Some criteria for the applicability of synthetic standards for laser spectral analysis of refractories

Summary The applicability of a series of synthetic standards for laser local analysis of refractories has been determined on the basis of 4 criteria: homogeneity, equality of the form and size of the craters formed by the laser beam, densities and plasma clouds. The validity of these criteria has been checked by comparison of the results received by electrone microprobe area scanning and by shooting the same places with a laser beam and reading the results with the help of synthetic standards.

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Kriterien zur Anwendbarkeit synthetischer Standards für die Laser-Spektralanalyse von feuerfesten Materialien

Zusammenfassung Die Anwendbarkeit von synthetischen Standards für die Laser-Lokalanalyse von feuerfesten Materialien wurde auf Grund von 4 Kriterien beurteilt: Homogenität, Gleichheit von Form und Größe der vom Laserstrahl verursachten Krater, Dichten und Plasmawolken. Die Gültigkeit dieser Kriterien wurde durch Vergleich der erhaltenen Ergebnisse mit den mit Hilfe der Elektronenmikrosonde erzielten Resultaten geprüft.

     

CATALASE INACTIVATION FOLLOWING PHOTOSENSITIZATION WITH TETRASULFONATEDMETALLOPHTHALOCYANINES

Abstract— Catalase (CAT) in solution or incorporated in erythrocytes and K562 leukemic cells is inactivated during photosensitization with tetrasulfonated metallophthalocyantnes (MePcS₄). The effect of added scavengers and D₂0 showed that both singlet oxygen and free radical species are involved in this process. Evidence was found that direct interactions of ground or excited-stated photosensitizers with CAT are not responsible for CAT inactivation. Specific techniques to probe early damage to the CAT structure involved optical and EPR spectroscopy, HPLC and polyacrylamide gel electrophoresis analyses. Different primary events of photosensitized protein damage included oxidation of cysteine residues as well as other amino acids, as demonstrated by the formation of carbon-centered free radicals and the loss of absorbance at λ= 275 nm. In parallel, we detected degradation of the CAT heme groups, accompanied by release of Fe(II) ions in solution. These combined phenomena initiate cross-linkages between CAT subunits and subsequent degradation of the protein with formation of irreversible aggregates in solution. Phthalocyanine-mediated photoinactivation of cell-bound CAT results in loss of protection against accumulating H₂0₂, providing an additional pathway of phototoxicity.     

A Universal Nano‐capillary Based Method of Catalyst Immobilization for Liquid‐Cell Transmission Electron Microscopy

A universal nano‐capillary based method for sample deposition on the silicon nitride membrane of liquid‐cell transmission electron microscopy (LCTEM) chips is demonstrated. It is applicable to all substances which can be dispersed in a solvent and are suitable for drop casting, including catalysts, biological samples, and polymers. Most importantly, this method overcomes limitations concerning sample immobilization due to the fragility of the ultra‐thin silicon nitride membrane required for electron transmission. Thus, a straightforward way is presented to widen the research area of LCTEM to encompass any sample which can be externally deposited beforehand. Using this method, Ni_xB nanoparticles are deposited on the μm‐scale working electrode of the LCTEM chip and in situ observation of single catalyst particles during ethanol oxidation is for the first time successfully monitored by means of TEM movies.     

Semi-empirical molecular orbital studies of porphine and phthalocyanine derivatives,to simulate their intermolecular interactions

Gound-state electronic properties of porphine, phthalocyanine, and their derivatives, photosensitizers with potential use in the photodynamic therapy of tumors, were studied by semiempirical (MNDO ) molecular orbital calculations. Geometry, bond orders, electron populations, and net atomic charges were analyzed. The obtained models were applied to study the intermolecular interactions of these molecules utilizing a classical mechanics approach. The dimerization characteristics of different derivatives were obtained by a separate evaluation of the contribution of electrostatic and steric factors. © 1993 John Wiley & Sons, Inc.     

Fully atomistic molecular‐mechanical model of liquid alkane oils: Computational validation

Fully atomistic molecular dynamics simulations were performed on liquid n‐pentane, n‐hexane, and n‐heptane to derive an atomistic model for middle‐chain‐length alkanes. All simulations were based on existing molecular‐mechanical parameters for alkanes. The computational protocol was optimized, for example, in terms of thermo‐ and barostat, to reproduce properly the properties of the liquids. The model was validated by comparison of thermal, structural, and dynamic properties of the normal alkane liquids to experimental data. Two different combinations of temperature and pressure coupling algorithms were tested. A simple differential approach was applied to evaluate fluctuation‐related properties with sufficient accuracy. Analysis of the data reveals a satisfactory representation of the hydrophobic systems behavior. Thermodynamic parameters are close to the experimental values and exhibit correct temperature dependence. The observed intramolecular geometry corresponds to extended conformations domination, whereas the intermolecular structure demonstrates all characteristics of liquid systems. Cavity size distribution function was calculated from coordinates analysis and was applied to study the solubility of gases in hexane and heptane oils. This study provides a platform for further in‐depth research on hydrophobic solutions and multicomponent systems. © 2014 Wiley Periodicals, Inc.     

Oxidation of 2'-deoxycytidine to four interconverting diastereomers of N1-carbamoyl-4,5-dihydroxy-2-oxoimidazolidine nucleosides

Modification of 2'-deoxycytidine (dCyd) by hydroxyl radicals and direct ionization leads to the formation of various oxidation products, including dCyd 5,6-glycols, 5-hydroxy-2'-deoxycytidine, and ring fragmentation products. The mechanism of oxidation is complex and poorly understood. In the present work, we have prepared four cis- and trans-diastereomers of N1-(2-deoxy-beta-D-erythro-pentofuranosyl)-1-carbamoyl-2-oxo-4,5-dihydroxyimidazolidine by bromination of dCyd followed by peroxidation of the resulting dCyd bromohydrins. The structure and stereochemistry of each product were determined by 1H NMR, 13C NMR, and 2D NOE analyses. The formation of imidazolidine products involves rearrangement of initial 5(6)-hydroxy-6(5)-hydroperoxides to C6-C2 endoperoxides, which subsequently decompose by a concerted pathway to imidazolidine products. A remarkable feature of the four diastereomers was their ability to interconvert via single and successive cycles of ring-chain tautomerism at N1-C5 and N3-C4, leading to epimerization of C5 and C4, respectively. The rate of isomerization was greater for cis-diastereomers compared to trans-diastereomers, and the rate sharply increased with pH (pH 9.0>7.0>5.5).     

On the algebraic curves for circular and folded strings in AdS5×S5

There have been recent advances in the construction of algebraic curves for certain classes of string solutions in the context of the AdS/CFT correspondence. In this paper we obtain the Lax operators and associated spectral curves for circular and folded string solutions in AdS ${}_5\times S^5$. In addition, we provide an original approach for the reconstruction of string solutions in S³ from their corresponding curves.