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Interactions of mast cell degranulating peptides with model membranes: A comparative biophysical study

CABRERA, Marcia Perez dos Santos; ARCISIO-MIRANDA, Manoel; COSTA, Laiana Cristina da; SOUZA, Bibiana Monson de; COSTA, Sabrina Thais Broggio; PALMA, Mario Sergio; RUGGIERO NETO, Joao; PROCOPIO, Joaquim
Fonte: ELSEVIER SCIENCE INC Publicador: ELSEVIER SCIENCE INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
47.806377%
In the last decade, there has been renewed interest in biologically active peptides in fields like allergy, autoimmume diseases and antibiotic therapy. Mast cell degranulating peptides mimic G-protein receptors, showing different activity levels even among homologous peptides. Another important feature is their ability to interact directly with membrane phospholipids, in a fast and concentration-dependent way. The mechanism of action of peptide HR1 on model membranes was investigated comparatively to other mast cell degranulating peptides (Mastoparan, Eumenitin and Anoplin) to evidence the features that modulate their selectivity. Using vesicle leakage, single-channel recordings and zeta-potential measurements, we demonstrated that HR1 preferentially binds to anionic bilayers, accumulates, folds, and at very low concentrations, is able to insert and create membrane spanning ion-selective pores. We discuss the ion selectivity character of the pores based on the neutralization or screening of the peptides charges by the bilayer head group charges or dipoles. (C) 2009 Elsevier Inc. All rights reserved.; WinEDR package[154550/2006-0]; WinEDR package; Council for Scientific and Technological Development (CNPq)[142566/2005-5]; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CAPES[301064/2004-0]; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); CAPES[310559/2006-5]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[06/57122-7]; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); FAPESP[07/09657-0]

Materiais micro e nanoestruturados para sensores de íons do tipo EGFET; Micro and nanostructured materials for EGFET ion sensor.

Silva, Glaucio Ribeiro
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 06/07/2009 PT
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Este trabalho descreve os resultados do estudo de materiais como óxido de manganês, nanotubos de carbono e feltro de carbono (puro e recoberto com nanotubos ou polianilina-Pani), assim como do desenvolvimento de dispositivos. Os dispositivos estudados estão relacionados a sensores de pH, utilizando esses materiais como membranas seletivas de H+ . Essas membranas funcionam como parte de dispositivos denominados EGFETs, cujo princípio de funcionamento é semelhante ao ISFET. Inicialmente utilizamos o óxido de manganês produzido através do método hidrotérmico com posterior fabricação de filmes finos desse material através da técnica de spray-pyrolysis. Esses filmes foram depositados variando a temperatura de deposição, a concentração da solução e o tipo de superfície do substrato de vidro, com o objetivo de investigar a resposta elétrica do EGFET em função da concentração de íons de H+ . As melhores sensibilidades foram de 50,1 mV/pH e 75 mV/pH no filmes produzidos no substrato de vidro rugoso e vidro liso, respectivamente, com 2g/l de concentração e temperatura de 80o C em ambos os filmes. Num segundo momento, trabalhamos com a produção de nanotubos de carbono e posterior fabricação de filmes finos também pela técnica de spray-pyrolysis...

Interactions of mast cell degranulating peptides with model membranes: A comparative biophysical study

dos Santos Cabrera, Marcia Perez; Arcisio-Miranda, Manoel; da Costa, Laiana Cristina; de Souza, Bibiana Monson; Broggio Costa, Sabrina Thais; Palma, Mario Sergio; Ruggiero Neto, Joao; Procopio, Joaquim
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 01-11
ENG
Relevância na Pesquisa
47.806377%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 06/57122-7; Processo FAPESP: 07/09657-0; In the last decade, there has been renewed interest in biologically active peptides in fields like allergy, autoimmume diseases and antibiotic therapy. Mast cell degranulating peptides mimic G-protein receptors, showing different activity levels even among homologous peptides. Another important feature is their ability to interact directly with membrane phospholipids, in a fast and concentration-dependent way. The mechanism of action of peptide HR1 on model membranes was investigated comparatively to other mast cell degranulating peptides (Mastoparan, Eumenitin and Anoplin) to evidence the features that modulate their selectivity. Using vesicle leakage, single-channel recordings and zeta-potential measurements, we demonstrated that HR1 preferentially binds to anionic bilayers, accumulates, folds, and at very low concentrations, is able to insert and create membrane spanning ion-selective pores. We discuss the ion selectivity character of the pores based on the neutralization or screening of the peptides charges by the bilayer head group charges or dipoles. (C) 2009 Elsevier B.V. All rights reserved.

Synthesis of faujasite membranes

Machado, Andreia Filipa Gouveia
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
ENG
Relevância na Pesquisa
38.672756%
Os processos de separação usando membranas são cada vez mais frequentes para aplicações industriais devido à superioridade técnica e económica deste tipo de metodologia. Os zeólitos são candidatos promissores para membranas de elevado desempenho porque combinam as vantagens das membranas inorgânicas, tais como estabilidade a elevadas temperaturas, resistência a meios agressivos e fácil modificação catalítica, com as características únicas de peneiro molecular, permuta iónica, adsorpção selectiva e catálise típica dos zeólitos. Entre os vários zeólitos, a faujasite é particularmente atractiva porque apresenta a estrutura mais aberta de todos os zeólitos conhecidos. Os seus poros largos (~7.4A) podem ser usados para aplicações envolvendo moléculas maiores comparativamente com as que podem ser acomodadas em outros zeólitos. O objectivo desta tese consiste na síntese de membranas de faujasite para separação de olefinas/parafinas. Para esta aplicação, o revestimento do suporte e a eliminação de defeitos que criam percursos intrazeolíticos são fundamentais. Desta forma, a optimização das condições de síntese e o conhecimento do efeito de cada variável na microstrutura e qualidade do material são essenciais. As membranas de faujasite foram sintetizadas hidrotermicamente em suportes tubulares de a(alpha)-Al2O3 pelo método de crescimento secundário a partir de géis e soluções. Os suportes foram revestidos por imersão numa suspensão aquosa de cristais de zeólitos e subsequente tratamento a 150ºC. Em seguida...

Inhibition of complex I by hydrophobic analogues of N-methyl-4-phenylpyridinium (MPP+) and the use of an ion-selective electrode to measure their accumulation by mitochondria and electron-transport particles.

Murphy, M P; Krueger, M J; Sablin, S O; Ramsay, R R; Singer, T P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/03/1995 EN
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47.90857%
N-methyl-4-phenylpyridinium (MPP+), the neurotoxic metabolite of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, kills dopaminergic neurons after its accumulation in mitochondria where it inhibits Complex I of the respiratory chain. MPP+ inhibits respiration by binding to both a hydrophobic and a hydrophilic site on Complex I and this inhibition is increased by the lipophilic tetraphenylboron anion (TPB-) which facilitates movement of MPP+ through membranes and its penetration to the hydrophobic binding site on Complex I. To investigate the inhibition of respiration by MPP(+)-like compounds, we have measured simultaneously NADH-linked mitochondrial respiration and the uptake and accumulation of the N-benzyl-4-styrylpyridinium and N-ethyl-4-styrylpyridinium cations in mitochondria using ion-selective electrodes. The data provide direct evidence that TPB- increases the inhibition not by increasing matrix concentration but by facilitating access to the inhibitory sites on Complex I. We have also compared the rates of uptake of MPP+ analogues of varied lipophilicity by the inner membrane and the development of inhibition of NADH oxidation, using an inverted mitochondrial inner membrane preparation and appropriate ion-selective electrodes. These experiments demonstrated that the amount of MPP+ analogue bound to the inner membrane greatly exceeded the quantity required for complete inhibition of NADH oxidation. Moreover...

POTENTIOMETRIC RESPONSE AND MECHANISM OF ANIONIC RECOGNITION OF HETEROCALIXARENE-BASED ION SELECTIVE ELECTRODES

Shishkanova, T.V.; Sýkora, D.; Sessler, J.L.; Král, V.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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The ion selective electrode (ISE)-based potentiometric approach is shown to be an effective means of characterizing the anion recognition sites in the molecular receptor calix[2]pyridino[2]pyrrole (CPP). In particular, potentiometric pH-measurements involving the use of experimental PVC-membranes based on CPP revealed the existence of both mono- and diprotonated forms of the receptor under readily accessible conditions. Based on these analyses, apparent surface protonation constants for this heterocalixarene were found to lie between 8.5–8.9 (pKB1) and 3.3–3.8 (pKB2). CPP was found to interact with targeted anionic analytes based on both coulombic and hydrogen bond interactions, as inferred from varying the kinds of ionic sites present within the membrane phase. Potentiometric selectivity studies revealed that CPP preferred “Y-shaped” anions (e.g. acetate, lactate, benzoate) over spherical anions (e.g. fluoride and chloride), fluoride over chloride within the set of spherical anions, and the ortho- isomer over the corresponding meta- and para- isomers in the case of hydroxybenzoate (salicylate and congeners). In the context of this study the advantages of potentiometric determinations of acetylsalicylic acid using optimized PVC-membranes based on CPP relative to more conventional PVC-membrane ISEs based on traditional anion exchanger were also demonstrated.

Calcium movement and membrane potential changes in the early phase of neutrophil activation by phorbol myristate acetate: a study with ion- selective electrodes

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/04/1982 EN
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To quantitate calcium movements and membrane potential changes in stimulated neutrophils, we have measured net fluxes of Ca2+ and of the lipophilic cation tetraphenyl phosphonium by a very sensitive ion- selective electrode system. Activation of neutrophils by 3 X 10(-8) M phorbol 12-myristate, 13-acetate induces a release of approximately 20% of total cell calcium, with an initial lag period of less than 10 s. The Ca2+ outflux is markedly reduced in ATP-depleted cells and in the presence of a calmodulin inhibitor, thereby suggesting that it occurs by activation of the ATP-driven Ca2+ pump of the neutrophil plasmalemma. Activation of neutrophils also induces a transiently increased exchange of medium 45Ca with cell calcium, which is measurable a few seconds after cell exposure to the stimulant and peaks at approximately 40 s. Stimulation of neutrophils after attainment of steady-state accumulation of tetraphenyl phosphonium (resting potential of -67 mV) results in a marked depolarization, with a lag period of approximately 60 s. The rate and extent of depolarization are reduced by 40 and 65%, respectively, in a low Na+ medium but are not modified by an inhibitor of anion exchange across membranes. A high-K+ medium depolarizes neutrophils without either modifying their resting oxidative metabolism or impairing stimulability by the phorbol ester. Phorbol 12-myristate...

Preparation, Characterization, and Analytical Application of Ramipril Membrane-Based Ion-Selective Electrode

Arida, Hassan; Ahmed, Mona; Ali, Abdallah
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
47.776016%
The fabrication and electrochemical evaluation of two PVC membrane-based Ion-Selective electrodes responsive for ramipril drug have been proposed. The sensitive membranes were prepared using ramipril-phosphomolibdate and ramipril-tetraphenylborate ion-pair complexes as electroactive sensing materials in plasticized PVC support. The electrodes based on these materials provide near-Nernestian response (sensitivity of 53 ± 0.5–54 ± 0.5 mV/concentration decade) covering the concentration range of 1.0 × 10−2–1.0 × 10−5 mol L−1 with a detection limit of 3.0 × 10−6–4.0 × 10−6 mol L−1. The suggested electrodes have been successfully used in the determination of ramipril drug in some pharmaceutical formulations using direct potentiometry with average recovery of >96% and mean standard deviation of <3% (n = 5).

Kinetic Modulation of Pulsed Chrono-potentiometric Polymeric Membrane Ion Sensors by Polyelectrolyte Multilayers

Xu, Yida; Xu, Chao; Shvarev, Alexey; Becker, Thomas; De Marco, Roland; Bakker, Eric
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
38.56629%
Polymeric membrane ion selective electrodes are normally interrogated by zero current potentiometry, and their selectivity is understood to be primarily dependent on an extraction/ion-exchange equilibrium between the aqueous sample and polymeric membrane. If concentration gradients in the contacting diffusion layers are insubstantial, the membrane response is thought to be rather independent of kinetic processes such as surface blocking effects. In this work, the surface of calcium-selective polymeric ion-selective electrodes is coated with polyelectrolyte multilayers as evidenced by zeta potential measurements, atomic force microscopy and electrochemical impedance spectroscopy. Indeed, such multilayers have no effect on their potentiometric response if the membranes are formulated in a traditional manner, containing a lipophilic ion-exchanger and a calcium-selective ionophore. However, drastic changes in the potential response are observed if the membranes are operated in a recently introduced kinetic mode using pulsed chronopotentiometry. The results suggest that the assembled nanostructured multilayers drastically alter the kinetics of ion transport to the sensing membrane, making use of the effect that polyelectrolyte multilayers have different permeabilities toward ions with different valences. The results have implications to the design of chemically selective ion sensors since surface localized kinetic limitations can now be used as an additional dimension to tune the operational ion selectivity.

Fluorous Polymeric Membranes for Ionophore-Based Ion-Selective Potentiometry: How Inert is Teflon AF?

Lai, Chun-Ze; Koseoglu, Secil S.; Lugert, Elizabeth C.; Boswell, Paul G.; Rábai, József; Lodge, Timothy P.; Bühlmann, Philippe
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 04/02/2009 EN
Relevância na Pesquisa
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Fluorous media are the least polar and polarizable condensed phases known. Their use as membrane materials considerably increases the selectivity and robustness of ion-selective electrodes (ISEs). In this research, a fluorous amorphous perfluoropolymer was used for the first time as a matrix for an ISE membrane. Electrodes for pH measurements with membranes composed of poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole]-co-poly(tetrafluoroethylene) (87% dioxole monomer content; known as Teflon AF2400) as polymer matrix, a linear perfluorooligoether as plasticizer, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate providing for ionic sites, and bis[(perfluorooctyl)propyl]-2,2,2-trifluoroethylamine as H+-ionophore were investigated. All electrodes had excellent potentiometric selectivities, showed Nernstian responses to H+ over a wide pH range, exhibited enhanced mechanical stability and maintained their selectivity over at least four weeks. For membranes of low ionophore concentration, the polymer affected the sensor selectivity noticeably at polymer concentrations exceeding 15%. Also, the membrane resistance increased quite strongly at high polymer concentrations, which cannot be explained by the Mackie–Meares obstruction model. The selectivities and resistances depend on the polymer concentration because of a functional group associated with Teflon AF2400...

Ion-Selective Electrodes with Unusual Response Functions: Simultaneous Formation of Ionophore–Primary Ion Complexes with Different Stoichiometries

Miyake, Masafumi; Chen, Li D.; Pozzi, Gianluca; Bühlmann, Philippe
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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It is well known that the selectivity of an ion-selective electrode (ISE) depends on the stoichiometry of the complexes between its ionophore and the target and interfering ions. It is all the more surprising that the possibility for the simultaneous occurrence of multiple target ion complexes with different complex stoichiometries was mostly ignored in the past. Here we report on the simultaneous formation of 1:1 and 1:2 complexes of a fluorophilic crown ether in fluorous ISE membranes, and how this results in what look like super-Nernstian responses. These increased response slopes are not caused by mass transfer limitations and can be readily explained with a phase boundary model, a finding that is supported by experimentally determined complex formation constants and excellent fits of response curves. Not only Cs+ but also the smaller ions Li+, Na+, K+, and NH4+ form 1:1 and 1:2 complexes with the fluorophilic crown ether, with cumulative formation constants of up to 1015.0 and 1021.0 for of the 1:1 and 1:2 complexes, respectively. Super-Nernstian responses of the type observed with these electrodes are probably not particularly rare, but lacking in the past an adequate discussion in the literature remained ignored or misinterpreted. Preliminary calculations also predict sub-Nernstian responses and potential dips of a similar origin. The proper understanding of such phenomena will facilitate the development of new ISEs based on ionophores that form complexes of higher stoichiometries.

An Ion-selective Electrode for Anion Perchlorate in Thick-film Technology

Segui, María Jesús; Lizondo-Sabater, Josefa; Martínez-Máñez, Ramon; Sancenon, Félix; Soto, Juan; Garcia-Breijo, Eduardo; Gil, Luis
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 07/04/2006 EN
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The ionophore 1,4,7,10,13-penta(n-octyl)-1,4,7,10,13-pentaazacyclopentadecane (L1) was used for the development of miniaturised perchlorate-selective electrodes in thick-film technology. Different PVC membranes containing L1 and the plasticizers o-nitrophenyl octyl ether (NPOE), dibutyl phthalate (DBP), bis(2-ethylhexyl)sebacate (DOS) and dibutyl sebacate (DBS) were prepared and placed on a graphite working electrode manufactured by using thick film serigraphic technology. The perchlorate selective electrode containing DBS as plasticizer showed a potentiometric Nernstian response of -57 mV per decade in a range of perchlorate concentration from 1 × 10-4 to 1 × 10-1 M with a detection limit of 5 × 10-5 M. The ion selective electrodes containing DBP and NPOE as plasticizers exhibit a working range from 6.3 × 10-5 to 1 × 10-1 M and 7.4 × 10-5 to 1 × 10-1 M for perchlorate, respectively, with a detection limit of ca. 2.2 × 10-5 M. For all three electrodes a response time of ca. 5 s was found. The prepared electrodes do not show appreciable decay of the slope for at least 25 days. Potentiometric selectivity coefficients (log KpotClO4-,X-) with respect to the primary anion perchlorate were evaluated using the fixed interference method. These coefficients are of the order of 10-1.7 or smaller...

Ion transport through electrolyte/polyelectrolyte multi-layers

Femmer, Robert; Mani, Ali; Wessling, Matthias
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 26/06/2015 EN
Relevância na Pesquisa
48.20038%
Ion transport of multi-ionic solutions through layered electrolyte and polyelectrolyte structures are relevant in a large variety of technical systems such as micro and nanofluidic devices, sensors, batteries and large desalination process systems. We report a new direct numerical simulation model coined EnPEn: it allows to solve a set of first principle equations to predict for multiple ions their concentration and electrical potential profiles in electro-chemically complex architectures of n layered electrolytes E and n polyelectrolytes PE. EnPEn can robustly capture ion transport in sub-millimeter architectures with submicron polyelectrolyte layers. We proof the strength of EnPEn for three yet unsolved architectures: (a) selective Na over Ca transport in surface modified ion selective membranes, (b) ion transport and water splitting in bipolar membranes and (c) transport of weak electrolytes.

A novel Ho(III) sensor based on N,N'-bis(2- pyridinecarboxamide)-1,2-benzene as a neutral ion carrier

Ganjali,Mohammad Reza; Rasoolipour,Solmaz; Rezapour,Morteza; Norouzi,Parviz; Amirnasr,Mehdi; Meghdadi,Soraia
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2006 EN
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N,N'-bis(2- pyridinecarboxamide)-1,2-benzene (H2BPB) was found to have a selective and sensitive behavior towards Ho(III) ion, in comparison to a large number of lanthanide, inner transition and representative metal ions and was hence applied as a neutral ionophore, for preparing an Ho(III) membrane sensor, with high selectivity and sensitivity. The membranes, also contain potassium tetrakis(p-chlorophenyl) borate as an anionic additives, and were tested by using different plasticizing solvent mediators such as benzyl acetate (BA), nitrobenzene (NB), and o-nitrophenyloctyl ether (NPOE). The optimum composition was found to be H2BPB-PVC- KTpClPB-BA with the ratios of 6.0: 30.0: 4.0: 60.0, respectively. Having a Nernstian response of 19.6 ± 0.2 mV per decade of Ho(III) activity, the linear range of the sensor was found to be relatively wide (from 1.0×10-5 to 1.0 ×10-2 mol L-1). It can work well in the pH range of 3.0-11.5. The lower detection limit (LDL) of the sensor was calculated to be 8.0 ×10-6 mol L-1. The excellent Ho(III)-selectivity of the proposed sensor with regard to most common metal ions, and especially, all lanthanide ions, is another advantage that can be mentioned about this sensor. The sensor was successfully used as an indicator electrode for titration of 25 mL of a 1.0 × 10-4 mol L-1 Ho(III) ions with a 1.0 × 10-2 mol L-1 EDTA...

Effect of plasticizer type on the potentiometric selectivity coefficient of electrodes for nitarte ion determination constructed by using PVC as polymeric membrane.

Yazdani-Pedram Zobeiri, Mehrdad; Cortés Nodarse, I.; Pérez Saavedra, J. J.; Arada Pérez, María de los Angeles
Fonte: Ministerio de Educación Superior Publicador: Ministerio de Educación Superior
Tipo: Artículo de revista
ES
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47.522954%
Seven types of chemical sensors based on polymeric liquid membranes for determination of nitrate ion have been prepared by using 3-nitro-o-xylene (NOX), tri-butyphosphate (TBP), bis-(2-ethylhexyl)sebacate (DOS), o-nitrophenyloctyl ether (o-NPOE), tris-2ethylhexylphosphate (TEHP), dioctylphthalate (DOP) and dibutylphthalate (DBP) as plasticizers, tri-octyl methyl ammonium chloride (TOMACI) as ionophoreas ionophore and poly (vinyl chloride) (PVC) as matrix. The experimental data was validated by calibrating each constructed sensor against a reference AG/AgCl electrode. The calibration parameters for each sensor was determined by applying the method of the addition solutions and the potentiometric selectivity coefficient (K Pot AB) of each electrode was determined by applying the method of mixed solutions. The response of the sensors was determined in relation with the lipophilicity od each plasticizer used solvent-mediator, its dielectric constant (er), polarity and viscosity. No correlation between the calculated calues for K Pot AB of the electrodes and dielectric constant of the plasticizers was observed.

Comportamiento de algunos parámetros de calibración de electrodos selectivos a nitrato, a diferentes concentraciones del ionóforo y del disolvente mediador.

Yazdani-Pedram Zobeiri, Mehrdad; Arada Pérez, María de los Angeles
Fonte: Asociación de Químicos e Ingenieros del Instituto Químico de Sarría Publicador: Asociación de Químicos e Ingenieros del Instituto Químico de Sarría
Tipo: Artículo de revista
ES
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The statistical evaluation of seven ion selective chemical sensors (ISE) for nitrate ion determination, based on polymeric membranes on a conductive support, has been carried out in this work. This was donw in order to determine the influence of ionophore concentration and that of solvent-mediator on the slope (S) and the practical detection limit (PDL). Tetradecilammonium nitrate (TDAN) was used as ionophore, polyvinylchloride (PVC) as matrix and seven plasticizers, namely, 3-nitro-o-xylene (NOX),Tributylphosphate(TBP), Bis (2-ethylhexyl) sebacate (DOS), o-Ntrophenyloctyl ether (o-NPOE), Tris -2ethyl-hexylphosphate (TEHP), Dioctylphthalate (DOP) and Dibutylphthalate (DBP) as solvent-mediators (SM). The amount of PVC employed was 29% by weight in all sensors while three different concentration of SM and that of ionophore was used. All constructed sensors presented Nernstian slopes with values of the Practical detection Limit (PDL) and Lower Limit on Linear Response (LLLR) in the range 10-6 - 10-5 mol/dm3. The sensitivity of the sensors was found to be independent from composition but the values pf PDL changes with the composition of the membrane. The selectivity coefficient on the electrode constructed by using 7% by weight of ionophore for an interfering anion with concentration of 10-2 mol/dm3 was determined by using the method of additions. The principal intgesssrfering anions were found to be CIO-3...

Influence of different plasticizers on the response of chemical sensors based on polymeric membranes for nitrate ion determination

Calvo Quintana, Josefina; Pérez Marín, Leonel; Yazdani-Pedram Zobeiri, Mehrdad; Arada Pérez, María de los Angeles
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artículo de revista
EN
Relevância na Pesquisa
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Seven types of ion-selective chemical sensors based on poly(vinyl chloride) (PVC) as polymeric membrane, for determination of nitrate ion, have been prepared by using 3-nitro-o-xylene (NOX), tributylphosphate (TBP), bis-(2-ethylhexyl) sebacate (DOS), o-nitrophenyloctyl ether (o-NPOE), tris-2-ethylhexylphosphate (TEHP), dioctylphthalate (DOP) and dibutylphthalate (DBP) as plasticizers and tetradecil ammonium nitrate TDAN) as ionophore. The response of each electrode was determined in relation to the lipophilicity of the plasticizer used, its rate of exudation to the aqueous phase, polarity, viscosity and its dielectric constant (e,). The experimental data was validated by calibrating the constructed electrodes against a reference Ag/AgCl electrode. The selectivity coefficient (K-AB(Pot)) of the electrodes was determined by applying the standard mixed solutions method. No correlation between K-AB(Pot) and epsilon(r) of the plasticizer was found. ATR-FIF-IR technique was used in order to evaluate the life-time of the polymeric membranes ion-selective electrodes (ISEs). The life-time of the electrodes was found to be limited fundamentally by the loss of the sensor and not due to the loss of the plasticizer. All the constructed ISEs showed Nernstian slopes with values of the practical detection limit (PDL) and lower limit of linear response (LLLR) in the range 10(-6) to 10(-5) mol/dm(3). The electrodes constructed by using o-NPOE and/or DBP showed the longest life-time...

Polystyrene nanoparticle exposure induces ion-selective pores in lipid bilayers

Negoda, Alexander; Kim, Kwang-Jin; Crandall, Edward D.; Worden, Robert M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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A diverse range of molecular interactions can occur between engineered nanomaterials (ENM) and biomembranes, some of which could lead to toxic outcomes following human exposure to ENM. In this study, we adapted electrophysiology methods to investigate the ability of 20 nm polystyrene nanoparticles (PNP) to induce pores in model bilayer lipid membranes (BLM) that mimic biomembranes. PNP charge was varied using PNP decorated with either positive (amidine) groups or negative (carboxyl) groups, and BLM charge was varied using dioleoyl phospholipids having cationic (ethylphosphocholine), zwitterionic (phosphocholine), or anionic (phosphatidic acid) headgroups. Both positive and negative PNP induced BLM pores for all lipid compositions studied, as evidenced by current spikes and integral conductance. Stable PNP-induced pores exhibited ion selectivity, with the highest selectivity for K+ (PK/PCl ~ 8.3) observed when both the PNP and lipids were negatively charged, and the highest selectivity for Cl− (PK/PCl ~ 0.2) observed when both the PNP and lipids were positively charged. This trend is consistent with the finding that selectivity for an ion in channel proteins is imparted by oppositely charged functional groups within the channel’s filter region. The PK/PCl value was unaffected by the voltage-ramp method...

Separació de compostos aniònics i neutres amb membranes de transport facilitat millores en la selectivitat /

Calzado Cuevas, Joan Antoni
Fonte: Bellaterra : Universitat Autònoma de Barcelona, Publicador: Bellaterra : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf; application/pdf; application/pdf; application/pdf
Publicado em //2001 CAT; CAT
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Consultable des del TDX; Títol obtingut de la portada digitalitzada; Les membranes han estat àmpliament emprades en molts processos, p.e. les membranes sintètiques d'ultrafiltració, macrofiltració o les de diàlisi. Al mateix temps, les membranes líquides (LM) han rebut un gran desenvolupament per crear-ne noves, de més selectives i estables per millorar el seu funcionament en els processos de separació en que intervenen reaccions químiques específiques. En aquest sentit, n'hi moltes aplicacions per a la separació de metalls i alguna per a espècies no metàl·liques. L'ús de ML comporta majors fluxos que a les membranes sòlides de filtració i la inclusió de transportadors també produeix una millor selectivitat. La interacció entre el transportador i el substrat indueix un transport facilitat amb el transportador que ha de ser ràpid i reversible per a aconseguir un transport adequat. La selectivitat prové de l'adequat enllaç o interacció entre el transportador i l'analit, així com d'una velocitat de reacció adient. De tot plegat podem deduir la possibilitat de dissenyar ML a mida, tot desenvolupant nous transportadors o identificant les molècules apropiades que compleixen aquests requisits. El present treball ha estat dirigit a la separació d'anions inorgànics i molècules neutres...

Application of Membrane-Selective Electrodes for the Determination of Naftidrofuryl Oxalate in the Presence of Its Alkaline Degradant in Tablets and Plasma

Abbas,Samah S.; Zaazaa,Hala E.; El-Ghobashy,Mohamed R.; Fayez,Yasmin M.; Fattah,Soheir A.
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2012 EN
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Membrane selective electrodes were used to determine Naftidrofuryl Oxalate (NFL) in presence of its alkaline degradate (I). The membrane selective electrodes include construction of water insoluble ion-association complexes. These are NFL-tetraphenyl borate (NFL-TPB), NFL-reinikate (NFL-R). These complexes are used as electroactive materials, in poly-vinyl chloride (PVC) matrix membrane sensors, for the determination of NFL. The performance characteristics of these sensors, evaluated according to IUPAC recommendations, reveal fast, stable and linear response for NFL. The sensors are used for determination of NFL in plasma. The suggested method was used to determine NFL in synthetic mixtures and in commercial tablets. The obtained results were statistically compared with official HPLC method, showing no significant difference with respect to accuracy and precision.