Dietary carotenoid lutein protects against DNA damage and alterations of the redox status induced by cisplatin in human derived HepG2 cells

Several epidemiological and experimental studies has been reported that lutein (LT) presents antioxidant properties. Aim of the present study was to investigate the protective effects of LT against oxidative stress and DNA damage induced by cisplatin (cDDP) in a human derived liver cell line (HepG2). Cell viability and DNA-damage was monitored by MU and comet assays. Moreover, different biochemical parameters related to redox status (glutathione, cytochrome-c and intracellular ROS) were also evaluated. A clear DNA-damage was seen with cDDP (1.0 mu M) treatment. In combination with the carotenoid, reduction of DNA damage was observed after pre- and simultaneous treatment of the cells, but not when the carotenoid was added to the cells after the exposure to cDDP. Exposure of the cells to cDDP also caused significant changes of all biochemical parameters and in co-treatment of the cells with LT, the carotenoid reverted these alterations. The results indicate that cDDP induces pronounced oxidative stress in HepG2 cells that is related to DNA damage and that the supplementation with the antioxidant LT may protect these adverse effects caused by the exposure of the cells to platinum compound, which can be a good predict for chemoprevention. (C) 2011 Elsevier Ltd. All rights reserved.

Electrooxidation of Ethanol on Pt and PtRu Surfaces Investigated by ATR Surface-Enhanced Infrared Absorption Spectroscopy

Herein, it was investigated for the first time the electro-oxidation of ethanol on Pt and PtRu electrodeposits in acidic media by using in situ surface enhanced infrared absorption spectroscopy with attenuated total reflection (ATR-SEIRAS). The experimental setup circumvents the weak absorbance signals related to adsorbed species, usually observed for rough, electrodeposited surfaces, and allows a full description of the CO coverage with the potential for both catalysts. The dynamics of adsorption-oxidation of CO was accessed by ATR-SEIRAS experiments (involving four ethanol concentrations) and correlated with expressions derived from a simple kinetic model. Kinetic analysis suggests that the growing of the CO adsorbed layer is nor influenced by the presence of Ru neither by the concentration of ethanol. The results suggest that the C-C scission is not related to the presence of Ru and probably happens at Pt sites.

Effect of the relationship between particle size, inter-particle distance, and metal loading of carbon supported fuel cell catalysts on their catalytic activity

The effect of the relationship between particle size (d), inter-particle distance (x(i)), and metal loading (y) of carbon supported fuel cell Pt or PtRu catalysts on their catalytic activity, based on the optimum d (2.5-3 nm) and x(i)/d (>5) values, was evaluated. It was found that for y < 30 wt%, the optimum values of both d and x(i)/d can be always obtained. For y >= 30 wt%, instead, the positive effect of a thinner catalyst layer of the fuel cell electrode than that using catalysts with y < 30 wt% is concomitant to a decrease of the effective catalyst surface area due to an increase of d and/or a decrease of x(i)/d compared to their optimum values, with in turns gives rise to a decrease in the catalytic activity. The effect of the x(i)/d ratio has been successfully verified by experimental results on ethanol oxidation on PtRu/C catalysts with same particle size and same degree of alloying but different metal loading. Tests in direct ethanol fuel cells showed that, compared to 20 wt% PtRu/C, the negative effect of the lower x(i)/d on the catalytic activity of 30 and 40 wt% PtRu/C catalysts was superior to the positive effect of the thinner catalyst layer.

Straightforward Synthesis of Carbon-Supported Ag Nanoparticles and Their Application for the Oxygen Reduction Reaction

In this paper we report a simple and environmentally friendly synthesis of silver nanoparticles (AgNps) and their activities towards the oxygen reduction reaction (ORR). Ultraviolet spectroscopy (UV-vis) and transmission electron microscopy confirmed the formation of poly(vinyl pyrrolidone)-protected colloidal AgNps through direct reduction of Ag+ by glycerol in alkaline medium at room temperature. For the ORR tests, the AgNps were directly produced onto carbon to yield the Ag/C catalyst. Levich plots revealed the process to occur via 2.7 electrons, suggesting that the carbon support contributes to the ORR. We discuss here possibilities of improving the catalytic properties of the Ag/C for ORR by optimizing the parameters of the synthesis.

Paper-Based Analytical Device for Electrochemical Flow-Injection Analysis of Glucose in Urine

This article describes a new design for a paper-based electrochemical system for flow injection analysis. Capillary wicking facilitates a gravity-driven flow of buffer solution continuously through paper and nitrocellulose, from a buffer reservoir at one end of the device to a sink at the other. A difference in height between the reservoir and the sink leads to a continuous and constant flow. The nitrocellulose lies horizontally on a working electrode, which consists of a thin platinum layer deposited on a solid support. The counter and reference electrodes are strategically positioned upstream in the buffer reservoir. A simple pipetting device was developed for reliable application of (sub)microliter volumes of sample without the need of commercial micropipets; this device did not damage the nitrocellulose membrane. Demonstration of the system for the determination of the concentration of glucose in urine resulted in a noninvasive, quantitative assay that could be used for diagnosis and monitoring of diabetes. This method does not require disposable test strips, with enzyme and electrodes, that are thrown away after each measurement Because of its low cost, this system could be used in medical environments that are resource-limited.

Electrodeposition of PVA-protected PtCo electrocatalysts for the oxygen reduction reaction in H2SO4

In this paper we report the electrosynthesis of PVA-protected PtCo films (PVA = poly(vinylalcohol)) and their activities towards the oxygen reduction reaction (ORR). PtCo electrodeposits were potentiostatically obtained in the presence and absence of PVA at distinct potentials. The film morphology and composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), which revealed that the use of PVA in the electrodeposition of PtCo films was decisive to achieve better film composition control. Cyclic voltammetry for PVA-protected PtCo films showed that the electrochemical surface area is dependent on the electrodeposition potentials and suggested different adsorption strengths of oxygen-containing species. Films produced in the presence of PVA presented the following activity order towards ORR as a function of the electrodeposition potential (vs. Ag/AgCl): -0.9 V> -0.8 V> -1.0 V> -0.7 V. In contrast, PtCo films electrodeposited in the absence of PVA displayed very similar activities regardless of the electrodeposition potential. The simplicity of the electrodeposition method combined with its effectiveness enabled the production of "model electrodes" for investigating the fundamental aspects of the reactions taking place in the fuel cell cathodes. (C) 2011 Elsevier B.V. All rights reserved.

Development of Plurimetallic Electrocatalysts Prepared by Decomposition of Polymeric Precursors for EtOH/O-2 Fuel Cell

This work aimed to develop plurimetallic electrocatalysts composed of Pt, Ru, Ni, and Sn supported on C by decomposition of polymeric precursors (DPP), at a constant metal: carbon ratio of 40:60 wt.%, for application in direct ethanol fuel cell (DEFC). The obtained nanoparticles were physico-chemically characterized by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). XRD results revealed a face-centered cubic crystalline Pt with evidence that Ni, Ru, and Sn atoms were incorporated into the Pt structure. Electrochemical characterization of the nanoparticles was accomplished by cyclic voltammetry (CV) and chronoamperometry (CA) in slightly acidic medium (0.05 mol L-1 H2SO4), in the absence and presence of ethanol. Addition of Sn to PtRuNi/C catalysts significantly shifted the ethanol and CO onset potentials toward lower values, thus increasing the catalytic activity, especially for the quaternary composition Pt64Sn15Ru13Ni8/C. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed determination of acetaldehyde and acetic acid as the main reaction products. The presence of Ru in alloys promoted formation of acetic acid as the main product of ethanol oxidation. The Pt64Sn15Ru13Ni8/C catalyst displayed the best performance for DEFC.

Superconductivity at 9.5 K in the Ti2GeC compound

We report on the investigation of the Ti2GeC properties by X-ray diffraction, magnetic and electrical resistivity measurements. Polycrystalline samples of Ti2GeC with nominal compositions were prepared by solid state reaction. X-ray powder patterns suggest that all peaks can be indexed with the hexagonal phase of Cr2AlC prototype. The temperature dependence of both electrical resistivity and magnetization indicate a bulk type-II superconductivity at 9.5 K. Magnetoresistive data suggest an upper critical field of B-c2 similar to 8.1 T and coherence length similar to 61 A degrees . Furthermore, the results highlight the highest critical temperature reported up to now for an H-phase.

Performance of a poly(2,5-benzimidazole)-based polymer electrolyte membrane fuel cell

The performance of an ABPBI-based High Temperature H-2/O-2 PEMFC system was studied under different experimental conditions. Increasing the temperature from 130 to 170 degrees C improved the cell performance, even though further increase was not beneficial for the system. Humidification of the H-2 stream ameliorated this behaviour, even though operating above 170 degrees C is not advisable in terms of cell performance. A significant electrolyte dehydration seems to negatively affect the fuel cell performance, especially in the case of the anode. In the presence of 2% vol. CO in the H-2 stream, the temperature exerted a positive effect on the cell performance, reducing the strong adsorption of this poison on the platinum sites. Moreover, humidification of the H-2 + CO stream increased the maximum power densities of the cell, further alleviating the CO poisoning effects. Actual CO-O-2 fuel cell results confirmed the significant beneficial effect of the relative humidity on the kinetics of the CO oxidation process. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Analog of the susceptibility spectrum for levitation forces between a superconductor and a permanent magnet

We report on the measurements of both vertical and lateral levitation forces between a permanent magnet NdFeB and a polycrystalline YBa4Cu6O7-delta superconductor. The analysis of the obtained results revealed an interesting correlation between the behavior of the forces in the field-cooled and zero-field-cooled regimes, resembling the structure of the so-called susceptibility spectrum chi ''(chi'). Such force-force diagrams can be useful for identifying flux distribution structure inside a superconducting material. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4743006]

Oxygen reduction reaction on a Pt/carbon fuel cell catalyst in the presence of trace quantities of ammonium ions: An RRDE study

The effect of trace quantities of ammonia on oxygen reduction reaction (ORR) on carbon-supported platinum catalysts in perchloric acid solutions is assessed using rotating ring disk electrode (RRDE) technique. The study demonstrates that ammonia has detrimental effects on ORR. The most significant effect takes place in the potential region above 0.7 V vs RHE. The effect is explained by the electrochemical oxidation of ammonia, which blocks Pt active sites and increases the formation of H2O2. This leads to losses in the disk currents and increments in the ring currents. The apparent losses in ORR currents may occur in two ways, namely, through the blocking of the active sites for ORR as well as by generating a small anodic current, which is believed to have a lower contribution. In addition, a detrimental effect of sodium cations in the potential range below 0.75 V vs RHE was demonstrated. This effect is most likely due to the co-adsorption of sodium cations and perchlorate anions on the Pt surface. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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.

Influence of Modifications to the Pechini Method on the Electroactivity and Stability of Pt-RuOx/C Catalysts

Since electrode electroactivity and stability depend directly on the nature, morphology, and structure of the material, we have investigated how modifications to the Pechini method during the synthesis of Pt-RuOx/C electrocatalysts affected catalyst activity. The structure and stability of the resulting materials were investigated after their submission to a large number of potential scans and to constant potential for a prolonged time period in sulfuric acid 0.5 mol L-1 and methanol 0.1 mol L-1 solution. DMFC tests were accomplished using membrane electrode assemblies (MEAs) prepared by hot-pressing a pretreated Nafion 117 membrane together with the prepared Pt-RuOx anodes and a Pt cathode (from E-TEK), in order to compare the catalytic activity of the materials prepared by different methods. The stability studies demonstrated that the catalyst whose resin/carbon support mixture was agitated in a balls mill before undergoing heat-treatment was more stable than the other prepared catalysts. The catalysts synthesized with the single resin consisting of Pt and Ru and subjected to ultrasound before heat-treatment furnished the highest power density in the single fuel cell. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.011208jes]

Development of Ternary and Quaternary Catalysts for the Electrooxidation of Glycerol

This work consisted in the preparation of platinum-based catalysts supported on carbon (Vulcan XC-72) and investigation of their physicochemical and electrochemical properties. Catalysts of the C/Pt-Ni-Sn-Me (Me = Ru or Ir) type were prepared by the Pechini method at temperature of 350 degrees C. Four different compositions were homemade: C/Pt60Sn10Ni30, C/Pt60Sn10Ni20Ru10, C/Pt60Sn10Ni10Ru20, and C/Pt60Sn10Ni10Ir20. These catalysts were electrochemically and physically characterized by cyclic voltammetry (CV), chronoamperometry (CA) in the presence of glycerol 1.0 mol dm(-3), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). XRD results showed the main peaks of face-centered cubic Pt. The particle sizes obtained from XRD and HRTEM experiments were close to values ranging from 3 to 8.5 nm. The CV results indicate behavior typical of Pt-based catalysts in acid medium. The CV and CA data reveal that quaternary catalysts present the highest current density for the electrooxidation of glycerol.

Mechanistic changes observed in heavy water for nitrate reduction reaction on palladium-modified Pt(hkl) electrodes

Reduction of nitrate on palladium-modified platinum single-crystal electrodes has been investigated both voltammetrically and spectroscopically in acidic media (pH = 1). Results obtained in H2O and D2O solvents are compared for the three crystallographic orientations. FTIR and differential electrochemical mass spectrometry (DEMS) results clearly indicate that the isotopic substitution of the solvent has a large effect in the mechanism of the reaction, changing the nature of the detected products. For Pt(111)/Pd and Pt(100)/Pd, N2O is detected as the main product of nitrate reduction when D2O is used as solvent, while no N2O is detected when the reaction is performed in H2O. For Pt(110)/Pd, N2O is detected in both solvents, although the use of D2O clearly favours the preferential formation of this product. The magnitude of voltammetric currents is also affected by the nature of the solvent. This has been analysed considering, in addition to the different product distribution, the existence of different transport numbers and optical constants of the solvent.