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Cyclic voltammetric analysis of 2-styrylchromones: Relationship with the antioxidant activity

Gomes, Ana; Fernandes, Eduarda; Garcia, M. Beatriz; Silva, Artur; Pinto, Diana; Santos, Clementina M.M.; Cavaleiro, José; Lima, José Costa
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
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56.66%
2-Styrylchromones (2-SC) are a chemical family of oxygen heterocyclic compounds, vinylogues of flavones (2-phenylchromones), whose occurrence in nature has been reported. Recently, several 2-SC derivatives were demonstrated to have antioxidant properties, namely, xanthine oxidase inhibition, hepatoprotection against pro-oxidant agents in cellular and non-cellular systems and scavenging activity against reactive oxygen and reactive nitrogen species (ROS and RNS). Considering these antioxidant properties, it may be hypothesised that the electrochemical redox behaviour of 2-SC contributes significantly to their activity. To test this hypothesis, the electrochemical behaviour of different 2-SC was studied, together with a number of flavonoids with well-known antioxidant activities, by cyclic voltammetry, and the results correlated to their ability to scavenge ROS and RNS. The results obtained showed that 2-SC with a catecholic B-ring have a low oxidation peak potential corresponding to the oxidation of the 30,40-OH (catechol) moiety. The compounds with a phenolic B-ring have a common peak, with oxidation potential values of about +0.4/+0.5 V versus Ag/AgCl, corresponding to the oxidation of the 40-OH. The oxidation of the hydroxyl substituents in the A-ring generated peaks of higher potentials (+0.7/+0.8 V vs Ag/AgCl). The results from the scavenging assays were in agreement with those obtained from the cyclic voltammetry...

Determination of 2,4,6-trichloroanisole by cyclic voltammetry

Freitas, Patrícia; Dias, L.G.; Peres, António M.; Castro, Luís M.; Veloso, Ana C.A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Conferência ou Objeto de Conferência
ENG
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66.51%
The electrochemical reduction of 2,4,6-trichloroanisole (TCA), a chlorinated arene with electron-donating substituents, was evaluated by cyclic voltammetry (CV). TCA is a major concern for the winery industry since it is related with “cork taint”, a wine defect. The results obtained showed that CV could be used to detect and quantify TCA in standard solutions. Linear relationships could be set between the current amplitude and TCA concentrations (R>0.990) with detection and quantification limits of 0.08 and 0.26 ppm. Although, these preliminary limits are higher than the human sensory threshold (5 ppt in wine), the simplicity of the methodology confers this study a possible role in the development of more efficient and less expensive process for TCA detection in the industry.

Electrochemical characterization of bioactive hydroxyxanthones by cyclic voltammetry

Santos, Clementina M.M.; Garcia, Beatriz; Silva, Artur; Santus, René; Morlière, Patrice; Fernandes, Eduarda
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.51%
The present study reports the electrochemical behavior of several phenolic and catecholic-substituted 2,3-diarylxanthones on a glassy carbon electrode, challenged by cyclic voltammetry at different pH values (4.0, 7.4, and 11.0). Higher pH values required lower anodic and cathodic peak voltages. The oxidation of catecholic groups occurred at lower peak potentials in a reversible and pH dependent manner. Anodic peak potentials appeared at higher pH values and were attributed to the electrochemically irreversible oxidation of the phenolic groups. The number and position of hydroxyl substituents were the determinants for the electrochemical behavior and found to correlate with the scavenging activity for reactive oxygen (ROS) and nitrogen species (RNS). A xanthone with two catechol units presented the lowest anodic potential voltage (Epa = 0.15 V) and proved to be the most effective ROS and RNS scavenger.

Cyclic voltammetry: a tool to quantify 2,4,6-trichloroanisole in aqueous samples from cork planks boiling industrial process

Peres, António M.; Freitas, Patrícia; Dias, Luís G.; Sousa, Mara E. B. C.; Castro, Luís M.; Veloso, Ana C. A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.51%
Chloroanisoles, namely 2,4,6-trichloroanisole, are pointed out as the primary responsible of the development of musty off-flavours in bottled wine, due to their migration from cork stoppers, which results in huge economical losses for wine industry. A prevention step is the detection of these compounds in cork planks before stoppers are produced. Mass spectrometry gas chromatography is the reference method used although it is far beyond economical possibilities of the majority of cork stoppers producers. In this work, a portable cyclic voltammetry approach was used to detect 2,4,6-trichloroanisole extracted from natural cork planks to the aqueous phase during the cork boiling industrial treatment process. Analyses were carried out under ambient conditions, in less than 15 min with a low use of solvent and without any sample pre-treatment. The proposed technique had detection (0.31±0.01 ng/L) and quantification (0.95±0.05 ng/L) limits lower than the human threshold detection level. For blank solutions, without 2,4,6-trichloroanisole addition, a concentration in the order of the quantification limit was estimated (1.0±0.2 ng/L), which confirms the satisfactory performance of the proposed methodology. For aqueous samples from the industrial cork planks boiling procedure...

Study of copper electrodeposition mechanism from a strike alkaline bath prepared with 1-hydroxyethane-1,1-diphosphonic acid through cyclic voltammetry technique

PECEQUILO, Cristiane Vargas; PANOSSIAN, Zehbour
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.51%
Copper strike baths are extensively used in metal plating industry as they present the ability to plate adherent copper layers on less-noble metal substrates such as steel and zinc die castings. However, in the last few years, due to environmental controls and safety policies for operators, the plating industry has been interested in replacing the toxic cyanide copper strike baths with environmentally friendly baths. A broad bibliographic review showed that the published papers, referring to the new nontoxic copper strike baths, are patents, having little or no emphasis focused on electrodeposition mechanisms. Therefore, it was decided to study the copper electrodeposition mechanism from a strike alkaline bath prepared with one of the most nontoxic chelating agents cited in many patents which is the 1-hydroxyethane-1,1-diphosphonic acid, known as HEDP. This acid forms very stable water soluble complexes with Cu(2+) ions, thus cupric sulfate was used for preparing the plating bath. The results obtained through a cyclic voltammetry technique showed that Cu(2+) ion reduction to Cu from an HEDP electrodeposition bath occurs via a direct reduction reaction without a formation of Cu(+) intermediates. (C) 2010 Elsevier Ltd. All rights reserved.; Atotech of Brazil; Institute for Technological Research of Sao Paulo State...

Uso da voltametria cíclica e da espectroscopia de impedância eletroquímica na determinação da área superficial ativa de eletrodos modificados à base de carbono; Use of cyclic voltammetry and electrochemical impedance spectroscopy for the determination of active surface area of modified carbon-based electrodes

Souza, Leticia Lopes de
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 28/07/2011 PT
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66.51%
Eletrodos à base de carbono, como os eletrodos de troca iônica, entre outros, têm aplicação principalmente no tratamento de efluentes industriais e rejeitos radioativos. Carbono é também amplamente utilizado em células a combustível como substrato para os eletrocatalisadores, por possuir elevada área superficial, que supera a sua área geométrica. O conhecimento desta superfície ativa total é importante na determinação das condições de operação de uma célula eletroquímica no que diz respeito às correntes a serem aplicadas (densidade de corrente). No presente estudo foram utilizadas duas técnicas eletroquímicas na determinação da área superficial ativa de eletrodos de carbono vítreo e poroso e eletrodos de troca iônica: espectroscopia de impedância eletroquímica (EIE) e voltametria cíclica (VC). Os experimentos foram realizados com soluções de KNO3 0,1 mol.L-1 em célula eletroquímica de três eletrodos: eletrodo de trabalho à base de carbono, eletrodo auxiliar de platina e eletrodo de referência de Ag/AgCl. Os eletrodos de carbono vítreo e de carbono poroso utilizado possuíam uma área geométrica de 3,14 x 10-2 cm2 e 2,83 10-1 cm2, respectivamente. O eletrodo de troca iônica foi preparado misturando-se grafite...

Determination of Glycerol in Biodiesel Using a Nickel(II) Oxyhydroxide Chemically Modified Electrode by Cyclic Voltammetry

Pott Marinho Ballottin, Daniela; Lataro Paim, Leonardo; Ramos Stradiotto, Nelson
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1751-1755
ENG
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66.51%
A glassy carbon electrode chemically modified with nickel oxyhydroxide from a nickel hexacyanoferrate (NiHCF) film was used to determine glycerol in biodiesel by cyclic voltammetry. The modified electrode exhibited a linear response to glycerol concentration in the range from 0.05 to 0.35mmol L-1, and a detection limit of 0.030mmol L-1. The glycerol concentration found in the biodiesel sample was 0.156mmol L-1. The method developed in this study showed a recovery of (100.3±5.0)%. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Monitoring biofilm formation by using cyclic voltammetry : effect of the experimental conditions on biofilm removal and activity

Gião, M. S.; Montenegro, M. I.; Vieira, M. J.
Fonte: IWA Publishing Publicador: IWA Publishing
Tipo: Artigo de Revista Científica
Publicado em //2003 ENG
Relevância na Pesquisa
66.56%
The effect of experimental conditions on cyclic voltammetry experiments on platinum electrodes covered with biofilms formed by Pseudomonas fluorescens for 2 hours was investigated. Results show that recycling the potential stabilizes the shape of the cyclic voltammogram after 135 cycles, but the observation of the electrodes by epifluorescence microscopy showed that cells are still adhered to the platinum surface. Some experimental conditions were changed during the electrochemical measurements – sweep rate, pH of the buffer and applied potential range. Some of these parameters had a strong impact on the bacteria that are adhered to the surface, increasing the death and removal in some circumstances.; Instituto de Biotecnologia e Química Fina (IBQF).; Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI) - POCTI/34945/EQU/2000.

The use of cyclic voltammetry to detect biofilms formed by Pseudomonas fluorescens on platinum electrodes

Vieira, M. J.; Espírito Santo, I. A. C. P.; Gião, M. S.; Montenegro, M. I.
Fonte: Taylor & Francis Publicador: Taylor & Francis
Tipo: Artigo de Revista Científica
Publicado em /08/2003 ENG
Relevância na Pesquisa
66.63%
The development of an electrochemical detector to monitor the in situ formation of biofilms is described. The detector consisted of an electrochemical cell containing three electrodes, whose response to the application of a potential profile to the working electrode was sensitive to the amount of biofilm present on the surface. The electrochemical technique used was repetitive cyclic voltammetry. Differences between the response of the uncolonised electrode and after Pseudomonas fluorescens biofilms of different ages were grown on its surface were determined. The results show that cyclic voltammetry applied to platinum electrodes can be used to detect young biofilms. The development of the shape of the voltammogram as the potential is cycled may constitute a means of providing information on the coverage of the surface. Observation of the platinum electrodes before and after the electrochemical measurements showed that even after 30 min of recycling, most of the cells were still adhered to the surface, although some may have lost viability.; Fundação para a Ciência e Tecnologia (FCT) - Programa Operacional "Ciência, Tecnologia, Inovação (POCTI) - POCTI/34945/EQU/2000.

Monitoring biofilm formation by using cyclic voltametry : effect of the experimental conditions on biofilm removal and activity

Marques, M. S.; Montenegro, M. I.; Vieira, M. J.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2002 ENG
Relevância na Pesquisa
56.45%
The effect of experimental conditions on cyclic voltammetry experiments on platinum electrodes covered with biofilms formed by Pseudomonas fluorescens for 2 hours was investigated. Results show that recycling the potencial stabilizes the shape of the cyclic voltammogram after 130 cycles, but the observation of this electrode by epifluorescence microscopy showed that cells are still adhered to the platinum surface. Some experimental conditions were changed during the electrochemical measurements – sweep rate, pH of the buffer and applied potential range. Some of these parameters had a strong impact on the bacteria that are adhered to the surface, increasing the death and removal in some circumstances.; Fundação para a Ciência e a Tecnologia (FCT)

Staining of wool using the reaction products of ABTS oxidation by Laccase : synergetic effects of ultrasound and cyclic voltammetry

Munteanu, Florentina-Daniela; Basto, Carlos; Gübitz, Georg M.; Paulo, Artur Cavaco
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /03/2007 ENG
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66.76%
The effects of ultrasound on 2,2′-Azinobis(3-ethylbenzothiazoline-6-sulfonate) enzymatic oxidation by laccase (Trametes villosa) has been studied by means of cyclic voltammetry. The reaction was allowed to proceed in the presence of a piece of wool and the coloration depth of the wool fabric was measured by means of K/S. It was observed that cyclic voltammetry is influenced the dyeing process and higher K/S values were obtained when the cyclic voltammetry was combined with the ultrasonic irradiation. Moreover, the K/S value is the sum of the values obtained when the wool staining is done in just the presence of cyclic voltammetry or in just the presence of ultrasound. The results obtained on the indigo carmine decolourization gives information on the importance of controlling the amount of ABTS+ formed during the ultrasonication process.

Cyclic Voltammetry of Organometallic Acetylide Complexes

Mendes, Paulo J. G.; Silva, Tiago J. L.
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Aula Formato: 30041 bytes; application/pdf
ENG
Relevância na Pesquisa
66.51%
We report herein the cyclic voltammetry behavior of the compounds [RuCp(L2)(CC{SC4H2}nA)] (L2=DPPE, 2 PPh3; A= NO2, CHO; n=1,2). The effect of the phosphines, length of the conjugated thiophene chain and acceptor (A) group will be addressed. Both the electrochemical and spectroscopic data will be correlated and the overall results will be discussed regarding to the SONLO properties of these compounds.

Cyclic Voltammetry of Ruthenium Complexes for Nonlinear Optics

Mendes, Paulo J. G.
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Aula Formato: 27039 bytes; application/pdf
ENG
Relevância na Pesquisa
66.51%
We report herein the cyclic voltammetry studies of the compounds [RuCp(P_P)(NC{SC4H2}nNO2)][PF6] (P_P=DPPE, (+)-DIOP; n=1-3) in dichloromethane and acetonitrile. The electronic richness of the organometallic moiety together with the evaluation of the corresponding HOMO-LUMO gaps and correlation with spectroscopic data will be addressed. The overall data will be used in order to give an insight on the SONLO properties of these compounds.

Evaluation of the Antioxidant Activity of New Coumarin Derivatives by Cyclic Voltammetry

Teixeira, Jorge; Martins, Sérgio; Palmeiro, Gonçalo; Pereira, António
Fonte: The 61st Annual Meeting of the International Society of Electrochemistry, Electrochemistry from Biology to Physics, Nice, France. Publicador: The 61st Annual Meeting of the International Society of Electrochemistry, Electrochemistry from Biology to Physics, Nice, France.
Tipo: Aula
ENG
Relevância na Pesquisa
66.63%
Free radicals, species with one or more unpaired electrons are produced in normal or pathological cell metabolism, from xenobiotics, or trough ionizing radiation. Electron acceptors such as molecular oxygen react easily with free radicals, to become radicals themselves. Oxygen free radicals or reactive oxygen species (ROS) such as superoxide anion radicals (O2 .-), hydrogen peroxide (H2O2), hydroxy radicals (.OH), and singlet oxygen (1O2) are continuously generated in cells exposed to an aerobic environment, and have been associated with the genesis of tumors as well as age-dependent diseases such atherosclerosis, arthritis, and neurodegenerative disorders. In this context, the chemopreventive role of antioxidants present in consumable fruits, vegetables, and beverages has received considerable attention and has been a growing interest in finding novel antioxidants in order to meet the requirements of pharmaceutical industries [1]. Several analytical methods have been used to evaluate the activity of antioxidant compounds, such as the cyclic voltammetry[2] and the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) assay[3]. In this work the antioxidant activity of two new synthetic coumarin derivatives, 3-bromo-6,7-dihydroxycoumarin and 6...

Complexes for NLO: Cyclic Voltammetry Study

Mendes, Paulo J. G.
Fonte: Portugaliae Electrochimica Acta Publicador: Portugaliae Electrochimica Acta
Tipo: Aula
ENG
Relevância na Pesquisa
66.51%
Organometallic compounds continue to attract considerable interest owing to their application in the field of nonlinear optics (NLO) [1]. For second-order nonlinear optics, strongly asymmetric systems are needed, which led to the development of typical push–pull systems in which the metal centre, bound to a highly polarizable conjugated backbone, acts as an electron donor (D) or acceptor (A) group. This is the case of the general family of η5-monocyclopentadienylmetal complexes presenting benzene- or thiophene-based conjugated ligands coordinated to the metal centre through nitrile or acetylide linkages which revealed to be much more efficient donor groups for second-order NLO purposes than the traditional organic donor groups [2,3]. Recently, a new promising approach has emerged that is the concept of switchable second-order nonlinear optical (SONLO) properties [4]. This makes possible to achieve a switch in the SONLO response between two forms since they have great difference in the magnitude of the corresponding first hyperpolarizabilities. The hyperpolarizability can be altered, for instance, by reducing the donor capacity of the donor moiety (D) by oxidation. Thus, the presence of redox-active metal centers together with a hyperpolarizable conjugated framework provides good opportunities for modulation of molecular NLO responses...

Cyclic Voltammetry Studies of η5-Monocyclopentadienyliron(II) Complexes

Mendes, Paulo J.
Fonte: VIII Iberic Meeting of Electrochemistry and XIII Meeting of The Portuguese Electrochemical Society Publicador: VIII Iberic Meeting of Electrochemistry and XIII Meeting of The Portuguese Electrochemical Society
Tipo: Aula
ENG
Relevância na Pesquisa
66.51%
Recently, organometallic complexes have emerged as potential building blocks for second-order nonlinear optical (SONLO) materials in view of their potential application in the area of integrated optics [1]. Organometallic complexes can possess low energy, sometimes intense, electronic charge transfer excitations that are responsible for the NLO response. Most of these electronic transitions are MLCT or LMCT excitations which energy can be related to the HOMO-LUMO gaps. Experimental work on 5-monocyclopentadienylmetal complexes with p-substituted benzonitrile chromophores showed the fundamental role played by the organometallic fragment, namely their electronic richness, in the second-order nonlinear optical response [2]. In addition, the first hyperpolarizability was found to decrease with increasing conjugation length of the chromophores, being the larger values associated to the lower HOMO-LUMO gaps [3,4]. For similar 5-monocyclopentadienyliron complexes possessing thiophene based conjugated backbone, an inverse trend on experimental first hyperpolarizability with increasing conjugation length was observed [5]. In order to obtain a deeper insight into the electronic richness of the organometallic moiety and to get an evaluation of the corresponding HOMO-LUMO gaps and the connection with NLO properties...

Experimental and Theoretical Studies of the Redox Potentials of Cyclic Nitroxides

Blinco, James P.; Hodgson, Jennifer; Morrow, Benjamin J.; Walker, James R.; Will, Geoffrey D.; Coote, Michelle; Bottle, Steven E
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.45%
(Chemical Equation Presented) The redox potentials of 25 cyclic nitroxides from four different structural classes (pyrrolidine, piperidine, isoindoline, and azaphenalene) were determined experimentally by cyclic voltammetry in acetonitrile, and also via h

Variable Scan Rate Cyclic Voltammetry and Theoretical Studies on Tocopherol (Vitamin E) Model Compounds

Yao, Wei Wei; Peng, Hong Mei; Webster, Richard D; Gill, Peter
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.51%
Variable scan rate (0.1-500 V s-1) cyclic voltammetry experiments were performed on a series of model tocopherol (vitamin E) compounds with differing degrees of methyl substitution around the aromatic (phenolic) ring. α-Tocopherol, with a fully methylate

The Influence of Metallic Oxides Formed by Repetitive Cyclic Voltammetry or Controlled Potential in the Reactivity of Ir/Hg System

Milaré,E.; Ionashiro,E. Y.; Maniette,Y.; Benedetti,A. V.; Fertonani,F. L.
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2003 EN
Relevância na Pesquisa
66.63%
Cyclic voltammetry and controlled potential electrolysis, and other analytical techniques were used to study the reactions of mercury with iridium oxides formed by repetitive cyclic voltammetry (RCV) or by controlled potential electrolysis (CPE) on pure iridium substrate. The oxides were formed in a Hg(I)-containing solution. The SEM images, XPS spectra and CV obtained after the RCV treatment showed a more attacked surface with less mercury on the Ir. On the contrary, the SEM images, XPS spectra and the CV for the electrode prepared by CPE indicated a less attacked surface with more Hg. The oxides formed when the CPE condition was applied inhibited the UPD of mercury.

Determination of Trace Metals by Differential Pulse Voltammetry at Chitosan Modified Electrodes

Martínez-Huitle,C.A.; Fernandes,N. Suely; Cerro-Lopez,M.; Quiroz,M.A.
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
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56.5%
Surface modification by chitosan (CT) on a glassy carbon electrode (GCE) was employed in the present study to determine metal traces (Cu, Pb, Cd, Co, As and Pt). Previous report about the chitosan film affinity toward positive or negative species demonstrated and allowed the application of these polymeric films for detecting heavy metals in aqueous solutions. The modified surface exhibited an affinity to chelating metal ions in solution, forming complexes. Differential pulse voltammetry combined with a pre-concentrating process and standard addition method were employed for trace analysis, obtaining the detection ranges (Cu (II) from 3.99´10-6 to 3.91´10-5 mol L-1, Pb(II) from 1.99´10-6 to 1.58´10-5 mol L-1, Cd(II) from 1.59´10-5 to 6.23´10-5 mol L-1, As(IV) from 7.99´10-6 to 5.04´10-5 mol L-1, Pt(IV) from 8.19´10-6 to 3.59´10-5 mol L-1, Co(II) from 6.11´10-4 to 2.78´10-3 mol L-1), calibrations plots and relevant equations for each metal. Finally, cyclic voltammetry technique was used to characterize the polymeric surface behavior in presence of different metals and during the differential pulse voltammetric analysis. The results are described and discussed in the light of the existing literature.