Ion Transport Characteristics Research Articles

Graphene oxide nanosheets/multi-walled carbon nanotubes hybrid as an excellent electrocatalytic material towards VO2+/VO2+ redox couples for vanadium redox flow batteries

A graphene oxide nanosheets/multi-walled carbon nanotubes (GO/MWCNTs) hybrid with excellent electrocatalytic redox reversibility towards VO2+/VO2+ redox couples for vanadium redox flow batteries (VRFB) has been prepared by an electrostatic spray technique after efficient ultrasonic treatment. The structures and electrochemical properties of GO/MWCNTs are investigated by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and cyclic voltammetry. GO/MWCNTs are shown to be cross-linked and form an electrocatalytic hybrid with an effective mixed conducting network, leading to efficiently fast ion and electron transport characteristics. Compared with the pure GO nanosheets and MWCNTs, GO/MWCNTs deliver a much better electrocatalytic redox reversibility towards the positive VO2+/VO2+ couple, especially for the reduction from VO2+ to VO2+. The excellent experimental results demonstrate that the newly developed hybrid material holds great promise in the application of VRFB.

Influence of structural ordering on ion transport in BiO0.5F2.0 bismuth oxyfluoride

The influence of structural defect ordering on ionic conductivity (σ) in the cubic (fluorite) modification of BiO0.5F2.0 oxyfluoride has been investigated. Upon cooling, the disordered fluorite BiO0.5F2.0 phase undergoes a reversible transition to an ordered form. This transition manifests itself as a jump in the temperature dependence σ(T) near 583 ± 6 K. The ordering of structural defects deteriorates the characteristics of ion transport in BiO0.5F2.0. At 500 K, the σ value for the ordered phase is 1 × 10−4 S/cm, whereas an extrapolation to this temperature for the disordered phase gives σ = 4 × 10−4 S/cm.

Localization and functional characterization of the human NKCC2 isoforms

Salt reabsorption across the apical membrane of cells in the thick ascending limb (TAL) of Henle is primarily mediated by the bumetanide-sensitive Na(+)/K(+)/2Cl(-) cotransporter NKCC2. Three full-length splice variants of NKCC2 (NKCC2B, NKCC2A and NKCC2F) have been described. The NKCC2 isoforms have specific localizations and transport characteristics, as assessed for rabbit, rat and mouse. In the present study, we aimed to address the localization and transport characteristics of the human NKCC2 isoforms. RT-PCR, in situ hybridization and uptake studies in Xenopus oocytes were performed to characterize human NKCC2 isoforms. All three classical NKCC2 isoforms were detected in the human kidney; in addition, we found splice variants with tandem duplicates of the variable exon 4. Contrary to rodents, in which NKCC2F is the most abundant NKCC2 isoform, NKCC2A was the dominant isoform in humans; similarly, isoform-specific in situ hybridization showed high expression levels of human NKCC2A along the TAL. Compared to NKCC2B and NKCC2F, human NKCC2A had the lowest Cl(-) affinity as determined by (86)Rb(+) uptake studies in oocytes. All NKCC2 isoforms were more efficiently inhibited by bumetanide than by furosemide. A sequence analysis of the amino acids encoded by exon 4 variants revealed high similarities between human and rodent NKCC2 isoforms, suggesting that differences in ion transport characteristics between species may be related to sequence variations outside the highly conserved sequence encoded by exon 4. The human NKCC2 is an example of how differential splicing forms the basis for a diversification of transporter protein function.

Dielectric Relaxation in CaO–Bi2O3–B2O3 Glasses

Glasses in the system CaO–Bi2O3–B2O3 (in molar ratio) have been prepared using melt‐quenching route. Ion transport characteristics were investigated for this glass using electric modulus, ac conductivity and impedance measurements. The ac conductivity was rationalized using Almond–West power law. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.76 eV, close to that the activation energy for dc conductivity (1.71 eV) indicating that the same species took part in both the processes. The stretched exponent β (0.5–0.6) is invariant with temperature for the present glasses.

Electrophysiology of the isolated and perfused midgut of adult female yellow fever mosquitoes (Aedes aegypti)

The midgut of adult, female mosquitoes receives the blood meal. Salt and water are rapidly absorbed and secreted by the Malpighian tubules. Later, nutrients are digested and absorbed. Transport in the midgut of adult mosquitoes has never been studied with isolated midguts. Isolated midguts were transferred into a bath with mosquito saline and mounted on perfusion pipettes connected to a syringe pump. The transepithelial voltage (Vte) was measured. Mounting midguts with the posterior end on the pipette allows continuous perfusion, and a small, lumen negative Vte was observed. Addition of theophylline (10 mmol/l, increasing intracellular cAMP concentrations) to the bathing solution resulted in a small, lumen positive Vte. Because a valve is located between midgut and hindgut, the posterior midgut is inflated when the anterior part connects to the perfusion pipette. When inflated with mosquito saline the initial, lumen negative Vte and the lumen positive Vte after addition of theophylline were markedly higher, suggesting that stretch is a stimulator for the ion transport characteristics reflected in Vte. Vte is inhibited with dinitrophenol, indicating that it reflects active ion transport. Financial support by the NIH (1R01AI063463‐01A2) and by a Wagner College Faculty Research Grant is gratefully acknowledged.

Ion transport characteristics in nanofiltration membranes: measurements and mechanisms

Research Article| March 01 2010 Ion transport characteristics in nanofiltration membranes: measurements and mechanisms Noeon Park; Noeon Park 1R&D Budget Coordination Division, Korea Institute of Science and Technology Evaluation and Planning (KISTEP), 11F Dongwon Industry Bldg, 275, Yangjae-dong, Seocho-gu, Seoul 137-130, South Korea Search for other works by this author on: This Site PubMed Google Scholar Jaeweon Cho; Jaeweon Cho 2Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712, South Korea Search for other works by this author on: This Site PubMed Google Scholar Seungkwan Hong; Seungkwan Hong 3Department of Civil, Environmental & Architectural Engineering, Korea University, 1, 5-ka, Anam-dong, Sungbuk-gu, Seoul 136-713, South Korea Search for other works by this author on: This Site PubMed Google Scholar Sangyoup Lee Sangyoup Lee 3Department of Civil, Environmental & Architectural Engineering, Korea University, 1, 5-ka, Anam-dong, Sungbuk-gu, Seoul 136-713, South Korea Tel.: +82-2-3290-3731 ; Fax: +82-2-928-7656; E-mail: sangyoup_lee@korea.ac.kr Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2010) 59 (2-3): 179–190. https://doi.org/10.2166/aqua.2010.034 Article history Received: April 30 2009 Accepted: November 13 2009 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Noeon Park, Jaeweon Cho, Seungkwan Hong, Sangyoup Lee; Ion transport characteristics in nanofiltration membranes: measurements and mechanisms. Journal of Water Supply: Research and Technology-Aqua 1 March 2010; 59 (2-3): 179–190. doi: https://doi.org/10.2166/aqua.2010.034 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Ion transport characteristics during nanofiltration (NF) were investigated by measuring effective osmotic pressure and diffusivity experimentally. Effective osmotic pressure and diffusivity were measured through lab-scale transport and diffusion tests. First, it was shown that the water flux across NF membranes decreased dramatically with increasing ionic strength because of the noticeable increase in effective osmotic pressure. Second, the results from transport experiments showed that the ion selectivity values, which were derived from the thermodynamic model, decreased with increasing ionic strength. Third, by analysing the data of measured osmotic pressure and diffusivity, it was demonstrated that the former and the latter increased and decreased, respectively, as ionic strength increased. The experimentally determined osmotic pressure across NF membranes was much lower than that calculated theoretically. At best, around 5% or less of the theoretical osmotic pressure was obtained under the experimental conditions investigated. The effective osmotic pressure and ion rejection decreased in the presence of nano-colloids. The influence of nano-colloids on ionic transport was found to be dependent on the concentration and size of the nano-colloids. Therefore, ion transport characteristics across NF membranes can be determined practically by measuring effective osmotic pressure and diffusivity as these reflect both feed water and membrane properties. effective diffusivity, effective osmotic pressure, ion transport characteristics, nano-colloids, nanofiltration This content is only available as a PDF. © IWA Publishing 2010 You do not currently have access to this content.

Primers on Molecular Pathways — Ion Channels: Key Regulators of Pancreatic Physiology

Ion transport across the cellular plasma membrane is important in almost every physiological process. This phenomenon is driven by the coordinated action of carriers, pumps and channels, which move ions in and out the cells and between different organelles. Ion channels are transmembrane proteins that provide a continuous aqueous pore through which ions can selectively move. The interest in these molecules has increased due to the recognition of diverse pathologies related with mutations in genes encoding these transmembrane proteins, now known as channelopathies. Ion channels play a variety of functions in the pancreas. Here, we briefly describe ion transport characteristics as well as their role in pancreas physiology and pathophysiology.

Ion transport and degradation studies of a polyaniline-modified electrode using SECM

The morphology and ion transport characteristics of polyaniline (PANI) films on a platinum electrode were investigated using scanning electrochemical microscopy method (SECM). An ultramicroelectrode (UME) tip was positioned close to the surface of a PANI-modified substrate electrode, and the current signal at the tip and substrate electrodes, during a substrate potential step or linear sweep were monitored simultaneously. Proton transport occurred on the PANI film at a pH of 6 during the first and second redox cycles of PANI was monitored at this pH. The chemical reaction pathway of PANI as a function of substrate potential was analyzed. Different species of degradation products were detected electrochemically at the SECM tip. Benzoquinone (BQ) was found to be the major product of anodic degradation of PANI. Chemical imaging of the anodic degradation of PANI was performed by SECM during applying different potential steps to the PANI. The anodic threshold of 0.75 V was suggested as the potential at which degradation of PANI begins.

Epithelia derived from human mammary tissue exhibits unique ion transport characteristics

Ion transport and barrier characteristics of mammary epithelium are poorly defined for most species, including humans. MCF10a cells, derived from non‐neoplastic human mammary tissue (Cancer Res 50: 6075, 1990), were cultured on permeable supports in typical medium (DMEM/F12) for 9‐17 days in the absence and presence of cholera toxin (Ct). At all time points tested, MCF10a cells generated an electrically tight epithelial barrier (1010±110 O cm2) that exhibited a positive short circuit current (Isc; 6.1±0.3 μA cm−2) indicative of net cation absorption or anion secretion. Cells cultured in Ct exhibited greater basal Isc and greater amiloride‐sensitive Isc (4.3 vs. 2.5 μA cm−2), indicating enhanced sodium absorption. Culturing the cells in the presence of forskolin (0.2 μM) did not replicate the Ct effect. Additionally, it was shown that the effect of Ct‐enhanced amiloride‐sensitive Isc was greatest at the shortest exposure period tested, 1 day. Regardless of culture conditions, acute exposure to forskolin (2 μM) induced a modest, slowly developing increase in Isc. Bumetanide and glibenclamide (300 μM) were associated with modest reductions in Isc (<0.7 μA cm−2). These results demonstrate that MCF10a cells provide a valuable model to identify transport mechanisms and regulatory pathways that can account for the unique composition of human milk. [NIH (P20‐RR017686), KS Ag Exp Stn, and KSU SUROP support]

Single nucleotide polymorphisms (SNPs) of human SLC26A9

Many diseases are caused by altered epithelial Cl− or HCO3− transport. Mutations in the SLC26A3 transporter are causative for congenital chloride‐losing diarrhea; however, no other SLC26 transporter plays such a direct genetic role in disorders of epithelial Cl− transport. SLC26A9 is expressed in the lung, stomach, intestine and kidney (lesser extent) but its physiological function in these epithelia is not clear. Thus far, no diseases result from SLC26A9 mutations. However, database analysis reveals three single nucleotide polymorphisms (SNPs). We reasoned that the human SLC26A9‐SNPs would provide insight into what a disease phenotype might be functionally manifest. Here we analyzed the ion transport characteristics of human SLC26A9 and its SNPs: V622L, V744M and H748R. Human SLC26A9 and its three SNPs were expressed in Xenopus laevis oocytes. Effects on ion transport were evaluated using ion selective electrodes and voltage clamping. Measuring Cl− and HCO3− flux, our results show that SLC26A9 is a Cl−/HCO3− exchanger. One SNP, V622L, is located in the C‐terminus just before the STAS domain of SLC26A9. V622L has ~50% function (current and Cl− transport). These results suggest that the possession of V622L allele in humans would decrease SLC26A9 function and modulate the risk for lung disease (cystic fibrosis), gut disease (gastric ulcer) or hypertension, due to reduced Cl− transport across epithelial cells.

Impact of ethylene carbonate on ion transport characteristics of PVdF–AgCF 3SO 3 polymer electrolyte system

The ionic transport in thin film plasticized polymer electrolytes based on polyvinylidene fluoride (PVdF) as the polymer host, silver triflate (AgCF 3SO 3) as salt and ethylene carbonate (EC) as plasticizer prepared by solution casting technique has been reported. Addition of silver triflate has resulted in an increase in the room temperature (298 K) electrical conductivity of the polymer from 10 −6 to 10 −5 S cm −1 whereas incorporation of EC as the plasticizer has further enhanced the conductivity value by an order of magnitude to 10 −4 S cm −1 owing to the possible decrease in crystallinity of the polymer matrix as revealed by the detailed temperature-dependent complex impedance, silver ionic transference number, Fourier transform infrared and X-ray diffraction measurements.

Parameter Sensitivity Analysis in Electrophysiological Models Using Multivariable Regression

Computational models of electrical activity and calcium signaling in cardiac myocytes are important tools for understanding physiology. The sensitivity of these models to changes in parameters is often not well-understood, however, because parameter evaluation can be a time-consuming, tedious process. I demonstrate here what I believe is a novel method for rapidly determining how changes in parameters affect outputs. In three models of the ventricular action potential, parameters were randomized, repeated simulations were run, important outputs were calculated, and multivariable regression was performed on the collected results. Random parameters included both maximal rates of ion transport and gating variable characteristics. The procedure generated simplified, empirical models that predicted outputs resulting from new sets of input parameters. The linear regression models were quite accurate, despite nonlinearities in the mechanistic models. Moreover, the regression coefficients, which represent parameter sensitivities, were robust, even when parameters were varied over a wide range. Most importantly, a side-by-side comparison of two similar models identified fundamental differences in model behavior, and revealed model predictions that were both consistent with, and inconsistent with, experimental data. This new method therefore shows promise as a tool for the characterization and assessment of computational models. The general strategy may also suggest methods for integrating traditional quantitative models with large-scale data sets obtained using high-throughput technologies.

Charge injection and charge separation as revealed by dynamic space charge measurement in poly(propylene-ethylene) copolymer films

The time resolved fast pulsed electroacoustic method is used to investigate the space charge characteristics in an additive-free poly(propylene-ethylene) copolymer in film form. The 190 μm thick films, sandwiched by aluminum (at the lower electrode) and semiconducting material (at the upper electrode), were submitted to dc and low frequency ac stress for various durations at various temperatures. The results show that under dc stress, homocharges accumulate near the lower electrodes and heterocharge near the upper electrode at 25 °C whereas at 50 °C, besides the similar space charge behavior as at 25 °C in the vicinity of the electrodes, a region of symmetric separation of charges of opposite polarity is detected in the bulk. In addition, the time for the symmetric separation emergence under high voltage application depends on the field intensity, being shorter for higher field. Similar charging characteristics were also found at 50 °C under low frequency (5 mHz) square 50 kV/mm rms stress, with surprisingly periodical feature, while only injected charge was observed at 0.1 Hz square rms 50 kV/mm stress. Combining dc data with ac data, it is shown that the space charge build up results from two contributing processes: the space charge formation adjacent to the electrode is due to electronic carriers injection and drift, whereas the symmetric space charge in the bulk shows ionic transport characteristics, which can be well fitted with an ionic transport model.

Influence of Ionomer Equivalent Weight on Kinetic and Transport Properties in PEFC MEAs

The ionomer/binder type and composition can influence both ionic and mass transport in a PEFC electrode. For an electrode to have minimum resistance to O2, proton and electron transport, the ionomer composition has to be optimized for its EW and volume fraction. An optimum ionomer composition in the electrode results in higher Pt utilization and hence better MEA performance. Ion and species transport characteristics of electrode layers containing PFSA ionomers with different EWs are examined in this study by analysis of MEA polarization data at different relative humidities. Steady state polarization curves were obtained with air and oxygen. The polarization data for MEAs was analyzed to determine the relative contributions of the different sources of polarization, namely activation losses, membrane resistance losses, ohmic losses in the electrode, and mass transport losses in the GDL and electrode.

Poly(vinylidene fluoride)–polydiphenylamine composite electrospun membrane as high-performance polymer electrolyte for lithium batteries

Composites of poly(vinylidene fluoride) (PVdF)–polydiphenylamine (PDPA) are electrospun as nanofibrous membranes, PVdF–PDPA-CFM (CFM represents composite nanofibrous membrane). Polymer electrolytes are prepared by loading lithium salts into PVdF–PDPA-CFM. Field emission scanning electron microscope (FESEM) images clearly inform that PVdF–PDPA-CFM has interconnected multi-fibrous layers with ultrafine porous structures. The average diameter of fibers in PVdF–PDPA-CFM is ∼200 nm for a loading of 0.5 wt.% of PDPA in the composite, which is far lesser than pristine PVdF membrane. There is inter-fiber twisting in the PVdF–PDPA-CFM that generates microcavities. These interconnected morphological features of PVdF–PDPA-CFM result in higher ionic conductivity, effective lithium ion transport and good interfacial characteristics with lithium electrode. Higher ionic conductivity, lithium ion transport number of about 0.48, higher liquid electrolyte uptake (>280%) with dimensional stability, lower interfacial resistance and higher electrochemical stability window of 5.18 V vs. Li for PVdF–PDPA-CFM electrolyte are witnessed. With these improved performance characteristics, PVdF–PDPA-CFM finds its suitability as polymer electrolyte for high-performance lithium rechargeable batteries.

Improved bond valence models for ion transport pathways in glasses

ABSTRACTStructure property function relationships provide valuable guidelines for a systematic development of functional materials. It is demonstrated how an augmented bond valence (BV) approach helps to establish such relationships in solid electrolytes. In principle it permits to identify mobile species, transport pathways and provides estimates for ion mobilities. In this work we discuss ion conduction pathways in glassy Lithium metasilicate as an illustrative example. The required representative local structure model is derived from Molecular Dynamics simulations, which provides the opportunity to compare the bond-valence-based predictions from a static structure model with a comprehensive analysis of a complete simulation trajectory. It is shown that understanding the bond valence mismatch as an effective Morse-type interaction opens up a way for systematically analyzing ion transport pathways and for a generally applicable method with improved reliability to predict ion transport characteristics in solid electrolytes from the structure model.

Hepatocyte nuclear factor-4α promotes differentiation of intestinal epithelial cells in a coculture system

Normal cellular models able to efficiently recapitulate intestinal epithelial cell differentiation in culture are not yet available. The aim of this work was to establish and genetically characterize a mesenchymal-epithelial coculture system to identify transcriptional regulators involved in this process. The deposition of rat intestinal epithelial cells on human intestinal mesenchymal cells led to the formation of clustered structures that expanded shortly after seeding. These structures were composed of polarized epithelial cells with brush borders and cell junction complexes. A rat GeneChip statistical analysis performed at different time points during this process identified hepatocyte nuclear factor-4alpha (HNF-4alpha) and hepatocyte nuclear factor-1alpha (HNF-1alpha) as being induced coincidently with the apparition of polarized epithelial structures. Stable introduction of HNF-4alpha in undifferentiated epithelial cells alone led to the rapid induction of HNF-1alpha and several intestinal-specific markers and metabolism-related genes for which mRNA was identified to be upregulated during epithelial differentiation. HNF-4alpha was capable to transactivate the calbindin 3 gene promoter, a process that was synergistically increased in the presence of HNF-1alpha. When HNF-4alpha-expressing cells were plated on mesenchymal cells, an epithelial monolayer formed rapidly with the apparition of dome structures that are characteristics of vectorial ion transport. Forced expression of HNF-1alpha alone did not result in dome structures formation. In sum, this novel coculture system functionally identified for the first time HNF-4alpha as an important modulator of intestinal epithelial differentiation and offers an innovative opportunity to investigate molecular mechanisms involved in this process.

Ionic Melt Electroltyes for Lithium Battery Applictions

Ionic melt electrolytes consisting of lithium salts of fluorosulfonamide anions covalently attached to oligomeric polyether chains were synthesized and characterized with respect to structure and ion transport characteristics. Conductivity data are reported for melts of variable ether- oxygen-to-lithium ratio, and for melts having different amounts of polyether plasticizers added. Conductivities are generally high relative to true polymer electrolytes.

Lithium-Conducting Ionic Melt Electrolytes from Polyether-Functionalized Fluorosulfonimide Anions

Ionic melt electrolytes consisting of lithium salts of fluorosulfonamide and fluorosulfonate anions covalently attached to oligomeric polyether chains were synthesized and characterized with respect to structure and ion transport characteristics. Conductivities are high relative to true polymer electrolytes. Galvanostatic DC polarization studies suggest that salt concentration polarization does not occur in the ionic melt electrolytes, whereas it does occur in otherwise similar electrolytes consisting of binary lithium salts dissolved in a liquid oligomeric polyether solvent.

Energy landscapes for mobile ions in ion conducting solids

Structure property function relationships provide valuable guidelines in the systematic development of advanced functional materials with tailored properties. It is demonstrated that an augmented bond valence approach can be effectively used to establish such relationships for solid electrolytes. A bond valence analysis of local structure models for disordered systems or interfaces based on reverse Monte Carlo (RMC) fits or molecular dynamics (MD) simulations yields quantitative predictions of the ion transport characteristics. As demonstrated here for a range of metaphosphate and diborate glasses, the complete description of the energy landscape for mobile ions also provides an effective tool for achieving a more detailed understanding of ion transport in glasses. The investigation of time evolutions can be included, if the bond valence analysis is based on MD trajectories. In principle, this allows quantifying the time and temperature dependence of pathway characteristics, provided that a suitable empirical force-field is available. For the example of LiPO3, the remaining differences between simulated and experimental structures are investigated and a compensation method is discussed.