A microbalança de cristais piezoeléctricos de quartzo (QCM) é um dispositivo
simples, compacto e barato, que já demonstrou poder ser utilizado na análise
de metais, tão importantes do ponto de vista ambiental e da saúde humana.
Como a sensibilidade e selectividade da QCM é determinada pelo revestimento
a sua selecção reveste-se da maior importância.
A aplicação de membranas líquidas selectivas a iões, comuns aos eléctrodos
vulgarmente utilizados, apresenta-se actualmente como uma boa opção de
revestimento. Assim, este trabalho surge como uma revisão sobre a QCM e da
sua caracterização, assim como um estudo da influência da composição da
membrana polimérica na sua sensibilidade e selectividade a alguns metais.
As membranas líquidas usadas nos sensores de massa baseavam-se em PVC
dissolvido em THF e incorporavam aditivos como plastificantes, ionórofos e um
sal lipofílico, que levaram a melhorias ao nível da sensibilidade e selectividade.
A caracterização dos cristais piezoeléctricos revestidos com as membranas
poliméricas foi feita utilizando um analisador de impedâncias. A sensibilidade
dos cristais revestidos com membranas de diferentes composições foi avaliada
e foram avançadas algumas explicações para a mesma...
Vpu is a small phosphorylated integral membrane protein encoded by the human immunodeficiency virus type 1 genome and found in the endoplasmic reticulum and Golgi membranes of infected cells. It has been linked to roles in virus particle budding and degradation of CD4 in the endoplasmic reticulum. However, the molecular mechanisms employed by Vpu in performance of these functions are unknown. Structural similarities between Vpu and the M2 protein of influenza A virus have raised the question of whether the two proteins are functionally analogous: M2 has been demonstrated to form cation-selective ion channels in phospholipid membranes. In this paper we provide evidence that Vpu, purified after expression in Escherichia coli, also forms ion channels in planar lipid bilayers. The channels are approximately five- to sixfold more permeable to sodium and potassium cations than to chloride or phosphate anions. A bacterial cross-feeding assay was used to demonstrate that Vpu can also form sodium-permeable channels in vivo in the E. coli plasma membrane.
Twelve different porins from the gram-negative bacteria Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, and Yersinia pestis were reconstituted into lipid bilayer membranes. Most of the porins, except outer membrane protein P, formed large, water-filled, ion-permeable channels with a single-channel conductance between 1.5 and 6 nS in 1 M KCl. The ions used for probing the pore structure had the same relative mobilities while moving through the porin pore as they did while moving in free solution. Thus the single-channel conductances of the individual porins could be used to estimate the effective channel diameters of these porins, yielding values ranging from 1.0 to 2.0 nm. Zero-current potential measurements in the presence of salt gradients across lipid bilayer membranes containing individual porins gave results that were consistent with the conclusions drawn from the single-channel experiments. For all porins except protein P, the channels exhibited a greater cation selectivity for less mobile anions and a greater anion selectivity for less mobile cations, which again indicated that the ions were moving inside the pores in a fashion similar to their movement in the aqueous phase. Three porins, PhoE and NmpC of E. coli and protein P of P. aeruginosa...
1. The ion channels on both the luminal and abluminal membranes of endocardial endothelial (EE) cells were separately recorded using the patch clamp technique in the guinea-pig heart. 2. The major population consisted of two types of non-selective cation channels, which showed open probabilities of 0.21 and 0.33 at the resting potential, and conductances of 36 and 11 pS, respectively. 3. The next major class was Cl- channels with an ohmic conductance of 409 pS. The channel was quiescent in the cell-attached mode but was activated by strong depolarization after excising the patch membrane. 4. The channels activated by intracellular Ca2+ were mainly K+ channels showing a 34 pS slope conductance and, less frequently, Ca(2+)-dependent K+ channels having a large conductance (210 pS). The inward rectifier K+ channel (32 pS) was also observed. 5. The non-selective cation channels were recorded on the luminal membrane, but scarcely on the abluminal membrane, suggesting an active transport of K+ and Na+ across the endocardium. 6. The resting membrane conductance of the EE cells may be provided mostly by non-selective cation channels and 34 pS Ca(2+)-dependent K+ channels.
Constitutional self-instructed membranes were developed and used for mimicking the adaptive structural functionality of natural ion-channel systems. These membranes are based on dynamic hybrid materials in which the functional self-organized macrocycles are reversibly connected with the inorganic silica through hydrophobic noncovalent interactions. Supramolecular columnar ion-channel architectures can be generated by reversible confinement within scaffolding hydrophobic silica mesopores. They can be structurally determined by using X-ray diffraction and morphologically tuned by alkali-salts templating. From the conceptual point of view, these membranes express a synergistic adaptive behavior: the simultaneous binding of the fittest cation and its anion would be a case of “homotropic allosteric interactions,” because in time it increases the transport efficiency of the pore-contained superstructures by a selective evolving process toward the fittest ion channel. The hybrid membranes presented here represent dynamic constitutional systems evolving over time to form the fittest ion channels from a library of molecular and supramolecular components, or selecting the fittest ion pairs from a mixture of salts demonstrating flexible adaptation.
The study deals with an aqueous phase application of Mixed Matrix Membranes (MMMs) for silver ion (Ag+) capture. Silica particles were functionalized with 3-mercaptopropyltrimethoxy silane (MPTMS) to introduce free thiol (-SH) groups on the surface. The particles were used as the dispersed phase in the polysulfone or cellulose acetate polymer matrix. The membranes were prepared by the phase inversion method to create more open and interconnected porous structures suitable for liquid phase applications. The effects of the silica properties such as particle size, specific surface area, and porous/nonporous morphology on the silver ion capture capacity were studied. It was demonstrated that the membranes are capable of selectively capturing silver from a solution containing significant concentrations of other metal ions like Ca2+. The membranes were studied to quantify the dynamic capacity for silver ion capture and its dependence on residence time through the adjustment of transmembrane pressure. The thiol-Ag+ interaction was quantified with Quartz Crystal Microbalance in a continuous flow mode experiment and the observations were compared with the membrane results. One dimensional unsteady state model with overall volumetric mass transfer coefficient was developed and solved to predict the silver concentration in the liquid phase and the solid silica phase along the membrane thickness at varying time. The breakthrough data predicted using the model is comparable with the experimental observations. The study demonstrates successful application of the functionalized silica-mixed matrix membranes for selective aqueous phase Ag+ capture with high capacity at low transmembrane pressures. The technique can be easily extended to other applications by altering the functionalized groups on the silica particles.
Hydrogen sulfide (H2S) has emerged as a new and important member in the group of gaseous signaling molecules. However, the molecular transport mechanism has not yet been identified. Because of structural similarities with H2O, it was hypothesized that aquaporins may facilitate H2S transport across cell membranes. We tested this hypothesis by reconstituting the archeal aquaporin AfAQP from sulfide reducing bacteria Archaeoglobus fulgidus into planar membranes and by monitoring the resulting facilitation of osmotic water flow and H2S flux. To measure H2O and H2S fluxes, respectively, sodium ion dilution and buffer acidification by proton release (H2S ⇆ H+ + HS−) were recorded in the immediate membrane vicinity. Both sodium ion concentration and pH were measured by scanning ion-selective microelectrodes. A lower limit of lipid bilayer permeability to H2S, PM,H2S ≥ 0.5 ± 0.4 cm/s was calculated by numerically solving the complete system of differential reaction diffusion equations and fitting the theoretical pH distribution to experimental pH profiles. Even though reconstitution of AfAQP significantly increased water permeability through planar lipid bilayers, PM,H2S remained unchanged. These results indicate that lipid membranes may well act as a barrier to water transport although they do not oppose a significant resistance to H2S diffusion. The fact that cholesterol and sphingomyelin reconstitution did not turn these membranes into an H2S barrier indicates that H2S transport through epithelial barriers...
The performance of solid-contact/coated wire type electrodes with plasticized PVC membranes containing metalloporphyrins as anion selective ionophores is reported. The membranes are deposited on transducers based on graphite pastes and graphite rods. The hydrophobicity of the underlying conductive transducer surface is found to be a key factor that influences the formation of an aqueous layer beneath the polymer film. Elimination of this ill-defined water layer greatly improves the electrochemical properties of the ion-sensors, such as EMF stability and life-time. Only highly lipophilic electrode substrates, namely graphite paste with mineral oil, were shown to prevent the formation of aqueous layer underneath the ion-sensing membrane. The possibility of employing Co(III)-tetraphenylporphyrin both as NO2− selective ionophore and as electron/ion conducting species to ensure ion-to-electron translation was also discussed based on the results of preliminary experiments.
Potassium (K+) channels are specialized membrane proteins able to facilitate and regulate the conduction of K+ ions through cell membranes. Comprising five specific cation binding sites (S0 to S4) formed by the backbone carbonyl groups of conserved residues common to all K+ channels, the narrow selectivity filter allows fast conduction of K+ while being highly selective for K+ ions over sodium (Na+) ions. To extend our knowledge of the microscopic mechanism underlying selectivity in K+ channels, we characterize the free energy landscapes governing the entry and translocation of a Na+ or a K+ ion from the extracellular side into the selectivity filter of KcsA. The entry process of an extracellular ion is examined in the presence of two additional K+ ions in the pore and the 3-ion potential of mean force (PMF) is computed using extensive all-atom umbrella sampling molecular dynamics simulations. A comparison of the PMFs yields a number of important results. First, the free energy minima corresponding to configurations with the extracellular K+ or Na+ ion in the binding site S0 or S1 are similar in depth, suggesting that the thermodynamic selectivity governed by the free energy minima for those two binding sites is insignificant. Second...
Bovine lactoferrampin (LFampinB) is a newly discovered antimicrobial peptide found in the N1-domain of bovine lactoferrin (268–284), and consists of 17 amino-acid residues. It is important to determine the orientation and structure of LFampinB in bacterial membranes to reveal the antimicrobial mechanism. We therefore performed 13C and 31P NMR, 13C-31P rotational echo double resonance (REDOR), potassium ion-selective electrode, and quartz-crystal microbalance measurements for LFampinB with mimetic bacterial membrane and molecular-dynamics simulation in acidic membrane. 31P NMR results indicated that LFampinB caused a defect in mimetic bacterial membranes. Ion-selective electrode measurements showed that ion leakage occurred for the mimetic bacterial membrane containing cardiolipin. Quartz-crystal microbalance measurements revealed that LFampinB had greater affinity to acidic phospholipids than that to neutral phospholipids. 13C DD-MAS and static NMR spectra showed that LFampinB formed an α-helix in the N-terminus region and tilted 45° to the bilayer normal. REDOR dephasing patterns between carbonyl carbon nucleus in LFampinB and phosphorus nuclei in lipid phosphate groups were measured by 13C-31P REDOR and the results revealed that LFampinB is located in the interfacial region of the membrane. Molecular-dynamics simulation showed the tilt angle to be 42° and the rotation angle to be 92.5° for Leu3...
Poly(3-hydroxybutyrate) (PHB) is a polyester of 3-hydroxybutyric acid (HB) that is ubiquitously present in all organisms. In higher eukaryotes PHB is found in the length of 10 to 100 HB units and can be present in free form as well as in association with proteins and inorganic polyphosphate. It has been proposed that PHB can mediate ion transport across lipid bilayer membranes. We investigated the ability of PHB to interact with living cells and isolated mitochondria and the effects of these interactions on membrane ion transport. We performed experiments using a fluorescein derivative of PHB (fluo-PHB). We found that fluo-PHB preferentially accumulated inside the mitochondria of HeLa cells. Accumulation of fluo-PHB induced mitochondrial membrane depolarization. This membrane depolarization was significantly delayed by the inhibitor of the mitochondrial permeability transition pore - Cyclosporin A. Further experiments using intact cells as well as isolated mitochondria confirmed that the effects of PHB directly linked to its ability to facilitate ion transport, including calcium, across the membranes. We conclude that PHB demonstrates ionophoretic properties in biological membranes and this effect is most profound in mitochondria due to the selective accumulation of the polymer in this organelle.
The aim of the work was to elucidate the nature of charge-selective properties of macroporous composite inorganic membranes modified with nanoparticles of hydrated zirconium dioxide. The membranes have been investigated using methods of standard contact porosimetry, potentiometry, electron microscopy and small-angle X-ray scattering. The ion exchanger has been found to deposit inside pores of ceramics. Differential curves of pore volume distribution have been resolved using Lorentz functions; each maximum has been related to structure elements of the matrix and ion exchanger by means of calculations according to homogeneous and heterogeneous geometrical models. It was found that the voids, the radius of which is 4 to 8 nm, are responsible for charge selectivity of the composite membranes. These pores are formed due to blocking of macropores of ceramics with aggregates of nanoparticles of the ion exchanger; the radius of these aggregates is 20 to 24 nm. The membranes were applied to desalination of the solution containing NaCl. The removal degree of the salt from the solution reached 95% and 9% for the composite and unmodified membranes, respectively.
Na(+)-coupled HCO(3)(-) transporters (NBCs) mediate the transport of bicarbonate ions across cell membranes and are thus ubiquitous regulators of intracellular pH. NBC dysregulation is associated with a range of diseases; for instance, NBCn1 is strongly up-regulated in a model of ErbB2-dependent breast cancer, a malignant and widespread cancer with no targeted treatment options, and single-nucleotide polymorphisms in NBCn1 genetically link to breast cancer development and hypertension. The N-cyanosulfonamide S0859 has been shown to selectively inhibit NBCs, and its availability on the gram scale is therefore of significant interest to the scientific community. Herein we describe a short and efficient synthesis of S0859 with an overall yield of 45 % from commercially available starting materials. The inhibitory effect of S0859 on recovery of intracellular pH after an acid load was verified in human and murine cancer cell lines in Ringer solutions. However, S0859 binds very strongly to components in plasma, and accordingly, measurements on isolated murine tissues showed no effect of S0859 at concentrations up to 50 μM.; Ann M. Larsen, Niels Krogsgaard-Larsen, Gitte Lauritzen, Christina W. Olesen, Steen Honoré Hansen, Ebbe Boedtkjer...
El objetivo general de esta Tesis es el desarrollo de diversos avances con electrodos selectivos de iones basados en membranas poliméricas plastificadas dentro de la Potenciometría Moderna, incluyendo la ampliación de sus aplicaciones analíticas en análisis toxicológico y biorremediación, análisis enzimático y análisis de fármacos y de bebidas.
La metodología llevada a cabo está basada en una serie de estrategias de actuación con los electrodos selectivos de iones de membrana polimérica plastificada, en cuanto a la optimización de los componentes de la membrana, el estudio de sus respuestas potenciométricas incluyendo respuestas dinámicas, el diseño de plataformas conductoras para su miniaturización y su aplicación en campos de interés actual.
Así, se ha construido un electrodo que responde a cationes alquilmetilimidazolio, componentes de líquidos iónicos. Además se han calculado los coeficientes de reparto de estos cationes entre las fases membrana/disolución y se ha utilizado como descriptor de la toxicidad de los líquidos iónicos correspondientes en distintos microorganismos. El electrodo se ha utilizado también para la determinación del catión 1-butil-3-metilimidazolio en aguas contaminadas...
El objetivo global de esta Tesis Doctoral fue la evaluación del uso de membranas poliméricas basadas en líquidos iónicos en el desarrollo de electrodos selectivos de iones y en procesos de separación de metales (Zn2+, Fe3+, Cu2+ y Cd2+) y compuestos orgánicos (α-pineno e ibuprofeno). Para alcanzar dicho objetivo se estudió, en primer lugar, la respuesta potenciométrica de un número de electrodos selectivos de iones basados en membranas poliméricas construidas con policloruro de vinilo (PVC) y uno de los dos líquidos iónicos: hexafluorofosfato de 1butil-3-metilimidazolio [C4C1Im][PF6] o cloruro de trihexiltetradecilfosfonio [C14C6C6C6P][Cl]. Adicionalmente se realizó la caracterización microscópica de las membranas integrantes de los electrodos selectivos de iones mediante Microscopía Electrónica de Barrido combinada con el análisis por Energía Dispersiva de Rayos X (SEM-EDX). Las membranas plastificadas con [C4C1Im][PF6], mostraron poca o ninguna respuesta hacia los aniones cloruro, nitrato y tiocianato, lo que las convierte en membranas útiles para la construcción de electrodos de referencia. Sin embargo, la membrana plastificada con 20% p/p [C14C6C6C6P][Cl] mostró una buena respuesta hacia los aniones inorgánicos mencionados por lo que se amplió el estudio de su respuesta hacia los aniones ibuprofeno...
Ion transport is the fundamental factor determining salinity tolerance in plants. The Review starts from differences in ion transport between salt tolerant halophytes and salt-sensitive plants with an emphasis on transport of potassium and sodium via plasma membranes. The comparison provides introductory information for increasing salinity tolerance. Effects of salt stress on ion transport properties of membranes show huge opportunities for manipulating ion fluxes. Further steps require knowledge about mechanisms of ion transport and individual genes of ion transport proteins. Initially, the Review describes methods to measure ion fluxes, the independent set of techniques ensures robust and reliable basement for quantitative approach. The Review briefly summarizes current data concerning Na+ and K+ concentrations in cells, refers to primary thermodynamics of ion transport and gives special attention to individual ion channels and transporters. Simplified scheme of a plant cell with known transport systems at the plasma membrane and tonoplast helps to imagine the complexity of ion transport and allows choosing specific transporters for modulating ion transport. The complexity is enhanced by the influence of cell size and cell wall on ion transport. Special attention is given to ion transporters and to potassium and sodium transport by HKT...
Cadmium (II) electrode based on plasticized PVC membranes with 1-furoyl-3,3-diethyl thiourea as ionophore and tributyl phosphate as plasticizer has been developed. The membrane was applied on a support of conducting epoxy resin. Some parameters of evaluation of the electrode are presented in this work. The constructed electrode showed linear response in the concentration range of 10(-6) -10(-3) mol/dm(3), had a slope of 28.5 mV/decade, a detection limit (DL) of 2.10(-6) mol/dm(3) and a lower limit of lineal range (LLLR) of 4.2. 10(-6) mol/dm(3). The static response time obtained was less than 20 seconds. The Cd/S relationship in the membrane was 1: 1, as was determined by chemical microanalysis of energy dispersive X-ray spectroscopy (EDS). The constructed electrodes had a life-time of 5 days.
Facilitated transport through polymer inclusion membranes (PIMs) is a promising method for simultaneous separation and removal of valuable and toxic metal ions from aqueous solutions. Recently, ionic liquids (ILs) have been used as extracting agents for metal ions due to their unique physicochemical properties. This paper presents research on the facilitated transport of cadmium(II) and copper(II) ions from aqueous chloride solutions through PIMs with phosphonium ILs as new selective ion carriers. Cellulose triacetate membranes containing o-nitrophenyl octyl ether (ONPOE) as a plasticizer and Cyphos IL 101 [trihexyl(tetradecyl)phosphonium chloride] or Cyphos IL 104 [trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate] as the ion carriers have been prepared and applied for investigations. Cd(II) ions were transported preferably from hydrochloric acid solutions containing Cu(II) ions through the PIMs. Higher selectivity coefficient of Cd(II) over Cu(II) (SCd/Cu) from 0.1 mol·dm−3 hydrochloric acid was obtained for PIM with Cyphos IL 104 as the ion carrier. The influence of HCl and NaCl concentrations in the source phase on metal ion transport across PIM doped with Cyphos 104 was studied. It was found that the initial fluxes of Cd(II) and Cu(II) increase with increasing chloride ions concentration in the source phase. The selectivity coefficient for Cd(II) over Cu(II) decreases with increasing HCl concentration in the source phase. The results suggest that the separation system presented in this paper can be useful for the removal of Cd(II) from acidic chloride solutions in the presence of Cu(II).
The conductivity of highly charged membranes is nearly constant, due to
counter-ions screening pore surfaces. Weakly charged porous media, or "leaky
membranes", also contain a significant concentration of co-ions, whose
depletion at high current leads to ion concentration polarization and
conductivity shock waves. To describe these nonlinear phenomena the absence of
electro-osmotic flow, a simple Leaky Membrane Model is formulated, based on
macroscopic electroneutrality and Nernst-Planck ionic fluxes. The model is
solved in cases of unsupported binary electrolytes: steady conduction from a
reservoir to a cation-selective surface, transient response to a current step,
steady conduction to a flow-through porous electrode, and steady conduction
between cation-selective surfaces in cross flow. The last problem is motivated
by separations in leaky membranes, such as shock electrodialysis. The article
begins with a tribute to Neal Amundson, whose pioneering work on shock waves in
chromatography involved similar mathematics.
Consultable des del TDX; Títol obtingut de la portada digitalitzada; Han estat preparats diversos sensors potenciomètrics basats en parells iònics insolubles (1:1) provinents de l'associació d'ions tensioactius, en particular el catió tetradodecilamoni i l'anió dodecilbenzesulfonat (DBS-). Els materials sensors, incorporats a una matriu polimèrica de clorur de polivinil (PVC) que contenia com a agent plastificant l'o-nitrofeniloctil èter, van ser aplicats sobre una resina conductora per tal de fornir elèctrodes sense solució interna de referència. La resposta d'aquests elèctrodes a dodecilsulfat (DS-) i DBS- així com la interferència de diversos anions inorgànics habituals i cations tensioactius va ser igualment examinada. Es presenten els principals paràmetres corresponents a l'avaluació d'aquests elèctrodes i els seus temps de resposta. Les membranes estudiades mostren un bon comportament en ser utilitzades com a sensors potenciomètrics per a tensioactius aniònics. Aquests elèctrodes van ser emprats en la determinació de mostres comercials d'anions tensioactius per mitjà de valoracions potenciomètriques amb el reactiu valorant Hyamine 1622 (Hy+), sense aparèixer discrepàncies en els resultats quan aquests es comparaven amb el mètode de la valoració amb indicador mixt de les dues fases. Les característiques globals de funcionament milloren les corresponents a l'elèctrode comercial de tensioactius Orion...