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Santiago de Queretaro, Mexico

Larios-Duran E.R.,University of Guadalajara | Antano-Lopez R.,CIDETEQ
Journal of Electroanalytical Chemistry | Year: 2011

A quantitative kinetic description of the adsorption of bromide on mercury is developed by combination of complementary approaches to the adsorption impedance data. Equivalent-circuit modeling is matched with mechanistic models. The resulting descriptions permit the estimation of absolute adsorption and desorption rate constants for Br- on Hg electrode by assuming either a Langmuir or a Frumkin adsorption isotherm. It is found that adsorption-desorption dynamics for the Hg/Br- system is well described by the transfer function based on the Frumkin isotherm, indicating a predominant role of adsorbate-adsorbate interactions. © 2011 Elsevier B.V. All rights reserved.

Martinez-Gonzalez E.,CIDETEQ | Frontana C.,CIDETEQ
Physical Chemistry Chemical Physics | Year: 2014

In this work, experimental evidence of the influence of the electron transfer kinetics during electron transfer controlled hydrogen bonding between anion radicals of metronidazole and ornidazole, derivatives of 5-nitro-imidazole, and 1,3-diethylurea as the hydrogen bond donor, is presented. Analysis of the variations of voltammetric EpIcvs. logK B[DH], where KB is the binding constant, allowed us to determine the values of the binding constant and also the electron transfer rate kO/Rs, confirmed by experiments obtained at different scan rates. Electronic structure calculations at the BHandHLYP/6-311++G(2d,2p) level for metronidazole, including the solvent effect by the Cramer/Truhlar model, suggested that the minimum energy conformer is stabilized by intramolecular hydrogen bonding. In this structure, the inner reorganization energy, λi,j, contributes significantly (0.5 eV) to the total reorganization energy of electron transfer, thus leading to a diminishment of the experimental kO/Rs. © 2014 the Partner Organisations.

Cardenas A.,CIDETEQ | Gomez M.,Metropolitan Autonomous University | Frontana C.,CIDETEQ
Electrochimica Acta | Year: 2014

Cupric Reducing Antioxidant Capacity method, CUPRAC, is a reliable assay for determining Total Antioxidant Capacity (TAC) in samples of foods, beverages and pharmaceutical formulations. In this work, an electrochemical approach was used to quantify antioxidant content employing a variation of the CUPRAC assay, as the concentrations of the participating species ([Cu(Nc)2] 2+ and [Cu(Nc)2]+) can be evaluated by electrochemical measurements. Then, monitoring the voltammetric peak and chronoamperometric diffusional current, it was possible to quantify the content of antioxidants, with high analytical performance. Statistical analysis allowed establishing parameters like linearity, detection and quantification limits, recovery, precision and trueness. These validation parameters demonstrate that electrochemical CUPRAC methods are comparable with the classical spectrophotometric method. Electrochemical CUPRAC was employed to determine antioxidant content in tea samples and the results showed that the content of flavonoids determined the required time for complete antioxidant consumption. © 2013 Elsevier Ltd.

Bustos E.,CIDETEQ | Godinez L.A.,CIDETEQ
International Journal of Electrochemical Science | Year: 2011

In this work, the basic theory and the applications of modified surfaces with nano-structured composites of Prussian Blue (PB) and Dendrimers, for the electrochemical detectors and electro-catalyze technologies, currently, represent some of the most promising approaches for the development of efficient and new materials for advanced electrochemical applications. As the PB interacts in supramolecular manner with PAMAM dendrimers in aqueous medium, across the hydrophobic zone of dendrimer, they form composites stables in solution with different generations of PAMAM. Dendrimers make the function of endoreceptors of PB forming composites of PB - PAMAM dendrimers, which can be used to construct PB films over gold surfaces, in covalent or electrostatic modification process, which can work as electro-catalysers to detect molecules with biologycal importance. © 2011 by ESG.

Gago A.S.,University of Poitiers | Morales-Acosta D.,CIDETEQ | Arriaga L.G.,CIDETEQ | Alonso-Vante N.,University of Poitiers
Journal of Power Sources | Year: 2011

This work reports the electrochemical measurements of 20 wt.% Ru xSey/C for oxygen reduction reaction (ORR) in presence of different concentration of HCOOH and its use as cathode catalyst in a microfluidic formic acid fuel cell (μFAFC). The results were compared to those obtained with commercial Pt/C. Half-cell electrochemical measurements showed that the chalcogenide catalyst has a high tolerance and selectivity towards ORR in electrolytes containing up to 0.1 M HCOOH. The depolarization effect was higher on Pt/C than on RuxSey/C by a factor of ca. 23. Both catalysts were evaluated as cathode of a μFAFC operating with different concentrations of HCOOH. When 0.5 M HCOOH was used, maximum current densities of 11.44 mA cm-2 and 4.44 mA cm-2 were obtained when the cathode was RuxSey/C and Pt/C, respectively. At 0.5 M HCOOH, the peak power density of the μFAFC was similar for both catalysts, ca. 1.9 mW cm-2. At 5 M HCOOH the power density of the μFAFC using RuxSey, was 9.3 times higher than the obtained with Pt/C. © 2010 Elsevier B.V.

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