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Anion Exchanger (anion + exchanger)
Selected AbstractsNovel Thorium Membrane Sensors with Anionic Response Based on Trioctylphosphine Oxide and Toluate IonophoresELECTROANALYSIS, Issue 19 2008Abstract Two novel potentiometric polymeric membrane sensors for rapid and accurate determination of thorium are described. These are based on the use of trioctylphosphine oxide (TOPO) and thorium toluate (Th-TA) as ionophores dispersed in poly(vinyl chloride) matrix membranes plasticized with nitrophenyloctyl ether. In strong nitric acid medium, Th(IV) nitrate is converted into [Th(NO3)6]2, complex and sensed as anionic divalent ion which exclude most cationic effect. Validation of the assay methods using the quality assurance standards (linearity range, accuracy, precision, within-day variability, between-day-repeatability, lower detection limit and sensitivity) reveals excellent performance characteristics of both sensors. The sensors exhibit near-Nernstian response for 1.0×10,6,1.0×10,1 M Th over the pH range 2.5,4.5. Calibration slopes of ,32.3±0.3 and ,27.2±0.2,mV/decade, precision of ±0.5 and ±0.8% and accuracy of 98.8±0.9 and 97.9±0.7% are obtained with TOPO and Th-TA based sensors, respectively. Negligible interferences are caused by most interfering mono-, di-, tri-, tetra-, penta-, and hexa-valent elements commonly associated with thorium in naturally occurring minerals and ores. High concentrations of Cl,, F,, SO42,, and NO3, ions have no diverse effect. Complete removal of the effect of the interferents in complex matrices is achieved by retention of [Th(NO3)6]2, complex from 5,M nitric acid/methanol mixture (1,:,9,v/v) on a strong anion exchanger, washing out the cationic interferents followed by stripping off thorium anion complex and measurements. Both sensors are used for determining thorium in certified thorium ore samples (20,120,mg Th/kg) and some naturally occurring ores (200,600,mg Th/kg). The results obtained agree fairly well with the certified labeled values or the data obtained using X-ray fluorescence spectrometry [source] Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device.ELECTROANALYSIS, Issue 5 2007Abstract Quaternized poly(4-vinylpyridine) (QPVP) has been incorporated as an anion exchanger into sol-gel derived silica films for use in a spectroelectrochemical sensor. The preparation, characteristics and performance of these films are described. The films, which are spin-coated onto the surface of a planar optically transparent electrode, are optically transparent and uniform. Scanning electron microscopy and spectroscopic ellipsometry have been used to examine film structure, thickness and optical properties. These films have been shown both spectroscopically and electrochemically to preconcentrate ferrocyanide, a model analyte for the sensor. The films can be regenerated for multiple measurements by exposure to 1,M KNO3. The effects of polymer molecular weight and storage conditions on film performance are described. The overall response of this film is comparable to the poly(dimethyldiallylammonium chloride)-silica films previously used for this sensor. [source] Novel Anion Exchangers for Electrodes with Improved Selectivity to Divalent AnionsELECTROANALYSIS, Issue 17 2004Vladimir Egorov Abstract It has been found that replacing of several long-chain alkyl substituents at the nitrogen atom of lipophilic quaternary ammonium salts (QAS) by methyls results in a dramatic increase of the potentiometric selectivity of ion-selective electrodes (ISE) with QAS-based plasticized PVC membranes to some divalent anions against the monovalent ones. The discussed effect of QAS cation nature on the potentiometric selectivity is also partly retained for ISE with neutral carrier-based membranes doped with QAS to provide anion permselectivity. This opens up new possibilities to control the potentiometric selectivity of ISE for divalent anions by the appropriate selection of the anion exchanger. [source] Bicarbonate-rich choleresis induced by secretin in normal rat is taurocholate-dependent and involves AE2 anion exchanger,HEPATOLOGY, Issue 2 2006Jesús M. Banales Canalicular bile is modified along bile ducts through reabsorptive and secretory processes regulated by nerves, bile salts, and hormones such as secretin. Secretin stimulates ductular cystic fibrosis transmembrane conductance regulator (CFTR),dependent Cl, efflux and subsequent biliary HCO3, secretion, possibly via Cl,/HCO3, anion exchange (AE). However, the contribution of secretin to bile regulation in the normal rat, the significance of choleretic bile salts in secretin effects, and the role of Cl,/HCO3, exchange in secretin-stimulated HCO3, secretion all remain unclear. Here, secretin was administered to normal rats with maintained bile acid pool via continuous taurocholate infusion. Bile flow and biliary HCO3, and Cl, excretion were monitored following intrabiliary retrograde fluxes of saline solutions with and without the Cl, channel inhibitor 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) or the Cl,/HCO3, exchange inhibitor 4,4,-diisothiocyanatostilbene-2,2,-disulfonic acid (DIDS). Secretin increased bile flow and biliary excretion of HCO3, and Cl,. Interestingly, secretin effects were not observed in the absence of taurocholate. Whereas secretin effects were all blocked by intrabiliary NPPB, DIDS only inhibited secretin-induced increases in bile flow and HCO3, excretion but not the increased Cl, excretion, revealing a role of biliary Cl,/HCO3, exchange in secretin-induced, bicarbonate-rich choleresis in normal rats. Finally, small hairpin RNA adenoviral constructs were used to demonstrate the involvement of the Na+ -independent anion exchanger 2 (AE2) through gene silencing in normal rat cholangiocytes. AE2 gene silencing caused a marked inhibition of unstimulated and secretin-stimulated Cl,/HCO3, exchange. In conclusion, maintenance of the bile acid pool is crucial for secretin to induce bicarbonate-rich choleresis in the normal rat and that this occurs via a chloride,bicarbonate exchange process consistent with AE2 function. (HEPATOLOGY 2006;43:266,275.) [source] Defective regulation of cholangiocyte Cl,/HCO,3 and Na+/H+ exchanger activities in primary biliary cirrhosisHEPATOLOGY, Issue 6 2002Saida Melero Primary biliary cirrhosis (PBC) is a disorder of unknown origin with autoimmune features. Recently, impaired biliary secretion of bicarbonate has been shown in patients with PBC. Here we have investigated whether bile duct epithelial cells isolated from PBC patients exhibit defects in transepithelial bicarbonate transport by analyzing the activities of 2 ion exchangers, Cl,/HCO,3 anion exchanger 2 (AE2) and Na+/H+ exchanger (NHE) in isolated cholangiocytes. AE2 and NHE activities were studied in basal conditions and after stimulation with cyclic adenosine monophosphate (cAMP) and extracellular adenosine triphosphate (ATP), respectively. Cholangiocytes were grown from needle liver biopsies from 12 PBC patients, 8 normal controls, and 9 patients with other liver diseases. Also, intrahepatic cholangiocytes were cultured after immunomagnetic isolation from normal liver tissue (n = 6), and from recipients undergoing liver transplantation for end-stage PBC (n = 9) and other forms of liver disease (n = 8). In needle-biopsy cholangiocytes, basal AE2 activity was significantly decreased in PBC as compared with normal livers and disease controls. In addition, we observed that though cAMP increased AE2 activity in cholangiocytes from both normal and non-PBC livers, this effect was absent in PBC cholangiocytes. Similarly, though in cholangiocytes from normal and disease control livers extracellular ATP induced a marked enhancement of NHE activity, cholangiocytes from PBC patients failed to respond to purinergic stimulation. In conclusion, our findings provide functional evidence that PBC cholangiocytes exhibit a widespread failure in the regulation of carriers involved in transepithelial H+/HCO,3 transport, thus, providing a molecular basis for the impaired bicarbonate secretion in this cholestatic syndrome. [source] Gastrin suppresses the interdependent expression of p16 and anion exchanger 1 favoring growth inhibition of gastric cancer cellsINTERNATIONAL JOURNAL OF CANCER, Issue 6 2010Hua Tian Abstract Our previous studies demonstrated that expression and interaction of p16 with anion exchanger 1 (AE1) in gastric cancer cells is correlated with progression and shorter survival of the cancer. In this article, the effects of gastrin on p16 and AE1 and its implication in prevention and treatment of gastric cancer were studied by molecular biology techniques, animal experiment and clinical analysis. The results showed that expression of p16 in human gastric body carcinoma was downregulated along with the progression of the cancer, suggesting the reverse correlations between gastrin and p16 in vivo. Further experiments indicated that gastrin suppressed the expression of p16 via the p16 promoter and thereafter resulted in the degradation of AE1 in gastric cancer cells. Silencing of AE1 or p16 significantly inhibited the proliferation of the cancer cells. Using a xenograft tumor model in nude mice, we showed that experimental systemic hypergastrinemia induced by the administration of omeprazole led to decreased expression of AE1 and p16 as well as to a marked growth inhibition of SGC7901 tumors. It is concluded that a moderate plasma gastrin level is beneficial to the growth inhibition of gastric cancer by suppressing the expression of AE1 and p16. This finding may have an important implication for the prevention and treatment of cancers arise in the gastric antrum. [source] Recovery of Limonoid Glucosides from Citrus MolassesJOURNAL OF FOOD SCIENCE, Issue 8 2002T.K. Schoch ABSTRACT: A method to recover multi-gram quantities of limonoid glucosides from citrus molasses using ion-exchange and styrene/divinylbenzene resins has been developed. A cation exchange resin is used to decolorize the molasses, while an anion exchanger is used to separate limonoid glucosides from other negatively charged compounds. Styrene/divinylbenzene resins are used to bind limonoid glucosides and remove water-soluble materials. The method affords approximately 5 grams of a water-soluble powder containing over 60% by weight limonoid glucosides per liter of molasses. An analysis of the efficiency of the method shows that less than 10% of the total limonoid glucosides are lost during recovery. [source] Molecular physiology of SLC4 anion exchangersEXPERIMENTAL PHYSIOLOGY, Issue 1 2006Seth L. Alper Plasmalemmal Cl,,HCO3, exchangers regulate intracellular pH and [Cl,] and cell volume. In polarized epithelial cells, they contribute also to transepithelial secretion and reabsorption of acid,base equivalents and of Cl,. Members of both the SLC4 and SLC26 mammalian gene families encode Na+ -independent Cl,,HCO3, exchangers. Human SLC4A1/AE1 mutations cause either the erythroid disorders spherocytic haemolytic anaemia or ovalocytosis, or distal renal tubular acidosis. SLC4A2/AE2 knockout mice die at weaning. Human SLC4A3/AE3 polymorphisms have been associated with seizure disorder. Although mammalian SLC4/AE polypeptides mediate only electroneutral Cl,,anion exchange, trout erythroid AE1 also promotes osmolyte transport and increased anion conductance. Mouse AE1 is required for DIDS-sensitive erythroid Cl, conductance, but definitive evidence for mediation of Cl, conductance is lacking. However, a single missense mutation allows AE1 to mediate both electrogenic SO42,,Cl, exchange or electroneutral, H+ -independent SO42,,SO42, exchange. In the Xenopus oocyte, the AE1 C-terminal cytoplasmic tail residues reported to bind carbonic anhydrase II are dispensable for Cl,,Cl, exchange, but required for Cl,,HCO3, exchange. AE2 is acutely and independently inhibited by intracellular and extracellular H+, and this regulation requires integrity of the most highly conserved sequence of the AE2 N-terminal cytoplasmic domain. Individual missense mutations within this and adjacent regions identify additional residues which acid-shift pHo sensitivity. These regions together are modelled to form contiguous surface patches on the AE2 cytoplasmic domain. In contrast, the N-terminal variant AE2c polypeptide exhibits an alkaline-shifted pHo sensitivity, as do certain transmembrane domain His mutants. AE2-mediated anion exchange is also stimulated by ammonium and by hypertonicity by a mechanism sensitive to inhibition by chelation of intracellular Ca2+ and by calmidazolium. This growing body of structure,function data, together with increased structural information, will advance mechanistic understanding of SLC4 anion exchangers. [source] Ion-exchange resins as drug delivery carriersJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2009Xiaodi Guo Abstract There are many reports in the literature referring to the utilization of drug bound to ion-exchange resin (drug,resinate), especially in the drug delivery area. Ion-exchange resin complexes, which can be prepared from both acidic and basic drugs, have been widely studied and marketed. Salts of cationic and anionic exchange resins are insoluble complexes in which drug release results from exchange of bound drug ions by ions normally present in body fluids. Resins used are polymers that contain appropriately substituted acidic groups, such as carboxylic and sulfonic for cation exchangers; or basic groups, such as quaternary ammonium group for anion exchangers. Variables relating to the resin are the exchange capacity; degree of cross-linking, which determines the permeability of the resin, its swelling potential, and the access of the exchange sites to the drug ion; the effective pKa of the exchanging group, which determines the exchange affinity; and the resin particle size, which controls accessibility to the exchange ions. In this review, the properties of ion-exchange resins, selection of drugs that lend themselves to such an approach, selection of the appropriate resin, preparation of drug,resinate, evaluation of drug release, recent developments of drug,resinates, and applications are discussed. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:3886,3902, 2009 [source] Monolithic poly(glycidyl methacrylate- co -divinylbenzene) capillary columns functionalized to strong anion exchangers for nucleotide and oligonucleotide separationJOURNAL OF SEPARATION SCIENCE, JSS, Issue 16 2006Wolfgang Wieder Abstract In the present work, poly(glycidyl methacrylate- co -divinylbenzene) monoliths were synthesized and further derivatized to obtain strong anion exchange supports. Capillary monoliths (65×0.2 mm id) were prepared in situ by copolymerization of glycidyl methacrylate and divinylbenzene, employing 1-decanol and tetrahydrofuran as porogens. The free epoxy groups were derivatized in a two step synthesis to obtain quaternary ammonium functionalities. On testing the pressure stability of the synthesized monolith, a highly linear dependence between flow rate and pressure drop was obtained, indicating the high stability of the material even at high flow rates. The morphology of the copolymer was investigated by scanning electron microscopy. Mercury intrusion porosimetry showed a narrow pore size distribution, having a maximum at 439 nm. On recording a van Deemter plot the number of theoretical plates per meter was found to be 59 324. The produced strong anion exchange monoliths turned out to be highly suitable for the separation of nucleotides and oligonucleotides. [source] Organic ion exchangers as beads.POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7-8 2006Synthesis, applications, characterization Abstract Two less explored strategies in the preparation of porous organic ion exchangers in bead form are presented in this paper: the preparation of macroporous strong base anion exchangers with N,N -diethyl-2-hydroxyethyl benzylammonium chloride units, a less explored chloromethylation reagent of the styrene-divinylbenzene copolymers being used, and the preparation of anion exchangers with primary amine groups by the aminolysis-hydrolysis reaction with 1,2-diaminoethane of the nitrile groups, contained in some porous copolymers of acrylonitrile-divinylbenzene, followed by the carboxymethylation of the primary amine groups to prepare chelating ion exchangers. The influence of porogen nature, monomers dilution and crosslinking degree on the properties of the ion exchangers was examined. Structural characterization, functionalization-morphology correlations, the ion exchange properties, and potential applications for the ion exchangers thus prepared have been discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||