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Tratamento de efluente contendo HEDP por eletrodiálise.; Treatment of effluent containing HEDP by electrodialysis.

Scarazzato, Tatiana
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 06/09/2013 PT
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37.909656%
Em processos de eletrodeposição, substâncias à base de cianeto são empregadas como complexantes e portadores do metal a ser depositado. Entretanto, a toxicidade associada ao cianeto e a evolução das legislações ambiental e trabalhista impulsionaram a exploração de matérias-primas alternativas aos sais cianídricos. Um estudo desenvolvido no Instituto de Pesquisas Tecnológicas avaliou a modificação de um banho comercial isento de cianeto para processos de deposição de cobre em substratos de Zamac. Neste estudo, foi utilizado um banho à base do ácido 1,hidroxietano-1,1- difosfônico, ou HEDP, um composto orgânico capaz de formar complexos estáveis com íons metálicos. Para viabilizar a substituição do cianeto pelo HEDP, deve-se consolidar uma metodologia para o tratamento do efluente gerado nas operações que o envolvam. A técnica de eletrodiálise surge como uma alternativa considerada limpa, que dispensa mudanças de fase e adição de produtos químicos ao processo. O método consiste na utilização de membranas íon-seletivas para promover a separação de espécies iônicas entre soluções utilizando a diferença de potencial elétrico entre dois pólos como força motriz. Neste trabalho, avaliou-se a aplicação da eletrodiálise no tratamento de um efluente galvânico à base de HEDP. Foram utilizadas soluções sintéticas simulando as águas de lavagem de um banho toque composto por complexos de cobre e HEDP. A construção das curvas de polarização permitiu a determinação da densidade de corrente limite a ser empregada na eletrodiálise. Nos ensaios de eletrodiálise...

Construção e avaliação de eletrodos seletivos ao antibiotico tiamulina

Maragareth Rita de Cassia Marques
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 31/12/1995 PT
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38.35295%
O antibiótico hidrogenofumarato de tiamulina pode ser determinado quantitativamente através de eletrodos seletivos. Esses eletrodos podem ser construídos com membranas de PVC, copolímero etileno/acetato de vinila (EVA) com os pares iônicos tetrafenilborato de tiamulina e fosfotungstato de tiamulina. A maioria dos eletrodos seletivos preparados apresentou resposta nernstiana na faixa de concentração de 1,0 x 10 a 1,0 x 10 mol/L de hidrogenofumarato de tiamulina e, em alguns casos, até 1,0x10 mol/L. Os limites de detecção encontrados foram da ordem de 10 a 10 mol/L. Esses eletrodos foram utilizados na determinação do teor de tiamulina em formulações de uso veterinário e na forma pura. Os resultados obtidos foram comparados estatisticamente com aqueles obtidos pelos métodos comumente utilizados, cromatografia líquida de alto desempenho para as formulações e titulação em meio não-aquoso para tiamulina na forma pura. Dependendo da composição da formulação contendo hidrogenofumarato de tiamulina, a determinação do teor deste antibiótico pode ser feita por potenciometria direta sem tratamento prévio da amostra. Mas, em alguns casos, isso não foi possível, sendo necessário processo de extração seguido de determinação com o eletrodo seletivo. Os métodos analíticos apresentaram boa correlação. Dependendo das condições de análise...

Permeability and Electrical Properties of Thin Lipid Membranes

Finkelstein, Alan; Cass, Albert
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/07/1968 EN
Relevância na Pesquisa
38.162717%
We present and discuss the permeability and electrical properties of thin lipid membranes, and the changes induced in these properties by several agents added to the aqueous phases after the membranes have formed. The unmodified membrane is virtually impermeable to ions and small "hydrophilic" solutes, but relatively permeable to water and "lipophilic" molecules. These properties are consistent with those predicted for a thin film of hydrocarbon through which matter is transported by dissolving in the membrane phase and then diffusing through it. The effect of cholesterol in reducing the water and "lipophilic" solute permeability is attributed to an increase of the "viscosity" of the hydrocarbon region, thus reducing the diffusion coefficient of molecules within this phase. The selective permeability of the membrane to iodide (I-) in the presence of iodine (I2) is attributed to the formation of polyiodides (perhaps I5-), which are presumed to be relatively soluble in the membrane because of their large size, and hence lower surface charge density. Thus, I2 acts as a carrier for I-. The effects of "excitability-inducing material" and the depsipeptides (particularly valinomycin) on ion permeability are reviewed. The effects of the polyene antibiotics (nystatin and amphotericin B) on ion permeability...

Backside Calibration Chronopotentiometry: Using Current to Perform Ion Measurements by Zeroing the Transmembrane Ion Flux

Xu, Yida; Ngeontae, Wittaya; Pretsch, Ernö; Bakker, Eric
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
38.45562%
A recent new direction in ion-selective electrode (ISE) research utilizes a stir effect to indicate the disappearance of an ion concentration gradient across a thin ion-selective membrane. This zeroing experiment allows one to evaluate the equilibrium relationship between front and backside solutions contacting the membrane by varying the backside solution composition. This method is attractive since the absolute potential during the measurement is not required, thus avoiding standard recalibrations from the sample solution and a careful control of the reference electrode potential. We report here on a new concept to alleviate the need to continuously vary the composition of the backside solution. Instead, transmembrane ion fluxes are counterbalanced at an imposed critical current. A theoretical model illustrates the relationship between the magnitude of this critical current and the concentration of analyte and countertransporting ions, and is found to correspond well with experimental results. The approach is demonstrated with lead(II)-selective membranes and protons as dominating interference ions, and the concentration of Pb2+ was successfully measured in tap water samples. The principle was further evaluated with calcium-selective membranes and magnesium as counterdiffusing species...

Transport of chloride and carboxyfluorescein through phospholipid vesicle membranes by heptapeptide amphiphiles

Ferdani, Riccardo; Li, Ruiqiong; Pajewski, Robert; Pajewska, Jolanta; Winter, Rudolph K.; Gokel, George W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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37.86004%
Seven synthetic anion transporters (SAT) of the general form R2N-COCH2OCH2CO-(Gly)3-Pro-(Gly)3-OR’ were prepared. Three pairs of compounds each contained twin n-hexyl, n-decyl, and n-octadecyl (R) groups at the N-terminus and one contained twin n-tetradecyl groups. Three of the compounds were C-terminated by benzyl and three by heptyl (R’) residues. The ability of these compounds to mediate ion release from phospholipid vesicles was assessed. Chloride release was measured by ion selective electrode measurements and by chloride quenching of the fluorescent dye lucigenin. Transport of the anion carboxyfluorescein (CF) was measured by fluorescence dequenching. Differences in both the C-(R’) and N-terminal (R) residues within the ionophores affected anion transport. The chloride release data acquired by ion selective electrode and fluorescence methods were similar but not identical. A possible carrier mechanism for Cl- transport was discredited. Both Cl- and CF anions were released from vesicles by these compounds. The results of CF and Cl- transport showed good consistency when the ionophore’s N-terminal chains were either decyl or octadecyl but not when they were hexyl. The transport of CF and Cl- appears to be fundamentally different when R is C6 compared to C10 or C18. Differences between the behavior of SATs with Cl- and CF were also reflected in negative ion mass spectrometric studies.

Limitations of Current Polarization for Lowering the Detection Limit of Potentiometric Polymeric Membrane Sensors

Höfler, Lajos; Bedlechowicz, Iwona; Vigassy, Tamás; Gyurcsányi, Róbert E.; Bakker, Eric; Pretsch, Ernö
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/05/2009 EN
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Ion fluxes across polymeric ion-selective membranes are a decisive parameter dictating the lower detection limit of potentiometric ion sensors. An applied current was earlier proposed to counteract such fluxes and reduce the detection limit to ultra-trace levels. So far, however, the method has not been used in practical situations since the correct current amplitude requires prior knowledge of the sample composition. This paper explores the use of the stir effect to evaluate the optimal current by theory and experiments. It is shown that the traditionally used steady-state model assuming a uniform distribution of ion exchanger in the membrane, fixed with time, violates the electroneutrality condition. A modified steady-state model is introduced that allows for a concentration tilt of the ion exchanger and predicts that a stir effect can indeed be utilized to find the optimal current. Ideally, by choosing the optimal current and very long measurement times, the thermodynamic detection limit might be obtained. However, in practice the stir effect declines at low concentrations and the conditions are far from steady state. Therefore, the improvement of the lower detection limit achievable by galvanostatic control is only about one order of magnitude. A numerical finite-difference approximation is shown to trace the experimental potential responses of silver-selective electrodes well...

Modern Directions for Potentiometric Sensors

Bakker, Eric; Chumbimuni-Torres, Karin
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/01/2008 EN
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This paper gives an overview of the newest developments of polymeric membrane ion-selective electrodes. A short essence of the underlying theory is given, emphasizing how the electromotive force may be used to assess binding constants of the ionophore, and how the selectivity and detection limit are related to the underlying membrane processes. The recent developments in lowering the detection limits of ISEs are described, including recent approaches of developing all solid state ISEs, and breakthroughs in detecting ultra-small quantities of ions at low concentrations. These developments have paved the way to use potentiometric sensors as in ultra-sensitive affinity bioanalysis in conjunction with nanoparticle labels. Recent results establish that potentiometry compares favorably to electrochemical stripping analysis. Other new developments with ion-selective electrodes are also described, including the concept of backside calibration potentiometry, controlled current coulometry, pulsed chronopotentiometry, and localized flash titration with ion-selective membranes to design sensors for the direct detection of total acidity without net sample perturbation. These developments have further opened the field for exciting new possibilities and applications.

Backside Calibration Potentiometry: Ion Activity Measurements with Selective Supported Liquid Membranes by Calibrating from the Inner Side of the Membrane

Malon, Adam; Bakker, Eric; Pretsch, Ernö
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/01/2007 EN
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In direct potentiometry, the magnitude of the measured potentials is used to determine the composition of the sample. While this places rather formidable demands on the required reproducibility of the associated potential measurements, typically on the order of microvolts, in vitro clinical analyses of blood samples are today successfully performed with direct potentiometry using ion-selective electrodes (ISEs). Unfortunately, most other analytical situations do not permit the sensor to be recalibrated every few minutes, as in environmental monitoring or in vivo measurements, and direct potentiometry is often bound to fail as an accurate method in these circumstances. This paper introduces a novel direction for potentiometric sensing, termed backside calibration potentiometry. Chemical asymmetries across thin supported liquid ISE membranes are assessed by determining the direction of potential drift upon changing the stirring rate on either side of the membrane. Disappearance of this drift indicates the disappearance of concentration gradients across the membrane and is used to determine the sample composition if the solution composition at the backside of the membrane and the interfering ion concentration in the sample are known. For practical determinations...

Sensitivity and Working Range of Backside Calibration Potentiometry

Ngeontae, Wittaya; Xu, Yida; Xu, Chao; Aeungmaitrepirom, Wanlapa; Tuntulani, Thawatchai; Pretsch, Ernö; Bakker, Eric
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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38.059438%
A new direction in potentiometric sensing, termed backside calibration potentiometry, was recently introduced. It makes use of the fact that the stir effect disappears in absence of ion-ionophore complex concentration gradient across supported liquid membrane ion-selective membranes. This method is especially suitable for measurements in which recalibration in the sample is not feasible, such as in remote monitoring applications. Here, a theoretical model is established to predict the working concentration range of the method. Lead(II)-selective Celgard membranes were used here with H+ as the dominant interfering ions. The emf difference for stirred and unstirred solutions was measured and the magnitude of this emf change as a function of the sample Pb2+ concentration was found to exhibit a bell shape that spans about three orders of magnitude. The concentration of interfering ions and the selectivity of the membrane were demonstrated to be important factors that affect the working range. Smaller ratios of primary ion concentrations at both aqueous sides of the membrane gave smaller emf difference values, and emf changes could still be observed with a logarithmic concentration ratio of 0.05. All experimental results correlated satisfactorily with the theoretical model.

Potentiometric Sensors Based on Fluorous Membranes Doped with Highly Selective Ionophores for Carbonate

Chen, Li D.; Mandal, Debaprasad; Pozzi, Gianluca; Gladysz, John A.; Bühlmann, Philippe
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Manganese(III) complexes of three fluorophilic salen derivatives were used to prepare ion-selective electrodes (ISEs) with ionophore-doped fluorous sensing membranes. Because of their extremely low polarity and polarizability, fluorous media are not only chemically very inert but also solvate potentially interfering ions poorly, resulting in a much improved discrimination of such ions. Indeed, the new ISEs exhibited selectivities for CO32− that exceed those of previously reported ISEs based on non-fluorous membranes by several orders of magnitude. In particular, the interference from chloride and salicylate was reduced by two and six orders of magnitude, respectively. To achieve this, the selectivities of these ISEs were fine-tuned by addition of non-coordinating hydrophobic ions (i.e., ionic sites) into the sensing membranes. Stability constants of the anion–ionophore complexes were determined from the dependence of the potentiometric selectivities on the charge sign of the ionic sites and the molar ratio of ionic sites and the ionophore. For this purpose, a previously introduced fluorophilic tetraphenylborate and a novel fluorophilic cation with a bis(triphenylphosphoranylidene)ammonium group, (Rf6(CH2)3)3PN+P(Rf6(CH2)3)3, were utilized. The optimum CO32− selectivities were found for sensing membranes composed of anionic sites and ionophore in a 1:4 molar ratio...

U.S. DOE Progress Towards Developing Low-Cost, High Performance, Durable Polymer Electrolyte Membranes for Fuel Cell Applications

Houchins, Cassidy; Kleen, Greg J.; Spendelow, Jacob S.; Kopasz, John; Peterson, David; Garland, Nancy L.; Ho, Donna Lee; Marcinkoski, Jason; Martin, Kathi Epping; Tyler, Reginald; Papageorgopoulos, Dimitrios C.
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 18/12/2012 EN
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Low cost, durable, and selective membranes with high ionic conductivity are a priority need for wide-spread adoption of polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). Electrolyte membranes are a major cost component of PEMFC stacks at low production volumes. PEMFC membranes also impose limitations on fuel cell system operating conditions that add system complexity and cost. Reactant gas and fuel permeation through the membrane leads to decreased fuel cell performance, loss of efficiency, and reduced durability in both PEMFCs and DMFCs. To address these challenges, the U.S. Department of Energy (DOE) Fuel Cell Technologies Program, in the Office of Energy Efficiency and Renewable Energy, supports research and development aimed at improving ion exchange membranes for fuel cells. For PEMFCs, efforts are primarily focused on developing materials for higher temperature operation (up to 120 °C) in automotive applications. For DMFCs, efforts are focused on developing membranes with reduced methanol permeability. In this paper, the recently revised DOE membrane targets, strategies, and highlights of DOE-funded projects to develop new, inexpensive membranes that have good performance in hot and dry conditions (PEMFC) and that reduce methanol crossover (DMFC) will be discussed.

Ion transport in broad bean leaf mesophyll under saline conditions

Percey, W.J.; Shabala, L.; Breadmore, M.C.; Guijt, R.M.; Bose, J.; Shabala, S.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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Main conclusion Salt stress reduces the ability of mesophyll tissue to respond to light. Potassium outward rectifying channels are responsible for 84 % of Na⁺ induced potassium efflux from mesophyll cells. Modulation in ion transport of broad bean (Vicia faba L.) mesophyll to light under increased apoplastic salinity stress was investigated using vibrating ion-selective microelectrodes (the MIFE technique). Increased apoplastic Na⁺ significantly affected mesophyll cells ability to respond to light by modulating ion transport across their membranes. Elevated apoplastic Na⁺ also induced a significant K⁺ efflux from mesophyll tissue. This efflux was mediated predominately by potassium outward rectifying channels (84 %) and the remainder of the efflux was through nonselective cation channels. NaCl treatment resulted in a reduction in photosystem II efficiency in a dose- and time-dependent manner. In particular, reductions in Fv‘/Fm‘ were linked to K⁺ homeostasis in the mesophyll tissue. Increased apoplastic Na⁺ concentrations induced vanadate-sensitive net H⁺ efflux, presumably mediated by the plasma membrane H⁺-ATPase. It is concluded that the observed pump’s activation is essential for the maintenance of membrane potential and ion homeostasis in the cytoplasm of mesophyll under salt stress.; William J. Percey...

Apical and basal membrane ion transport mechanisms in bovine retinal pigment epithelium.

Joseph, D P; Miller, S S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1991 EN
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1. Intracellular voltage recordings using conventional and double-barrelled chloride-selective microelectrodes have been used to identify several transport mechanisms at the apical and basolateral membranes of the isolated bovine retinal pigment epithelium (RPE)-choroid preparation. Intracellular recordings were obtained from two cell populations, melanotic (pigmented) and amelanotic (non-pigmented). The electrical properties of these two populations are practically identical. For melanotic cells the average apical resting membrane potential (VA) is -61 +/- 2 mV (mean +/- S.E.M., n = 49 cells, thirty-three eyes). For these cells the ratio of apical to basolateral membrane resistance (a) was 0.22 +/- 0.02. The mean transepithelial voltage and resistance were 6 +/- 1 mV and 138 +/- 7 omega cm2, respectively. 2. The apical membrane, which faces the distal retina, contains a Ba(2+)-inhibitable K+ conductance and a ouabain-inhibitable, electrogenic Na(+)-K+ pump. In addition it contains a bumetanide-sensitive mechanism, the putative Na(+)-K(+)-Cl- cotransporter. The basolateral membrane contains a DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid)-inhibitable chloride channel. The relative conductances of the apical and basolateral membranes to K+ and Cl- are TK approximately 0.9 and TCl approximately 0.7...

Sensores optoquímicos integrados basados en guías de onda

Puyol Bosch, M. del Mar
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
Publicado em //2003 SPA; SPA
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38.4937%
Consultable des del TDX; Títol obtingut de la portada digitalitzada; Con el fin de solucionar los problemas derivados de la falta de sensibilidad o la alta complejidad de los sensores ópticos integrados basados en medidas de absorbancia, a lo largo de la tesis se diseñó y construyó una plataforma versátil, viable para el desarrollo de dispositivos sensores basados en óptica integrada, para la determinación selectiva de diferentes analitos. Éste se basa en un dispositivo construido mediante guías de onda planas, integradas en una matriz de silicio. Además, para simplificar su diseño instrumental, el acoplamiento del dispositivo a la fuente de luz y al detector se realiza mediante fibras ópticas. El diseño planteado para cumplir los requisitos citados consiste en un circuito microfabricado de guías de onda ARROW y en una membrana químicamente activa, de un determinado grosor, depositada en una zona definida del circuito de guías, que actúa simultáneamente como parte de la estructura plana de guiado y como elemento de reconocimiento. El mecanismo de transducción se basa en el fenómeno de absorción, que es modulado por la membrana selectiva al interaccionar con el analito presente en la disolución. Se formularon diversas membranas poliméricas que incorporaban cromoionóforos NIR sensibles a protón de la familia de las cetocianinas y se formuló y caracterizó una membrana modelo selectiva de ión cadmio compuesta por la combinación de una de las cetocianinas (5ee) evaluadas previamente en un sensor integrado...

Desenvolupament de sensors potenciomètrics d'estat sòlid per a usos mediambientals i agroalimentaris

Artigas Pursals, Judit
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
Publicado em //2003 CAT; CAT
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38.550115%
Consultable des del TDX; Títol obtingut de la portada digitalitzada; L'ús de sensors químics ha experimentat un augment important en la indústria, en l'anàlisi clínic o en el camp mediambiental, degut principalment a les avantatges que ofereixen respecte algunes tècniques d'anàlisi (ús d'instrumental econòmic i fàcil d'emprar per tal de realitzar les mesures així com per construir els sensors o la versatilitat del disseny i de la configuració dels sensors en són dos exemples). La integració global del procés analític que ofereixen els sensors ha permès obtenir informació en temps real i in situ, desenvolupant equips portàtils, de baix cost i d'ús fàcil. Actualment, es comercialitzen sensors com a eines útils per millorar el control de processos industrials, per monitoritzar paràmetres d'interès, per aprofundir en estudis a llarg temps o per controlar la qualitat de productes. Paral·lelament a l'increment en nombre de cases comercials i de tipus de sensors comercials, s'ha incrementat també el nombre d'aplicacions i el nombre de mètodes de referència que inclouen l'ús de mètodes potenciomètrics. La present tesi té com a objectiu global el disseny, la construcció i l'avaluació de nous sensors potenciomètrics d'estat sòlid així com la instrumentació i el material necessari per tal d'utilitzar-los en aplicacions de l'àmbit mediambiental i agroalimentari. Per tal de construir els sensors s'empraren transductors tant diferents com els electrodes selectius d'ions (ESIs)...

Desenvolupament de noves membranes per a la millora de la seva estabilitat : caracterització i estudi comparatiu de les diferents membranes envers al transport de metalls en solucions aquoses /

Resina Gallego, Montserrat
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2008 CAT; CAT
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38.209602%
S'han preparat noves membranes híbrides pel transport de metalls amb la finalitat de millorar l'estabilitat mecànica i química, el temps de vida i la pèrdua de transportador de les membranes líquides suportades (SLM) ja existents. La inclusió del transportador a la matriu polimèrica de les membranes És una de les millores proposades respecte a la inestabilitat de les (SLM). A més, els materials híbrids presenten certs avantatges respecte als materials orgànics i inorgànics considerats de forma independent. Les noves membranes proposades estan basades en una barreja orgànica (triacetat celálulosa, CTA) i materials organosilícics (diclorodimetilsilà i tetraetoxisilà, DCDMS i TEOS, respectivament) com a suport de membranes. La preparació de les membranes s'ha optimitzat variant la quantitat de transportador àcid Di(2-etilhexilfosfòric, D2EHPA) i plastificants (2-Nitrofeniloctilèter, NPOE i/o Tris(2-butoxietil)fosfat), TBEP). Les tècniques d'Espectroscòpia Infraroja amb Reflexió Total Atenuada, la Microscòpia Electrònica de Rastreig, l'Anàlisi Termogravimètrica, la Ressonància Magnètica Nuclear de 29Si i la Difracció de Raigs-X han estat emprades per a caracteritzar les membranes híbrides i per a tenir una correlació entre les propietats estructurals amb els valors de permeabilitat dels ions metàl·lics. El transport s'ha avaluat fent servir D2EHPA i D2EHDTPA àcid Di(2¬etilhexilditofosfòric) sota les mateixes condicions experimentals. Els experiments de transport reportats tracten tant amb el transport de solucions sintètiques monocomponents com ara el transport selectiu de barreges binaries i ternàries de diferents ions metàl·lics. S'ha trobat que variant la composició de les membranes...

Desarrollo de un analizador automático para la determinación del ion plomo en muestras medioambientales

Fonseca Ortíz, Omarilis
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 //2004 SPA; SPA
Relevância na Pesquisa
38.34595%
Consultable des del TDX; Títol obtingut de la portada digitalitzada; La necesidad creciente de conservación y preservación del medio natural exige un riguroso control de diversos contaminantes, hecho que implica frecuentes determinaciones de especies potencialmente tóxicas en los diferentes medios, ya sea aire, agua o suelos. Esto ha impulsado las investigaciones dirigidas a mejorar los procedimientos analíticos existentes de manera tal que puedan suministrar información fiable, en tiempo real y en continuo de los diferentes parámetros de interés medioambiental. En este contexto, en la presente tesis se ha planteado como objetivo el desarrollo de un analizador automático para el control de plomo en redes de distribución de agua potable y en muestras contaminadas de suelos. El control de este parámetro es de vital importancia si consideramos los efectos adversos que causa este metal tóxico en la salud humana. Este trabajo de investigación se enmarca dentro de un convenio de colaboración existente con la empresa Aguas de Barcelona y ha tenido la colaboración de su empresa filial de ingeniería ADASA SISTEMAS S.A. Para desarrollar el analizador de plomo se propuso el uso de Sensores Químicos como elementos de detección (concretamente electrodos selectivos de iones)...

The cytotoxic plant protein, beta-puothionin, forms ion channels in lipid membranes

Hughes, P; Dennis, Elizabeth; Whitecross, Malcolm; Llewellyn, Danny; Gage, Peter
Fonte: American Society for Biochemistry and Molecular Biology Inc Publicador: American Society for Biochemistry and Molecular Biology Inc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
38.095784%
Thionins are small cysteine-containing, amphipathic plant proteins found in seeds and vegetative tissues of a number of plant genera. Many of them have been shown to be toxic to microorganisms such as fungi, yeast, and bacteria and also to mammalian cells. It has been suggested that thionins are present in seeds to protect them, and the germinating seedling, from attack by phytopathogenic microorganisms, but the mechanism by which they kill cells remains unclear. Using electrophysiological measurements, we have shown that β-purothionin from wheat flour can form cation-selective ion channels in artificial lipid bilayer membranes and in the plasmalemma of rat hippocampal neurons. We suggest that the generalized toxicity of thionins is due to their ability to generate ion channels in cell membranes, resulting in the dissipation of ion concentration gradients essential for the maintenance of cellular homeostasis.

Cation-selective ion channels formed by p7 of hepatitis C virus are blocked by hexamethylene amiloride

Premkumar, Anita; Wilson, L; Ewart, Gary; Gage, Peter
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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A 63 residue peptide, p7, encoded by hepatitis C virus was synthesised and tested for ion channel activity in lipid bilayer membranes. Ion channels formed by p7 had a variable conductance: some channels had conductances as low as 14 pS. The reversal potential of currents flowing through the channels formed by p7 showed that they were permeable to potassium and sodium ions and less permeable to calcium ions. Addition of Ca2+ to solutions made channels formed by p7 less potassium- or sodium-selective. Hexamethylene amiloride, a drug previously shown to block ion channels formed by Vpu encoded by HIV-1, blocked channels formed by p7. In view of the increasing number of peptides encoded by viruses that have been shown to form ion channels, it is suggested that ion channels may play an important role in the life cycle of many viruses and that drugs that block these channels may prove to be useful antiviral agents.

An Electrochemical Biosensor for Acrylamide Determination: Merits and Limitations

Silva,Nelson A.F.; Matos,Manuel J.; Karmali,Amin; Rocha,Maria M.
Fonte: Sociedade Portuguesa de Electroquímica Publicador: Sociedade Portuguesa de Electroquímica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2011 EN
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The present work reports the results concerning the development and implementation of the first electrochemical biosensor for acrylamide determination, based on a direct biochemical interaction between the analyte and intact bacterial cells, with intracellular enzymatic activity. The biological recognition element consisted of whole cells of Pseudomonas aeruginosa containing intracellular amidase activity, which catalyses the hydrolysis of acrylamide producing ammonium ion (NH4+) and acrylic acid. The transduction process was accomplished by means of an ammonium ion selective electrode. Whole cells were firstly immobilized on single discs of polymeric membranes, such as polyethersulphone, nylon and polycarbonate, which were, then, attached to the surface of the selective electrode. However, it was observed a significant loss of cells each time the biosensor was used, namely at the beginning of the assay, when the membranes were attached to the ammonium electrode, and after the assay, when removed for storage purposes. This evidence determined a premature decrease in the biosensor's stability. Instead of using single membrane discs, a ''sandwich'' design, with two membrane discs was considered. This way the cells remain contained between the membranes...