Página 1 dos resultados de 1273 itens digitais encontrados em 0.011 segundos

Gold is not a Faradaic-Efficient Borohydride Oxidation Electrocatalyst: An Online Electrochemical Mass Spectrometry Study

CHATENET, Marian; LIMA, Fabio H. B.; TICIANELLI, Edson A.
Fonte: ELECTROCHEMICAL SOC INC Publicador: ELECTROCHEMICAL SOC INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
26.967107%
Direct borohydride fuel cells are promising high energy density portable generators. However, their development remains limited by the complexity of the anodic reaction: The borohydride oxidation reaction (BOR) kinetics is slow and occurs at high overvoltages, while it may compete with the heterogeneous hydrolysis of BH(4)(-). Nevertheless, one usually admits that gold is rather inactive toward the heterogeneous hydrolysis of BH(4)(-) and presents some activity regarding the BOR, therefore yielding to the complete eight-electron BOR. In the present paper, by coupling online mass spectrometry to electrochemistry, we in situ monitored the H(2) yield during BOR experiments on sputtered gold electrodes. Our results show non-negligible H(2) generation on Au on the whole BOR potential range (0-0.8 V vs reversible hydrogen electrode), thus revealing that gold cannot be considered as a faradaic-efficient BOR electrocatalyst. We further propose a relevant reaction pathway for the BOR on gold that accounts for these findings.; CAPES/COFECUB[Ph598/08]

Magnetic coupled electrochemistry: Exploring the use of superparamagnetic nanoparticles for capturing, transporting and concentrating trace amounts of analytes

CONDOMITTI, Ulisses; ZUIN, Andre; NOVAK, Miguel A.; ARAKI, Koiti; TOMA, Henrique Eisi
Fonte: ELSEVIER SCIENCE INC Publicador: ELSEVIER SCIENCE INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
26.967107%
We propose the use of functionalized superparamagnetic nanoparticles for capturing, and transporting analytes, in association with an external miniature magnet to deposit such nanocarrier species at the electrode surface. This approach can be employed for the electroanalytical determination of chemical species capable of interacting with the nanoparticles, or in the opposite case, to block their response at the electrode surface. The concept was successfully demonstrated by using aminofunctionalized nanoparticles to block the discharge of hexacyanoferrate(II) ions, and to enhance the signals of aquapentacyanoferrate(II) ions via coordination to the surface amino groups. Selective analysis was also performed for silver ions, surpassing the stripping methods in terms of versatility and usefulness. (C) 2010 Elsevier B.V. All rights reserved.

Electronic Perspective on the Electrochemistry of Prussian Blue Films

Agrisuelas, J.; Bueno, P. R.; Ferreira, F. F.; Gabrielli, C.; Garcia-Jareno, J. J.; Gimenez-Romero, D.; Perrot, H.; Vicente, F.
Fonte: Electrochemical Soc Inc Publicador: Electrochemical Soc Inc
Tipo: Artigo de Revista Científica Formato: P74-P80
ENG
Relevância na Pesquisa
36.967107%
The derivative of the voltabsommetric scans, together with previous nano-electrogravimetric and X-ray diffraction results, allow different electrochemical processes to be distinguished during the Prussian blue (PB) voltammetric scan. Potassium, proton, and hydrated proton counterions involved in PB electrochemistry are related here to the electrochemical reactions of specific Fe sites. Potassium counterions show two different sites for their insertion: one located in the crystalline framework and another in ferrocyanide vacancies. From the monitoring of electroactive Fe sites, the covalent-exchange model is suggested as one of the first approaches to explain the origin of the PB magnetic ordering observed at room temperature during voltammetric scanning.

Direct electrochemistry of the Desulfovibrio gigas aldehyde oxidoreductase

Moura, Isabel; Santos, Margarida M. Correia dos; Sousa, Patrícia M. P.; Gonçalves, M. Lurdes S.; Romão, M. João; Moura, José J. G.
Fonte: Blackwell Publishing Publicador: Blackwell Publishing
Tipo: Artigo de Revista Científica
Publicado em //2004 ENG
Relevância na Pesquisa
36.967107%
Eur. J. Biochem. 271, 1329–1338 (2004); This work reports on the direct electrochemistry of the Desulfovibrio gigas aldehyde oxidoreductase (DgAOR), a molybdenum enzyme of the xanthine oxidase family that contains three redox-active cofactors: two [2Fe-2S] centers and a molybdopterin cytosine dinucleotide cofactor. The voltammetric behavior of the enzyme was analyzed at gold and carbon (pyrolytic graphite and glassy carbon) electrodes. Two different strategies were used: one with the molecules confined to the electrode surface and a second with DgAOR in solution. In all of the cases studied, electron transfer took place, although different redox reactions were responsible for the voltammetric signal. From a thorough analysis of the voltammetric responses and the structural properties of the molecular surface of DgAOR, the redox reaction at the carbon electrodes could be assigned to the reduction of the more exposed iron cluster, [2Fe-2S] II, whereas reduction of the molybdopterin cofactor occurs at the gold electrode. Voltammetric results in the presence of aldehydes are also reported and discussed.

Electrochemistry and green chemical processes: electrochemical ozone production

Silva,Leonardo M. da; Santana,Mário H. P.; Boodts,Julien F. C.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2003 EN
Relevância na Pesquisa
36.967107%
After an introductory discussion emphasising the importance of electrochemistry for the so-called Green Chemical Processes, the article presents a short discussion of the classical ozone generation technologies. Next a revision of the electrochemical ozone production technology focusing on such aspects as: fundamentals, latest advances, advantages and limitations of this technology is presented. Recent results about fundamentals of electrochemical ozone production obtained in our laboratory, using different electrode materials (e.g. boron doped diamond electrodes, lead dioxide and DSAÒ-based electrodes) also are presented. Different chemical processes of interest to the solution of environmental problems involving ozone are discussed.

Eletroquímica computacional - princípios e diretrizes para utilização

Lopes,Mauro Chierici
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 PT
Relevância na Pesquisa
27.118423%
In this paper, a detailed guide for the application of computational electrochemistry is presented. The basic framework of the electrochemical models and their computational solutions are described. We highlighted that the availability of commercial software allows application of the technique by experimentalists with minimal mathematical and computational expertise. The most used packages are indicated. Simulations of typical examples are presented and some references cited to illustrate the wide applicability of computational electrochemistry.

Electrochemistry of vitamin E hydro-alcoholic solutions

Giacomelli,Cristiano; Giacomelli,Fernando Carlos; Alves,Luciano Ortigara; Timbola,Ana Karina; Spinelli,Almir
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2004 EN
Relevância na Pesquisa
36.967107%
The electrochemistry of vitamin E hydro-alcoholic solutions of pH 3.1 to 12.1 was studied by cyclic voltammetry, controlled potential electrolysis, thin layer chromatography and UV-Vis, IR and 13C NMR spectroscopy. The presence of water was found to have important implications on the chemical stability of electrogenerated species. Vitamin E exhibits three oxidation peaks in hydro-alcoholic solutions at glassy carbon electrodes in contrast to just a single peak in other solvents. Although the electrochemical reaction at the first peak was found to be the same in presence and in absence of water, which is a one-step two-electron transfer process, two heterogeneous electrochemical reactions and three homogeneous chemical reactions following this peak were established based on electrochemical evidences for the first time in alcohol aqueous conditions. This insight is considered to be very important provided the mediator character of vitamin E in the electron transfer between aqueous and lipid phase in the organism.

The electrochemistry of simple inorganic molecules in room temperature ionic liquids

Silvester,Debbie S.; Rogers,Emma I.; Barrosse-Antle,Laura E.; Broder,Tessa L.; Compton,Richard G.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 EN
Relevância na Pesquisa
36.967107%
The electrochemistry of simple inorganic compounds in room temperature ionic liquids (RTILs) is reviewed and some new work in this area is presented. This paper focuses on the comparison between electrochemical behaviour in RTILs and in conventional aprotic solvents. Some compounds (iodides, O2, NO2, SO2, NH3) display similar reactions and mechanisms in RTILs as in aprotic solvents (as is observed for organic compounds). However other species (nitrates, PCl3, POCl3) show remarkably different behaviour to traditional solvents. This makes RTILs very promising media for the study of inorganic compounds, and highlights the need for more investigations in this exciting area.

Analysis of the electrochemistry of hemes with Ems spanning 800 mV

Zheng, Zhong; Gunner, M. R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/05/2009 EN
Relevância na Pesquisa
27.118423%
The free energy of heme reduction in different proteins is found to vary over more than 18 kcal/mol. It is a challenge to determine how proteins manage to achieve this enormous range of Ems with a single type of redox cofactor. Proteins containing 141 unique hemes of a-, b-, and c-type, with bis-His, His-Met, and aquo-His ligation were calculated using Multi-Conformation Continuum Electrostatics (MCCE). The experimental Ems range over 800 mV from −350 mV in cytochrome c3 to 450 mV in cytochrome c peroxidase (vs. SHE). The quantitative analysis of the factors that modulate heme electrochemistry includes the interactions of the heme with its ligands, the solvent, the protein backbone, and sidechains. MCCE calculated Ems are in good agreement with measured values. Using no free parameters the slope of the line comparing calculated and experimental Ems is 0.73 (R2 = 0.90), showing the method accounts for 73% of the observed Em range. Adding a +160 mV correction to the His-Met c-type hemes yields a slope of 0.97 (R2 = 0.93). With the correction 65% of the hemes have an absolute error smaller than 60 mV and 92% are within 120 mV. The overview of heme proteins with known structures and Ems shows both the lowest and highest potential hemes are c-type...

Grafting aryl diazonium cations to polycrystalline gold: Insights into film structure using gold oxide reduction redox probe electrochemistry and contact angle behavior

Paulik, M.; Brooksby, P.; Abell, A.; Downard, A.
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
27.220928%
The structure and properties of thin organic films electrografted to conducting surfaces by reduction of the corresponding diazonium salts are not well understood. In this work we used electrochemistry and contact angle measurements to characterize multilayer carboxyphenyl and methylphenyl films grafted to Au surfaces. Freshly grafted films contain material that can be readily removed during potential cycling and sonication. Observation of Au oxide surface electrochemistry confirms a porous bulk film structure as previously found for films electrografted to carbon surfaces. The charge associated with Au oxide reduction was used to estimate the upper limit for surface concentration of modifiers directly attached to the surface after careful preparation of the Au surface prior to and after grafting. Values for the surface concentration of the modifier in the range of 3-4 × 10⁻¹⁰ mol cm⁻² indicate that the first layer of the films is loosely packed. The close correspondence of surface concentration with that previously found for a "monolayer equivalent" of nitrophenyl film covalently grafted to smooth carbon surfaces ((2.5 ± 0.5) × 10⁻¹⁰ mol cm⁻²) supports a similar film formation mechanism, that is, formation of a Au-C bond. We also show that sonication of the Au surface considerably alters the Au oxide reduction charge of an initially well-defined bare Au surface. Hence...

Electrochemistry of catechol terminated monolayers with Cu(II), Ni(II) and, Fe(III) cations: A model for the marine adhesive interface

Brooksby, P.; Schiel, D.; Abell, A.
Fonte: Amer Chemical Soc Publicador: Amer Chemical Soc
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
Relevância na Pesquisa
36.967107%
The redox electrochemistry of hydroquinone and Cu2+-, Ni2+-, and Fe3+-hydroquinone complexes immobilized at the SAM interface has been studied in aqueous solutions with pH 5 to 12 using cyclic voltammetry. Self-assembled monolayers were constructed with terminal hydroquinone residues designed to model marine adhesive proteins that use the DOPA (3,4-dihydroxyphenylalanine) moiety. Coordination of metal to the hydroquinone group results in a shift to the ligand oxidation potential, with the value for Delta E p,a dependent on the solution pH and identity of the metal. Cu2+ shifts the hydroquinone oxidation by -285 mV (pH 8.8), and Ni2+ by -194 mV (pH 9.16). The hydroquinone oxidation was shifted by -440 mV at pH 5 for Fe3+ solutions examined up to pH 7. By contrast, reduction of the quinone is unperturbed by the presence of Cu2+, Ni2+, and Fe3+ ions. Implications of these results to the mechanism of marine adhesion are discussed.; Paula A. Brooksby, David R. Schiel and Andrew D. Abell; Copyright © 2008 American Chemical Society

Electrochemistry of ferrocenoyl β-peptide monolayers on gold; Electrochemistry of ferrocenoyl beta-peptide monolayers on gold

Brooksby, P.; Anderson, K.; Downard, A.; Abell, A.
Fonte: Amer Chemical Soc Publicador: Amer Chemical Soc
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
37.118423%
The electrochemistry of self-assembled monolayers (SAMs) on gold containing a lipoic acid linker, the beta-peptide sequence (beta(3)Val-beta(3)Ala-beta(3)Leu)(n) for n = 1, 2, and a terminal ferrocenyl group has been described for the first time. Circular dichroism (CD), NMR, and molecular modeling were used to evaluate the beta-peptide structure in solution, while the monolayer film organization and electron-transfer kinetics were evaluated by cyclic voltammetry, chronoamperometry (CA), and ellipsometry. The peptides were assembled from trifluoroethanol solutions, where they are linear (n = 1) or helical (n = 2) based on CD, NMR, ellipsometry, and modeling evidence. The structure of the SAMs is less well understood. There is evidence for noncompact layers that allow electrolyte ions to approach the interface. Electron-transfer rates for n = 1, 2 were found to be 2500 and 1200 s(-1), respectively, and CA evidence indicated that the transfer is based on the hopping mechanism.; Paula A. Brooksby, Kelly H. Anderson, Alison J. Downard and Andrew D. Abell

Preparation, characterization and electrochemistry of carbon nanotubes directly attached to Si(100) surfaces

Yu, J.; Shapter, J.; Quinton, J.; Johnston, M.; Beattie, D.
Fonte: IEEE; Online Publicador: IEEE; Online
Tipo: Conference paper
Publicado em //2006 EN
Relevância na Pesquisa
36.967107%
We present a new approach for directly organizing single-walled carbon nanotubes (SWCNTs) onto silicon surface. The ordered assembly of SWCNTs was made by the surface condensation reaction with hydroxyl terminated silicon. X-ray photoelectron spectra, Raman spectroscopy and atomic force microscopy show that the shortened SWCNTs have been organized successfully on silicon. The electrochemistry of SWCNT array exhibits good electrochemical reversibility and enhanced conductivity.; Jingxian Yu, Joe Shapter, Jamie Quinton, Martin Johnston, and David Beattie

Concepções de egressos da licenciatura em Química sobre eletroquímica

Bragança, Michell Henrique de
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
27.39474%
Este trabalhou apresenta resultados de investigação sobre as concepções de egressos do curso de Licenciatura em Química da Universidade Federal de Uberlândia, com relação ao ensino e aprendizagem de eletroquímica. Para a coleta de dados realizamos entrevistas que foram conduzidas coletivamente, com aproximações à metodologia de grupo focal, o qual foi constituído por cinco professores. As entrevistas foram gravadas em áudio e vídeo e, posteriormente, transcritas para realizar a análise das falas dos participantes que foi feita pelo cruzamento com as informações obtidas da literatura. A partir dessa análise pudemos identificar algumas concepções dos professores sobre ciência e sobre o ensino de eletroquímica. Pela análise dos relatos dos participantes da pesquisa e pelas informações obtidas da literatura, constatamos que os mesmos tiveram um aprendizado com várias lacunas durante a educação básica. Verificamos, também, que a formação em nível superior, foi pouco destacada pelos participantes quanto ao seu aprendizado sobre o conteúdo de eletroquímica. Entretanto, as experiências profissionais com a eletroquímica em sala de aula, ou os conhecimentos adquiridos em outras disciplinas durante a graduação...

A história, evolução e crescimento da Eletroquímica: Eletroanalítica nestes últimos 25 anos

Avaca,Luis Alberto; Tokoro,Roberto
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2002 PT
Relevância na Pesquisa
27.118423%
This text describes the development of Electrochemistry and Electroanalytical Chemistry in Brazil from the pioneers at the IQ/USP in the 70's to the present day status. It explains how the members of the scientific community organized themselves before the establishment in 1993 of a specific division within the Brazilian Chemical Society (SBQ) through bi-ennial meetings (Brazilian Symposium of Electrochemistry and Electroanalytical Chemistry - SIBEE). Those SIBEE meetings, in a present number of 12, are described individually giving some emphasis on their organizers, the invited speakers and the statistics and overall structure of the event. The activities of the Electrochemistry and Electroanalytical Chemistry Division of the SBQ from 1993 are also briefly discussed as well as some considerations are made on the present and future of these fields.

Protein Cleavage, Disulfide Bonds Reduction, Metabolite Synthesis and Much More Using Electrochemistry/MS

Purkerson, J.; Kraj, A.; Eysberg, M.; Chervet, J.P.; Powers, J.
Fonte: Association of Biomolecular Resource Facilities Publicador: Association of Biomolecular Resource Facilities
Tipo: Artigo de Revista Científica
Publicado em /10/2011 EN
Relevância na Pesquisa
27.220928%
Recently, the scope of Electrochemistry (EC) upfront MS has been extended from mimicking drug metabolism towards new applications such as: protein/peptide cleavage, disulfide bonds reduction, covalent drug-protein binding, etc. In this presentation we will show the application of on-line EC/MS as a powerful tool to simulate various oxidation and reduction processes in life sciences. A specially designed μ-preparative electrochemical flow cell will be presented. The cell allows the synthesis of sufficient amounts of metabolites in a few minutes for subsequent use as reference material (e.g. NMR or MS). New scanning method was applied for oxidation of the highly concentrated samples (mM range) to achieve high yield in the metabolites formation. Stable oxidation conditions were obtained without the need of any cell maintenance for a prolonged period of time. Electrochemistry up front MS can be applied for protein and peptide cleavage (as a promising new approach to enzymatic digestion). Electrochemical cleavage of proteins and peptides occurs very specifically at C-terminal of the Tyrosine and Tryptophan peptide bonds. Examples of oxidative cleavage will be presented. Disulfide bonds are one of the most important post-translational modifications for proteins. In this poster we present the structural analysis of biologically active peptides and proteins containing disulfide bonds (e.g....

Phase field modeling of electrochemistry II: Kinetics

Guyer, J. E.; Boettinger, W. J.; Warren, J. A.; McFadden, G. B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.118423%
The kinetic behavior of a phase field model of electrochemistry is explored for advancing (electrodeposition) and receding (electrodissolution) conditions in one dimension. We described the equilibrium behavior of this model in [J. E. Guyer, W. J. Boettinger, J.A. Warren, and G. B. McFadden, ``Phase field modeling of electrochemistry I: Equilibrium'', cond-mat/0308173]. We examine the relationship between the parameters of the phase field method and the more typical parameters of electrochemistry. We demonstrate ohmic conduction in the electrode and ionic conduction in the electrolyte. We find that, despite making simple, linear dynamic postulates, we obtain the nonlinear relationship between current and overpotential predicted by the classical ``Butler-Volmer'' equation and observed in electrochemical experiments. The charge distribution in the interfacial double layer changes with the passage of current and, at sufficiently high currents, we find that the diffusion limited deposition of a more noble cation leads to alloy deposition with less noble species.; Comment: v3: To be published in Phys. Rev. E v2: Attempt to work around turnpage bug. Replaced color Fig. 4a with grayscale 13 pages, 7 figures in 10 files, REVTeX 4, SIunits.sty...

PCK of teaching electrochemistry in chemistry teachers: A case in Johannesburg, Gauteng Province, South Africa

Rollnick,Marissa; Mavhunga,Elizabeth
Fonte: Universidad Nacional Autónoma de México, Facultad de Química Publicador: Universidad Nacional Autónoma de México, Facultad de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2014 EN
Relevância na Pesquisa
36.967107%
Electrochemistry is an important topic in chemistry due to its wide application in everyday life. Although it is found in most high school curricula throughout the world, it is commonly regarded as an abstract and difficult topic to teach. This paper explores the teacher knowledge possessed by a diverse group of South African grade 12 teachers for teaching this topic. Two types of teacher knowledge were explored - knowledge of the content to be taught and topic specific pedagogical content knowledge. Topic specific content knowledge is the ability to reason about teaching the topic through 5 components regarded as important for the transformation of content knowledge, viz. Learner Prior Knowledge, Curricular Saliency, What is difficult to teach, Representations and Conceptual Teaching Strategies. 64 teachers responded to two instruments, measuring the two teacher knowledge bases. Results reflected the socio-diversity of the teachers with overall moderately high scores obtained on content knowledge which were not necessarily matched by good TSPCK. Reasons for this are explored.

Electrostatic Effects in Biosorption: The Role of the Electrochemistry

Lodeiro,Pablo; Barriada,José L.; Herrero,Roberto; Vicente,Manuel E. Sastre de
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2007 EN
Relevância na Pesquisa
36.967107%
Biosorption is the passive sequestration of pollutants by non-metabolizing non-living biomass. The technique emerged in 1980’s as a possible alternative method for wastewater treatments in an environmentally friendly manner. In this paper it is shown that a basic research in biosorption processes is closely related to the field of Electrochemistry according to the conceptual division of this area in Ionics and Electrodics.

Design Bases for Modulated Complexation by Electrochemistry

Sánchez,J.O.; Tejeda,P.R.
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2007 EN
Relevância na Pesquisa
36.967107%
The treatment of liquid organic phases to remove undesirable compounds is currently a priority in different industries. In oil refinery, it is necessary to reduce sulphur compounds, in gasolines, to below 50 ppm.The traditional form is catalytic hydrodesulphuration; however, this system is not effective for some compounds, e.g., alkyl substituted dibenzothiophenes. The processes for modulated complexation by electrochemistry are based on the capacity of a complexing agent, in a certain oxidation state, to form a bond with the molecule to be removed from a liquid phase. If the contaminant, the solute, is in an organic phase, the complexant must be soluble in aqueous phase. When the complexant is formed and in contact with both phases the contaminant is extracted. In a second stage, the complexing agent is oxidized (or reduced) to a state of less affinity to the contaminant, and the aqueous phase is placed in contact with a new organic phase where the contaminant will be discharged and concentrated. The complexant agent in aqueous phase is reduced (or oxidized) to its state of higher affinity for the contaminant and recirculated to the extraction stage. In this work, we present the conditions necessary for this process to be feasible...