Chemical Selectivity during the Electro-Oxidation of Ethanol on Unsupported Pt Nanoparticles

In this paper we present results on the electro-oxidation of ethanol on unsupported (carbon free) platinum nanoparticles, considering the effects of the alcohol concentration. The case of the so-called dual pathway mechanism during the electro-oxidation of ethanol showed to be influenced by the surface coverage of adsorbed carbon monoxide (COad) at unsupported platinum. The influences of adsorbed intermediates were followed by in situ infrared spectroscopy (FTIR) and by electrochemical experiments. Unsupported platinum showed that the reaction leads to the formation of CO2 and acetic acid as main products at low concentrations of ethanol (0.01 to 0.1 mol L-1). At least in this case of 0.01 mol L-1 ethanol, most formation of CO2 occurred via COad (indirect pathway). At higher concentration of ethanol, however, most CO2 was formed via a reactive intermediate such as acetaldehyde (direct pathway). In addition, in this higher concentration of ethanol, the acetic acid was produced via formation of adsorbed acetaldehyde (via acetate) at higher overpotentials. In case of the acetic acid formation, a dual pathway was identified during the electro-oxidation of ethanol at low alcohol concentrations, whereas a parallel pathway occurred without the formation of adsorbed acetate intermediates at low overpotentials. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.101203jes] All rights reserved.

Inhibition of LDL-oxidation and antioxidant properties related to polyphenol content of hydrophilic fractions from seaweed Halimeda Incrassata (Ellis) Lamouroux

LDL oxidation and oxidative stress are closely related to atherosclerosis. Therefore, natural antioxidants have been studied as promising candidates. In the present study, the LDL oxidation inhibition activity of bioactive compounds from Halimeda incrassata seaweed. associated to antioxidant capacity, was evaluated in vitro. Experimental work was conducted with lyophilized aqueous extract and phenolic-rich fractions of the seaweed and their effect on LDL oxidation was evaluated using heparin-precipitated LDL (hep-LDL) with exposure to Cu2+ ions and AAPH as the free radical generator. H. incrassata had a protective effect for hep-LDL in both systems and the presence of phenolic compounds contributed to the activity where phenolic-rich fractions showed significant capacity for inhibition of oxidation mediated by Cu2+ ions. The observed effect could be related to the antioxidant potential of polar fractions evidenced by reducing activity and DPPH center dot radical scavenging. The results obtained in vitro further support the antioxidant and LDL oxidation inhibition properties of H. incrassata and further knowledge toward future phytotherapeutic application of the seaweed.

CuO-CeO2 catalysts synthesized in one-step: Characterization and PROX performance

PEM fuel cells seem to be the most affordable and commercially viable hydrogen-based cells, the biggest challenge being to obtain CO-free H-2 (<100 ppm) as the fuel. In this study, the use of CuO-CeO2 catalysts in preferential oxidation of CO to obtain CO-free H-2 (PROX reaction) was investigated. Ce1-xCuxO2 catalysts, with x (mol%) = 0, 0.01, 0.03, 0.05 and 0.10, were synthesized in one-step by the polymeric precursor method, to obtain a very fine dispersion and strong metal-support interaction, to favor active copper species and a preference for the PROX reaction. The results obtained from catalyzed reactions and characterization of the catalysts by XRD, Rietveld refinement, BET surface area, UV-Vis and TPR, suggest that this one-step synthesis method gives rise to catalysts with copper species selective for the PROX reaction, which reaches a maximum rate on Ce0.97Cu0.03O2 catalyst. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Lipase-catalyzed kinetic resolution of beta-borylated carboxylic esters

The kinetic resolution of chiral beta-borylated carboxylic esters via lipase-catalyzed hydrolysis and transesterification reactions was studied. The enantioselective hydrolysis catalyzed by CAL-B furnished the beta-borylated carboxylic acid with reasonable enantiomeric excess (62% ee), while both methyl and ethyl beta-borylated carboxylic esters were recovered with excellent ee (>99%). Meanwhile, the transesterification reaction of beta-borylated carboxylic esters and several alcohols, catalyzed by CAL-B, only indicated a high selectivity when ethanol and methyl-(beta-pinacolylboronate)-butanoate were used as substrates, which gave ethyl-(beta-pinacolylboronate)-butanoate with >99% ee. (C) 2012 Elsevier Ltd. All rights reserved.

Oscillatory electro-oxidation of glycerol on platinum

This paper describes the experimental study of the oscillatory electro-oxidation of glycerol on platinum under galvanostatic control. The system was investigated in both acidic and alkaline media and for different glycerol concentrations. In acidic supporting electrolyte, the oscillatory behavior is rather simple and the main features such as period, amplitude and waveform are barely affected by the glycerol concentration. A more complex picture including the presence of different temporal patterns and strong dependence with glycerol concentration emerges in alkaline medium. In both media, the composite oscillations visit two clearly discernible potential windows, and potential oscillations in alkaline media are observed only when the working electrode is kept stationary. The mechanistic implications of our findings are discussed in connection with available data obtained under close-to-equilibrium conditions. (C) 2012 Elsevier Ltd. All rights reserved.

Effect of natural antioxidant combinations on lipid oxidation in cooked chicken meat during refrigerated storage

The effect of combinations of sage, oregano and honey on lipid oxidation in cooked chicken meat during refrigeration at 4 degrees C for 96 h was determined. Chicken samples (thigh and breast) were then separated into five groups; control; butylated hydroxytoluene; oregano + sage; oregano + sage + 5%honey and oregano + sage + 10%honey. Quantitative measurements of thiobarbituric acid reactive substances, conjugated dienes, hexanal, fatty acids, cholesterol and cholesterol oxides were used as indicators of lipid oxidation. Acceptability and preference were also evaluated. The effectiveness of the natural antioxidants for reducing the velocity of lipid oxidation in cooked chicken thigh and breast was demonstrated after 48 and 96 h of refrigeration at 4 degrees C. The treatments that presented the lowest hexanal values after 96 h of refrigeration were oregano + sage + 5%honey and oregano + sage + 10%honey. Only traces of free cholesterol oxides were found (25-OH, 7-k, 7 alpha-OH and 7 beta-OH). The natural antioxidants protected cooked chicken meat from oxidation processes and resulted in great acceptability. (C) 2012 Elsevier Ltd. All rights reserved.

Performance and selectivity of PtxSn/C electro-catalysts for ethanol oxidation prepared by reduction with different formic acid concentrations

Carbon supported Pt-Sn catalysts were prepared by reduction of Pt and Sn precursors with formic acid and characterized in terms of structure, morphology and surface properties. The electrocatalytic activity for ethanol oxidation was studied in a direct ethanol fuel cell (DEFC) at 70 degrees C and 90 degrees C. Electrochemical and physico-chemical data indicated that a proper balance of Pt and Sn species in the near surface region was necessary to maximize the reaction rate. The best atomic surface composition, in terms of electrochemical performance, was Pt:Sn 65:35 corresponding to a bulk composition 75:25 namely Pt3Sn1/C. The reaction products of ethanol electro-oxidation in single cell and their distribution as a function of the nature of catalyst were determined. Essentially, acetaldehyde and acetic acid were detected as the main reaction products; whereas, a lower content of CO2 was formed. The selectivity toward acetic acid vs. acetaldehyde increased with the increase of the Sn content and decreased by decreasing the concentration of the reducing agent used in the catalyst preparation. According to the recent literature, these results have been interpreted on the basis of ethanol adsorption characteristics and ligand effects occurring for Sn-rich electrocatalysts. (C) 2012 Elsevier Ltd. All rights reserved.

On the temperature stability of extracellular hemoglobin of Glossoscolex paulistus, at different oxidation states: SAXS and DLS studies

Glossoscolex paulistus hemoglobin (HbGp) was studied by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). DLS melting curves were measured for met-HbGp at different concentrations. SAXS temperature studies were performed for oxy-, cyanomet- and met-HbGp forms, at several pH values. At pH 5.0 and 6.0, the scattering curves are identical from 20 to 60 degrees C, and R-g is 108 angstrom, independent of the oxidation form. At pH 7.0, protein denaturation and aggregation occurs above 55 degrees C and 60 degrees C, for oxy and met-HbGp, respectively. Cyanomet-HbGp, at pH 7.0, is stable up to 60 degrees C. At alkaline pH (8.0-9.0) and higher temperature, an irreversible dissociation process is observed, with a decrease of R-g, D-max and I(0). Analysis by p(r), obtained from GNOM, and OLIGOMER, was used to fit the SAXS experimental scattering curves by a combination of theoretical curves obtained for HbLt fragments from the crystal structure. Our results show clearly the increasing contribution of smaller molecular weight fragments, as a function of increasing pH and temperature, as well as, the order of thermal stabilities: cyanomet-> oxy- > met-HbGp. (C) 2012 Elsevier B.V. All rights reserved.

Release of NO from a nitrosyl ruthenium complex through oxidation of mitochondrial NADH and effects on mitochondria

Nitrosyl ruthenium complexes are promising NO donor agents with numerous advantages for the biologic applications of NO. We have characterized the NO release from the nitrosyl ruthenium complex [Ru(NO2)(bpy)(2)(4-pic)](+) (I) and the reactive oxygen/nitrogen species (ROS/RNS)-mediated NO actions on isolated rat liver mitochondria. The results indicated that oxidation of mitochondrial NADH promotes NO release from (I) in a manner mediated by NO2 formation (at neutral pH) as in mammalian cells, followed by an oxygen atom transfer mechanism (OAT). The NO released from (I) uncoupled mitochondria at low concentrations/incubation times and inhibited the respiratory chain at high concentrations/incubation times. In the presence of ROS generated by mitochondria NO gave rise to peroxynitrite, which, in turn, inhibited the respiratory chain and oxidized membrane protein-thiols to elicit a Ca2+-independent mitochondrial permeability transition; this process was only partially inhibited by cyclosporine-A, almost fully inhibited by the thiol reagent N-ethylmaleimide (NEM) and fully inhibited by the NO scavenger 2-(4-carboxyphenyl)-4,45,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). These actions correlated with the release of cytochrome c from isolated mitochondria as detected by Western blotting analysis. These events, typically involved in cell necrosis and/or apoptosis denote a potential specific action of (I) and analogs against tumor cells via mitochondria-mediated processes. (C) 2012 Elsevier Inc. All rights reserved.

Exploiting the enantioselectivity of Baeyer-Villiger monooxygenases via boron oxidation

The enantioselective carbon-boron bond oxidation of several chiral boron-containing compounds by Baeyer-Villiger monooxygenases was evaluated. PAMO and M446G PAMO conveniently oxidized 1-phenylethyl boronate into the corresponding 1-(phenyl)ethanol (ee = 82-91%). Cyclopropyl boronic esters were also oxidized but with no enantioselectivity. beta-Boryl carboxylic esters were not oxidized by any BVMOs. (C) 2012 Elsevier Ltd. All rights reserved.

New Approaches for the Ethanol Oxidation Reaction of Pt/C on Carbon Cloth Using ATR-FTIR

This work describes the study of the ethanol oxidation reaction of a Pt/C Etek electrocatalyst that was supported on different substrates, such as gold, glassy carbon and carbon cloth treated with PTFE. In the ethanol oxidation reaction, the activity varies with the substrate, as well as the pathways for ethanol oxidation, as studied by an ATR-FTIR in situ setup using the carbon cloth as the electrocatalyst support. The electrocatalyst Pt/C supported on gold starts acetaldehyde production from ethanol oxidation at an onset potential of 0.1 V less than that observed for the same process on Teflon-treated carbon cloth. The Pt/C supported on the carbon cloth starts its CO2 production for the same oxidation process at 0.2 V less than on the Pt/C supported on gold substrate. The differences in catalytic activity for the ethanol oxidation reaction depend not only on the electrocatalyst but also on various electrode factors, such as the substrate, the roughness of the electrode and the charge transfer resistance.

One-Pot, Three-Step Reaction of 5-[(Trimethylsilyl)ethynyl]pyrrolidin-2-one with Azides Catalyzed by Cu-I: Synthesis of a Novel Class of 1,4-Disubstituted 1,2,3-Triazoles

A very fast, easy and efficient synthesis is described for a novel and biologically important class of 1,4-disubstituted-4-(5-pyrrolidin-2-one)-1,2,3-triazoles by an ultrasound-assisted one-pot, three-step click reaction sequence of 5-[(trimethylsilyl)ethynyl]pyrrolidin-2-one with organic azides mediated by catalytic Cu-I salts.

Synthesis of Chromanes and 4H-Chromenes: Exploring the Oxidation of 2H-Chromenes and Dihydro-1-benzoxepines by Hypervalent Iodine(III)

The reaction of various oxygen-containing benzo-fused cycloalkenes were studied with the hypervalent iodine reagent hydroxy(tosyloxy) iodo]benzene [PhI(OH)OTs, HTIB]. 2H-Chromene and 4-methyl-2H-chromene resulted in substituted 4H-chromene and cis-3,4-dialkoxy-4-methyl-3,4-dihydro-2H-chromenes, respectively. Ring contraction to chromanes and benzofurans was observed for dihydrobenzoxepines and 2,2-dimethyl-2H-chromenes, respectively.

An EQCM-D study of the influence of chloride on the lead anodic oxidation

The influence of chloride on the electrodeposition of lead films and their dissolution in anodic stripping voltammetric experiments was examined. Gold substrates were plated with lead films, and mass changes were monitored by using the electrochemical quartz crystal microbalance with dissipation factor (EQCM-D). The results showed that the amount of electrodeposited lead is slightly dependent on the chloride concentration. The charge/mass ratio data indicated the presence of Pb(I) and Pb(II) as a result of film dissolution, and the precipitation and deposition of PbCl2 onto the electrode surface. Scanning electron microscopy images revealed that the morphology of the lead film was strongly influenced by chloride present in the plating solution and that much rougher films were obtained in comparison with those obtained in the absence of chloride. The rate of the anodic dissolution was higher for lead films with higher surface areas, which lead to an increase in their stripping voltammetric currents. (C) 2012 Elsevier Ltd. All rights reserved.

Study of CuO/CeO2 catalyst with for preferential CO oxidation reaction in hydrogen-rich feed (PROX-CO)

The CuO/CeO2 system was investigated as a catalyst for preferential CO oxidation reaction in hydrogen-rich feed (PROX-CO). The catalysts were prepared by deposition-precipitation (DEP) and co-precipitation (COP) methods and the catalytic performance reveals that the preparation method influences the properties of solids prepared, where a direct consequence is the difference in behavior of the catalysts in the PROX-CO reaction. A high specific area and a better dispersion of the metallic phase were obtained in the catalyst prepared by co-precipitation. The redox properties during the reaction were reported by measures of temperature programmed reduction (TPR), OSC measurements and X-ray absorption near edge structure (XANES-TPR) in situ showed the relationship between the preparation method, the physicochemical characteristics and redox properties in the PROX-CO reaction. By this means, the good dispersion of CuO and the best oxygen capacity are the response of the high performance of CuO/CeO2-COP catalysts for the PROX-CO reaction. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.