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Chloride Ions (chloride + ion)
Selected AbstractsEnhancement of Methanol Tolerance in DMFC Cathode: Addition of Chloride IonsCHEMPHYSCHEM, Issue 10 2008Sunghyun Uhm Dr. Abstract In the operation of a direct methanol fuel cell, the modification by chloride ions on the surface of a Pt cathode can facilitate the extraordinary increase of power performance and long-term stability. Analyzing the results of cyclic voltammograms and electrochemical impedance spectroscopy, the positive shift of Pt oxidation onset potential and the depression of oxidation current are observed, which results from the role of chloride as surface inhibitor. In addition, O2 temperature-programmed desorption and X-ray photoelectron spectroscopy also reveal that the suppression of Pt surface oxide can be best understood in terms of lower binding of oxygen species by the alteration of electronic state of Pt atoms. Such a reduced surface oxide formation not only provides more efficient proton adsorption sites with high selectivity but also decreases the mixed potential by crossover methanol, resulting in higher performance and stability even under high voltage long-term operation. [source] Gold(I) Complexes of P,N Ligands and Their Catalytic ActivityEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2010Chosu Khin Abstract Gold(I) complexes were readily prepared by reaction of the respective ligands with (Me2S)AuCl in CH2Cl2. Complexes of formula LAuCl {L = diphenyl(2-pyridyl)phosphane (PPh2Py), (R)-(+)-4-[(2)-(diphenylphosphanyl)-1-naphthyl]- N -[(R)-1-phenylethyl]-1-phthalazinamine (PINAP)} were obtained when a 1:1 molar ratio of ligand to starting gold precursor was used. When a 2:1 ratio of ligand to gold precursor was used with PPh2Py or MandyPhos as ligands, complexes of the type L2AuCl were obtained. All complexes were fully characterized, and single-crystal X-ray structures could be determined for four complexes. Chloride ions were removed by reaction with silver salts, such as AgNTf2, AgOTf and AgBF4, for the use of these complexes as catalysts. After the catalytic reaction with alkynes and alcohols in acetonitrile, a unique trinuclear gold(I) complex derived from [(PPh2Py)Au]BF4 could be characterized by X-ray structural analysis, showing a mode of catalyst deactivation. [source] Influence of complexation with chloride on the responses of a lux-marked bacteria bioassay to cadmium, copper, lead, and mercuryENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2000Charoon Sarin Abstract The toxicity of a heavy metal in solution to a microorganism depends not only on its concentration but also on pH and the concentrations of any aqueous complexing ligands in the microorganism's environment. This paper reports on the use of different inorganic resuscitation media and effect of the chloride ion, Cl,, on the bioluminescence response of a bacterial biosensor, Escherichia coli HB101 (pUCD607), to four metals: Cd, Cu, Hg, and Pb. The toxicity tests were conducted at pH 4, using 0.1 M KNO3 as resuscitation medium and adding KCl to investigate effect of Cl, concentration. The species distributions of metals as a function of Cl, concentration were calculated using GeoChem-PC. Resuscitation in 0.1 M KC1 gave significantly higher light output than that in 0.1 M KNO3, demonstrating that Cl, in the resuscitation medium has a direct effect on the bioluminescence response of the E. coli biosensor. Increasing concentrations of Cl, ions increased the toxicity of Hg, apparently because of the formation of HgCl,3, and increased the toxicity of Pb because of PbCl+ formation. The toxicity of Cu decreased at high Cl, concentrations as free Cu2+ decreased, in accordance with the free ion model. Concentrations of Cl, had no significant effect on the toxicity of Cd. This study clearly demonstrates that the chloro-complexes of some heavy metals can be toxic and, for Pb and Hg, more toxic than the free ion. [source] Monomeric and Dimeric Copper(II) Complexes of a Pyrrole-Containing Tridentate Schiff-Base LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2009Rongqing Li Abstract Three copper(II) complexes of (L1),, [CuL1Cl] (1), [CuL1Br]n (2) and [Cu2(L1)2(,1,3 -NCS)2] (3), and two copper(II) complexes of HL1, [Cu(HL1)X2] (X = Cl,, 4; X = Br,, 5), have been prepared and characterised [where HL1 is the Schiff-base ligand derived from pyrrole-2-carbaldehyde and 2-aminomethylpyridine]. The removal of a chloride ion and deprotonation of [Cu(HL1)Cl2] (4) to form [CuL1Cl] (1) worked well. However, attempts to protonate [CuL1Cl] with HCl to re-form [Cu(HL1)Cl2] were not successful. X-ray structure determinations revealed that 1 is a N3Cl-coordinated square-planar copper(II) monomer [CuL1Cl], whereas 3 is a doubly end-to-end thiocyanate-bridged square-pyramidal copper(II) dimer [Cu2(L1)2(,1,3 -NCS)2]. The structure determinations on 4 and 5 showed that in both cases the copper(II) ion is in a distorted square-planar N2X2 environment, with the pyrrole NH remaining non-deprotonated and uncoordinated. Variable-temperature magnetic susceptibility investigations carried out on the end-to-end thiocyanate doubly bridged square-pyramidal copper(II) dimer 3 showed that no magnetic coupling occurs between the two copper(II) ions; it exhibits Curie-like magnetic behaviour.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Kinetics and mechanism of oxidation of antimony(III) by keggin-type 12-tungstocobaltate(III) in aqueous hydrochloric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003B. D. Bhosale The reaction between Sb(III) and [CoIIIW12O40]5, proceeds with two, one-electron steps; formation of unstable Sb(IV) is the slow first step followed by its reaction with another oxidant in a fast step. The reaction rate is unaffected by the [H+] as there are no protonation equlibria involved with both the reactants, whereas the accelerating effect of chloride ion is due to the formation of an active chlorocomplex of the reductant, SbCl63,. Increase in the ionic strength and decrease in the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer-sphere complex between the reactants. The activation parameters were also determined and these values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 9,14, 2003 [source] Kinetics and mechanism of oxidation of aurate(I) by peroxydisulphate in aqueous hydrochloric acidINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2002R. M. Babshet The reaction between Au(I), generated by reaction of thallium(I) with Au(III), and peroxydisulphate was studied in 5 mol dm,3 hydrochloric acid. The reaction proceeds with the formation of an ion-pair between peroxydisulphate and chloride ion as the Michealis,Menten plot was linear with intercept. The ion-pair thus formed oxidizes AuCl2, in a slow two-electron transfer step without any formation of free radicals. The ion-pair formation constant and the rate constant for the slow step were determined as 113 ± 20 dm,3 mol,1 and 5.0 ± 1.0 × 10,2 dm3 mol,1 s,1, respectively. The reaction was retarded by hydrogen ion, and formation of unreactive protonated form of the reductant, HAuCl2, causes the rate inhibition. From the hydrogen ion dependence of the reaction rate, the protonation constant was calculated to be as 0.6 ± 0.1 dm3 mol,1. The activation parameters were determined and the values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 589,594, 2002 [source] Antibacterial activity of novel insoluble bead-shaped polymer-supported multiquaternary ammonium saltsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010E. Murugan Abstract This study describes the effect of antibacterial activity of newly reported five different novel insoluble bead-shaped polymer-supported multiquaternary ammonium salts (PM quats) viz., bis-quat, tris-quat (2 Nos.), tetrakis-quat, hexakis-quat containing two, three, four, and six quaternary ammonium groups, respectively. The presence of number of quaternary ammonium groups in each salt was established already through Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and chloride ion analyzes. The antibacterial activities of these five different PM quats against three different bacteria viz., Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa were investigated by serial dilution and spread plate method and compared the same with a monoquat containing single quaternary ammonium group. The extent of antibacterial activity has been measured in terms of colony forming units (CFU) at different time intervals. The observed results show that all the PM quats exhibited excellent-antibacterial activity against each bacterium. On the basis of the CFU values, the antibacterial activity was found to increase from bis-quat to hexakis-quat, which reveals that the activity of PM quats increases with increase in the number of quaternary ammonium groups. The mechanism of interaction of quats with bacterial cytoplasmic membrane has been explained as an adsorption-like phenomenon. The reusability of highly active hexakis-quat against Staphylococcus aureus was studied and the activity was found to reduce after first cycle. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effect of chloride ion on dissolution of different salt forms of haloperidol, a model basic drugJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2005Shoufeng Li Abstract The effect of chloride ion (Cl,) on dissolution rates of hydrochloride, mesylate (methanesulfonate) and phosphate salt forms of a model drug, haloperidol, was investigated. The dissolution rates of the salts in 0.01M HCl from rotating disks followed the order of mesylate,,,phosphate,>,hydrochloride. With additional chloride ion, a decrease in dissolution rate of the hydrochloride salt was observed due to the common ion effect. Dissolution rates of mesylate and phosphate salts also decreased due to their conversion to the HCl salt form on the surfaces of dissolving disks, however, the dissolution rates of mesylate and phosphate salts under identical chloride ion concentrations were still higher than that of the HCl salt. In powder dissolution studies, it was observed that kinetics of nonhydrochloride-to-hydrochloride salt conversion play a major role in dissolution; the mesylate dissolved completely (<5 min) before its dissolution rate could be impeded by its conversion to the hydrochloride salt form. Therefore, despite the potential for conversion to a hydrochloride salt form, certain nonhydrochloride salt forms may still be preferred for dosage form development due to kinetic advantages during dissolution, such as higher apparent dissolution rate of a nonhydrochloride salt before it could completely convert to the hydrochloride form. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2224,2231, 2005 [source] The Hammett equation applied to the nucleophilic displacement of ions and ion pairs on substituted benzenesulphonatesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2001Sergio Alunni Abstract Nucleophilic substitution on meta - and para -substituted methyl benzenesulphonates was studied with two chloride salts with different structures: NBu4Cl or KCl-Kryptofix 2,2,2. Treating the results with the Acree equation shows that the reaction proceeds by two reaction paths, one involving the chloride ion and the other, slower one, involving the ion pairs. Treating the results with the Hammett equation gives consistent data, and shows that , is positive and nearly the same for the two reaction paths (,,,,+2). The reactivity of methyl p -nitrobenzenesulphonate was compared with that of the corresponding ethyl derivative, and it is shown that the methyl derivative reacts faster than the ethyl derivative in both paths. The results are interpreted based on the assumption that in both paths a negative charge is developed on the leaving group in the transition state, and that the activated complex is linear. Copyright © 2001 John Wiley and Sons, Ltd. [source] Protein,Protein Interaction of a Pharaonis Halorhodopsin Mutant Forming a Complex with Pharaonis Halobacterial Transducer Protein II Detected by Fourier-Transform Infrared Spectroscopy,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Yuji Furutani Pharaonis halorhodopsin (pHR) functions as a light-driven inward chloride ion pump in Natoronomonas pharaonis, while pharaonis phoborhodopsin (ppR; also called pharaonis sensory rhodopsin II, pSRII), is a light sensor for negative phototaxis. ppR forms a 2:2 complex with its cognate transducer protein (pHtrII) through intramembranous hydrogen bonds: Tyr199ppR,Asn74pHtrII and Thr189ppR,Glu43 pHtrII, Ser62pHtrII. It was reported that a pHR mutant (P240T/F250Y), which possesses the hydrogen-bonding sites, impairs its pumping activity upon complexation with pHtrII. In this study, effect of the complexation with pHtrII on the structural changes upon formation of the K, L1 and L2 intermediates of pHR was investigated by use of Fourier-transform infrared spectroscopy. The vibrational changes of Tyr250pHR and Asn74pHtrII were detected for the L1 and L2 intermediates, supporting that Tyr250pHR forms a hydrogen bond with Asn74pHtrII as similarly to Tyr199ppR. The conformational changes of the retinal chromophore were never affected by complexation with pHtrII, but amide-I vibrations were clearly different in the absence and presence of pHtrII. The molecular environment around Asp156pHR in helix D is also slightly affected. These additional structural changes are probably related to blocking of translocation of a chloride ion from the extracellular to the cytoplasmic side during the photocycle. [source] Electrochemical Deodorization and Disinfection of Hog ManureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2007Dorin Bejan Abstract Electrolysis of liquid hog manure under direct current achieved amelioration of odour, in terms of both odour quality and odour intensity, and simultaneously reduced the population of odour-causing bacteria by two orders of magnitude. A comparison of anode materials indicated that hydroxyl radical-forming anodes (boron-doped diamond and Ebonex) were the most effective, but unfortunately these materials are not yet available commercially in large size format. Dimensionally stable anodes composed of Ti/IrO2 were found to be satisfactory; lead-based anodes leached unacceptable quantities of inorganic lead into the treated manure, and graphite anodes tended to disintegrate on long-term use. The mechanism of action of the bactericidal effect involves a combination of toxicity by O2 that is released at the anode and hypochlorination due to the chloride ion that is present in manure. The proposed technology was shown to be successful at the 27 L scale in an on-farm demonstration. L'électrolyse du purin de porc liquide avec un courant continu a permis d'améliorer l'odeur, tant en qualité qu'en intensité, et simultanément, de réduire la population de bactéries à l'origine de l'odeur de deux ordres de grandeur. Une comparaison des matériaux anodiques indique que les anodes formant des radicaux libres d'hydroxyle (diamant amélioré au bore et Ebonex) sont les plus efficaces, mais malheureusement ces matériaux ne sont pas encore disponibles en grand quantité dans le commerce. On a trouvé que des anodes dimensionnellement stables composées de Ti/IrO2 étaient satisfaisantes, tandis que les anodes à base de plomb ont donné des quantités inacceptables de plomb lixivié non organique dans le purin traité et les anodes graphites tendent à se désintégrer avec une utilisation prolongée. Le mécanisme d'action de l'effet bactéricide implique une combinaison de toxicité par l'O2 qui est libéré à l'anode et par l'hypochloruration à cause de l'ion de chlorure présent dans le purin. On montre que la technologie proposée est un succès dans une démonstration à l'échelle de 27 L dans une ferme [source] {[SmCl(en)4][In2Te4]}n: an indium telluride with a one-dimensional sinusoidal chainACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Chun-Ying Li The title compound, catena -poly[[chloridotetrakis(ethylenediamine-,2N,N,)samarium(III)] [indium(III)-di-,-tellurido-indium(III)-di-,-tellurido]], {[SmCl(C2H8N2)4][In2Te4]}n, consists of a one-dimensional sinusoidal {[InTe2],}n anionic chain and [SmCl(en)4]2+ cations (en is ethylenediamine). The only other previously reported lanthanide analogue, viz. [LaCl(en)4][In2Te4], contains more usual linear one-dimensional {[InTe2],}n anion chains [Chen, Li, Chen & Proserpio (1998). Inorg. Chim. Acta, 273, 255,258]. The one-dimensional polymeric {[InTe2],}n chain is built of InTe4 tetrahedra sharing opposite edges. The SmIII ion in the [SmCl(en)4]2+ cation is nine-coordinated by eight N atoms from four bidentate en molecules and by one chloride ion to form a monocapped square-antiprismatic geometry. The presence or absence of N,H...Cl hydrogen bonding is shown to affect the conformation of the anion. [source] Getting the best out of long-wavelength X-rays: de novo chlorine/sulfur SAD phasing of a structural protein from ATVACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2010Adeline Goulet The structure of a 14,kDa structural protein from Acidianus two-tailed virus (ATV) was solved by single-wavelength anomalous diffraction (SAD) phasing using X-ray data collected at 2.0,Å wavelength. Although the anomalous signal from methionine sulfurs was expected to suffice to solve the structure, one chloride ion turned out to be essential to achieve phasing. The minimal data requirements and the relative contributions of the Cl and S atoms to phasing are discussed. This work supports the feasibility of a systematic approach for the solution of protein crystal structures by SAD based on intrinsic protein light atoms along with associated chloride ions from the solvent. In such cases, data collection at long wavelengths may be a time-efficient alternative to selenomethionine substitution and heavy-atom derivatization. [source] The structure of Vibrio cholerae extracellular endonuclease I reveals the presence of a buried chloride ionACTA CRYSTALLOGRAPHICA SECTION D, Issue 11 2006Bjørn Altermark The crystal structure of a periplasmic/extracellular endonuclease from Vibrio cholerae has been solved at low and at neutral pH. Crystals grown at pH 4.6 and 6.9 diffracted to 1.6,Å (on BM01A at the ESRF) and 1.95,Å (on a rotating-anode generator), respectively. The structures of the endonuclease were compared with the structure of a homologous enzyme in V. vulnificus. The structures of the V. cholerae enzyme at different pH values are essentially identical to each other and to the V. vulnificus enzyme. However, interesting features were observed in the solvent structures. Both V. cholerae structures reveal the presence of a chloride ion completely buried within the core of the protein, with the nearest solvent molecule approximately 7,Å away. Magnesium, which is essential for catalysis, is present in the structure at neutral pH, but is absent at low pH, and may partly explain the inactivity of the enzyme at lower pH. [source] Structure of pig heart citrate synthase at 1.78,Å resolutionACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2009Steven B. Larson Pig heart citrate synthase was crystallized from a small-molecule cocktail containing cystamine dihydrochloride, aspartame and benzamidine hydrochloride. The structure was refined to an R factor of 0.179 (Rfree = 0.222) using synchrotron data to a resolution of 1.78,Å. The model includes the full-length protein, a chloride ion, a sulfate ion, 305 water molecules and an unexpected moiety attached through a disulfide linkage to Cys184, which was modeled as a half-cystamine molecule generated by disulfide exchange with the cystamine in the small-molecule cocktail. [source] Diastereo- and Enantioselective Intramolecular [2+2],Photocycloaddition Reactions of 3-(,,-Alkenyl)- and 3-(,,-Alkenyloxy)-Substituted 5,6-Dihydro-1H -pyridin-2-onesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2010Dominik Albrecht Dr. Abstract 3-(,,-Alkenyl)-substituted 5,6-dihydro-1H -pyridin-2-ones 2,4 were prepared as photocycloaddition precursors either by cross-coupling from 3-iodo-5,6-dihydro-1H -pyridin-2-one (8) or,more favorably,from the corresponding ,-(,,-alkenyl)-substituted ,-valerolactams 9,11 by a selenylation/elimination sequence (56,62,% overall yield). 3-(,,-Alkenyloxy)-substituted 5,6-dihydro-1H -pyridin-2-ones 5 and 6 were accessible in 43 and 37,% overall yield from 3-diazopiperidin-2-one (15) by an ,,,-chloroselenylation reaction at the 3-position followed by nucleophilic displacement of a chloride ion with an ,-alkenolate and oxidative elimination of selenoxide. Upon irradiation at ,=254,nm, the precursor compounds underwent a clean intramolecular [2+2] photocycloaddition reaction. Substrates 2 and 5, tethered by a two-atom chain, exclusively delivered the respective crossed products 19 and 20, and substrates 3, 5, and 6, tethered by longer chains, gave the straight products 21,23. The completely regio- and diastereoselective photocycloaddition reactions proceeded in 63,83,% yield. Irradiation in the presence of the chiral templates (,)- 1 and (+)- 31 at ,75,°C in toluene rendered the reactions enantioselective with selectivities varying between 40 and 85,%,ee. Truncated template rac - 31 was prepared as a noranalogue of the well-established template 1 in eight steps and 56,% yield from the Kemp triacid (24). Subsequent resolution delivered the enantiomerically pure templates (,)- 31 and (+)- 31. The outcome of the reactions is compared to the results achieved with 4-substituted 5,6-dihydro-1H -pyridin-2-ones and quinolones. [source] Role of the two type II myosins, Myo2 and Myp2, in cytokinetic actomyosin ring formation and function in fission yeastCYTOSKELETON, Issue 3 2003Daniel P. Mulvihill Abstract The formation and contraction of a cytokinetic actomyosin ring (CAR) is essential for the execution of cytokinesis in fission yeast. Unlike most organisms in which its composition has been investigated, the fission yeast CAR contains two type II myosins encoded by the genes myo2+ and myp2+. myo2+ is an essential gene whilst myp2+ is dispensable under normal growth conditions. Myo2 is hence the major contractile protein of the CAR whilst Myp2 plays a more subtle and, as yet, incompletely documented role. Using a fission yeast strain in which the chromosomal copy of the myo2+ gene is fused to the gene encoding green fluorescent protein (GFP), we analysed CAR formation and function in the presence and absence of Myp2. No change in the rate of CAR contraction was observed when Myp2 was absent although the CAR persisted longer in the contracted state and was occasionally observed to split into two discrete rings. This was also observed in myp2, cells following actin depolymerisation with latrunculin. CAR contraction in the absence of Myp2 was completely abolished in the presence of elevated levels of chloride ions. Thus, Myp2 appears to contribute to the stability of the CAR, in particular at a late stage of CAR contraction, and to be a component of the signalling pathway that regulates cytokinesis in response to elevated levels of chloride. To determine whether the presence of two type II myosins was a feature of cytokinesis in other fungi that divide by septation, we searched the genomes of two filamentous fungi, Aspergillus fumigatus and Neurospora crassa, for myosin genes. As in fission yeast, both A. fumigatus and N. crassa contained myosins of classes I, II, and V. Unlike fission yeast, both contained a single type II myosin gene that, on the basis of its tail structure, was more reminiscent of Myp2 than Myo2. The significance of these observations to our understanding of septum to formation and cleavage is discussed. Cell Motil. Cytoskeleton 54:208,216, 2003. © 2003 Wiley-Liss, Inc. [source] Optimization of the Composition of Interfaces in Miniature Planar Chloride ElectrodesELECTROANALYSIS, Issue 15-16 2003Renata Paciorek Abstract Different solid contact arrangements for miniature screen-printed electrodes and silicon based electrodes for chloride ions were investigated. As an inner contact the electrochemically deposited gold on screen-printed silver and platinum (silicon based electrodes) were used. As the ion-exchanger for chloride methyl-tri- n -tetradecylammonium chloride with PVC or Tecoflex as the polymer matrix was used. The influence of different intermediate layers between inner contact and the ion selective membrane was studied. The best characteristic of the electrode was obtained for electrodes containing gold contact and conductive polymer (poly-3-octylthiophene) with adhesive admixture between the inner contact and the proper ion selective membrane. [source] Dual stacking of unbuffered saline samples, transient isotachophoresis plus induced pH junction focusingELECTROPHORESIS, Issue 10 2003Sang-Hee Shim Abstract A dual stacking mechanism based on transient isotachophoresis (TITP) and induced pH junction focusing is demonstrated as a means to increase the concentration sensitivity in capillary electrophoresis of highly saline samples. When stacking was carried out with an unbuffered saline sample of fluorescein between two zones of low mobility background electrolyte at high pH under an electric field of reverse polarity, two transient peaks at both boundaries of the sample zone were observed. One peak at the rear boundary could be inferred as a transient isotachophoretic stacked zone. Through computer simulations of an unbuffered sample with a high concentration of sodium chloride, we showed that the fast moving zones of sodium and chloride ions induced pH changes at both boundaries to satisfy the electroneutrality condition and that the peak at the front boundary was due to the induced pH junction. To verify the pH changes, an indicator, thymol blue, was added to an NaCl solution and the color changes under an electric field were observed. The proposed mechanism was supported by observing the dual stacking procedure for an unbuffered sample of 4-nitrophenol and measuring additional sensitivity enhancements by dual stacking for ten weakly acidic compounds. For the ten analytes including nucleoside phosphates, every dual stacking of an unbuffered sample exhibited an additional enhancement up to 86% larger than that of usual transient isotachophoresis of the corresponding buffered sample without loss of separation efficiency and reproducibility. Therefore, it would be useful to skip over buffering in sample preparation for TITP, contrary to the general recommendation. [source] THIS ARTICLE HAS BEEN RETRACTED Tn5530 from Burkholderia cepacia strain 2a encodes a chloride channel protein essential for the catabolism of 2,4-dichlorophenoxyacetic acidENVIRONMENTAL MICROBIOLOGY, Issue 1 2007Antonio Sebastianelli Summary Chloride channel proteins (ClC) are found in living systems where they transport chloride ions across cell membranes. Recently, the structure/function of two prokaryotic ClC has been determined but little is known about the role of these proteins in the microbial metabolism of chlorinated compounds. Here we show that transposon Tn5530 from Burkholderia cepacia strain 2a encodes a ClC protein (BcClC) which is responsible for expelling Cl, ions generated during the catabolism of 2,4-dichlorophenoxyacetic acid (a chlorinated herbicide). We found that BcClC has the ability to transport Cl, ions across reconstituted proteoliposome membranes. We created two mutants in which the intrachannel glutamate residue of the protein, known to be responsible for opening and closing the channel (i.e. gating), was changed in order to create constitutively open and closed forms. We observed that cells carrying the closed-channel protein accumulated Cl, ions intracellularly leading to a decrease in intracellular pH, cell stasis and death. Further, we established that BcClC has the same gating mechanism as that reported for the ClC protein from Salmonella typhimurium. Our results show that the physiological role of ClC is to maintain cellular homeostasis which can be impaired by the catabolism of chlorinated compounds. [source] Oxidation kinetics of pentachlorophenol by manganese dioxideENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2006Ling Zhao Abstract This study examined the abiotic transformation kinetics of pentachlorophenol (PCP) by manganese dioxide (MnO2) at different solution chemistry and initial concentrations of PCP and MnO2. The measured PCP transformation rates were found to be on the order of 1.07 with respect to [PCP] and 0.91 and 0.87 with respect to [MnO2] and [H+], respectively. Dissolved Mn2+ and Ca2+ as background electrolytes considerably decreased the reaction rate because of their adsorption and hence blocking of active sites on MnO2 surfaces. The dechlorination number, 0.59 chloride ions per transformed PCP after a 1-h reaction, suggests that a fraction of the transformed PCP was not dechlorinated and may be coupled directly to dimeric products. Gas chromatography/ mass spectrometry and liquid chromatography/mass spectrometry/mass spectrometry techniques were used to identify two isomeric nonachlorohydroxybiphenylethers as major products and 2,3,5,6-tetrachloro-1,4-hydroquinone and tetrachlorocatechol as minor products. Product identification suggested that the reaction may include two parallel reactions to form either dimers or 2,3,5,6-tetrachloro-1,4-hydroquinone and tetrachlorocatechol via simultaneous dehydrochlorination and hydroxylation. [source] Chemical and Electrochemical Behaviours of a New Phenolato-Bridged Complex [(L)MnIIMnII(L)]2+.EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006Dinuclear Mono-µ-Oxido [(L)MnIII(µ-O)MnIII/IV(L)]2+/3+ Species, Pathways to Mononuclear Chlorido [(L)MnII/III/IVCl]0/1/2+ Abstract The X-ray structure of a new dinuclear phenolato-bridged Mn2II complex abbreviated as [(L)MnMn(L)]2+ (1), where LH is the [N4O] phenol containing ligand N,N -bis(2-pyridylmethyl)- N, -salicylidene-ethane-1,2-diamine ligand, is reported. A J value of ,3.3 cm,1 (H = ,J,1·,2) was determined from the magnetic measurements and the 9.4 GHz EPR spectra of both powder and frozen acetonitrile solution samples were analyzed with temperature. The cyclic voltammetry of 1 displays a reversible anodic wave at E1/2 = 0.46 V vs. SCE associated with the two-electron oxidation of 1 yielding the dinuclear Mn2III complex [(L)MnMn(L)]4+ (2). The easy air oxidation of 1 gives the mono-,-oxido Mn2III complex [(L)Mn(, - O)Mn(L)]2+ (3). A rational route to the formation of the mixed-valence Mn2III,IV complex [(L)Mn(, - O)Mn(L)]3+ (4) starting from 1 by bulk electrolysis at EP = 0.75 V vs. SCE in the presence of one equiv. of base per manganese ion is also briefly reported. Addition of chloride ions to 1 led to the cleavage of the phenolato bridges to give the mononuclear MnII complex [(L)MnCl] (5). Cyclic voltammetry of 5 displays two reversible anodic waves at E1/2 = 0.21 and E1/2 = 1.15 V vs. SCE, assigned to the two successive one-electron abstractions giving the MnIII and MnIV species [(L)MnCl]+ (6) and [(L)MnCl]2+ (7), respectively. The electronic signatures from UV/Visible and EPR spectroscopy of the electrochemically prepared samples of 6 and 7 confirmed the respective oxidation states. For instance, 7 displays a broad and intense absorption band characteristic of a phenolato to MnIV charge-transfer transition at 690 nm (2000 M,1,cm,1) and its 9.4 GHz EPR spectrum shows a strong transition at g = 5.2 consistent with a rhombically distorted S = 3/2 system with a zero-field splitting dominating the Zeeman effect. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Small-angle X-ray scattering study of the smart thermo-optical behavior of zirconyl aqueous colloidsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000L.A. Chiavacci The smart thermo-optical systems studied here are based on the unusual thermoreversible sol-gel transition of zirconyl chloride aqueous solution modified by sulfuric acid in the molar ratio Zr/SO4:3/1. The transparency to the visible light changes during heating due to light scattering. This feature is related to the aggregates growth that occurs during gelation. These reversible changes can be controlled by the amount of chloride ions in solution. The thermoreversible sol-gel transition temperature increases from 323 to 343 K by decreasing the molar ratio Cl/Zr from 7.0 to 1.3. In this work the effect of the concentration of chloride ions on the structural characteristics of the system has been analyzed by in situ SAXS measurements during the sol-gel transition carried out at 323 and 333 K. The experimental SAXS curves of sols exhibit three regions at small, medium and high scattering vectors characteristics of Guinier, fractal and Porod regimes, respectively. The radius of primary particles, obtained from the crossover between the fractal and Porod regimes, remains almost invariable with the chloride concentration, and the value (4 Å) is consistent with the size of the molecular precursor. During the sol-gel transition the aggregates grow with a fractal structure and the fractal dimensionality decreases from 2.4 to 1.8. This last value is characteristic of a cluster-cluster aggregation controlled by a diffusion process. Furthermore, the time exponent of aggregate growth presents values of 0.33 and 1, typical of diffusional and hydrodynamic motions. A crossover between these two regimes is observed. [source] Synthesis of anion exchange polystyrene membranes for the electrolysis of sodium chlorideAICHE JOURNAL, Issue 4 2008Sonny Sachdeva Abstract We have prepared a cross-linked polystyrene anion exchange composite membrane for the electrolysis of sodium chloride to produce sodium hydroxide by selective removal of chloride ions. The composite membrane is homogeneously modified by gas phase nitration, followed by amination using hydrazine hydrate, and further reaction with dichloroethane and triethylamine to introduce quaternary ammonium charges on it. We showed that the membrane is specific to the transport of chloride ions through its pores. The performance of the membrane has been evaluated in terms of current efficiency and power consumption, and the effect of various parameters like current density, initial salt concentration, and circulation rate is studied. The maximum current efficiency obtained is 96.5% and the corresponding power consumption is 0.1216 kWh/mol at 5.2 N initial salt concentration and current density of 254 A/m2. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chlorideJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2008Alexander Schöning Abstract The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH4NO3 and 0.5 M NH4Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl2) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one-to-one. However, for all heavy metals NH4Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH4Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl2) values and/or contents of OC were taken into account. In comparison to NH4Cl, NH4NO3 proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH4NO3 is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation-exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH4NO3 method. However, the applicability of the NH4NO3 method to other soils still needs to be investigated. [source] A SERS probe of adenyl residues available for intermolecular interactions.JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2001Part I, adenyl, fingerprint' This work validated a SERS probe able to compare adenyl reactivity in DNA and RNA. A Creighton silver colloid including adenine (A) [or 2, -deoxyadenosine 5, -phosphate (pdA)] from 2 × 10,3 to 2 × 10,8M is stabilized in the absence or presence of chloride. Concentration-dependent SER spectral profiles reveal how A may interact with (Ag)n+ sites. At concentration ,2 × 10,5M adsorption of (A)n clusters prevents the colloid from undergoing salt effects. Adsorption via N1/N3 is allowed whereas C6NH2 is involved in self-association. At [A] <2 × 10,5M with chloride, hydrogen bonding between chloride and the C6NH2 group enhances C6N electronegativity, which assists C6N/N7 cooperative adsorption. Complex A(Cl,) entities compete with individual chloride ions for adsorption on silver. Very similar C6N/N7 adenyl adsorption occurs for pdA but only above 2 × 10,5M. Chloride,adenyl bonding is reduced and pdA self-association is weaker than adenine self-association. Steric factors, repulsive electrostatic forces and phosphate competitive reactivity with respect to chloride may explain the much higher pdA concentration needed to saturate the silver surface compared with A. Mg2+,phosphate complexation entails concentration-dependent opposite effects on adenyl reactivity with (Ag)n+ sites. Cytosine, thymine and guanine base or corresponding nucleotides deliver weaker SER spectra and much higher SERS responses for chloride adsorption compared with A or pdA. This reveals a weaker adsorption of the oxo bases, assumed to result from alternative oxo and nitrogen interactions with the (Ag)n+ sites. Copyright © 2001 John Wiley & Sons, Ltd. [source] EXAFS characterization of oxaliplatin anticancer drug and its degradation in chloride mediaJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2006Diane Bouvet Oxaliplatin is a second-generation platinum-based anticancer drug. Its degradation is studied in solution, in the presence of chloride ions (in neutral or acidic media) in excess. In both cases the degradation product precipitates immediately. The EXAFS spectra of these products show that they are identical. EXAFS modeling and refinement of the first coordination sphere shows that two light atoms are replaced by two chloride ions. The complete refinement of the local structure is possible by studying the multiple-scattering signal. The results show that the main multiple-scattering contribution is due to the binding oxalato group and that the degradation product is [Cl2 -(diaminocyclohexane)-Pt(II)]. [source] Molecular Dynamics Simulations of the Orientation and Reorientational Dynamics of Water and Polypyrrole Rings as a Function of the Oxidation State of the PolymerMACROMOLECULAR THEORY AND SIMULATIONS, Issue 1 2005Jose J. López Cascales Abstract Summary: Polypyrrole is one of the most widely-studied conducting polymers due to its steady electrochemical response and good chemical stability in different solvents, including organic and inorganic ones. In this work, we provide for the first time valuable information in atomic detail concerning the steady and dynamic properties of pyrrole rings as a function of the oxidation state of the polymer. The study was carried out by Classical molecular dynamics simulation, where the system was modelled by 256 polypyrrole chains of 10 pyrrole rings each. Water was explicitly introduced in our simulations. Besides the uncharged or reduced state, two steady oxidation states of the polymer have been simulated by introducing a net charge (+1) on 85 and 256 of the polypyrrole chains. To balance the charges emerging in these oxidised states, 85 and 256 chloride ions (Cl,1) respectively, were introduced into the system. From an analysis of the simulated trajectories, the orientation and relaxation times of water and pyrrole rings were evaluated for the different oxidation states of the polymer across the polypyrrole/water interface. The calculated densities for different oxidation states describe the swelling or shrinking process during electrochemical oxidation or reduction respectively. The rotational relaxation times calculated for the polypyrrole rings decrease with increasing oxidation of the polymer, which is in a good agreement with experimental electrochemical data. Almost no variation in pyrrole ring orientation was measured for the different oxidation states of the polymer, even compared with polypyrrole bulk. As regards the water structure in the vicinity of the polypyrrole/water interface, both the orientation and orientation relaxation time were strongly affected by the presence of charges in the polymer. Thus, the water dipole was strongly orientated in the vicinity of the water/polypyrrole interface and its orientational relaxation time increased by one order of magnitude compared with bulk water, even when only one-third of the total polymer chains were oxidised. The results attained in this work were validated with experimental results, when they were available. Polypyrrole ring orientation and water orientation at the polypyrrole/water interface. (a) 256 rPPy and (b)171 rPPy,+,85 oPPy. [source] Electrochemical impedance spectroscopy study of surface films formed on copper in aqueous environmentsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2005A. Srivastava Abstract The electrochemical behavior of pure copper has been studied in aqueous environments using linear polarization and electrochemical impedance spectroscopy (EIS) techniques as a function of immersion time. The effect of pollutants (like chloride, sulfide and ammonium ions) on the nature of films formed on the copper surface has been studied. All the surfaces revealed the presence of a porous oxide layer. The corrosion resistance decreased with increasing amount of chloride ions. The addition of Na2S in the environments in the absence of any chloride species was beneficial for corrosion resistance. EIS data suggested that the capacitance of the films formed in chloride environments was higher. The surfaces obtained in presence of chloride ions were relatively rough and deeply attacked. The total impedance decreased after 432 h of immersion in solutions possessing chloride ions. The damaging role of chloride ions and the relatively less severe effect of sulfide ions were noted. [source] Inhibition of corrosion of AZ91 magnesium alloy in ethylene glycol solution in presence of chloride anionsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2005E. Slavcheva Abstract The influence of chloride ions on the corrosion of AZ91 magnesium alloy in water/ethylene glycol solutions and the inhibiting effect of lactobiono-tallowamide (LTA) were investigated using electrochemical and surface analysis methods. Potentiodynamic polarization curves in aqueous solution of ethylene glycol (50:50w%) containing 0.1 g.L,1 chloride and up to 0.5 g.L,1 LBT were obtained at room and at elevated temperatures. The chloride anions showed a distinct deteriorating effect as they caused pit initiation and accelerated the dissolution of the tested alloy. The selected organic compound demonstrated good protective properties against corrosion of AZ91 magnesium alloy and behaved as inhibitor of mixed type hindering both the cathodic and the anodic partial reactions. It showed inhibition efficiency of 77% at relatively low concentration of 0.2 g.L,1 and was considered as a promising corrosion inhibitor. The mechanism of inhibition was discussed on the basis of the electrochemical impedance spectroscopy (EIS) and XRD analysis of the surface. [source] | |||||||||||||||||||||||||||||||