Influence of structure on the antioxidant activity of indolinic nitroxide radicals

An in vitro study was carried out to verify whether the chain length of a substituent on an indolinic nitroxide could influence its antioxidant activity in different biological environments subjected to oxidative stress. Three distinct indolinic nitroxides were synthesized and compared with vitamin E and Trolox (a hydrophilic analogue of vitamin E), where the only difference between the nitroxides was the length of the hydrocarbon chain in the 2-position of indole, namely 2 (C2), 10 (C10), and 18 (C18) carbons. All the nitroxides were effective in preventing oxidation of bovine serum albumin, but to different extents, with the longer chain derivatives being more efficient. However, the C2 compound was the most efficient in preventing lipid peroxidation in microsomal membranes. The C2 and C18 compounds, Trolox, and vitamin E protected microsomal protein oxidation to the same extent at the highest concentration used (13 microM). The nitroxide with a C10 chain was less effective in this system. The influence of these compounds on the enzymatic activity of two mitochondrial proteins subjected to oxidative stress was also studied by means of oxygraph measurements. Mitochondrial rotenone-sensitive NADH oxidase and succinate oxidase responded differently to BuOOH-induced radical chemistry, and the compounds under study also protected the activity of the two enzymes but to different extents. The results clearly demonstrate that indolinic nitroxides are very efficient antioxidants, protecting both lipids and proteins from peroxidation. The indole structure influences the antioxidant efficacy in biological systems.     

Detection of DNA damage in stressed trout nucleated erythrocytes using the comet assay: protection by nitroxide radicals

Because previous literature reports have demonstrated that nucleated trout erythrocytes in conditions of oxidative stress are subjected to both membrane damage and a decrease in the enzymatic defense systems (glutathione peroxidase), which in turn lead to hemolysis, the present study was undertaken to determine whether DNA may be affected too, prior to the hemolytic event. Impairment of DNA in stressed trout erythrocytes was assessed using the comet assay--a rapid and sensitive, single-cell gel electrophoresis technique used to detect primary DNA damage in individual cells. In addition, indolinic and quinolinic nitroxide radicals were included in the study to determine their efficacy as antioxidants against free-radical-induced DNA damage. The parameters, tail length, tail intensity, and tail moment, used as an index of DNA damage, have shown that trout erythrocytes exposed to oxidative stress experience DNA damage prior to hemolysis and that the nitroxides significantly prevent this damage. This result provides further information about the potential use of these compounds as antioxidants in biological systems.     

Selective catalytic transformations of methanol to C2-C3 hydrocarbons over the new zeolite type LZ 132

The small pore zeolite HLZ 132 exhibits, in comparison with other zeolites, an increased selectivity for the transformation of methanol to ethylene in the reaction temperature range 350–500 °C: the weight ratio of C₂H₄ to C₃H₆ in the products ranges between 1 and 4 at WHSV=2 h^–1. Besides the effect of the reactant shape selectivity this fact may be interpreted by the participation of the asymmetrical methoxy groups in the surface as well as by proton-donor centres of lower acidity which do not catalyze the oligomerization of ethylene but which do the more basic molecule of propylene, thereby generating polyene-type coke.     

An ensemble evolutionary constraint-based approach to understand the emergence of metabolic phenotypes

Constraint-based modeling is largely used in computational studies of metabolism. We propose here a novel approach that aims to identify ensembles of flux distributions that comply with one or more target phenotype(s). The methodology has been tested on a small-scale model of yeast energy metabolism. The target phenotypes describe the differential pattern of ethanol production and O₂ consumption observed in “Crabtree-positive” and “Crabtree-negative” yeasts in changing environment (i.e., when the upper limit of glucose uptake is varied). The ensembles were obtained either by selection among sampled flux distributions or by means of a search heuristic (genetic algorithm). The former approach provided indication about the probability to observe a given phenotype, but the resulting ensembles could not be unambiguously partitioned into “Crabtree-positive” and “Crabtree-negative” clusters. On the contrary well-separated clusters were obtained with the latter method. The cluster analysis further allowed identification of distinct groups within each target phenotype. The method may thus prove useful in characterizing the design principles underlying metabolic plasticity arising from evolving physio-pathological or developmental constraints.     

Recent Advances on High-Speed and Holographic Two-Photon Direct Laser Writing

Two-Photon Lithography, thanks to its very high sub-diffraction resolution, has become the lithographic technique par excellence in applications requiring small feature sizes and complex 3D pattering. Despite this, the fabrication times required for extended structures remain much longer than those of other competing techniques (UV mask lithography, nanoimprinting, etc.). Its low throughput prevents its wide adoption in industrial applications. To increase it, over the years different solutions have been proposed, although their usage is difficult to generalize and may be limited depending on the specific application. A promising strategy to further increase the throughput of Two-Photon Lithography, opening a concrete window for its adoption in industry, lies in its combination with holography approaches: in this way it is possible to generate dozens of foci from a single laser beam, thus parallelizing the fabrication of periodic structures, or to engineer the intensity distribution on the writing plane in a complex way, obtaining 3D microstructures with a single exposure. Here, the fundamental concepts behind high-speed Two-Photon Lithography and its combination with holography are discussed, and the literary production of recent years that exploits such techniques is reviewed, and contextualized according to the topic covered.     

The solid-state rearrangement of the Wells-Dawson K6P2W18O62·10H2O to a stable Keggin-type heteropolyanion phase: a catalyst for the selective oxidation of isobutane to isobutene

The thermal and structural stability of the Wells-Dawson-type heteropoly compound K₆P₂W₁₈O₆₂·10H₂O was examined by FT-IR spectroscopy, X-ray powder diffraction, thermogravimetric analysis and HRTEM. It was found that calcination at temperatures higher than 850 K led to the formation of a Keggin-type compound K₃PW₁₂O₄₀, containing small amounts of an additional phase originated from the high-temperature interaction between potassium phosphate (K₃PO₄ formed during the decomposition of the K₆P₂W₁₈O₆₂·10H₂O) and the Keggin-type compound itself. The Keggin-type product showed a higher activity in the selective oxidative dehydrogenation of isobutane to isobutene compared to both the Wells-Dawson precursor and to pure, authentic K₃PW₁₂O₄₀. This higher activity can be tentatively attributed to the presence of an amorphous layer of unknown stoichiometry at the surface of the thermally rearranged Wells-Dawson compound.     

Mathematical modeling of the partial hydrogenation of vegetable oil in a monolithic stirrer reactor

Experimental and theoretical studies on the partial hydrogenation of vegetable oil in a monolithic stirrer reactor are reported. A complete mathematical model of the reactor was developed, including hydrogenation and isomerization kinetics, catalyst deactivation, external gas–liquid and liquid–solid as well as internal mass transfer. The experimental studies were carried out in a Pd/Al₂O₃/Al monolithic stirrer reactor, at a wide range of temperatures (353–373 K), pressures (414–552 kPa), and catalyst loadings (0.00084–0.00527 kg_Pd,exp m^?3). Based on this model, simulated data can be used to evaluate the catalyst (Pd/Al₂O₃/Al) and the hydrogenation process in consecutive catalytic tests under different operating conditions. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3524–3533, 2014