Sintering behavior and thermal expansion of zirconia–titanium composites

The dilatometric and thermogravimetric methods were used to investigate the sintering conditions of 3Y–ZrO₂ and 3Y–ZrO₂–Ti composites. For the materials preparation, the nanometric zirconia stabilized by 3 mol% Y₂O₃ powder and micrometric titanium powder (3 and 10 vol%) were used. The green body samples were formed by slip casting method. The morphology of samples microstructures was determined by SEM observations. The stereological analysis of zirconia and zirconia–titanium composites was carried out using computer program. The density was measured using the Archimedes method. The hardness of sinters was also investigated. Addition of Ti into ZrO₂ influenced the sintering behavior and thermal expansion of obtained composites. The analysis of the sintering process and characteristic temperatures confirmed the increase of onset and final temperature of shrinkage with the increase in Ti content. The changes of the thermal expansion curves for the pure zirconia and 3Y–ZrO₂–Ti composites were the result of the αTi → βTi transformation and the transition temperature of the zirconia m → t transformation. The zirconia and composite samples were characterized by relative density about 98%, close to theoretical density. The slight growth of zirconia grains was observed.     

Overmodulation of projections as signal‐to‐noise enhancement method in EPR imaging

A study concerning the image quality in electron paramagnetic resonance imaging in two‐dimensional spatial experiments is presented. The aim of the measurements was to improve the signal‐to‐noise ratio (SNR) of the projections and the reconstructed image by applying modulation amplitude higher than the radical electron paramagnetic resonance linewidth. Data were gathered by applying four constant modulation amplitudes, where one was below 1/3 (A_mod = 0.04 mT) of the radical linewidth (ΔB_pp = 0.14 mT). Three other modulation amplitude values were used in this experiment, leading to undermodulated (A_mod < 1/3 ΔB_pp), partially overmodulated (A_mod ~ 1/3 ΔB_pp) and fully overmodulated (A_mod > > 1/3 ΔB_pp) projections. The advantages of an applied overmodulation condition were demonstrated in the study performed on a phantom containing four shapes of 1.25 mM water solution of 2, 2, 6, 6‐tetramethyl‐1‐piperidinyloxyl. It was shown that even when the overmodulated reference spectrum was used in the deconvolution procedure, as well as the projection itself, the phantom shapes reconstructed as images directly correspond to those obtained in undermodulation conditions. It was shown that the best SNR of the reconstructed images is expected for the modulation amplitude close to 1/3 of the projection linewidth, which is defined as the distance from the first maximum to the last minimum of the gradient‐broadened spectrum. For higher modulation amplitude, the SNR of the reconstructed image is decreased, even if the SNR of the measured projection is increased. Copyright © 2015 John Wiley & Sons, Ltd.     

Absolute configurations, predominant conformations, and tautomeric structures of enantiomeric tert-butylphenylphosphinothioic acid.

Vibrational absorption and circular dichroism spectra of dextrorotatory, levorotatory, and racemic mixture of tert-butylphenylphosphinothioic acid have been measured in CCl(4) solutions in the 2000-900 cm(-1) region. The conformations for both tautomeric structures of (S)-tert-butylphenylphosphinothioic acid are investigated using the B3LYP functional with the 6-31G* basis set. For the most stable conformation, the absorption and VCD spectra are predicted ab initio using the B3LYP functional with 6-31G*, 6-311G(2d, 2p), 6-31+G, and 6-311G(3df, 3pd) basis sets. A different functional, B3PW91, was also used with the 6-31G* basis set. The predicted spectra are compared to the experimental spectra. The comparison indicates that (-)-tert-butylphenylphosphinothioic acid is of the (S)-configuration and exists in only one tautomeric structure and one conformation in CCl(4) solution.     

Deactivation of carbon supported palladium catalyst in direct formic acid fuel cell

A new carbon black supported palladium catalyst for direct formic acid fuel cell applications has been prepared and characterized by X-ray diffraction. Bi-modal distribution of Pd crystallite sizes was observed. The average Pd size for crystallites in small size and large size ranges were about 2.7 nm and 11.2 nm, respectively. The initial activity of the catalyst in the oxidation of formic acid tested in a fuel cell was similar to a commercial well dispersed 20 wt.% Pd/Vulcan. The rates of the fuel cell power decay were measured for formic acid of two purities for various current loadings. The results showed that various mechanisms contribute to the decrease of cell power with time. In direct formic acid fuel cell (DFAFC) fed with a very pure HCOOH accumulation of CO₂ gas bubbles in anode catalyst layer is responsible for observed power decay. In DFAFC fed with a pure for analysis (p.a.) grade formic acid the formation of CO_ads poison from the formic acid impurities is the main deactivation reason.     

Biocatalytic oxidation of thiophosphoryl compounds: a new chemo-enzymatic approach to enantiomeric insecticidal thionophosphates and their oxons

The biocatalytic oxidation of racemic O-S-dimethyl O-p-nitrophenyl phosphorodithioate 5 catalyzed by chloroperoxidase from Caldariomyces fumago resulted in the formation of the (?)-(S)-enantiomer of the corresponding oxon 4 and unoxidized substrate 5 with a (+)-(R)-configuration. Both compounds were obtained with very high enantiomeric excesses, 99.6% and 97%, respectively. The thionation reaction of the resulting (?)-(S)-oxon 4 with Lawesson’s reagent gave (?)-(S)-phosphorodithioate 5 with full stereoselectivity, while the oxidation of unreacted substrate (+)-(R)-5 with iodoxybenzene afforded oxon (+)-(R)-4 with 94.9% ee.     

New Procedures for the Oxidation of Sulfides to Sulfoxides and Sulfones

New reagents for the oxidation of sulfides to the corresponding sulfoxides and sulfones are presented.     

Sub-lethal Photodynamic Damage to ARPE-19 Cells Transiently Inhibits Their Phagocytic Activity†

Efficient phagocytosis of photoreceptor outer segments (POS) membranes by retinal pigment epithelium (RPE) plays a key role in biological renewal of these highly peroxidizable structures. Here, we tested whether photodynamic treatment, mediated by merocyanine 540 (MC 540), rose Bengal or a zinc-substituted chlorophyllide inhibited phagocytic activity of ARPE-19 cells in vitro. Specific phagocytosis of fluorescein-5-isothiocyanate-labeled POS isolated from cow retinas and nonspecific phagocytosis of fluorescent polystyrene beads were measured by flow cytometry. Photodynamic treatment, mediated by all three photosensitizers with sub-threshold doses, induced significant inhibition of the cell-specific phagocytosis. The nonspecific phagocytosis was inhibited by photodynamic treatment mediated only by MC 540. The inhibition of phagocytosis was a reversible phenomenon and after 24 h, the photodynamically treated cells exhibited phagocytic activity that was comparable with that of untreated cells. This study provides proof of principle that sub-threshold photodynamic treatment of ARPE-19 cells with appropriate photosensitizers is a convenient experimental approach for in vitro study of the effects of oxidative stress on specific phagocytic activity of RPE cells. We postulate that oxidative damage to key components of the cell phagocytic machinery may be responsible for severe impairment of its activity, which can lead to retinal degeneration.     

Characterization and optimization of the laser-produced plasma EUV source at 13.5 nm based on a double-stream Xe/He gas puff target

The paper describes a debris-free, efficient laser-produced plasma source emitting EUV radiation. The source is based on a double-stream Xe/He gas-puff. Its properties and spectroscopic signatures are characterized and discussed. The spatio-spectral features of the EUV emission are investigated. We show a large body of results related to the intensity and brightness of the EUV emission, its spatial, temporal, and angular behavior and the effect of the repetition rate as well. A conversion efficiency of laser energy into EUV in-band energy at 13.5 nm of 0.42% has been gained. The electron temperature and electron density of the source were estimated by means of a novel method using the FLY code. The experimental data and the Hullac code calculations are compared and discussed. The source is well suited for EUV metrology purposes. The potential of the source for application in EUV lithography was earlier demonstrated in the optical characterization of Mo/Si multi-layer mirrors and photo-etching of polymers.     

Synthesis,crystal structures,spectroscopic studies and antibacterial properties of a series of mononuclear cobalt(III) Schiff base complexes

New complexes of cobalt(III) with the tridentate and tetradentate Schiff base ligands: 3-methoxy-2-{(Z)[(2-hydroxyphenyl)imino]methyl}phenol (H₂L¹), 4-[(2-hydroxyphenyl)imino]-2-pentanone (H₂L²); and 2-((E)-1-(2-((E)-1-(2-hydroxy-4,5-dimethylphenyl)ethylideneamino)ethylimino)ethyl)-4,5 dimethylphenol (H₂L³), namely [Co^III(L¹)(N-MeIm)₃]PF₆ (1), [Co^III(L¹)(py)₃]ClO₄ (2), [Co(L¹)(py)₃][Co(L¹)₂] (3) and [Co^III(L²)(N-MeIm)₃]PF₆ (4) and [Co(L³)(N-MeIm)₂]PF₆ (5), were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of the complexes were determined by X-ray crystallography. In each of these complexes, the cobalt(III) centre has a slightly distorted octahedral environment, utilizing all available coordination centres of the ligands. The complexes were also screened for in vitro antibacterial activities against four human pathogenic bacteria, and their minimum inhibitory concentrations indicated good antibacterial activities.     

Ultrafast Dynamics of the Transoid-cis Isomer Formed in Photochromic Reaction from 3H-Naphthopyran

Recent efforts in designing new 3H-naphthopyran derivatives have been focused on efficient coloration process with a short fading time of the colored transoid-cis TC isomer. It is desirable to avoid photoisomerization of TC leading to transoid-trans TT isomers in the photoreaction. Long lifetime of TT can hamper fast applications such as dynamic holographic materials and molecular actuators, the residual color is one of the serious issues for photochromic lenses. Herein we characterize the photophysical and photochemical channels of TC excited state deactivation competing with the unwanted TC → TT isomerization process. Transient absorption spectroscopy reveals a very short lifetime of the singlet excited TC (≈0.8 ps) and its deactivation channels as S₁→S₀ internal conversion (major), intersystem crossing S₁→T₁, pyran ring formation, photoenolization and TC → TT isomerization. Computations support the S₁→S₀ and T₁→S₀ channels as responsible for photostabilization of the TC form.