, it was retained for the next reaction cycles.

ABSTRACTSintering of pure cordierite 2MgO:2Al2O3:5SiO2, and cordierite with the addition of 5 mass % TeO2was studied. Green bodies were prepared from powder mixtures mechanically activated in a high-energy planetary mill, shaped by uniaxial (20 MPa) and cold isostatic pressing (1000 MPa). The pressure-less sintering of these specimens was performed at 1350°C for 1 h. High relative density over 95% of the theoretical value was obtained through solid-state reaction and pressure-less sintering of powder activated for 40 min, and for the first time reported in the literature. Phase composition and microstructures of sintered samples were determined by XRD and SEM, coupled with EDS mapping. The real part of the complex relative permittivity of the samples was measured at 200 MHz. The loss tangent of all samples was below the resolution of the measurement setup. A strong correlation between the relative permittivity and the density agrees with previously published data.

Multiferroic materials attracted a lot of attention in recent years because of their significant scientific interest and technological applications. The multiferroic core/shell powders have a better connectivity between the phases, resulting in superior dielectric and magneto electric properties. In this study, the influence of preparation condition on structure and properties of BaTiO3/α-Fe2O3core/shell composite materials was examined. The five samples were obtained by varying synthesis conditions, such as synthesized method (co-precipitation and sonochemical method) and pH values of solution. XRD and Raman spectroscopy analyses were performed in order to determine phase composition and structural changes within samples. Morphology modifications were examined by SEM and EDS analyses. Finally, effect of structural and microstructural changes on magnetic and electrical properties was detected and explained.

Herein, the ability of gamma irradiation to enhance the photoluminescence properties of graphene quantum dots (GQDs) was investigated. Different doses of γ-irradiation were used on GQDs to examine the way in which their structure and optical properties can be affected. The photoluminescence quantum yield was increased six times for the GQDs irradiated with high doses compared to the nonirradiated material. Both photoluminescence lifetime and values of optical band gap were increased with the dose of applied gamma irradiation. In addition, the exploitation of the gamma-irradiated GQDs as photosensitizers was examined by monitoring the production of singlet oxygen under UV illumination. The main outcome was that the GQDs irradiated at lower doses act as better photoproducers than the ones irradiated at higher doses. These results corroborate that the structural changes caused by gamma irradiation have a direct impact on GQD ability to produce singlet oxygen and their photostability under prolonged UV illumination. This makes low-dose irradiated GQDs promising candidates for photodynamic therapy.

In this paper the influence of tribophysical activation on non-isothermal sintering of barium titanate has been investigated. BaTiO3 powders were tribophysically activated in a planetary ball mill for 0, 60 and 120 min., pressed and non-isothermally sintered up to 1380oC. Dilatometric analysis was performed in air in the temperature range from room temperature to 1380oC with heating rates of 10, 20 and 30oC/min. The samples were analyzed by the X-ray powder diffraction method. Investigation of the morphology of microstructure constituents was performed using the scanning electron microsocopy method. With the purpose of optimizing technological parameters the results obtained by microstructure analysis were correlated with the results of quantitative dilatometric analysis.

The conformations of (Z)- and (E)-5-oxo-B-nor-5,10-secocholest-1(10)-en-3β-yl acetates (2 and 3, resp.) were examined by a combination of X-ray crystallographic analysis and NMR spectroscopy, with emphasis on the geometry of the cyclononenone moiety. The 1H- and 13C-NMR spectra showed that the unsaturated nine-membered ring of (E)-isomer 3 in C6D6 and (D6)acetone solution exists in a sole conformation of type 4;B1, which is similar to its solid-state conformation. The (Z)-isomer 2 in C6D6, CDCl3, and (D6)acetone solution, however, exists in two conformational forms of different families, with different orientation of the carbonyl group, the predominant form (85%) corresponding to the conformation of type 4;A1 and the minor (15%) to the conformation A2 present also in the crystalline state. In this solid-state conformations of the nine-membered ring of both compounds, the 19-Me and 5-oxo groups are ‘β’-oriented. The NMR analysis suggests that the nine-membered ring of 4 has a conformation of type 4;C1 in CDCl3 solution.

In this paper a practical approach to the analysis of sintering of BaTiO3 using the Master Sintering Curve concept has been presented. Non-isothermal sintering of high-purity non-doped BaTiO3 ceramics was monitored using a sensitive dilatometer at three different heating rates (10, 20 and 30 oC/min) up to 1380oC. Densification of BaTiO3 during sintering was analyzed using the Master Curve Sintering Theory. A MSC was defined characterizing the sintering behavior of barium-titanate regardless of the heating rate. Construction of the MSC enabled estimation of the process activation energy. Using defined MSC, densification behavior of BaTiO3 ceramics during sintering can be predicted for arbitrary temperature-time excursions and these predictions can be used in controlling and planning the sintering process of this material.

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Oxidations of 5α-hydroxy-B-norcholestan-3β-yl acetate (8) with Pb(OAc)4 under thermal or photolytic conditions or in the presence of iodine afforded only complex mixtures of compounds. However, the HgO/I2 version of the hypoiodite reaction gave as the primary products the stereoisomeric (Z)- and (E)-1(10)-unsaturated 5,10-seco B-nor-derivatives 10 and 11, and the stereoisomeric (5R,10R)- and (5S,10S)-acetals 14 and 15 (Scheme 4). Further reaction of these compounds under conditions of their formation afforded, in addition, the A-nor 1,5-cyclization products 13 and 16 (from 10) and 12 (from 11) (see also Scheme 6) and the 6-iodo-5,6-secolactones 17 and 19 (from 14 and 15, resp.) and 4-iodo-4,5-secolactone 18 (from 15) (see also Scheme 7). Oxidations of 5β-hydroxy-B-norcholestan-3β-yl acetate (9) with both hypoiodite-forming reagents (Pb(OAc)4/I2 and HgO/I2) proceeded similarly to the HgO/I2 reaction of the corresponding 5α-hydroxy analogue 8. Photolytic Pb(OAc)4 oxidation of 9 afforded, in addition to the (Z)- and (E)-5,10-seco 1(10)-unsaturated ketones 10 and 11, their isomeric 5,10-seco 10(19)-unsaturated ketone 22, the acetal 5-acetate 21, and 5β,19-epoxy derivative 23 (Scheme 9). Exceptionally, in the thermal Pb(OAc)4 oxidation of 9, the 5,10-seco ketones 10, 11, and 22 were not formed, the only reaction being the stereoselective formation of the 5,10-ethers with the β-oriented epoxy bridge, i.e. the (10R)-enol ether 20 and (5S,10R)-acetal 5-acetate 21 (Scheme 8). Possible mechanistic interpretations of the above transformations are discussed.

Gene identification and gene discovery in new genomic sequences is one of the most timely computational questions addressed by bioinformatics scientists. This computational research has resulted in several systems that have been used successfully in many whole-genome analysis projects. As the number of such systems grows the need for a rigorous way to combine the predictions becomes more essential.

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Oxidations of 14α-hydroxy-5α-cholestan-3β-yl acetate (5) with lead tetraacetate under thermal or photolytic conditions or in the presence of iodine proceed mainly by fragmentation of the C(13)−C(14) bond to give as the primary products the 13,18-didehydro-13,14-seco derivative 6 and the (E )-Δ¹²-13,14-seco ketone 11, respectively. Further transformations of these compounds under conditions of their formation afforded, in addition, the acetoxy derivatives 7 – 9 (from 6), and the D-homo-C-nor compound 12 and (12R,13R)-epoxide 13 (from 11). Unexpectedly, the photolytic lead-tetraacetate oxidation of 5 resulted partly (to ca. 20%) in a reversible fragmentation involving scission and recombination of the C(8)−C(14) bond followed by formation of the 14β,22-ether 10. Possible mechanisms for the observed transformations are discussed.

Ozonolysis of the Δ8(14)-unsaturated steroids 1a,b afforded, instead of the expected 8,14-dioxo-8,14-seco derivatives 2a,b two stereoisomeric Δ7-unsaturated ozonides 3a,b and 4a,b.