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A new DTL-electrode holder for recording of electroretinograms in animals

SCHATZ, A.; WILLMANN, G.; ENDERLE, H.; SLIESORAITYTE, I.; MESSIAS, A.; BARTZ-SCHMIDT, K. U.; ZRENNER, E.; GEKELER, F.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Purpose: Contact lens electrodes (CLEs) are frequently used to register electroretinograms (ERGs) in small animals such as mice or rats. CLEs are expensive to buy or difficult to be produced individually. In addition, CLE`s have been noticed to elicit inconstant results and they carry potential to injure the cornea. Therefore, a new electrode holder was constructed based on the clinically used DTL-electrode and compared to CLEs. Material and methods: ERGs were recorded with both electrode types in nine healthy Brown-Norway rats under scotopic conditions. For low intensity responses a Naka-Rushton function was fitted and the parameters V(max), k and n were analyzed. The a-wave, b-wave and oscillatory potentials were analyzed for brighter flash intensities (1-60 scot cd s/m(2)). Repeatability was assessed for both electrode types in consecutive measurements. Results: The new electrode holder was faster in setting up than the CLE and showed lower standard deviations. No corneal alterations were observed. Slightly higher amplitudes were recorded in most of the measurements with the new electrode holder (except amplitudes induced by 60 cd s/m(2)). A Bland-Altman test showed good agreement between the DTL holder and the CLE (mean difference 35.2 mu V (Holder-CLE)). Pearson`s correlation coefficient for test-retest-reliability was r = 0.783. Conclusions: The DTL holder was superior in handling and caused far less corneal problems than the CLE and produced comparable or better electrophysiological results. The minimal production costs and the possibility of adapting the DTL holder to bigger eyes...

Evaluation of a carbon paste electrode modified with organofunctionalised SBA-15 nanostructured silica in the simultaneous determination of divalent lead, copper and mercury ions

CESARINO, Ivana; MARINO, Glimaldo; MATOS, Jivaldo do Rosario; CAVALHEIRO, Eder Tadeu Gomes
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
376.67332%
The performance of a carbon paste electrode (CPE) modified with SBA-15 nanostructured silica organofunctionalised with 2-benzothiazolethiol in the simultaneous determination of Pb(II), Cu(II) and Hg(II) ions in natural water and sugar cane spirit (cachaca) is described. Pb(II), Cu(II) and Hg(II) were pre-concentrated on the surface of the modified electrode by complexing with 2-benzothiazolethiol and reduced at a negative potential (-0.80 V). Then the reduced products were oxidised by DPASV procedure. The fact that three stripping peaks appeared on the voltammograms at the potentials of -0.48 V (Pb2+), -0.03 V (Cu2+) and +0.36 V (Hg2+) in relation to the SCE, demonstrates the possibility of simultaneous determination of Pb2+, Cu2+ and Hg2+. The best results were obtained under the following optimised conditions: 100 mV pulse amplitude, 3 min accumulation time, 25 mV s(-1) scan rate in phosphate solution pH 3.0. Using such parameters, calibration graphs were linear in the concentration ranges of 3.00-70.0 x 10(-7) mol L-1 (Pb2+), 8.00-100.0 X 10(-7) mol L-1 (Cu2+) and 2.00-10.0 x 10(-6) mol L-1 (Hg2+). Detection limits of 4.0 x 10(-8) mol L-1 (Pb2+), 2.0 x 10(-7) mol L-1 (Cu2+) and 4.0 x 10(-7) mol L-1 (Hg2+) were obtained at the signal noise ratio (SNR) of 3. The results indicate that this electrode is sensitive and effective for simultaneous determination of Pb2+...

The processes involved in the Se electrodeposition and dissolution on Au electrode: the H2Se formation

SOLALIENDRES, M. O.; MANZOLI, A.; SALAZAR-BANDA, G. R.; EGUILUZ, K. I. B.; TANIMOTO, S. T.; MACHADO, S. A. S.
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
379.74273%
The processes involved in the Se electrodeposition, mainly the one related to the formation of H2Se species on Au electrode in perchloric acid solutions, have been investigated through cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), rotating ring-disc electrode (RRDE), and atomic force microscopy (AFM) techniques. In the experiments performed with the EQCM, with the potential sweep in the negative direction, the responses for the mass variation were divided in three well-defined potential regions: A (from 1.55 to 0.35 V), B (from 0.35 to -0.37 V), and C (from -0.37 to -0.49 V). It was verified that the following processes can occur, respectively: the species (AuO)(2)H2SeO3 was desorbed during the AuO reduction, the reduction of Se(IV) to Se(0), and the formation of H2Se. When the potential was swept in the positive direction, the responses for the mass variation were divided in four well-defined potential regions: D (from -0.49 to 0.66 V), E (from 0.66 to 0.99 V), F (from 0.99 to 1.26 V), and G (from 1.26 to 1.55 V), and the described processes in these regions were, respectively: the Se deposition and adsorption of water molecules and/or perchlorate ions, the Se dissolution, the Se incorporating mass in the form of HO-Se...

Simultaneous voltammetric determination of paracetamol and caffeine in pharmaceutical formulations using a boron-doped diamond electrode

LOURENCAO, Bruna Claudia; MEDEIROS, Roberta Antigo; ROCHA-FILHO, Rorneu C.; MAZO, Luiz Henrique; FATIBELLO-FILHO, Orlando
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
378.4212%
A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential Pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials Of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 x 10(-7) mol L(-1) to 8.3 x 10(-7) mol L(-1) for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 x 10(-7) mol L-1 and 3.5 x 10(-8) mol L(-1), respectively. The proposed method Was Successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level). (C) 2008 Elsevier BY. All rights reserved.; FAPESP[2007/05894-9]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CNPq; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Ear and electrode effects reduce within-group variability in middle latency response amplitude measures

Weihing, Jeffrey; Schochat, Eliane; Musiek, Frank
Fonte: INFORMA HEALTHCARE; LONDON Publicador: INFORMA HEALTHCARE; LONDON
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
385.76242%
Objectives: To establish normative amplitude values for relative difference measurements of the middle latency response (MLR) in normal-hearing pediatrics and to determine if these measurements provided a significant reduction of within-group variability when compared to raw, absolute amplitude measures. A relative amplitude difference is defined in the present paper as the difference in Na-Pa amplitude between two electrodes (e.g. vertical bar Na-Pa at C3 minus Na-Pa at C4 vertical bar, or electrode effects) or between two ears (e.g. vertical bar Na-Pa on left ear stimulation minus Na-Pa on right ear stimulation vertical bar, or ear effects). In contrast, an absolute amplitude is defined as a single Na-Pa measurement made at one electrode for stimulation of one ear (e.g. Na-Pa measured at C3 on left ear stimulation). Design: Cross-sectional study. Study sample: 155 pediatrics with normal peripheral and central hearing, and no history of psychological, neurological, or learning disability issues. Results: Within-group variability was significantly smaller for relative differences when compared to absolute amplitude measures. Electrode effects showed significantly less variability than ear effects. Normative values for ear and electrode effects were reported. Conclusions: Relative differences may provide better utility in the clinical diagnosis of central auditory pathology in pediatrics when compared to absolute amplitude measures because these difference measures show significantly lower variability when examined across subjects.; FAPESP - Fundacao de Amparo a Pesquisa do Estado de Sao Paulo; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)

Maturação do sistema auditivo em crianças ouvintes normais: potenciais evocados auditivos de longa latência; Hearing system maturation in normally hearing children: long latency auditory evoked potentials

Ventura, Luzia Maria Pozzobom
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/10/2008 PT
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Os potenciais evocados auditivos de longa latência fornecem dados objetivos sobre a funcionalidade das estruturas corticais auditivas. O objetivo do presente estudo foi caracterizar a maturação do sistema auditivo central em crianças com audição normal por meio destes potenciais. Foram avaliados 56 indivíduos de ambos os sexos, com audição dentro dos padrões de normalidade, comprovada por audiometria e imitanciometria, sendo 46 crianças, de três a 12 anos, e 10 adultos jovens, os quais foram incluídos a título de comparação com a casuística infantil. O equipamento utilizado disponibilizava dois canais de registro, sendo um destinado à captação dos potenciais evocados auditivos de longa latência e outro, ao registro do artefato gerado pelo movimento ocular, visando ao seu controle. Os potenciais foram registrados com os indivíduos em estado de alerta, assistindo a um vídeo mudo, por meio de eletrodos posicionados em Cz (ativo) e A2 (referência) e os movimentos oculares, por eletrodos em posição supra e infra-orbital esquerda; o eletrodo terra foi colocado em A1. Foram analisados os valores de latência e de amplitude dos componentes P1, N1 e P2, bem como a morfologia destes componentes de acordo com a idade. Para verificar a reprodutibilidade dos potenciais registrados...

Estudo dos potenciais evocados auditivos em indivíduos com queixa de zumbido; Study of auditory evoked potentials in individuals with tinnitus complaint

Santos Filha, Valdete Alves Valentins dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/09/2009 PT
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INTRODUÇÃO: na tentativa de elucidar alguns aspectos relacionados ao zumbido, levantou-se a hipótese de alteração nas vias auditivas centrais. Diante disso, os potenciais evocados auditivos podem representar uma alternativa para detectar possíveis alterações auditivas centrais que possam estar presentes nesta população e que indiquem o provável sítio gerador desse sintoma. OBJETIVO: caracterizar os potenciais evocados auditivos de curta, média e longa latências em indivíduos com e sem queixa de zumbido e expostos a ruído ocupacional. MÉTODO: foram avaliados 60 sujeitos expostos a ruído de origem ocupacional com níveis de pressão sonora elevados (maior que 85 dBA), tanto do gênero masculino quanto feminino, na faixa etária entre 29 e 50 anos de idade, sendo 30 com queixa de zumbido (grupo pesquisa) e 30 sem queixa de zumbido (grupo controle). Foram realizados os potenciais evocados auditivos de curta, média e longa latências. RESULTADOS: na análise dos potenciais de curta latência, foi observado um aumento predominante das latências das ondas I e III, bem como, alteração de tronco encefálico baixo em 16 indivíduos do grupo pesquisa. Quanto aos potenciais de média latência, observou-se médias maiores para a latência da onda Na nas modalidades C4/A1 e C3/A2 no grupo pesquisa...

Viabilidade do uso do eletrodo de mercúrio como indicador, no estudo da formação de complexos, no sistema Hg(II)/S2O32+, em meio aquoso (OU) Viabilidade do uso do eletrodo de mercurio, no estudo da formação de complexos, no sistema Hg(II)/tiossulfato; Viability of use of a mercury electrode in the study of complex formation in the Hg(II)Thiosulphate system

Tavares, Marina Franco Maggi
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/12/1986 PT
Relevância na Pesquisa
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O presente trabalho procura dar continuidade a uma das linhas de pesquisa desenvolvida pelo Grupo de Química Analítica do Instituto de Química da Universidade de são Paulo: o estudo da formação de complexos. O sistema Hg(II) / S2O2-3 foi analisado potenciometricamente, com a finalidade de identificar o número de complexos formados, assim como estimar as constantes de estabilidade envolvidas no fenônemo de complexação. Tal equilíbrio foi levado a termo a 25,0 ± 0,1°C, e força iônica 2,00M, sendo detectados quatro espécies complexas. O modelo matemático que melhor se ajustou aos dados experimentais fornecidos pelo sistema, conta com os seguintes valores para as constantes globais de formação: β1 1 = x 1024 M-1 (valor atribuído) β2 = (8,0 ± 2,8) x 1027 M-2 β3 = (1,71 ± 0,03) x 1030 M-3 β4 = (3,07 ± 0,77) x 1030 M-4. Na região de baixa concentração analítica de ligante, 5mM, o acesso experimental foi limitado pela precipitação de sulfeto mercúrico sendo impossível obter informaçôes sobre a primeira espécie. O comportamento do mercúrio no sistema Hg(II) / S2O2-3 foi estudado de uma forma mais abrangente, sendo estendido ao meio não complexante, onde o equilíbrio de dismutação do cátion mercuroso governa. Nas mesmas condições de temperatura e força iônica anteriores...

Estudo fundamental da eletro-oxidação de etanol sobre eletrodo de níquel em meio alcalino; Fundamental study of the electro-oxidation of ethanol on nickel electrode in alkaline medium

Barbosa, Amaury Franklin Benvindo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/08/2014 PT
Relevância na Pesquisa
379.76977%
O mecanismo e cinética da oxidação de etanol sobre níquel em soluções de hidróxido de sódio em condições experimentais bem definidas, que incluíram a variação da concentração do etanol, potencial final da varredura anódica, temperatura da solução (tanto na temperatura de 25 °C quanto da ordem de -15 °C), e variação da velocidade de varredura, são discutidos em termos da formação de óxidos de níquel de valência superior. Na primeira parte deste estudo foi utilizado voltametria cíclica e foram encontradas evidências para um processo de intermediação envolvendo a molécula do etanol e as espécies β-NiOOH formadas sobre a superfície do eletrodo em E ≥ 1,3 V vs. ERH. Em baixas concentrações de etanol (≤ 0,2 mol L-1) a etapa determinante da velocidade da reação é governada por um processo de difusão. Em concentrações mais altas (> 0,2 mol L-1) esta reação passou a ser governada por um processo de transferência de carga entre a molécula do etanol e as espécies Ni3+. O aumento da concentração deslocou o potencial do pico da oxidação do etanol para potenciais mais positivos. A diminuição da temperatura afetou a cinética desta reação, diminuindo a j e provocando um deslocamento do potencial de início da oxidação do etanol para potenciais mais positivos. Foi possível observar a partir das características dos perfis voltamétricos...

Electrocatalytic activity under oscillatory regime: The electro-oxidation of formic acid on ordered Pt3Sn intermetallic phase

Perini, Nickson; Sitta, Elton; Angelo, Antonio C.D.; Varela, Hamilton
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 23-26
ENG
Relevância na Pesquisa
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Despite the considerable progress in the understanding of the mechanistic aspects of the oscillatory electro-oxidation of C1 molecules, there are apparently no systematic studies concerning the impact of surface modifiers on the oscillation dynamics. Herein we communicate on the oscillatory electro-oxidation of formic acid on ordered Pt3Sn intermetallic phase, and compare the results with those obtained on a polycrystalline platinum electrode. Overall, the obtained results were very reproducible, robust and allowed a detailed analysis on the correlation between the catalytic activity and the oscillation dynamics. The presence of Sn in the intermetallic electrode promotes drastic effects on the oscillatory dynamics. The decrease in the mean electrode potential and in the oscillation frequency, as well as the pronounced increase in the number oscillations (and also in the oscillation time), was discussed in connection with the substantial catalytic enhancement of the Pt3Sn towards the electro-oxidation of formic acid. The self-organized potential oscillations were used to probe the electrocatalytic activity of the Pt3Sn electrode and compare it with that for polycrystalline Pt. The presence of Sn resulted in a significant decrease (2-11 times...

Electrochemical behavior of rhodium acetamidate immobilized on a carbon paste electrode: a hydrazine sensor

Gil,Eric de S.; Kubota,Lauro T.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2000 EN
Relevância na Pesquisa
374.25324%
The electrochemical behavior of rhodium acetamidate immobilized in carbon paste electrode and the consequences for sensor construction were evaluated. The electrode showed good stability and redox properties. Two reversible redox couples with midpoint potentials between 0.15 and 0.55 V vs SCE were observed. However, peak resolution in voltammetric studies was very dependent on the supporting electrolyte. The correlation between coordinating power of the electrolyte and peak potential suggests that the electrolyte can coordinate through the axial position of the complexes. Furthermore, the axial position may be also the catalytic site, as a catalytical response was observed for hydrazine oxidation. A good linear response range for hydrazine was fit by the equation i = 23.13 (± 0.34) c , where i = current in mA and c = concentration in mol dm-3 in the range of 10-5 up to 10-2 mol dm-3. The low applied potential (<300 mV) indicates a good device for hydrazine sensor, minimizing interference problems. The short response time (~1 s) may be useful in flow injection analysis. Furthermore, this system was very stable presenting good repeatability even after 30 measurements with a variance of 0.5 %.

Rhodium-Prussian Blue modified carbon paste electrode (Rh-PBMCPE) for amperometric detection of hydrogen peroxide

Ivama,Viviane Midori; Serrano,Silvia H. P.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2003 EN
Relevância na Pesquisa
376.67332%
Prussian Blue was deposited at carbon paste electrode surface from a solution containing 2.0 x 10-3 mol L-1 K3[Fe(CN)6], 3.0 x 10-3 mol L-1 FeCl3 and 1.0 x 10-2 mol L-1 HCl using two controlled potentials. To improve the stability of the modified electrode it was 50 times cycled in a solution containing 1.0 x 10-3 mol L-1 RhCl3, 0.50 mol L-1 KCl and 0.010 mol L-1 HCl in the potential range from - 0.40 V to 0.60 V at 60 mV s-1. The Rh - Prussian Blue carbon paste modified electrode (Rh-PBMCPE) showed good stability during amperometric catalytic determination of H2O2 at 0.040 V, without ascorbic and uric acids interferences. The current changed linearly with H2O2 concentrations in the range of 5.0 x 10-5 - 8.6 x 10-4 mol L-1. The estimated detection limit was 2.8 x 10-5 mol L-1 with sensibility changing from 1.32 to 0.96 A mol-1 L cm-2 along five days (180 determinations).

Micro-agar salt bridge in patch-clamp electrode holder stabilizes electrode potentials

Shao, Xuesi M.; Feldman, Jack L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
391.95156%
Maintaining a stable electrode potential is critical for patch-clamp measurements. The electrode potential of conventional patch electrode-holder assembly, where an Ag/AgCl wire is in direct contact with the patch pipette filling solution, is subject to drift if the pipette solution contains a low concentration of chloride ions (Cl−). We developed an agar bridge of 3 M KCl filled in a polyimide microtubing which forms an electrical connection between an Ag/AgCl wire and the pipette solution. We examined the offset potentials of the micro-agar salt bridge electrode assembly in parallel with a conventional electrode assembly in generic recording conditions (the pipette solution contained 5 mM NaCl). The junction potential between the Ag/AgCl wire and the pipette filling solution in the conventional electrode contributed to most of the offset potential drift observed during the course of 30 min recordings. The drift was up to 27.3 mV after several changes of the glass pipette. In contrast, the micro-agar salt bridge stabilized the electrode potential within typically 2 mV without affecting the patch electrode resistance, capacitance or noise level. Numerical simulations showed that Cl− diffusion from the agar bridge to the tip caused a negligible 0.4 μM Cl− concentration change at the pipette tip within 30 min. This method is easy to implement and provides long-term recording stability. The micro-agar salt bridge can fit in most commercial patch electrode holders and can be conveniently maintained.

Selectivity of Local Field Potentials in Macaque Inferior Temporal Cortex

Kreiman, Gabriel; Hung, Chou; Poggio, Tomaso; DiCarlo, James
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 1 p.; 154663209 bytes; 29794050 bytes; application/postscript; application/pdf
EN_US
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378.72535%
While single neurons in inferior temporal (IT) cortex show differential responses to distinct complex stimuli, little is known about the responses of populations of neurons in IT. We recorded single electrode data, including multi-unit activity (MUA) and local field potentials (LFP), from 618 sites in the inferior temporal cortex of macaque monkeys while the animals passively viewed 78 different pictures of complex stimuli. The LFPs were obtained by low-pass filtering the extracellular electrophysiological signal with a corner frequency of 300 Hz. As reported previously, we observed that spike counts from MUA showed selectivity for some of the pictures. Strikingly, the LFP data, which is thought to constitute an average over large numbers of neurons, also showed significantly selective responses. The LFP responses were less selective than the MUA responses both in terms of the proportion of selective sites as well as in the selectivity of each site. We observed that there was only little overlap between the selectivity of MUA and LFP recordings from the same electrode. To assess the spatial organization of selective responses, we compared the selectivity of nearby sites recorded along the same penetration and sites recorded from different penetrations. We observed that MUA selectivity was correlated on spatial scales up to 800 m while the LFP selectivity was correlated over a larger spatial extent...

One-Electron Oxidation and Reduction Potentials of Nitroxide Antioxidants: A Theoretical Study

Hodgson, Jennifer; Namazian, Mansoor; Bottle, Steven E; Coote, Michelle
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
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470.57215%
High-level ab initio calculations have been used to determine the oxidation and reduction potentials of a large number of nitroxides including derivatives of piperidine, pyrrolidine, isoindoline, and azaphenalene, substituted with COOH, NH2, NH3+, OCH3, O

Calculation of two-electron reduction potentials for some quinone derivatives in aqueous solution using Møller-Plesset perturbation theory

Namazian, Mansoor; Siahrostami, Samira; Noorbala, Mohammad; Coote, Michelle
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
467.64234%
Møller-Plesset perturbation theory at the level of third order (MP3) is used to compute two-electron reduction potentials for some substituted benzoquinones in aqueous solution. The calculations are carried out at the MP2 and MP3 levels with the use of c

Joint Density-Functional Theory of the Electrode-Electrolyte Interface: Application to Fixed Electrode Potentials, Interfacial Capacitances, and Potentials of Zero Charge

Letchworth-Weaver, Kendra; Arias, T. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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384.53074%
This work explores the use of joint density-functional theory, a new form of density-functional theory for the ab initio description of electronic systems in thermodynamic equilibrium with a liquid environment, to describe electrochemical systems. After reviewing the physics of the underlying fundamental electrochemical concepts, we identify the mapping between commonly measured electrochemical observables and microscopically computable quantities within an, in principle, exact theoretical framework. We then introduce a simple, computationally efficient approximate functional which we find to be quite successful in capturing a priori basic electrochemical phenomena, including the capacitive Stern and diffusive Gouy-Chapman regions in the electrochemical double layer, quantitative values for interfacial capacitance, and electrochemical potentials of zero charge for a series of metals. We explore surface charging with applied potential and are able to place our ab initio results directly on the scale associated with the Standard Hydrogen Electrode (SHE). Finally, we provide explicit details for implementation within standard density-functional theory software packages at negligible computational cost over standard calculations carried out within vacuum environments.; Comment: 18 pages...

Calculation of two-electron reduction potentials for some quinone derivatives in aqueous solution using Møller-Plesset perturbation theory

Namazian, Mansoor; Siahrostami, Samira; Noorbala, Mohammad; Coote, Michelle
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
467.64234%
Møller-Plesset perturbation theory at the level of third order (MP3) is used to compute two-electron reduction potentials for some substituted benzoquinones in aqueous solution. The calculations are carried out at the MP2 and MP3 levels with the use of c

Tuning the Initial Electronucleation Mechanism of Palladium on Glassy Carbon Electrode

Alemu,Tibebu; Assresahegn,Birhanu D; Soreta,Tesfaye R
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
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383.34234%
Electrochemical metal nucleation is the method for the formation of metal nanoparticles on the electrode surface. Studying the early stage of electronucleation is simpler than other methods as the driving force for nucleation is achieved by changing deposition potentials and concentration of metal ions. In this work, the potential step electrochemical deposition of palladium was studied from its chloride solution at room temperature on glassy carbon electrode surface. The nucleation mechanism was studied by analysis of the resulting current transients. Accordingly, the initial electro-nucleation mechanism of palladium nanoparticles was found to be varying depending on deposition conditions such as deposition potential and palladium concentration. It can be changed from 3D instantaneous (for all deposition potentials studied and in higher electrolytic concentration) to 3D progressive nucleation mechanism (for lower deposition potential and lower electrolytic concentration). In addition, the nucleation rate for each deposition potential as well as the concentration has been determined. The nucleation rate in this research is used to calculate the nuclei density and found to decrease from more negative deposition potential to more positive deposition potential in agreement with the observed shift in electronucleation mechanism.

Electrochemical Behaviour of Copper Nitroprusside Generated in situ Onto the Graphite Paste Electrode Surface, and its Application in the Determination of N-Acethylcysteine

Carmo,D. Ribeiro do; Silva,R. Moutinho da; Stradiotto,N. Ramos
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2005 PT
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Copper nitroprusside (CuNP) was generated on the graphite paste electrode using a new methodology of the preparation. The electrochemical studies were carried out by cyclic voltammetry technique. The cyclic voltammogram of the modified electrode, CuNP showed two redox couples (E0’)1=0.22 and (E0’)2=0.88 V vs. SCE attributed to Cu(I)/Cu(II) and Fe(II)(CN)5NO/Fe(III)(CN)5NO, respectively. The nature of the cation affect the (E0’)1 and (E0’)2, as current intensity, shifting the E0’ for more positive potentials, for two redox processes. The voltammograms obtained with different KCl concentrations (0.1-3.0 mol L-1) exhibit a shift in the (E0’)1 to more positive potentials; this change was linear with the supporting electrolyte concentrations change. It was verified that the (E0’)1 remained practically constant at pH between 6 and 3. However, a new process with (E0’)3 (0.48 V) appears at pH<3 and it was ascribed to formation of intermediary species. The redox couple at (E0’)2=0.88 V presents an electrocatalytic response for N-acethylcysteine. The modified graphite paste electrode gives a linear response between 5.0´10-4 to 1.0´10-2 mol L-1 of N-acethylcysteine with a detection limit of 4.5´10-4 (±5%) mol L-1 (n=3) and an amperometric sensitivity of 4.9 mA/mmol L-1. The electrocatalytic oxidation of N-acethylcysteine compounds by the mediator has been used for the determination of N-acethylcysteine in a commercially pharmaceutical available product.