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Sample records for cation exchange reactions

  1. Forging Colloidal Nanostructures via Cation Exchange Reactions

    PubMed Central

    2016-01-01

    Among the various postsynthesis treatments of colloidal nanocrystals that have been developed to date, transformations by cation exchange have recently emerged as an extremely versatile tool that has given access to a wide variety of materials and nanostructures. One notable example in this direction is represented by partial cation exchange, by which preformed nanocrystals can be either transformed to alloy nanocrystals or to various types of nanoheterostructures possessing core/shell, segmented, or striped architectures. In this review, we provide an up to date overview of the complex colloidal nanostructures that could be prepared so far by cation exchange. At the same time, the review gives an account of the fundamental thermodynamic and kinetic parameters governing these types of reactions, as they are currently understood, and outlines the main open issues and possible future developments in the field. PMID:26891471

  2. Cu Vacancies Boost Cation Exchange Reactions in Copper Selenide Nanocrystals

    PubMed Central

    2015-01-01

    We have investigated cation exchange reactions in copper selenide nanocrystals using two different divalent ions as guest cations (Zn2+ and Cd2+) and comparing the reactivity of close to stoichiometric (that is, Cu2Se) nanocrystals with that of nonstoichiometric (Cu2–xSe) nanocrystals, to gain insights into the mechanism of cation exchange at the nanoscale. We have found that the presence of a large density of copper vacancies significantly accelerated the exchange process at room temperature and corroborated vacancy diffusion as one of the main drivers in these reactions. Partially exchanged samples exhibited Janus-like heterostructures made of immiscible domains sharing epitaxial interfaces. No alloy or core–shell structures were observed. The role of phosphines, like tri-n-octylphosphine, in these reactions, is multifaceted: besides acting as selective solvating ligands for Cu+ ions exiting the nanoparticles during exchange, they also enable anion diffusion, by extracting an appreciable amount of selenium to the solution phase, which may further promote the exchange process. In reactions run at a higher temperature (150 °C), copper vacancies were quickly eliminated from the nanocrystals and major differences in Cu stoichiometries, as well as in reactivities, between the initial Cu2Se and Cu2–xSe samples were rapidly smoothed out. These experiments indicate that cation exchange, under the specific conditions of this work, is more efficient at room temperature than at higher temperature. PMID:26140622

  3. Alloyed Copper Chalcogenide Nanoplatelets via Partial Cation Exchange Reactions

    PubMed Central

    2014-01-01

    We report the synthesis of alloyed quaternary and quinary nanocrystals based on copper chalcogenides, namely, copper zinc selenide–sulfide (CZSeS), copper tin selenide–sulfide (CTSeS), and copper zinc tin selenide–sulfide (CZTSeS) nanoplatelets (NPLs) (∼20 nm wide) with tunable chemical composition. Our synthesis scheme consisted of two facile steps: i.e., the preparation of copper selenide–sulfide (Cu2–xSeyS1–y) platelet shaped nanocrystals via the colloidal route, followed by an in situ cation exchange reaction. During the latter step, the cation exchange proceeded through a partial replacement of copper ions by zinc or/and tin cations, yielding homogeneously alloyed nanocrystals with platelet shape. Overall, the chemical composition of the alloyed nanocrystals can easily be controlled by the amount of precursors that contain cations of interest (e.g., Zn, Sn) to be incorporated/alloyed. We have also optimized the reaction conditions that allow a complete preservation of the size, morphology, and crystal structure as that of the starting Cu2–xSeyS1–y NPLs. The alloyed NPLs were characterized by optical spectroscopy (UV–vis–NIR) and cyclic voltammetry (CV), which demonstrated tunability of their light absorption characteristics as well as their electrochemical band gaps. PMID:25050455

  4. Sn Cation Valency Dependence in Cation Exchange Reactions Involving Cu2-xSe Nanocrystals

    PubMed Central

    2014-01-01

    We studied cation exchange reactions in colloidal Cu2-xSe nanocrystals (NCs) involving the replacement of Cu+ cations with either Sn2+ or Sn4+ cations. This is a model system in several aspects: first, the +2 and +4 oxidation states for tin are relatively stable; in addition, the phase of the Cu2-xSe NCs remains cubic regardless of the degree of copper deficiency (that is, “x”) in the NC lattice. Also, Sn4+ ions are comparable in size to the Cu+ ions, while Sn2+ ones are much larger. We show here that the valency of the entering Sn ions dictates the structure and composition not only of the final products but also of the intermediate steps of the exchange. When Sn4+ cations are used, alloyed Cu2–4ySnySe NCs (with y ≤ 0.33) are formed as intermediates, with almost no distortion of the anion framework, apart from a small contraction. In this exchange reaction the final stoichiometry of the NCs cannot go beyond Cu0.66Sn0.33Se (that is Cu2SnSe3), as any further replacement of Cu+ cations with Sn4+ cations would require a drastic reorganization of the anion framework, which is not possible at the reaction conditions of the experiments. When instead Sn2+ cations are employed, SnSe NCs are formed, mostly in the orthorhombic phase, with significant, albeit not drastic, distortion of the anion framework. Intermediate steps in this exchange reaction are represented by Janus-type Cu2-xSe/SnSe heterostructures, with no Cu–Sn–Se alloys. PMID:25340627

  5. Simulated Transport of Three Cations Through Porous Media: Effect of Different Approaches to Modeling Cation Exchange Reactions

    NASA Astrophysics Data System (ADS)

    Grant, S. A.; Mansell, R. S.; Bloom, S. A.; Rhue, R. D.

    1995-01-01

    Batch cation exchange and column experiments were conducted to evaluate selectivity coefficients which have been suggested for describing cation exchange reactions in solute transport models. Vanselow selectivity coefficients were calculated for cation exchange equilibria with a cation resin and for equilibria reported in the literature with a Yolo loam soil. Experimental column data were compared with data from simulations generated by a numerical solute transport model to evaluate Vanselow, Gaines-Thomas, and statistical thermodynamic selectivity coefficients. With the cation resin, the statistical thermodynamic selectivity coefficient gave the most reliable estimate of column effluent cation concentrations. In a column packed with the Yolo loam soil, the Vanselow selectivity coefficient gave the most accurate prediction of column response. Use of variable (as opposed to fixed) Vanselow selectivity coefficients gave more accurate predictions of column experiments. The use of ternary cation exchange data did not improve predictions of column response.

  6. Analytical solutions for flow in porous media with multicomponent cation exchange reactions

    NASA Astrophysics Data System (ADS)

    Venkatraman, Ashwin; Hesse, Marc A.; Lake, Larry W.; Johns, Russell T.

    2014-07-01

    Multicomponent cation exchange reactions have important applications in groundwater remediation, disposal of nuclear wastes as well as enhanced oil recovery. The hyperbolic theory of conservation laws can be used to explain the nature of displacements observed during flow with cation exchange reactions between flowing aqueous phase and stationary solid phase. Analytical solutions have been developed to predict the effluent profiles for a particular case of heterovalent cations (Na+, Ca2+ and Mg2+) and an anion (Cl-) for any combination of constant injection and constant initial composition using this theory. We assume local equilibrium, neglect dispersion and model the displacement as a Riemann problem using mass action laws, the charge conservation equation and the cation exchange capacity equation. The theoretical predictions have been compared with experimental data available at two scales—the laboratory scale and the field scale. The theory agrees well with the experimental data at both scales. Analytical theory predictions show good agreement with numerical model, developed using finite differences.

  7. Influence of the Ion Coordination Number on Cation Exchange Reactions with Copper Telluride Nanocrystals.

    PubMed

    Tu, Renyong; Xie, Yi; Bertoni, Giovanni; Lak, Aidin; Gaspari, Roberto; Rapallo, Arnaldo; Cavalli, Andrea; Trizio, Luca De; Manna, Liberato

    2016-06-01

    Cu2-xTe nanocubes were used as starting seeds to access metal telluride nanocrystals by cation exchanges at room temperature. The coordination number of the entering cations was found to play an important role in dictating the reaction pathways. The exchanges with tetrahedrally coordinated cations (i.e., with coordination number 4), such as Cd(2+) or Hg(2+), yielded monocrystalline CdTe or HgTe nanocrystals with Cu2-xTe/CdTe or Cu2-xTe/HgTe Janus-like heterostructures as intermediates. The formation of Janus-like architectures was attributed to the high diffusion rate of the relatively small tetrahedrally coordinated cations, which could rapidly diffuse in the Cu2-xTe NCs and nucleate the CdTe (or HgTe) phase in a preferred region of the host structure. Also, with both Cd(2+) and Hg(2+) ions the exchange led to wurtzite CdTe and HgTe phases rather than the more stable zinc-blende ones, indicating that the anion framework of the starting Cu2-xTe particles could be more easily deformed to match the anion framework of the metastable wurtzite structures. As hexagonal HgTe had never been reported to date, this represents another case of metastable new phases that can only be accessed by cation exchange. On the other hand, the exchanges involving octahedrally coordinated ions (i.e., with coordination number 6), such as Pb(2+) or Sn(2+), yielded rock-salt polycrystalline PbTe or SnTe nanocrystals with Cu2-xTe@PbTe or Cu2-xTe@SnTe core@shell architectures at the early stages of the exchange process. In this case, the octahedrally coordinated ions are probably too large to diffuse easily through the Cu2-xTe structure: their limited diffusion rate restricts their initial reaction to the surface of the nanocrystals, where cation exchange is initiated unselectively, leading to core@shell architectures. Interestingly, these heterostructures were found to be metastable as they evolved to stable Janus-like architectures if annealed at 200 °C under vacuum. PMID:27177274

  8. Influence of the Ion Coordination Number on Cation Exchange Reactions with Copper Telluride Nanocrystals.

    PubMed

    Tu, Renyong; Xie, Yi; Bertoni, Giovanni; Lak, Aidin; Gaspari, Roberto; Rapallo, Arnaldo; Cavalli, Andrea; Trizio, Luca De; Manna, Liberato

    2016-06-01

    Cu2-xTe nanocubes were used as starting seeds to access metal telluride nanocrystals by cation exchanges at room temperature. The coordination number of the entering cations was found to play an important role in dictating the reaction pathways. The exchanges with tetrahedrally coordinated cations (i.e., with coordination number 4), such as Cd(2+) or Hg(2+), yielded monocrystalline CdTe or HgTe nanocrystals with Cu2-xTe/CdTe or Cu2-xTe/HgTe Janus-like heterostructures as intermediates. The formation of Janus-like architectures was attributed to the high diffusion rate of the relatively small tetrahedrally coordinated cations, which could rapidly diffuse in the Cu2-xTe NCs and nucleate the CdTe (or HgTe) phase in a preferred region of the host structure. Also, with both Cd(2+) and Hg(2+) ions the exchange led to wurtzite CdTe and HgTe phases rather than the more stable zinc-blende ones, indicating that the anion framework of the starting Cu2-xTe particles could be more easily deformed to match the anion framework of the metastable wurtzite structures. As hexagonal HgTe had never been reported to date, this represents another case of metastable new phases that can only be accessed by cation exchange. On the other hand, the exchanges involving octahedrally coordinated ions (i.e., with coordination number 6), such as Pb(2+) or Sn(2+), yielded rock-salt polycrystalline PbTe or SnTe nanocrystals with Cu2-xTe@PbTe or Cu2-xTe@SnTe core@shell architectures at the early stages of the exchange process. In this case, the octahedrally coordinated ions are probably too large to diffuse easily through the Cu2-xTe structure: their limited diffusion rate restricts their initial reaction to the surface of the nanocrystals, where cation exchange is initiated unselectively, leading to core@shell architectures. Interestingly, these heterostructures were found to be metastable as they evolved to stable Janus-like architectures if annealed at 200 °C under vacuum.

  9. Time-Resolved Structural Analysis of Cation Exchange Reactions in Birnessite Using Synchrotron XRD

    NASA Astrophysics Data System (ADS)

    Lopano, C. L.; Heaney, P. J.; Post, J. E.; Hanson, J. C.; Lee, Y.; Komarneni, S.

    2002-12-01

    Birnessite ((Na,Ca,Mn2+) Mn7O142.8H2O) is a layered Mn-oxide with a 7.2Å spacing between the Mn octahedral sheets. Since birnessite is an abundant phase in soils, desert varnishes, and ocean nodules, it plays a significant role in soil and groundwater chemistry. Experiments by Golden et al. (1986,1987) have demonstrated that Na-buserite (hydrated birnessite) readily exchanges Na+ for a variety of other cations, including K+, Mg2+, Ca2+, Ba2+, Ni2+, and Sr2+. In light of its high cation exchange capacity, birnessite is industrially important for ion and molecular sieves and cathodic materials. In addition, birnessite serves as a precursor in the synthesis of todorokite, which has a 3x3 tunnel structure and is used as an octahedral sieve. We monitored cation-exchange reactions in birnessite by time-resolved X-ray powder diffraction with a simple flow-through cell at the National Synchrotron Light Source. The flow-through cell was developed by Lee and Parise at SUNY-Stony Brook, and this work represents its first application to Mn oxides. A series of synthetic Na-birnessite samples were saturated with chloride solutions containing dissolved K+, Mg2+, and Ba2+, ranging from 0.1M to 0.001M. Powder X-ray diffraction patterns were collected every ~ 3 minutes. The synchrotron experiments revealed that complete cation exchange occurs within three hours, and significant modifications of the arrangements of interlayer cations and water molecules accompany the exchange. Specifically, the replacement of Na by Mg resulted in the continuous growth of a discrete buserite-like phase with a 10Å layer spacing, while replacement of Na by K and Ba retained the 7Å spacing. K replacement of Na resulted in gradually decreasing peak intensity and peak merging. The Ba exchange yielded an abrupt decrease in diffraction intensities followed by a more gradual lattice change over the last 2 hours. Rietveld analysis led to the first determination of the structure of Ba-birnessite in space

  10. Independent control of the shape and composition of ionic nanocrystals through sequential cation exchange reactions

    SciTech Connect

    Luther, Joseph Matthew; Zheng, Haimei; Sadtler, Bryce; Alivisatos, A. Paul

    2009-07-06

    Size- and shape-controlled nanocrystal growth is intensely researched for applications including electro-optic, catalytic, and medical devices. Chemical transformations such as cation exchange overcome the limitation of traditional colloidal synthesis, where the nanocrystal shape often reflects the inherent symmetry of the underlying lattice. Here we show that nanocrystals, with established synthetic protocols for high monodispersity, can be templates for independent composition control. Specifically, controlled interconversion between wurtzite CdS, chalcocite Cu2S, and rock salt PbS occurs while preserving the anisotropic dimensions unique to the as-synthesized materials. Sequential exchange reactions between the three sulfide compositions are driven by the disparate solubilites of the metal ion exchange pair in specific coordinating molecules. Starting with CdS, highly anisotropic PbS nanorods are created, which serve as an important material for studying strong 2-dimensional quantum confinement, as well as for optoelectronic applications. Furthermore, interesting nanoheterostructures of CdS|PbS are obtained by precise control over ion insertion and removal.

  11. Mineral carbonation of gaseous carbon dioxide using a clay-hosted cation exchange reaction.

    PubMed

    Kang, Il-Mo; Roh, Ki-Min

    2013-01-01

    The mineral carbonation method is still a challenge in practical application owing to: (1) slow reaction kinetics, (2) high reaction temperature, and (3) continuous mineral consumption. These constraints stem from the mode of supplying alkaline earth metals through mineral acidification and dissolution. Here, we attempt to mineralize gaseous carbon dioxide into calcium carbonate, using a cation exchange reaction of vermiculite (a species of expandable clay minerals). The mineralization is operated by draining NaCI solution through vermiculite powders and continuously dropping into the pool of NaOH solution with CO2 gas injected. The mineralization temperature is regulated here at 293 and 333 K for 15 min. As a result of characterization, using an X-ray powder diffractometer and a scanning electron microscopy, two types of pure CaCO3 polymorphs (vaterite and calcite) are identified as main reaction products. Their abundance and morphology are heavily dependent on the mineralization temperature. Noticeably, spindle-shaped vaterite, which is quite different from a typical vaterite morphology (polycrystalline spherulite), forms predominantly at 333 K (approximately 98 wt%).

  12. Modelling of geochemical reactions and experimental cation exchange in MX 80 bentonite.

    PubMed

    Montes-H, G; Fritz, B; Clement, A; Michau, N

    2005-10-01

    Bentonites are widely used for waste repository systems because of their hydrodynamic, surface and chemical-retention properties. MX 80 bentonite (bentonite of Wyoming) contains approximately 85% Na/Ca-montmorillonite and 15% accessory minerals. The dominant presence of Na/Ca-montmorillonite in this clay mineral could cause it to perform exceptionally well as an engineered barrier for a radioactive waste repository because this buffer material is expected to fill up by swelling the void between canisters containing waste and the surrounding ground. However, the Na/Ca-montmorillonite could be transformed to other clay minerals as a function of time under repository conditions. Previous modelling studies based on the hydrolysis reactions have shown that the Na/Ca-montmorillonite-to-Ca-montmorillonite conversion is the most significant chemical transformation. In fact, this chemical process appears to be a simple cation exchange into the engineered barrier. The purpose of the present study was two-fold. Firstly, it was hoped to predict the newly formed products of bentonite-fluid reactions under repository conditions by applying a thermokinetic hydrochemical code (KIRMAT: Kinetic Reactions and Mass Transport). The system modelled herein was considered to consist of a 1-m thick zone of water-saturated engineered barrier. This non-equilibrated system was placed in contact with a geological fluid on one side, which was then allowed to diffuse into the barrier, while the other side was kept in contact with iron-charged water. Reducing initial conditions ( [P(O)2 approximately equals 0] ; Eh=-200 mV) and a constant reaction temperature (100 degrees C) were considered. Secondly, it was hoped to estimate the influence of inter-layer cations (Ca and Na) on the swelling behaviour of the MX 80 bentonite by using an isothermal system of water vapour adsorption and an environmental scanning electron microscope (ESEM) coupled with a digital image analysis (DIA) program. Here, the

  13. Test procedure for cation exchange chromatography

    SciTech Connect

    Cooper, T.D.

    1994-08-24

    The purpose of this test plan is to demonstrate the synthesis of inorganic antimonate ion exchangers and compare their performance against the standard organic cation exchangers. Of particular interest is the degradation rate of both inorganic and organic cation exchangers. This degradation rate will be tracked by determining the ion exchange capacity and thermal stability as a function of time, radiation dose, and chemical reaction.

  14. Cu3-xP Nanocrystals as a Material Platform for Near-Infrared Plasmonics and Cation Exchange Reactions

    PubMed Central

    2015-01-01

    Synthesis approaches to colloidal Cu3P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump–probe measurements on platelet-shaped Cu3-xP NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu3P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-xP NCs. It is likely that both the LSPR and the p-type character of our Cu3-xP NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu3-xP NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu3-xP NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-xP is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu3-xP/InP heterostructures, as a consequence of the fact that the exchange between Cu+ and In3+ ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu3-xP NCs an interesting material platform from which to access other metal phosphides by cation exchange. PMID:25960605

  15. Room Temperature Cation Exchange Reaction in Nanocrystals for Ultrasensitive Speciation Analysis of Silver Ions and Silver Nanoparticles.

    PubMed

    Huang, Ke; Xu, Kailai; Tang, Jie; Yang, Lu; Zhou, Jingrong; Hou, Xiandeng; Zheng, Chengbin

    2015-07-01

    To evaluate the toxicity of silver nanoparticles (AgNPs) and Ag(+) and gain deep insight into the transformation of AgNPs in the environment or organisms, ultrasensitive analytical methods are needed for their speciation analysis. About 40-fold of Cd(2+) in CdTe ionic nanocrystals can be "bombarded-and-exploded" (exchanged) in less than 1 min simply by mixing the nanocrystals with Ag(+) solution at room temperature, while this cation exchange reaction did not occur when only silver nanoparticles were present. On the basis of this striking difference, an ultrasensitive method was developed for speciation analysis of Ag(+) and AgNPs in complex matrices. The released Cd(2+) was reduced to its volatile species by sodium tetrahydroborate, which was separated and swept to an inductively coupled plasma mass spectrometer (ICPMS) or an atomic fluorescence spectrometer (AFS) for the indirect but ultrasensitive detection of Ag(+). Owing to the remarkable signal amplification via the cation exchange reaction and the advantages of chemical vapor generation for sampling, the limit of detection was 0.0003 μg L(-1) for Ag(+) by ICPMS, which was improved by 100-fold compared to the conventional method. Relative standard deviations are better than 2.5% at a concentration of 0.5 μg L(-1) Ag(+) or AgNPs regardless of the detector. The proposed method retains several unique advantages, including ultrahigh sensitivity, speciation analysis, simplicity and being organic reagent-free, and has been successfully utilized for speciation analysis of Ag(+) and AgNPs in environmental water samples and paramecium cells. PMID:26017198

  16. Reversible dissociation and ligand-glutathione exchange reaction in binuclear cationic tetranitrosyl iron complex with penicillamine.

    PubMed

    Syrtsova, Lidia; Sanina, Natalia; Lyssenko, Konstantin; Kabachkov, Evgeniy; Psikha, Boris; Shkondina, Natal'ja; Pokidova, Olesia; Kotelnikov, Alexander; Aldoshin, Sergey

    2014-01-01

    This paper describes a comparative study of the decomposition of two nitrosyl iron complexes (NICs) with penicillamine thiolic ligands [Fe2(SC5H11NO2)2(NO)4]SO4 ·5H2O (I) and glutathione- (GSH-) ligands [Fe2(SC10H17N3O6)2(NO)4]SO4 ·2H2O (II), which spontaneously evolve to NO in aqueous medium. NO formation was measured by a sensor electrode and by spectrophotometric methods by measuring the formation of a hemoglobin- (Hb-) NO complex. The NO evolution reaction rate from (I)  k 1 = (4.6 ± 0.1)·10(-3) s(-1) and the elimination rate constant of the penicillamine ligand k 2 = (1.8 ± 0.2)·10(-3) s(-1) at 25°C in 0.05 M phosphate buffer,  pH 7.0, was calculated using kinetic modeling based on the experimental data. Both reactions are reversible. Spectrophotometry and mass-spectrometry methods have firmly shown that the penicillamine ligand is exchanged for GS(-) during decomposition of 1.5·10(-4) M (I) in the presence of 10(-3) M GSH, with 76% yield in 24 h. As has been established, such behaviour is caused by the resistance of (II) to decomposition due to the higher affinity of iron to GSH in the complex. The discovered reaction may impede S-glutathionylation of the essential enzyme systems in the presence of (I) and is important for metabolism of NIC, connected with its antitumor activity.

  17. Cation exchange reactions controlling desorption of Sr-90(2+) from coarse-grained contaminated sediments at the Hanford site, Washington

    SciTech Connect

    McKinley, James P.; Zachara, John M.; Smith, Steven C.; Liu, Chongxuan

    2007-01-15

    Nuclear waste that bore 90Sr2+ was accidentally leaked into the vadose zone at the Hanford site, and was immobilized at relatively shallow depths in sediments containing little apparent clay or silt-sized components. Sr2+, 90Sr2+, Mg2+, and Ca2+ was desorbed and total inorganic carbon concentration was monitored during the equilibration of this sediment with varying concentrations of Na+, Ca2+. A cation exchange model previously developed for similar sediments was applied to these results as a predictor of final solution compositions. The model included binary exchange reactions for the four operant cations and an equilibrium dissolution/precipitation reaction for calcite. The model successfully predicted the desorption data. The contaminated sediment was also examined using digital autoradiography, a sensitive tool for imaging the distribution of radioactivity. The exchanger phase containing 90Sr was found to consist of smectite formed from weathering of mesostasis glass in basaltic lithic fragments. These clasts are a significant component of Hanford formation sands. The relatively small but significant cation exchange capacity of these sediments was thus a consequence of reaction with physically sequestered clays in sediment that contained essentially no fine-grained material. The nature of this exchange component explained the relatively slow (scale of days) evolution of desorption solutions. The experimental and model results indicated that there is little risk of migration of 90Sr2+ to the water table.

  18. A facile route to synthesize CdZnSe core–shell-like alloyed quantum dots via cation exchange reaction in aqueous system

    SciTech Connect

    Sheng, Yingzhuo; Wei, Jumeng; Liu, Bitao; Peng, Lingling

    2014-09-15

    Highlights: • Water-soluble CdZnSe alloyed QDs synthesized by cation exchange reaction. • The as-prepared CdZnSe QDs have fairly good luminescence properties. • The surface defects of obtained QDs were removed due to the alloyed structure. - Abstract: Water-soluble CdZnSe alloyed nanocrystals have been successfully prepared via “green” cation exchange reaction in aqueous system. The X-ray diffraction (XRD) patterns indicate that the as-prepared nanocrystals had high crystallinity and small particle size of 4–5 nm. The absorption spectra of CdZnSe show red shift of 100 nm from 375 to 475 nm. Moreover, the band-gap photoluminescent (PL) emission has a red shift of 50 nm from 430 to 480 nm with the increase of the reaction time. On the basis of the PL properties and transmission electron microscopy (TEM) images, one kind of core–shell-like structure model was proposed, which resulted from the different cation exchange reaction rates. This structure could greatly improve the luminescence properties by the removal of surface defect of quantum dots. This work would support potential applications in optoelectronic devices, and biomedical tags fields.

  19. Metal chalcogenide nanoparticle gel networks: Their formation mechanism and application for novel material generation and heavy metal water remediation via cation exchange reactions

    NASA Astrophysics Data System (ADS)

    Palhares, Leticia F.

    The dissertation research is focused on (1) uncovering the mechanism of metal chalcogenide nanoparticle gel formation; (2) extending the cation exchange reaction protocol to zinc sulfide gel networks, with the goal of accessing new aerogel chemistries and understanding the factors that drive the process; and (3) conducting a quantitative analysis of the ability of ZnS aerogels to remove heavy metal ions from aqueous solutions. The mechanism of metal chalcogenide nanoparticle gel formation was investigated using Raman spectroscopy and X-ray Photoelectron Spectroscopy to probe the chemical changes that occur during the gelation process. These techniques suggest that the bonding between the particles in the CdSe nanoparticle gels is due to the oxidation of surface selenide species, forming covalent Se--Se bonds. Treating the gel networks with a suitable reducing agent, such as a thiol, breaks the covalent bond and disperses the gel network. The addition of sodium borohydride, a "pure" reducing agent, also breaks down the gel network, strengthening the hypothesis that the reducing character of the thiols, not their ligation ability, is responsible for the gel network breakdown. UV-Vis spectroscopy, Transmission Electron Microscopy and Powder X-ray Diffraction were used to analyze the particles after successive gelation-dispersion cycles. The primary particle size decreases after repeated oxidation-reduction cycles, due to nanoparticle surface etching. This trend is observed for CdSe and CdS gel networks, allowing for the proposition that the oxidative-reductive mechanism responsible for the formation-dispersion of the gels is general, applying to other metal chalcogenide nanocrystals as well. The cation exchange reaction previously demonstrated for CdSe gels was extended to ZnS gel networks. The exchange occurs under mild reaction conditions (room temperature, methanol solvent) with exchanging ions of different size, charge and mobility (Ag+, Pb2+, Cd2+ , Cu2+). The

  20. Determination of the Cation-Exchange Capacity of Muscovite Mica.

    PubMed

    Osman; Suter

    2000-04-01

    High cation-exchange capacity (CEC) muscovite mica with a homoionic surface was prepared by replacing the Li(+) surface ions of partially delaminated Li-mica with K(+). The CEC of this K-mica was determined by exchanging its surface cations with Cs(+), NH(+)(4), methylene blue (MB(+)), and copper triethylenetetramine [Cu(trien)(2+)]. The kinetics of these exchange reactions were studied and showed large differences depending on their relative affinities to mica. The NH(4)(+)/K(+) exchange was slow, while the Cs(+) and Cu(trien)(2+)/K(+) exchange was fast. The MB(+)/K(+) exchange was quite slow and was not completed even after 99 h. Insufficient reaction time is one of the main reasons for the contradictory results reported in the literature for the CEC of aluminosilicates obtained by different methods. The CEC of mica can be photometrically measured by exchanging its surface cations with Cu(trien)(2+). Copyright 2000 Academic Press.

  1. Ceramic Spheres From Cation Exchange Beads

    NASA Technical Reports Server (NTRS)

    Dynys, F. W.

    2003-01-01

    Porous ZrO2 and hollow TiO2 spheres were synthesized from a strong acid cation exchange resin. Spherical cation exchange beads, polystyrene based polymer, were used as a morphological-directing template. Aqueous ion exchange reaction was used to chemically bind (ZrO)(2+) ions to the polystyrene structure. The pyrolysis of the polystyrene at 600 C produces porous ZrO2 spheres with a surface area of 24 sq m/g with a mean sphere size of 42 microns. Hollow TiO2 spheres were synthesized by using the beads as a micro-reactor. A direct surface reaction - between titanium isopropoxide and the resin beads forms a hydrous TiO2 shell around the polystyrene core. The pyrolysis of the polystyrene core at 600 C produces hollow anatase spheres with a surface area of 42 sq m/g with a mean sphere size of 38 microns. The formation of ceramic spheres was studied by XRD, SEM and B.E.T. nitrogen adsorption measurements.

  2. Cation exchange capacity of pine bark substrates

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cation exchange capacity (CEC) is an important soil and substrate chemical property. It describes a substrate's ability to retain cation nutrients. Higher CEC values for a substrate generally result in greater amounts of nutrients retained in the substrate and available for plant uptake, and great...

  3. Advancements in Anion Exchange Membrane Cations

    SciTech Connect

    Sturgeon, Matthew R.; Long, Hai; Park, Andrew M.; Pivovar, Bryan S.

    2015-10-15

    Anion-exchange membrane fuel cells (AME-FCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been utilized as the hydroxide conductor in AEMs. Herein we approach AEMs from two directions. First and foremost we study the stability of several different cations in a hydroxide solution at elevated temperatures. We specifically targeted BTMA and methoxy and nitro substituted BTMA. We've also studied the effects of adding an akyl spacer units between the ammonium cation and the phenyl group. In the second approach we use computational studies to predict stable ammonium cations, which are then synthesized and tested for stability. Our unique method to study cation stability in caustic conditions at elevated temperatures utilizes Teflon Parr reactors suitable for use under various temperatures and cation concentrations. NMR analysis was used to determine remaining cation concentrations at specific time points with GCMS analysis verifying product distribution. We then compare the experimental results with calculated modeling stabilities. Our studies show that the electron donating methoxy groups slightly increase stability (compared to that of BTMA), while the electron withdrawing nitro groups greatly decrease stability in base. These results give insight into possible linking strategies to be employed when tethering a BTMA like ammonium cation to a polymeric backbone; thus synthesizing an anion exchange membrane.

  4. A facile route to violet- to orange-emitting CdxZn1-xSe alloy nanocrystals via cation exchange reaction

    NASA Astrophysics Data System (ADS)

    Zhong, Xinhua; Feng, Yaoyu; Zhang, Yuliang; Gu, Zhenyu; Zou, Lei

    2007-09-01

    The most advanced CdSe-based binary semiconductor system does not work well for emission in the short wavelength spectral region from 420 to 500 nm, which is of special interest for the preparation of nanocrystal-based blue LEDs and white light generation. CdxZn1-xSe alloy nanocrystals are proven to be an attractive alternative as their emission color can be tuned from the UV spectral region (ZnSe) to the red region (CdSe) by changing the composition of the Zn/Cd ratio in the alloy. Herein we report a facile and 'green' alloying approach for the preparation of highly luminescent CdxZn1-xSe nanocrystals via cation exchange reaction of the pre-prepared ZnSe nanocrystals with Cd2+ at intermediate temperatures. Through this new synthetic strategy, high-quality alloy QDs with different desired emission wavelengths or colors (ranging from 370 to 600 nm) can be made reproducibly and precisely by varying the predetermined amounts of the reaction precursors.

  5. Determination of the cation-exchange capacity of muscovite mica

    SciTech Connect

    Osman, M.A.; Suter, U.W.

    2000-04-01

    High cation-exchange capacity (CEC) muscovite mica with a homoionic surface was prepared by replacing the Li{sup +} surface ions of partially delaminated Li-mica with K{sup +}. The CEC of this K-mica was determined by exchanging its surface cations with Cs{sup +}, NH{sub 4}{sup +}, methylene blue (MB{sup +}), and copper triethylenetetramine [Cu(trien){sup 2+}]. The kinetics of these exchange reactions were studied and showed large differences depending on their relative affinities to mica. The NH{sub 4}{sup +}/K{sup +} exchange was slow, while the Cs{sup +} and Cu(trien){sup 2+}/K{sup +} exchange was fast. The MB{sup +}/K{sup +} exchange was quite slow and was not completed even after 99 h. Insufficient reaction time is one of the main reasons for the contradictory results reported in the literature for the CEC of aluminosilicates obtained by different methods. The CEC of mica can be photometrically measured by exchanging its surface cations with Cu(trien){sup 2+}.

  6. Alkaline earth metal cation exchange: effect of mobile counterion and dissolved organic matter.

    PubMed

    Indarawis, Katrina; Boyer, Treavor H

    2012-04-17

    The goal of this research was to provide an improved understanding of the interactions between alkaline earth metals and DOM under conditions that are encountered during drinking water treatment with particular focus on cation exchange. Both magnetically enhanced and nonmagnetic cation exchange resins were converted to Na, Mg, Ca, Sr, and Ba mobile counterion forms as a novel approach to investigate the exchange behavior between the cations and the interactions between the cations and DOM. The results show that cation exchange is a robust process for removal of Ca(2+) and Mg(2+) considering competition with cations on the resin surface and presence of DOM. DOM was actively involved during the cation exchange process through complexation, adsorption, and coprecipitation reactions. In addition to advancing the understanding of ion exchange processes for water treatment, the results of this work are applicable to membrane pretreatment to minimize fouling, treatment of membrane concentrate, and precipitative softening.

  7. Selective Facet Reactivity During Cation Exchange in Cadmium Sulfide Nanorods

    SciTech Connect

    Sadtler, Bryce; Demchenko, Denis; Zheng, Haimei; Hughes, Steven; Merkle, Maxwell; Dahmen, Ulrich; Wang, Lin-Wang; Alivisatos, A. Paul

    2008-12-18

    The partial transformation of ionic nanocrystals through cation exchange has been used to synthesize nanocrystal heterostructures. We demonstrate that the selectivity for cation exchange to take place at different facets of the nanocrystal plays an important role in determining the resulting morphology of the binary heterostructure. In the case of copper I (Cu+) cation exchange in cadmium sulfide (CdS) nanorods, the reaction starts preferentially at the ends of the nanorods such that copper sulfide (Cu2S) grows inwards from either end. The resulting morphology is very different from the striped pattern obtained in our previous studies of silver I (Ag+) exchange in CdS nanorods where non-selective nucleation of silver sulfide (Ag2S) occurs. From interface formation energies calculated for several models of epitaxialconnections between CdS and Cu2S or Ag2S, we infer the relative stability of each interface during the nucleation and growth of Cu2S or Ag2S within the CdS nanorods. The epitaxial connections of Cu2S to the end facets of CdS nanorods minimize the formation energy, making these interfaces stable throughout the exchange reaction. However, as the two end facets of wurtzite CdS nanorods are crystallographically nonequivalent, asymmetric heterostructures can be produced.

  8. Atomistic understanding of cation exchange in PbS nanocrystals using simulations with pseudoligands

    NASA Astrophysics Data System (ADS)

    Fan, Zhaochuan; Lin, Li-Chiang; Buijs, Wim; Vlugt, Thijs J. H.; van Huis, Marijn A.

    2016-05-01

    Cation exchange is a powerful tool for the synthesis of nanostructures such as core-shell nanocrystals, however, the underlying mechanism is poorly understood. Interactions of cations with ligands and solvent molecules are systematically ignored in simulations. Here, we introduce the concept of pseudoligands to incorporate cation-ligand-solvent interactions in molecular dynamics. This leads to excellent agreement with experimental data on cation exchange of PbS nanocrystals, whereby Pb ions are partially replaced by Cd ions from solution. The temperature and the ligand-type control the exchange rate and equilibrium composition of cations in the nanocrystal. Our simulations reveal that Pb ions are kicked out by exchanged Cd interstitials and migrate through interstitial sites, aided by local relaxations at core-shell interfaces and point defects. We also predict that high-pressure conditions facilitate strongly enhanced cation exchange reactions at elevated temperatures. Our approach is easily extendable to other semiconductor compounds and to other families of nanocrystals.

  9. Solvent-dependent cation exchange in metal-organic frameworks.

    PubMed

    Brozek, Carl K; Bellarosa, Luca; Soejima, Tomohiro; Clark, Talia V; López, Núria; Dincă, Mircea

    2014-06-01

    We investigated which factors govern the critical steps of cation exchange in metal-organic frameworks by studying the effect of various solvents on the insertion of Ni(2+) into MOF-5 and Co(2+) into MFU-4l. After plotting the extent of cation insertion versus different solvent parameters, trends emerge that offer insight into the exchange processes for both systems. This approach establishes a method for understanding critical aspects of cation exchange in different MOFs and other materials.

  10. CATION EXCHANGE METHOD FOR THE RECOVERY OF PROTACTINIUM

    DOEpatents

    Studier, M.H.; Sullivan, J.C.

    1959-07-14

    A cation exchange prccess is described for separating protactinium values from thorium values whereby they are initially adsorbed together from an aqueous 0.1 to 2 N hydrochloric acid on a cation exchange resin in a column. Then selectively eluting the thorium by an ammonium sulfate solution and subsequently eluting the protactinium by an oxalate solution.

  11. Cation exchange properties of zeolites in hyper alkaline aqueous media.

    PubMed

    Van Tendeloo, Leen; de Blochouse, Benny; Dom, Dirk; Vancluysen, Jacqueline; Snellings, Ruben; Martens, Johan A; Kirschhock, Christine E A; Maes, André; Breynaert, Eric

    2015-02-01

    Construction of multibarrier concrete based waste disposal sites and management of alkaline mine drainage water requires cation exchangers combining excellent sorption properties with a high stability and predictable performance in hyper alkaline media. Though highly selective organic cation exchange resins have been developed for most pollutants, they can serve as a growth medium for bacterial proliferation, impairing their long-term stability and introducing unpredictable parameters into the evolution of the system. Zeolites represent a family of inorganic cation exchangers, which naturally occur in hyper alkaline conditions and cannot serve as an electron donor or carbon source for microbial proliferation. Despite their successful application as industrial cation exchangers under near neutral conditions, their performance in hyper alkaline, saline water remains highly undocumented. Using Cs(+) as a benchmark element, this study aims to assess the long-term cation exchange performance of zeolites in concrete derived aqueous solutions. Comparison of their exchange properties in alkaline media with data obtained in near neutral solutions demonstrated that the cation exchange selectivity remains unaffected by the increased hydroxyl concentration; the cation exchange capacity did however show an unexpected increase in hyper alkaline media.

  12. Cation-exchange chromatography of monoclonal antibodies

    PubMed Central

    Urmann, Marina; Graalfs, Heiner; Joehnck, Matthias; Jacob, Lothar R

    2010-01-01

    A novel cation-exchange resin, Eshmuno™ S, was compared to Fractogel® SO3− (M) and Toyopearl GigaCap S-650M. The stationary phases have different base matrices and carry specific types of polymeric surface modifications. Three monoclonal antibodies (mAbs) were used as model proteins to characterize these chromatographic resins. Results from gradient elutions, stirred batch adsorptions and confocal laser scanning microscopic investigations were used to elucidate binding behavior of mAbs onto Eshmuno™ S and Fractogel® SO3− and the corresponding transport mechanisms on these two resins. The number of charges involved in mAb binding for Eshmuno™ S is lower than for Fractogel® SO3−, indicating a slightly weaker electrostatic interaction. Kinetics from batch uptake experiments are compared to kinetic data obtained from confocal laser scanning microscopy images. Both experimental approaches show an accelerated protein adsorption for the novel stationary phase. The influence of pH, salt concentrations and residence times on dynamic binding capacities was determined. A higher dynamic binding capacity for Eshmuno™ S over a wider range of pH values and residence times was found compared to Fractogel® SO3− and Toyopearl GigaCap S-650M. The capture of antibodies from cell culture supernatant, as well as post-protein A eluates, were analyzed with respect to their host cell protein (hcp) removal capabilities. Comparable or even better hcp clearance was observed at much higher protein loading for Eshmuno™ S than Fractogel® SO3− or Toyopearl GigaCap S-650M. PMID:20559022

  13. From Light Impurity Doping to Complete Cation Exchange in Semiconductor Nanocrystals: The Role of Coulomb Interactions

    NASA Astrophysics Data System (ADS)

    Erwin, Steven; Ott, Florian; Norris, David

    2014-03-01

    Cation exchange is a reversible chemical reaction used to create new materials by replacing one type of cation with another, usually from solution. We have developed an atomistic model describing cation exchange in semiconductor nanocrystals. The model uses a small set of results obtained from DFT calculations for Ag-doped CdSe. From these we constructed a kinetic Monte Carlo model to address finite temperatures and time scales beyond the reach of DFT. Our simulations span a wide range of Ag concentrations, from light doping to full cation exchange. Thus our model provides a single conceptual framework in which these two phenomena can be understood as limiting endpoints. The results of the simulations are consistent with several experimentally observed aspects of both phenomena. An unexpected finding of our simulations is that the Coulomb interaction plays a central, but changing, role as the Ag concentration varies from light doping to fully cation exchanged. For example, if the Coulomb interaction is strongly screened then cation exchange is suppressed or stopped. When only moderately screened, Coulomb effects play an unanticipated but important role for both doping and cation exchange.

  14. A Scale Model of Cation Exchange for Classroom Demonstration.

    ERIC Educational Resources Information Center

    Guertal, E. A.; Hattey, J. A.

    1996-01-01

    Describes a project that developed a scale model of cation exchange that can be used for a classroom demonstration. The model uses kaolinite clay, nails, plywood, and foam balls to enable students to gain a better understanding of the exchange complex of soil clays. (DDR)

  15. All-Inorganic Germanium Nanocrystal Films by Cationic Ligand Exchange.

    PubMed

    Wheeler, Lance M; Nichols, Asa W; Chernomordik, Boris D; Anderson, Nicholas C; Beard, Matthew C; Neale, Nathan R

    2016-03-01

    We introduce a new paradigm for group IV nanocrystal surface chemistry based on room temperature surface activation that enables ionic ligand exchange. Germanium nanocrystals synthesized in a gas-phase plasma reactor are functionalized with labile, cationic alkylammonium ligands rather than with traditional covalently bound groups. We employ Fourier transform infrared and (1)H nuclear magnetic resonance spectroscopies to demonstrate the alkylammonium ligands are freely exchanged on the germanium nanocrystal surface with a variety of cationic ligands, including short inorganic ligands such as ammonium and alkali metal cations. This ionic ligand exchange chemistry is used to demonstrate enhanced transport in germanium nanocrystal films following ligand exchange as well as the first photovoltaic device based on an all-inorganic germanium nanocrystal absorber layer cast from solution. This new ligand chemistry should accelerate progress in utilizing germanium and other group IV nanocrystals for optoelectronic applications.

  16. All-inorganic Germanium nanocrystal films by cationic ligand exchange

    DOE PAGES

    Wheeler, Lance M.; Nichols, Asa W.; Chernomordik, Boris D.; Anderson, Nicholas C.; Beard, Matthew C.; Neale, Nathan R.

    2016-01-21

    In this study, we introduce a new paradigm for group IV nanocrystal surface chemistry based on room temperature surface activation that enables ionic ligand exchange. Germanium nanocrystals synthesized in a gas-phase plasma reactor are functionalized with labile, cationic alkylammonium ligands rather than with traditional covalently bound groups. We employ Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies to demonstrate the alkylammonium ligands are freely exchanged on the germanium nanocrystal surface with a variety of cationic ligands, including short inorganic ligands such as ammonium and alkali metal cations. This ionic ligand exchange chemistry is used to demonstrate enhanced transport inmore » germanium nanocrystal films following ligand exchange as well as the first photovoltaic device based on an all-inorganic germanium nanocrystal absorber layer cast from solution. This new ligand chemistry should accelerate progress in utilizing germanium and other group IV nanocrystals for optoelectronic applications.« less

  17. Atomistic understanding of cation exchange in PbS nanocrystals using simulations with pseudoligands

    PubMed Central

    Fan, Zhaochuan; Lin, Li-Chiang; Buijs, Wim; Vlugt, Thijs J. H.; van Huis, Marijn A.

    2016-01-01

    Cation exchange is a powerful tool for the synthesis of nanostructures such as core–shell nanocrystals, however, the underlying mechanism is poorly understood. Interactions of cations with ligands and solvent molecules are systematically ignored in simulations. Here, we introduce the concept of pseudoligands to incorporate cation-ligand-solvent interactions in molecular dynamics. This leads to excellent agreement with experimental data on cation exchange of PbS nanocrystals, whereby Pb ions are partially replaced by Cd ions from solution. The temperature and the ligand-type control the exchange rate and equilibrium composition of cations in the nanocrystal. Our simulations reveal that Pb ions are kicked out by exchanged Cd interstitials and migrate through interstitial sites, aided by local relaxations at core–shell interfaces and point defects. We also predict that high-pressure conditions facilitate strongly enhanced cation exchange reactions at elevated temperatures. Our approach is easily extendable to other semiconductor compounds and to other families of nanocrystals. PMID:27160371

  18. Porous Ceramic Spheres From Cation Exchange Beads

    NASA Technical Reports Server (NTRS)

    Dynys, Fred

    2005-01-01

    This document is a slide presentation that examines the use of a simple templating process to produce hollow ceramic spheres with a pore size of 1 to 10 microns. Using ion exchange process it was determined that the method produces porous ceramic spheres with a unique structure: (i.e., inner sphere surrounded by an outer sphere.)

  19. High-speed simultaneous ion-exclusion/cation-exchange chromatography of anions and cations on a weakly acidic cation-exchange resin column.

    PubMed

    Mori, Masanobu; Tanaka, Kazuhiko; Helaleh, Murad I H; Xu, Qun; Ikedo, Mikaru; Ogura, Yutaka; Sato, Shinji; Hu, Wenzhi; Hasebe, Kiyoshi; Haddad, Paul R

    2003-05-16

    The simultaneous ion-exclusion/cation-exchange separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin of 3 microm particle size was used to achieve the simultaneous high-speed separation of anions and cations (Cl(-), NO3(-), SO4(2-), Na(+), K(+), NH4(+), Ca(2+) and Mg(2+)) commonly found in environmental samples. The high-speed simultaneous separation is based on a combination of the ion-exclusion mechanism for the anions and the cation-exchange mechanism for cations. The complete separation of the anions and cations was achieved in 5 min by elution with 15 mM tartaric acid-2.5 mM 18-crown-6 at a flow-rate of 1.5 ml/min. Detection limits at S/N=3 ranged from 0.36 to 0.68 microM for anions and 0.63-0.99 microM for cations. This method has been applied to the simultaneous determination of anions and cations in several environmental waters with satisfactory results.

  20. Reaction of bovine cytochrome c oxidase with hydrogen peroxide produces a tryptophan cation radical and a porphyrin cation radical.

    PubMed

    Rigby, S E; Jünemann, S; Rich, P R; Heathcote, P

    2000-05-23

    Oxidized bovine cytochrome c oxidase reacts with hydrogen peroxide to generate two electron paramagnetic resonance (EPR) free radical signals (Fabian, M., and Palmer, G. (1995) Biochemistry 34, 13802-13810). These radicals are associated with the binuclear center and give rise to two overlapped EPR signals, one signal being narrower in line width (DeltaHptp = 12 G) than the other (DeltaHptp = 45 G). We have used electron nuclear double resonance (ENDOR) spectrometry to identify the two different chemical species giving rise to these two EPR signals. Comparison of the ENDOR spectrum associated with the narrow signal with that of compound I of horseradish peroxidase (formed by reaction of that enzyme with hydrogen peroxide) demonstrates that the two species are virtually identical. The chemical species giving rise to the narrow signal is therefore identified as an exchange-coupled porphyrin cation radical similar to that formed in horseradish peroxidase compound I. Comparison of the ENDOR spectrum of compound ES (formed by the reaction of hydrogen peroxide with cytochrome c peroxidase) with that of the broad signal indicates that the chemical species giving rise to the broad EPR signal in cytochrome c oxidase is probably an exchange coupled tryptophan cation radical. This is substantiated using H(2)O/D(2)O solvent exchange experiments where the ENDOR difference spectrum of the broad EPR signal of cytochrome c oxidase shows a feature consistent with hyperfine coupling to the exchangeable N(1) proton of a tryptophan cation radical.

  1. Two-dimensional peptide separation improving sensitivity of selected reaction monitoring-based quantitative proteomics in mouse liver tissue: comparing off-gel electrophoresis and strong cation exchange chromatography.

    PubMed

    Schäfer, Alexander; von Toerne, Christine; Becker, Silke; Sarioglu, Hakan; Neschen, Susanne; Kahle, Melanie; Hauck, Stefanie M; Ueffing, Marius

    2012-10-16

    Protein expression analysis is one of the most powerful tools to further the understanding of biological systems. Progress in the field of mass spectrometry has shifted focus from gel-based approaches to the upcoming LC-selected reaction monitoring (SRM) technique which combines high technical accuracy with absolute quantification of proteins and the capability for high-throughput analyses. Due to these properties, LC-SRM has the potential to become the foundation for biomarker analysis, targeted hypothesis driven proteomic studies and contribute to the field of systems biology. While the performance of LC-SRM applied to samples from various bodily fluids, particularly plasma, and microorganisms has been extensively investigated, there is only little experience with its application to animal tissue samples. Here, we show that a conventional one-dimensional LC-SRM workflow applied to mouse liver tissue suffers from a shortcoming in terms of sensitivity for lower abundance proteins. This problem could be solved through the extension of the standard workflow by an additional dimension of separation at the peptide level prior to online LC-SRM. For this purpose, we used off-gel electrophoresis (OGE) which is also shown to outperform strong cation exchange (SCX) in terms of resolution, gain of signal intensity, and predictability of separation. The extension of the SRM workflow by a high resolving peptide separation technique is an ideal combination as it allows the addition of stable isotope standards directly after trytic digestion and will increase the dynamic range of protein abundances amenable by SRM in animal tissue.

  2. Cu₂Se and Cu Nanocrystals as Local Sources of Copper in Thermally Activated In Situ Cation Exchange.

    PubMed

    Casu, Alberto; Genovese, Alessandro; Manna, Liberato; Longo, Paolo; Buha, Joka; Botton, Gianluigi A; Lazar, Sorin; Kahaly, Mousumi Upadhyay; Schwingenschloegl, Udo; Prato, Mirko; Li, Hongbo; Ghosh, Sandeep; Palazon, Francisco; De Donato, Francesco; Mozo, Sergio Lentijo; Zuddas, Efisio; Falqui, Andrea

    2016-02-23

    Among the different synthesis approaches to colloidal nanocrystals, a recently developed toolkit is represented by cation exchange reactions, where the use of template nanocrystals gives access to materials that would be hardly attainable via direct synthesis. Besides, postsynthetic treatments, such as thermally activated solid-state reactions, represent a further flourishing route to promote finely controlled cation exchange. Here, we report that, upon in situ heating in a transmission electron microscope, Cu2Se or Cu nanocrystals deposited on an amorphous solid substrate undergo partial loss of Cu atoms, which are then engaged in local cation exchange reactions with Cu "acceptor" phases represented by rod- and wire-shaped CdSe nanocrystals. This thermal treatment slowly transforms the initial CdSe nanocrystals into Cu(2-x)Se nanocrystals, through the complete sublimation of Cd and the partial sublimation of Se atoms. Both Cu "donor" and "acceptor" particles were not always in direct contact with each other; hence, the gradual transfer of Cu species from Cu2Se or metallic Cu to CdSe nanocrystals was mediated by the substrate and depended on the distance between the donor and acceptor nanostructures. Differently from what happens in the comparably faster cation exchange reactions performed in liquid solution, this study shows that slow cation exchange reactions can be performed at the solid state and helps to shed light on the intermediate steps involved in such reactions. PMID:26816347

  3. Cu2Se and Cu Nanocrystals as Local Sources of Copper in Thermally Activated In Situ Cation Exchange

    PubMed Central

    2016-01-01

    Among the different synthesis approaches to colloidal nanocrystals, a recently developed toolkit is represented by cation exchange reactions, where the use of template nanocrystals gives access to materials that would be hardly attainable via direct synthesis. Besides, postsynthetic treatments, such as thermally activated solid-state reactions, represent a further flourishing route to promote finely controlled cation exchange. Here, we report that, upon in situ heating in a transmission electron microscope, Cu2Se or Cu nanocrystals deposited on an amorphous solid substrate undergo partial loss of Cu atoms, which are then engaged in local cation exchange reactions with Cu “acceptor” phases represented by rod- and wire-shaped CdSe nanocrystals. This thermal treatment slowly transforms the initial CdSe nanocrystals into Cu2–xSe nanocrystals, through the complete sublimation of Cd and the partial sublimation of Se atoms. Both Cu “donor” and “acceptor” particles were not always in direct contact with each other; hence, the gradual transfer of Cu species from Cu2Se or metallic Cu to CdSe nanocrystals was mediated by the substrate and depended on the distance between the donor and acceptor nanostructures. Differently from what happens in the comparably faster cation exchange reactions performed in liquid solution, this study shows that slow cation exchange reactions can be performed at the solid state and helps to shed light on the intermediate steps involved in such reactions. PMID:26816347

  4. Effects of exchanged cation on the microporosity of montmorillonite

    USGS Publications Warehouse

    Rutherford, D.W.; Chiou, C.T.; Eberl, D.D.

    1997-01-01

    The micropore volumes of 2 montmorillonites (SAz- 1 and SWy-1), each exchanged with Ca, Na, K, Cs and tetramethylammonium (TMA) ions, were calculated from the measured vapor adsorption data of N2 and neo-hexane by use of t- and ??s-plots. The corresponding surface areas of the exchanged clays were determined from Brunauer-Emmett-Teller (BET) plots of N2 adsorption data. Micropore volumes and surface areas of the samples increased with the size of exchanged cation: TMA > Cs > K> Ca > Na. The SAz-1 exchanged clays showed generally greater micropore volumes and surface areas than the corresponding SWy-1 clays. The vapor adsorption data and d(001) measurements for dry clay samples were used together to evaluate the likely locations and accessibility of clay micropores, especially the relative accessibility of their interlayer spacing. For both source clays exchanged with Na, Ca and K ions, the interlayer spacing appeared to be too small to admit nonpolar gases and the accessible micropores appeared to have dimensions greater than 5.0 A??, the limiting molecular dimension of neo -hexane. In these systems, there was a good consistency of micropore volumes detected by N2 and neo-hexane. When the clays were intercalated with relatively large cations (TMA and possibly Cs), the large layer expansion created additional microporosity, which was more readily accessible to small N2 than to relatively large neo-hexane. Hence, the micropore volume as detected by N2 was greater than that detected by neo-hexane. The micropore volumes with pore dimensions greater than 5 A?? determined for clays exchanged with Na, Ca and K likely resulted from the pores on particle edges and void created by overlap regions of layers. The increase in micropore volumes with pore dimensions less than 5 A?? determined for clays exchanged with TMA and possibly Cs could be caused by opening of the interlayer region by the intercalation of these large cations.

  5. Samarium Ion Exchanged Montmorillonite for High Temperature Cumene Cracking Reaction

    NASA Astrophysics Data System (ADS)

    Binitha, N. N.; Silija, P. P.; Suraj, V.; Yaakob, Z.; Sugunan, S.

    2011-02-01

    Montmorillonite clay is cation exchanged with samarium and its catalytic influence in cumene cracking reaction is investigated. Effect of exchange with sodium ions on further exchange with samarium ions is also noted. Acidity measurements are done using Temperature Programmed Desorption (TPD) of ammonia. The retention of basic structure is proved from FTIR spectra and XRD patterns. Elemental analysis result shows that samarium exchange has occurred, which is responsible for the higher catalytic activity. Surface area and pore volume remains more or less unaffected upon exchange. Thermogravimetric analysis indicates the enhanced thermal stability on exchanging. Cumene cracking reaction is carried out at atmospheric pressure in a fixed bed glass reactor at 673 K. The predominance of Brønsted acidity is confirmed from high selectivity to benzene.

  6. Cation–cation interactions and cation exchange in a series of isostructural framework uranyl tungstates

    SciTech Connect

    Balboni, Enrica; Burns, Peter C.

    2014-05-01

    The isotypical compounds (UO{sub 2}){sub 3}(WO{sub 6})(H{sub 2}O){sub 5} (1), Ag(UO{sub 2}){sub 3}(WO{sub 6})(OH)(H{sub 2}O){sub 3} (2), K(UO{sub 2}){sub 3}(WO{sub 6})OH(H{sub 2}O){sub 4} (3), Rb(UO{sub 2}){sub 3}(WO{sub 6})(OH)(H{sub 2}O){sub 3.5} (4), and Cs(UO{sub 2}){sub 3}(WO{sub 6})OH(H{sub 2}O){sub 3} (5) were synthesized, characterized, and their structures determined. Each crystallizes in space group Cc. (1): a=12.979 (3), b=10.238 (2), c=11.302 (2), β=102.044 (2); (2): a=13.148 (2), b=9.520 (1), c=11.083 (2), β=101.568 (2); (3): a=13.111 (8), b=9.930 (6), c=11.242 (7), β=101.024 (7); (4): a=12.940 (2), b=10.231 (2), c=11.259(2), β=102.205 (2); (5): a=12.983 (3), b=10.191 (3), c=11.263 (4), β=101.661 (4). Compounds 1–5 are a framework of uranyl and tungsten polyhedra containing cation–cation interactions. The framework has three symmetrically distinct U(VI) cations, one tungsten, sixteen to eighteen oxygen atoms, and in 2–5, one monovalent cation. Each atom occupies a general position. Each U(VI) cation is present as a typical (UO{sub 2}){sup 2+} uranyl ion in an overall pentagonal bipyramidal coordination environment. Each pentagonal bipyramid shares two equatorial edges with two other pentagonal bipyramids, forming a trimer. Trimers are connected into chains by edge-sharing with WO{sub 6} octahedra. Chains are linked through cation–cation interactions between two symmetrically independent uranyl ions. This yields a remarkably complex system of intersecting channels that extend along [0 0 1] and [−1 1 0]. The cation exchange properties of 2 and 3 were characterized at room temperature and at 140 °C. - Graphical abstract: Chains of uranium and tungsten polyhedra are connected into a three dimensional framework by cation–cation interactions occurring between two symmetrically independent uranyl pentagonal bipyramids. Monovalent cations present in channels within the structure can be exchanged by room temperature or mild hydrothermal

  7. Sorption mechanism and predictive models for removal of cationic organic contaminants by cation exchange resins.

    PubMed

    Jadbabaei, Nastaran; Zhang, Huichun

    2014-12-16

    Understanding the sorption mechanism of organic contaminants on cation exchange resins (CXRs) will enable application of these resins for the removal of cationic organic compounds from contaminated water. In this study, sorption of a diverse set of 12 organic cations and 8 neutral aromatic solutes on two polystyrene CXRs, MN500 and Amberlite 200, was examined. MN500 showed higher sorbed concentrations due to its microporous structure. The sorbed concentrations followed the same trend of aromatic cations > aliphatic cations > neutral solutes for both resins. Generally, solute-solvent interactions, nonpolar moiety of the solutes, and resin matrix can affect selectivity of the cations. Sorbed concentrations of the neutral compounds were significantly less than those of the cations, indicating a combined effect of electrostatic and nonelectrostatic interactions. By conducting multiple linear regression between Gibbs free energy of sorption and Abraham descriptors for all 20 compounds, polarity/polarizability (S), H-bond acidity (A), induced dipole (E), and electrostatic (J(+)) interactions were found to be involved in the sorption of the cations by the resins. After converting the aqueous sorption isotherms to sorption from the ideal gas-phase by water-wet resins, a more significant effect of J(+) was observed. Predictive models were then developed based on the linear regressions and validated by accurately estimating the sorption of different test set compounds with a root-mean-square error range of 0.91-1.1 and 0.76-0.85 for MN500 and Amberlite 200, respectively. The models also accurately predicted sorption behavior of aniline and imidazole between pH 3 and 10. PMID:25409479

  8. Cation exchange interaction between antibiotic ciprofloxacin and montmorillonite.

    PubMed

    Wang, Chih-Jen; Li, Zhaohui; Jiang, Wei-Teh; Jean, Jiin-Shuh; Liu, Chia-Chuan

    2010-11-15

    Exploring the interactions between antibiotics and soils/minerals is of great importance in resolving their fate, transport, and elimination in the environment due to their frequent detection in wastewater, river water, sewage sludge and soils. This study focused on determining the adsorption properties and mechanisms of interaction between antibiotic ciprofloxacin and montmorillonite (SAz-1), a swelling dioctahedral mineral with Ca(2+) as the main interlayer cation. In acidic and neutral aqueous solutions, a stoichiometric exchange between ciprofloxacin and interlayer cations yielded an adsorption capacity as high as 330 mg/g, corresponding to 1.0 mmol/g. When solution pH was above its pK(a2) (8.7), adsorption of ciprofloxacin was greatly reduced due to the net repulsion between the negatively charged clay surfaces and the ciprofloxacin anion. The uptake of ciprofloxacin expanded the basal spacing (d(001)) of montmorillonite from 15.04 to 17.23 A near its adsorption capacity, confirming cation exchange within the interlayers in addition to surface adsorption. Fourier transform infrared results further suggested that the protonated amine group of ciprofloxacin in its cationic form was electrostatically attracted to negatively charged sites of clay surfaces, and that the carboxylic acid group was hydrogen bonded to the basal oxygen atoms of the silicate layers. The results indicate that montmorillonite is an effective sorbent to remove ciprofloxacin from water. PMID:20675045

  9. Electron spin resonance spectroscopic studies of radical cation reactions

    SciTech Connect

    Dai, S.

    1990-01-01

    A spin Hamiltonian suitable for theoretical analyses of ESR spectra is derived using the general effective Hamiltonian theory in the usual Schroedinger representation. The Permutation Indices method is extended to obtain the dynamic exchange equations used in ESR lineshape simulation. The correlation between [beta]-hydrogen coupling constants and their geometric orientations are derived using a perturbation method. The three electron bond model is extended to rationalize unimolecular rearrangements of radical cations. The ring-closed radical cations of 9,10-octalin oxide and synsesquinorbornene oxide have been characterized by ESR spectroscopy in the CFCl[sub 3] matrix at low temperature. The self-electron-transfer rate constants between the methyl viologen dication and cation have been determined by dynamic ESR lineshape simulations at room temperature in allyl alcohol, water, methanol and propargyl alcohol solvents. The radical cation formed by the radiolytic oxidation of allylamine in Freon matrices at 77 K is the 3-iminiopropyl distonic species(3-iminium-1-propyl radical). The nucleophilic endocylization of the but-3-en-1-ol radical cation to the protonated tetrahydrofuran-3-yl radical was observed in the radiolytic oxidation of but-3-en-1-ol in Freon matrices. ESR studies of the radiolytic oxidation of 1,5-hexdiyne have resulted in characterization the 1,5-hexadiyne radical cation isomerizing to the 1,2,4,5-hexatetraene radical cation. The symmetric (C[sub 2v]) bicyclo[3.3.0]-octa-2,6-diene-4,8-diyl(a bridged 1,4-bishomobenzene species) radical cation is produced by the radiolytic oxidation of semibullvalene in Freon matrices. The ring-opening 3,4-dimethylenecyclobutene radical cation to 1,2,4,5-hexatetraene radical cation was observed in the photolysis of 3,4-dimethylenecyclobutene radical cation. The cyclooctatetraene radical cation generated by radiolytic oxidation photoisomerizes to bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation.

  10. Cation exchange on the nanoscale: an emerging technique for new material synthesis, device fabrication, and chemical sensing.

    PubMed

    Rivest, Jessy B; Jain, Prashant K

    2013-01-01

    Cation exchange is an age-old technique for the chemical conversion of liquids or extended solids by place-exchanging the cations in an ionic material with a different set of cations. The technique is undergoing a major revival with the advent of high-quality nanocrystals: researchers are now able to overcome the limitations in bulk systems and fully exploit cation exchange for materials synthesis and discovery via rapid, low-temperature transformations in the solid state. In this tutorial review, we discuss cation exchange as a promising materials synthesis and discovery tool. Exchange on the nanoscale exhibits some unique attributes: rapid kinetics at room temperature (orders of magnitude faster than in the bulk) and the tuning of reactivity via control of nanocrystal size, shape, and surface faceting. These features make cation exchange a convenient tool for accessing nanocrystal compositions and morphologies for which conventional synthesis may not be established. A simple exchange reaction allows extension of nanochemistry to a larger part of the periodic table, beyond the typical gamut of II-VI, IV-VI, and III-V materials. Cation exchange transformations in nanocrystals can be topotactic and size- and shape-conserving, allowing nanocrystals synthesized by conventional methods to be used as templates for production of compositionally novel, multicomponent, or doped nanocrystals. Since phases and compositions resulting from an exchange reaction can be kinetically controlled, rather than governed by the phase diagram, nanocrystals of metastable and hitherto inaccessible compositions are attainable. Outside of materials synthesis, applications for cation exchange exist in water purification, chemical staining, and sensing. Since nanoscale cation exchange occurs rapidly at room temperature, it can be integrated with sensitive environments such as those in biological systems. Cation exchange is already allowing access to a variety of new materials and processes

  11. Chromatographic behaviors of proteins on cation-exchange column.

    PubMed

    Li, Rong; Chen, Guo-Liang; Zhao, Wen-Ming

    2004-12-01

    A weak cation-exchanger (XIDACE-WCX) has been synthesized by the indirect method. The chromatographic characteristics of the synthesized packing was studied in detail. The standard protein mixture and lysozyme from egg white were separated with the prepared chromatographic column. The chromatographic thermodynamics of proteins was studied in a wide temperature range. Thermodynamic parameters standard enthalpy change (deltaH0) and standard entropy change (deltaS0) and compensation temperature (beta) at protein denaturation were determined in the chromatographic system. By using obtained deltaS0, the conformational change of proteins was judged in the chromatographic process. The linear relationship between deltaH0 and deltaS0 can be used to identify the identity of the protein retention mechanism in the weak cation-exchange chromatography. The interaction between weak cation-exchanger and metal ions was investigated. Several metal chelate columns were prepared. The effects of introducing metal ion into the naked column on protein retention and the retention mechanism of proteins in the metal chalet affinity chromatography were discussed. PMID:15689030

  12. Simultaneous ion-exclusion/cation-exchange chromatography of anions and cations in acid rain waters on a weakly acidic cation-exchange resin by elution with sulfosalicylic acid.

    PubMed

    Tanaka, K; Ohta, K; Haddad, P R; Fritz, J S; Miyanaga, D A; Hu, W; Hasebe, K

    2000-07-01

    A simple, selective, and sensitive method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was developed using ion-exclusion/ cation-exchange chromatography with conductimetric detection. A weakly acidic cation-exchange resin column (Tosho TSKgel OA-PAK-A) and a sulfosalicylic acid-methanol-water eluent was used. With a mobile phase comprising 1.25 mM sulfosalicylic acid in methanol-water (7.5:92.5) at 1.2 ml/min, simultaneous separation and detection of the above anions and cations was achieved in about 30 min. Linear calibration plots of peak area versus concentration were obtained over the concentration ranges 0-1.0 mM for anions (R=0.9991) and 0-0.5 mM for cations (R=0.9994). Detection limits calculated at S/N=3 ranged from 4.2 to 14.8 ppb for the anions and from 2.4 to 12.1 ppb for the cations. The reproducibility of retention times was 0.14-0.15% relative standard deviation (RSD) for anions and 0.18-0.31% for cations, and reproducibility of chromatographic peak areas was 1.22-1.75% RSD for anions and 1.81-2.10% for cations. The method was applied successfully to the simultaneous determination of anions and cations in aerosols transported from mainland China to central Japan, as determined by a meteorological satellite data analyzer.

  13. High-performance ion-exclusion/cation-exchange chromatography of anions and cations in acid rain waters on a weakly acidic cation-exchange resin.

    PubMed

    Tanaka, K; Ohta, K; Haddad, P R; Fritz, J S; Miyanaga, A; Hu, W; Hasebe, K; Lee, K P; Sarzanini, C

    2001-06-22

    A new method for the simultaneous determination of anions (sulfate, nitrate, and chloride) and cations (sodium, ammonium, potassium, magnesium, and calcium) in acid rain waters was investigated using high-performance ion-exclusion/cation-exchange chromatography with conductimetric detection on a separation column packed with a polymethacrylate-based weakly acidic cation-exchange resin in the hydrogen-form and an eluent comprising 1.5 mM sulfosalicylic acid-6 mM 18-crown-6 at pH 2.6, operated at 1.5 ml/min. Effective separation and highly sensitive conductimetric detection for the anions and the cations was achieved in about 14 min. Since the ionic balance (equivalents of anions/equivalents of cations) of acid rain waters of different pH (4.40-4.67) ranged from 0.97 to 0.94, evaluation of the water quality of acid rain was possible. This method was successfully applied to the simultaneous determination of the anions and the cations in acid rain transported from mainland China and North Korea to central Japan monitored by a meteorological satellite data analyzer.

  14. DNA strand exchange stimulated by spontaneous complex formation with cationic comb-type copolymer.

    PubMed

    Kim, Won Jong; Akaike, Toshihiro; Maruyama, Atsushi

    2002-10-30

    Cationic comb-type copolymers (CCCs) composed of a polycation backbone and water-soluble side chains accelerate by 4-5 orders the DNA strand exchange reaction (SER) between double helical DNA and its homologous single-strand DNA. The accelerating effect is considered due to alleviation of counterion association during transitional intermediate formation in sequential displacement pathway. CCCs stabilize not only matured hybrids but also the nucleation complex to accelerate hybridization. PMID:12392411

  15. Exchangeable cation composition of the smectite-rich plate boundary fault at the Japan Trench

    NASA Astrophysics Data System (ADS)

    Kameda, Jun; Inaoi, Chisaki; Conin, Marianne

    2016-04-01

    To better understand physicochemical processes in smectite-rich fault zones, we examined exchangeable cation composition of samples from the slip zone of the 2011 Tohoku-oki earthquake (Mw9.0) recovered by the Integrated Ocean Drilling Program Expedition 343. Our chemical analyses revealed that the exchangeable Ca2+ and Mg2+ are enriched in the slip zone, while Na+ is depleted. K+ shows a complicated depth profile probably due to K fixation. Based on fluid chemistry data, we estimated apparent selectivity coefficients of exchange reactions in the ternary Ca2+-Mg2+-Na+ system. The results suggest that the Na+ to Mg2+ exchange reaction on smectite might have progressed in the slip zone. One explanation for this feature is local progress of the reaction triggered by coseismic thermogenesis during the earthquake. Considering that the frictional property of smectite gouge is dependent on the exchangeable cation composition, chemical processes as observed in this study are intimately linked to physical aspect of smectite-bearing faults.

  16. Solubility and cation exchange in phosphate rock and saturated clinoptilolite mixtures

    NASA Technical Reports Server (NTRS)

    Allen, E. R.; Hossner, L. R.; Ming, D. W.; Henninger, D. L.

    1993-01-01

    Mixtures of zeolite and phosphate rock (PR) have the potential to provide slow-release fertilization of plants in synthetic soils by dissolution and ion-exchange reactions. This study was conducted to examine solubility and cation-exchange relationships in mixtures of PR and NH4- and K-saturated clinoptilolite (Cp). Batch-equilibration experiments were designed to investigate the effect of PR source, the proportion of exchangeable K and NH4, and the Cp to PR ratio on solution N, P, K, and Ca concentrations. The dissolution and cation-exchange reactions that occurred after mixing NH4- and K-saturated Cp with PR increased the solubility of the PR and simultaneously released NH4 and K into solution. The more reactive North Carolina (NC) PR rendered higher solution concentrations of NH4 and K when mixed with Cp than did Tennessee (TN) PR. Solution P concentrations for the Cp-NC PR mixture and the Cp-TN PR mixture were similar. Solution concentrations of N, P, K, and Ca and the ratios of these nutrients in solution varied predictably with the type of PR, the Cp/PR ratio, and the proportions of exchangeable K and NH4 on the Cp. Our research indicated that slow-release fertilization using Cp/PR media may provide adequate levels of N, P, and K to support plant growth. Solution Ca concentrations were lower than optimum for plant growth.

  17. CATIONIC EXCHANGE PROCESS FOR THE SEPARATION OF RARE EARTHS

    DOEpatents

    Choppin, G.R.; Thompson, S.G.; Harvey, B.G.

    1960-02-16

    A process for separating mixtures of elements in the lanthanum and actinium series of the periodic table is described. The mixture of elements is dissolved in 0.05 M HCI, wherein the elements exist as tripositive ions. The resulting solution is then transferred to a column of cationic exchange resin and the column eluted with 0.1 to 0.6 M aqueous ammonium alpha hydroxy isobutyrate solution of pH 3.8 to 5.0. The use of ammonium alpha hydroxy isobutyrate as an eluting agent results in sharper and more rapid separations than previously obtainable with eluants such as citric, tartaric, glycolic, and lactic acids.

  18. Chemistry of alkali cation exchanged faujasite and mesoporous NaX using alkyl halides and phosphates

    NASA Astrophysics Data System (ADS)

    Lee, Min-Hong

    The purpose of this work was to increase the reactivity of Faujasite X (NaX) zeolite toward the reactive decontamination of materials subject to nucleophilic attack by means of zeolite cation optimization and by means of the synthesis of mesoporous Faujasite X. Primary alkyl halides and trialkyl phosphates have been the test materials on which the cation-optimized and mesoporous zeolites have been tested. In the alkali cation optimization work, reactions of methyl iodide and 1-chloropropane with alkali metal cation exchanged Faujasite zeolite X were investigated at room temperature. The reactivity of the framework and the product formation were shown to depend on zeolite framework counter-cation. A quantitative study of zeolite product formation has been carried out, primarily using solid-state NMR spectroscopy. Large alkali cations showed preference toward substitution chemistry. In contrast, alkyl halide exposed LiX and NaX zeolites underwent both substitution and elimination. Subsequently introduced water molecules led to hydrolysis of framework species that was sensitive to framework counter-cation. The mesoporous NaX zeolites work undertakes to test whether an improvement in surface chemical reactivity can be achieved by introducing mesopores into the already reactive nucleophilic microporous NaX zeolite. Incorporation of the polydiallyl dimethyl ammonium chloride (PDADMAC) template and the formation of mesopores in Faujasite X zeolite (NaX) were successful and well-characterized. The mesopores are proposed to have occurred from incorporation of the cationic PDADMAC polymer into the zeolite by compensating zeolite framework charge. Subsequent sodium cation exchange of calcined mesoporous NaX was shown to restore the chemical reactivity characteristic of as-synthesized NaX. Trialkyl organophosphorous compounds underwent substitution reactions. The reactivity of both microporous and mesoporous Faujasite zeolite X and the product formation was shown to depend on

  19. Mobilization of Roadside Soil Cation Pools by Exchange with Road Deicers

    NASA Astrophysics Data System (ADS)

    Rossi, R.; Bain, D.

    2014-12-01

    Over the past sixty years, road deicers (i.e., road salt) have been applied to roadways in high latitudes to improve traffic conditions in winter weather. However, the dissolution of road deicers in highway runoff create waters with high total dissolved solids (TDS), specifically high concentrations of sodium, which can mobilize soil metals via soil cation exchange reactions. While several studies have detailed the interactions of high TDS solutions and surface and ground waters, limited attention is paid to the impacts of high TDS solutions on near-road soils. Between 2013 and 2014, soil water samples were collected from a roadside transect of lysimeter nests in Pittsburgh, PA. Soil water samples were analyzed for metal concentrations and resulting data used to examine cation dynamics. Patterns in soil water calcium and magnesium concentrations follow patterns in soil water sodium concentrations. In our samples, the highest major cation concentrations are found at the deepest lysimeters, suggesting major cations are mobilized to, and potentially accumulate in, deeper soil horizons. Concentration peaks in the downslope soil waters lag concentration peaks at the near-road nest by two months, indicating that road salt plumes persist and migrate following the road salting season. Characterizing the interactions of high TDS solutions and roadside soil cation pools clarifies our understanding of metal dynamics in the roadside environment. A deeper understanding of these processes is necessary to effectively restore and manage watersheds as high TDS solutions (i.e., road deicing, hydraulic fracturing, and marginal irrigation water) increasingly influence ecosystem function.

  20. Several textural properties of compacted and cation-exchanged bentonite

    NASA Astrophysics Data System (ADS)

    Montes-Hernandez, G.; Duplay, J.; Géraud, Y.; Martinez, L.

    2006-08-01

    One of the principal applications for bentonite is in drilling muds. Moreover it is widely used as a suspending and stabilizing agent, and as an adsorbent or clarifying agent, in many industries. Recently the bentonites have been proposed as engineered barriers for radioactive waste repository because these materials are supposed to build up a better impermeable zone around wastes by swelling. For these reasons, a textural characterization of bentonites in the laboratory is very important. The aim in this study was to estimate several textural properties of compacted and cation-exchanged bentonite by using Hg-porosimetry, N2-adsorption, water vapour adsorption, scanning electron microscopy (SEM) observations and environmental scanning electron microscopy-digital images analysis measurements. For that, bulk samples were mechanically compressed at atmospheric conditions by using a uniaxial system at four different pressures (21, 35, 49, and 63 MPa) in order to obtain four physical densities. On the other hand, the bulk samples of bentonite were treated separately with four concentrated solutions (1N concentration) of sodium, potassium, magnesium and calcium chlorides in order to obtain a homoionic interlayer cation in the clay phase. The results showed that the macro-porosity (porous size>50 nm) and eventually the mesoporosity (porous size 2 50 nm) are affected by the uniaxial compaction. In this case, a transformation of the shape of the macro-pores network from tube to crack was observed. On the other hand, the swelling potential and water content are governed by the relative humidity and by the nature of interlayer cation.

  1. Separation of certain carboxylic acids utilizing cation exchange membranes

    DOEpatents

    Chum, Helena L.; Sopher, David W.

    1984-01-01

    A method of substantially separating monofunctional lower carboxylic acids from a liquid mixture containing the acids wherein the pH of the mixture is adjusted to a value in the range of from about 1 to about 5 to form protonated acids. The mixture is heated to an elevated temperature not greater than about 100.degree. C. and brought in contact with one side of a perfluorinated cation exchange membrane having sulfonate or carboxylate groups or mixtures thereof with the mixture containing the protonated acids. A pressure gradient can be established across the membrane with the mixture being under higher pressure, so that protonated monofunctional lower carboxylic acids pass through the membrane at a substantially faster rate than the remainder of the mixture thereby substantially separating the acids from the mixture.

  2. Separation of certain carboxylic acids utilizing cation exchange membranes

    DOEpatents

    Chum, H.L.; Sopher, D.W.

    1983-05-09

    A method of substantially separating monofunctional lower carboxylic acids from a liquid mixture containing the acids wherein the pH of the mixture is adjusted to a value in the range of from about 1 to about 5 to form protonated acids. The mixture is heated to an elevated temperature not greater than about 100/sup 0/C and brought in contact with one side of a perfluorinated cation exchange membrane having sulfonate or carboxylate groups or mixtures thereof with the mixture containing the protonated acids. A pressure gradient can be established across the membrane with the mixture being under higher pressure, so that protonated monofunctional lower carboxylic acids pass through the membrane at a substantially faster rate than the remainder of the mixture thereby substantially separating the acids from the mixture.

  3. Cation exchange pretreatment studies for high recovery - Yuma desalting plant

    SciTech Connect

    Kaakinen, J.W.; Laverty, P.E.

    1983-10-01

    The main purpose of the High Recovery Test Program was to obtain feasibility design data for cation exchange softening to allow a greater fractional recovery of desalted product water at the YDP(Yuma Desalting Plant). Compared to the original YDP design with 70-percent desalting recovery, additional removal of calcium in the desalting feed would allow recoveries over 90 percent. Pilot plant equipment to test this process was operated at the YDTF(Yuma Desalting Test Facility) and consisted of an IX unit and an electrodialyzer to supply reject-brine regenerant for the IX experiments. Gypsum scale buildup in the resin bed could be avoided by regeneration with a high upward flow rate causing a fluidized bed. Reuse of regenerant was also beneficial. Results show that the ion exchange high recovery pretreatment process is highly feasible, and that it is technically possible to achieve high recovery in the YDP. Numerous recommendations for a plant design are given and future studies are noted.

  4. Computer simulation of displacement cation exchange chromatography: separation of trivalent actinides and lanthanides

    SciTech Connect

    Forsberg, C.W.

    1980-05-01

    A first-generation mathematical model of displacement cation exchange chromatography (CES) was constructed. The model incorporated the following phenomena: diffusion of cations up and down the column, diffusion of cations from the bulk liquid to the resin surface, and equilibrium of cations between liquid and solid resin beads. A limited number of experiments with rare earths using DTPA as the separation agent were undertaken to increase the current understanding of the processes involved in cation exchange chromatography. The numerical computer program based on the mathematical model was written in FORTRAN IV for use on the IBM 360 series of computers.

  5. Enhanced DOC removal using anion and cation ion exchange resins.

    PubMed

    Arias-Paic, Miguel; Cawley, Kaelin M; Byg, Steve; Rosario-Ortiz, Fernando L

    2016-01-01

    Hardness and DOC removal in a single ion exchange unit operation allows for less infrastructure, is advantageous for process operation and depending on the water source, could enhance anion exchange resin removal of dissolved organic carbon (DOC). Simultaneous application of cationic (Plus) and anionic (MIEX) ion exchange resin in a single contact vessel was tested at pilot and bench scales, under multiple regeneration cycles. Hardness removal correlated with theoretical predictions; where measured hardness was between 88 and 98% of the predicted value. Comparing bench scale DOC removal of solely treating water with MIEX compared to Plus and MIEX treated water showed an enhanced DOC removal, where removal was increased from 0.5 to 1.25 mg/L for the simultaneous resin application compared to solely applying MIEX resin. A full scale MIEX treatment plant (14.5 MGD) reduced raw water DOC from 13.7 mg/L to 4.90 mg/L in the treated effluent at a bed volume (BV) treatment rate of 800, where a parallel operation of a simultaneous MIEX and Plus resin pilot (10 gpm) measured effluent DOC concentrations of no greater than 3.4 mg/L, even at bed volumes of treatment 37.5% greater than the full scale plant. MIEX effluent compared to simultaneous Plus and MIEX effluent resulted in differences in fluorescence intensity that correlated to decreases in DOC concentration. The simultaneous treatment of Plus and MIEX resin produced water with predominantly microbial character, indicating the enhanced DOC removal was principally due to increased removal of terrestrially derived organic matter. The addition of Plus resin to a process train with MIEX resin allows for one treatment process to remove both DOC and hardness, where a single brine waste stream can be sent to sewer at a full-scale plant, completely removing lime chemical addition and sludge waste disposal for precipitative softening processes. PMID:26624231

  6. Effect of sodium and calcium cations on the ion-exchange affinity of organic cations for soil organic matter.

    PubMed

    Droge, Steven; Goss, Kai-Uwe

    2012-06-01

    Sorption of organic cations to soil organic matter was studied using dynamic column experiments with different compositions of electrolytes in aqueous eluents. The sorption affinity of the tested variety of charged compounds, including primary, secondary, and tertiary amines and quaternary ammonium compounds, all showed the same response to different medium compositions. The sorption affinity to Pahokee peat (i) strongly decreased with increasing electrolyte concentration, up to a factor 250 due to tested electrolyte compositions alone, (ii) was higher in NaCl solutions than in CaCl(2) solutions of similar ionic strength, and (iii) was more sensitive to a decrease in NaCl than to a decrease in CaCl(2), though the selectivity coefficients were not significantly different. For a weak base that was tested in eluent pH either above or below its pK(a), we demonstrated that the sorption affinity of (iv) the neutral base was hardly affected by different electrolyte compositions, comparable to a neutral reference compound, (v) the protonated weak base was strongly affected by different electrolyte compositions, and (vi) the protonated base was in the same range, or stronger, compared to the neutral base. Mass action law equations for ion-exchange reactions predicted similar trends in a qualitative but not in a quantitative way. More complex models are required to fully account for the contributions of ionic interactions to the sorption of organic cations. These results imply that risk assessment models for organic bases should take ion-exchange processes into account when estimating soil sorption coefficients and bioavailability. PMID:22540998

  7. Influence of pine bark particle size and pH on cation exchange capacity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cation exchange capacity (CEC) describes the maximum quantity of cations a soil or substrate can hold while being exchangeable with the soil solution. While CEC has been studied for peat-based substrates, relatively little work has documented factors that affect CEC of pine bark substrates. The ob...

  8. Reactive transport modeling of multicomponent cation exchange at the laboratory and field scale

    SciTech Connect

    Steefel, Carl I.

    2004-04-01

    Multicomponent ion exchange models have been successful in describing the chromatographic separation of cations in both laboratory and field settings. Their chief advantage lies in their ability to capture the competitive effects of other cations that may be present. By incorporating exchanger activity coefficients calculated on the basis of the Gibbs-Duhem equation applied to the exchanger phase, it is possible to correct for the non-ideality of exchange. The use of multiple exchange sites can also substantially improve the ability of the cation exchange models to describe adsorption and retardation. All of these benefits are associated with relatively little additional computational burden. Even where the cost of the multicomponent cation exchange calculations are considered too high, the models are useful in calculating distribution coefficients for the environmental conditions of interest.

  9. (3+2)-Cycloaddition Reactions of Oxyallyl Cations

    PubMed Central

    Li, Hui; Wu, Jimmy

    2014-01-01

    The (3+2)-cycloaddition reaction involving oxyallyl cations has proven to be a versatile and efficient approach for the construction of five-membered carbo- and heterocycles, which are prevalent frameworks in natural products and pharmaceuticals. The following article will provide a brief summary of recent disclosures on this process featuring chemo-, regio- and diastereoselective oxyallyl cycloadditions with both electron-rich and electron-deficient 2π partners. PMID:25598556

  10. Simultaneous ion-exclusion chromatography and cation-exchange chromatography of anions and cations in environmental water samples on a weakly acidic cation-exchange resin by elution with pyridine-2,6-dicarboxylic acid.

    PubMed

    Ding, M Y; Tanaka, K; Hu, W; Hasebe, K; Haddad, P R

    2001-05-01

    A non-suppressed conductivity detection ion chromatographic method using a weakly acidic cation-exchange column (Tosoh TSKgel OApak-A) was developed for the simultaneous separation and determination of common inorganic anions (Cl-, NO3- and SO4(2-)) and cations (Na+, NH4+, K+, Mg2+ and Ca2+). A satisfactory separation of these anions and cations on the weakly acidic cation-exchange column was achieved in 25 min by elution with a mixture of 1.6 mmol L-1 pyridine-2,6-dicarboxylic acid and 8.0 mmol L-1 18-crown-6 at flow rate of 1.0 mL min-1. On this weakly acidic cation-exchange resin, anions were retained by an ion-exclusion mechanism and cations by a cation-exchange mechanism. The linear range of the peak area calibration curves for all analytes were up to two orders of magnitude. The detection limits calculated at S/N = 3 ranged from 0.25 to 1.9 mumol L-1 for anions and cations. The ion-exclusion chromatography-cation-exchange chromatography method developed in this work was successfully applied to the simultaneous determination of major inorganic anions and cations in rainwater, tap water and snow water samples.

  11. Thermodynamic parameters of cation exchange in MOF-5 and MFU-4l.

    PubMed

    Brozek, Carl K; Dincă, Mircea

    2015-07-28

    We present a method for approximating thermodynamic parameters ΔG(P,T)°, ΔH, and ΔS for the cation exchange process in metal-organic frameworks, as exemplified by Ni(2+) exchange into Zn4O(1,4-benzenedicarboxylate)3 (MOF-5) and Co(2+) exchange into MOF-5 and Zn5Cl4(bis(1H-1,2,3-triazolo-[4,5-b],[4',5'-i])dibenzo-[1,4]-dioxin)3 (MFU-4l). For these examples, we find that the cation exchange process is endergonic and that parameters such as solvent and cation identity impact the thermodynamics.

  12. Annealed perfluorinated cation exchange polymers for corrosion resistant coatings

    SciTech Connect

    Kinlen, P.J.; Silverman, D.C. )

    1993-11-01

    Casting and annealing a perfluorinated cation exchange (Nafion) polymer onto aluminum or 316SS results in a system which inhibits pitting and crevice corrosion that normally occurs in the presence of chloride ions and dissolved oxygen. This inhibition is believed to results from the unique chloride ion rejection properties of the annealed Nafion coating. Under neutral and basic conditions (pH > 5), localized corrosion is suppressed. Potentiodynamic polarization scans of the annealed Nafion coated aluminum and 316SS positive to the potential of the bare electrode does not produce pits. Electrochemical impedance results show that corrosion is unchanged after the coated alloy has been polarized above the pitting potential. In addition, the electrochemical impedance results indicate that the electrical resistance of the coating is low, hardly increasing the uncompensated resistance above that found for the bare metal. Hence, the movement of water and positive ions through the coating is unhindered Long-term stability and long-term corrosion inhibition afforded by the polymer must still be assessed to determine the practical limits of applicability of this coating system.

  13. Adsorption of reovirus to clay minerals: effects of cation-exchange capacity, cation saturation, and surface area.

    PubMed Central

    Lipson, S M; Stotzky, G

    1983-01-01

    The adsorption of reovirus to clay minerals has been reported by several investigators, but the mechanisms defining this association have been studied only minimally. The purpose of this investigation was to elucidate the mechanisms involved with this interaction. More reovirus type 3 was adsorbed, in both distilled and synthetic estuarine water, by low concentrations of montmorillonite than by comparable concentrations of kaolinite containing a mixed complement of cations on the exchange complex. Adsorption to the clays was essentially immediate and was correlated with the cation-exchange capacity of the clays, indicating that adsorption was primarily to negatively charged sites on the clays. Adsorption was greater with low concentrations of clays in estuarine water than in distilled water, as the higher ionic strength of the estuarine water reduced the electrokinetic potential of both clay and virus particles. The addition of cations (as chloride salts) to distilled water enhanced adsorption, with divalent cations being more effective than monovalent cations and 10(-2) M resulting in more adsorption than 10(-3) M. Potassium ions suppressed reovirus adsorption to montmorillonite, probably by collapsing the clay lattices and preventing the expression of the interlayer-derived cation-exchange capacity. More virus was adsorbed by montmorillonite made homoionic to various mono-, di-, and trivalent cations (except by montmorillonite homoionic to potassium) than by comparable concentrations of kaolinite homoionic to the same cations. The sequence of the amount of adsorption to homoionic montmorillonite was Al greater than Ca greater than Mg greater than Na greater than K; the sequence of adsorption to kaolinite was Na greater than Al greater than Ca greater than Mg greater than K. The constant partition-type adsorption isotherms obtained when the clay concentration was maintained constant and the virus concentration was varied indicated that a fixed proportion of the

  14. Intracellular acidification-induced alkali metal cation/H+ exchange in human neutrophils

    PubMed Central

    1987-01-01

    Pretreatment of isolated human neutrophils (resting pHi congruent to 7.25 at pHo 7.40) with 30 mM NH4Cl for 30 min leads to an intracellular acidification (pHi congruen to 6.60) when the NH4Cl prepulse is removed. Thereafter, in 140 mM Na+ medium, pHi recovers exponentially with time (initial rate, approximately 0.12 pH/min) to reach the normal resting pHi by approximately 20 min, a process that is accomplished mainly, if not exclusively, though an exchange of internal H+ for external Na+. This Na+/H+ countertransport is stimulated by external Na+ (Km congruent to 21 mM) and by external Li+ (Km congruent to 14 mM), though the maximal transport rate for Na+ is about twice that for Li+. Both Na+ and Li+ compete as substrates for the same translocation sites on the exchange carrier. Other alkali metal cations, such as K+, Rb+, or Cs+, do not promote pHi recovery, owing to an apparent lack of affinity for the carrier. The exchange system is unaffected by ouabain or furosemide, but can be competitively inhibited by the diuretic amiloride (Ki congruent to 8 microM). The influx of Na+ or Li+ is accompanied by an equivalent counter-reflux of H+, indicating a 1:1 stoichiometry for the exchange reaction, a finding consistent with the lack of voltage sensitivity (i.e., electroneutrality) of pHi recovery. These studies indicate that the predominant mechanism in human neutrophils for pHi regulation after intracellular acidification is an amiloride-sensitive alkali metal cation/H+ exchange that shares a number of important features with similar recovery processes in a variety of other mammalian cell types. PMID:3694176

  15. Controlled methyl-esterification of pectin catalyzed by cation exchange resin.

    PubMed

    Peng, Xiaoxia; Yang, Guang; Fan, Xingchen; Bai, Yeming; Ren, Xiaomeng; Zhou, Yifa

    2016-02-10

    This study developed a new method to methyl-esterify pectin using a cation exchange resin. Homogalacturonan (HG)-type pectin (WGPA-3-HG) and rhamnogalacturonan (RG)-I-type pectin (AHP-RG) obtained from the roots of Panax ginseng and sunflower heads, respectively, were used as models. Compared to commonly used methyl-esterification methods that use either methyl iodide or acidified methanol, the developed method can methyl-esterify both HG- and RG-I-type pectins without degrading their structures via β-elimination or acid hydrolysis. In addition, by modifying reaction conditions, including the mass ratio of resin to pectin, reaction time, and temperature, the degree of esterification can be controlled. Moreover, the resin and methanol can be recycled to conserve resources, lower costs, and reduce environmental pollution. This new methodology will be highly useful for industrial esterification of pectin. PMID:26686175

  16. Simultaneous determination of anions and cations by ion-exclusion chromatography-cation-exchange chromatography with tartaric acid/18-crown-6 as eluent.

    PubMed

    Kwon, S M; Lee, K P; Tanaka, K; Ohta, K

    1999-07-30

    Ion-exclusion chromatography-cation-exchange chromatography was developed for the simultaneous separation of common inorganic anions and cations (Cl-, NO3- and SO4(2-); Na+, NH4+, K+, Mg2+ and Ca2+) on a weakly acidic cation-exchange column by elution with weak acid. Generally, the resolution among these monovalent cations was only moderate, thereby hindering the determination of these analytes in natural-water samples. Therefore, 18-crown-6 was added to the eluent to improve the resolution. A good separation of these anions and cations on a weakly acidic cation-exchange column was achieved in 30 min by elution with 5 mM tartaric acid/6 mM 18-crown-6/methanol-water (7.5:92.5). The ion-exclusion chromatography-cation-exchange chromatography method developed here was successfully applied to the separation of major anions and cations in an environmental water sample.

  17. Bovine whey fractionation based on cation-exchange chromatography.

    PubMed

    Hahn, R; Schulz, P M; Schaupp, C; Jungbauer, A

    1998-02-01

    Bovine whey proteins have potential applications in veterinary medicine, food industry and as supplements for cell culture media. A fractionation scheme for the economically interesting proteins, such as IgG, lactoferrin and lactoperoxidase, based on cation exchangers was the goal of our investigations. A chromatographic process was developed where alpha-lactalbumin passes through the column and separation of the desired proteins is achieved. Four different cation-exchange media (S-HyperD-F, S-Sepharose FF, Fractogel EMD SO3- 650 (S) and Macro-Prep High S Support) were compared in regard to their dynamic binding capacity for IgG and their different elution behaviours when sequential step gradients with NaCl buffers were applied. Peak fractions were analyzed by size-exclusion chromatography and sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Lactoperoxidase activity was monitored by the oxidation of o-phenylenediamine. In order to explain the different resolution behaviours, isocratic runs with pure standards of whey proteins were performed. The k' values were calculated and plotted against salt concentration. Fractogel EMD had the highest binding capacity for IgG, 3.7 mg/ml gel at a linear flow-rate of 100 cm/h, but the resolution was low compared to that with the other three media. S-Hyper D and S-Sepharose FF showed lower capacities, 3.3 and 3.2 mg/ml gel, respectively, but exhibited better protein resolution. These effects could be partially explained by the k' versus salt concentration plots. The binding capacity of Macro-Prep S was considerably lower compared to that of the other resins investigated because its selectivity for whey proteins was completely different. S-Sepharose FF and S-Hyper D combine relatively high dynamic capacity for IgG and good resolution. Compared to studies with standard proteins, such as 100 mg/ml bovine serum albumin for S-Hyper D, their binding capacities were very low. Even after removal of low-molecular-mass compounds

  18. Determining the cation exchange capacity of montmorillonite by simultaneous thermal analysis method

    NASA Astrophysics Data System (ADS)

    Boeva, N. M.; Bocharnikova, Yu. I.; Belousov, P. E.; Zhigarev, V. V.

    2016-08-01

    A way of determining the cation exchange capacity of montmorillonite by simultaneous thermal analysis is developed using as an example the bentonites of the 10th Khutor deposit (Republic of Khakassia) and the Vodopadnyi area (Sakhalin Island). A correlation is established between the cation exchange capacity of smectite and its weight loss upon heating in the range of dehydration; the enthalpy of dehydration of montmorillonite; and the weight loss and the enthalpy of thermal dissociation of ethylene glycol contained in the interlayer space of the mineral's crystal structure. These data open up new possibilities for determining the cation exchange capacity of montmorillonite, the most important technological indicator of the natural clay nanomineral.

  19. Black Carbon Increases Cation Exchange Capcity in Soils

    SciTech Connect

    Liang,B.; Lehmann, J.; Solomon, D.; Kinyangi, J.; Grossman, J.; ONeill, B.; Skjemstad, J.; Thies, J.; Luizao, F.; et al.

    2006-01-01

    Black Carbon (BC) may significantly affect nutrient retention and play a key role in a wide range of biogeochemical processes in soils, especially for nutrient cycling. Anthrosols from the Brazilian Amazon (ages between 600 and 8700 yr BP) with high contents of biomass-derived BC had greater potential cation exchange capacity (CEC measured at pH 7) per unit organic C than adjacent soils with low BC contents. Synchrotron-based near edge X-ray absorption fine structure (NEXAFS) spectroscopy coupled with scanning transmission X-ray microscopy (STXM) techniques explained the source of the higher surface charge of BC compared with non-BC by mapping cross-sectional areas of BC particles with diameters of 10 to 50 {micro}m for C forms. The largest cross-sectional areas consisted of highly aromatic or only slightly oxidized organic C most likely originating from the BC itself with a characteristic peak at 286.1 eV, which could not be found in humic substance extracts, bacteria or fungi. Oxidation significantly increased from the core of BC particles to their surfaces as shown by the ratio of carboxyl-C/aromatic-C. Spotted and non-continuous distribution patterns of highly oxidized C functional groups with distinctly different chemical signatures on BC particle surfaces (peak shift at 286.1 eV to a higher energy of 286.7 eV) indicated that non-BC may be adsorbed on the surfaces of BC particles creating highly oxidized surface. As a consequence of both oxidation of the BC particles themselves and adsorption of organic matter to BC surfaces, the charge density (potential CEC per unit surface area) was greater in BC-rich Anthrosols than adjacent soils. Additionally, a high specific surface area was attributable to the presence of BC, which may contribute to the high CEC found in soils that are rich in BC.

  20. Cation Exchange Selectivity versus concentration of competing heavy metal cations (Pb2+,Zn2+) : case of Na-montmorillonite

    NASA Astrophysics Data System (ADS)

    Oueslati, W.; Mefath, M.; Ben Rhaiem, H.; Ben Haj Amara, A.

    2009-11-01

    Cation Exchange Selectivity (CES) for Wyoming montmorillonite was determined by equilibration of the clay with a mixed equinormal solution containing two competing cations (i.e. Pb2+, Zn2+). This paper aims at characterizing the structural change and selectivity of a Na-dioctahedral smectite (Wy-Na). The quantitative analysis of XRD patterns is achieved using an indirect method based on the comparison of XRD experimental patterns to calculated ones. Two reference samples were prepared by saturation with Pb2+ or Zn2+ (i.e. two heavy metal cations occurring in hold house trash). The resulting complexes were respectively labelled Wy-Pb and Wy-Zn. After that, the Wy-Na sample was dispersed in solutions containing 0.5Pb2+ and 0.5Zn2+ with different concentrations (from 10-2 N to 10-4 N) in order to understand the concentration effect on the selectivity process of the Na-montmorillonite. The XRD quantitative analysis shows that for low concentrations the d001 spacing value corresponds to Wy-Na complex, whereas for high concentrations the d001 spacing value can be attributed to the Wy-Zn and/or Wy-Pb. At low concentrations, the sample presents a homogeneous state and the cation exchange capacity is saturated with Na+ cation which is characterized by one water layer hydration state (1W). For high concentrations, interstratified hydration behavior appears and the clay has a tendency to exchange in minor contribution the Zn2+ cation and in major contribution Pb2+ cation characterized by a mixed hydration state between one (1W) and two water layers (2W).

  1. Preparation of poly(glycidylmethacrylate-divinylbenzene) weak acid cation exchange stationary phases with succinic anhydride, phthalic anhydride, and maleic anhydride for ion chromatography.

    PubMed

    Liu, Junwei; Wang, Yong; Wu, Shuchao; Zhang, Peimin; Zhu, Yan

    2016-08-01

    In this work, poly(glycidylmethacrylate-divinylbenzene) microspheres were prepared and applied for the preparation of weak acid cation exchange stationary phases. Succinic anhydride, phthalic anhydride, and maleic anhydride were selected as carboxylation reagents to prepare three weak acid cation exchangers by direct chemical derivatization reaction without solvent or catalyst. The diameters and dispersity of the microspheres were characterized by scanning electron microscopy; the amount of accessible epoxy groups and mechanical stability were also measured. The weak acid cation exchangers were characterized by Fourier transform infrared spectroscopy; the content of carboxyl groups was measured by traditional acid base titration method. The chromatographic properties were characterized and compared by separating alkali, alkaline earth metal ions and ammonium and polar amines. The separation properties enhanced in the order of succinic anhydride, phthalic anhydride, and maleic anhydride modified poly(glycidylmethacrylate-divinylbenzene) cation exchangers.

  2. Preparation of poly(glycidylmethacrylate-divinylbenzene) weak acid cation exchange stationary phases with succinic anhydride, phthalic anhydride, and maleic anhydride for ion chromatography.

    PubMed

    Liu, Junwei; Wang, Yong; Wu, Shuchao; Zhang, Peimin; Zhu, Yan

    2016-08-01

    In this work, poly(glycidylmethacrylate-divinylbenzene) microspheres were prepared and applied for the preparation of weak acid cation exchange stationary phases. Succinic anhydride, phthalic anhydride, and maleic anhydride were selected as carboxylation reagents to prepare three weak acid cation exchangers by direct chemical derivatization reaction without solvent or catalyst. The diameters and dispersity of the microspheres were characterized by scanning electron microscopy; the amount of accessible epoxy groups and mechanical stability were also measured. The weak acid cation exchangers were characterized by Fourier transform infrared spectroscopy; the content of carboxyl groups was measured by traditional acid base titration method. The chromatographic properties were characterized and compared by separating alkali, alkaline earth metal ions and ammonium and polar amines. The separation properties enhanced in the order of succinic anhydride, phthalic anhydride, and maleic anhydride modified poly(glycidylmethacrylate-divinylbenzene) cation exchangers. PMID:27288092

  3. Cation Exchange Synthesis and Unusual Resistive Switching Behaviors of Ag2Se Nanobelts.

    PubMed

    Guo, Zheng; Li, Min-Qiang; Liu, Jin-Huai; Huang, Xing-Jiu

    2015-12-16

    Ag2Se nanobelts are prepared through employing ZnSe nanobelts as templates via a facile cation exchange approach. The templates are derived from precursor ZnSe·0.5N2 H4 nanobelts, which are synthesized by a simple hydrothermal method. As-synthesized precursor nanobelts are with 200 nm in width and several hundreds of micrometers in length. Annealed in N2 , they are transformed into ZnSe nanobelts with preserving their initial morphology. Following with a complete replacement of Zn(2+) by Ag(+), Ag2Se nanobelts with single crystalline are obtained via a cation-exchange reaction. Combined with the Langmuir-Blodgett assembly technique, regular films of ZnSe nanobelts can be achieved on transparent glass substrates and Si wafers with interdigital Au electrode arrays. Further, the optical and electrical evolutions are investigated from ZnSe nanobelts to Ag2 Se nanobelts. Finally, the resistive switching characteristic are carefully explored for Ag2Se nanobelts regularly arranged on interdigital Au microelectrodes. The results indicate that it is analogous to complementary resistive switching behaviors, which is different from that of traditional two terminal devices about previously reported Ag2Se. In order to clarify this phenomenon, a possible mechanism has been proposed and indirectly demonstrated through in situ SEM (scanning electron microscropy) observation.

  4. Radical Cation/Radical Reactions: A Fourier Transform Ion Cyclotron Resonance Study of Allyl Radical Reacting with Aromatic Radical Cations

    PubMed Central

    Russell, Amber L.; Rohrs, Henry W.; Read, David; Giblin, Daryl E.; Gaspar, Peter P.; Gross, Michael L.

    2010-01-01

    A method for the study of reactions of open-shell neutrals (radicals) and radical cations is described. Pyrolysis (25–1500 °C) of thermally labile compounds, such as, 1,5-hexadiene via a Chen nozzle yields a seeded beam of reactive species in helium. The pyrolysis products are then analyzed by electron ionization (EI) or reacted with stored ions. Electron ionization of the pyrolysis products of 1,5-hexadiene shows that both the allyl radical and allene are generated. Reactions of benzene radical cations and the pyrolysis products of 1,5-hexadiene result in carbon-carbon bond formation. Those reactions of allyl radical with the benzene radical cation yield the C7H7+ ion of m/z 91, permitting an unusual entry into arenium ions. The reaction of allene with benzene radical cation in contrast yields C9H10+. and C9H9+. PMID:20401179

  5. Calcium Solubility and Cation Exchange Properties in Zeoponic Soil

    NASA Technical Reports Server (NTRS)

    Beiersdorfer, Raymond E.

    1999-01-01

    An important aspect of a regenerative life support system at a Lunar or Martian outpost is the ability to produce food. Essential plant nutrients, as well as a solid support substrate, can be provided by: (1) treated Lunar or Martian regolith; (2) a synthetic soil or (3) some combination of both. A synthetic soil composed of ammonium- and potassium-saturated chinoptlolite (a zeolite mineral) and apatite, can provide slow-release fertilization of plants via dissolution and ion-exchange reactions. Previous equilibrium studies (Beiersdorfer, 1997) on mixtures of synthetic hydroxyapatite and saturated-clinoptilolite indicate that the concentrations of macro-nutrients such as ammonium, phosphorous, potassium, magnesium, and calcium are a function of the ratio of chinoptilolite to apatite in the sample and to the ratio of potassium to ammonium on the exchange sites in the clinoptilolite. Potassium, ammonium, phosphorous, and magnesium are available to plants at sufficient levels. However, calcium is deficient, due to the high degree of calcium adsorption by the clinoptilolite. Based on a series of batch-equilibration experiments, this calcium deficiency can be reduced by (1) treating the clinoptilolite with CaNO3 or (2) adding a second Ca-bearing mineral (calcite, dolomite or wollastonite) to the soil. Treating the Cp with CaNO3 results in increased Ca in solution, decreased P in solution and decreased NH4 in solution. Concentrations of K were not effected by the CaNO3 treatment. Additions of Cal, Dol and Wol changed the concentrations of Ca and P in solution in a systematic fashion. Cal has the greatest effect, Dol the least and Wol is intermediate. The changes are consistent with changes expected for a common ion effect with Ca. Higher concentrations of Ca in solution with added Cal, Dol or Wol do not result in changes in K or NH4 concentrations.

  6. Aspects of the super-equivalent sorption of glycine by cation exchanger KU-2-8

    NASA Astrophysics Data System (ADS)

    Khokhlova, O. N.; Khokhlov, V. Yu.; Trunaeva, E. S.; Nechaeva, L. S.

    2016-07-01

    The structure formed in a sorbent during the super-equivalent sorption of glycine by cation exchanger KU-2-8 is optimized via quantum chemical simulation. The differential thermodynamic characteristics of ion exchange and super-equivalent sorption in the studied system are calculated using a thermodynamic approach that allows us to describe the simultaneous exchange and super-equivalent sorption of compounds by ion-exchangers.

  7. Preparation of decarboxylic-functionalized weak cation exchanger and application for simultaneous separation of alkali, alkaline earth and transition metals.

    PubMed

    Peng, Yahui; Gan, Yihui; He, Chengxia; Yang, Bingcheng; Guo, Zhimou; Liang, Xinmiao

    2016-06-01

    A novel weak cation exchanger (WCX) with dicarboxyl groups functionalized has been developed by clicking mercaptosuccinic acid onto silica gel. The simple synthesis starts with modification of silica gel with triethoxyvinylsilane, followed by efficient coupling vinyl-bonded silica with mercaptosuccinic acid via a "thiol-ene" click reaction. The obtained WCX demonstrated good separation and high selectivity towards common metals. Simultaneous separation of 10 alkali, alkaline earth and transition metals was achieved within 12min. Ion exchange and complex mechanism dominates the separation process. Its utility was demonstrated for determination of metals in tap water. PMID:27130093

  8. Tuning the Magnetic Properties of Metal Oxide Nanocrystal Heterostructures by Cation Exchange

    PubMed Central

    2013-01-01

    For three types of colloidal magnetic nanocrystals, we demonstrate that postsynthetic cation exchange enables tuning of the nanocrystal’s magnetic properties and achieving characteristics not obtainable by conventional synthetic routes. While the cation exchange procedure, performed in solution phase approach, was restricted so far to chalcogenide based semiconductor nanocrystals, here ferrite-based nanocrystals were subjected to a Fe2+ to Co2+ cation exchange procedure. This allows tracing of the compositional modifications by systematic and detailed magnetic characterization. In homogeneous magnetite nanocrystals and in gold/magnetite core shell nanocrystals the cation exchange increases the coercivity field, the remanence magnetization, as well as the superparamagnetic blocking temperature. For core/shell nanoheterostructures a selective doping of either the shell or predominantly of the core with Co2+ is demonstrated. By applying the cation exchange to FeO/CoFe2O4 core/shell nanocrystals the Neél temperature of the core material is increased and exchange-bias effects are enhanced so that vertical shifts of the hysteresis loops are obtained which are superior to those in any other system. PMID:23362940

  9. Equilibrium Model for Ion Exchange Between Multivalent Cations and Zeolite-A in a Molten Salt

    SciTech Connect

    Supathorn Phongikaroon; Michael Simpson

    2005-10-01

    A two-site equilibrium model that previously only accommodated monovalent cations has been extended to include divalent and trivalent cations for ion exchange between zeolite-A and molten chloride salts, a process being considered for concentrating nuclear fission products into high level waste forms. Equilibrium constants were determined by fitting the model to equilibrium data sets for ion exchange between zeolite-A and Cs ternary salt (CsCl-LiCl-KCl), Rb ternary salt (RbCl-LiCl-KCl), Na ternary salt (NaCl-LiCl-KCl), Sr ternary salt (SrCl2-LiCl-KCl), and U ternary salt (UCl3-LiCl-KCl). The results reveal a good fit between the experimental data sets and the model. The two ion exchange sites, framework sites and occluded sites, demonstrate different relative selectivities for the cations. It was found that Sr2_ is the preferred cation in the ion exchange site, and Cs_ is the preferred cation in the occlusion site. Meanwhile, Li_ has the highest combined selectivity when both ion exchange and occlusion sites are considered. Interestingly, divalent and trivalent species are more preferred in the ion exchange site than the monovalent species with the exception of Li_.

  10. Phase-selective cation-exchange chemistry in sulfide nanowire systems.

    PubMed

    Zhang, Dandan; Wong, Andrew B; Yu, Yi; Brittman, Sarah; Sun, Jianwei; Fu, Anthony; Beberwyck, Brandon; Alivisatos, A Paul; Yang, Peidong

    2014-12-17

    As a cation-deficient, p-type semiconductor, copper sulfide (Cu(2-x)S) shows promise for applications such as photovoltaics, memristors, and plasmonics. However, these applications demand precise tuning of the crystal phase as well as the stoichiometry of Cu(2-x)S, an ongoing challenge in the synthesis of Cu(2-x)S materials for a specific application. Here, a detailed transformation diagram of cation-exchange (CE) chemistry from cadmium sulfide (CdS) into Cu(2-x)S nanowires (NWs) is reported. By varying the reaction time and the reactants' concentration ratio, the progression of the CE process was captured, and tunable crystal phases of the Cu(2-x)S were achieved. It is proposed that the evolution of Cu(2-x)S phases in a NW system is dependent on both kinetic and thermodynamic factors. The reported data demonstrate that CE can be used to precisely control the structure, composition, and crystal phases of NWs, and such control may be generalized to other material systems for a variety of practical applications.

  11. Selective cation exchange in the core region of Cu2-xSe/Cu2-xS core/shell nanocrystals.

    PubMed

    Miszta, Karol; Gariano, Graziella; Brescia, Rosaria; Marras, Sergio; De Donato, Francesco; Ghosh, Sandeep; De Trizio, Luca; Manna, Liberato

    2015-09-30

    We studied cation exchange (CE) in core/shell Cu2-xSe/Cu2-xS nanorods with two cations, Ag(+) and Hg(2+), which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature. At the initial stage of the reaction, the guest ions diffused through the Cu2-xS shell and reached the Cu2-xSe core, replacing first Cu(+) ions within the latter region. These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange. For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions. PMID:26360611

  12. Selective Cation Exchange in the Core Region of Cu2–xSe/Cu2–xS Core/Shell Nanocrystals

    PubMed Central

    2015-01-01

    We studied cation exchange (CE) in core/shell Cu2–xSe/Cu2–xS nanorods with two cations, Ag+ and Hg2+, which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature. At the initial stage of the reaction, the guest ions diffused through the Cu2–xS shell and reached the Cu2–xSe core, replacing first Cu+ ions within the latter region. These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange. For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions. PMID:26360611

  13. Selective cation exchange in the core region of Cu2-xSe/Cu2-xS core/shell nanocrystals.

    PubMed

    Miszta, Karol; Gariano, Graziella; Brescia, Rosaria; Marras, Sergio; De Donato, Francesco; Ghosh, Sandeep; De Trizio, Luca; Manna, Liberato

    2015-09-30

    We studied cation exchange (CE) in core/shell Cu2-xSe/Cu2-xS nanorods with two cations, Ag(+) and Hg(2+), which are known to induce rapid exchange within metal chalcogenide nanocrystals (NCs) at room temperature. At the initial stage of the reaction, the guest ions diffused through the Cu2-xS shell and reached the Cu2-xSe core, replacing first Cu(+) ions within the latter region. These experiments prove that CE in copper chalcogenide NCs is facilitated by the high diffusivity of guest cations in the lattice, such that they can probe the whole host structure and identify the preferred regions where to initiate the exchange. For both guest ions, CE is thermodynamically driven as it aims for the formation of the chalcogen phase characterized by the lower solubility under the specific reaction conditions.

  14. Cation exchange at the secondary building units of metal-organic frameworks.

    PubMed

    Brozek, C K; Dincă, M

    2014-08-21

    Cation exchange is an emerging synthetic route for modifying the secondary building units (SBUs) of metal-organic frameworks (MOFs). This technique has been used extensively to enhance the properties of nanocrystals and molecules, but the extent of its applications for MOFs is still expanding. To harness cation exchange as a rational tool, we need to elucidate its governing factors. Not nearly enough experimental observations exist for drawing these conclusions, so we provide a conceptual framework for approaching this task. We address which SBUs undergo exchange, why certain ions replace others, how the framework influences the process, the role of the solvent, and current applications. Using these guidelines, certain trends emerge from the available data and missing experiments become obvious. If future studies follow this framework, then a more comprehensive body of observations will furnish a deeper understanding of cation exchange and inspire future applications.

  15. Kinetic Analyses of Cation Exchange Rates in Synthetic Birnessite Measured by Time- Resolved Synchrotron X-ray Diffraction

    NASA Astrophysics Data System (ADS)

    Lopano, C. L.; Heaney, P. J.; Post, J. E.; Bandstra, J.; Brantley, S. L.

    2006-05-01

    Birnessite is the most abundant and chemically important layer-structure Mn-oxide phase found in soils, desert varnishes, and ocean nodules. It also is industrially important for use in battery technology and octahedral sieves. Due to the poorly crystalline nature of natural birnessite, synthetic analogues typically have been employed in studies that explore the structural response of birnessite to variations in interlayer composition. For this work, we measured changes in unit-cell parameters over time to quantify the degree of cation exchange as a function of concentration. Aqueous K+, Cs+, and Ba2+ cations at varying concentrations at pH 7 were exchanged for interlayer Na+ in synthetic birnessite (Na0.58(Mn4+1.42,Mn3+0.58)O4·1.5H2O) using a simple flow- through cell, and the exchange products were monitored via time-resolved X-ray powder diffraction at the National Synchrotron Light Source. Powder X-ray diffraction patterns were collected every 2-3 minutes. Rietveld analyses of X-ray diffraction patterns for K- and Ba-exchanged birnessite revealed a decrease in unit- cell volume over time. In contrast, Cs+ substitution increased cell volume. For all three cations, the crystallographic data indicate that exchange occurred in two stages. A rapid and dramatic change in unit-cell volume was followed by a modest adjustment over longer timescales. Fourier electron difference syntheses revealed that the rapid, initial stage of exchange was marked by re-configuration of the interlayer species, whereas the second, protracted phase of substitution represented ordering into the newly established interlayer positions. For the first time, we have modeled the kinetics of interlayer substitution in Na-birnessite. For purposes of comparison, we have employed a simple one-stage reaction (i.e., Na-birnessite → K-birnessite) and a two stage reaction (i.e,. Na-birnessite → K-birnessitedisordered → K- birnessiteordered). For exchange with 0.01 M KCl solutions, the single

  16. Charge exchange of a polar molecule at its cation

    SciTech Connect

    Buslov, E. Yu. Zon, B. A.

    2011-01-15

    The Landau-Herring method is used to derive an analytic expression for the one-electron exchange interaction of a polar molecule with its positively charged ion, induced by a {sigma}-electron. Analogously to the classical Van der Pole method, the exchange interaction potential is averaged over the rotational states of colliding particles. The resonant charge-transfer cross section is calculated, and the effect of the dipole moments of the core on the cross section is analyzed. It is shown that allowance for the dependence of the exchange potential on the orientation of the dipole moments relative to the molecular axis may change the dependence of the cross section on the velocity of colliding particles, which is typical of the resonant charge exchange, from the resonance to the quasi-resonance dependence.

  17. Nutrient leaching from conifer needles in relation to foliar apoplast cation-exchange capacity

    SciTech Connect

    Turner, D.P.; van Broekhuizen, H.J.

    1992-01-01

    Limited evidence to date suggests that acidic precipitation promotes leaching of nutrient cations from conifer foliage. In order to evaluate the relative contribution of the apoplast cation exchange complex and symplast nutrient pools to the leached ions, the magnitude of potential foliar leaching in response to acidic precipitation was compared to foliar apoplast cation exchange capacity (CEC) for two conifer tree species (Pseudotsuga menziesii and Picea engelmanii). Leaching increased with decreasing pH and increasing time of immersion. At pH 2.1 and 3.1, equivalents of H+ depleted from the acidic solutions approximated equivalent of cations gained by the solutions. Maximum amounts leached were less than 40 micro equiv/g dry weight of needles for all ions combined. Measured foliar apoplast CEC for these species was approximately 120 micro equiv/g dry weight of needles. These relative magnitudes indicated that the apoplast provided the leached ions.

  18. Synthesis and adsorption properties of the cation exchange forms of OFF-type zeolite

    NASA Astrophysics Data System (ADS)

    Gorshunova, K. K.; Travkina, O. S.; Kustov, L. M.; Kutepov, B. I.

    2016-03-01

    The possibility of the ion-exchange of Na+ and K+ cations contained in OFF-type zeolite for H+, Ni2+, Cu2+, Co2+, and La3+ cations is investigated. Chemical and phase compositions, the morphology of crystals, and the adsorption properties of synthesized samples are studied via X-ray fluorescence and X-ray diffraction analysis, IR spectroscopy, scanning electron microscopy, and adsorption measurements.

  19. Cation exchange in a glacial till drumlin at a road salt storage facility.

    PubMed

    Ostendorf, David W; Xing, Baoshan; Kallergis, Niki

    2009-05-12

    We use laboratory and field data to calibrate existing geochemical and transport models of cation exchange induced by contamination of an unconfined aquifer at a road salt storage facility built upon a glacial till drumlin in eastern Massachusetts. A Gaines and Thomas selectivity coefficient K models the equilibrium sodium and divalent cation distribution in the groundwater and solid matrix, while an existing method of characteristics model describes the advective transport of total dissolved cations and sorbed sodium. Laboratory isotherms of split spoon soil samples from the drumlin calibrate K with an average value of 0.0048 (L/g)(1/2) for a measured cation exchange capacity of 0.057 meq/g dry soil. Ten years of monitoring well data document groundwater flow and the advection of conservative chloride due to outdoor storage and handling of road salt at the site. The monitoring well cation data and retarded transport model offer an independent K calibration of 0.0040 to 0.0047 (L/g)(1/2): the consistency of the field and laboratory selectivity coefficient calibrations endorse this application of the Gaines and Thomas and method of characteristics models. The advancing deicing agent plume releases divalent cations from the till into the groundwater, so that monitoring well samples do not reflect the chemical composition of the road salt. In this regard, dissolved divalent cation milliequivalent concentrations are as high as 80% of the total dissolved cationic concentrations in the salt contaminated monitoring well samples, far greater than their 2.5% level in the road salt stored at the site. Cation exchange can thus obscure attempts to hindcast stored road salt sodium water table concentration from monitoring well sample stoichiometry, or to predict sodium impacts on groundwater or receiving stream quality downgradient of the well.

  20. Cation exchange in a glacial till drumlin at a road salt storage facility

    NASA Astrophysics Data System (ADS)

    Ostendorf, David W.; Xing, Baoshan; Kallergis, Niki

    2009-05-01

    We use laboratory and field data to calibrate existing geochemical and transport models of cation exchange induced by contamination of an unconfined aquifer at a road salt storage facility built upon a glacial till drumlin in eastern Massachusetts. A Gaines and Thomas selectivity coefficient K models the equilibrium sodium and divalent cation distribution in the groundwater and solid matrix, while an existing method of characteristics model describes the advective transport of total dissolved cations and sorbed sodium. Laboratory isotherms of split spoon soil samples from the drumlin calibrate K with an average value of 0.0048 (L/g) 1/2 for a measured cation exchange capacity of 0.057 meq/g dry soil. Ten years of monitoring well data document groundwater flow and the advection of conservative chloride due to outdoor storage and handling of road salt at the site. The monitoring well cation data and retarded transport model offer an independent K calibration of 0.0040 to 0.0047 (L/g) 1/2: the consistency of the field and laboratory selectivity coefficient calibrations endorse this application of the Gaines and Thomas and method of characteristics models. The advancing deicing agent plume releases divalent cations from the till into the groundwater, so that monitoring well samples do not reflect the chemical composition of the road salt. In this regard, dissolved divalent cation milliequivalent concentrations are as high as 80% of the total dissolved cationic concentrations in the salt contaminated monitoring well samples, far greater than their 2.5% level in the road salt stored at the site. Cation exchange can thus obscure attempts to hindcast stored road salt sodium water table concentration from monitoring well sample stoichiometry, or to predict sodium impacts on groundwater or receiving stream quality downgradient of the well.

  1. Exchangeable cations-mediated photodegradation of polycyclic aromatic hydrocarbons (PAHs) on smectite surface under visible light.

    PubMed

    Jia, Hanzhong; Li, Li; Chen, Hongxia; Zhao, Yue; Li, Xiyou; Wang, Chuanyi

    2015-04-28

    Clay minerals saturated with different exchangeable cations are expected to play various roles in photodegradation of polycyclic aromatic hydrocarbons (PAHs) via direct and/or indirect pathways on clay surfaces. In the present study, anthracene and phenanthrene were selected as molecule probes to investigate the roles of exchangeable cations on their photodegradation under visible light irradiation. For five types of cation-modified smectite clays, the photodegradation rate of anthracene and phenanthrene follows the order: Fe(3+)>Al(3+)>Cu(2+)>Ca(2+)>K(+)>Na(+), which is consistent with the binding energy of cation-π interactions between PAHs and exchangeable cations. The result suggests that PAHs photolysis rate depends on cation-π interactions on clay surfaces. Meanwhile, the deposition of anthracene at the Na(+)-smectite and K(+)-smectite surface favors solar light absorption, resulting in enhanced direct photodecomposition of PAHs. On the other hand, smectite clays saturated with Fe(3+), Al(3+), and Cu(2+) are highly photoreactive and can act as potential catalysts giving rise to oxidative radicals such as O2(-) , which initiate the transformation of PAHs. The present work provides valuable insights into understanding the transformation and fate of PAHs in the natural soil environment and sheds light on the development of technologies for contaminated land remediation. PMID:25621830

  2. Exchangeable cations-mediated photodegradation of polycyclic aromatic hydrocarbons (PAHs) on smectite surface under visible light.

    PubMed

    Jia, Hanzhong; Li, Li; Chen, Hongxia; Zhao, Yue; Li, Xiyou; Wang, Chuanyi

    2015-04-28

    Clay minerals saturated with different exchangeable cations are expected to play various roles in photodegradation of polycyclic aromatic hydrocarbons (PAHs) via direct and/or indirect pathways on clay surfaces. In the present study, anthracene and phenanthrene were selected as molecule probes to investigate the roles of exchangeable cations on their photodegradation under visible light irradiation. For five types of cation-modified smectite clays, the photodegradation rate of anthracene and phenanthrene follows the order: Fe(3+)>Al(3+)>Cu(2+)>Ca(2+)>K(+)>Na(+), which is consistent with the binding energy of cation-π interactions between PAHs and exchangeable cations. The result suggests that PAHs photolysis rate depends on cation-π interactions on clay surfaces. Meanwhile, the deposition of anthracene at the Na(+)-smectite and K(+)-smectite surface favors solar light absorption, resulting in enhanced direct photodecomposition of PAHs. On the other hand, smectite clays saturated with Fe(3+), Al(3+), and Cu(2+) are highly photoreactive and can act as potential catalysts giving rise to oxidative radicals such as O2(-) , which initiate the transformation of PAHs. The present work provides valuable insights into understanding the transformation and fate of PAHs in the natural soil environment and sheds light on the development of technologies for contaminated land remediation.

  3. Conformations of cationized linear oligosaccharides revealed by FTMS combined with in-ESI H/D exchange.

    PubMed

    Kostyukevich, Yury; Kononikhin, Alexey; Popov, Igor; Nikolaev, Eugene

    2015-10-01

    Previously (Kostyukevich et al. Anal Chem 2014, 86, 2595), we have reported that oligosaccharides anions are produced in the electrospray in two different conformations, which differ by the rate of gas phase hydrogen/deuterium (H/D) exchange reaction. In the present paper, we apply the in-electrospray ionization (ESI) source H/D exchange approach for the investigation of the oligosaccharides cations formed by attaching of metal ions (Na, K) to the molecule. It was observed that the formation of different conformers can be manipulated by varying the temperature of the desolvating capillary of the ESI interphase. Separation of the conformers was performed using gas phase H/D approach. Because the conformers have different rates of the H/D exchange reaction, the deuterium distribution spectrum becomes bimodal. It was found that the conformation corresponding to the slow H/D exchange rate dominates in the spectrum when the capillary temperature is low (~200 °C), and the conformation corresponding to the fast H/D exchange rate dominates at high (~400 °C) temperatures. In the intermediate temperature region, two conformers are present simultaneously. It was also observed that large oligosaccharide requires higher temperature for the formation of another conformer. It was found that the presence of the conformers considerably depends on the solvent used for ESI and the pH. We have compared these results with the previously performed in-ESI source H/D exchange experiments with peptides and proteins.

  4. Glutathione-based zwitterionic stationary phase for hydrophilic interaction/cation-exchange mixed-mode chromatography.

    PubMed

    Shen, Aijin; Li, Xiuling; Dong, Xuefang; Wei, Jie; Guo, Zhimou; Liang, Xinmiao

    2013-11-01

    As a naturally hydrophilic peptide, glutathione was facilely immobilized onto silica surface to obtain a novel hydrophilic interaction/cation-exchange mixed-mode chromatographic stationary phase (Click TE-GSH) via copper-free "thiol-ene" click chemistry. The resulting material was characterized by solid state (13)C/CP MAS NMR and elemental analysis. The measurement of ζ-potential indicated the cation-exchange characteristics and adjustable surface charge density of Click TE-GSH material. The influence of acetonitrile content and pH value on the retention of ionic compounds was investigated for understanding the chromatographic behaviors. The results demonstrated that Click TE-GSH column could provide both hydrophilic and cation-exchange interaction. Taking advantage of the good hydrophilicity and inherent cation-exchange characteristics of Click TE-GSH material, the resolution of neutral fructosan with high degree of polymerization (DP), basic chitooligosaccharides and strongly acidic carrageenan oligosaccharides was successfully realized in hydrophilic interaction chromatography (HILIC), hydrophilic interaction/cation-exchange mixed-mode chromatography (HILIC/CEX), cation-exchange chromatography (CEX) and electrostatic repulsion/hydrophilic interaction chromatography (ERLIC). On the other hand, the separation of standard peptides varying in hydrophobicity/hydrophilicity and charge was achieved in both CEX and HILIC/CEX mode with high efficiency and distinct selectivity. To further demonstrate the versatility and applicability of Click TE-GSH stationary phase, the separation of a human serum albumin (HSA) tryptic digest was performed in HILIC/CEX mode. Peptides were adequately resolved and up to 86 HSA peptides were identified with sequence coverage of 85%. The results indicated the good potential of Click TE-GSH material in glycomics and proteomics. PMID:24075460

  5. Effect of cation contamination and hydrated pressure loading on the mechanical properties of proton exchange membranes

    NASA Astrophysics Data System (ADS)

    Jia, Ruiliang; Han, Binghong; Levi, Kemal; Hasegawa, Takuya; Ye, Jiping; Dauskardt, Reinhold H.

    Perfluorosulfonic acid (PFSA) polymer membranes are widely used as electrolyte thin films to transport protons in proton exchange membrane (PEM) fuel cells. The mechanical degradation of the membrane represents a common failure mode that limits the operational life of the fuel cells. In the present work, effect of contamination related to cation exchange on the mechanical reliability of PEMs was investigated. We applied the bulge test technique to assess the mechanical properties of Nafion ® PFSA membranes simulating pressure loading on hydrated PEMs in fuel cells. The corresponding elastic moduli of Nafion ® before and after cation exchange were analyzed and compared with the results measured by uniaxial tension experiments at selected humidity conditions, showing increasing stiffness with the increase of cation radius. We also used the out-of-plane tearing test method to characterize the fracture behaviors of PEMs. The effects of cation exchange and water absorption on mechanical and fracture properties of PEMs at different temperatures are discussed in terms of cation and water interactions with the molecular structure of PFSA polymers.

  6. Formation of ZnSe/Bi{sub 2}Se{sub 3} QDs by surface cation exchange and high photothermal conversion

    SciTech Connect

    Jia, Guozhi; Wang, Peng; Zhang, Yanbang; Wu, Zengna; Li, Qiang; Yao, Jianghong; Chang, Kai

    2015-08-15

    Water-dispersed core/shell structure ZnSe/Bi{sub 2}Se{sub 3} quantum dots were synthesized by ultrasonicwave-assisted cation exchange reaction. Only surface Zn ion can be replaced by Bi ion in ZnSe quantum dots, which lead to the ultrathin Bi{sub 2}Se{sub 3} shell layer formed. It is significance to find to change the crystal of QDs due to the acting of ultrasonicwave. Cation exchange mechanism and excellent photothermal conversion properties are discussed in detail.

  7. PEP Carboxykinase Exchange Reaction in Photosynthetic Bacteria 1

    PubMed Central

    Cooper, T. G.; Benedict, C. R.

    1968-01-01

    This paper describes some new characteristics of the phosphoenolpyruvate carboxykinase CO2-oxaloacetate exchange reaction in purified preparations of Rhodospirillum rubrum. The enzymatic activity has been purified 169-fold. Nucleotide diphosphates substitute for nucleotide triphosphates in the exchange reaction. Nucleotide diphosphates will not support the synthesis of phosphoenolpyruvate from oxaloacetate. This reaction differs significantly from the CO2-oxaloacetate exchange reaction in higher plants and animals. PMID:5661493

  8. [Determination of soil exchangeable base cations by using atomic absorption spectrophotometer and extraction with ammonium acetate].

    PubMed

    Zhang, Yu-ge; Xiao, Min; Dong, Yi-hua; Jiang, Yong

    2012-08-01

    A method to determine soil exchangeable calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) by using atomic absorption spectrophotometer (AAS) and extraction with ammonium acetate was developed. Results showed that the accuracy of exchangeable base cation data with AAS method fits well with the national standard referential soil data. The relative errors for parallel samples of exchangeable Ca and Mg with 66 pair samples ranged from 0.02%-3.14% and 0.06%-4.06%, and averaged to be 1.22% and 1.25%, respectively. The relative errors for exchangeable K and Na with AAS and flame photometer (FP) ranged from 0.06%-8.39% and 0.06-1.54, and averaged to be 3.72% and 0.56%, respectively. A case study showed that the determination method for exchangeable base cations by using AAS was proven to be reliable and trustable, which could reflect the real situation of soil cation exchange properties in farmlands. PMID:23156790

  9. Impact of sediment-seawater cation exchange on Himalayan chemical weathering fluxes

    NASA Astrophysics Data System (ADS)

    Lupker, Maarten; France-Lanord, Christian; Lartiges, Bruno

    2016-08-01

    Continental-scale chemical weathering budgets are commonly assessed based on the flux of dissolved elements carried by large rivers to the oceans. However, the interaction between sediments and seawater in estuaries can lead to additional cation exchange fluxes that have been very poorly constrained so far. We constrained the magnitude of cation exchange fluxes from the Ganga-Brahmaputra river system based on cation exchange capacity (CEC) measurements of riverine sediments. CEC values of sediments are variable throughout the river water column as a result of hydrological sorting of minerals with depth that control grain sizes and surface area. The average CEC of the integrated sediment load of the Ganga-Brahmaputra is estimated ca. 6.5 meq 100 g-1. The cationic charge of sediments in the river is dominated by bivalent ions Ca2+ (76 %) and Mg2+ (16 %) followed by monovalent K+ (6 %) and Na+ (2 %), and the relative proportion of these ions is constant among all samples and both rivers. Assuming a total exchange of exchangeable Ca2+ for marine Na+ yields a maximal additional Ca2+ flux of 28 × 109 mol yr-1 of calcium to the ocean, which represents an increase of ca. 6 % of the actual river dissolved Ca2+ flux. In the more likely event that only a fraction of the adsorbed riverine Ca2+ is exchanged, not only for marine Na+ but also Mg2+ and K+, estuarine cation exchange for the Ganga-Brahmaputra is responsible for an additional Ca2+ flux of 23 × 109 mol yr-1, while ca. 27 × 109 mol yr-1 of Na+, 8 × 109 mol yr-1 of Mg2+ and 4 × 109 mol yr-1 of K+ are re-absorbed in the estuaries. This represents an additional riverine Ca2+ flux to the ocean of 5 % compared to the measured dissolved flux. About 15 % of the dissolved Na+ flux, 8 % of the dissolved K+ flux and 4 % of the Mg2+ are reabsorbed by the sediments in the estuaries. The impact of estuarine sediment-seawater cation exchange appears to be limited when evaluated in the context of the long-term carbon cycle and

  10. Tree species affect cation exchange capacity (CEC) and cation binding properties of organic matter in acid forest soils.

    PubMed

    Gruba, Piotr; Mulder, Jan

    2015-04-01

    Soil organic matter (SOM) in forest soil is of major importance for cation binding and acid buffering, but its characteristics may differ among soils under different tree species. We investigated acidity, cation exchange properties and Al bonding to SOM in stands of Scots pine, pedunculate oak, Norway spruce, European beech and common hornbeam in southern Poland. The content of total carbon (Ct) was by far the major contributor to total cation exchange capacity (CECt) even in loamy soils and a strong relationship between Ct and CECt was found. The slope of the regression of CECt to Ct increased in the order hornbeam≈oak

  11. Tree species affect cation exchange capacity (CEC) and cation binding properties of organic matter in acid forest soils.

    PubMed

    Gruba, Piotr; Mulder, Jan

    2015-04-01

    Soil organic matter (SOM) in forest soil is of major importance for cation binding and acid buffering, but its characteristics may differ among soils under different tree species. We investigated acidity, cation exchange properties and Al bonding to SOM in stands of Scots pine, pedunculate oak, Norway spruce, European beech and common hornbeam in southern Poland. The content of total carbon (Ct) was by far the major contributor to total cation exchange capacity (CECt) even in loamy soils and a strong relationship between Ct and CECt was found. The slope of the regression of CECt to Ct increased in the order hornbeam≈oak

  12. A method for the production of weakly acidic cation exchange resins

    NASA Astrophysics Data System (ADS)

    Heller, H.; Werner, F.; Mitschker, A.; Diehl, H. V.; Schaefer, A.

    1991-12-01

    The invention relates to a nonpolluting method for the production of weakly acidic cation exchange resins by saponification of cross-linked acrylonitrile bead polymers, with an alkaline saponification agent at elevated temperature, according to which method the bead polymer and alkaline saponification agent are jointly added only at elevated temperature.

  13. DEMINERALIZER BUILDING, TRA608. CATION AND ANION EXCHANGERS LINE UP ALONG ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    DEMINERALIZER BUILDING, TRA-608. CATION AND ANION EXCHANGERS LINE UP ALONG NORTH WALL ON CONCRETE PLATFORMS. INL NEGATIVE NO. 2527. Unknown Photographer, 6/12/1951 - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

  14. Exchangeable Cation Hydration Properties Strongly Influence Soil Sorption of Nitroaromatic Compounds

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Nitroaromatic compounds (NACs) are commonly found as soil contaminants in military training sites and manufacturing facilities, and may adversely affect human and ecosystem health. Exchangeable cation effects on p-nitrocyanobenzene (p-NCB) and 1,4-dinitrobenzene (1,4-DNB) sorption by the Webster soi...

  15. Selective separation of sodium ions from a mixture with phenylalanine by Donnan dialysis with a profiled sulfogroup cation exchange membrane

    NASA Astrophysics Data System (ADS)

    Vasil'eva, V. I.; Goleva, E. A.

    2013-11-01

    The possibility of separating ions of metal from a mixture with ampholyte (an amino acid) by Donnan dialysis with an MK-40 sulfogroup cation exchange membrane is demonstrated. Conditions ensuring the selectivity and intensity of the mass transfer of sodium ions from a mixture with bipolar phenylalanine ions into a diffusate containing hydrochloric acid through a cation exchange membrane are found.

  16. Exchangeable Cations in the Soils of Quercus Dominated Forests in Northeastern Austria

    NASA Astrophysics Data System (ADS)

    Yan, Shuai; Bruckman, Viktor J.; Glatzel, Gerhard

    2010-05-01

    In northeastern Austria there is a growing interest in increased utilisation of forest biomass for energy. This study focuses on soil properties and nutrient pool characteristics in deciduous forests in order to provide advice for forest management. We (i) quantified selected exchangeable cations in the soils of our study area and (ii) identified the effects of stand age, soil type, soil depth and soil pH on exchangeable cations and cation exchange capacity (CEC). Nine permanent Quercus petraea dominated plots on sandy, clayey cambisols and calcic chernozem were selected for our study. From each plot 18 soil samples were collected in a systematic grid by means of a soil corer with 70 mm diameter to a maximum depth of 60 cm. Soil pH, exchangeable mineral elements K, Ca, Mg, Na, Mn, Al, and Fe were determined in five geometric soil horizons. Statistical analysis showed that (i) forest age did not influence the exchangeable K content of the sandy soils; (ii) the exchangeable K content decreased with increasing stand age in clayey cambisols; (iii) exchangeable K, Na and Mg were higher in calcic chernozems and clayey cambisols (iv) exchangeable Fe was significantly higher in sandy forest soils except in the 60-80 years old stand; (v) exchangeable Fe was below detection limit in calcic chernozem soils. A comparison of exchangeable cations revealed that (i) Ca is the key element of base cations (ii) the content of base cations is strongly significantly higher in calcic chernozem soils (iii) calcic chernozem soils have the highest CEC. CEC ranged from 38 to 190 μmol/g in the entire research area. Base cations, acid cations and CEC differ with soil depth as followed (i) in sandy and clayey cambisols, CEC had a minimum in 20 cm depth and then increased with soil depth to 50 cm; (ii) CEC decreased steadily with soil depth in calcic chernozems. As expected, CEC is significantly positively correlated (Pearson correlation coefficient 0.661, P<0.01) with the pH of the soil. The

  17. Structure-Property Relationships in Hydroxide-Exchange Membranes with Cation Strings and High Ion-Exchange Capacity.

    PubMed

    Wang, Junhua; Gu, Shuang; Xiong, Ruichang; Zhang, Bingzi; Xu, Bingjun; Yan, Yushan

    2015-12-21

    A series of poly(2,4-dimethyl-1,4-phenylene oxide) hydroxide-exchange membranes (HEMs) with cation strings containing a well-defined number of cations (CS-n) and similar, high ion-exchange capacities are synthesized to investigate the effect of cation distribution on key HEM properties. As the number of cations on each string grows, the size of the ionic clusters increases from 10 to 55 nm. Well-connected ion pathways and a hydrophobic framework are observed for n≥4. The enhanced phase segregation increases the hydroxide conductivity from CS-1 to CS-6 (30 to 65 mS cm(-1) ) and suppresses the water uptake (from 143 % to 62 %). Moreover, molar hydroxide conductivities for CS-n membranes show two distinctive stages as n increases: ∼23 S cm(2)  mol(-1) for n≤3; and ∼34 cm(2)  mol(-1) for n≥4.

  18. Surface-orientation-dependent distribution of subsurface cation-exchange defects in olivine-phosphate nanocrystals.

    PubMed

    Chung, Sung-Yoon; Choi, Si-Young; Kim, Tae-Hwan; Lee, Seongsu

    2015-01-27

    Atomic-scale exchange between two different cations of similar size in crystalline oxides is one of the major types of point defects when multiple cations in oxygen interstitials are arrayed in an ordered manner. Although a number of studies have been performed on a variety of Li-intercalation olivine phosphates to determine the distribution of exchange defects in bulk, understanding of the thermodynamic stability of the defects in subsurface regions and its dependency on the crystallographic orientation at the surface has remained elusive. Through a combination of small-angle neutron scattering, atomic-scale direct probing with scanning transmission electron microscopy, and theoretical ab initio calculations, we directly demonstrate that the antisite exchange defects are distributed in a highly anisotropic manner near the surfaces of LiFePO4 crystals. Moreover, a substantial amount of cation exchanges between Li and Fe sites is identified as an energetically favorable configuration in some surface regions, showing excellent agreement with the calculation results of negative defect formation energies. The findings in this study provide insight into developing better ways to avoid degradation of lithium mobility through the surface as well as scientifically notable features regarding the distribution of exchange defects in olivine phosphates.

  19. First principles derived, transferable force fields for CO2 adsorption in Na-exchanged cationic zeolites.

    PubMed

    Fang, Hanjun; Kamakoti, Preeti; Ravikovitch, Peter I; Aronson, Matthew; Paur, Charanjit; Sholl, David S

    2013-08-21

    The development of accurate force fields is vital for predicting adsorption in porous materials. Previously, we introduced a first principles-based transferable force field for CO2 adsorption in siliceous zeolites (Fang et al., J. Phys. Chem. C, 2012, 116, 10692). In this study, we extend our approach to CO2 adsorption in cationic zeolites which possess more complex structures. Na-exchanged zeolites are chosen for demonstrating the approach. These methods account for several structural complexities including Al distribution, cation positions and cation mobility, all of which are important for predicting adsorption. The simulation results are validated with high-resolution experimental measurements of isotherms and microcalorimetric heats of adsorption on well-characterized materials. The choice of first-principles method has a significant influence on the ability of force fields to accurately describe CO2-zeolite interactions. The PBE-D2 derived force field, which performed well for CO2 adsorption in siliceous zeolites, does not do so for Na-exchanged zeolites; the PBE-D2 method overestimates CO2 adsorption energies on multi-cation sites that are common in cationic zeolites with low Si/Al ratios. In contrast, a force field derived from the DFT/CC method performed well. Agreement was obtained between simulation and experiment not only for LTA-4A on which the force field fitting is based, but for other two common adsorbents, NaX and NaY.

  20. Cation exchange in a temporally fluctuating thin freshwater lens on top of saline groundwater

    NASA Astrophysics Data System (ADS)

    Eeman, S.; De Louw, P. G. B.; Van der Zee, S. E. A. T. M.

    2016-10-01

    In coastal-zone fields with a high groundwater level and sufficient rainfall, freshwater lenses are formed on top of saline or brackish groundwater. The fresh and the saline water meet at shallow depth, where a transition zone is found. This study investigates the mixing zone that is characterized by this salinity change, as well as by cation exchange processes, and which is forced by seepage and by rainfall which varies as a function of time. The processes are first investigated for a one-dimensional (1D) stream tube perpendicular to the interface concerning salt and major cation composition changes. The complex sequence of changes is explained with basic cation exchange theory. It is also possible to show that the sequence of changes is maintained when a two-dimensional field is considered where the upward saline seepage flows to drains. This illustrates that for cation exchange, the horizontal component (dominant for flow of water) has a small impact on the chemical changes in the vertical direction. The flow's horizontal orientation, parallel to the interface, leads to changes in concentration that are insignificant compared with those that are found perpendicular to the interface, and are accounted for in the 1D flow tube. Near the drains, differences with the 1D considerations are visible, especially in the longer term, exceeding 100 years. The simulations are compared with field data from the Netherlands which reveal similar patterns.

  1. A rice tonoplastic calcium exchanger, OsCCX2 mediates Ca2+/cation transport in yeast

    PubMed Central

    Yadav, Akhilesh K.; Shankar, Alka; Jha, Saroj K.; Kanwar, Poonam; Pandey, Amita; Pandey, Girdhar K.

    2015-01-01

    In plant cell, cations gradient in cellular compartments is maintained by synergistic action of various exchangers, pumps and channels. The Arabidopsis exchanger family members (AtCCX3 and AtCCX5) were previously studied and belong to CaCA (calcium cation exchangers) superfamily while none of the rice CCXs has been functionally characterized for their cation transport activities till date. Rice genome encode four CCXs and only OsCCX2 transcript showed differential expression under abiotic stresses and Ca2+ starvation conditions. The OsCCX2 localized to tonoplast and suppresses the Ca2+ sensitivity of K667 (low affinity Ca2+ uptake deficient) yeast mutant under excess CaCl2 conditions. In contrast to AtCCXs, OsCCX2 expressing K667 yeast cells show tolerance towards excess Na+, Li+, Fe2+, Zn2+ and Co2+ and suggest its ability to transport both mono as well as divalent cations in yeast. Additionally, in contrast to previously characterized AtCCXs, OsCCX2 is unable to complement yeast trk1trk2 double mutant suggesting inability to transport K+ in yeast system. These finding suggest that OsCCX2 having distinct metal transport properties than previously characterized plant CCXs. OsCCX2 can be used as potential candidate for enhancing the abiotic stress tolerance in plants as well as for phytoremediation of heavy metal polluted soil. PMID:26607171

  2. A rice tonoplastic calcium exchanger, OsCCX2 mediates Ca2+/cation transport in yeast.

    PubMed

    Yadav, Akhilesh K; Shankar, Alka; Jha, Saroj K; Kanwar, Poonam; Pandey, Amita; Pandey, Girdhar K

    2015-11-26

    In plant cell, cations gradient in cellular compartments is maintained by synergistic action of various exchangers, pumps and channels. The Arabidopsis exchanger family members (AtCCX3 and AtCCX5) were previously studied and belong to CaCA (calcium cation exchangers) superfamily while none of the rice CCXs has been functionally characterized for their cation transport activities till date. Rice genome encode four CCXs and only OsCCX2 transcript showed differential expression under abiotic stresses and Ca(2+) starvation conditions. The OsCCX2 localized to tonoplast and suppresses the Ca(2+) sensitivity of K667 (low affinity Ca(2+) uptake deficient) yeast mutant under excess CaCl2 conditions. In contrast to AtCCXs, OsCCX2 expressing K667 yeast cells show tolerance towards excess Na(+), Li(+), Fe(2+), Zn(2+) and Co(2+) and suggest its ability to transport both mono as well as divalent cations in yeast. Additionally, in contrast to previously characterized AtCCXs, OsCCX2 is unable to complement yeast trk1trk2 double mutant suggesting inability to transport K(+) in yeast system. These finding suggest that OsCCX2 having distinct metal transport properties than previously characterized plant CCXs. OsCCX2 can be used as potential candidate for enhancing the abiotic stress tolerance in plants as well as for phytoremediation of heavy metal polluted soil.

  3. Ion-exchange selectivities of periderm and cuticular membranes toward alkali cations

    SciTech Connect

    Ersoz, M.; Duncan, H.J.

    1994-08-01

    The ion-exchange selectivities of lithium, sodium, potassium, and cesium on isolated potato periderm (Solanum tuberosum) and pear fruit cuticular membranes were investigated; the general order of preference both for cation selectivities and ion-exchange capacities was lithium > sodium > potassium > cesium. The potato periderm and pear fruit cuticular membranes exhibited a behavior typical of ion-exchange resins of the weak acid type. At constant pH 7, the ion-exchange capacities of periderm and cuticular membranes increased with hydrated ionic radius, and also with increasing pH and neutral salt concentration, and decreased with crystal ionic radius. Counterion selectivities also exhibited the same behavior. The ion-exchange properties are discussed in terms of the structure and function of potato periderm and pear fruit cuticular membranes.

  4. Effect of quinidine on cation exchange in cultured cells.

    PubMed

    McCall, D

    1976-06-01

    The effects of quinidine on membrane ion exchange were examined using monolayer cultures of mammalian cells. Quinidine, in concentrations from 10(-6) to 10(-3) M, produced a prompt inhibition of the passive Na influx, dose-dependent along a sigmoid log dose-response curve. This effect was at a maximum for each concentration of the drug within 30 seconds of application. Passive Na influx (pmol/cm2/sec) decreased from 18.8 to 17.6 (P less than .05) and 10.5 (P less than .001) in the presence of 10(-6) and 10(-3) M quinidine, respectively. In the continued presence of quinidine, there was no further time-dependent effect on the Na influx, nor was there any tendency for the influx to recover. Washing the cells free of quinidine, however, resulted in a return of Na influx to control levels within 1 to 3 minutes. After 1 to 2 minute of quinidine treatment, coupled active Na efflux/K influx rapidly declined, reaching minimum values for each concentration between 2 to 4 minutes of drug treatment. Beyond that time, active Na/K fluxes again increased, but to values which remained significantly less than control, for up to 4 hours. Ten minutes of exposure to quinidine were required before any demonstrable effect on the passive K efflux could be recorded. In the presence of quinidine, there was reduced membrane turnover of both Na and K, but such that after a brief initial period (10 minutes or less) both ions were in flux equilibrium, explaining the absence of change in [Nai] and [Ki] in the presence of quinidine. Calculations of Ec1 indicated that, when present for 4 hours, quinidine did not change the Em in these cells although significant (P less than .001) reductions in apparent PNa and Pk values were recorded. The effect on PNa was much greater than that on Pk. The quinidine-induced flux changes occurred in a definite temporal sequence suggesting that they could all be explained on the basis of one direct initial action. This initial direct action, namely the prompt

  5. Mathematical Modeling of Cation Contamination in a Proton-exchange Membrane

    SciTech Connect

    Weber, Adam; Delacourt, Charles

    2008-09-11

    Transport phenomena in an ion-exchange membrane containing both H+ and K+ are described using multicomponent diffusion equations (Stefan-Maxwell). A model is developed for transport through a Nafion 112 membrane in a hydrogen-pump setup. The model results are analyzed to quantify the impact of cation contamination on cell potential. It is shown that limiting current densities can result due to a decrease in proton concentration caused by the build-up of contaminant ions. An average cation concentration of 30 to 40 percent is required for appreciable effects to be noticed under typical steady-state operating conditions.

  6. Composite membranes prepared from cation exchange membranes and polyaniline and their transport properties in electrodialysis

    SciTech Connect

    Sata, Tshikatsu; Ishii, Yuuko; Kawamura, Kohei; Matsusaki, Koji

    1999-02-01

    A cation exchange membrane was modified with polyaniline by polymerizing aniline with ammonium peroxodisulfate on the membrane surfaces, producing a membrane with polyaniline layers on both surfaces or a membrane with a single polyaniline layer on the surface. The modified membranes, composite membranes, showed sodium ion permselectivity in electrodialysis compared with divalent cations at an optimum polymerization time. The electronic conductivity of dry membranes showed a maximum (ca. 5 {times} 10{sup {minus}3} S/cm) at the same polymerization time as the time to attain a maximum value of the sodium ion permselectivity. Because emeraldine-based polyaniline is conductive and has a cationic charge, the sodium ion permselectivity is based on the difference in the electrostatic repulsion forces of the cationic charge on the membrane surface of a desalting side to divalent cations and sodium ions. In fact, the selective permeation of sodium ions appeared only when the layer faced the desalting side of the membrane, and was affected by dissociation of polyaniline. Further oxidized polyaniline, pernigraniline-based polyaniline, did not affect the permselectivity between cations, and the diffusion coefficient of neutral molecules, urea, increased with increasing polymerization time. Sodium ion permselectivity was maintained with repeated electrodialysis.

  7. The Prowess of Photogenerated Amine Radical Cations in Cascade Reactions: From Carbocycles to Heterocycles.

    PubMed

    Morris, Scott A; Wang, Jiang; Zheng, Nan

    2016-09-20

    Cascade reactions represent a class of ideal organic reactions because they empower efficiency, elegance, and novelty. However, development of cascade reactions remains a daunting task for synthetic chemists. Radicals are known to be well suited for cascade reactions. Compared with widely used carbon-based radicals, nitrogen-based radicals, such as neutral aminyl radicals and protonated aminyl radicals (amine radical cations), are underutilized, although they are behind some notable synthetic methods such as the Hofmann-Löffler-Freytag reaction. The constraint on their usage is generally attributed to the limited number of available stable precursors. Since amine radical cations offer increased reactivity and selectivity in chemical transformations compared with neutral aminyl radicals, their generation is of utmost importance. Recently, a surge of reports has been revealed using visible light photoredox catalysis. It has been demonstrated that amines can act as an electron donor in a reductive quenching cycle while the amine itself is oxidized to the amine radical cation. Although a number of methods exist to generate amine radical cations, the photochemical formation of these species offers many practical advantages. In this Account, we discuss our journey to the development of annulation reactions with various π-bonds and electrophilic addition reactions to alkenes using photogenerated amine radical cations. Various carbocycles and heterocycles are produced by these reactions. In our annulation work, we first show that single electron photooxidation of cyclopropylanilines to the amine radical cations triggers ring opening of the strained carbocycle, producing distonic radical cations. These odd-electron species are shown to react with alkenes and alkynes to yield the corresponding cyclopentanes and cyclopentenes in an overall redox neutral process. Further development of this annulation reaction allows us to achieve the [4 + 2] annulation of cyclobutylanilines

  8. The Prowess of Photogenerated Amine Radical Cations in Cascade Reactions: From Carbocycles to Heterocycles.

    PubMed

    Morris, Scott A; Wang, Jiang; Zheng, Nan

    2016-09-20

    Cascade reactions represent a class of ideal organic reactions because they empower efficiency, elegance, and novelty. However, development of cascade reactions remains a daunting task for synthetic chemists. Radicals are known to be well suited for cascade reactions. Compared with widely used carbon-based radicals, nitrogen-based radicals, such as neutral aminyl radicals and protonated aminyl radicals (amine radical cations), are underutilized, although they are behind some notable synthetic methods such as the Hofmann-Löffler-Freytag reaction. The constraint on their usage is generally attributed to the limited number of available stable precursors. Since amine radical cations offer increased reactivity and selectivity in chemical transformations compared with neutral aminyl radicals, their generation is of utmost importance. Recently, a surge of reports has been revealed using visible light photoredox catalysis. It has been demonstrated that amines can act as an electron donor in a reductive quenching cycle while the amine itself is oxidized to the amine radical cation. Although a number of methods exist to generate amine radical cations, the photochemical formation of these species offers many practical advantages. In this Account, we discuss our journey to the development of annulation reactions with various π-bonds and electrophilic addition reactions to alkenes using photogenerated amine radical cations. Various carbocycles and heterocycles are produced by these reactions. In our annulation work, we first show that single electron photooxidation of cyclopropylanilines to the amine radical cations triggers ring opening of the strained carbocycle, producing distonic radical cations. These odd-electron species are shown to react with alkenes and alkynes to yield the corresponding cyclopentanes and cyclopentenes in an overall redox neutral process. Further development of this annulation reaction allows us to achieve the [4 + 2] annulation of cyclobutylanilines

  9. Formation of pseudomorphic nanocages from Cu2O nanocrystals through anion exchange reactions.

    PubMed

    Wu, Hsin-Lun; Sato, Ryota; Yamaguchi, Atsushi; Kimura, Masato; Haruta, Mitsutaka; Kurata, Hiroki; Teranishi, Toshiharu

    2016-03-18

    The crystal structure of ionic nanocrystals (NCs) is usually controlled through reaction temperature, according to their phase diagram. We show that when ionic NCs with different shapes, but identical crystal structures, were subjected to anion exchange reactions under ambient conditions, pseudomorphic products with different crystal systems were obtained. The shape-dependent anionic framework (surface anion sublattice and stacking pattern) of Cu2O NCs determined the crystal system of anion-exchanged products of CuxS nanocages. This method enabled us to convert a body-centered cubic lattice into either a face-centered cubic or a hexagonally close-packed lattice to form crystallographically unusual, multiply twinned structures. Subsequent cation exchange reactions produced CdS nanocages while preserving the multiply-twinned structures. A high-temperature stable phase such as wurtzite ZnS was also obtained with this method at ambient conditions. PMID:26989249

  10. Dehydration enthalpy of alkali-cations-exchanged montmorillonite from thermogravimetric analysis.

    PubMed

    Kharroubi, M; Balme, S; Henn, F; Giuntini, J C; Belarbi, H; Haouzi, A

    2009-01-15

    Dehydration of a series of homoionic alkali-exchanged montmorillonites is studied at different treatment temperatures by means of thermogravimetric analysis. More specifically, we investigate the last stages of dehydration when the number of adsorbed water molecules corresponds, at maximum, to a monolayer. Weight losses are measured at several constant temperatures as a function of time. Application of Van't Hoff's law yields the dehydration enthalpy. Trends and data similar to those reported from other experimental conditions are found. Comparison with X-ray data and with the dissociation enthalpy of alkali cation/water complexes shows that dehydration of weakly hydrated homoionic alkali montmorillonites results from the competition between opposite energy contributions due to (i) the cation solvation, (ii) the hydration of the silicate interlayer surface, and (iii) the structural swelling. So, depending on the balance between these various energy contributions, different behaviors are observed according to the nature of the alkali cations. PMID:18973904

  11. Multicolour synthesis in lanthanide-doped nanocrystals through cation exchange in water

    PubMed Central

    Han, Sanyang; Qin, Xian; An, Zhongfu; Zhu, Yihan; Liang, Liangliang; Han, Yu; Huang, Wei; Liu, Xiaogang

    2016-01-01

    Meeting the high demand for lanthanide-doped luminescent nanocrystals across a broad range of fields hinges upon the development of a robust synthetic protocol that provides rapid, just-in-time nanocrystal preparation. However, to date, almost all lanthanide-doped luminescent nanomaterials have relied on direct synthesis requiring stringent controls over crystal nucleation and growth at elevated temperatures. Here we demonstrate the use of a cation exchange strategy for expeditiously accessing large classes of such nanocrystals. By combining the process of cation exchange with energy migration, the luminescence properties of the nanocrystals can be easily tuned while preserving the size, morphology and crystal phase of the initial nanocrystal template. This post-synthesis strategy enables us to achieve upconversion luminescence in Ce3+ and Mn2+-activated hexagonal-phased nanocrystals, opening a gateway towards applications ranging from chemical sensing to anti-counterfeiting. PMID:27698348

  12. Multicolour synthesis in lanthanide-doped nanocrystals through cation exchange in water

    NASA Astrophysics Data System (ADS)

    Han, Sanyang; Qin, Xian; An, Zhongfu; Zhu, Yihan; Liang, Liangliang; Han, Yu; Huang, Wei; Liu, Xiaogang

    2016-10-01

    Meeting the high demand for lanthanide-doped luminescent nanocrystals across a broad range of fields hinges upon the development of a robust synthetic protocol that provides rapid, just-in-time nanocrystal preparation. However, to date, almost all lanthanide-doped luminescent nanomaterials have relied on direct synthesis requiring stringent controls over crystal nucleation and growth at elevated temperatures. Here we demonstrate the use of a cation exchange strategy for expeditiously accessing large classes of such nanocrystals. By combining the process of cation exchange with energy migration, the luminescence properties of the nanocrystals can be easily tuned while preserving the size, morphology and crystal phase of the initial nanocrystal template. This post-synthesis strategy enables us to achieve upconversion luminescence in Ce3+ and Mn2+-activated hexagonal-phased nanocrystals, opening a gateway towards applications ranging from chemical sensing to anti-counterfeiting.

  13. Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

    ERIC Educational Resources Information Center

    Mirich, Anne; Miller, Trisha Hoette; Klotz, Elsbeth; Mattson, Bruce

    2015-01-01

    Two gas phase deuterium/hydrogen exchange reactions are described utilizing a simple inexpensive glass catalyst tube containing 0.5% Pd on alumina through which gas mixtures can be passed and products collected for analysis. The first of these exchange reactions involves H[subscript 2] + D[subscript 2], which proceeds at temperatures as low as 77…

  14. Use of Cation Exchange Chromatography for Human C-peptide Isotope Dilution – Mass Spectrometric Assay

    PubMed Central

    Stoyanov, Alexander V.; Rohlfing, Curt L.; Connolly, Shawn; Roberts, Matthew L.; Nauser, Christopher L.; Little, Randie R.

    2016-01-01

    An application of ion exchange chromatography for C-peptide analysis is described here. At the stage of C-peptide isolation, a strong cation exchanger (SP HP or MonoS) was used to purify the analyte from ballast proteins and peptides. The conditions of ion-exchange chromatographic separations were optimized using theoretical modeling of the net surface electric charge of the peptide as a function of pH. The purified and concentrated sample was further subjected to LC-MS/MS. In order to improve the reliability of analysis, two fragment ions were monitored simultaneously both for native C-peptide and internal standard, isotopically labeled C-peptides analogues (fragments with m/z of 927.7 and 147.2). Using ion-exchange chromatography, it became possible to process larger sample volumes, important for testing patients with very low C peptide levels, compared to currently used solid phase extraction methods. PMID:22098929

  15. Evaluation of the field-scale cation exchange capacity of Hanford sediments

    SciTech Connect

    Steefel, C.I.

    2003-02-01

    Three-dimensional simulations of unsaturated flow, transport, and multi-component, multi-site cation exchange in the vadose zone were used to analyze the migration of a plume resulting from a leak of the SX-115 tank at the Hanford site, USA. The match within about 0.5 meters of the positions of retarded sodium and potassium fronts suggests that the laboratory-derived parameters may be used in field-scale simulations of radionuclide migration at the Hanford site.

  16. Emission spectrographic determination of barium in sea water using a cation exchange concentration procedure

    USGS Publications Warehouse

    Szabo, B. J.; Joensuu, O.

    1967-01-01

    A concentration technique employing Dowex 50W cation exchange resin is described for the determination of barium in sea water. The separated barium is precipitated as fluoride together with calcium and strontium and measured by emission spectrographic analysis. The vertical distribution of barium in sea water has been measured in the Caribbean Sea and the Atlantic Ocean. The barium content varied between 7 and 23 ??g. per liter; in two profiles, the lowest concentrations were at a depth of about 1000 meters.

  17. Hydrogeochemistry and cation-exchange processes in the coastal aquifer of Mar Del Plata, Argentina

    NASA Astrophysics Data System (ADS)

    Martínez, D. E.; Bocanegra, E. M.

    2002-06-01

    The aquifer of Mar del Plata is unconfined and composed of silt and fine sand. The sand fraction is mainly quartz, potassium feldspars, chalcedony, and gypsum. Volcanic-glass shards (40-60%) dominate the silt fraction, and the clays are of the smectite and illite groups. Calcium carbonate, in caliche form, constitutes about 10-20% of the sediment. Groundwater flow is from west to east, and discharge is in the Atlantic Ocean. Because of overexploitation, the flow direction was reversed in a coastal belt about 3.5 km wide, and this has resulted in seawater intrusion. The groundwater is the CaHCO3 type in the recharge zone, and becomes NaHCO3 type towards the discharge area. Salinization by marine intrusion and seawater/fresh-water mixing produces an increase in the major-ion concentrations of the groundwater. The calcium content of the groundwater is higher and the sodium content is lower than those that would be expected if the mixing is considered as just the addition of seawater and fresh water in determined proportions without reactive processes taking place. Hydrogeochemical modeling was applied to the study of hydrogeochemical processes, mainly cation exchange, using the codes NETPATH and PHREEQM. Calcite and gypsum equilibrium, together with cation exchange, are the main hydrogeochemical processes. Cation-exchange capacity of the solid phase was determined by empirical calculations and experimental methods. The affinity order for the groundwater in contact with the aquifer matrix is Ca>Mg>Na in the regional-flow system, but the order is reversed in the salinization process. Reactive transport modeling using the code PHREEQM is useful for analyzing cation exchange in a marine-intrusion process.

  18. Some investigations on the radiation stability of a strongly acidic cation exchange resin

    NASA Astrophysics Data System (ADS)

    Dessouki, A. M.; Zahran, A. H.; Rabie, A. M.; Amer, S. I.

    The radiation-chemical stability of Merck Cation Exchanger I, a strongly acidic sulphonated cation exchanger of the polymerization type based on styrene-divinylbenze (DVB) copolymers was investigated. The radiation stability of the resin was assessed from the change in exchange capacity, loss in weight, change in swelling behaviour and formation of new exchange groups. The loss in capacity was 44 and 32% for resin specimens in the H +-form irradiated to 1000 Mrad in air and in vacuum, respectively. The Na +-form of the exchanger showed high resistance to radiation and the loss in capacity did not exceed 7% at a dose of 1000 Mrad. The loss in capacity was accompanied by a loss in weight and a decrease in the degree of swelling of the irradiated resin. The formation of new functional groups of the carboxylic and phenolic types was confirmed. The amount of these group increases with the increase in the integral dose. The amount of sulphuric acid formed as a result of irradiating the resin in the dry and moist states was determined. An increase in the moisture content of the resin resulted in a marked decrease in its radiation stability.

  19. Cation Exchange in Dynamic 3D Porous Magnets: Improvement of the Physical Properties.

    PubMed

    Grancha, Thais; Acosta, Alvaro; Cano, Joan; Ferrando-Soria, Jesús; Seoane, Beatriz; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio

    2015-11-16

    We report two novel three-dimensional porous coordination polymers (PCPs) of formulas Li4{Mn4[Cu2(Me3mpba)2]3}·68H2O (2) and K4{Mn4[Cu2(Me3mpba)2]3}·69H2O (3) obtained-via alkali cation exchange in a single-crystal to single-crystal process-from the earlier reported anionic manganese(II)-copper(II) PCP of formula Na4{Mn4[Cu2(Me3mpba)2]3}·60H2O (1) [Me3mpba(4-) = N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. This postsynthetic process succeeds where the direct synthesis in solution from the corresponding building blocks fails and affords significantly more robust PCPs with enhanced magnetic properties [long-range 3D magnetic ordering temperatures for the dehydrated phases (1'-3') of 2.0 (1'), 12.0 (2'), and 20.0 K (3')]. Changes in the adsorptive properties upon postsynthetic exchange suggest that the nature, electrostatic properties, mobility, and location of the cations within the framework are crucial for the enhanced structural stability. Overall, these results further confirm the potential of postsynthetic methods (including cation exchange) to obtain PCPs with novel or enhanced physical properties while maintaining unaltered their open-framework structures. PMID:26492551

  20. Cation Exchange in Dynamic 3D Porous Magnets: Improvement of the Physical Properties.

    PubMed

    Grancha, Thais; Acosta, Alvaro; Cano, Joan; Ferrando-Soria, Jesús; Seoane, Beatriz; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio

    2015-11-16

    We report two novel three-dimensional porous coordination polymers (PCPs) of formulas Li4{Mn4[Cu2(Me3mpba)2]3}·68H2O (2) and K4{Mn4[Cu2(Me3mpba)2]3}·69H2O (3) obtained-via alkali cation exchange in a single-crystal to single-crystal process-from the earlier reported anionic manganese(II)-copper(II) PCP of formula Na4{Mn4[Cu2(Me3mpba)2]3}·60H2O (1) [Me3mpba(4-) = N,N'-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. This postsynthetic process succeeds where the direct synthesis in solution from the corresponding building blocks fails and affords significantly more robust PCPs with enhanced magnetic properties [long-range 3D magnetic ordering temperatures for the dehydrated phases (1'-3') of 2.0 (1'), 12.0 (2'), and 20.0 K (3')]. Changes in the adsorptive properties upon postsynthetic exchange suggest that the nature, electrostatic properties, mobility, and location of the cations within the framework are crucial for the enhanced structural stability. Overall, these results further confirm the potential of postsynthetic methods (including cation exchange) to obtain PCPs with novel or enhanced physical properties while maintaining unaltered their open-framework structures.

  1. Comparison of gaseous oxidized Hg measured by KCl-coated denuders, and nylon and cation exchange membranes.

    PubMed

    Huang, Jiaoyan; Miller, Matthieu B; Weiss-Penzias, Peter; Gustin, Mae Sexauer

    2013-07-01

    The chemical compounds that make up gaseous oxidized mercury (GOM) in the atmosphere, and the reactions responsible for their formation, are not well understood. The limitations and uncertainties associated with the current method applied to measure these compounds, the KCl-coated denuder, are not known due to lack of calibration and testing. This study systematically compared the uptake of specific GOM compounds by KCl-coated denuders with that collected using nylon and cation exchange membranes in the laboratory and field. In addition, a new method for identifying different GOM compounds using thermal desorption is presented. Different GOM compounds (HgCl2, HgBr2, and HgO) were found to have different affinities for the denuder surface and the denuder underestimated each of these compounds. Membranes measured 1.3 to 3.7 times higher GOM than denuders in laboratory and field experiments. Cation exchange membranes had the highest collection efficiency. Thermodesorption profiles for the release of GOM compounds from the nylon membrane were different for HgO versus HgBr2 and HgCl2. Application of the new field method for collection and identification of GOM compounds demonstrated these vary as a function of location and time of year. Understanding the chemistry of GOM across space and time has important implications for those developing policy regarding this environmental contaminant. PMID:23651121

  2. Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization.

    PubMed

    Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

    2016-08-01

    The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M(+.) decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques. Graphical Abstract ᅟ.

  3. Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization.

    PubMed

    Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

    2016-08-01

    The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M(+.) decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques. Graphical Abstract ᅟ. PMID:27126470

  4. Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

    NASA Astrophysics Data System (ADS)

    Vaikkinen, Anu; Kauppila, Tiina J.; Kostiainen, Risto

    2016-08-01

    The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M+. decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques.

  5. Effect of blastfurnace slag addition to Portland cement for cationic exchange resins encapsulation

    NASA Astrophysics Data System (ADS)

    Lafond, E.; Cau Dit Coumes, C.; Gauffinet, S.; Chartier, D.; Le Bescop, P.; Stefan, L.; Nonat, A.

    2013-07-01

    In the nuclear industry, cement-based materials are extensively used to encapsulate spent ion exchange resins (IERs) before their final disposal in a repository. It is well known that the cement has to be carefully selected to prevent any deleterious expansion of the solidified waste form, but the reasons for this possible expansion are not clearly established. This work aims at filling the gap. The swelling pressure of IERs is first investigated as a function of ions exchange and ionic strength. It is shown that pressures of a few tenths of MPa can be produced by decreases in the ionic strength of the bulk solution, or by ion exchanges (2Na+ instead of Ca2+, Na+ instead of K+). Then, the chemical evolution of cationic resins initially in the Na+ form is characterized in CEM I (Portland cement) and CEM III (Portland cement + blastfurnace slag) cements at early age and an explanation is proposed for the better stability of CEM III material.

  6. Effects of the anion salt nature on the rate constants of the aqueous proton exchange reactions.

    PubMed

    Paredes, Jose M; Garzon, Andres; Crovetto, Luis; Orte, Angel; Lopez, Sergio G; Alvarez-Pez, Jose M

    2012-04-28

    The proton-transfer ground-state rate constants of the xanthenic dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II), recovered by Fluorescence Lifetime Correlation Spectroscopy (FLCS), have proven to be useful to quantitatively reflect specific cation effects in aqueous solutions (J. M. Paredes, L. Crovetto, A. Orte, J. M. Alvarez-Pez and E. M. Talavera, Phys. Chem. Chem. Phys., 2011, 13, 1685-1694). Since these phenomena are more sensitive to anions than to cations, in this paper we have accounted for the influence of salts with the sodium cation in common, and the anion classified according to the empirical Hofmeister series, on the proton transfer rate constants of TG-II. We demonstrate that the presence of ions accelerates the rate of the ground-state proton-exchange reaction in the same order than ions that affect ion solvation in water. The combination of FLCS with a fluorophore undergoing proton transfer reactions in the ground state, along with the desirable feature of a pseudo-dark state when the dye is protonated, allows one unique direct determination of kinetic rate constants of the proton exchange chemical reaction. PMID:22421957

  7. Reactions and structural investigation of chlorpromazine radical cation

    NASA Astrophysics Data System (ADS)

    Joshi, Ravi; Ghanty, Tapan K.; Mukherjee, T.

    2008-10-01

    Experimental and theoretical studies have been carried out to understand pro-oxidant behaviour of chlorpromazine radical cation (CPZ rad + ). Pulse radiolysis studies have shown that CPZ rad + oxidizes physiological antioxidants (uric acid and bilirubin), and biomolecules like, tyrosine and proteins (bovine serum albumin and casein), thereby acting as a pro-oxidant. Ab-initio quantum chemical calculations suggest structural and electronic changes on oxidation of CPZ. The calculations with Hartree-Fock and density functional methods show that ring nitrogen atom is the site of electron removal from CPZ and sulfur atom is the site of maximum spin in CPZ rad + . The calculations also suggest that oxidation of CPZ leads to increase in planarity of the tricyclic ring as well as tilting of alkyl side chain towards chlorine containing ring. The structural changes on oxidation of CPZ and spin delocalization in CPZ rad + fairly explain the pro-oxidant activity of CPZ.

  8. Impregnating titanium phosphate nanoparticles onto a porous cation exchanger for enhanced lead removal from waters.

    PubMed

    Jia, Kun; Pan, Bingcai; Lv, Lu; Zhang, Qingrui; Wang, Xiaoshu; Pan, Bingjun; Zhang, Weiming

    2009-03-15

    Titanium phosphate (TiP) exhibits preferable sorption toward lead ion in the presence of competing calcium ions at high levels, however, it is present as fine or ultrafine particles and cannot be directly employed in fixed-bed or any flow-through systems due to the excessive pressure drop and poor mechanical strength. In the present study a new hybrid sorbent TiP-001 was fabricated by impregnating titanium phosphate (TiP) nanoparticles onto a strongly acidic cation exchanger D-001 for enhanced lead removal from waters. D-001 was selected as a host material mainly because of the Donnan membrane effect resulting from the immobilized sulfonic acid groups bound on the exchanger matrix, which would enhance permeation of the target metal cation prior to effective sequestration. TiP-001 was characterized by transmission electron micrograph (TEM), X-ray diffraction (XRD), and pH-titration. Batch and column sorption onto TiP-001 was assayed to evaluate its performance as compared to the host exchanger D-001. Lead sorption onto TiP-001 is a pH-dependent process due to the ion-exchange nature, and its sorption kinetics follows the pseudo-second-order model well. Compared to D-001, TiP-001 displays highly selective lead sorption in the presence of competing calcium cations at concentration of several orders higher than the target metal. Fixed-bed sorption of a synthetic feeding solution indicates that lead retention by TiP-001 results in a conspicuous decrease of this toxic metal from 0.50 to below 0.010 mg/L (drinking water standard recommended by WHO). Moreover, its feasible regeneration by dilute HCl solution also favors TiP-001 to be a feasible sorbent for enhanced lead removal from water. PMID:19101673

  9. Erionite-Na upon heating: dehydration dynamics and exchangeable cations mobility.

    PubMed

    Ballirano, Paolo; Pacella, Alessandro

    2016-01-01

    Erionite is a fibrous zeolite significantly more tumorigenic than crocidolite asbestos upon inhalation. In recent years, several papers have been published aimed at characterizing from the crystal-chemical point of view erionite fibres. As their toxicity has been ascribed to Fe acquired within the human body, studies aimed at characterizing the iron topochemistry have also been published, suggesting a possible important role played by the ionic exchange properties and cations mobility of this zeolite on developing carcinogenicity. Here we report the analysis results of the thermal behaviour of erionite-Na, which has been found to deviate significantly from that of erionite-K. This result is in contrast with the current scientific view that differences in weighted ionic potential, Si/Al ratio and size of exchangeable cations result in significantly different thermal behaviours, all those parameters being nearly identical or very similar in both species. The different mobility of the extraframework cations observed in erionite samples with dissimilar chemistry is of particular interest within the frame of the hypothesis that their biological activity could depend, apart from surface interactions, also on bulk effects. PMID:26948139

  10. Erionite-Na upon heating: dehydration dynamics and exchangeable cations mobility

    NASA Astrophysics Data System (ADS)

    Ballirano, Paolo; Pacella, Alessandro

    2016-03-01

    Erionite is a fibrous zeolite significantly more tumorigenic than crocidolite asbestos upon inhalation. In recent years, several papers have been published aimed at characterizing from the crystal-chemical point of view erionite fibres. As their toxicity has been ascribed to Fe acquired within the human body, studies aimed at characterizing the iron topochemistry have also been published, suggesting a possible important role played by the ionic exchange properties and cations mobility of this zeolite on developing carcinogenicity. Here we report the analysis results of the thermal behaviour of erionite-Na, which has been found to deviate significantly from that of erionite-K. This result is in contrast with the current scientific view that differences in weighted ionic potential, Si/Al ratio and size of exchangeable cations result in significantly different thermal behaviours, all those parameters being nearly identical or very similar in both species. The different mobility of the extraframework cations observed in erionite samples with dissimilar chemistry is of particular interest within the frame of the hypothesis that their biological activity could depend, apart from surface interactions, also on bulk effects.

  11. Incorporation of phthalocyanines by cationic and anionic clays via ion exchange and direct synthesis

    SciTech Connect

    Carrado, K.A.; Botto, R.E.; Winans, R.E. ); Forman, J.E. )

    1993-04-01

    Phthalocyanines (Pc) and metallophthalocyanines were incorporated into the galleries of anionic and cationic clays via ion exchange and in situ crystallization of the synthetic clay layers. Intercalation compounds between the layered magnesium silicate clay hectorite and cationic phthalocyanines were directly prepared by refluxing for 2 days aqueous solutions of silica sol, magnesium hydroxide, lithium flouride, and either alcian blue dyes (Cu(II)Pc) or 15-crown-5 tetra-substituted phthalocyanine (15C5Pc). The CuPc dyes are tetrapositively charged through peripheral quaternary ammonium groups, whereas the 15C5Pc is electrically neutral. Anionic clays prepared by hydrolysis of mixed solutions of aluminum nitrate, magnesium nitrate, and copper(II) phthalocyaninetetrasulfonic acid, tetrasodium salt (CuPcTs) in sodium hydroxide resulted in crystallization of an intercalation compound between a layered double hydroxide (LDH) and this anionic Pc. The material prepared by ion exchange of CuPcTs into a wet, freshly prepared LDH was superior in crystallinity. The phthalocyanines are oriented parallel to cationic hectorite clay layers (gallery heights 4.5-6.5[angstrom]) and perpendicular to anionic layered double hydroxide clay layers (gallery height 18,2[angstrom]) in correlation with their hosts' respective layer charge densities. 32 refs., 4 figs., 2 tabs.

  12. Chabazite: stable cation-exchanger in hyper alkaline concrete pore water.

    PubMed

    Van Tendeloo, Leen; Wangermez, Wauter; Kurttepeli, Mert; de Blochouse, Benny; Bals, Sara; Van Tendeloo, Gustaaf; Martens, Johan A; Maes, André; Kirschhock, Christine E A; Breynaert, Eric

    2015-02-17

    To avoid impact on the environment, facilities for permanent disposal of hazardous waste adopt multibarrier design schemes. As the primary barrier very often consists of cement-based materials, two distinct aspects are essential for the selection of suitable complementary barriers: (1) selective sorption of the contaminants in the repository and (2) long-term chemical stability in hyperalkaline concrete-derived media. A multidisciplinary approach combining experimental strategies from environmental chemistry and materials science is therefore essential to provide a reliable assessment of potential candidate materials. Chabazite is typically synthesized in 1 M KOH solutions but also crystallizes in simulated young cement pore water, a pH 13 aqueous solution mainly containing K(+) and Na(+) cations. Its formation and stability in this medium was evaluated as a function of temperature (60 and 85 °C) over a timeframe of more than 2 years and was also asessed from a mechanistic point of view. Chabazite demonstrates excellent cation-exchange properties in simulated young cement pore water. Comparison of its Cs(+) cation exchange properties at pH 8 and pH 13 unexpectedly demonstrated an increase of the KD with increasing pH. The combined results identify chabazite as a valid candidate for inclusion in engineered barriers for concrete-based waste disposal.

  13. Synthesis, characterization and applications of a new cation exchanger tamarind sulphonic acid (TSA) resin.

    PubMed

    Singh, A V; Sharma, Naresh Kumar; Rathore, Abhay S

    2012-01-01

    A new composite cation exchanger, tamarind sulphonic acid (TSA) resin has been synthesized. The chemically modified TSA ion exchange resin has been used for the removal and preconcentration of Zn2+, Cd2+, Fe2+, Co2+ and Cu2+ ions in aqueous solution and effluent from the Laxmi steel plant in Jodhpur, India. This type of composite represents a new class of hybrid ion exchangers with good ion exchange capacity, stability, reproducibility and selectivity for toxic metal ions found in effluent from the steel industry. The characterization of the resin was carried out by determining the ion-exchange capacity, elemental analysis, pH titration, Fourier transform infrared spectra and thermal analysis. The distribution coefficients (K(d)) of toxic metal ions were determined in a reference aqueous solution and the steel plant effluent at different pH values; the absorbency of different metal ions on the TSA resin was studied for up to 10 cycles. The adsorption of different metal ions on TSA resin follows the order: Co2+ > Cu2+ > Zn2+ > Fe2+ > Cd2+. The ion exchange capacity of TSA resin is 2.87%. PMID:22629619

  14. Crystal structure and cation exchanging properties of a novel open framework phosphate of Ce (IV)

    NASA Astrophysics Data System (ADS)

    Bevara, Samatha; Achary, S. N.; Patwe, S. J.; Sinha, A. K.; Mishra, R. K.; Kumar, Amar; Kaushik, C. P.; Tyagi, A. K.

    2016-05-01

    Herein we report preparation, crystal structure and ion exchanging properties of a new phosphate of tetravalent cerium, K2Ce(PO4)2. A monoclinic structure having framework type arrangement of Ce(PO4)6 units formed by CeO8 square-antiprism and PO4 tetrahedra is assigned for K2Ce(PO4)2. The K+ ions are occupied in the channels formed by the Ce(PO4)6 and provide overall charge neutrality. The unique channel type arrangements of the K+ make them exchangeable with other cations. The ion exchanging properties of K2Ce(PO4)2 has been investigated by equilibrating with solution of 90Sr followed by radiometric analysis. In optimum conditions, significant exchange of K+ with Sr2+ with Kd ~ 8000 mL/g is observed. The details of crystal structure and ion exchange properties are explained and a plausible mechanism for ion exchange is presented.

  15. Aza-crown ether complex cation ionic liquids: preparation and applications in organic reactions.

    PubMed

    Song, Yingying; Cheng, Chen; Jing, Huanwang

    2014-09-26

    Aza-crown ether complex cation ionic liquids (aCECILs) were devised, fabricated, and characterized by using NMR spectroscopy, MS, thermogravimetric differential thermal analysis (TG-DTA), elemental analysis and physical properties. These new and room-temperature ILs were utilized as catalysts in various organic reactions, such as the cycloaddition reaction of CO2 to epoxides, esterification of acetic acid and alcohols, the condensation reaction of aniline and propylene carbonate, and Friedel-Crafts alkylation of indole with aldehydes were investigated carefully. In these reactions, the ionic liquid exhibited cooperative catalytic activity between the anion and cation. In addition, the aza-[18-C-6HK][HSO4]2 was the best acidic catalyst in the reactions of esterification and Friedel-Crafts alkylation under mild reaction conditions. PMID:25154312

  16. Aza-crown ether complex cation ionic liquids: preparation and applications in organic reactions.

    PubMed

    Song, Yingying; Cheng, Chen; Jing, Huanwang

    2014-09-26

    Aza-crown ether complex cation ionic liquids (aCECILs) were devised, fabricated, and characterized by using NMR spectroscopy, MS, thermogravimetric differential thermal analysis (TG-DTA), elemental analysis and physical properties. These new and room-temperature ILs were utilized as catalysts in various organic reactions, such as the cycloaddition reaction of CO2 to epoxides, esterification of acetic acid and alcohols, the condensation reaction of aniline and propylene carbonate, and Friedel-Crafts alkylation of indole with aldehydes were investigated carefully. In these reactions, the ionic liquid exhibited cooperative catalytic activity between the anion and cation. In addition, the aza-[18-C-6HK][HSO4]2 was the best acidic catalyst in the reactions of esterification and Friedel-Crafts alkylation under mild reaction conditions.

  17. Comprehensive kinetic studies of acidic oil continuous esterification by cation-exchange resin in fixed bed reactors.

    PubMed

    Cheng, Yu; Feng, Yaohui; Ren, Yanbiao; Liu, Xuan; Gao, Aoran; He, Benqiao; Yan, Feng; Li, Jianxin

    2012-06-01

    Biodiesel produced by esterification from molar ratio of methanol to free fatty acid (FFA) as 25:1 in presence of triglyceride was carried out with cation-exchange resin as a heterogeneous catalyst in three different scales of fixed bed reactors from minireactor (6.8 mm × 110 mm) to pilot scale reactor (70 mm × 1260 mm) at 338 K. The kinetic study of esterification was undertaken in terms of pseudo-homogeneous mechanism and performed as a first order reaction with elimination of the solid-liquid internal and external mass transfer resistances. Moreover, a kinetic model of FFA esterification was developed to illustrate the relationship between the FFA conversion and the catalyst bed height of fixed bed reactor. The model was also suitable for various resins in fixed bed reactor. The theoretical predictions were in agreement with the experimental data with root mean square (RMS) errors <10.

  18. Emerging roles of alkali cation/proton exchangers in organellar homeostasis

    PubMed Central

    Orlowski, John; Grinstein, Sergio

    2016-01-01

    The regulated movement of monovalent cations such as H+, Li+, Na+ and K+ across biological membranes influences a myriad of cellular processes and is fundamental to all living organisms. This is accomplished by a multiplicity of ion channels, pumps and transporters. Our insight into their molecular, cellular and physiological diversity has increased greatly in the past few years with the advent of genome sequencing, genetic manipulation and sophisticated imaging techniques. One of the revelations from these studies is the emergence of novel alkali cation/protons exchangers that are present in endomembranes, where they function to regulate not only intraorganellar pH but also vesicular biogenesis, trafficking and other aspects of cellular homeostasis. PMID:17646094

  19. Carbon dioxide and nitrogen adsorption on cation-exchanged SSZ-13 zeolites.

    PubMed

    Pham, Trong D; Liu, Qingling; Lobo, Raul F

    2013-01-15

    Samples of high-silica SSZ-13, ion exchanged with protons and alkali-metal cations Li(+), Na(+), and K(+), were investigated using adsorption isotherms of CO(2) and N(2). The results show that Li-, Na-SSZ-13 have excellent CO(2) capacity at ambient temperature and pressure; in general, Li-SSZ-13 shows the highest capacity for N(2), CO(2) particularly in the low-pressure region. The effect of cation type and Si/Al ratio (6 and 12) on the adsorption properties was investigated through analysis of adsorption isotherms and heats of adsorption. The separation of CO(2) in a flue gas mixture was evaluated for these adsorbents in the pressure swing adsorption and vacuum pressure adsorption processes. PMID:23249267

  20. Effects of exchanged cation and layer charge on the sorption of water and EGME vapors on montmorillonite clays

    USGS Publications Warehouse

    Chiou, C.T.; Rutherford, D.W.

    1997-01-01

    The effects of exchanged cation and layer charge on the sorption of water and ethylene glycol monoethyl ether (EGME) vapors on montmorillonite have been studied on SAz-1 and SWy-1 source clays, each exchanged respectively with Ca, Na, K, Cs and tetramethylammonium (TMA) cations. The corresponding lattice expansions were also determined, and the corresponding N2 adsorption data were provided for comparison. For clays exchanged with cations of low hydrating powers (such as K, Cs and TMA), water shows a notably lower uptake than does N2 at low relative pressures (P/P0). By contrast, EGME shows higher uptakes than N2 on all exchanged clays at all P/P0. The anomaly for water is attributed to its relatively low attraction for siloxane surfaces of montmorillonite because of its high cohesive energy density. In addition to solvating cations and expanding interlayers, water and EGME vapors condense into small clay pores and interlayer voids created by interlayer expansion. The initial (dry) interlayer separation varies more significantly with cation type than with layer charge; the water-saturated interlayer separation varies more with cation type than the EGME-saturated interlayer separation. Because of the differences in surface adsorption and interlayer expansion for water and EGME, no general correspondence is found between the isotherms of water and EGME on exchanged clays, nor is a simple relation observed between the overall uptake of either vapor and the cation solvating power. The excess interlayer capacities of water and of EGME that result from lattice expansion of the exchanged clays are estimated by correcting for amounts of vapor adsorption on planar clay surfaces and of vapor condensation into intrinsic clay pores. The resulting data follow more closely the relative solvating powers of the exchanged cations.

  1. Reducing the Cation Exchange Capacity of Lithium Clay to Form Better Dispersed Polymer-Clay Nanocomposites

    NASA Technical Reports Server (NTRS)

    Liang, Maggie

    2004-01-01

    Polymer-clay nanocomposites have exhibited superior strength and thermo- oxidative properties as compared to pure polymers for use in air and space craft; however, there has often been difficulty completely dispersing the clay within the matrices of the polymer. In order to improve this process, the cation exchange capacity of lithium clay is first lowered using twenty-four hour heat treatments of no heat, 130 C, 150 C, or 170 C to fixate the lithium ions within the clay layers so that they are unexchangeable. Generally, higher temperatures have generated lower cation exchange capacities. An ion exchange involving dodecylamine, octadecylamine, or dimethyl benzidine (DMBZ) is then employed to actually expand the clay galleries. X-ray diffraction and transmission electron microscopy can be used to determine whether the clay has been successfully exfoliated. Finally, resins of DMBZ with clay are then pressed into disks for characterization using dynamic mechanical analyzer and oven- aging techniques in order to evaluate their glass transition, modulus strength, and thermal-oxidative stability in comparison to neat DMBZ. In the future, they may also be tested as composites for flexural and laminar shear strength.

  2. [Cation exchanges during the process of Cd(2+) absorption by Alfalfa in aqueous solutions].

    PubMed

    Li, Yue-Peng; Yin, Hua; Ye, Jin-Shao; Peng, Hua; Qin, Hua-Ming; Long, Yan; He, Bao-Yan; Zhang, Na; Tong, Yao; Peng, Su-Fen

    2011-11-01

    A hydroponic experiment was conducted to investigate the cation exchanges during the process of Cd2+ absorption by Alfalfa in aqueous solution. The absorption efficiency of Alfalfa plants with 0-10 mg x L(-1) Cd2+ treatments, changes of Na+, K+, Mg2+, Ca2+ and NH4(+) concentration, and the variation of pH values at different absorption time (0, 1, 2, 4, 8, 12, 24 and 72 h) were studied separately. The multiple linear regressions between Cd2+ absorption and cation variation were analyzed. The results indicated that when Cd2+ concentrations were 0.1, 1, 5, 10 mg x L(-1), the absorption efficiencies of Cd2+ by Alfalfa after 72 h were 85.86%, 52.14%, 15.97% and 7.81%. Cation exchange was involved in the removal of Cd2+ by Alfalfa in aqueous solution. Except for NH4(+), the concentrations of cationic metals Na+, K+, Mg2+ and Ca2+ in aqueous solution increased over time, which increased 11.30% - 61.72%, 21.44% - 98.73%, 24.09% - 8.90% and 37.04% - 191.96%, respectively. Kinetic studies illuminated that the release of Na+, K+, Mg2+ and Ca2+ by Alfalfa in Cd2+ solution with initial concentrations of 0, 0. 1, 1, 5, 10 mg x L(-1) best fitted pseudo-second-order equation,while the NH4(+) release fitted this model when Cd2+ concentrations were 1, 5, 10 mg x L(-1). The gradual decrease of pH during adsorption of Cd2+ by Alfalfa was observed. As the competition ion of Cd2+, H+ might affect the capacity of Alfalfa root system to absorb Cd2+. The ternary linear equation results demonstrated that the content of Cd2+ absorption by Alfalfa strongly related with the release of Ca2+, Mg2+, Na+. And this exchange mainly occurred among Cd2+ and divalent cations. PMID:22295633

  3. The use of some ion-exchange sorbing tracer cations in in-situ experiments in high saline groundwaters

    SciTech Connect

    Byegaard, J.; Skarnemark, G.; Skaalberg, M.

    1995-12-31

    The possibility to use alkali metals and alkaline earth metals as slightly sorbing tracers in in-situ sorption experiments in high saline groundwaters has been investigated. The cation exchange characteristics of granite and some fracture minerals (chlorite and calcite) have been studied using the proposed cations as tracers. The results show low Kd`s for Na, Ca and Sr ({approximately}0.1 ml/g), while the sorption is higher for the more electropositive cations (Rb, Cs and Ba). A higher contribution of irreversible sorption can also be observed for the latter group of cations. For calcite the sorption of all the tracers, except Ca, is lower compared to the corresponding sorption to granite and chlorite. Differences in selectivity coefficients and cation exchange capacity are obtained when using different size fractions of crushed granite. The difference is even more pronounced when comparing crushed granite to intact granite.

  4. Stability and isomerization reactions of phenyl cation C6H5+ isomers

    NASA Astrophysics Data System (ADS)

    Shi, Dandan; Yang, Xue; Zhang, Xiaomei; Shan, Shimin; Xu, Haifeng; Yan, Bing

    2016-03-01

    As a key polyatomic molecular cation that plays a pivotal role in growth of the polycyclic aromatic hydrocarbons, phenyl cation C6H5+ exhibits various isomers and isomerization reactions. Investigation on the structure and stability of the isomers as well as the isomerization is important for better understanding the chemical reactions involving C6H5+ cations. In this work, we have performed a theoretical study on the stability and isomerization reactions of C6H5+ isomers at density functional theory B3LYP/6-311G (d, p) level. We have obtained a total of 60 isomers of C6H5+ cations, most of which are reported for the first time. The geometries, vibrational frequencies, thermodynamic properties and stability of 28 out of 60 isomers have been summarized in detail. Different ring-to-ring and ring-to-chain isomerization pathways, which are connected via 28 transition states, have been investigated using the intrinsic reaction coordinate method. The results show that the isomerization reactions occur via hydrogen migration followed by bond-breaking and reconstruction.

  5. Pullulan Production by Aureobasidium pullulans ATCC 201253 Cells Adsorbed onto Cellulose Anion and Cation Exchangers

    PubMed Central

    West, Thomas P.

    2012-01-01

    The anion exchanger phosphocellulose and the cation exchanger triethylaminoethyl cellulose were used to immobilize cells of the fungus Aureobasidium pullulans ATCC 201253 and the adsorbed cells were subsequently investigated for their ability to produce the polysaccharide pullulan using batch fermentation. The cells adsorbed on the triethylaminoethyl cellulose at pH 7.5 produced higher pullulan levels than those cells immobilized on phosphocellulose at pH 4.0 for 2 cycles of 168 h at 30 °C. Relative to the initial cycle of 168 h, pullulan production by the cells immobilized on the triethylaminoethyl cellulose decreased slightly after 168 h of the second production cycle while pullulan production by the phosphocellulose-immobilized cells remained about the same after 168 h of the second production cycle. PMID:23762749

  6. Chromatographic cation exchange separation of decigram quantities of californium and other transplutonium elements

    SciTech Connect

    Benker, D.E.; Chattin, F.R.; Collins, E.D.; Knauer, J.B.; Orr, P.B.; Ross, R.G.; Wiggins, J.T.

    1981-01-01

    Decigram quantities of highly radioactive transplutonium elements are routinely partitioned at TRU by chromatographic elution from cation resin using AHIB eluents. Batch runs containing up to 200 mg of /sup 252/Cf can be made in about 5 h (2 h to load the feed and 3 h for the elution), with two high-pressure ion exchange columns, a small one for the initial loading of the feed and a large one for the elution. The separations achieved in the column are preserved by routing the column effluent through an alpha detector and using the response from the detector to select appropriate product fractions. The high-pressure ion exchange process has been reliable and relatively easy to operate; therefore it will continue to be used for partitioning transplutonium elements at TRU. 3 figures, 1 table.

  7. [Yield of pigment cation-radicals in the reaction of quinone photooxidation of chlorophyll].

    PubMed

    Kostikov, A P; Sadovnikova, N A; Evstigneev, V B

    1976-01-01

    Photoinduced transfer of electrons in alkohol solutions of chlorophyll and its deuterated analog, deuterochlorophyll containing the quinoses: p-benzoquinone, chloranyl, duroquinone, 1,4-naftoquinone and ubiquinone (coenzyme Q6) is studied. It is shown that pigment cation-radical and quinone anion-radical are the primary products of photoreaction. A relationship between stationary concentrations of deuterochlorophyll and p-benzoquinone radicals and quinone concentration in solution is obtained. The reaction mechanism and causes of other authors' (G. Tollin et al.) failure in finding pigment cation-radicals which are formed in the reaction of the latter with quinoses are discussed. It is shown that optimal conditions for accumulating photoinduced cation-radicals of the pigment in pigment solutions of chlorophyll with quinones are lowered temperature, high viscosity of the solvent, low pH of the solution, careful purification of the quinone from hydroquinone admixture.

  8. Cation-exchange chromatography of peptides on poly(2-sulfoethyl aspartamide)-silica.

    PubMed

    Alpert, A J; Andrews, P C

    1988-06-29

    A strong cation-exchange material, poly(2-sulfoethyl aspartamide)-silica (PolySULFOETHYL Aspartamide) was developed for purification and analysis of peptides by high-performance liquid chromatography. All peptides examined were retained at pH 3, even when the amino terminus was the only basic group. Peptides were eluted in order of increasing number of basic residues with a salt gradient. Capacity was high, as was selectivity and column efficiency. This new column material displays modest mixed-mode effects, allowing the resolution of peptides having identical charges at a given pH. The selectivity can be manipulated by the addition of organic solvent to the mobile phases; this increases the retention of some peptides and decreases the retention of others. The retention in any given case may reflect a combination of steric factors and non-electrostatic interactions. Selectivity was complementary to that of reversed-phase chromatography (RPC) materials. Excellent purifications were obtained by sequential use of PolySULFOETHYL Aspartamide and RPC columns for purification of peptides from crude tissue extracts. The new cation exchanger is quite promising as a supplement to RPC for general peptide chromatography. PMID:2844843

  9. Preparation and characterization of high capacity, strong cation-exchange fiber based adsorbents.

    PubMed

    Schwellenbach, Jan; Taft, Florian; Villain, Louis; Strube, Jochen

    2016-05-20

    Motivated by the demand for more economical capture and polishing steps in downstream processing of protein therapeutics, a novel strong cation-exchange chromatography stationary phase based on polyethylene terephthalate (PET) high surface area short-cut fibers is presented. The fiber surface is modified by grafting glycidyl methacrylate (GMA) via surface-initiated atom transfer radical polymerization (SI-ATRP) and a subsequent derivatization leading to sulfonic acid groups. The obtained cation-exchange fibers have been characterized and compared to commercially available resin and membrane based adsorbers. High volumetric static binding capacities for lysozyme (90mg/mL) and polyclonal human IgG (hIgG, 92mg/mL) were found, suggesting an efficient multi-layer binding within the grafted hydrogel layer. A packed bed of randomly orientated fibers has been tested for packing efficiency, permeability and chromatographic performance. High dynamic binding capacities for lysozyme (50mg/mL) and hIgG (54mg/mL) were found nearly independent of the bed-residence time, revealing a fast mass-transport mechanism. Height equivalent to a theoretical plate (HETP) values in the order of 0.1 cm and a peak asymmetry factor (AF) of 1.8 have been determined by tracer experiments. Additionally inverse size-exclusion chromatography (iSEC) revealed a bimodal structure within the fiber bed, consisting of larger transport channels, formed by the voidage between the fibers, and a hydrogel layer with porous properties. PMID:27106396

  10. Numerical simulation of cesium and strontium migration through sodium bentonite altered by cation exchange with groundwater components

    SciTech Connect

    Jacobsen, J.S.; Carnahan, C.L.

    1988-10-01

    Numerical simulations have been used to investigate how spatial and temporal changes in the ion exchange properties of bentonite affect the migration of cationic fission products from high-level waste. Simulations in which fission products compete for exchange sites with ions present in groundwater diffusing into the bentonite are compared to simulations in which the exchange properties of bentonite are constant. 12 refs., 3 figs., 2 tabs.

  11. Effect of ionophores on the rate of intramolecular cation exchange in durosemiquinone ion pairs

    NASA Technical Reports Server (NTRS)

    Eastman, M. P.; Bruno, G. V.; Mcguyer, C. A.; Gutierrez, A. R.; Shannon, J. M.

    1979-01-01

    The effects of the ionophores 15-crown-5 (15C5), 18-crown-6 (18C6), dibenzo-18-crown-6 (DBC) and cryptand 222 (C222) on intramolecular cation exchange in ion pairs of the sodium salt of the durosemiquinone anion in benzene solution are investigated. Electron paramagnetic resonance spectra of the 18C6 and 15C5 complexes with durosemiquinone reduced by contact with a sodium mirror show an alternating line width which indicates that the sodium ion is being exchanged between equivalent sites near the oxygens of the semiquinone with activation energies of 8.7 and 6.0 kcal/mole and Arrhenius preexponential factors of 9 x 10 to the 12th/sec and 10 to the 12th/sec, respectively. Spectra obtained for the DBC complexes show no evidence of exchange, while those of C222 indicate rapid exchange. It is also noted that the hyperfine splitting constants measured do not change over the 50-K temperature interval studied.

  12. Morphologically Aligned Cation-Exchange Membranes by a Pulsed Electric Field for Reverse Electrodialysis.

    PubMed

    Lee, Ju-Young; Kim, Jae-Hun; Lee, Ju-Hyuk; Kim, Seok; Moon, Seung-Hyeon

    2015-07-21

    A low-resistance ion-exchange membrane is essential to achieve the high-performance energy conversion or storage systems. The formation methods for low-resistance membranes are various; one of the methods is the ion channel alignment of an ion-exchange membrane under a direct current (DC) electric field. In this study, we suggest a more effective alignment method than the process with the DC electric field. First, an ion-exchange membrane was prepared under a pulsed electric field [alternating current (AC) mode] to enhance the effectiveness of the alignment. The membrane properties and the performance in reverse electrodialysis (RED) were then examined to assess the membrane resistance and ion selectivity. The results show that the membrane electrical resistance (MER) had a lower value of 0.86 Ω cm(2) for the AC membrane than 2.13 Ω cm(2) observed for the DC membrane and 4.30 Ω cm(2) observed for the pristine membrane. Furthermore, RED achieved 1.34 W/m(2) of maximum power density for the AC membrane, whereas that for the DC membrane was found to be 1.14 W/m(2) [a RED stack assembled with CMX, used as a commercial cation-exchange membrane (CEM), showed 1.07 W/m(2)]. Thereby, the novel preparation process for a remarkable low-resistance membrane with high ion selectivity was demonstrated.

  13. New cation-exchange material based on a sulfonated 3,4-ethylenedioxythiophene monomer

    NASA Astrophysics Data System (ADS)

    Stéphan, O.; Schottland, P.; Le Gall, P.-Y.; Chevrot, C.

    1998-06-01

    The electrochemical oxidation, in aqueous medium, of a 3,4-ethylenedioxythiophene monomer functionalized by a sulfonate group exhibiting cation-exchange properties, allows the synthesis of a new type of water-soluble material. In order to synthesize in water, by oxidative electropolymerization, polymer films of controlled thickness containing attached sulfonate groups, we have investigated the polymerization of the functionalized monomer in the presence of the unsubstituted one without supporting electrolyte. Using an equimolar mixture (0.01 mol/l) of both monomers, copolymers exhibiting cation exchange abilities have been synthesized. As an example, th easy incorporation of hexaamine-ruthenium(III) into one of these copolymers is briefly reported. L'oxydation électrochimique en milieu aqueux d'un monomère de type 3,4- éthylènedioxythiophène fonctionnalisé par un groupement sulfonate permet d'envisager la synthèse d'un nouveau type de polymère hydrosoluble. Afin d'obtenir électrochimiquement en milieu aqueux, un film de polymère d'épaisseur contrôlée contenant des groupements sulfonates, nous avons evisagé de polymériser ce monomère en présence de son homologue non substitué. En partant d'un mélange équimolaire (0.01 mol/l) des deux monomères et en l'absence d'électrolyte support, nous avons synthétisé un matériau possédant des propriétés d'échange de cations. A titre d'exemple, nous présentons brièvement l'incorporation d'un complexe hexaaminé du ruthénium(III) dans un de ces copolymères.

  14. Comparison of the hammerhead cleavage reactions stimulated by monovalent and divalent cations.

    PubMed Central

    O'Rear, J L; Wang, S; Feig, A L; Beigelman, L; Uhlenbeck, O C; Herschlag, D

    2001-01-01

    Although the hammerhead reaction proceeds most efficiently in divalent cations, cleavage in 4 M LiCl is only approximately 10-fold slower than under standard conditions of 10 mM MgCl2 (Murray et al., Chem Biol, 1998, 5:587-595; Curtis & Bartel, RNA, 2001, this issue, pp. 546-552). To determine if the catalytic mechanism with high concentrations of monovalent cations is similar to that with divalent cations, we compared the activities of a series of modified hammerhead ribozymes in the two ionic conditions. Nearly all of the modifications have similar deleterious effects under both reaction conditions, suggesting that the hammerhead adopts the same general catalytic structure with both monovalent and divalent cations. However, modification of three ligands previously implicated in the binding of a functional divalent metal ion have substantially smaller effects on the cleavage rate in Li+ than in Mg2+. This result suggests that an interaction analogous to the interaction made by this divalent metal ion is absent in the monovalent reaction. Although the contribution of this divalent metal ion to the overall reaction rate is relatively modest, its presence is needed to achieve the full catalytic rate. The role of this ion appears to be in facilitating formation of the active structure, and any direct chemical role of metal ions in hammerhead catalysis is small. PMID:11345432

  15. Solubility and Cation Exchange Properties of Synthetic Hydroxyapatite and Clinoptilolite Mixtures

    NASA Technical Reports Server (NTRS)

    Beiersdorfer, Raymond E.; Ming, Douglas W.

    2003-01-01

    A zeoponic plant growth system is defined as the cultivation of plants in artificial soils, which have zeolites as a major component. These systems: 1) can serve as a controllable and renewable fertilization system to provide plant growth nutrients; 2) can mitigate the adverse effects of contamination due to leaching of highly soluble and concentrated fertilizers; and 3) are being considered as substrates for plant growth in regenerative life-support systems for long-duration space missions. Batch-equilibrium studies of the dissolution and ion-exchange properties of mixtures of naturally-occurring Wyoming clinoptilolite (a zeolite) exchanged with K(+) or NH4(+); and synthetic hydroxyapatite were conducted to determine: 1) the plant availability of the macro-nutrients NH4-N, P, K, Ca, and Mg and 2) the effects of varying the clinoptilolite to hydroxyapatite ratio and the ratio of exchangeable cations (K(+) vs. NH4(+)) on clinoptilolite extraframework sites. The nutrients NH4-N (19.7 to 73.6 mg L(sup -1), P (0.57 to 14.99 mg L(sup- 1), K (14.8 to 104.9 mg L(sup -1), and Mg (0.11 to 6.68mg L(sup -1) are available to plants at sufficient levels. Solution Ca concentrations (0.47 to 3.40 mg L(sup -1) are less than optimal. Solution concentrations of NH4(+), K(+), Ca(2+), and Mg(2+) all decreased with increasing clinoptilolite to hydroxyapatite ratio in the sample. Solution concentrations of phosphorous initially increased, reached a maximum value and then decreased with increasing clinoptilolite to hydroxyapatite ratio in the sample. The NH4(+) -exchanged clinoptilolite is more efficient in dissolving synthetic hydroxyapatite than the K(+) -exchanged clinoptilolite. This suggests that NH4(+), which is less selective at clinoptilolite extraframework sites than K(+) is exchanged more readily by Ca(2+) and thereby enhances the dissolution of the synthetic hydroxyapatite.

  16. Evolution of hollow TiO2 nanostructures via the Kirkendall effect driven by cation exchange with enhanced photoelectrochemical performance.

    PubMed

    Yu, Yanhao; Yin, Xin; Kvit, Alexander; Wang, Xudong

    2014-05-14

    Hollow nanostructures are promising building blocks for electrode scaffolds and catalyst carriers in energy-related systems. In this paper, we report a discovery of hollow TiO2 nanostructure evolution in a vapor-solid deposition system. By introducing TiCl4 vapor pulses to ZnO nanowire templates, we obtained TiO2 tubular nanostructures with well-preserved dimensions and morphology. This process involved the cation exchange reaction between TiCl4 vapor and ZnO solid and the diffusion of reactants and products in their vapor or solid phases, which was likely a manifestation of the Kirkendall effect. The characteristic morphologies and the evolution phenomena of the hollow nanostructures from this vapor-solid system were in a good agreement with the Kirkendall effect discovered in solution systems. Complex hollow TiO2 nanostructures were successfully acquired by replicating various ZnO nanomorphologies, suggesting that this unique cation exchange process could also be a versatile tool for nanostructure replication in vapor-solid growth systems. The evolution of TiO2 nanotubes from ZnO NW scaffolds was seamlessly integrated with TiO2 NR branch growth and thus realized a pure TiO2-phased 3D NW architecture. Because of the significantly enlarged surface area and the trace amount of Zn left in the TiO2 crystals, such 3D TiO2 nanoforests demonstrated enhanced photoelectrochemical performance particularly under AM (air mass) 1.5G illumination, offering a new route for hierarchical functional nanomaterial assembly and application.

  17. Carbonyl-Olefin Exchange Reaction and Related Chemistry

    NASA Astrophysics Data System (ADS)

    Jossifov, Christo; Kalinova, Radostina

    A new carbon—carbon double bond forming reaction (carbonyl olefin exchange reaction) mediated by transition metal catalytic systems has been discovered. The catalytic systems used (transition metal halides or oxohalides alone or in combination with Lewis acids) are active only in the case when the two reacting groups are in one molecules and are conjugated. In addition these systems accelerate other reactions which run simultaneously with the carbonyl olefin metathesis rendering a detailed investigation of the process very complicated.

  18. Dearomative Indole (3 + 2) Reactions with Azaoxyallyl Cations--New Method for the Synthesis of Pyrroloindolines.

    PubMed

    DiPoto, Maria C; Hughes, Russell P; Wu, Jimmy

    2015-12-01

    Herein, we report the first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations. Computational studies using density functional theory (DFT) (B3LYP-D3/6-311G**++) support a stepwise reaction pathway in which initial C-C bond formation takes place at C3 of indole, followed by ring closure to give the observed products. Insights gleaned from these calculations indicate that the solvent, either TFE or HFIP, can stabilize the transition state through H-bonding interactions with oxygen of the azaoxyallyl cation and other relevant intermediates, thereby increasing the rates of these reactions. PMID:26562355

  19. Dearomative Indole (3 + 2) Reactions with Azaoxyallyl Cations--New Method for the Synthesis of Pyrroloindolines.

    PubMed

    DiPoto, Maria C; Hughes, Russell P; Wu, Jimmy

    2015-12-01

    Herein, we report the first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations. Computational studies using density functional theory (DFT) (B3LYP-D3/6-311G**++) support a stepwise reaction pathway in which initial C-C bond formation takes place at C3 of indole, followed by ring closure to give the observed products. Insights gleaned from these calculations indicate that the solvent, either TFE or HFIP, can stabilize the transition state through H-bonding interactions with oxygen of the azaoxyallyl cation and other relevant intermediates, thereby increasing the rates of these reactions.

  20. Permethyl Cobaltocenium (Cp*2Co+) as an Ultra-Stable Cation for Polymer Hydroxide-Exchange Membranes

    NASA Astrophysics Data System (ADS)

    Gu, Shuang; Wang, Junhua; Kaspar, Robert B.; Fang, Qianrong; Zhang, Bingzi; Bryan Coughlin, E.; Yan, Yushan

    2015-06-01

    Hydroxide (OH-)-exchange membranes (HEMs) are important polymer electrolytes enabling the use of affordable and earth-abundant electrocatalysts for electrochemical energy-conversion devices such as HEM fuel cells, HEM electrolyzers, and HEM solar hydrogen generators. Many HEM cations exist, featuring desirable properties, but new cations are still needed to increase chemical stability at elevated temperatures. Here we introduce the permethyl cobaltocenium [(C5Me5)2Co(III)+ or Cp*2Co+] as an ultra-stable organic cation for polymer HEMs. Compared with the parent cobaltocenium [(C5H5)2Co(III)+ or Cp2Co+], Cp*2Co+ has substantially higher stability and basicity. With polysulfone as an example, we demonstrated the feasibility of covalently linking Cp*2Co+ cation to polymer backbone and prepared Cp*2Co+-functionalized membranes as well. The new cation may be useful in designing more durable HEM electrochemical devices.

  1. Permethyl Cobaltocenium (Cp*2Co+) as an Ultra-Stable Cation for Polymer Hydroxide-Exchange Membranes.

    PubMed

    Gu, Shuang; Wang, Junhua; Kaspar, Robert B; Fang, Qianrong; Zhang, Bingzi; Bryan Coughlin, E; Yan, Yushan

    2015-06-29

    Hydroxide (OH(-))-exchange membranes (HEMs) are important polymer electrolytes enabling the use of affordable and earth-abundant electrocatalysts for electrochemical energy-conversion devices such as HEM fuel cells, HEM electrolyzers, and HEM solar hydrogen generators. Many HEM cations exist, featuring desirable properties, but new cations are still needed to increase chemical stability at elevated temperatures. Here we introduce the permethyl cobaltocenium [(C5Me5)2Co(III)(+) or Cp(*)2Co(+)] as an ultra-stable organic cation for polymer HEMs. Compared with the parent cobaltocenium [(C5H5)2Co(III)(+) or Cp2Co(+)], Cp(*)2Co(+) has substantially higher stability and basicity. With polysulfone as an example, we demonstrated the feasibility of covalently linking Cp(*)2Co(+) cation to polymer backbone and prepared Cp(*)2Co(+)-functionalized membranes as well. The new cation may be useful in designing more durable HEM electrochemical devices.

  2. Permethyl Cobaltocenium (Cp*2Co+) as an Ultra-Stable Cation for Polymer Hydroxide-Exchange Membranes

    PubMed Central

    Gu, Shuang; Wang, Junhua; Kaspar, Robert B.; Fang, Qianrong; Zhang, Bingzi; Bryan Coughlin, E.; Yan, Yushan

    2015-01-01

    Hydroxide (OH−)-exchange membranes (HEMs) are important polymer electrolytes enabling the use of affordable and earth-abundant electrocatalysts for electrochemical energy-conversion devices such as HEM fuel cells, HEM electrolyzers, and HEM solar hydrogen generators. Many HEM cations exist, featuring desirable properties, but new cations are still needed to increase chemical stability at elevated temperatures. Here we introduce the permethyl cobaltocenium [(C5Me5)2Co(III)+ or Cp*2Co+] as an ultra-stable organic cation for polymer HEMs. Compared with the parent cobaltocenium [(C5H5)2Co(III)+ or Cp2Co+], Cp*2Co+ has substantially higher stability and basicity. With polysulfone as an example, we demonstrated the feasibility of covalently linking Cp*2Co+ cation to polymer backbone and prepared Cp*2Co+-functionalized membranes as well. The new cation may be useful in designing more durable HEM electrochemical devices. PMID:26119573

  3. Destruction of gel sulfonated cation-exchangers of the KU-2 type under the influence of hydrogen peroxide

    SciTech Connect

    Roginskaya, B.S.; Zavadovskaya, A.S.; Znamenskii, Yu.P.; Paskhina, N.A.; Dobrova, E.I.

    1988-10-20

    The purpose of this work was to study the mechanism of interaction of Soviet sulfonated cation-exchangers of the KU-2 type with hydrogen peroxide. It is shown that under the influence of hydrogen peroxide sulfonated cation-exchangers begin, after a certain induction period, to lose capacity and to release destruction products into water; the length of the induction period increases with the degree of cross-linking. In a given time of contact between the resin and the solution the degree of destruction falls with increase of cross-linking. The principal product of destruction of sulfonated cation-exchangers is an aromatic sulfonic acid containing oxidized groups in the side chains.

  4. Adsorptional removal of methylene blue by guar gum-cerium (IV) tungstate hybrid cationic exchanger.

    PubMed

    Gupta, V K; Pathania, Deepak; Singh, Pardeep; Kumar, Amit; Rathore, B S

    2014-01-30

    Guar gum-cerium (IV) tungstate nanocomposite (GG/CTNC) cationic exchanger was synthesized using simple sol gel method. The GG/CTNC was characterized using X-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectrophotometer (EDX). The XRD studies confirmed amorphous and fibrous in nature of GG/CTNC. The high percentage of oxygen in the nanocomposite material confirmed the functionality tungstate (WO4(-)). The ion exchange capacity of GG/CTNC for Na(+) ion was observed to be 1.30 mequivg(-1). The hybrid exchanger was used as potential adsorbent for the removal of methylene blue (MB) from aqueous system. The correlation coefficients value indicated a good fit of monolayer Langmuir model to the adsorption of methylene blue onto GG/CTNC. The adsorption kinetic study revealed that the adsorption process followed the pseudo second order kinetic. The Gibbs free energy (ΔG) values confirmed the spontaneous nature of adsorption process.

  5. Characterization of perfluorinated cation-exchange membranes MF-4SC surface modified with halloysite nanotubes

    NASA Astrophysics Data System (ADS)

    Filippov, A.; Afonin, D.; Kononenko, N.; Shkirskaya, S.

    2015-10-01

    The electrical conductivity and diffusion permeability through perfluorinated cation-exchange membranes MF-4SC (Russian analog of the Nafion-type membrane), whose surface is modified by nanotubes of halloysite using short exposures of low temperature microwave plasma, are theoretically investigated using the Nernst-Planck approach. The method of quantitative evaluation of physicochemical parameters (individual and averaged diffusion coefficients and averaged distribution coefficients of ion pairs in the membrane) of the systems `electrolyte solution - bi-layer ion-exchange membrane - water/electrolyte solution', which was proposed by us earlier, is further developed. The aforementioned parameters of modified MF-4SC/halloysite membranes were found using the least squares method. For this purpose we used electrical conductivity as well as diffusion permeability data experimentally obtained for NaCl and HCl solutions of different concentration. A new model of bi-layer membrane system can be used for refining the calculated results by taking into account the difference between co- and counter-ion diffusivities inside the membrane layers. We showed that grafting the layer of halloysite nanotubes onto the membrane surface noticeably affects the exchange capacity as well as the structural and transport characteristics of the original perfluorinated membrane. In particular, such a membrane may show weak asymmetry of diffusion permeability when its position inside a measuring cell is changed. Hybrid MF-4SC/halloysite membranes can thus be productively used in fuel cells and catalysis.

  6. Continuous process of preparation of n-butyl(meth)acrylate by esterification of (meth)acrylic acid by butanol on thermostable sulfo-cation exchanger

    SciTech Connect

    Zheleznaya, L.L.; Karakhanov, R.A.; Lunin, A.F.; Magadov, R.S.; Meshcheryakov, S.V.; Mkrtychan, V.R.; Fomin, V.A.

    1987-11-10

    The authors propose an effective thermostable sulfo-cation exchanger based on polymers with a system of conjugated bonds, sulfopolyphenylene ketone (SPP) differing from the known cation exchangers by the high thermostability (up to 250/sup 0/C), and also having the effect of the stabilization of the double bond in unsaturated monomers. The combination of inhibiting and cation exchange properties makes it also possible to use these sulfo-cation exchangers in the processes of esterification of (meth)acrylic acids by alcohols without addition of special inhibitors. The SPP catalyst was tested in esterification processes of acrylic an methacrylic acid by butanol at a pilot plant.

  7. Esterification of oleic acid in a three-phase, fixed-bed reactor packed with a cation exchange resin catalyst.

    PubMed

    Son, Sung Mo; Kimura, Hiroko; Kusakabe, Katsuki

    2011-01-01

    Esterification of oleic acid was performed in a three-phase fixed-bed reactor with a cation exchange resin catalyst (Amberlyst-15) at high temperature, which was varied from 80 to 120 °C. The fatty acid methyl ester (FAME) yields in the fixed-bed reactor were increased with increases in the reaction temperature, methanol flow rate and bed height. Moreover, the FAME yields were higher than those obtained using a batch reactor due to an equilibrium shift toward the product that resulted from continuous evaporation of the produced water. In addition, there was no catalyst deactivation during the esterification of oleic acid. However, addition of sunflower oil to the oleic acid reduced the FAME yield obtained from simultaneous esterification and transesterification. The FAME yield was 97.5% at a reaction temperature of 100 °C in the fixed-bed with a height of 5 cm when the methanol and oleic acid feed rates were 8.6 and 9.0 mL/h, respectively.

  8. Cobalt determination in natural waters using cation-exchange liquid chromatography with luminol chemiluminescence detection

    SciTech Connect

    Boyle, E.A.; Handy, B.; van Geen, A.

    1987-06-01

    A method has been developed for the analysis of cobalt in natural waters by cation-exchange liquid chromatography using chemiluminescence detection. Cobalt can be determined directly in freshwater samples on 500-..mu..L samples with a detection limit of 20 pmol/kg; larger samples provide proportionately lower detection limits. Seawater samples can be analyzed on 100-mL samples following APDC solvent extraction; the detection limit of this method is 5 pmol/kg. The precision of the method is +/- 5%. The method should also be applicable to the analysis of V, Cu, and Fe in natural waters. Equipment is low in cost and transportable and can be used in the field.

  9. Phenolic cation exchange resin material for recovery of cesium and strontium

    DOEpatents

    Ebra, Martha A.; Wallace, Richard M.

    1983-01-01

    A phenolic cation exchange resin with a chelating group has been prepared by reacting resorcinol with iminodiacetic acid in the presence of formaldehyde at a molar ratio of about 1:1:6. The material is highly selective for the simultaneous recovery of both cesium and strontium from aqueous alkaline solutions, such as, aqueous alkaline nuclear waste solutions. The organic resins are condensation polymers of resorcinol and formaldehyde with attached chelating groups. The column performance of the resins compares favorably with that of commercially available resins for either cesium or strontium removal. By combining Cs.sup.+ and Sr.sup.2+ removal in the same bed, the resins allow significant reduction of the size and complexity of facilities for processing nuclear waste.

  10. Phenolic cation-exchange resin material for recovery of cesium and strontium. [Patent application

    DOEpatents

    Ebra, M.A.; Wallace, R.M.

    1982-05-05

    A phenolic cation exchange resin with a chelating group has been prepared by reacting resorcinol with iminodiacetic acid in the presence of formaldehyde at a molar ratio of about 1:1:6. The material is highly selective for the simultaneous recovery of both cesium and strontium from aqueous alkaline solutions, such as, aqueous alkaline nuclear wate solutions. The organic resins are condensation polymers of resorcinol and formaldehyde with attached chelating groups. The column performance of the resins compares favorably with that of commercially available resins for either cesium or strontium removal. By combining Cs/sup +/ and Sr/sup 2 +/ removal in the same bed, the resins allow significant reduction of the size and complexity of facilities for processing nuclear waste.

  11. Chromatographic cation exchange separation of decigram quantities of californium and other transplutonium elements

    SciTech Connect

    Benker, D.E.; Chattin, F.R.; Collins, E.D.; Knauer, J.B.; Orr, P.B.; Ross, R.G.; Wiggins, J.T.

    1980-01-01

    Decigram quantities of highly radioactive transplutonium elements are routinely partitioned at TRU by chromatographic elution from cation resin using AHIB eluent. By using two high-pressure ion exchange columns, a small one for the initial loading of the feed and a large one for the elution, batch runs containing up to 200 mg of /sup 252/Cf can be made in about 5 hours (2 hours to load the feed and 3 hours for the elution). The number of effluent product fractions and the amount of actinides that must be collected in intermediate fractions are minimized by monitoring response from a flow-through alpha-detector. This process has been reliable and relatively easy to operate, and will continue to be used for partitioning transplutonium elements at TRU.

  12. Determination of magnesium in alumina ceramics by atomic absorption spectrometry after separation by cation exchange chromatography

    SciTech Connect

    van der Walt, T.N.; Strelow, F.W.E.

    1985-12-01

    A method is presented for the determination of traces of magnesium in alumina ceramics. After dissolution in an orthophosphoric acid-sulfuric acid mixture the magnesium is separated from the large excess of aluminum by cation exchange chromatography, using a 4% cross-linked resin and 0.50 M oxalic acid as eluting agent. Magnesium is finally determined by atomic absorption spectrometry using an acetylene-nitrous oxide flame. By use of Suprapur reagents and beakers made of Teflon, contamination can be reduced to ca. 2..mu..g with a variation between multiple blank runs of ca. 0.4 ..mu..g. About 3 ppm of magnesium in 1-g samples can be determined with approximately the same variation while larger amounts of magnesium (200-300 ppm in the alumina ceramics) show a variation of only +/- 1 ppm. 12 references, 1 table.

  13. A New Cation-Exchange Method for Accurate Field Speciation of Hexavalent Chromium

    USGS Publications Warehouse

    Ball, James W.; McCleskey, R. Blaine

    2003-01-01

    A new cation-exchange method for field speciation of Cr(VI) has been developed to meet present stringent regulatory standards and to overcome the limitations of existing methods. The new method allows measurement of Cr(VI) concentrations as low as 0.05 micrograms per liter, storage of samples for at least several weeks prior to analysis, and use of readily available analytical instrumentation. The sensitivity, accuracy, and precision of the determination in waters over the pH range of 2 to 11 and Fe concentrations up to 1 milligram per liter are equal to or better than existing methods such as USEPA method 218.6. Time stability of preserved samples is a significant advantage over the 24-hour time constraint specified for USEPA method 218.6.

  14. Electrochemical catalytic treatment of wastewater by metal ion supported on cation exchange resin.

    PubMed

    Wang, Ying; Wang, Bo; Ma, Hongzhu

    2006-10-11

    The electrochemical oxidation of phenol in synthetic wastewater and paper mill wastewater catalyzed by metal ion supported on cation exchange resin in suspended bed electrolytic reactor with graphite electrode has been investigated. The catalyst was characterized by SEM and XPS spectra and the effects of pH, the different metal ion and NaCl on the efficiency of the electrochemical oxidation phenol process were also studied. It was found that the catalyst containing Fe(3+) had the highest electrochemical catalytic activity for the electrochemical oxidation of phenol. When the initial concentration of phenol was 200 ppm, up to 90% chemical oxygen demand (COD) removal was obtained in 10 min. When the catalyst containing Fe(3+) was used to the paper mill wastewater, it still showed high efficiency. The COD removal could get to 75% in 60 min.

  15. Adsorption of paraquat on soil organic matter: effect of exchangeable cations and dissolved organic carbon.

    PubMed

    Gondar, Dora; López, Rocío; Antelo, Juan; Fiol, Sarah; Arce, Florencio

    2012-10-15

    Herbicides that interact with soil organic matter do so with both the solid and the dissolved fractions, so that the distribution of herbicide between the soil solution and solid phases is determined by competitive effects. In the present study, adsorption experiments were carried out with the cationic herbicide paraquat and untreated and acid-washed samples of a peat soil, at different values of pH and ionic strength. Less herbicide was adsorbed onto the untreated peat than onto the acid-washed peat; the difference was due to the presence of exchangeable cations, as demonstrated in experiments carried out by adding Ca(2+) to suspensions of acid-washed peat. The results were interpreted by an electrostatic model and the fitting parameters indicated that the adsorption constants were the same for both samples of peat, although the number of binding sites available was different. Simultaneous resolution of the adsorption equilibrium of paraquat for the soil organic matter (SOM) and of the binding equilibrium between paraquat and dissolved organic matter (DOM) enabled the distribution of paraquat between the solid and solution phases to be determined. The increased solubility of the SOM with increasing pH led to a decrease in the fraction of paraquat retained on the peat surface above pH 5.5, which favors the mobility of the herbicide in the soil.

  16. Ion-exchange and selectivity behavior of thermally treated and. gamma. -irradiated phases of zirconium(IV) arsenophosphate cation exchanger: separation of Al(III) from some metal ions and removal of cations from water

    SciTech Connect

    Varshney, K.G.; Varshney, K.; Agrawal, S.

    1983-01-01

    Ion-exchange and selectivity behavior of zirconium(IV) arsenophosphate (ZAP) has been studied systematically after thermal and irradiation treatments. As a result, an increase in the ion-exchange capacity and a complete reversal in the selectivity sequence for some common metal ions has been observed on heating. The modified phase of ZAP has been utilized successfully for the quantitative separation of aluminum from numerous metal ions and for the removal of cations from water. 5 figures, 3 tables.

  17. Enhanced Cd2+ -selective root-tonoplast-transport in tobaccos expressing Arabidopsis cation exchangers.

    PubMed

    Koren'kov, V; Park, S; Cheng, N-H; Sreevidya, C; Lachmansingh, J; Morris, J; Hirschi, K; Wagner, G J

    2007-01-01

    Several Arabidopsis CAtion eXchangers (CAXs) encode tonoplast-localized transporters that appear to be major contributors to vacuolar accumulation/sequestration of cadmium (Cd(2+)), an undesirable pollutant ion that occurs in man largely as a result of dietary consumption of aerial tissues of food plants. But, ion-selectivity of individual CAX transporter types remains largely unknown. Here, we transformed Nicotiana tabacum with several CAX genes driven by the Cauliflower Mosaic Virus (CaMV) 35S promoter and monitored divalent cation transport in root-tonoplast vesicles from these plants in order to select particular CAX genes directing high Cd(2+) antiporter activity in root tonoplast. Comparison of seven different CAX genes indicated that all transported Cd(2+), Ca(2+), Zn(2+), and Mn(2+) to varying degrees, but that CAX4 and CAX2 had high Cd(2+) transport and selectivity in tonoplast vesicles. CAX4 driven by the CaMV 35S and FS3 [figwort mosaic virus (FMV)] promoters increased the magnitude and initial rate of Cd(2+)/H(+) exchange in root-tonoplast vesicles. Ion selectivity of transport in root-tonoplast vesicles isolated from FS3::CAX4-expressing plant lines having a range of gene expression was Cd(2+)>Zn(2+)>Ca(2+)>Mn(2+) and the ratios of maximal Cd(2+) (and Zn(2+)) versus maximal Ca(2+) and Mn(2+) transport were correlated with the levels of CAX4 expression. Root Cd accumulation in high CAX4 and CAX2 expressing lines was increased in seedlings grown with 0.02 muM Cd. These observations are consistent with a model in which expression of an Arabidopsis-gene-encoded, Cd(2+)-efficient antiporter in host plant roots results in greater root vacuole Cd(2+) transport activity, increased root Cd accumulation, and a shift in overall root tonoplast ion transport selectivity towards higher Cd(2+) selectivity. Results support a model in which certain CAX antiporters are somewhat more selective for particular divalent cations.

  18. Radiation induced redox reactions and fragmentation of constituent ions in ionic liquids II. Imidazolium cations.

    SciTech Connect

    Shkrob, I. A.; Marin, T. W.; Chemerisov, S. D.; Hatcher, J.; Wishart, J.

    2011-04-14

    In part 1 of this study, radiolytic degradation of constituent anions in ionic liquids (ILs) was examined. The present study continues the themes addressed in part 1 and examines the radiation chemistry of 1,3-dialkyl substituted imidazolium cations, which currently comprise the most practically important and versatile class of ionic liquid cations. For comparison, we also examined 1,3-dimethoxy- and 2-methyl-substituted imidazolium and 1-butyl-4-methylpyridinium cations. In addition to identification of radicals using electron paramagnetic resonance spectroscopy (EPR) and selective deuterium substitution, we analyzed stable radiolytic products using {sup 1}H and {sup 13}C nuclear magnetic resonance (NMR) and tandem electrospray ionization mass spectrometry (ESMS). Our EPR studies reveal rich chemistry initiated through 'ionization of the ions': oxidation and the formation of radical dications in the aliphatic arms of the parent cations (leading to deprotonation and the formation of alkyl radicals in these arms) and reduction of the parent cation, yielding 2-imidazolyl radicals. The subsequent reactions of these radicals depend on the nature of the IL. If the cation is 2-substituted, the resulting 2-imidazolyl radical is relatively stable. If there is no substitution at C(2), the radical then either is protonated or reacts with the parent cation forming a C(2)-C(2) {sigma}{sigma}*-bound dimer radical cation. In addition to these reactions, when methoxy or C{sub {alpha}}-substituted alkyl groups occupy the N(1,3) positions, their elimination is observed. The elimination of methyl groups from N(1,3) was not observed. Product analyses of imidazolium liquids irradiated in the very-high-dose regime (6.7 MGy) reveal several detrimental processes, including volatilization, acidification, and oligomerization. The latter yields a polymer with m/z of 650 {+-} 300 whose radiolytic yield increases with dose (0.23 monomer units per 100 eV for 1-methyl-3-butylimidazolium

  19. Radiation induced redox reactions and fragmentation of constituent ions in ionic liquids. 2. Imidazolium cations.

    PubMed

    Shkrob, Ilya A; Marin, Timothy W; Chemerisov, Sergey D; Hatcher, Jasmine L; Wishart, James F

    2011-04-14

    In part 1 of this study, radiolytic degradation of constituent anions in ionic liquids (ILs) was examined. The present study continues the themes addressed in part 1 and examines the radiation chemistry of 1,3-dialkyl substituted imidazolium cations, which currently comprise the most practically important and versatile class of ionic liquid cations. For comparison, we also examined 1,3-dimethoxy- and 2-methyl-substituted imidazolium and 1-butyl-4-methylpyridinium cations. In addition to identification of radicals using electron paramagnetic resonance spectroscopy (EPR) and selective deuterium substitution, we analyzed stable radiolytic products using (1)H and (13)C nuclear magnetic resonance (NMR) and tandem electrospray ionization mass spectrometry (ESMS). Our EPR studies reveal rich chemistry initiated through "ionization of the ions": oxidation and the formation of radical dications in the aliphatic arms of the parent cations (leading to deprotonation and the formation of alkyl radicals in these arms) and reduction of the parent cation, yielding 2-imidazolyl radicals. The subsequent reactions of these radicals depend on the nature of the IL. If the cation is 2-substituted, the resulting 2-imidazolyl radical is relatively stable. If there is no substitution at C(2), the radical then either is protonated or reacts with the parent cation forming a C(2)-C(2) σσ*-bound dimer radical cation. In addition to these reactions, when methoxy or C(α)-substituted alkyl groups occupy the N(1,3) positions, their elimination is observed. The elimination of methyl groups from N(1,3) was not observed. Product analyses of imidazolium liquids irradiated in the very-high-dose regime (6.7 MGy) reveal several detrimental processes, including volatilization, acidification, and oligomerization. The latter yields a polymer with m/z of 650 ± 300 whose radiolytic yield increases with dose (~0.23 monomer units per 100 eV for 1-methyl-3-butylimidazolium trifluorosulfonate). Gradual

  20. Quantification of unsaturated-zone alteration and cation exchange in zeolitized tuffs at Yucca Mountain, Nevada, USA

    NASA Astrophysics Data System (ADS)

    Vaniman, David T.; Chipera, Steve J.; Bish, David L.; Carey, J. William; Levy, Schön S.

    2001-10-01

    Zeolitized horizons in the unsaturated zone (UZ) at Yucca Mountain, Nevada, USA, are an important component in concepts for a high-level nuclear waste repository at this site. The use of combined quantitative X-ray diffraction and geochemical analysis allows measurement of the chemical changes that accompanied open-system zeolitization at Yucca Mountain. This approach also provides measures of the extent of chemical migration that has occurred in these horizons as a result of subsequent cation exchange. Mass-balance analysis of zeolitized horizons with extensive cation exchange (drill hole UZ-16) and with only minimal cation exchange (drill hole SD-9) shows that Al is essentially immobile. Although zeolitization occurred in an open system, the mass transfer of constituents other than water is relatively small in initial zeolitization, in contrast to the larger scales of cation exchange that can occur after zeolites have formed. Cation exchange in the clinoptilolite ± mordenite zeolitized horizons is seen in downward-diminishing concentration gradients of Ca, Mg, and Sr exchanged for Na and (to lesser extent) K. Comparison with data from drill hole SD-7, which has multiple zeolitized horizons above the water table, shows that the upper horizons accumulate Ca, Mg, and Sr to such an extent that transport of these elements to the deepest UZ zeolitized horizon can be blocked. Quantitative analysis of zeolite formation yields insight into processes that are implied from laboratory studies and modeling efforts but are otherwise unverified at the site. Such analysis also yields information not provided by or contradicted by some models of flow and transport. The results include the following: (1) evidence of effective downward flow through zeolitic horizons despite the low permeability of these horizons, (2) evidence that alkaline-earth elements accumulated by zeolites are mostly derived from eolian materials in surface soils, (3) validation of the very effective

  1. Strategies for generating peptide radical cations via ion/ion reactions.

    PubMed

    Gilbert, Joshua D; Fisher, Christine M; Bu, Jiexun; Prentice, Boone M; Redwine, James G; McLuckey, Scott A

    2015-02-01

    Several approaches for the generation of peptide radical cations using ion/ion reactions coupled with either collision induced dissociation (CID) or ultraviolet photo dissociation (UVPD) are described here. Ion/ion reactions are used to generate electrostatic or covalent complexes comprised of a peptide and a radical reagent. The radical site of the reagent can be generated multiple ways. Reagents containing a carbon-iodine (C-I) bond are subjected to UVPD with 266-nm photons, which selectively cleaves the C-I bond homolytically. Alternatively, reagents containing azo functionalities are collisionally activated to yield radical sites on either side of the azo group. Both of these methods generate an initial radical site on the reagent, which then abstracts a hydrogen from the peptide while the peptide and reagent are held together by either electrostatic interactions or a covalent linkage. These methods are demonstrated via ion/ion reactions between the model peptide RARARAA (doubly protonated) and various distonic anionic radical reagents. The radical site abstracts a hydrogen atom from the peptide, while the charge site abstracts a proton. The net result is the conversion of a doubly protonated peptide to a peptide radical cation. The peptide radical cations have been fragmented via CID and the resulting product ion mass spectra are compared to the control CID spectrum of the singly protonated, even-electron species. This work is then extended to bradykinin, a more broadly studied peptide, for comparison with other radical peptide generation methods. The work presented here provides novel methods for generating peptide radical cations in the gas phase through ion/ion reaction complexes that do not require modification of the peptide in solution or generation of non-covalent complexes in the electrospray process.

  2. Air-Stable and Efficient PbSe Quantum-Dot Solar Cells Based upon ZnSe to PbSe Cation-Exchanged Quantum Dots.

    PubMed

    Kim, Sungwoo; Marshall, Ashley R; Kroupa, Daniel M; Miller, Elisa M; Luther, Joseph M; Jeong, Sohee; Beard, Matthew C

    2015-08-25

    We developed a single step, cation-exchange reaction that produces air-stable PbSe quantum dots (QDs) from ZnSe QDs and PbX2 (X = Cl, Br, or I) precursors. The resulting PbSe QDs are terminated with halide anions and contain residual Zn cations. We characterized the PbSe QDs using UV-vis-NIR absorption, photoluminescence quantum yield spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Solar cells fabricated from these PbSe QDs obtained an overall best power conversion efficiency of 6.47% at one sun illumination. The solar cell performance without encapsulation remains unchanged for over 50 days in ambient conditions; and after 50 days, the National Renewable Energy Laboratory certification team certified the device at 5.9%.

  3. Acid-rain monitoring in east Asia with a portable-type ion-exclusion-cation-exchange chromatographic analyzer.

    PubMed

    Tanaka, K; Ohta, K; Haddad, P R; Fritz, J S; Lee, K P; Hasebe, K; Ieuji, A; Miyanaga, A

    1999-07-30

    A monitoring system consisting of a portable-type conductimetric ion-exclusion-cation-exchange chromatographic (CEC) analyzer and a meteorological satellite data analyzer has been investigated for the evaluation of the effects of acid precipitation on natural and urban environments in East Asia. The portable ion-exclusion-CEC analyzer uses a polymethacrylate-based weakly acidic cation-exchange resin column in the H(+)-form and a weak-acid eluent (tartaric acid-methanol-water) and is applied for the simultaneous determination of anions (SO4(2)-, NO3-, and Cl-) and cations (Na+, NH4+, K+, Mg2+, and Ca2+) in precipitation transported from mainland China to central Japan, as mapped by the meteorological satellite data analyzer. Linear calibration graphs of peak area versus concentration for anions and cations were observed in the concentration range 0-1.0 mM for the anions and 0-0.5 mM for the cations. Detection limits at a signal-to-noise ratio of 3 were in the range 5.18-12.1 ppb for the anions and 6.58-16.5 ppb for the cations. The practical utility of this monitoring system is presented.

  4. Estimating Soil Cation Exchange Capacity from Soil Physical and Chemical Properties

    NASA Astrophysics Data System (ADS)

    Bateni, S. M.; Emamgholizadeh, S.; Shahsavani, D.

    2014-12-01

    The soil Cation Exchange Capacity (CEC) is an important soil characteristic that has many applications in soil science and environmental studies. For example, CEC influences soil fertility by controlling the exchange of ions in the soil. Measurement of CEC is costly and difficult. Consequently, several studies attempted to obtain CEC from readily measurable soil physical and chemical properties such as soil pH, organic matter, soil texture, bulk density, and particle size distribution. These studies have often used multiple regression or artificial neural network models. Regression-based models cannot capture the intricate relationship between CEC and soil physical and chemical attributes and provide inaccurate CEC estimates. Although neural network models perform better than regression methods, they act like a black-box and cannot generate an explicit expression for retrieval of CEC from soil properties. In a departure with regression and neural network models, this study uses Genetic Expression Programming (GEP) and Multivariate Adaptive Regression Splines (MARS) to estimate CEC from easily measurable soil variables such as clay, pH, and OM. CEC estimates from GEP and MARS are compared with measurements at two field sites in Iran. Results show that GEP and MARS can estimate CEC accurately. Also, the MARS model performs slightly better than GEP. Finally, a sensitivity test indicates that organic matter and pH have respectively the least and the most significant impact on CEC.

  5. Simultaneous Isolation of Lactoferrin and Lactoperoxidase from Bovine Colostrum by SPEC 70 SLS Cation Exchange Resin

    PubMed Central

    Liang, Yafei; Wang, Xuewan; Wu, Mianbin; Zhu, Wanping

    2011-01-01

    In this work, simultaneous isolation of lactoferrin (Lf) and lactoperoxidase (Lp) from defatted bovine colostrum by one-step cation exchange chromatography with SPEC 70 SLS ion-exchange resin was investigated. A RP-HPLC method for Lf and Lp determination was developed and optimized as the following conditions: detection wavelength of 220 nm, flow rate of 1 mL/min and acetonitrile concentration from 25% to 75% within 20 min. The adsorption process of Lf on SPEC 70 SLS resin was optimized using Lf standard as substrate. The maximum static binding capacity of SPEC 70 SLS resin was of 22.0 mg/g resin at 15 °C, pH 7.0 and adsorption time 3 h. The Lf adsorption process could be well described by the Langmuir adsorption isotherm model, with a maximum adsorption capacity of 21.73 mg/g resin at 15 °C. In batch fractionation of defatted colostrum, the binding capacities of SPEC 70 SLS resin for adsorbing Lf and Lp simultaneously under the abovementioned conditions were 7.60 and 6.89 mg/g resin, respectively, both of which were superior to those of CM Sepharose F.F. or SP Sepharose F.F. resins under the same conditions. As a result, SPEC 70 SLS resin was considered as a successful candidate for direct and economic purification of Lf and Lp from defatted colostrum. PMID:22016715

  6. Simultaneous isolation of lactoferrin and lactoperoxidase from bovine colostrum by SPEC 70 SLS cation exchange resin.

    PubMed

    Liang, Yafei; Wang, Xuewan; Wu, Mianbin; Zhu, Wanping

    2011-09-01

    In this work, simultaneous isolation of lactoferrin (Lf) and lactoperoxidase (Lp) from defatted bovine colostrum by one-step cation exchange chromatography with SPEC 70 SLS ion-exchange resin was investigated. A RP-HPLC method for Lf and Lp determination was developed and optimized as the following conditions: detection wavelength of 220 nm, flow rate of 1 mL/min and acetonitrile concentration from 25% to 75% within 20 min. The adsorption process of Lf on SPEC 70 SLS resin was optimized using Lf standard as substrate. The maximum static binding capacity of SPEC 70 SLS resin was of 22.0 mg/g resin at 15 °C, pH 7.0 and adsorption time 3 h. The Lf adsorption process could be well described by the Langmuir adsorption isotherm model, with a maximum adsorption capacity of 21.73 mg/g resin at 15 °C. In batch fractionation of defatted colostrum, the binding capacities of SPEC 70 SLS resin for adsorbing Lf and Lp simultaneously under the abovementioned conditions were 7.60 and 6.89 mg/g resin, respectively, both of which were superior to those of CM Sepharose F.F. or SP Sepharose F.F. resins under the same conditions. As a result, SPEC 70 SLS resin was considered as a successful candidate for direct and economic purification of Lf and Lp from defatted colostrum.

  7. Comparing the gas-phase fragmentation reactions of protonated and radical cations of the tripeptides GXR

    NASA Astrophysics Data System (ADS)

    Wee, Sheena; O'Hair, Richard A. J.; McFadyen, W. David

    2004-05-01

    Electrospray ionization (ESI) mass spectrometry of methanolic solutions of mixtures of the copper salt (2,2':6',2''-terpyridine)copper(II) nitrate monohydrate ([Cu(II)(tpy)(NO3)2].H2O) and a tripeptide GXR (where X = 1 of the 20 naturally occurring amino acids) yielded [Cu(II)(tpy)(GXR)][radical sign]2+ ions, which were then subjected to collision induced dissociation (CID). In all but one case (GRR), these [Cu(II)(tpy)(GXR)][radical sign]2+ ions fragment to form odd electron GXR[radical sign]+ radical cations with sufficient abundance to examine their gas-phase fragmentation reactions. The GXR[radical sign]+ radical cations undergo a diverse range of fragmentation reactions which depend on the nature of the side chain of X. Many of these reactions can be rationalized as arising from the intermediacy of isomeric distonic ions in which the charge (i.e. proton) is sequestered by the highly basic arginine side chain and the radical site is located at various positions on the tripeptide including the peptide back bone and side chains. The radical sites in these distonic ions often direct the fragmentation reactions via the expulsion of small radicals (to yield even electron ions) or small neutrals (to form radical cations). Both classes of reaction can yield useful structural information, allowing for example, distinction between leucine and isoleucine residues. The gas-phase fragmentation reactions of the GXR[radical sign]+ radical cations are also compared to their even electron [GXR+H]+ and [GXR+2H]2+ counterparts. The [GXR+H]+ ions give fewer sequence ions and more small molecule losses while the [GXR+2H]2+ ions yield more sequence information, consistent with the [`]mobile proton model' described in previous studies. In general, all three classes of ions give complementary structural information, but the GXR[radical sign]+ radical cations exhibit a more diverse loss of small species (radicals and neutrals). Finally, links between these gas-phase results and key

  8. A General Copper-Catalyzed Vinylic Halogen Exchange Reaction.

    PubMed

    Nitelet, Antoine; Evano, Gwilherm

    2016-04-15

    An efficient and general system for the halogen exchange reaction in alkenyl halides has been developed. Upon reaction with catalytic amounts of copper iodide and trans-N,N'-dimethylcyclohexane-1,2-diamine in the presence of tetramethylammonium chloride or bromide, a wide range of easily accessible alkenyl iodides can be smoothly transformed to their far less available chlorinated and brominated derivatives in excellent yields and with full retention of the double bond geometry. This reaction also enables the chlorination of bromoalkenes and could be extended to the use of gem-dibromoalkenes. PMID:27031868

  9. Bimolecular Coupling Reactions through Oxidatively Generated Aromatic Cations: Scope and Stereocontrol

    PubMed Central

    Cui, Yubo; Villafane, Louis A.; Clausen, Dane J.

    2013-01-01

    Chromenes, isochromenes, and benzoxathioles react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to form stable aromatic cations that react with a range of nucleophiles. These oxidative fragment coupling reactions provide rapid access to structurally diverse heterocycles. Conducting the reactions in the presence of a chiral Brønsted acid results in the formation of an asymmetric ion pair that can provide enantiomerically enriched products in a rare example of a stereoselective process resulting from the generation of a chiral electrophile through oxidative carbon–hydrogen bond cleavage. PMID:23913987

  10. Laboratory Experiments on the Reactions of PAH Cations with Molecules and Atoms of Interstellar Interest

    NASA Technical Reports Server (NTRS)

    LePage, V.; Lee, H. S.; Bierbaum, V. M.; Snow, T. P.

    1996-01-01

    The C10H8(+) cation and its dehydrogenated derivatives, C10H7(+) and C10H6(+), have been studied using a selected ion flow tube (SIFT). Reactions with molecules and atoms of interstellar interest show that C10H8(+) reacts with N md O to give neutral products HCN and CO, respectively. C10H6(+) and C10H6(+) are moderately reactive and reactions proceed through association with molecules. The implications of these results for the depletion of C10H(n)(+) in the interstellar medium are briefly discussed.

  11. Production of U{sub 3}O{sub 8} Using Macroporous Sulfonate Cation Exchange Resins in the Bead Form

    SciTech Connect

    Mosley, W.C.

    2001-08-16

    The use of cation exchange resin to product U{sub 3}O{sub 8} suitable for powder metallurgy fabrication of reactor fuel tubes with Al-U{sub 3}O{sub 8} cores is being investigated. This report presents the results of those studies.

  12. Synthesis and properties of a cation exchange resin prepared by the pyrolysis of starch in the presence of phytic acid

    SciTech Connect

    Lehrfeld, J.

    1995-12-01

    A material having cation exchange and adsorption properties was prepared by the controlled pyrolysis of starch in the presence of a commercial phytic acid solution. Resins can be prepared with binding capacities of 0.7-5.7 meq/g. These resins also have the ability to remove atrazine from aqueous solutions.

  13. Geometric phase effects in ultracold hydrogen exchange reaction

    NASA Astrophysics Data System (ADS)

    Hazra, Jisha; Kendrick, Brian K.; Balakrishnan, N.

    2016-10-01

    The role of the geometric phase effect on chemical reaction dynamics is explored by examining the hydrogen exchange process in the fundamental H+HD reaction. Results are presented for vibrationally excited HD molecules in the v = 4 vibrational level and for collision energies ranging from 1 μK to 100 K. It is found that, for collision energies below 3 K, inclusion of the geometric phase leads to dramatic enhancement or suppression of the reaction rates depending on the final quantum state of the HD molecule. The effect was found to be the most prominent for rotationally resolved integral and differential cross sections but it persists to a lesser extent in the vibrationally resolved and total reaction rate coefficients. However, no significant GP effect is present in the reactive channel leading to the D+H2 product or in the D+H2 (v=4,j=0) \\to HD+H reaction. A simple interference mechanism involving inelastic (nonreactive) and exchange scattering amplitudes is invoked to account for the observed GP effects. The computed results also reveal a shape resonance in the H+HD reaction near 1 K and the GP effect is found to influence the magnitude of the resonant part of the cross section. Experimental detection of the resonance may allow a sensitive probe of the GP effect in the H+HD reaction.

  14. Synthesis of Mesostructured Copper Sulfide by Cation Exchange and Liquid Crystal Templating

    SciTech Connect

    Lubeck, C R; Doyle, F M; Gash, A E; Satcher, J H; Han, T Y

    2005-08-01

    describe for the first time, the successful synthesis of highly ordered, mesostructured Cu{sub x}S, by combining the templating of the supramolecular assemblies of non-ionic amphiphilic polymer method with the cation exchange method to transform mesostructured cadmium sulfide (CdS) into mesostructured copper sulfides (CuS, Cu{sub 2}S).

  15. FORMATE—PYRUVATE EXCHANGE REACTION IN STREPTOCOCCUS FAECALIS II.

    PubMed Central

    Oster, M. O.; Wood, N. P.

    1964-01-01

    Oster, M. O. (A. & M. College of Texas, College Station), and N. P. Wood. Formate-pyruvate exchange reaction in Streptococcus faecalis. II. Reaction conditions for cell extracts. J. Bacteriol. 87:104–113. 1964.—In contrast to intact cells of Streptococcus faecalis, no stimulation of the formate-pyruvate exchange reaction was observed in cell extracts when yeast extract was added to the reaction mixture. A heated extract of Micrococcus lactilyticus, vitamin K5, ferrous sulfate, and ferrous ammonium sulfate stimulated an active exchange by protecting the system from oxygen. Tetrahydrofolate, 2,3-dimercaptopropanol, and sodium sulfide provided partial protection, whereas ascorbate, glutathione, sodium hydrosulfite, ammonium sulfide, and sodium bisulfite gave insufficient protection or were inhibitory. Oxidation-reduction (O-R) indicators were not inhibitory and were used to estimate the O-R potentials of reaction mixtures. A potential at least as negative as −125 mv was estimated to be necessary to preserve or initiate formate-pyruvate exchange activity. The reaction operated over a narrow pH range when strict anaerobic conditions were not maintained but, when the system was suitably poised, the pH range was broader. The influence of high phosphate concentrations was less under strictly anaerobic conditions, and orthophosphate could be replaced by small amounts of pyrophosphate. Effect of temperature, time, and amount of extract is presented. Addition of reduced benzyl viologen and hydrogen-saturated palladium in the buffer during 8 hr of dialysis prevented inactivation of extracts. Recovery of activity could be obtained after ammonium sulfate treatment when a combination of palladium chloride, neutral red, and hydrogen bubbling were used. PMID:14102842

  16. Carbonyl-Olefin Exchange Reaction: Present State and Outlook

    NASA Astrophysics Data System (ADS)

    Kalinova, Radostina; Jossifov, Christo

    The carbonyl-olefin exchange reaction (COER) is a new reaction between carbonyl group and olefin double bond, which has a formal similarity with the olefin metathesis (OM) - one carbon atom in the latter is replaced with an oxygen atom. Till now the new reaction is performed successfully only when the two functional groups (carbonyl group and olefin double bond) are in one molecule and are conjugated. The α, β-unsaturated carbonyl compounds (substituted propenones) are the compounds with such a structure. They polymerize giving substituted polyacetylenes. The chain propagation step of this polymerization is in fact the COER. The question arises: is it possible the COER to take place when the two functional groups are not in one molecule and are not conjugated, and could this reaction became an alternative of the existing carbonyl olefination reactions?

  17. Millisecond Kinetics of Nanocrystal Cation Exchange UsingMicrofluidic X-ray Absorption Spectroscopy

    SciTech Connect

    Chan, Emory M.; Marcus, Matthew A.; Fakra, Sirine; Elnaggar,Mariam S.; Mathies, Richard A.; Alivisatos, A. Paul

    2007-05-07

    We describe the use of a flow-focusing microfluidic reactorto measure the kinetics of theCdSe-to-Ag2Se nanocrystal cation exchangereaction using micro-X-ray absorption spectroscopy (mu XAS). The smallmicroreactor dimensions facilitate the millisecond mixing of CdSenanocrystal and Ag+ reactant solutions, and the transposition of thereaction time onto spatial coordinates enables the in situ observation ofthe millisecond reaction with mu XAS. XAS spectra show the progression ofCdSe nanocrystals to Ag2Se over the course of 100 ms without the presenceof long-lived intermediates. These results, along with supporting stoppedflow absorption experiments, suggest that this nanocrystal cationexchange reaction is highly efficient and provide insight into how thereaction progresses in individual particles. This experiment illustratesthe value and potential of in situ microfluidic X-ray synchrotrontechniques for detailed studies of the millisecond structuraltransformations of nanoparticles and other solution-phase reactions inwhich diffusive mixing initiates changes in local bond structures oroxidation states.

  18. Consecutive oxygen-for-sulfur exchange reactions between vanadium oxide cluster anions and hydrogen sulfide.

    PubMed

    Jia, Mei-Ye; Xu, Bo; Deng, Ke; He, Sheng-Gui; Ge, Mao-Fa

    2014-09-18

    Vanadium oxide cluster anions Vm(16)On(-) and Vm(18)On(-) were prepared by laser ablation and reacted with hydrogen sulfide (H2S) in a fast flow reactor under thermal collision conditions. A time-of-flight mass spectrometer was used to detect the cluster distributions before and after the interactions with H2S. The experiments suggest that the oxygen-for-sulfur (O/S) exchange reaction to release water was evidenced in the reactor for most of the cluster anions: VmOn(-) + H2S → VmOn-1S(-) + H2O. For reactions of clusters VO3(-) and VO4(-) with H2S, consecutive O/S exchange reactions led to the generation of sulfur containing vanadium oxide cluster anions VO3-kSk(-) (k = 1-3) and VO4-kSk(-) (k = 1-4). Density functional theory calculations were performed for the reactions of VO3-4(-) with H2S, and the results indicate that the O/S exchange reactions are both thermodynamically and kinetically favorable, which supports the experimental observations. The reactions of VmOn(+) cluster cations with H2S have been reported previously (Jia, M.-Y.; Xu, B.; Ding, X.-L.; Zhao, Y.-X.; He, S.-G.; Ge, M.-F. J. Phys. Chem. C 2012, 116, 9043), and this study of cluster anions provides further new insights into the transformations of H2S over vanadium oxides at the molecular level.

  19. Gamma-aminobutyric acid production using immobilized glutamate decarboxylase followed by downstream processing with cation exchange chromatography.

    PubMed

    Lee, Seungwoon; Ahn, Jungoh; Kim, Yeon-Gu; Jung, Joon-Ki; Lee, Hongweon; Lee, Eun Gyo

    2013-01-15

    We have developed a gamma-aminobutyric acid (GABA) production technique using his-tag mediated immobilization of Escherichia coli-derived glutamate decarboxylase (GAD), an enzyme that catalyzes the conversion of glutamate to GABA. The GAD was obtained at 1.43 g/L from GAD-overexpressed E. coli fermentation and consisted of 59.7% monomer, 29.2% dimer and 2.3% tetramer with a 97.6% soluble form of the total GAD. The harvested GAD was immobilized to metal affinity gel with an immobilization yield of 92%. Based on an investigation of specific enzyme activity and reaction characteristics, glutamic acid (GA) was chosen over monosodium glutamate (MSG) as a substrate for immobilized GAD, resulting in conversion of 2.17 M GABA in a 1 L reactor within 100 min. The immobilized enzymes retained 58.1% of their initial activities after ten consecutive uses. By using cation exchange chromatography followed by enzymatic conversion, GABA was separated from the residual substrate and leached GAD. As a consequence, the glutamic acid was mostly removed with no detectable GAD, while 91.2% of GABA was yielded in the purification step.

  20. Near-Infrared Emitting CuInSe2/CuInS2 Dot Core/Rod Shell Heteronanorods by Sequential Cation Exchange

    PubMed Central

    2015-01-01

    The direct synthesis of heteronanocrystals (HNCs) combining different ternary semiconductors is challenging and has not yet been successful. Here, we report a sequential topotactic cation exchange (CE) pathway that yields CuInSe2/CuInS2 dot core/rod shell nanorods with near-infrared luminescence. In our approach, the Cu+ extraction rate is coupled to the In3+ incorporation rate by the use of a stoichiometric trioctylphosphine-InCl3 complex, which fulfills the roles of both In-source and Cu-extracting agent. In this way, Cu+ ions can be extracted by trioctylphosphine ligands only when the In–P bond is broken. This results in readily available In3+ ions at the same surface site from which the Cu+ is extracted, making the process a direct place exchange reaction and shifting the overall energy balance in favor of the CE. Consequently, controlled cation exchange can occur even in large and anisotropic heterostructured nanocrystals with preservation of the size, shape, and heterostructuring of the template NCs into the product NCs. The cation exchange is self-limited, stopping when the ternary core/shell CuInSe2/CuInS2 composition is reached. The method is very versatile, successfully yielding a variety of luminescent CuInX2 (X = S, Se, and Te) quantum dots, nanorods, and HNCs, by using Cd-chalcogenide NCs and HNCs as templates. The approach reported here thus opens up routes toward materials with unprecedented properties, which would otherwise remain inaccessible. PMID:26449673

  1. Bandgap tunable colloidal Cu-based ternary and quaternary chalcogenide nanosheets via partial cation exchange

    NASA Astrophysics Data System (ADS)

    Ramasamy, Parthiban; Kim, Miri; Ra, Hyun-Soo; Kim, Jinkwon; Lee, Jong-Soo

    2016-04-01

    Copper based ternary and quaternary semiconductor nanostructures are of great interest for the fabrication of low cost photovoltaics. Although well-developed syntheses are available for zero dimensional (0D) nanoparticles, colloidal synthesis of two dimensional (2D) nanosheets remains a big challenge. Here we report, for the first time, a simple and reproducible cation exchange approach for 2D colloidal Cu2GeSe3, Cu2ZnGeSe4 and their alloyed Cu2GeSxSe3-x, Cu2ZnGeSxSe4-x nanosheets using pre-synthesized Cu2xSe nanosheets as a template. A mechanism for the formation of Cu2-xSe nanosheets has been studied in detail. In situ oxidation of Cu+ ions to form a CuSe secondary phase facilitates the formation of Cu2-xSe NSs. The obtained ternary and quaternary nanosheets have average lateral size in micrometers and thickness less than 5 nm. This method is general and can be extended to produce other important ternary semiconductor nanosheets such as CuIn1-xGaxSe2. The optical band gap of these nanosheets is tuned from 1 to 1.48 eV, depending on their composition.Copper based ternary and quaternary semiconductor nanostructures are of great interest for the fabrication of low cost photovoltaics. Although well-developed syntheses are available for zero dimensional (0D) nanoparticles, colloidal synthesis of two dimensional (2D) nanosheets remains a big challenge. Here we report, for the first time, a simple and reproducible cation exchange approach for 2D colloidal Cu2GeSe3, Cu2ZnGeSe4 and their alloyed Cu2GeSxSe3-x, Cu2ZnGeSxSe4-x nanosheets using pre-synthesized Cu2xSe nanosheets as a template. A mechanism for the formation of Cu2-xSe nanosheets has been studied in detail. In situ oxidation of Cu+ ions to form a CuSe secondary phase facilitates the formation of Cu2-xSe NSs. The obtained ternary and quaternary nanosheets have average lateral size in micrometers and thickness less than 5 nm. This method is general and can be extended to produce other important ternary

  2. Plant cation/H(+) exchangers (CAXs): biological functions and genetic manipulations

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Inorganic cations play decisive roles in many cellular and physiological processes and are essential components of plant nutrition. Therefore, the uptake of cations and their redistribution must be precisely controlled. Vacuolar antiporters are important elements in mediating the intracellular seque...

  3. Theoretical investigation of the reactions of La atom and La+ cation with carbonyl sulfide

    NASA Astrophysics Data System (ADS)

    Dai, Guo-Liang; Wang, Chuan-Feng; Jin, Yan-Xian; Zhao, Jie; Zhong, Ai-Guo; Han, De-Man

    2010-06-01

    The potential energy surfaces for the La+SCO and La++ SCO reactions have been theoretically investigated by using the DFT (B3LYP/ECP/6-311+G(2 d)) level of theory. Both ground and excited state potential energy surfaces (PES) are discussed. The present results show that the reaction mechanism is insertion mechanism both along the C-S and C-O bond activation branches, but the C-S bond activation is much more favorable in energy than the C-O bond activation. The reaction of La atom with SCO was shown to occur preferentially on the ground state (doublet) PES throughout the reaction process, and the experimentally observed species, have been explained according to the mechanisms revealed in this work. While for the reaction between La+ cation with SCO, it involves potential energy curve-crossing which dramatically affects reaction mechanism, and the crossing points (CPs) have been localized by the approach suggested by Yoshizawa et al. Due to the intersystem crossing existing in the reaction process of La+ with SCO, the products SLa+(η2CO) and OLa+(η2CS) may not form. This mechanism is different from that of La + SCO system. All our theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction.

  4. EPR and DFT Study of the Polycyclic Aromatic Radical Cations from Friedel-Crafts Alkylation Reactions

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Wu, An-an; Gao, Li-guo; Wang, Han-qing

    2009-02-01

    Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating system, with m-xylene, or p-xylene and alkyl chloride. The results indicate that the observed electron paramagnetic resonance spectra are due to polycyclic aromatic radicals formed from the parent hydrocarbons. It is suggested that benzyl halides produced in the Friedel-Crafts alkylation reactions undergo Scholl self-condensation to give polycyclic aromatic hydrocarbons, which are converted into corresponding polycyclic aromatic radical cations in the presence of AlCl3. The identification of observed two radicals 2,6-dimethylanthracene and 1,4,5,8-tetramethylanthracene were supported by density functional theory calculations using the B3LYP/6-31G(d,p)//B3LYP/6-31G(d) approach. The theoretical coupling constants support the experimental assignment of the observed radicals.

  5. Sorption of chlorimuron-ethyl on montmorillonite clays: effects of exchangeable cations, pH, and ionic strength.

    PubMed

    Ren, Wenjie; Teng, Ying; Zhou, Qixing; Paschke, Albrecht; Schüürmann, Gerrit

    2014-10-01

    Sorption interaction of chlorimuron-ethyl with montmorillonite clays was investigated under varied types of exchangeable cation, pH, and ionic strength conditions. Chlorimuron-ethyl sorption on bentonites exhibited pronounced cation dependency, and the sorption ability increased as the sequence Ca(2+)- < Na(+)- < Al(3+)- < Fe(3+)-bentonite, due to different sorption mechanisms, whereas the cation dependency was influenced by the clay type and much weaker for montmorillonites. The decrease of pH at the range of 4.0-6.0 prominently increased sorption of chlorimuron-ethyl on all cation-exchanged montmorillonite clays, and nearly a neglected sorption (about 2 %) can be observed at pH over 7.0. In the presence of CaCl2, sorption of chlorimuron-ethyl on Fe(3+)-bentonite was promoted because of complexion of Ca(2+) and the surface of Fe(3+)-bentonite. However, as the concentration of CaCl2 increased, chlorimuron-ethyl sorption on Ca(2+)- and Fe(3+)-exchanged bentonite decreased, suggesting that Ca bridging was not the prevailing mechanism for sorption of chlorimuron-ethyl on these clays. Furthermore, chlorimuron-ethyl sorption was relatively sensitive to pH, and the change of pH may obscure effect of other factors on the sorption, so it was quite necessary to control pH at a constant value when the effect of other factor was being studied. PMID:25028319

  6. Fabrication, characterization and photocatalytic properties of Ag/AgI/BiOI heteronanostructures supported on rectorite via a cation-exchange method

    SciTech Connect

    Chen, Yunfang; Fang, Jianzhang; Lu, Shaoyou; Wu, Yan; Chen, Dazhi; Huang, Liyan; Xu, Weicheng; Zhu, Ximiao; Fang, Zhanqiang

    2015-04-15

    Highlights: • Ag/AgI/BiOI-rectorite was prepared by twice cation-exchange process. • Ag/AgI/BiOI-rectorite photocatalyst possessed SPR and adsorption capacity. • Ag/AgI/BiOI-rectorite exhibited highly photocatalytic activity. • Trapped holes and ·O{sub 2}{sup −} were formed active species in the photocatalytic system. - Abstract: In this work, a new plasmonic photocatalyst Ag/AgI/BiOI-rectorite was prepared via a cation exchange process. The photocatalyst had been characterized by X-ray powder diffraction (XRD), Raman spectra, nitrogen sorption (BET), field-emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity, which was evaluated by degradation of rhodamine B (RhB) and bisphenol A (BPA) under visible light irradiation, was enhanced significantly by loading Ag/AgI/BiOI nanoparticles onto rectorite. The photogenerated holes and superoxide radical (·O{sub 2}{sup −}) were both formed as active species for the photocatalytic reactions under visible light irradiation. The existence of metallic Ag particles, which possess the surface plasmon resonance effect, acted as an indispensable role in the photocatalytic reaction.

  7. Ambient preparation and reactions of gas phase silver cluster cations and anions.

    PubMed

    Wleklinski, Michael; Sarkar, Depanjan; Hollerbach, Adam; Pradeep, Thalappil; Cooks, R Graham

    2015-07-28

    Electrospray ionization of metal salt solutions followed by ambient heating transforms the resulting salt clusters into new species, primarily naked ionic metal clusters. The experiment is done by passing the clusters through a heated coiled loop outside the mass spectrometer which releases the counter-anion while generating the anionic or cationic naked metal cluster. The nature of the anion in the starting salt determines the type of metal cluster observed. For example, silver acetate upon heating generates only positive silver clusters, Ag(n)(+), but silver fluoride generates both positive and negative silver clusters, Ag(n)(+/-) (3 < n < 20). Both unheated and heated metal salt sprays yield ions with characteristic geometric and electronic magic numbers. There is also a strong odd/even effect in the cationic and anionic silver clusters. Thermochemical control is suggested as the basis for favored formation of the observed clusters, with anhydride elimination occurring from the acetates and fluorine elimination from the fluorides to give cationic and anionic clusters, respectively. Data on the intermediates observed as the temperature is ramped support this. The naked metal clusters react with gaseous reagents in the open air, including methyl substituted pyridines, hydrocarbons, common organic solvents, ozone, ethylene, and propylene. Argentation of hydrocarbons, including saturated hydrocarbons, is shown to occur and serves as a useful analytical ionization method. The new cluster formation methodology allows investigation of ligand-metal binding including in reactions of industrial importance, such as olefin epoxidation. These reactions provide insight into the physicochemical properties of silver cluster anions and cations. The potential use of the ion source in ion soft landing is demonstrated by reproducing the mass spectra of salts heated in air using a custom surface science instrument. PMID:26105831

  8. Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.

    PubMed Central

    Komatsu, Y; Koizumi, M; Sekiguchi, A; Ohtsuka, E

    1993-01-01

    The negative strand of the satellite RNA of tobacco ringspot virus (sTobRV(-)) contains a hairpin catalytic domain that shows self-cleavage and self-ligation activities in the presence of magnesium ions. We describe here that the minimal catalytic domain can catalyze a cross-ligation reaction between two kinds of substrates in trans. The cross-ligated product increased when the reaction temperature was decreased during the reaction from 37 degrees C to 4 degrees C. A two-stranded hairpin ribozyme, divided into two fragments between G45 and U46 in a hairpin loop, showed higher ligation activity than the nondivided ribozyme. The two stranded ribozyme also catalyzed an exchange reaction of the 3'-portion of the cleavage site. Images PMID:8441626

  9. Alkali recovery using PVA/SiO2 cation exchange membranes with different -COOH contents.

    PubMed

    Hao, Jianwen; Gong, Ming; Wu, Yonghui; Wu, Cuiming; Luo, Jingyi; Xu, Tongwen

    2013-01-15

    By changing -COOH content in poly(acrylic acid-co-methacryloxypropyl trimethoxy silane (poly(AA-co-γ-MPS)), a series of PVA/SiO(2) cation exchange membranes are prepared from sol-gel process of poly(AA-co-γ-MPS) in presence of poly(vinyl alcohol) (PVA). The membranes have the initial decomposition temperature (IDT) values of 236-274 °C. The tensile strength (TS) ranges from 17.4 MPa to 44.4 MPa. The dimensional stability in length (DS-length) is in the range of 10%-25%, and the DS-area is in the range of 21%-56% in 65 °C water. The water content (W(R)) ranges from 61.2% to 81.7%, the ion exchange capacity (IEC) ranges from 1.69 mmol/g to 1.90 mmol/g. Effects of -COOH content on diffusion dialysis (DD) performance also are investigated for their potential applications. The membranes are tested for recovering NaOH from the mixture of NaOH/Na(2)WO(4) at 25 - 45 °C. The dialysis coefficients of NaOH (U(OH)) are in the range of 0.006-0.032 m/h, which are higher than those of the previous membranes (U(OH): 0.0015 m/h, at 25 °C). The selectivity (S) can reach up to 36.2. The DD performances have been correlated with the membrane structure, especially the continuous arrangement of -COOH in poly(AA-co-γ-MPS) chain.

  10. Influence of competing inorganic cations on the ion exchange equilibrium of the monovalent organic cation metoprolol on natural sediment.

    PubMed

    Niedbala, Anne; Schaffer, Mario; Licha, Tobias; Nödler, Karsten; Börnick, Hilmar; Ruppert, Hans; Worch, Eckhard

    2013-02-01

    The aim of this study was to systematically investigate the influence of the mono- and divalent inorganic ions Na(+) and Ca(2+) on the sorption behavior of the monovalent organic cation metoprolol on a natural sandy sediment at pH=7. Isotherms for the beta-blocker metoprolol were obtained by sediment-water batch tests over a wide concentration range (1-100000 μg L(-1)). Concentrations of the competing inorganic ions were varied within freshwater relevant ranges. Data fitted well with the Freundlich sorption model and resulted in very similar Freundlich exponents (n=0.9), indicating slightly non-linear behavior. Results show that the influence of Ca(2+) compared to Na(+) is more pronounced. A logarithmic correlation between the Freundlich coefficient K(Fr) and the concentration or activity of the competing inorganic ions was found allowing the prediction of metoprolol sorption on the investigated sediment at different electrolyte concentrations. Additionally, the organic carbon of the sediment was completely removed for investigating the influence of organic matter on the sorption of metoprolol. The comparison between the experiments with and without organic carbon removal revealed no significant contribution of the organic carbon fraction (0.1%) to the sorption of metoprolol on the in this study investigated sediment. Results of this study will contribute to the development of predictive models for the transport of organic cations in the subsurface.

  11. Charge exchange reactions and solar neutrino detection in 81Br

    NASA Astrophysics Data System (ADS)

    Liu, K. F.; Gabbard, F.

    1983-01-01

    The feasibility of 81Br as the detector of the solar neutrino flux hinges upon the knowledge of the Gamow-Teller matrix element from the ground state of 81Br to the 52- state at 0.457 MeV in 81Kr. The possibility of obtaining this matrix element is discussed in terms of the (p, n) and (3He, t) charge exchange reactions. NUCLEAR REACTIONS 81Br(p, n)81Kr and 81Br(3He, t)81Kr Gamow-Teller transitions; solar neutrino detection.

  12. Nonbonded, attractive cation-pi interactions in azide-mediated asymmetric ring expansion reactions.

    PubMed

    Katz, Christopher E; Ribelin, Timothy; Withrow, Donna; Basseri, Yashar; Manukyan, Anna K; Bermudez, Amy; Nuera, Christian G; Day, Victor W; Powell, Douglas R; Poutsma, Jennifer L; Aubé, Jeffrey

    2008-05-01

    The influence of attractive, nonbonded interactions on the reactions of 1,2- and 1,3-hydroxyalkyl azides with ketones has been investigated through experimental and computational means. A series of 1,3-hydroxyalkyl azides bearing electronically tuned aromatic groups at the 2 position were prepared and reacted along with several derivatives designed to conformationally restrict the rotational orientation of the aromatic substituent. These studies showed that a cation-pi interaction between an aryl moiety and an N2(+) leaving group plays a role in determining the stereoselectivity of these reactions. A series of ab initio calculations supported this hypothesis. A computational and experimental analysis suggested a primarily steric model for the analogous reactions of substituted 2-azido-1-ethanol analogues. PMID:18396910

  13. [Exchange reactions in brain tissue under chronic ethanol intoxication].

    PubMed

    Gil'miiarova, F N; Radomskaia, V M; Vinogradova, L N

    1982-01-01

    The paper deals with characterization of systems utilizing ethanol and reactions conjugated with its exchange in the brain tissue under chronic alcohol intoxication. The following is established: the absence of the alcoholdehydrogenase pathway of ethanol oxidation in rabbits, unbalanced splitting of carbohydrates under two-months ethanol load, disturbance of oxidative processes in the tricarboxylic acids cycle, a decrease in the pool of oxidized nicotin amide coenzymes. PMID:7036487

  14. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, Frank P.; Herbst, Ronald S.

    1995-01-01

    The isotopes of boron, .sup.10 B and .sup.11 B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF.sub.3 and a liquid BF.sub.3 . donor molecular addition complex formed between BF.sub.3 gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone.

  15. Coherent population trapping probed by charge exchange reactions

    NASA Astrophysics Data System (ADS)

    Gieler, M.; Aumayr, F.; Windholz, L.

    1992-12-01

    Coherent trapping of atomic population in sodium induced by two-frequency laser light has been studied by using a charge exchange reaction for probing the upper level population. When the two-photon resonance condition occurs, the signal due to electron capture from excited Na*(3p) atoms by He2+ projectile ions exhibits the characteristic ``black resonance'' dip, indicating (by nonoptical means) that the fraction of Na atoms in the excited state actually drops to zero.

  16. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, F.P.; Herbst, R.S.

    1995-05-30

    The isotopes of boron, {sup 10}B and {sup 11}B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF{sub 3} and a liquid BF{sub 3} donor molecular addition complex formed between BF{sub 3} gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone. 1 Fig.

  17. Momentum transfer in relativistic heavy ion charge-exchange reactions

    NASA Technical Reports Server (NTRS)

    Townsend, L. W.; Wilson, J. W.; Khan, F.; Khandelwal, G. S.

    1991-01-01

    Relativistic heavy ion charge-exchange reactions yield fragments (Delta-Z = + 1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (Delta-Z = 1, -2,...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.

  18. EXFOR SYSTEMS MANUAL NUCLEAR REACTION DATA EXCHANGE FORMAT.

    SciTech Connect

    MCLANE,V.; NUCLEAR DATA CENTER NETWORK

    2000-05-19

    EXFOR is an exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Centers Network. This document has been written for use by the members of the Network and includes matters of procedure and protocol, as well as detailed rules for the compilation of data. Users may prefer to consult EXFOR Basics' for a brief description of the format.

  19. Tuning Equilibrium Compositions in Colloidal Cd1-xMnxSe Nanocrystals Using Diffusion Doping and Cation Exchange.

    PubMed

    Barrows, Charles J; Chakraborty, Pradip; Kornowske, Lindsey M; Gamelin, Daniel R

    2016-01-26

    The physical properties of semiconductor nanocrystals can be tuned dramatically via composition control. Here, we report a detailed investigation of the synthesis of high-quality colloidal Cd1-xMnxSe nanocrystals by diffusion doping of preformed CdSe nanocrystals. Until recently, Cd1-xMnxSe nanocrystals proved elusive because of kinetic incompatibilities between Mn(2+) and Cd(2+) chemistries. Diffusion doping allows Cd1-xMnxSe nanocrystals to be prepared under thermodynamic rather than kinetic control, allowing access to broader composition ranges. We now investigate this chemistry as a model system for understanding the characteristics of nanocrystal diffusion doping more deeply. From the present work, a Se(2-)-limited reaction regime is identified, in which Mn(2+) diffusion into CdSe nanocrystals is gated by added Se(2-), and equilibrium compositions are proportional to the amount of added Se(2-). At large added Se(2-) concentrations, a solubility-limited regime is also identified, in which x = xmax = ∼0.31, independent of the amount of added Se(2-). We further demonstrate that Mn(2+) in-diffusion can be reversed by cation exchange with Cd(2+) under exactly the same reaction conditions, purifying Cd1-xMnxSe nanocrystals back to CdSe nanocrystals with fine tunability. These chemistries offer exceptional composition control in Cd1-xMnxSe NCs, providing opportunities for fundamental studies of impurity diffusion in nanocrystals and for development of compositionally tuned nanocrystals with diverse applications ranging from solar energy conversion to spin-based photonics. PMID:26643033

  20. On-column refolding of bone morphogenetic protein-2 using cation exchange resin.

    PubMed

    Rane, Anuja M; Jonnalagadda, Sriramakamal; Li, Zhiyu

    2013-08-01

    Refolding is often the bottle-neck step in producing recombinant proteins from inclusion bodies of Escherichia coli, especially for dimer proteins. The refolding process is protein specific, engaging a lot of time and cost to optimize conditions so that the thermodynamics favor protein refolding over competitive aggregation. Bone morphogenetic protein-2 (BMP-2) is a potent osteogenic agent having significant applications in bone regeneration therapy. In this study, we present a novel solid-phase refolding method for rapid and efficient refolding of recombinant BMP-2 dimer from E. coli. We employed a weak cation exchange resin as the adsorbing support, with decreasing gradient of denaturing agent and exposure to oxidizing conditions for adequate disulfide bond formation. Refolded BMP-2 was further purified using size exclusion chromatography and analyzed for its secondary structure and biological activity. The purified BMP-2 dimer showed dose-dependent induction of alkaline phosphatase (ALP) activity in MC3T3 pre-osteoblast cells, thus translating the success of our refolding method. This simple and rapid method can also be applied in refolding and purification of other BMP-2 like dimer proteins. PMID:23748143

  1. The self-diffusion of water and saturated aliphatic alcohols in cation-exchange membranes

    NASA Astrophysics Data System (ADS)

    Volkov, V. I.; Kotov, V. V.; Netesova, G. A.

    2008-07-01

    The self-diffusion of water, methanol, ethanol, isopropanol, and butanol in membranes based on polyethylene and sulfonated copolymer of styrene and divinylbenzene (MK-100) and membranes based on sulfo-containing aromatic polyamides (PA) and a copolymer of 1,2,4,5-benzenetetracarboxylic acid with 4,4'-diaminodiphenyl oxide (PAK) was investigated by the pulsed magnetic field gradient NMR technique. In MK-100 sulfo cation-exchange membranes and PAK carboxylic membranes, two types of sorbate molecules with translational mobilities differing by an order of magnitude were observed. It was established that, in these membranes, the major diffusant portion was transferred trough transport channels formed by functional groups of membranes, counterions, and diffusant molecules (ionogenic channels). The conclusion was drawn that, in PA membranes, water and alcohol molecules were distributed uniformly and carbonyl croups of the polymeric matrix participated in the formation of transport channels. Relations between the structure of membranes, the character of diffusant-polymeric matrix interaction, and the translational mobility of sorbate molecules were found.

  2. Solvent modulation strategy for superior antibody monomer/aggregate separation in cation exchange chromatography.

    PubMed

    Kluters, Simon; Frech, Christian; von Hirschheydt, Thomas; Schaubmar, Andreas; Neumann, Sebastian

    2015-12-01

    Cation exchange chromatography (CEX) is an integral part of many downstream processes for monoclonal antibodies (mAbs). However, in some cases CEX methods with standard mobile phase conditions do not lead to a sufficient removal of soluble antibody aggregates. The addition of neutral polymers such as polyethylene glycol (PEG) to the mobile phase can improve the separation of proteins in IEC remarkably. The applicability of this solvent modulation technique is limited by protein precipitation at higher PEG concentrations. To overcome this limitation solubility enhancers like polyols and amino acids can be added to the mobile phase. These additives are known to inhibit PEG-induced protein precipitation in solution. This new solvent modulation strategy was tested with three different mAbs on two different CEX resins in the presence of PEG in combination with various solubility enhancers. In order to assess the general applicability of this method, mAbs were selected that show major differences with respect to their sensitivity to PEG-induced precipitation and monomer/aggregate resolution performance that is achieved by CEX under standard conditions. For all three mAbs precipitation could be prevented without elimination of the positive PEG-effect. The addition of solubility enhancers gives access to improved separation at elevated PEG concentrations and high protein loadings without running into precipitation issues. Our data indicate that this method is generically applicable and leads to a superior antibody monomer/aggregate separation. PMID:26520020

  3. Kinetics and Thermodynamics of Reserpine Adsorption onto Strong Acidic Cationic Exchange Fiber

    PubMed Central

    Guo, Zhanjing; Liu, Xiongmin; Huang, Hongmiao

    2015-01-01

    The kinetics and thermodynamics of the adsorption process of reserpine adsorbed onto the strong acidic cationic exchange fiber (SACEF) were studied by batch adsorption experiments. The adsorption capacity strongly depended on pH values, and the optimum reserpine adsorption onto the SACEF occurred at pH = 5 of reserpine solution. With the increase of temperature and initial concentration, the adsorption capacity increased. The equilibrium was attained within 20 mins. The adsorption process could be better described by the pseudo-second-order model and the Freundlich isotherm model. The calculated activation energy Ea was 4.35 kJ/mol. And the thermodynamic parameters were: 4.97<ΔH<7.44 kJ/mol, -15.29<ΔG<-11.87 kJ/mol and 41.97<ΔS<47.35 J/mol·K. The thermodynamic parameters demonstrated that the adsorption was an endothermic, spontaneous and feasible process of physisorption within the temperature range between 283 K and 323 K and the initial concentration range between 100 mg/L and 300 mg/L. All the results showed that the SACEF had a good adsorption performance for the adsorption of reserpine from alcoholic solution. PMID:26422265

  4. Isolation of lactoperoxidase using different cation exchange resins by batch and column procedures.

    PubMed

    Fweja, Leonard Wt; Lewis, Michael J; Grandison, Alistair S

    2010-08-01

    Lactoperoxidase (LP) was isolated from whey protein by cation-exchange using Carboxymethyl resin (CM-25C) and Sulphopropyl Toyopearl resin (SP-650C). Both batch and column procedures were employed and the adsorption capacities and extraction efficiencies were compared. The resin bed volume to whey volume ratios were 0.96:1.0 for CM-25C and 0.64:1.0 for SP-650 indicating higher adsorption capacity of SP-650 compared with CM-25C. The effluent LP activity depended on both the enzyme activity in the whey and the amount of whey loaded on the column within the saturation limits of the resin. The percentage recovery was high below the saturation point and fell off rapidly with over-saturation. While effective recovery was achieved with column extraction procedures, the recovery was poor in batch procedures. The whey-resin contact time had little impact on the enzyme adsorption. SDS PAGE and HPLC analyses were also carried out, the purity was examined and the proteins characterised in terms of molecular weights. Reversed phase HPLC provided clear distinction of the LP and lactoferrin (LF) peaks. The enzyme purity was higher in column effluents compared with batch effluents, judged on the basis of the clarity of the gel bands and the resolved peaks in HPLC chromatograms.

  5. Nitrogen removal from wastewater through microbial electrolysis cells and cation exchange membrane

    PubMed Central

    2014-01-01

    Vulnerability of water resources to nutrients led to progressively stricter standards for wastewater effluents. Modification of the conventional procedures to meet the new standards is inevitable. New technologies should give a priority to nitrogen removal. In this paper, ammonium chloride and urine as nitrogen sources were used to investigate the capacity of a microbial electrolysis cell (MEC) configured by cation exchange membrane (CEM) for electrochemical removal of nitrogen over open-and closed-circuit potentials (OCP and CCP) during biodegradation of organic matter. Results obtained from this study indicated that CEM was permeable to both organic and ammonium nitrogen over OCP. Power substantially mediated ammonium migration from anodic wastewater to the cathode, as well. With a urine rich wastewater in the anode, the maximum rate of ammonium intake into the cathode varied from 34.2 to 40.6 mg/L.h over CCP compared to 10.5-14.9 mg/L.h over OCP. Ammonium separation over CCP was directly related to current. For 1.46-2.12 mmol electron produced, 20.5-29.7 mg-N ammonium was removed. Current also increased cathodic pH up to 12, a desirable pH for changing ammonium ion to ammonia gas. Results emphasized the potential for MEC in control of ammonium through ammonium separation and ammonia volatilization provided that membrane characteristic is considered in their development. PMID:24533446

  6. Morphology and microtopology of cation-exchange polymers and the origin of the overlimiting current.

    PubMed

    Balster, J; Yildirim, M H; Stamatialis, D F; Ibanez, R; Lammertink, R G H; Jordan, V; Wessling, M

    2007-03-01

    In electrodialysis desalination processes, the operating current density is limited by concentration polarization. In contrast to other membrane processes such as ultrafiltration, in electrodialysis, current transport above the limiting current is possible. In this work, the origin of the overlimiting current at cation-exchange polymers is investigated. We show that, under certain experimental conditions, electroconvection is the origin of the overlimiting conductance. The theory concerning electroconvection predicts a shortening of the plateau length of membranes with increased conductive or geometrical heterogeneity. We investigate the influence of these two parameters and show that the creation of line undulations on the membrane surface normal to the flow direction, having distances in the range of approximately 50-200% of the boundary-layer thickness, lead to an earlier onset of the overlimiting current. The plateau length of the undulated membranes is reduced by up to 60% compared to that of a flat membrane. These results verify the existence of electroconvection as a mechanism destabilizing the laminar boundary layer at the liquid-membrane interface and causing ionic transport above the limiting current density.

  7. Forensic analysis of hallucinogenic mushrooms and khat (Catha edulis Forsk) using cation-exchange liquid chromatography.

    PubMed

    Laussmann, Tim; Meier-Giebing, Sigrid

    2010-02-25

    Hallucinogenic mushrooms (e.g. Psilocybe and Panaeolus species) as well as leaves and young shoots of the khat tree (Catha edulis Forsk) are illicit drugs in many countries. The exact concentration of the hallucinogenic alkaloids psilocin and psilocybin in mushrooms and the sympathomimetic alkaloids cathinone and cathine in khat is usually essential for jurisdiction. Facing an increasing number of mushroom and khat seizures by German customs authorities, a convenient comprehensive quantitative HPLC method based on cation-exchange liquid chromatography for these rather "exotic" drugs has been developed which avoids time-consuming multi-step sample preparation or chemical derivatization procedures. Using this method a number of different hallucinogenic fungi species and products that are mainly distributed via the internet have been analysed (dried and fresh Psilocybe cubensis Singer as well as P. cubensis collected from "grow boxes", Panaeolus cyanescens Berkeley and Broome and so-called "philosopher stones" (sclerotia of Psilocybe species)). Highest total amounts of psilocin have been detected in dried P. cyanescens reaching up to 3.00+/-0.24 mg per 100 mg. The distribution of khat alkaloids in different parts of the khat shoots has been studied. High concentrations of cathinone have not only been detected in leaves but also in green parts and barks of stalks. Additionally, the sample treatment for fresh mushroom and khat samples has been optimised. Highest amounts of alkaloids were found when fresh material was freeze-dried.

  8. Adsorption equilibrium and kinetics of monomer-dimer monoclonal antibody mixtures on a cation exchange resin.

    PubMed

    Reck, Jason M; Pabst, Timothy M; Hunter, Alan K; Wang, Xiangyang; Carta, Giorgio

    2015-07-10

    Adsorption equilibrium and kinetics are determined for a monoclonal antibody (mAb) monomer and dimer species, individually and in mixtures, on a macroporous cation exchange resin both under the dilute limit of salt gradient elution chromatography and at high protein loads and low salt based on batch adsorption equilibrium and confocal laser scanning microscopy (CLSM) experiments. In the dilute limit and weak binding conditions, the dimer/monomer selectivity in 10mM phosphate at pH 7 varies between 8.7 and 2.3 decreasing with salt concentration in the range of 170-230mM NaCl. At high protein loads and strong binding conditions (0-60mM NaCl), the selectivity in the same buffer is near unity with no NaCl added, but increases gradually with salt concentration reaching high values between 2 and 15 with 60mM added NaCl. For these conditions, the two-component adsorption kinetics is controlled by pore diffusion and is predicted approximately by a dual shrinking core model using parameters based on single component equilibrium and kinetics measurements.

  9. Sorption of (226)Ra from oil effluents onto synthetic cation exchangers.

    PubMed

    Al Attar, Lina; Safia, Bassam

    2013-07-30

    Increasing environmental awareness is being urged for the safe disposal of (226)Ra-contaminated production water generated in the oil industry. Birnessite, antimony silicate and their cationic derivatives were studied for the take-up of (226)Ra using the batch-type method under experimentally determined parameters, viz. contact time, solution-solid ratio and (226)Ra concentration. Data was expressed in terms of distribution coefficients. Sorption experiments were performed in different concentrations of nitric acid in order to speculate the mechanism of (226)Ra uptake. Variation in the magnitude of sorption efficiency of the materials in the presence of the major components of waste streams, i.e. Na(+), K(+) and Ca(2+), revealed that K(+) was the greatest competitor and Na(+) the least. The application of the materials to sorb (226)Ra from actual oil co-production water samples, collected from Der Ezzor and Al Fourat petroleum companies (DEZPC and AFPC), was interpreted in terms of the exchange properties of the materials and water characterisation. Of the parameters studied, the selectivity of materials was shown to be greatly dependent on the pH of wastewater to be treated. PMID:23623032

  10. Cation- and anion-exchanges induce multiple distinct rearrangements within metallosupramolecular architectures.

    PubMed

    Riddell, Imogen A; Ronson, Tanya K; Clegg, Jack K; Wood, Christopher S; Bilbeisi, Rana A; Nitschke, Jonathan R

    2014-07-01

    Different anionic templates act to give rise to four distinct Cd(II)-based architectures: a Cd2L3 helicate, a Cd8L12 distorted cuboid, a Cd10L15 pentagonal prism, and a Cd12L18 hexagonal prism, which respond to both anionic and cationic components. Interconversions between architectures are driven by the addition of anions that bind more strongly within a given product framework. The addition of Fe(II) prompted metal exchange and transformation to a Fe4L6 tetrahedron or a Fe10L15 pentagonal prism, depending on the anionic templates present. The equilibrium between the Cd12L18 prism and the Cd2L3 triple helicate displayed concentration dependence, with higher concentrations favoring the prism. The Cd12L18 structure serves as an intermediate en route to a hexafluoroarsenate-templated Cd10L15 complex, whereby the structural features of the hexagonal prism preorganize the system to form the structurally related pentagonal prism. In addition to the interconversion pathways investigated, we also report the single-crystal X-ray structure of bifluoride encapsulated within a Cd10L15 complex and report solution state data for J-coupling through a CH···F(-) hydrogen bond indicating the strength of these interactions in solution.

  11. Adsorption equilibrium and kinetics of monomer-dimer monoclonal antibody mixtures on a cation exchange resin.

    PubMed

    Reck, Jason M; Pabst, Timothy M; Hunter, Alan K; Wang, Xiangyang; Carta, Giorgio

    2015-07-10

    Adsorption equilibrium and kinetics are determined for a monoclonal antibody (mAb) monomer and dimer species, individually and in mixtures, on a macroporous cation exchange resin both under the dilute limit of salt gradient elution chromatography and at high protein loads and low salt based on batch adsorption equilibrium and confocal laser scanning microscopy (CLSM) experiments. In the dilute limit and weak binding conditions, the dimer/monomer selectivity in 10mM phosphate at pH 7 varies between 8.7 and 2.3 decreasing with salt concentration in the range of 170-230mM NaCl. At high protein loads and strong binding conditions (0-60mM NaCl), the selectivity in the same buffer is near unity with no NaCl added, but increases gradually with salt concentration reaching high values between 2 and 15 with 60mM added NaCl. For these conditions, the two-component adsorption kinetics is controlled by pore diffusion and is predicted approximately by a dual shrinking core model using parameters based on single component equilibrium and kinetics measurements. PMID:26028510

  12. Rapid analysis for theophylline in serum by use of high-pressure cation-exchange chromatography.

    PubMed

    Weinberger, M; Chidsey, C

    1975-06-01

    We have developed a quantitative assay for serum theophylline by high-pressure cation-exchange chromatography. As little as 0.1-ml aliquots of serum were prepared for analysis simply by diluting them with a solution of the internal standard (8-chlorotheophylline). Theophylline and the internal standard were eluted in 17 and 27.5 min, respectively, and the peaks for them were distinct from those of other xanthines and uric acids. We encountered no interference when we used: (a) plasma obtained from blood anticoagulated with citrate; (b) hemolyzed, lipemic, or icteric serum; or (c) 52 samples from patients who were receiving various other medications. An analysis of calibration suggested that errors greater than plus or minus 2.6 mg/liter, a clinically acceptable range, were highly unlikely. Sensitivity was sufficient to identify less than 2.5 mg/liter. This assay was compared with the usual method involving solvent extraction and absorbance measurement in the ultraviolet and found to have similar accuracy, although it is easier, faster, requires less sample, and potentially is more specific.

  13. Simultaneous determination of cation exchange capacity and surface area of acid activated bentonite powders by methylene blue sorption

    NASA Astrophysics Data System (ADS)

    Yener, Nilgün; Biçer, Cengiz; Önal, Müşerref; Sarıkaya, Yüksel

    2012-01-01

    To distinguish the ion exchanged and physically adsorbed methylene blue cations (MB+) on ionic surfaces, acid activated bentonite samples were used as porous adsorbents. A natural calcium bentonite (CaB) sample from Enez/Edirne, Turkey, was acid activated at 90 °C for 16 h with various HCl/CaB ratios. The irreversible exchange and physical adsorption of MB+ cations on the ionic solids have simultaneously occurred. The ion exchanged (mex) and physically adsorbed (mad) MB+ contents were obtained as the values of sorption capacity at c = 0 and the increase to a plateaus of adsorption isotherms, respectively. The mad value was taken to be monolayer adsorption capacity. Cation exchange capacity (CEC) and specific surface area (SMB) for each sample were calculated from the mex and mad values, respectively. Also, the BET specific surface areas (SBET) and pore size distribution were determined from low temperature nitrogen adsorption/desorption data. A linear correlation between the SMB and SBET values was found.

  14. Modulation of the serine base exchange enzyme activity of rat brain membranes by amphiphilic cations and amphiphilic anions.

    PubMed

    Kanfer, J N; McCartney, D G

    1993-04-01

    The biosynthesis of phosphatidylserine in mammalian tissues is catalyzed by the serine base exchange enzyme. The activity of this membrane-bound enzyme can be manipulated by amphiphiles. Amphiphilic cations, such as oleylamine, W-7, chlorpromazine, and didodecyldimethylamine, stimulate the serine base exchange activity. Amphiphilic anions, such as bis(2-ethylhexyl) hydrogen phosphate and cholesterol sulfate, inhibit the serine base exchange activity. These effects are more pronounced at pH 7.0 than at the pH optimum of 8.5 for this enzyme. Both the stimulators and the inhibitors alter the Vmax values without changing the Km value for serine, suggesting that their mechanism of action is related to interactions of the membrane-bound cosubstrate, phosphatidylethanolamine, with the membrane-bound enzyme. The optimal concentration of stimulator varies with the amount of membrane protein present; however, supraoptimal concentrations cause inhibitions. It is proposed that the amphiphilic cations enhance the interaction of the phosphorylethanolamine moiety of the membrane-bound cosubstrate with the enzyme and the amphiphilic anions interfere with such an interaction. Some of the pharmacological properties of these amphiphilic cations, employed clinically as antidepressants, may be mediated by modulation of the serine base exchange enzyme activity.

  15. Single Photon Initiated Decomposition Rearrangement Reactions (spidrr) of Organic Molecules Mediated by the Ni+ Cation

    NASA Astrophysics Data System (ADS)

    Bellert, Darrin; Mansell, Adam; Theis, Zachary; Gutierrez, Michael

    2016-06-01

    The Bellert group at Baylor University has developed a novel method for performing single photon initiated decomposition rearrangement reactions (SPIDRR) of organic molecules mediated by a transition metal cation. The advantage that SPIDRR affords is the direct measurement of first order microcanonical rate constants, k(E), determined at resolved internal energies. Furthermore, the SPIDRR technique measures kinetic details of exothermic reactions where product production is limited only by submerged activation barriers (kinetic barriers that are at energies below the separated reactant limit). Thus, such reactions approach unit efficiency, are thermodynamically driven, and are of greater relevance to catalytic research. Direct measurements of k(E) values extend to isotopically labelled species that provide direct measurement of the kinetic isotope effect (KIE), furnishing unique insight into the mechanistic details of a reaction. This talk presents results from the visible photon initiated, Ni+ induced decarbonylation reaction of propionaldehyde. Here a rather unique energy dependent behavior of the measured rate constants was observed and attributed to a dynamic competition between parallel reaction coordinates available to the photo-excited precursor. RRKM calculations in concert with high level DFT is used to support and further experimental results.

  16. Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

    PubMed Central

    Nishikata, Takashi; Abela, Alexander R; Huang, Shenlin

    2016-01-01

    Summary Cationic palladium(II) complexes have been found to be highly reactive towards aromatic C–H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN)4](BF4)2 or a nitrile-free cationic palladium(II) complex generated in situ from the reaction of Pd(OAc)2 and HBF4, effectively catalyzes C–H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C–H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1) C–H activation to generate a cationic palladacycle; (2) reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3) regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II) complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied. PMID:27340491

  17. Synthesis of Capsule-like Porous Hollow Nanonickel Cobalt Sulfides via Cation Exchange Based on the Kirkendall Effect for High-Performance Supercapacitors.

    PubMed

    Tang, Yongfu; Chen, Shunji; Mu, Shichun; Chen, Teng; Qiao, Yuqing; Yu, Shengxue; Gao, Faming

    2016-04-20

    To construct a suitable three-dimensional structure for ionic transport on the surface of the active materials for a supercapacitor, porous hollow nickel cobalt sulfides are successfully synthesized via a facile and efficient cation-exchange reaction in a hydrothermal process involving the Kirkendall effect with γ-MnS nanorods as a sacrificial template. The formation mechanism of the hollow nickel cobalt sulfides is carefully illustrated via the tuning reaction time and reaction temperature during the cation-exchange process. Due to the ingenious porous hollow structure that offers a high surface area for electrochemical reaction and suitable paths for ionic transport, porous hollow nickel cobalt sulfide electrodes exhibit high electrochemical performance. The Ni(1.77)Co(1.23)S4 electrode delivers a high specific capacity of 224.5 mAh g(-1) at a current density of 0.25 A g(-1) and a high capacity retention of 87.0% at 10 A g(-1). An all-solid-state asymmetric supercapacitor, assembled with a Ni(1.77)Co(1.23)S4 electrode as the positive electrode and a homemade activated carbon electrode as the negative electrode (denoted as NCS//HMC), exhibits a high energy density of 42.7 Wh kg(-1) at a power density of 190.8 W kg(-1) and even 29.4 Wh kg(-1) at 3.6 kW kg(-1). The fully charged as-prepared asymmetric supercapacitor can light up a light emitting diode (LED) indicator for more than 1 h, indicating promising practical applications of the hollow nickel cobalt sulfides and the NCS//HMC asymmetric supercapacitor.

  18. Synthesis of Capsule-like Porous Hollow Nanonickel Cobalt Sulfides via Cation Exchange Based on the Kirkendall Effect for High-Performance Supercapacitors.

    PubMed

    Tang, Yongfu; Chen, Shunji; Mu, Shichun; Chen, Teng; Qiao, Yuqing; Yu, Shengxue; Gao, Faming

    2016-04-20

    To construct a suitable three-dimensional structure for ionic transport on the surface of the active materials for a supercapacitor, porous hollow nickel cobalt sulfides are successfully synthesized via a facile and efficient cation-exchange reaction in a hydrothermal process involving the Kirkendall effect with γ-MnS nanorods as a sacrificial template. The formation mechanism of the hollow nickel cobalt sulfides is carefully illustrated via the tuning reaction time and reaction temperature during the cation-exchange process. Due to the ingenious porous hollow structure that offers a high surface area for electrochemical reaction and suitable paths for ionic transport, porous hollow nickel cobalt sulfide electrodes exhibit high electrochemical performance. The Ni(1.77)Co(1.23)S4 electrode delivers a high specific capacity of 224.5 mAh g(-1) at a current density of 0.25 A g(-1) and a high capacity retention of 87.0% at 10 A g(-1). An all-solid-state asymmetric supercapacitor, assembled with a Ni(1.77)Co(1.23)S4 electrode as the positive electrode and a homemade activated carbon electrode as the negative electrode (denoted as NCS//HMC), exhibits a high energy density of 42.7 Wh kg(-1) at a power density of 190.8 W kg(-1) and even 29.4 Wh kg(-1) at 3.6 kW kg(-1). The fully charged as-prepared asymmetric supercapacitor can light up a light emitting diode (LED) indicator for more than 1 h, indicating promising practical applications of the hollow nickel cobalt sulfides and the NCS//HMC asymmetric supercapacitor. PMID:27031254

  19. Anion- or Cation-Exchange Membranes for NaBH4/H2O2 Fuel Cells?

    PubMed Central

    Šljukić, Biljana; Morais, Ana L.; Santos, Diogo M. F.; Sequeira, César A. C.

    2012-01-01

    Direct borohydride fuel cells (DBFC), which operate on sodium borohydride (NaBH4) as the fuel, and hydrogen peroxide (H2O2) as the oxidant, are receiving increasing attention. This is due to their promising use as power sources for space and underwater applications, where air is not available and gas storage poses obvious problems. One key factor to improve the performance of DBFCs concerns the type of separator used. Both anion- and cation-exchange membranes may be considered as potential separators for DBFC. In the present paper, the effect of the membrane type on the performance of laboratory NaBH4/H2O2 fuel cells using Pt electrodes is studied at room temperature. Two commercial ion-exchange membranes from Membranes International Inc., an anion-exchange membrane (AMI-7001S) and a cation-exchange membrane (CMI-7000S), are tested as ionic separators for the DBFC. The membranes are compared directly by the observation and analysis of the corresponding DBFC’s performance. Cell polarization, power density, stability, and durability tests are used in the membranes’ evaluation. Energy densities and specific capacities are estimated. Most tests conducted, clearly indicate a superior performance of the cation-exchange membranes over the anion-exchange membrane. The two membranes are also compared with several other previously tested commercial membranes. For long term cell operation, these membranes seem to outperform the stability of the benchmark Nafion membranes but further studies are still required to improve their instantaneous power load. PMID:24958292

  20. Preparation of Cation-Exchange Particle Designed for High-Speed Collection of Proteins by Radiation-Induced Graft Polymerization

    NASA Astrophysics Data System (ADS)

    Sekiya, Yuta; Shimoda, Yuichi; Umeno, Daisuke; Saito, Kyoichi; Furumoto, Goro; Shirataki, Hironobu; Shinohara, Naoyuki; Kubota, Noboru

    A cation-exchange polymer brush was immobilized onto a polyethylene-based particle with an average diameter of 35 μm by radiation-induced graft polymerization of glycidyl methacrylate and subsequent sulfonation with sodium sulfite. A lysozyme solution was forced to flow through a bed (height 2 cm, cross-sectional area 0.61 cm2) charged with the resultant cation-exchange particles at a space velocity ranging from 500 to 2300 h-1. From a viewpoint of equilibrium binding capacity and elution percentage of lysozyme, the dose of electron beam and the degree of GMA grafting were optimized to be 200 kGy and 100%, respectively. The bed exhibited a constant dynamic binding capacity of lysozyme 14 mg⁄mL irrespective of space velocity due to negligible diffusional mass-transfer resistance.

  1. Tabletop imaging of structural evolutions in chemical reactions demonstrated for the acetylene cation

    NASA Astrophysics Data System (ADS)

    Ibrahim, Heide; Wales, Benji; Beaulieu, Samuel; Schmidt, Bruno E.; Thiré, Nicolas; Fowe, Emmanuel P.; Bisson, Éric; Hebeisen, Christoph T.; Wanie, Vincent; Giguére, Mathieu; Kieffer, Jean-Claude; Spanner, Michael; Bandrauk, André D.; Sanderson, Joseph; Schuurman, Michael S.; Légaré, François

    2014-07-01

    The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging, we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using vacuum ultraviolet light from a free-electron laser. Here we show that 266 nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and quantitative ab initio trajectory simulations.

  2. Tabletop imaging of structural evolutions in chemical reactions demonstrated for the acetylene cation.

    PubMed

    Ibrahim, Heide; Wales, Benji; Beaulieu, Samuel; Schmidt, Bruno E; Thiré, Nicolas; Fowe, Emmanuel P; Bisson, Éric; Hebeisen, Christoph T; Wanie, Vincent; Giguére, Mathieu; Kieffer, Jean-Claude; Spanner, Michael; Bandrauk, André D; Sanderson, Joseph; Schuurman, Michael S; Légaré, François

    2014-01-01

    The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging, we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using vacuum ultraviolet light from a free-electron laser. Here we show that 266 nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and quantitative ab initio trajectory simulations.

  3. Transition metal-catalysed (4 + 3) cycloaddition reactions involving allyl cations.

    PubMed

    Fernández, Israel; Mascareñas, José Luis

    2012-01-28

    In this emerging area article, we focus on novel intramolecular transition metal catalysed (4 + 3)-cycloaddition reactions of allenedienes in which the allene acts as an allylic-cation surrogate. This process has emerged as a powerful tool for the construction not only of complex seven-membered rings containing compounds but also different types of useful molecular skeletons by the proper selection of the catalyst. The transformation proceeds with high chemo- and stereoselectivity mainly because it occurs through an exo-like concerted transition state which exhibits a clear in-plane aromatic character. Despite that, different reaction mechanisms (i.e. stepwise processes) are also possible depending on the nucleophilicity of the diene moiety.

  4. Tabletop imaging of structural evolutions in chemical reactions demonstrated for the acetylene cation.

    PubMed

    Ibrahim, Heide; Wales, Benji; Beaulieu, Samuel; Schmidt, Bruno E; Thiré, Nicolas; Fowe, Emmanuel P; Bisson, Éric; Hebeisen, Christoph T; Wanie, Vincent; Giguére, Mathieu; Kieffer, Jean-Claude; Spanner, Michael; Bandrauk, André D; Sanderson, Joseph; Schuurman, Michael S; Légaré, François

    2014-01-01

    The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging, we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using vacuum ultraviolet light from a free-electron laser. Here we show that 266 nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and quantitative ab initio trajectory simulations. PMID:25034613

  5. Mixed-mode reversed-phase and ion-exchange separations of cationic analytes on polybutadiene-coated zirconia.

    PubMed

    Hu, Yue; Yang, Xiqin; Carr, Peter W

    2002-08-30

    The retention and selectivity of the chromatographic separation of basic (cationic) analytes on a polybutadiene-coated zirconia (PBD-ZrO2) stationary phase have been studied in greater detail than in previous studies. These separations are strongly influenced by the chemistry of the accessible surface of zirconia. In the presence of buffers which contain hard Lewis bases (e.g., phosphate, fluoride, carboxylic acids) zirconia's surface becomes negatively charged due to adsorption of the buffer anion at the hard Lewis acid sites. Consequently, under most conditions (e.g., neutral pH), cationic analytes undergo both hydrophobic and cation-exchange interactions. This mixed-mode retention process generally leads to greater retention factors for cations relative to those on silica-based reversed phases despite the lower surface areas of the zirconia phase, but, more importantly, adsorption of hard Lewis bases can be used to control the chromatographic selectivity for cationic analytes on these zirconia-based stationary phases. In contrast to our prior work, here we show that when mixed-mode retention takes place, both retention and selectivity are easily adjusted by changing the type of hard Lewis base buffer anion, the type of buffer counter-ion (e.g., sodium, potassium, ammonium), the pH, and the ionic strength of the eluent as well as the type and amount of organic modifier. PMID:12236500

  6. Separation of proteins by cation-exchange sequential injection chromatography using a polymeric monolithic column.

    PubMed

    Masini, Jorge Cesar

    2016-02-01

    Since sequential injection chromatography (SIC) emerged in 2003, it has been used for separation of small molecules in diverse samples, but separations of high molar mass compounds such as proteins have not yet been described. In the present work a poly(glycidyl methacrylate-co-ethylene dimethacrylate) (GMA-co-EDMA) monolithic column was prepared by free radical polymerization inside a 2.1-mm-i.d. activated fused silica-lined stainless steel tubing and modified with iminodiacetic acid (IDA). The column was prepared from a mixture of 24% GMA, 16% EDMA, 20% cyclohexanol, and 40% 1-dodecanol (all% as w/w) containing 1% of azobisisobutyronitrile (AIBN) (in relation to monomers). Polymerization was done at 60 °C for 24 h. The polymer was modified with 1.0 M IDA (in 2 M Na2CO3, pH 10.5) at 80 °C for 16 h. Separation of myoglobin, ribonuclease A, cytochrome C, and lysozyme was achieved at pH 7.0 (20 mM KH2PO4/K2HPO4) using a salt gradient (NaCl). Myoglobin was not retained, and the other proteins were separated by a gradient of NaCl created inside the holding coil (4 m of 0.8-mm-i.d. PTFE tubing) by sequential aspiration of 750 and 700 μL of 0.2 and 0.1 M NaCl, respectively. As the flow was reversed toward the column (5 μL s(-1)) the interdispersion of these solutions created a reproducible gradient which separated the proteins in 10 min, with the following order of retention: ribonuclease A < cytochrome C < lysozyme. The elution order was consistent with a cation-exchange mechanism as the retention increased with the isoelectric points.

  7. Probing the Complementarity of FAIMS and Strong Cation Exchange Chromatography in Shotgun Proteomics

    NASA Astrophysics Data System (ADS)

    Creese, Andrew J.; Shimwell, Neil J.; Larkins, Katherine P. B.; Heath, John K.; Cooper, Helen J.

    2013-03-01

    High field asymmetric waveform ion mobility spectrometry (FAIMS), also known as differential ion mobility spectrometry, coupled with liquid chromatography tandem mass spectrometry (LC-MS/MS) offers benefits for the analysis of complex proteomics samples. Advantages include increased dynamic range, increased signal-to-noise, and reduced interference from ions of similar m/ z. FAIMS also separates isomers and positional variants. An alternative, and more established, method of reducing sample complexity is prefractionation by use of strong cation exchange chromatography. Here, we have compared SCX-LC-MS/MS with LC-FAIMS-MS/MS for the identification of peptides and proteins from whole cell lysates from the breast carcinoma SUM52 cell line. Two FAIMS approaches are considered: (1) multiple compensation voltages within a single LC-MS/MS analysis (internal stepping) and (2) repeat LC-MS/MS analyses at different and fixed compensation voltages (external stepping). We also consider the consequence of the fragmentation method (electron transfer dissociation or collision-induced dissociation) on the workflow performance. The external stepping approach resulted in a greater number of protein and peptide identifications than the internal stepping approach for both ETD and CID MS/MS, suggesting that this should be the method of choice for FAIMS proteomics experiments. The overlap in protein identifications from the SCX method and the external FAIMS method was ~25 % for both ETD and CID, and for peptides was less than 20 %. The lack of overlap between FAIMS and SCX highlights the complementarity of the two techniques. Charge state analysis of the peptide assignments showed that the FAIMS approach identified a much greater proportion of triply-charged ions.

  8. A new cation-exchange method for accurate field speciation of hexavalent chromium

    USGS Publications Warehouse

    Ball, J.W.; McCleskey, R.B.

    2003-01-01

    A new method for field speciation of Cr(VI) has been developed to meet present stringent regulatory standards and to overcome the limitations of existing methods. The method consists of passing a water sample through strong acid cation-exchange resin at the field site, where Cr(III) is retained while Cr(VI) passes into the effluent and is preserved for later determination. The method is simple, rapid, portable, and accurate, and makes use of readily available, inexpensive materials. Cr(VI) concentrations are determined later in the laboratory using any elemental analysis instrument sufficiently sensitive to measure the Cr(VI) concentrations of interest. The new method allows measurement of Cr(VI) concentrations as low as 0.05 ??g 1-1, storage of samples for at least several weeks prior to analysis, and use of readily available analytical instrumentation. Cr(VI) can be separated from Cr(III) between pH 2 and 11 at Cr(III)/Cr(VI) concentration ratios as high as 1000. The new method has demonstrated excellent comparability with two commonly used methods, the Hach Company direct colorimetric method and USEPA method 218.6. The new method is superior to the Hach direct colorimetric method owing to its relative sensitivity and simplicity. The new method is superior to USEPA method 218.6 in the presence of Fe(II) concentrations up to 1 mg 1-1 and Fe(III) concentrations up to 10 mg 1-1. Time stability of preserved samples is a significant advantage over the 24-h time constraint specified for USEPA method 218.6.

  9. Cation exchange capacity of loess and overlying soil in the non-carbonate loess sections, North-Western Croatia

    NASA Astrophysics Data System (ADS)

    Tomašić, Nenad; Kampić, Štefica; Cindrić, Iva Juranović; Pikelj, Kristina; Lučić, Mavro; Mavrić, Danijela; Vučetić, Tajana

    2013-12-01

    The adsorption properties in terms of cation exchange capacity and their relation to the soil and sediment constituents (clay minerals, Fe-, Mn-, and Al-oxyhydroxides, organic matter) were investigated in loess, soil-loess transition zone, and soil at four loess-soil sections in North-Western Croatia. Cation exchange capacity of the bulk samples, the samples after oxalate extraction of Fe, Mn and Al, and after removal of organic matter, as well as of the separated clay fraction, was determined using copper ethylenediamine. Cation exchange capacity (pH˜7) of the bulk samples ranges from 5 to 12 cmol c /kg in soil, from 7 to 15 cmol c /kg in the soil-loess transition zone, and from 12 to 20 cmol c /kg in loess. Generally, CEC values increase with depth. Oxalate extraction of Fe, Mn, and Al, and removal of organic matter cause a CEC decrease of 3-38% and 8-55%, respectively, proving a considerable influence of these constituents to the bulk CEC values. In the separated clay fraction (<2 μm) CEC values are up to several times higher relative to those in the bulk samples. The measured CEC values of the bulk samples generally correspond to the clay mineral content identified. Also, a slight increase in muscovite/illite content with depth and the vermiculite occurrence in the loess horizon are concomitant with the CEC increase in deeper horizons, irrespective of the sample pretreatment.

  10. Cation exchange capacity of loess and overlying soil in the non-carbonate loess sections, North-Western Croatia

    NASA Astrophysics Data System (ADS)

    Tomašić, Nenad; Kampić, Štefica; Cindrić, Iva; Pikelj, Kristina; Lučić, Mavro; Mavrić, Danijela; Vučetić, Tajana

    2013-12-01

    The adsorption properties in terms of cation exchange capacity and their relation to the soil and sediment constituents (clay minerals, Fe-, Mn-, and Al-oxyhydroxides, organic matter) were investigated in loess, soil-loess transition zone, and soil at four loess-soil sections in North-Western Croatia. Cation exchange capacity of the bulk samples, the samples after oxalate extraction of Fe, Mn and Al, and after removal of organic matter, as well as of the separated clay fraction, was determined using copper ethylenediamine. Cation exchange capacity (pH˜7) of the bulk samples ranges from 5 to 12 cmolc/kg in soil, from 7 to 15 cmolc/kg in the soil-loess transition zone, and from 12 to 20 cmolc/kg in loess. Generally, CEC values increase with depth. Oxalate extraction of Fe, Mn, and Al, and removal of organic matter cause a CEC decrease of 3-38% and 8-55%, respectively, proving a considerable influence of these constituents to the bulk CEC values. In the separated clay fraction (<2 μm) CEC values are up to several times higher relative to those in the bulk samples. The measured CEC values of the bulk samples generally correspond to the clay mineral content identified. Also, a slight increase in muscovite/illite content with depth and the vermiculite occurrence in the loess horizon are concomitant with the CEC increase in deeper horizons, irrespective of the sample pretreatment.

  11. A weak cation-exchange monolith as stationary phase for the separation of peptide diastereomers by CEC.

    PubMed

    Ludewig, Ronny; Nietzsche, Sandor; Scriba, Gerhard K E

    2011-01-01

    A CEC weak cation-exchange monolith has been prepared by in situ polymerization of acrylamide, methylenebisacrylamide and 4-acrylamidobutyric acid in a decanol-dimethylsulfoxide mixture as porogen. The columns were evaluated by SEM and characterized with regard to the separation of diastereomers and α/β-isomers of aspartyl peptides. Column preparation was reproducible as evidenced by comparison of the analyte retention times of several columns prepared simultaneously. Analyte separation was achieved using mobile phases consisting of acidic phosphate buffer and ACN. Under these conditions the peptides migrated due to their electrophoretic mobility but the EOF also contributed as driving force as a function of the pH of the mobile phase due to increasing dissociation of the carboxyl groups of the polymer. Raising the pH of the mobile phase also resulted in deprotonation of the peptides reducing analyte mobility. Due to these mechanisms each pair of diastereomeric peptides displayed the highest resolution at a different pH of the buffer component of the mobile phase. Comparing the weak-cation exchange monolith to an RP monolith and a strong cation-exchange monolith different elution order of some peptide diastereomers was observed, clearly illustrating that interactions with the stationary phase contribute to the CEC separations.

  12. Retardation of ammonium and potassium transport through a contaminated sand and gravel aquifer: The Role of cation exchange

    USGS Publications Warehouse

    Ceazan, M.L.; Thurman, E.M.; Smith, R.L.

    1989-01-01

    The role of cation exchange in the retardation of ammonium (NH4+) and potassium (K+) transport in a shallow sand and gravel aquifer was evaluated by use of observed distributions of NH4+ and K+ within a plume of sewage-contaminated groundwater, small-scale tracer injection tests, and batch sorption experiments on aquifer material. Both NH4+ and K+ were transported ???2 km in the 4-km-long contaminant plume (retardation factor, Rf = 2.0). Sediments from the NH4+-containing zone of the plume contained significant quantities of KCl-extractable NH4+ (extraction distribution coefficient, Kd,extr = 0.59-0.87 mL/g of dry sediment), and when added to uncontaminated sediments, NH4+ sorption followed a linear isotherm. Small-scale tracer tests demonstrated that NH4+ and K+ were retarded (Rf =3.5) relative to a nonreactive tracer (Br-). Sorption of dissolved NH4+ was accompanied by concomitant release of calcium (Ca2+), magnesium (Mg2+), and sodium (Na+) from aquifer sediments, suggesting involvement of cation exchange. In contrast, nitrate (NO3-) was not retarded and cleanly separated from NH4+ and K+ in the small-scale tracer tests. This study demonstrates that transport of NH4+ and K+ through a sand and gravel aquifer can be markedly affected by cation-exchange processes even at a clay content less than 0.1%.

  13. EXFOR systems manual: Nuclear reaction data exchange format

    SciTech Connect

    McLane, V.

    1996-07-01

    This document describes EXFOR, the exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Centers Network. In addition to storing the data and its bibliographic information, experimental information, including source of uncertainties, is also compiled. The status and history of the data set is also included, e.g., the source of the data, any updates which have been made, and correlations to other data sets. The exchange format, as outlined, is designed to allow a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in an easily machine-readable format (for checking and indicating possible errors) and a format that can be read by personnel (for passing judgment on and correcting any errors indicated by the machine).

  14. Cation Exchange Combined with Kirkendall Effect in the Preparation of SnTe/CdTe and CdTe/SnTe Core/Shell Nanocrystals.

    PubMed

    Jang, Youngjin; Yanover, Diana; Čapek, Richard Karel; Shapiro, Arthur; Grumbach, Nathan; Kauffmann, Yaron; Sashchiuk, Aldona; Lifshitz, Efrat

    2016-07-01

    Controlling the synthesis of narrow band gap semiconductor nanocrystals (NCs) with a high-quality surface is of prime importance for scientific and technological interests. This Letter presents facile solution-phase syntheses of SnTe NCs and their corresponding core/shell heterostructures. Here, we synthesized monodisperse and highly crystalline SnTe NCs by employing an inexpensive, nontoxic precursor, SnCl2, the reactivity of which was enhanced by adding a reducing agent, 1,2-hexadecanediol. Moreover, we developed a synthesis procedure for the formation of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. The cation exchange of Sn(2+) by Cd(2+) at the surface allowed primarily the formation of SnTe/CdTe core/shell NCs. Further continuation of the reaction promoted an intensive diffusion of the Cd(2+) ions, which via the Kirkendall effect led to the formation of the inverted CdTe/SnTe core/shell NCs. PMID:27331900

  15. (p,n) Charge-Exchange Reactions in Inverse Kinematics

    NASA Astrophysics Data System (ADS)

    Lipschutz, Samuel; NSCL E10003 Collaboration

    2014-09-01

    Charge-exchange experiments at intermediate energy yield important information about collective excitations with spin-isospin degrees of freedom. The properties of isovector giant resonances in neutron-rich rare-isotopes provide stringent tests of theoretical models and are important inputs for modeling of astrophysical phenomena. The (p,n) charge-exchange reaction in inverse kinematics has been developed as a new tool for investigating isovector giant resonances in rare isotopes. The technique, which involves the detection of low-energy neutrons that recoil from a hydrogen target, while detecting fast beam-like ejectiles in a magnetic spectrometer, was successfully employed at NSCL to study the 56Ni(p,n) reaction. Continuing with this technique a 16C(p,n) experiment at 100 MeV/u aimed at extracting isovector multipole strengths up to excitation energies of 30 MeV was preformed. The Low Energy Neutron Detector Array (LENDA) and the Versatile Array of Neutron Detectors at Low Energy (VANDLE) were utilized in combination with the Ursinus Liquid Hydrogen Target and the S800 spectrometer to perform this experiment. Preliminary results will be shown. Charge-exchange experiments at intermediate energy yield important information about collective excitations with spin-isospin degrees of freedom. The properties of isovector giant resonances in neutron-rich rare-isotopes provide stringent tests of theoretical models and are important inputs for modeling of astrophysical phenomena. The (p,n) charge-exchange reaction in inverse kinematics has been developed as a new tool for investigating isovector giant resonances in rare isotopes. The technique, which involves the detection of low-energy neutrons that recoil from a hydrogen target, while detecting fast beam-like ejectiles in a magnetic spectrometer, was successfully employed at NSCL to study the 56Ni(p,n) reaction. Continuing with this technique a 16C(p,n) experiment at 100 MeV/u aimed at extracting isovector multipole

  16. Ion-exchange chromatography of mono- and divalent cations in natural waters on a weak-acid anion-exclusion column.

    PubMed

    Tanaka, K; Ohta, K; Haddad, P R; Fritz, J S

    1998-04-24

    Ion-exchange chromatography with indirect conductimetric detection for the simultaneous determination of mono- and divalent cations is investigated using an anion-exclusion chromatographic column packed with polymethacrylate-based weakly acidic cation-exchange resin in the H+ form (Tosoh TSKgel OA-PAK-A, 300 mm x 7.8 mm I.D.). An eluent comprising a strong acid, a weak organic acid, methanol and water is used. Using 0.75 mM sulfuric acid, 2 mM tartaric acid, 7.5% (v/v) methanol in water as eluent, the monovalent cations (Na+, NH4+, and K+) and divalent cations (Mg2+ and Ca2+) were separated simultaneously by a cation-exchange mechanism in about 25 min. The application of this method to the analysis of several natural waters including rain, river, lake, underground and forest soil waters for estimating acid rain effects on the natural and urban environments is presented.

  17. Gas-Phase Reactions of Atomic Gold Cations with Linear Alkanes (C2-C9).

    PubMed

    Zhang, Ting; Li, Zi-Yu; Zhang, Mei-Qi; He, Sheng-Gui

    2016-06-30

    To develop proper ionization methods for alkanes, the reactivity of bare or ligated transition metal ions toward alkanes has attracted increasing interests. In this study, the reactions of the gold cations with linear alkanes from ethane up to nonane (CnH2n+2, n = 2-9) under mild conditions have been characterized by mass spectrometry and density functional theory calculations. When reacting with Au(+), small alkanes (n = 2-6) were confirmed to follow specific reaction channels of dehydrogenation for ethane and hydride transfer for others to generate product ions characteristic of the original alkanes, which indicates that Au(+) can act as a reagent ion to ionize alkanes from ethane to n-hexane. Strong dependence of the chain length of alkanes was observed for the rate constants and reaction efficiencies. Extensive fragmentation took place for larger alkanes (n > 6). Theoretical results show that the fragmentation induced by the hydride transfer occurs after the release of AuH. Moreover, the fragmentation of n-heptane was successfully avoided when the reaction took place in a high-pressure reactor. This implies that Au(+) is a potential reagent ion to ionize linear and even the branched alkanes. PMID:27266670

  18. Charge-exchange reactions with a radioactive triton beam

    SciTech Connect

    Jaenecke, J.

    1998-12-21

    A high-resolution (t, {sup 3}He) test experiment has been performed recently by making use of a secondary triton beam produced by fragmentation of {alpha}-particles. The purpose of this charge-exchange experiment was to achieve good energy resolution in an (n,p)-type reaction at intermediate bombarding energies. The experiment was carried out with the K1200 cyclotron at the National Superconducting Cyclotron Laboratory using the A1200 beam-analysis system and the S800 magnetic spectrometer. The beam-analysis system was used to transport the energy-dispersed radioactive triton beam from the production target to the target position, and the magnetic spectrometer was used to focus the dispersion-matched {sup 3}He particles from the (t, {sup 3}He) reaction at 0 degree sign onto the focal plane of the spectrometer. An energy resolution of 200-250 keV was achieved.

  19. Isotope exchange reaction on Li 2ZrO 3

    NASA Astrophysics Data System (ADS)

    Baba, Atsushi; Nishikawa, Masabumi; Eguchi, Takanori

    1997-11-01

    Lithium meta-zirconate, Li 2ZrO 3, is considered as a strong candidate for the tritium breeding material in a D-T fusion reactor. The isotope exchange reaction rate between hydrogen isotopes in the purge gas and tritium on the surface of Li 2ZrO 3 has not been quantified yet, although helium gas with hydrogen or deuterium is planned to be used as the blanket purge gas in the recent blanket designs. The mass transfer coefficient representing the isotope exchange reaction between H 2 and D 2O or that between D 2 and H 2O in the Li 2ZrO 3 is experimentally obtained as KF,ex1 = 1.60 × 10 2 exp(- 121[kJ/mol]/RT) in this work. Discussions about the effect of temperature, concentration of hydrogen in the purge gas or flow rate of the purge gas on the conversion of tritiated water to tritium gas, HT instead of H 2, are also performed.

  20. Use of zirconium(IV) arsenophosphate columns for cation exchange separation of metal ions interfering in the spectrophotometric determination of uranium with sodium diethyl dithiocarbamate

    SciTech Connect

    Varshney, K.G.; Agrawal, S.; Anwar, S.; Varshney, K.

    1985-01-01

    A simple cation exchange method has been developed for the quantitative separation of uranium from some metal ions which generally interfere in its spectrophotometric determination using sodium diethyl dithiocarbamate as a reagent. The method requires only a single bed operation and enables a satisfactory (Error + or - separation of uranium (UO/sub 2/ (II)) up to 1080 ..mu..g from ten metal ions on a 2 g column of zirconium (IV) arsenophosphate cation exchanger in H(I) form.

  1. Comparison between methods using copper, lanthanum, and colorimetry for the determination of the cation exchange capacity of plant cell walls.

    PubMed

    Wehr, J Bernhard; Blamey, F Pax C; Menzies, Neal W

    2010-04-28

    The determination of the cation exchange capacity (CEC) of plant cell walls is important for many physiological studies. We describe the determination of cell wall CEC by cation binding, using either copper (Cu) or lanthanum (La) ions, and by colorimetry. Both cations are strongly bound by cell walls, permitting fast and reproducible determinations of the CEC of small samples. However, the dye binding methods using two cationic dyes, Methylene Blue and Toluidine Blue, overestimated the CEC several-fold. Column and centrifugation methods are proposed for CEC determination by Cu or La binding; both provide similar results. The column method involves packing plant material (2-10 mg dry mass) in a chromatography column (10 mL) and percolating with 20 bed volumes of 1 mM La or Cu solution, followed by washing with deionized water. The centrifugation method uses a suspension of plant material (1-2 mL) that is centrifuged, and the pellet is mixed three times with 10 pellet volumes of 1 mM La or Cu solution followed by centrifugation and final washing with deionized water. In both methods the amount of La or Cu bound to the material was determined by spectroscopic methods.

  2. Cationic Chiral Fluorinated Oxazaborolidines. More Potent, Second-Generation Catalysts for Highly Enantioselective Cycloaddition Reactions.

    PubMed

    Mahender Reddy, Karla; Bhimireddy, Eswar; Thirupathi, Barla; Breitler, Simon; Yu, Shunming; Corey, E J

    2016-02-24

    The coordination of chiral ligands to Lewis acid metal derivatives, a useful strategy for enantioselective, electrophilic catalysis, generally leads to a lower level of catalytic activity than that of the original uncomplexed compound. Activation by further attachment of a proton or strong Lewis acid to the complex provides a way to overcome the deactivating effect of a chiral ligand. The research described herein has demonstrated that further enhancement of catalytic activity is possible by the judicious placement of fluorine substituents in the chiral ligand. This approach has led to a new, second-generation family of chiral oxazaborolidinium cationic species which can be used to effect many Diels-Alder reactions in >95% yield and >95% ee using catalyst loadings at the 1-2 mol % level. The easy recovery of the chiral ligand makes the application of these new catalysts especially attractive for large-scale synthesis.

  3. A boron-boron coupling reaction between two ethyl cation analogues

    NASA Astrophysics Data System (ADS)

    Litters, Sebastian; Kaifer, Elisabeth; Enders, Markus; Himmel, Hans-Jörg

    2013-12-01

    The design of larger architectures from smaller molecular building blocks by element-element coupling reactions is one of the key concerns of synthetic chemistry, so a number of strategies were developed for this bottom-up approach. A general scheme is the coupling of two elements with opposing polarity or that of two radicals. Here, we show that a B-B coupling reaction is possible between two boron analogues of the ethyl cation, resulting in the formation of an unprecedented dicationic tetraborane. The bonding properties in the rhomboid B4 core of the product can be described as two B-B units connected by three-centre, two-electron bonds, sharing the short diagonal. Our discovery might lead the way to the long sought-after boron chain polymers with a structure similar to the silicon chains in β-SiB3. Moreover, the reaction is a prime textbook example of the influence of multiple-centre bonding on reactivity.

  4. Charge-exchange reaction by Reggeon exchange and W{sup +}W{sup −}-fusion

    SciTech Connect

    Schicker, R.

    2015-04-10

    Charge-exchange reactions at high energies are examined. The existing cross section data on the Reggeon induced reaction pp → n + Δ{sup ++} taken at the ZGS and ISR accelerators are extrapolated to the energies of the RHIC and LHC colliders. The interest in the charge-exchange reaction induced by W{sup ±}-fusion is presented, and the corresponding QCD-background is examined.

  5. The investigation on cationic exchange capacity of zeolites: the use as selective ion trappers in the electrokinetic soil technique.

    PubMed

    Ursini, Ornella; Lilla, Edo; Montanari, Roberta

    2006-09-21

    The cation exchange capacity (CEC) of porous zeolites allows to adsorb in the framework cavities the cations as pollutant heavy metal ions. We investigate the CEC behaviour of different zeolites in different experimental conditions; in solution where the ion's mobility is spontaneous and free and in the electrokinetic system where the ion's mobility is driven by the electric field. The aim of this study is to investigate if the CEC is an useful property to create a special interface region of zeolites, that if placed in the electrokinetic cell, just before the cathode, could allow to capture and concentrate the heavy metallic ions, during their migrating process. The zeolite 13X investigated in the electrokinetic proofs, retains a good high ions adsorption, even if quite smaller than the relevant free solution condition and well acts as confined trap for the heavy metal ions. In fact no trace of metallic deposition are present on the electrode's surface. PMID:16716501

  6. Role of a Guanidinium Cation-Phosphodianion Pair in Stabilizing the Vinyl Carbanion Intermediate of Orotidine 5'-Phosphate Decarboxylase-Catalyzed Reactions.†

    PubMed Central

    Goryanova, Bogdana; Goldman, Lawrence M.; Amyes, Tina L.; Gerlt, John A; Richard, John P.

    2013-01-01

    The side chain cation of Arg235 provides a 5.6 and 2.6 kcal/mol stabilization of the transition states for orotidine 5'-monophosphate decarboxylase from Saccharomyces cerevisiae (OMPDC) catalyzed reactions of OMP and 5-fluoroorotidine 5'-monophosphate (FOMP), respectively, a 7.2 kcal/mol stabilization of the vinyl carbanion-like transition state for enzyme-catalyzed exchange of the C-6 proton of 5-fluorouridine 5'-monophosphate (FUMP), but no stabilization of the transition states for enzyme-catalyzed decarboxylation of truncated substrates 1-(β-d-erythrofuranosyl)orotic acid and 1-(β-d-erythrofuranosyl) 5-fluorouracil. These observations show that the transition state stabilization results from formation of a protein cation-phosphodianion pair, and that there is no detectable stabilization from an interaction between the side chain and the pyrimidine ring of substrate. The 5.6 kcal/mol side chain interaction with the transition state for the decarboxylation reaction is 50% of the total 11.2 kcal/mol transition state stabilization by interactions with the phosphodianion of OMP, while the 7.2 kcal/mol side-chain interaction with the transition state for the deuterium exchange reaction is a larger 78% of the total 9.2 kcal/mol transition state stabilization by interactions with the phosphodianion of FUMP. The effect of the R235A mutation on the enzyme-catalyzed deuterium exchange is expressed predominantly as a change in the turnover number kex while the effect on the enzyme-catalyzed decarboxylation of OMP is expressed predominantly as a change in the Michaelis constant Km. These results are rationalized by a mechanism in which the binding of OMP, compared with FUMP, provides a larger driving force for conversion of OMPDC from an inactive open conformation to a productive, active, closed conformation. PMID:24053466

  7. In-situ graft-polymerization preparation of cation-exchange supermacroporous cryogel with sulfo groups in glass columns.

    PubMed

    Yao, Kejian; Yun, Junxian; Shen, Shaochuan; Chen, Fang

    2007-07-20

    Graft polymerization of monomer chains with expected functional groups onto the matrix pore surfaces by initiator is an effective approach for introducing ion-exchange groups to cryogel matrix to get anion- or cation-exchange supermacroporous cryogels. In this work, a novel cation-exchange cryogel with sulfo binding groups was prepared by grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) onto polyacrylamide-based cryogels in glass columns. The grafting polymerization was achieved in an in-situ manner which was performed by pumping the initiator and the reactive solution of graft monomer with sulfo binding groups directly through a cryogel bed pre-produced in a glass column under frozen condition. The axial liquid dispersion characteristics within the monolithic cryogel beds before and after the in-situ polymerization were compared by measuring residence time distributions (RTDs) at various liquid flow rates using tracer pulse-response method. Microstructure morphology of pores within cryogels was analyzed by scanning electron microscopy (SEM). Chromatography of lysozyme was carried out to reveal the protein breakthrough and elution characteristics in the obtained cryogel beds.

  8. In-situ graft-polymerization preparation of cation-exchange supermacroporous cryogel with sulfo groups in glass columns.

    PubMed

    Yao, Kejian; Yun, Junxian; Shen, Shaochuan; Chen, Fang

    2007-07-20

    Graft polymerization of monomer chains with expected functional groups onto the matrix pore surfaces by initiator is an effective approach for introducing ion-exchange groups to cryogel matrix to get anion- or cation-exchange supermacroporous cryogels. In this work, a novel cation-exchange cryogel with sulfo binding groups was prepared by grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) onto polyacrylamide-based cryogels in glass columns. The grafting polymerization was achieved in an in-situ manner which was performed by pumping the initiator and the reactive solution of graft monomer with sulfo binding groups directly through a cryogel bed pre-produced in a glass column under frozen condition. The axial liquid dispersion characteristics within the monolithic cryogel beds before and after the in-situ polymerization were compared by measuring residence time distributions (RTDs) at various liquid flow rates using tracer pulse-response method. Microstructure morphology of pores within cryogels was analyzed by scanning electron microscopy (SEM). Chromatography of lysozyme was carried out to reveal the protein breakthrough and elution characteristics in the obtained cryogel beds. PMID:17517417

  9. A combined EPR and DFT study of the overcrowded aromatic radical cations from Friedel-Crafts alkylation reactions

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Tang, Fu Ming; Wu, Yi Fang

    2011-09-01

    Electron paramagnetic resonance and electron-nuclear double resonance methods were used to study the polycyclic aromatic radical cations produced in a Friedel-Crafts alkylating system, and the following radical cations were indentified: 3,6,11,14-tetramethyl dibenzo (a, c) triphylene and 2,6-dimethyl-9,10-di(p-methylbenzyl) anthracene radical cations. The results indicate that the observed electron paramagnetic resonance spectra are due to overcrowded polycyclic aromatic radical cations formed from the parent hydrocarbons. It is suggested that benzyl halides produced in the Friedel-Crafts alkylation reactions undergo Scholl condensation to give polycyclic aromatic hydrocarbons, which are converted into corresponding polycyclic aromatic radical cations in the presence of AlCl 3. We carried out the theoretical calculation of the isotropic 1H hyperfine coupling constants for studied both PAHs radical cations. The results indicate that the IEFPCM-DFT calculation at B3LYP level with 6-31++G(d,p), EPRII and EPRIII basis sets could well support the experimental hfcc assignment of the observed radicals. Optimized geometry indicates that the aromatic rings in both PAHs radical cations twisted significantly out of co-planarity.

  10. Consistent effects of canopy vs. understory nitrogen addition on the soil exchangeable cations and microbial community in two contrasting forests.

    PubMed

    Shi, Leilei; Zhang, Hongzhi; Liu, Tao; Zhang, Weixin; Shao, Yuanhu; Ha, Denglong; Li, Yuanqiu; Zhang, Chuangmao; Cai, Xi-an; Rao, Xingquan; Lin, Yongbiao; Zhou, Lixia; Zhao, Ping; Ye, Qing; Zou, Xiaoming; Fu, Shenglei

    2016-05-15

    Anthropogenic N deposition has been well documented to cause substantial impacts on the chemical and biological properties of forest soils. In most studies, however, atmospheric N deposition has been simulated by directly adding N to the forest floor. Such studies thus ignored the potentially significant effect of some key processes occurring in forest canopy (i.e., nitrogen retention) and may therefore have incorrectly assessed the effects of N deposition on soils. Here, we conducted an experiment that included both understory addition of N (UAN) and canopy addition of N (CAN) in two contrasting forests (temperate deciduous forest vs. subtropical evergreen forest). The goal was to determine whether the effects on soil exchangeable cations and microbial biomass differed between CAN and UAN. We found that N addition reduced pH, BS (base saturation) and exchangeable Ca and increased exchangeable Al significantly only at the temperate JGS site, and reduced the biomass of most soil microbial groups only at the subtropical SMT site. Except for soil exchangeable Mn, however, effects on soil chemical properties and soil microbial community did not significantly differ between CAN and UAN. Although biotic and abiotic soil characteristics differ significantly and the responses of both soil exchangeable cations and microbial biomass were different between the two study sites, we found no significant interactive effects between study site and N treatment approach on almost all soil properties involved in this study. In addition, N addition rate (25 vs. 50 kg N ha(-1) yr(-1)) did not show different effects on soil properties under both N addition approaches. These findings did not support previous prediction which expected that, by bypassing canopy effects (i.e., canopy retention and foliage fertilization), understory addition of N would overestimate the effects of N deposition on forest soil properties, at least for short time scale.

  11. Consistent effects of canopy vs. understory nitrogen addition on the soil exchangeable cations and microbial community in two contrasting forests.

    PubMed

    Shi, Leilei; Zhang, Hongzhi; Liu, Tao; Zhang, Weixin; Shao, Yuanhu; Ha, Denglong; Li, Yuanqiu; Zhang, Chuangmao; Cai, Xi-an; Rao, Xingquan; Lin, Yongbiao; Zhou, Lixia; Zhao, Ping; Ye, Qing; Zou, Xiaoming; Fu, Shenglei

    2016-05-15

    Anthropogenic N deposition has been well documented to cause substantial impacts on the chemical and biological properties of forest soils. In most studies, however, atmospheric N deposition has been simulated by directly adding N to the forest floor. Such studies thus ignored the potentially significant effect of some key processes occurring in forest canopy (i.e., nitrogen retention) and may therefore have incorrectly assessed the effects of N deposition on soils. Here, we conducted an experiment that included both understory addition of N (UAN) and canopy addition of N (CAN) in two contrasting forests (temperate deciduous forest vs. subtropical evergreen forest). The goal was to determine whether the effects on soil exchangeable cations and microbial biomass differed between CAN and UAN. We found that N addition reduced pH, BS (base saturation) and exchangeable Ca and increased exchangeable Al significantly only at the temperate JGS site, and reduced the biomass of most soil microbial groups only at the subtropical SMT site. Except for soil exchangeable Mn, however, effects on soil chemical properties and soil microbial community did not significantly differ between CAN and UAN. Although biotic and abiotic soil characteristics differ significantly and the responses of both soil exchangeable cations and microbial biomass were different between the two study sites, we found no significant interactive effects between study site and N treatment approach on almost all soil properties involved in this study. In addition, N addition rate (25 vs. 50 kg N ha(-1) yr(-1)) did not show different effects on soil properties under both N addition approaches. These findings did not support previous prediction which expected that, by bypassing canopy effects (i.e., canopy retention and foliage fertilization), understory addition of N would overestimate the effects of N deposition on forest soil properties, at least for short time scale. PMID:26930308

  12. Synthesis, characterization and ion-exchange properties of a new and novel 'organic-inorganic' hybrid cation-exchanger: Nylon-6,6, Zr(IV) phosphate.

    PubMed

    Inamuddin; Khan, Shakeel Ahmad; Siddiqui, Weqar Ahmad; Khan, Asif Ali

    2007-02-15

    Organic-inorganic hybrid materials enable the integration of useful organic and inorganic characteristics within a single molecular-scale composite. Unique ion-exchange properties of these types of materials have been observed, and many others can be envisioned for this promising class of materials. In this paper, we describe the ion-exchange and physico-chemical properties of one family of self-assembling organic-inorganic hybrid based on nylon-6,6, framework with Zr(IV) phosphate an inorganic ion-exchanger. The physico-chemical properties of this hybrid material were determined using atomic absorption spectrophotometry (AAS), CHN elemental analysis, ICP-MS, UV-vis spectrophotometry, FTIR, TGA-DTA and scanning electron microscope (SEM) studies. Ion-exchange capacity (IEC), thermal stability and distribution behavior, etc. were also carried out to understand the cation-exchange behavior of the material. On the basis of distribution studies, the material was found to be highly selective for Hg(II), a highly toxic environmental pollutant. Its selectivity was examined by achieving some important binary separations like Hg(II)-Mg(II), Hg(II)-Zn(II), Hg(II)-Fe(III), Hg(II)-Bi(III), etc. Thus, the relatively new field of "organic-inorganic" hybrids offers a variety of exciting technological opportunities to decrease the environmental pollution.

  13. Ion chromatographic separation of inorganic ions using a combination of hydrophilic interaction chromatographic column and cation-exchange resin column.

    PubMed

    Arai, Kaori; Mori, Masanobu; Hironaga, Takahiro; Itabashi, Hideyuki; Tanaka, Kazuhiko

    2012-04-01

    A combination of hydrophilic interaction chromatographic (HILIC) column and a weakly acidic cation-exchange resin (WCX) column was used for simultaneous separation of inorganic anions and cations by ion chromatography (IC). Firstly, the capability of HILIC column for the separation of analyte ions was evaluated under acidic eluent conditions. The columns used were SeQuant ZIC-HILIC (ZIC-HILIC) with a sulfobetaine-zwitterion stationary phase (ZIC-HILIC) and Acclaim HILIC-10 with a diol stationary phase (HILIC-10). When using tartaric acid as the eluent, the HILIC columns indicated strong retentions for anions, based on ion-pair interaction. Especially, HILIC-10 could strongly retain anions compared with ZIC-HILIC. The selectivity for analyte anions of HILIC-10 with 5 mmol/L tartaric acid eluent was in the order of I(-) > NO3(-) > Br(-) > Cl(-) > H2PO4(-). However, since HILIC-10 could not separate analyte cations, a WCX column (TSKgel Super IC-A/C) was connected after the HILIC column in series. The combination column system of HILIC and WCX columns could successfully separate ten ions (Na+, NH4+, K+, Mg2+, Ca2+, H2PO4(-), Cl(-), Br(-), NO3(-) and I(-)) with elution of 4 mmol/L tartaric acid plus 8 mmol/L 18-crown-6. The relative standard deviations (RSDs) of analyte ions by the system were in the ranges of 0.02% - 0.05% in retention times and 0.18% - 5.3% in peak areas through three-time successive injections. The limits of detection at signal-to-noise ratio of 3 were 0.24 - 0.30 micromol/L for the cations and 0.31 - 1.2 micromol/L for the anions. This system was applied for the simultaneous determination of the cations and the anions in a vegetable juice sample with satisfactory results.

  14. The role of metal ions in chemical evolution - Polymerization of alanine and glycine in a cation-exchanged clay environment

    NASA Technical Reports Server (NTRS)

    Lawless, J. G.; Levi, N.

    1979-01-01

    The effect of the exchangeable cation on the condensation of glycine and alanine was investigated using a series of homoionic bentonites. A cycling procedure of drying, warming and wetting was employed. Peptide bond formation was observed, and the effectiveness of metal ions to catalyze the condensation was Cu(2+) greater than Ni(2) approximately equals Zn(2+) greater than Na(+). Glycine showed 6% of the monomer incorporated into oligomers with the largest detected being the pentamer. Alanine showed less peptide bond formation (a maximum of 2%) and only the dimer was observed.

  15. Swelling and electro-osmotic properties of cation-exchange membranes with different structures in methanol-water media

    NASA Astrophysics Data System (ADS)

    Barragán, V. M.; Villaluenga, J. P. G.; Godino, M. P.; Izquierdo-Gil, M. A.; Ruiz-Bauzá, C.; Seoane, B.

    Electro-osmosis experiments through three cation-exchange membranes with different morphology and similar electric properties have been performed using methanol-water solutions under different experimental conditions. The influence on the electro-osmotic transport of the percentage of methanol on solvent with two different electrolytes, NaCl and LiCl, has been studied. The experimental results show that the presence of methanol in the solutions affects strongly the electro-osmotic flow, and this influence is different depending on the membrane morphology. Correlations among electro-osmotic permeability, swelling behavior, and cell resistance are studied for these membrane systems at different percentages of methanol in solvent.

  16. Simple preparation of solid-phase microextraction fiber with cation exchange capacities using poly(butadiene-maleic acid).

    PubMed

    Zhu, Yingli; Shen, Guobin; Zhang, Feifang; Yang, Bingcheng

    2013-01-01

    A simply way was proposed to prepare solid-phase microextraction (SPME) fiber with cation-exchange functional groups by the thermally initiated radical polymerization of poly(butadiene-maleic acid) (PBMA) copolymer onto a silica capillary. The capacity of the fiber coating could be easily controlled by fabricating successive layers of PBMA. The performance of the fiber combined with ion chromatography was evaluated by choosing Mg(2+) and Ca(2+) as model analytes; ∼13 and ∼51-fold enrichment factors for Mg(2+) and Ca(2+) were obtained, respectively. PMID:24107568

  17. Gas-phase reactions of polycyclic aromatic hydrocarbon cations and their nitrogen-containing analogs with H atoms

    SciTech Connect

    Demarais, Nicholas J.; Yang, Zhibo; Bierbaum, Veronica M.; Snow, Theodore P. E-mail: Zhibo.Yang@ou.edu E-mail: Theodore.Snow@Colorado.edu

    2014-03-20

    We have studied the reactions of polycyclic aromatic hydrocarbon cations and their nitrogen-containing analogs with H atoms. Reaction rate constants are measured at 300 K using a flowing afterglow-selected ion flow tube. We have implemented the laser induced acoustic desorption technique to allow the study of large, non-volatile species in the gas phase. The extension of this work from previous studies shows that the reactivity of polycyclic aromatic hydrocarbon cations with H atoms reaches a constant value for large cations. There is a small difference in reactivity when comparing molecules of different size and geometry; however, no difference in reactivity was found when nitrogen was incorporated into the ring.

  18. Spin-Isospin responses via charge exchange reactions of RI beams at SHARAQ

    SciTech Connect

    Shimoura, Susumu

    2012-11-12

    Nuclear spectroscopy via direct reactions of RI beams is discussed focusing on characteristics of charge-exchange reactions of RI beams. Recent experiments using the SHARAQ spectrometer at the RIBF are presented, where isovector spin monopole and spin-non-flip monopole responses are studied by charge exchange reaction of RI beams. Some experimental plans and perspectives are also presented.

  19. Full cell study of Diels Alder poly(phenylene) anion and cation exchange membranes in vanadium redox flow batteries

    DOE PAGES

    Pezeshki, Alan M.; Fujimoto, Cy; Sun, Che -Nan; Mench, Matthew M.; Zawodzinski, Thomas A.; Tang, Z. J.

    2015-11-14

    In this paper, we report on the performance of Diels Alder poly(phenylene) membranes in vanadium redox flow batteries. The membranes were functionalized with quaternary ammonium groups to form an anion exchange membrane (QDAPP) and with sulfonic acid groups to form a cation exchange membrane (SDAPP). Both membrane classes showed similar conductivities in the battery environment, suggesting that the ion conduction mechanism in the material is not strongly affected by the moieties along the polymer backbone. The resistance to vanadium permeation in QDAPP was not improved relative to SDAPP, further suggesting that the polarity of the functional groups do not playmore » a significant role in the membrane materials tested. Both QDAPP and SDAPP outperformed Nafion membranes in cycling tests, with both achieving voltage efficiencies above 85% while maintaining 95% coulombic efficiency while at a current density of 200 mA/cm2.« less

  20. Full cell study of Diels Alder poly(phenylene) anion and cation exchange membranes in vanadium redox flow batteries

    SciTech Connect

    Pezeshki, Alan M.; Fujimoto, Cy; Sun, Che -Nan; Mench, Matthew M.; Zawodzinski, Thomas A.; Tang, Z. J.

    2015-11-14

    In this paper, we report on the performance of Diels Alder poly(phenylene) membranes in vanadium redox flow batteries. The membranes were functionalized with quaternary ammonium groups to form an anion exchange membrane (QDAPP) and with sulfonic acid groups to form a cation exchange membrane (SDAPP). Both membrane classes showed similar conductivities in the battery environment, suggesting that the ion conduction mechanism in the material is not strongly affected by the moieties along the polymer backbone. The resistance to vanadium permeation in QDAPP was not improved relative to SDAPP, further suggesting that the polarity of the functional groups do not play a significant role in the membrane materials tested. Both QDAPP and SDAPP outperformed Nafion membranes in cycling tests, with both achieving voltage efficiencies above 85% while maintaining 95% coulombic efficiency while at a current density of 200 mA/cm2.

  1. Diverse functions and molecular properties emerging for CAX Cation/H+ exchangers in plants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Steep concentration gradients of many ions are actively maintained, with lower concentrations typically located in the cytosol, and higher concentrations in organelles and outside the cell. The vacuole is an important storage organelle for many ions. The concentration gradient of cations is establis...

  2. Suitability of the methylene blue test for determination of cation exchange capacity of clay minerals related to ammonium acetate method

    NASA Astrophysics Data System (ADS)

    Milošević, Maja; Logar, Mihovil; Dojčinović, Biljana; Erić, Suzana

    2015-04-01

    Cation exchange capacity (CEC) represents one of the most important parameters of clay minerals which reflects their ability to exchange cations with liquid phases in near contact. Measurement of CEC is used for characterizing sample plasticity, adsorbing and swelling properties which later define their usage in industrial purposes. Several methods have been developed over the years for determination of layer charge, charge density, charge distribution, etc. and have been published in numerous papers (Czimerova et al., 2006; Yukselen and Kaya, 2008). The main goal of present study is comparison of suitability of more recent method - methylene blue test in regard to older method - ammonium acetate for determination of CEC. For this study, we selected one montmorillonite clay (Bogovina, Serbia) and two mainly kaolinite clays (Miličinica, Serbia). Chemicals used for CEC determinations were solution of methylene blue (MB)(14*10-6M/ml) and ammonium acetate (AA) solution (1M). The obtained results are showing generally lower values in case of MB method. The main difference is due to molecular aggregation of MB on the clay surface. AA method is highly sensitive to the presence of CaO. Release of Ca ion from the sample into the solution can limit the saturation of exchange sites by the ammonium ion. This is clearly visible in case of montmorillonite clay. Fe2+ and Mg ions are difficult to move by the ammonium ion because of their ion radius, but in case of MB molecule there is no such restriction in removing them from the exchange sites. MB solution, even in a low concentration (2*10-6M/ml), is showing preferable results in moving the ions from their positions which is already visible after adding a small quantity of solution (25cm3). Both MB-titration and MB-spot test yield similar results and are much simpler methods than AA and they also give other information such as specific surface area (external and internal) whereas AA method only provides information about

  3. Preparation and applications of weak acid cation exchanger based on monodisperse poly(ethylvinylbenzene-co-divinylbezene) beads.

    PubMed

    Zhu, Yan; Yongxin, Chen; Mingli, Ye; Fritz, James S

    2005-08-26

    New technology is reported here for the synthesis of an effective weak acid-cation exchanger for ion chromatography. Monodisperse macroporous poly(ethylvinylbenzene-co-divinylbezene) (PEVB-DVB) beads of 5 microm diameter were prepared by a two-step swelling and polymerization method. Then carboxyl groups were introduced by polymerization of maleic anhydride with unreacted vinyl groups on the resin beads, followed by hydrolysis of the maleic anhydride groups. A column packed with the carboxylate beads was used to separate alkali and alkaline earth metal ions in a single isocratic run. Separations were found to be better than those with similar resin particles that are simply coated with maleic acid. The columns containing the new particles were 100% compatible with solvents commonly used for HPLC. Additionally, the prepared column was stable and could be used for a long time in a wide range of pH. The column gave good resolution, low detection limits and good repeatability for the separation of common cations. Satisfactory results were also obtained for separations of organic amines and of common cations in rainwater.

  4. On-line cation exchange for suppression of adduct formation in negative-ion electrospray mass spectrometry of nucleic acids.

    PubMed

    Huber, C G; Buchmeiser, M R

    1998-12-15

    One major difficulty in the analysis of nucleic acids by electrospray mass spectrometry is represented by the affinity of the polyanionic sugar-phosphate backbone for nonvolatile cations, especially ubiquitous sodium and potassium ions. A simple on-line sample preparation system comprising a microflow pumping system and 45 x 0.8-mm-i.d. microcolumns packed with weak or strong cation-exchange resins is described for the efficient removal of cations from nucleic acid samples. Samples were analyzed by flow injection analysis at a 3-5 microL/min flow of 10 mM triethylamine in 50% water-50% acetonitrile. After on-line desalting, mass spectra of oligonucleotides revealed no significant sodium adduct peaks. Moreover, signal-to-noise ratios were greatly enhanced compared to direct injection of the samples. Electrospray mass spectrometry with on-line sample preparation allowed accurate molecular mass determinations of picomole amounts of crude oligonucleotide preparations ranging in size from 8 to 80 nucleotides within a few minutes. The good linearity of the calibration plot (R2 = 0.9988) over at least 2 orders of magnitude and a relative standard deviation in peak areas of less than 9% permitted the sensitive quantitative measurement of oligonucleotides in a concentration range of 0.2-20 microM with selected-ion monitoring. Finally, the on-line sample preparation system was evaluated for the mass spectrometric analysis of complex oligonucleotide mixtures. PMID:9868919

  5. Effect of cationic molecules on the oxygen reduction reaction on fuel cell grade Pt/C (20 wt%) catalyst in potassium hydroxide (aq, 1 mol dm(-3)).

    PubMed

    Ong, Ai Lien; Inglis, Kenneth K; Whelligan, Daniel K; Murphy, Sam; Varcoe, John R

    2015-05-14

    This study investigates the effect of 1 mmol dm(-3) concentrations of a selection of small cationic molecules on the performance of a fuel cell grade oxygen reduction reaction (ORR) catalyst (Johnson Matthey HiSPEC 3000, 20 mass% Pt/C) in aqueous KOH (1 mol dm(-3)). The cationic molecules studied include quaternary ammonium (including those based on bicyclic systems) and imidazolium types as well as a phosphonium example: these serve as fully solubilised models for the commonly encountered head-groups in alkaline anion-exchange membranes (AAEM) and anion-exchange ionomers (AEI) that are being developed for application in alkaline polymer electrolyte fuel cells (APEFCs), batteries and electrolysers. Both cyclic and hydrodynamic linear sweep rotating disk electrode voltammetry techniques were used. The resulting voltammograms and subsequently derived data (e.g. apparent electrochemical active surface areas, Tafel plots, and number of [reduction] electrons transferred per O2) were compared. The results show that the imidazolium examples produced the highest level of interference towards the ORR on the Pt/C catalyst under the experimental conditions used. PMID:25877304

  6. A quantum chemical topological analysis of the C-C bond formation in organic reactions involving cationic species.

    PubMed

    Domingo, Luis R; Pérez, Patricia

    2014-07-21

    ELF topological analysis of the ionic Diels-Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C-C single bond formation. The C-C bond formation begins in the short range of 2.00-1.96 Åvia a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic character of the iminium cation is responsible for the negative activation energy found in the gas phase. On the other hand, the analysis of the radical P(k)(o) Parr functions of the iminium cation, and the nucleophilic P(k)(-) Parr functions of Cp makes the characterisation of the most favourable two-center interaction along the formation of the C-C single bond possible. PMID:24901220

  7. A quantum chemical topological analysis of the C-C bond formation in organic reactions involving cationic species.

    PubMed

    Domingo, Luis R; Pérez, Patricia

    2014-07-21

    ELF topological analysis of the ionic Diels-Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C-C single bond formation. The C-C bond formation begins in the short range of 2.00-1.96 Åvia a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic character of the iminium cation is responsible for the negative activation energy found in the gas phase. On the other hand, the analysis of the radical P(k)(o) Parr functions of the iminium cation, and the nucleophilic P(k)(-) Parr functions of Cp makes the characterisation of the most favourable two-center interaction along the formation of the C-C single bond possible.

  8. Preliminary studies of an 18-crown-6 ether modified magnetic cation exchange polymer in rapid (90)Sr bioassay.

    PubMed

    Hrdina, Amy; Lai, Edward; Li, Chunsheng; Sadi, Baki; Kramer, Gary

    2011-08-01

    A cation exchange polymer resin embedded with magnetic nanoparticles and modified with crown ether was developed for urinalysis to rapidly monitor levels of (90)Sr exposure in humans who have been involved in a nuclear event. Invention of the resin matrix of 2-acrylamido-2-methyl-1-propanesulfonic acid cross-linked with divinylbenzene incorporated a Sr(2+) chelating agent, di-tert-butyl-cyclohexano-18-crown-6 through surface immobilization using a molecular modifier 1-octanol. The performance of these magnetic cation exchange resin particles was investigated by separating (90)Sr in the presence of (90)Y progeny. Masking agents and precipitants were examined to ascertain that sodium hydroxide at pH 7.5 was capable of selectively removing 89 ± 2% (90)Y before subsequent (90)Sr uptake. Preliminary investigations in rapid urinalysis were successful in isolating 83 ± 2% (90)Sr when pH was optimized to 9, with a sample turnover time <2 h, which is promising for radiological emergencies.

  9. Toward Separating Alpha-lactalbumin and Beta-lactoglobulin Proteins from Whey through Cation-exchange Adsorption

    NASA Astrophysics Data System (ADS)

    El-Sayed, Mayyada; Chase, Howard

    2009-05-01

    This paper describes the cation-exchange adsorption of the two major whey proteins, alpha-lactalbumin (ALA) and beta-lactoglobulin (BLG) with the purpose of establishing a process for isolating them from cow's milk whey. The single- and two-component adsorption of 1.5 mg/ml ALA and 3 mg/ml BLG to the cation-exchanger SP Sepharose FF at 20° C using 0.1 M acetate buffer of pH 3.7 was studied. Langmuir isotherm parameters were determined for the pure proteins. In two-component systems, BLG breakthrough curve exhibited an overshoot phenomenon that gave evidence for the presence of a competitive adsorption between the two proteins. Complete separation occurred and it was possible to obtain each of the two proteins in a pure form. The process was then applied to a whey concentrate mixture where incomplete separation took place. However, BLG was produced with 95% purity and a recovery of 80%, while ALA showed an 84% recovery with low purity.

  10. [Enhanced Performance of Rolled Membrane Electrode Assembly by Adding Cation Exchange Resin to Anode in Microbial Fuel Cells].

    PubMed

    Mei, Zhuo; Zhang, Zhe; Wang, Xin

    2015-11-01

    The membrane electrode assembly (MEA) with an anode-membrane-cathode structure ban reduce the distance between anode and cathode to improve the power of microbial fuel cells (MFCs). Here in order to further promote the performance of MFCs, a novel MEA was constructed by rolling-press method without noble metal material, and the Ohmic resistance decreased to 3-5 Ω. The maximum power density was 446 mW x m(-2) when acetate was used as the substrate. Solid spheres (like polystyrene balls and glass microspheres) were added into anode to enhance the transportation of electrolyte to cathode, resulting in a 10% increase in power density by producing macropores on and in the anode during rolling process. Cation exchange resin was added to accelerate the transportation of proton through the anode so that the power density further increased to 543 mW x m(-2). Meanwhile, the stability of cell voltage and Coulomb efficiency of MFC were both enhanced after the addition of cation exchange resin. PMID:26911023

  11. [Enhanced Performance of Rolled Membrane Electrode Assembly by Adding Cation Exchange Resin to Anode in Microbial Fuel Cells].

    PubMed

    Mei, Zhuo; Zhang, Zhe; Wang, Xin

    2015-11-01

    The membrane electrode assembly (MEA) with an anode-membrane-cathode structure ban reduce the distance between anode and cathode to improve the power of microbial fuel cells (MFCs). Here in order to further promote the performance of MFCs, a novel MEA was constructed by rolling-press method without noble metal material, and the Ohmic resistance decreased to 3-5 Ω. The maximum power density was 446 mW x m(-2) when acetate was used as the substrate. Solid spheres (like polystyrene balls and glass microspheres) were added into anode to enhance the transportation of electrolyte to cathode, resulting in a 10% increase in power density by producing macropores on and in the anode during rolling process. Cation exchange resin was added to accelerate the transportation of proton through the anode so that the power density further increased to 543 mW x m(-2). Meanwhile, the stability of cell voltage and Coulomb efficiency of MFC were both enhanced after the addition of cation exchange resin.

  12. Uncertainties of Gaseous Oxidized Mercury Measurements Using KCl-Coated Denuders, Cation-Exchange Membranes, and Nylon Membranes: Humidity Influences.

    PubMed

    Huang, Jiaoyan; Gustin, Mae Sexauer

    2015-05-19

    Quantifying the concentration of gaseous oxidized mercury (GOM) and identifying the chemical compounds in the atmosphere are important for developing accurate local, regional, and global biogeochemical cycles. The major hypothesis driving this work was that relative humidity affects collection of GOM on KCl-coated denuders and nylon membranes, both currently being applied to measure GOM. Using a laboratory manifold system and ambient air, GOM capture efficiency on 3 different collection surfaces, including KCl-coated denuders, nylon membranes, and cation-exchange membranes, was investigated at relative humidity ranging from 25 to 75%. Recovery of permeated HgBr2 on KCl-coated denuders declined by 4-60% during spikes of relative humidity (25 to 75%). When spikes were turned off GOM recoveries returned to 60 ± 19% of permeated levels. In some cases, KCl-coated denuders were gradually passivated over time after additional humidity was applied. In this study, GOM recovery on nylon membranes decreased with high humidity and ozone concentrations. However, additional humidity enhanced GOM recovery on cation-exchange membranes. In addition, reduction and oxidation of elemental mercury during experiments was observed. The findings in this study can help to explain field observations in previous studies.

  13. Analytical cation-exchange chromatography to assess the identity, purity, and N-terminal integrity of human lactoferrin.

    PubMed

    van Veen, Harrie A; Geerts, Marlieke E J; van Berkel, Patrick H C; Nuijens, Jan H

    2002-10-01

    Human lactoferrin (hLF) is an iron-binding glycoprotein involved in the innate host defense. The positively charged N-terminal domain of hLF mediates several of its activities by interacting with ligands such as bacterial lipopolysaccharide (LPS), specific receptors, and other proteins. This cationic domain is highly susceptible to limited proteolysis, which impacts on the affinity of hLF for the ligand. An analytical method, employing cation-exchange chromatography on Mono S, was developed to assess the N-terminal integrity of hLF preparations. The method, which separates N-terminally intact hLF from hLF species lacking two (Gly(1)-Arg(2)) or three (Gly(1)-Arg(2)-Arg(3)) residues, showed that 5-58% of total hLF in commercially obtained preparations was N-terminally degraded. The elution profile of hLF on Mono S unequivocally differed from lactoferrins from other species as well as homologous and other whey proteins. Analysis of fresh human whey samples revealed two variants of N-terminally intact hLF, but not limitedly proteolyzed hLF. Mono S chromatography of 2 out of 26 individual human whey samples showed a rare polymorphic hLF variant with three N-terminal arginines (Gly(1)-Arg(2)-Arg(3)-Arg(4)-Ser(5)-) instead of the usual variant with four N-terminal arginines (Gly(1)-Arg(2)-Arg(3)-Arg(4)-Arg(5)-Ser(6)-). In conclusion, Mono S cation-exchange chromatography appeared a robust method to assess the identity, purity, N-terminal integrity, and the presence of polymorphic and intact hLF variants. PMID:12381362

  14. Thermodynamic clarification of the curious ferric/potassium ion exchange accompanying the electrochromic redox reactions of prussian blue, iron(III) hexacyanoferrate(II).

    PubMed

    Rosseinsky, David R; Glasser, Leslie; Jenkins, H Donald Brooke

    2004-08-25

    The recent Glasser-Jenkins method for lattice-energy prediction, applied to an examination of the solid-state thermodynamics of the cation exchanges that occur in electrochromic reactions of Prussian Blue, provides incisive thermodynamic clarification of an ill-understood ion exchange that accompanies particularly the early electrochromic cycles. A volume of 0.246 +/- 0.017 nm(3) formula unit(-1) for the ferrocyanide ion, Fe(II)[(CN)(6)],(4-) is first established and then used, together with other formula unit-volume data, to evaluate the changes of standard enthalpy, entropy, and Gibbs energy in those ion-exchange reactions. The results impressively show by how much the exchange of interstitial Fe(3+) ions by alkali metal ions, usually exemplified by K+, is thermodynamically favored.

  15. Elimination and exchange of trifluoroacetate counter-ion from cationic peptides: a critical evaluation of different approaches.

    PubMed

    Roux, Stéphane; Zékri, Elisabeth; Rousseau, Bernard; Paternostre, Maïté; Cintrat, Jean-Christophe; Fay, Nicolas

    2008-03-01

    Most synthesized peptides are nowadays produced using solid-phase procedures. Due to cleavage and purification conditions, they are mainly obtained in the presence of trifluoroacetic acid (TFA) and, for cationic peptides, as trifluoroacetate (TF-acetate) salts. However, TF-acetate interferes with physicochemical characterizations using infrared spectroscopy and might significantly affect the in vivo studies. Thus, TF-acetate exchange by another counter-ion is often required. Up to now, the classical procedure has consisted of freeze-drying the peptide several times in the presence of an excess of a stronger acid than TFA (pKa approximately 0): generally HCl (pKa = - 7). This approach means that working at pH < 1 can induce peptide degradation. We therefore tested three different approaches to exchange the tightly bound TF-acetate counter-ion from the dicationic octapeptide lanreotide: (i) reverse-phase HPLC, (ii) ion-exchange resin, and (iii) deprotonation/reprotonation cycle of the amino groups. The first two approaches allow the partial to almost complete exchange of the TF-acetate counter-ion by another ion from an acid weaker than TFA, such as acetic acid (pKa = 4.5), and the third requires a basic solution that permits the complete removal of TF-acetate counter-ion. The efficiency of these three procedures was tested and compared by using different analytical techniques such as 19F-NMR, 1H-NMR and attenuated total reflectance Fourier transformed infrared spectroscopy (ATR FT-IR). We also show that ATR-IR can be used to monitor the TFA removal. The counter-ion exchange procedures described in this study are easy to carry out, fast, harmless and reproducible. Moreover, two of them offer the very interesting possibility of exchanging the initial TF-acetate by any other counter-ion. PMID:18035848

  16. Fibrous polymer grafted magnetic chitosan beads with strong poly(cation-exchange) groups for single step purification of lysozyme.

    PubMed

    Bayramoglu, Gulay; Tekinay, Turgay; Ozalp, V Cengiz; Arica, M Yakup

    2015-05-15

    Lysozyme is an important polypetide used in medical and food applications. We report a novel magnetic strong cation exchange beads for efficient purification of lysozyme from chicken egg white. Magnetic chitosan (MCHT) beads were synthesized via phase inversion method, and then grafted with poly(glycidyl methacrylate) (p(GMA)) via the surface-initiated atom transfer radical polymerization (SI-ATRP). Epoxy groups of the grafted polymer, were modified into strong cation-exchange groups (i.e., sulfonate groups) in the presence of sodium sulfite. The MCTH and MCTH-g-p(GMA)-SO3H beads were characterized by ATR-FTIR, SEM, and VSM. The sulphonate groups content of the modified MCTH-g-p(GMA)-4 beads was found to be 0.53mmolg(-1) of beads by the potentiometric titration method. The MCTH-g-p(GMA)-SO3H beads were first used as an ion-exchange support for adsorption of lysozyme from aqueous solution. The influence of different experimental parameters such as pH, contact time, and temperature on the adsorption process was evaluated. The maximum adsorption capacity was found to be 208.7mgg(-1) beads. Adsorption of lysozyme on the MCTH-g-p(GMA)-SO3H beads fitted to Langmuir isotherm model and followed the pseudo second-order kinetic. More than 93% of the adsorbed lysozyme was desorbed using Na2CO3 solution (pH 11.0). The purity of the lysozyme was checked by HPLC and SDS gel electrophoresis. In addition, the MCTH-g-p(GMA)-SO3H beads prepared in this work showed promising potential for separation of various anionic molecules. PMID:25864009

  17. The role of nonmagnetic d0 vs. d10B-type cations on the magnetic exchange interactions in osmium double perovskites

    NASA Astrophysics Data System (ADS)

    Feng, Hai L.; Yamaura, Kazunari; Tjeng, Liu Hao; Jansen, Martin

    2016-11-01

    Polycrystalline samples of double perovskites Ba2BOsO6 (B=Sc, Y, In) were synthesized by solid state reactions. They adopt the cubic double perovskite structures (space group, Fm-3m) with ordered B and Os arrangements. Ba2BOsO6 (B=Sc, Y, In) show antiferromagnetic transitions at 93 K, 69 K, and 28 K, respectively. The Weiss-temperatures are -590 K for Ba2ScOsO6, -571 K for Ba2YOsO6, and -155 K for Ba2InOsO6. Sc3+ and Y3+ have the open-shell d0 electronic configuration, while In3+ has the closed-shell d10. This indicates that a d0 B-type cation induces stronger overall magnetic exchange interactions in comparison to a d10. Comparison of Ba2BOsO6 (B=Sc, Y, In) to their Sr and Ca analogues shows that the structural distortions weaken the overall magnetic exchange interactions.

  18. Kinetic approach to evaluate the energy and entropy of activation for the exchange of alkaline earth metal ions on tin(IV) tungstate cation exchanger

    SciTech Connect

    Varshney, K.G.; Khan, A.A.; Varshney, K.; Agrawal, S.

    1984-01-01

    A new approach based on the Nernst-Planck equations has been applied to study the reaction kinetics on the surface of tin(IV) tungstate for the Mg(II)-H(I), Ca(II)-H(I), Sr(II)-H(I) and Ba(II)-H(I) exchanges under the conditions favouring a particle diffusion phenomenon. On the basis of these studies the various physical parameters such as the effective diffusion coefficients, activation energies and entropies of activation have been evaluated which give some informations regarding the mechanism of ion-exchange on the surface of inorganic materials. 25 references, 3 figures, 3 tables.

  19. Layered polyaniline composites with cation-exchanging properties for positive electrodes of rechargeable lithium batteries

    SciTech Connect

    Morita, Masayuki; Miyazaki, Seijiro; Ishikawa, Masashi; Matsuda, Yoshiharu . Dept. of Applied Chemistry and Chemical Engineering); Tajima, Hidehiko . Nagasaki Research and Development Center); Adachi, Kazuyuki; Anan, Fumimiasa . Research Lab.)

    1995-01-01

    Layered polyaniline/polyaniline-polyanion composite films (PAn-X/PAn-PA) were synthesized by electrochemical oxidation of aniline in aqueous acid solutions (HCl, HClO[sub 4]) followed by polymerization in poly(styrene-4-sulfonic acid) (PSSH) solutions. The films consist of inner polyaniline (PAn) layers doped with smaller size anions (X) and outer PSS-doped PAn layers. The resulting films showed high redox activities with cation-transfer properties in organic electrolyte solutions. The improved charge/discharge characteristics of the composite films gave an expectation of higher energy density for the full cell with lithium negative electrode.

  20. Ae4 (Slc4a9) is an electroneutral monovalent cation-dependent Cl-/HCO3- exchanger.

    PubMed

    Peña-Münzenmayer, Gaspar; George, Alvin T; Shull, Gary E; Melvin, James E; Catalán, Marcelo A

    2016-05-01

    Ae4 (Slc4a9) belongs to the Slc4a family of Cl(-)/HCO3 (-) exchangers and Na(+)-HCO3 (-) cotransporters, but its ion transport cycle is poorly understood. In this study, we find that native Ae4 activity in mouse salivary gland acinar cells supports Na(+)-dependent Cl(-)/HCO3 (-) exchange that is comparable with that obtained upon heterologous expression of mouse Ae4 and human AE4 in CHO-K1 cells. Additionally, whole cell recordings and ion concentration measurements demonstrate that Na(+) is transported by Ae4 in the same direction as HCO3 (-) (and opposite to that of Cl(-)) and that ion transport is not associated with changes in membrane potential. We also find that Ae4 can mediate Na(+)-HCO3 (-) cotransport-like activity under Cl(-)-free conditions. However, whole cell recordings show that this apparent Na(+)-HCO3 (-) cotransport activity is in fact electroneutral HCO3 (-)/Na(+)-HCO3 (-) exchange. Although the Ae4 anion exchanger is thought to regulate intracellular Cl(-) concentration in exocrine gland acinar cells, our thermodynamic calculations predict that the intracellular Na(+), Cl(-), and HCO3 (-) concentrations required for Ae4-mediated Cl(-) influx differ markedly from those reported for acinar secretory cells at rest or under sustained stimulation. Given that K(+) ions share many properties with Na(+) ions and reach intracellular concentrations of 140-150 mM (essentially the same as extracellular [Na(+)]), we hypothesize that Ae4 could mediate K(+)-dependent Cl(-)/HCO3 (-) exchange. Indeed, we find that Ae4 mediates Cl(-)/HCO3 (-) exchange activity in the presence of K(+) as well as Cs(+), Li(+), and Rb(+) In summary, our results strongly suggest that Ae4 is an electroneutral Cl(-)/nonselective cation-HCO3 (-) exchanger. We postulate that the physiological role of Ae4 in secretory cells is to promote Cl(-) influx in exchange for K(+)(Na(+)) and HCO3 (-) ions.

  1. Mechanism of protodesorption-exchange of heavy metal cations for protons in a heterophase system of H2O-H2SO4-MSO4-cellulose sorbent.

    PubMed

    Kozlov, V A; Nikiforova, T E; Loginova, V A; Koifman, O I

    2015-12-15

    The influence of pH on the distribution of metal cations [Cd(II), Cu(II), Fe(II), Ni(II), Zn(II)] in a four-component heterophase system (H2O-H2SO4-MSO4-cellulose sorbent) was studied. Protodesorption of metal cations was studied with indicator and constant quantities of [MSO4] salts and constant solvent-sorbent ratio. Linear dependence lgКDМ2+=f(рН) with tgα=1/2 of the КDМ2+ metal ions distribution coefficients from the acidity of the aqueous phase is observed in logarithmic coordinates. Depression of the exponent corresponding to proton involvement in protodesorption from 2 (theory) to 0.5 (experiment) indicates that anions of the aqueous phase are involved in the process of exchange of metal cation for proton on the anionic centers of the sorbent, which corresponds to participation of the salt and acid components of the system in molecular non-dissociated form in an equivalent proportion H2SO4/MSO4=1/1. Different behavior of the salt and acid components in ion exchange of cations for cations and cations for protons is due to the differences in the constraint coefficients of their molecular and ionic forms which must be taken into consideration in equations describing thermodynamics of the interphase exchange.

  2. Dextran-grafted cation exchanger based on superporous agarose gel: adsorption isotherms, uptake kinetics and dynamic protein adsorption performance.

    PubMed

    Shi, Qing-Hong; Jia, Guo-Dong; Sun, Yan

    2010-07-30

    A novel chromatographic medium for high-capacity protein adsorption was fabricated by grafting dextran (40kDa) onto the pore surfaces of superporous agarose (SA) beads. The bead was denoted as D-SA. D-SA, SA and homogeneous agarose (HA) beads were modified with sulfopropyl (SP) group to prepare cation exchangers, and the adsorption and uptake of lysozyme on all three cation-exchange chromatographic beads (SP-HA, SP-SA and SP-D-SA) were investigated at salt concentrations of 6-50mmol/L. Static adsorption experiments showed that the adsorption capacity of SP-D-SA (2.24mmol/g) was 78% higher than that of SP-SA (1.26mmol/g) and 54% higher than that of SP-HA (1.45mmol/g) at a salt concentration of 6mmol/L. Moreover, salt concentration had less influence on the adsorption capacity and dissociation constant of SP-D-SA than it did on SP-HA, suggesting that dextran-grafted superporous bead is a more potent architecture for chromatographic beads. In the dynamic uptake of lysozyme to the three cation-exchange beads, the D(e)/D(0) (the ratio of effective pore diffusivity to free solution diffusivity) values of 1.6-2.0 were obtained in SA-D-SA, indicating that effective pore diffusivities of SP-D-SA were about two times higher than free solution diffusivity for lysozyme. At 6mmol/L NaCl, the D(e) value in SA-D-SA (22.0x10(-11)m(2)/s) was 14.4-fold greater than that in SP-HA. Due to the superior uptake kinetics in SA-D-SA, the highest dynamic binding capacity (DBC) and adsorption efficiency (the ratio of DBC to static adsorption capacity) was likewise found in SP-D-SA. It is thus confirmed that SP-D-SA has combined the advantages of superporous matrix structure and drafted ligand chemistry in mass transport and offers a new opportunity for the development of high-performance protein chromatography.

  3. Proton-sensitive cation channels and ion exchangers in ischemic brain injury: new therapeutic targets for stroke?

    PubMed Central

    Leng, Tiandong; Shi, Yejie; Xiong, Zhi-Gang; Sun, Dandan

    2014-01-01

    Ischemic brain injury results from complicated cellular mechanisms. The present therapy for acute ischemic stroke is limited to thrombolysis with the recombinant tissue plasminogen activator (rtPA) and mechanical recanalization. Therefore, a better understanding of ischemic brain injury is needed for the development of more effective therapies. Disruption of ionic homeostasis plays an important role in cell death following cerebral ischemia. Glutamate receptor-mediated ionic imbalance and neurotoxicity have been well established in cerebral ischemia after stroke. However, non-NMDA receptor-dependent mechanisms, involving acid-sensing ion channel 1a (ASIC1a), transient receptor potential melastatin 7 (TRPM7), and Na+/H+ exchanger isoform 1 (NHE1), have recently emerged as important players in the dysregulation of ionic homeostasis in the CNS under ischemic conditions. These H+-sensitive channels and/or exchangers are expressed in the majority of cell types of the neurovascular unit. Sustained activation of these proteins causes excessive influx of cations, such as Ca2+, Na+, and Zn2+, and leads to ischemic reperfusion brain injury. In this review, we summarize recent pre-clinical experimental research findings on how these channels/exchangers are regulated in both in vitro and in vivo models of cerebral ischemia. The blockade or transgenic knockdown of these proteins was shown to be neuroprotective in these ischemia models. Taken together, these non-NMDA receptor-dependent mechanisms may serve as novel therapeutic targets for stroke intervention. PMID:24467911

  4. Isolation of cross-linked peptides by diagonal strong cation exchange chromatography for protein complex topology studies by peptide fragment fingerprinting from large sequence databases.

    PubMed

    Buncherd, Hansuk; Roseboom, Winfried; Ghavim, Behrad; Du, Weina; de Koning, Leo J; de Koster, Chris G; de Jong, Luitzen

    2014-06-27

    Knowledge of spatial proximity of amino acid residues obtained by chemical cross-linking and mass spectrometric analysis provides information about protein folding, protein-protein interactions and topology of macromolecular assemblies. We show that the use of bis(succinimidyl)-3-azidomethyl glutarate as a cross-linker provides a solution for two major analytical problems of cross-link mapping by peptide fragment fingerprinting (PFF) from complex sequence databases, i.e., low abundance of protease-generated target peptides and lack of knowledge of the masses of linked peptides. Tris(carboxyethyl)phosphine (TCEP) reduces the azido group in cross-linked peptides to an amine group in competition with cleavage of an amide bond formed in the cross-link reaction. TCEP-induced reaction products were separated by diagonal strong cation exchange (SCX) from unmodified peptides. The relation between the sum of the masses of the cleavage products and the mass of the parent cross-linked peptide enables determination of the masses of candidate linked peptides. By reversed phase LC-MS/MS analysis of secondary SCX fractions, we identified several intraprotein and interprotein cross-links in a HeLa cell nuclear extract, aided by software tools supporting PFF from the entire human sequence database. The data provide new information about interacting protein domains, among others from assemblies involved in splicing.

  5. Isolation and Characterization of the 2,2'-Azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) Radical Cation-Scavenging Reaction Products of Arbutin.

    PubMed

    Tai, Akihiro; Ohno, Asako; Ito, Hideyuki

    2016-09-28

    Arbutin, a glucoside of hydroquinone, has shown strong 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation-scavenging activity, especially in reaction stoichiometry. This study investigated the reaction mechanism of arbutin against ABTS radical cation that caused high stoichiometry of arbutin in an ABTS radical cation-scavenging assay. HPLC analysis of the reaction mixture of arbutin and ABTS radical cation indicated the existence of two reaction products. The two reaction products were purified and identified to be a covalent adduct of arbutin with an ABTS degradation fragment and 3-ethyl-6-sulfonate benzothiazolone. A time-course study of the radical-scavenging reactions of arbutin and the two reaction products suggested that one molecule of arbutin scavenges three ABTS radical cation molecules to generate an arbutin-ABTS fragment adduct as a final reaction product. The results suggest that one molecule of arbutin reduced two ABTS radical cation molecules to ABTS and then cleaved the third ABTS radical cation molecule to generate two products, an arbutin-ABTS fragment adduct and 3-ethyl-6-sulfonate benzothiazolone.

  6. Isolation and Characterization of the 2,2'-Azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) Radical Cation-Scavenging Reaction Products of Arbutin.

    PubMed

    Tai, Akihiro; Ohno, Asako; Ito, Hideyuki

    2016-09-28

    Arbutin, a glucoside of hydroquinone, has shown strong 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation-scavenging activity, especially in reaction stoichiometry. This study investigated the reaction mechanism of arbutin against ABTS radical cation that caused high stoichiometry of arbutin in an ABTS radical cation-scavenging assay. HPLC analysis of the reaction mixture of arbutin and ABTS radical cation indicated the existence of two reaction products. The two reaction products were purified and identified to be a covalent adduct of arbutin with an ABTS degradation fragment and 3-ethyl-6-sulfonate benzothiazolone. A time-course study of the radical-scavenging reactions of arbutin and the two reaction products suggested that one molecule of arbutin scavenges three ABTS radical cation molecules to generate an arbutin-ABTS fragment adduct as a final reaction product. The results suggest that one molecule of arbutin reduced two ABTS radical cation molecules to ABTS and then cleaved the third ABTS radical cation molecule to generate two products, an arbutin-ABTS fragment adduct and 3-ethyl-6-sulfonate benzothiazolone. PMID:27607833

  7. Oxygen exchange reaction kinetics for cerium(IV) oxide at 1000 °C

    SciTech Connect

    Whiting, Christofer E. Douglas, John M.; Cremeans, Bethany M.; Barklay, Chadwick D.; Kramer, Daniel P.

    2014-10-15

    Bulk oxygen exchange rate kinetics on CeO{sub 2} at 1000 °C were observed to have a first order dependence on the fraction of reaction remaining and to be independent of oxygen partial pressure, total pressure, particle size, and specific surface area. This suggests that the exchange reaction is dominated by an internal chemical reaction that is occurring throughout the bulk of the material, and not at the material surface. Oxygen exchange rates were limited by this internal chemical reaction for all CeO{sub 2} powders studied (15 nm to −325 mesh), and had a rate constant of 1.19×10{sup −2} s{sup −1} with a time to completion of 617 s. These results are similar to the exchange rates observed previously on PuO{sub 2}, suggesting that oxygen exchange on PuO{sub 2} may also be dominated by an internal chemical reaction under similar conditions. This work will help guide future experiments on {sup 238}PuO{sub 2} oxygen exchange reactions. - Graphical abstract: Oxygen exchange kinetics on CeO{sub 2} at 1000 °C are independent of a wide range of experimental conditions and exhibit first-order chemical reaction kinetics. - Highlights: • Stable oxygen exchange rates obtained on a variety of CeO{sub 2} powders at 1000 °C. • Exchange rates are independent of atmospheric composition and specific surface area. • Exchange rates are limited by an internal chemical reaction, not a surface reaction. • CeO{sub 2} exchange rates appear similar to the rates observed on PuO{sub 2} at 1000 °C.

  8. Preparation and evaluation of rigid porous polyacrylamide-based strong cation-exchange monolithic columns for capillary electrochromatography.

    PubMed

    Dong, Jing; Ou, Junjie; Dong, Xiaoli; Wu, Renan; Ye, Mingliang; Zou, Hanfa

    2007-11-01

    A CEC monolithic column with strong cation-exchange (SCX) stationary phase based on hydrophilic monomers was prepared by in situ polymerization of acrylamide, methylenebisacrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in a complete organic binary porogenic solvent consisting of DMSO and dodecanol. The sulfonic groups provided by the monomer AMPS on the surface of the stationary phase generate an EOF from anode to cathode, and serve as an SCX stationary phase at the same time. The monolithic stationary phase exhibited normal-phase chromatographic behavior for neutral analytes. For charged analytes, electrostatic interaction/repulsion with the monolith was observed. The strong SCX monolithic column has been successfully employed in the electrochromatographic separation of basic drugs, peptides, and alkaloids extracted from natural products.

  9. Quantitative Analysis of Cations in Solutions Using ion Exchange Filter Paper by X-ray Fluorescence Spectrometry

    NASA Astrophysics Data System (ADS)

    Taketani, Y.; Fujimaki, H.

    2007-12-01

    The strong acid cation exchange filter, CP-1, were applied to X-ray fluorescence (XRF) for trace elements in aqueous solution. In this study, the objective elements were Cu, Zn, Pb, and Cd. The measurement of the X-ray intensity determined the optimum methods of XRF analyses using the CP-1 filter. The optimum area that sample solutions penetrated was inside the determining area. The proper material to underlay CP-1 filter was glass bead. The calibration curves that determined by this study calculated the limit values of determination. These values were 0.72 micro gram for Cu and Zn. The method of separation and concentration using the CP-1 filter enable the quantitative analyses of trace heavy metals easily.

  10. Colorimetric Humidity and Solvent Recognition Based on a Cation-Exchange Clay Mineral Incorporating Nickel(II)-Chelate Complexes.

    PubMed

    Hosokawa, Hitoshi; Mochida, Tomoyuki

    2015-12-01

    Solvatochromic nickel(II) complexes with diketonato and diamine ligands were incorporated into a saponite clay by ion exchange, and their colorimetric humidity- and solvent-recognition properties were investigated. These powders exhibit color change from red to blue-green depending on humidity, and the detection range can be controlled by modifying the metal complex. The humidity response takes advantage of the humidity-dependent water content in clay and the coordination of water molecules to the metal complex in equilibrium. The addition of organic solvents to the powders causes a color change to occur, varying from red to blue-green depending on the donor number of the solvent, thereby enabling solvent recognition. In the clay, the affinity of less sterically hindered complexes to water or solvent molecules is decreased compared with that in solution because the cationic complexes interact with the anionic layers in the clay. Incorporating diethylene glycol into the materials produced thermochromic powders.

  11. Preparation and evaluation of rigid porous polyacrylamide-based strong cation-exchange monolithic columns for capillary electrochromatography.

    PubMed

    Dong, Jing; Ou, Junjie; Dong, Xiaoli; Wu, Renan; Ye, Mingliang; Zou, Hanfa

    2007-11-01

    A CEC monolithic column with strong cation-exchange (SCX) stationary phase based on hydrophilic monomers was prepared by in situ polymerization of acrylamide, methylenebisacrylamide, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in a complete organic binary porogenic solvent consisting of DMSO and dodecanol. The sulfonic groups provided by the monomer AMPS on the surface of the stationary phase generate an EOF from anode to cathode, and serve as an SCX stationary phase at the same time. The monolithic stationary phase exhibited normal-phase chromatographic behavior for neutral analytes. For charged analytes, electrostatic interaction/repulsion with the monolith was observed. The strong SCX monolithic column has been successfully employed in the electrochromatographic separation of basic drugs, peptides, and alkaloids extracted from natural products. PMID:17924588

  12. Strong cation exchange chiral stationary phase--a comparative study in high-performance liquid chromatography and subcritical fluid chromatography.

    PubMed

    Wolrab, Denise; Macíková, Pavla; Boras, Mario; Kohout, Michal; Lindner, Wolfgang

    2013-11-22

    The performance of a strong cation exchange-type (SCX) chiral stationary phase (CSP) was evaluated with subcritical fluid chromatography (subFC) and high performance liquid chromatography (HPLC). The chromatographic conditions in subFC were optimized by changing the amount of polar organic modifier, concentration of a basic additive in the modifier, system pressure and temperature. In this way the concentration of in situ formed transient ionic species could be varied. The gradual change of the concentration of the transient buffer, i.e. gradient elution conditions in subFC, was found beneficial for separation of a mixture of racemic compounds. The strength and amount of the in situ formed buffer was estimated on the basis of comparative experiments in subSFC and HPLC.

  13. Selective separation and purification of highly polar basic compounds using a silica-based strong cation exchange stationary phase.

    PubMed

    Long, Zhen; Guo, Zhimou; Xue, Xingya; Zhang, Xiuli; Nordahl, Lilly; Liang, Xinmiao

    2013-12-01

    Compared to moderately and weakly hydrophilic bases, highly polar basic compounds are even more difficult to separate due to their poor retention in reversed phase (RP) mode. This study described the successful applications of a strong cation exchange (SCX) stationary phase to achieve symmetric peak shape, adequate retention and selectivity in the separation of very polar basic compounds. Salt and acetonitrile concentrations were adjusted to optimize the separation. Good correlations (R(2)=0.998-1.000) between the logarithm of the retention factor and the logarithm of salt or acetonitrile concentration were obtained. Gradients generated by changing salt or acetonitrile concentration were compared for the analysis of different highly polar bases. Although all of the analytes were eluted more quickly with an acetonitrile gradient, the effect of the gradients tested on peak width and peak shape varied with respect to analyte. In addition, the effects of different types of cation and anion additives were also investigated. After separation parameters were acquired, the SCX-based method was utilized to analyze highly hydrophilic alkaloids from Scopolia tangutica Maxim with high separation efficiency (plate numbers>32,000 m(-1)). Concurrently, one very polar alkaloid fraction was purified with symmetric peak shape using the current method. Our results suggest that SCX stationary phase can be used as an alternative to RP stationary phase in the analysis and purification of highly hydrophilic basic compounds. PMID:24267097

  14. Cation Exchange Strategy for the Encapsulation of a Photoactive CO-Releasing Organometallic Molecule into Anionic Porous Frameworks.

    PubMed

    Carmona, Francisco J; Rojas, Sara; Sánchez, Purificación; Jeremias, Hélia; Marques, Ana R; Romão, Carlos C; Choquesillo-Lazarte, Duane; Navarro, Jorge A R; Maldonado, Carmen R; Barea, Elisa

    2016-07-01

    The encapsulation of the photoactive, nontoxic, water-soluble, and air-stable cationic CORM [Mn(tacn)(CO)3]Br (tacn = 1,4,7-triazacyclononane) in different inorganic porous matrixes, namely, the metalorganic framework bio-MOF-1, (NH2(CH3)2)2[Zn8(adeninate)4(BPDC)6]·8DMF·11H2O (BPDC = 4,4'-biphenyldicarboxylate), and the functionalized mesoporous silicas MCM-41-SO3H and SBA-15-SO3H, is achieved by a cation exchange strategy. The CO release from these loaded materials, under simulated physiological conditions, is triggered by visible light. The results show that the silica matrixes, which are unaltered under physiological conditions, slow the kinetics of CO release, allowing a more controlled CO supply. In contrast, bio-MOF-1 instability leads to the complete leaching of the CORM. Nevertheless, the degradation of the MOF matrix gives rise to an enhanced CO release rate, which is related to the presence of free adenine in the solution.

  15. Effect of exchangeable cations on apparent diffusion of Ca 2+ ions in Na- and Ca-montmorillonite mixtures

    NASA Astrophysics Data System (ADS)

    Kozaki, T.; Sawaguchi, T.; Fujishima, A.; Sato, S.

    Compacted Na-bentonite, of which the major mineral is montmorillonite, is a candidate buffer material for the geological disposal of high-level radioactive waste. A potential alteration of the bentonite in a repository is the partial replacement of the exchangeable cations of Na + with Ca 2+. The Ca 2+ cations could be released from cementitious materials and diffuse into the buffer material in the repository. In this study, to evaluate the alteration that could reduce the performance of the bentonite buffer, the apparent diffusion coefficients of HTO and Ca 2+ ions were determined from non-steady, one-dimensional diffusion experiments using Na- and Ca-montmorillonite mixtures with different ionic equivalent fractions of Ca 2+ ions. The apparent diffusion coefficient of HTO at a dry density of 1.0 Mg m -3 slightly increased with an increase in the ionic equivalent fraction of Ca 2+ ions. However, the apparent diffusion coefficient of Ca 2+ and the activation energy for diffusion at the same dry density were independent of the ionic equivalent fraction of Ca 2+ ions. These findings suggest that unlike HTO, which can be postulated to diffuse mainly in pore water, Ca 2+ ion diffusion could occur predominantly in interlayer spaces, of which the basal spacing was determined to be constant by the XRD technique.

  16. Quantification of melamine in human urine using cation-exchange based high performance liquid chromatography tandem mass spectrometry.

    PubMed

    Panuwet, Parinya; Nguyen, Johnny V; Wade, Erin L; D'Souza, Priya E; Ryan, P Barry; Barr, Dana Boyd

    2012-03-01

    Melamine and cyanuric acid have been implicated as adulterants in baby formula in China and pet foods in North America. In China, the effect of melamine or melamine-cyanuric acid adulteration lead to kidney stone development and acute renal failure in thousands of Chinese infants. A selective and sensitive analytical method was developed to measure melamine in human urine in order to evaluate the extent of potential health implications resulting from the consumption of these types of adulterated products in the general US population. This method involves extracting melamine from human urine using cation-exchange solid-phase extraction, chromatographically separating it from its urinary matrix co-extractants on a silica-based, strong-cation exchange analytical column using high performance liquid chromatography, and analysis using positive mode electrospray ionization tandem mass spectrometry. Quantification was performed using modified, matrix-based isotope dilution calibration covering the concentration range of 0.50-100 ng/mL. The limit of detection, calculated using replicates of blank and low level spiked samples, was 0.66 ng/mL and the relative standard deviations were between 6.89 and 14.9%. The relative recovery of melamine was 101-106%. This method was tested for viability by analyzing samples collected from the general US population. Melamine was detected in 76% of the samples tested, with a geometric mean of 2.37 ng/mL, indicating that this method is suitable for reliably detecting background exposures to melamine or other chemicals from which it can be derived. PMID:22309774

  17. Advance chromatin extraction enhances performance and productivity of cation exchange chromatography-based capture of Immunoglobulin G monoclonal antibodies.

    PubMed

    Nian, Rui; Gagnon, Pete

    2016-07-01

    The impact of host cell-derived chromatin was investigated on the performance and productivity of cation exchange chromatography as a method for capture-purification of an IgG monoclonal antibody. Cell culture supernatant was prepared for loading by titration to pH 6.0, dilution with water to a conductivity of 4mS/cm, then microfiltration to remove solids. DNA content was reduced 99% to 30ppm, histone host cell protein content by 76% to 6300ppm, non-histone host cell protein content by 15% to 321,000ppm, and aggregates from 33% to 15%. IgG recovery was 83%. An alternative preparation was performed, adding octanoic acid, allantoin, and electropositive particles to the harvest at pH 5.3, then removing solids. DNA content was reduced to<1 ppb, histones became undetectable, non-histones were reduced to 24,000ppm, and aggregates were reduced to 2.4%. IgG recovery was 95%. This treatment increased dynamic capacity (DBC) of cation exchange capture to 173g/L and enabled the column to reduce non-histone host proteins to 671ppm. Step recovery was 99%. A single multimodal polishing step further reduced them to 15ppm and aggregates to <0.1%. Overall process recovery was 89%. Productivity at feed stream IgG concentrations of 5-10g/L was roughly double the productivity of a same-size protein A column with a DBC of 55g/L. PMID:27247214

  18. Common Ion Effects In Zeoponic Substrates: Dissolution And Cation Exchange Variations Due to Additions of Calcite, Dolomite and Wollastonite

    NASA Technical Reports Server (NTRS)

    Beiersdorfer, R. E.; Ming, D. W.; Galindo, C., Jr.

    2003-01-01

    c1inoptilolite-rich tuff-hydroxyapatite mixture (zeoponic substrate) has the potential to serve as a synthetic soil-additive for plant growth. Essential plant macro-nutrients such as calcium, phosphorous, magnesium, ammonium and potassium are released into solution via dissolution of the hydroxyapatite and cation exchange on zeolite charged sites. Plant growth experiments resulting in low yield for wheat have been attributed to a Ca deficiency caused by a high degree of cation exchange by the zeolite. Batch-equilibration experiments were performed in order to determine if the Ca deficiency can be remedied by the addition of a second Ca-bearing, soluble, mineral such as calcite, dolomite or wollastonite. Variations in the amount of calcite, dolomite or wollastonite resulted in systematic changes in the concentrations of Ca and P. The addition of calcite, dolomite or wollastonite to the zeoponic substrate resulted in an exponential decrease in the phosphorous concentration in solution. The exponential rate of decay was greatest for calcite (5.60 wt. % -I), intermediate for wollastonite (2.85 wt.% -I) and least for dolomite (1.58 wt.% -I). Additions of the three minerals resulted in linear increases in the calcium concentration in solution. The rate of increase was greatest for calcite (3.64), intermediate for wollastonite (2.41) and least for dolomite (0.61). The observed changes in P and Ca concentration are consistent with the solubilities of calcite, dolomite and wollastonite and with changes expected from a common ion effect with Ca. Keywords: zeolite, zeoponics, common-ion effect, clinoptilolite, hydroxyapatite

  19. The group separation of the rare-earth elements and yttrium from geologic materials by cation-exchange chromatography

    USGS Publications Warehouse

    Crock, J.G.; Lichte, F.E.; Wildeman, T.R.

    1984-01-01

    Demand is increasing for the determination of the rare-earth elements (REE) and yttrium in geologic materials. Due to their low natural abundance in many materials and the interferences that occur in many methods of determination, a separation procedure utilizing gradient strong-acid cation-exchange chromatography is often used to preconcentrate and isolate these elements from the host-rock matrix. Two separate gradient strong-acid cation-exchange procedures were characterized and the major elements as well as those elements thought to provide the greatest interference for the determination of the REE in geologic materials were tested for separation from the REE. Simultaneous inductively coupled argon plasma-atomic emission spectroscopy (ICAP-AES) measurements were used to construct the chromatograms for the elution studies, allowing the elution patterns of all the elements of interest to be determined in a single fraction of eluent. As a rock matrix, U.S. Geological Survey standard reference BCR-1 basalt was digested using both an acid decomposition procedure and a lithium metaborate fusion. Hydrochloric and nitric acids were tested as eluents and chromatograms were plotted using the ICAP-AES data; and we observed substantial differences in the elution patterns of the REE and as well as in the solution patterns of Ba, Ca, Fe and Sr. The nitric acid elution required substantially less eluent to elute the REE and Y as a group when compared to the hydrochloric acid elution, and provided a clearer separation of the REE from interfering and matrix elements. ?? 1984.

  20. The rapid identification of elution conditions for therapeutic antibodies from cation-exchange chromatography resins using high-throughput screening.

    PubMed

    McDonald, Paul; Tran, Benjamin; Williams, Christopher R; Wong, Marc; Zhao, Ti; Kelley, Brian D; Lester, Philip

    2016-02-12

    Cation-exchange chromatography is widely used in the purification of therapeutic antibodies, wherein parameters such as elution pH and counterion concentration require optimization for individual antibodies across different chromatography resins. With a growing number of antibodies in clinical trials and the pressure to expedite process development, we developed and automated a high-throughput batch-binding screen to more efficiently optimize elution conditions for cation-exchange chromatography resins. The screen maps the binding behavior of antibodies and impurities as a function of pH and counterion concentration in terms of a partition coefficient (Kp). Using this approach, the binding behavior of a library of antibodies was assessed on Poros 50HS and SP Sepharose Fast Flow resins. The diversity in binding behavior between antibodies and across resins translated to the requirement of a variable counterion concentration to elute each antibody. This requirement can be met through the use of a gradient elution. However, a gradient of increasing counterion concentration spans the transition from binding to non-binding for impurities as well as the antibody, resulting in the elution of impurities within the antibody elution peak. Step elution conditions that selectively elute the antibody while retaining impurities on the resin can now be rapidly identified using our high-throughput approach. We demonstrate that by correlating antibody Kp to elution pool volume and yield on packed-bed columns and through the calculation of a separation factor, we can efficiently optimize step elution conditions that maximize impurity clearance and yield for each antibody. PMID:26803905

  1. Physical characterization of the state of motion of the phenalenyl spin probe in cation-exchanged faujasite zeolite supercages with pulsed EPR

    NASA Astrophysics Data System (ADS)

    Doetschman, D. C.; Dwyer, D. W.; Fox, J. D.; Frederick, C. K.; Scull, S.; Thomas, G. D.; Utterback, S. G.; Wei, J.

    1994-08-01

    The molecular motion of the phenalenyl (PNL) spin probe in the supercages of cation-exchanged X and Y zeolites (faujasites) has been physically characterized by pulsed and continuous wave (CW) electron paramagnetic resonance (EPR). Both X and Y zeolites, whose cation sites were exchanged with the alkali metal ions, Li +, Na +, K +, Rb + and Cs + were examined. There is a good correspondence between the temperature dependences of the PNL electron spin phase memory time and the CW EPR spectra. Both display evidence of a thermal activation from a stationary, non-rotating molecular state to a low-temperature state of in-plane rotation (Das et al., Chem Phys. 143 (1990) 253). The rate of in-plane rotation is an activated process, with E* | / R=1289 |+- 35 K and 1462 ± 47 K in NaX and KX zeolites, respectively. The rotation appears to be about an axis along which the half-filled, non-bonding π orbital interacts with the exchanged cation in the supercage. Both CW and pulsed EPR also show a higher temperature activation from the in-plane rotating state to an effectively isoptropic state of rotation of PNL in which the PNL-cation bond is thought to be broken, with E* ⊥ / R=2050 ± 110 K, 1956 ± 46K, 1335 ± 97 K in LiX, NaX and KX zeolites, respectively. The strength of the PNL-cation bonding decreases with increasing cation atomic number as indicated by E* ⊥ and the peripheral repulsion (crowding) of PNL increases with cation size as indicated E* |. There are qualitative indications that the binding of PNL to the cations in the Y zeolite is stronger than in the X zeolite.

  2. 2-Acrylamido-2-methyl-1-propanesulfonic Acid Grafted Poly(vinylidene fluoride-co-hexafluoropropylene)-Based Acid-/Oxidative-Resistant Cation Exchange for Membrane Electrolysis.

    PubMed

    Pandey, Ravi P; Das, Arindam K; Shahi, Vinod K

    2015-12-30

    For developing acid-/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM), macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was carried out by controlled chemical grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). To introduce the unsaturation suitable for chemical grafting, dehydrofluorination of commercially available PVDF-co-HFP was achieved under alkaline medium. Sulfonated copolymer (SCP) was prepared by the free radical copolymerization of dehydofluorinated PVDF-co-HFP (DHPVDF-co-HFP) and AMPS in the presence of free radical initiator. Prepared SCP-based CEMs were analyzed for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. High bound water content avoids the membrane dehydration, and most optimal (SCP-1.33) membrane exhibited about ∼2.5-fold high bound water content in comparison with that of Nafion117 membrane. Bunsen reaction of iodine-sulfur (I-S) was successfully performed by direct-contact-mode membrane electrolysis in a two-compartment electrolytic cell using different SCP membranes. High current efficiency (83-99%) confirmed absence of any side reaction and 328.05 kJ mol-H2(-1) energy was required for to produce 1 mol of H2 by electrolytic cell with SCP-1.33 membrane. In spite of low conductivity for reported SCP membrane in comparison with that of Nafion117 membrane, SCP-1.33 membrane was assessed as suitable candidate for electrolysis because of its low-cost nature and excellent stabilities in highly acidic environment may be due to partial fluorinated segments in the membrane structure.

  3. 2-Acrylamido-2-methyl-1-propanesulfonic Acid Grafted Poly(vinylidene fluoride-co-hexafluoropropylene)-Based Acid-/Oxidative-Resistant Cation Exchange for Membrane Electrolysis.

    PubMed

    Pandey, Ravi P; Das, Arindam K; Shahi, Vinod K

    2015-12-30

    For developing acid-/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM), macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was carried out by controlled chemical grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). To introduce the unsaturation suitable for chemical grafting, dehydrofluorination of commercially available PVDF-co-HFP was achieved under alkaline medium. Sulfonated copolymer (SCP) was prepared by the free radical copolymerization of dehydofluorinated PVDF-co-HFP (DHPVDF-co-HFP) and AMPS in the presence of free radical initiator. Prepared SCP-based CEMs were analyzed for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. High bound water content avoids the membrane dehydration, and most optimal (SCP-1.33) membrane exhibited about ∼2.5-fold high bound water content in comparison with that of Nafion117 membrane. Bunsen reaction of iodine-sulfur (I-S) was successfully performed by direct-contact-mode membrane electrolysis in a two-compartment electrolytic cell using different SCP membranes. High current efficiency (83-99%) confirmed absence of any side reaction and 328.05 kJ mol-H2(-1) energy was required for to produce 1 mol of H2 by electrolytic cell with SCP-1.33 membrane. In spite of low conductivity for reported SCP membrane in comparison with that of Nafion117 membrane, SCP-1.33 membrane was assessed as suitable candidate for electrolysis because of its low-cost nature and excellent stabilities in highly acidic environment may be due to partial fluorinated segments in the membrane structure. PMID:26642107

  4. Removal of lead compounds from polyvinylchloride in electric wires and cables using cation-exchange resin.

    PubMed

    Tsunekawa, Masami; Ito, Mayumi; Yuta, Sasaki; Tomoo, Sakai; Hiroyoshi, Naoki

    2011-07-15

    Recycling treatment of cable insulation resin generated from electric wires and cables was investigated. Conventional insulation PVC contains a lead component, tribase, as a thermal stabilizer and lead removal is necessary to recycle this PVC as insulation resin. This paper describes a solid surface adsorption method using ion exchange resin to remove the fine lead containing particles from PVC dissolved solution. Low lead concentration in the recovered PVC, complying with the requirements of RoHS, was achieved.

  5. Functionalized Mesoporous Silica via an Aminosilane Surfactant Ion Exchange Reaction: Controlled Scaffold Design and Nitric Oxide Release

    PubMed Central

    2015-01-01

    Nitric oxide-releasing mesoporous silica nanoparticles (MSNs) were prepared using an aminosilane-template surfactant ion exchange reaction. Initially, bare silica particles were synthesized under basic conditions in the presence of cetyltrimethylammonium bromide (CTAB). These particles were functionalized with nitric oxide (NO) donor precursors (i.e., secondary amines) via the addition of aminosilane directly to the particle sol and a commensurate ion exchange reaction between the cationic aminosilanes and CTAB. N-Diazeniumdiolate NO donors were formed at the secondary amines to yield NO-releasing MSNs. Tuning of the ion exchange-based MSN modification approach allowed for the preparation of monodisperse particles ranging from 30 to 1100 nm. Regardless of size, the MSNs stored appreciable levels of NO (0.4–1.5 μmol mg–1) with tunable NO release durations (1–33 h) dependent on the aminosilane modification. Independent control of NO release properties and particle size was achieved, demonstrating the flexibility of this novel MSN synthesis over conventional co-condensation and surface grafting strategies. PMID:26717238

  6. The use of laboratory-determined ion exchange parameters in the predictive modelling of field-scale major cation migration in groundwater over a 40-year period.

    PubMed

    Carlyle, Harriet F; Tellam, John H; Parker, Karen E

    2004-01-01

    An attempt has been made to estimate quantitatively cation concentration changes as estuary water invades a Triassic Sandstone aquifer in northwest England. Cation exchange capacities and selectivity coefficients for Na(+), K(+), Ca(2+), and Mg(2+) were measured in the laboratory using standard techniques. Selectivity coefficients were also determined using a method involving optimized back-calculation from flushing experiments, thus permitting better representation of field conditions; in all cases, the Gaines-Thomas/constant cation exchange capacity (CEC) model was found to be a reasonable, though not perfect, first description. The exchange parameters interpreted from the laboratory experiments were used in a one-dimensional reactive transport mixing cell model, and predictions compared with field pumping well data (Cl and hardness spanning a period of around 40 years, and full major ion analyses in approximately 1980). The concentration patterns predicted using Gaines-Thomas exchange with calcite equilibrium were similar to the observed patterns, but the concentrations of the divalent ions were significantly overestimated, as were 1980 sulphate concentrations, and 1980 alkalinity concentrations were underestimated. Including representation of sulphate reduction in the estuarine alluvium failed to replicate 1980 HCO(3) and pH values. However, by including partial CO(2) degassing following sulphate reduction, a process for which there is 34S and 18O evidence from a previous study, a good match for SO(4), HCO(3), and pH was attained. Using this modified estuary water and averaged values from the laboratory ion exchange parameter determinations, good predictions for the field cation data were obtained. It is concluded that the Gaines-Thomas/constant exchange capacity model with averaged parameter values can be used successfully in ion exchange predictions in this aquifer at a regional scale and over extended time scales, despite the numerous assumptions inherent in

  7. The use of laboratory-determined ion exchange parameters in the predictive modelling of field-scale major cation migration in groundwater over a 40-year period.

    PubMed

    Carlyle, Harriet F; Tellam, John H; Parker, Karen E

    2004-01-01

    An attempt has been made to estimate quantitatively cation concentration changes as estuary water invades a Triassic Sandstone aquifer in northwest England. Cation exchange capacities and selectivity coefficients for Na(+), K(+), Ca(2+), and Mg(2+) were measured in the laboratory using standard techniques. Selectivity coefficients were also determined using a method involving optimized back-calculation from flushing experiments, thus permitting better representation of field conditions; in all cases, the Gaines-Thomas/constant cation exchange capacity (CEC) model was found to be a reasonable, though not perfect, first description. The exchange parameters interpreted from the laboratory experiments were used in a one-dimensional reactive transport mixing cell model, and predictions compared with field pumping well data (Cl and hardness spanning a period of around 40 years, and full major ion analyses in approximately 1980). The concentration patterns predicted using Gaines-Thomas exchange with calcite equilibrium were similar to the observed patterns, but the concentrations of the divalent ions were significantly overestimated, as were 1980 sulphate concentrations, and 1980 alkalinity concentrations were underestimated. Including representation of sulphate reduction in the estuarine alluvium failed to replicate 1980 HCO(3) and pH values. However, by including partial CO(2) degassing following sulphate reduction, a process for which there is 34S and 18O evidence from a previous study, a good match for SO(4), HCO(3), and pH was attained. Using this modified estuary water and averaged values from the laboratory ion exchange parameter determinations, good predictions for the field cation data were obtained. It is concluded that the Gaines-Thomas/constant exchange capacity model with averaged parameter values can be used successfully in ion exchange predictions in this aquifer at a regional scale and over extended time scales, despite the numerous assumptions inherent in

  8. Combined Utilization of Cation Exchanger and Neutral Receptor to Volume Reduction of Alkaline Tank Waste by Separation of Sodium Salts

    SciTech Connect

    Levitskaia, Tatiana G.; Lumetta, Gregg J.; Moyer, Bruce A.

    2004-03-29

    In this report, novel approaches to the selective liquid-liquid extraction separation of sodium hydroxide and sodium nitrate from high-level alkaline tank waste will be discussed. Sodium hydroxide can be successfully separated from alkaline tank-waste supernatants by weakly acidic lipophilic hydroxy compounds via a cation-exchange mechanism referred to as pseudo hydroxide extraction. In a multi-cycle process, as sodium hydroxide in the aqueous phase becomes depleted, it is helpful to have a neutral sodium receptor in the extraction system to exploit the high nitrate concentration in the waste solution to promote sodium removal by an ion-pair extraction process. Simultaneous utilization of an ionizable organic hydroxy compound and a neutral extractant (crown ether) in an organic phase results in the synergistic enhancement of ion exchange and improved separation selectivity due to the receptor's strong and selective sodium binding. Moreover, combination of the hydroxy compound and the crown ether provides for mutually increased solubility, even in a non-polar organic solvent. Accordingly, application of Isopar{reg_sign} L, a kerosene-like alkane solvent, becomes feasible. This investigation involves examination of such dual-mechanism extraction phases for sodium extraction from simulated and actual salt cake waste solutions. Sodium salts can be regenerated upon the contact of the loaded extraction phases with water. Finally, conditions of potential extraction/strip cycling will be discussed.

  9. Electrophilic Pt(II) complexes: precision instruments for the initiation of transformations mediated by the cation-olefin reaction.

    PubMed

    Felix, Ryan J; Munro-Leighton, Colleen; Gagné, Michel R

    2014-08-19

    A discontinuity exists between the importance of the cation-olefin reaction as the principal C-C bond forming reaction in terpene biosynthesis and the synthetic tools for mimicking this reaction under catalyst control; that is, having the product identity, stereochemistry, and functionality under the control of a catalyst. The main reason for this deficiency is that the cation-olefin reaction starts with a reactive intermediate (a carbocation) that reacts exothermically with an alkene to reform the reactive intermediate; not to mention that reactive intermediates can also react in nonproductive fashions. In this Account, we detail our efforts to realize catalyst control over this most fundamental of reactions and thereby access steroid like compounds. Our story is organized around our progress in each component of the cascade reaction: the metal controlled electrophilic initiation, the propagation and termination of the cyclization (the cyclase phase), and the turnover deplatinating events. Electrophilic Pt(II) complexes efficiently initiate the cation-olefin reaction by first coordinating to the alkene with selection rules that favor less substituted alkenes over more substituted alkenes. In complex substrates with multiple alkenes, this preference ensures that the least substituted alkene is always the better ligand for the Pt(II) initiator, and consequently the site at which all electrophilic chemistry is initiated. This control element is invariant. With a suitably electron deficient ligand set, the catalyst then activates the coordinated alkene to intramolecular addition by a second alkene, which initiates the cation-olefin reaction cascade and generates an organometallic Pt(II)-alkyl. Deplatination by a range of mechanisms (β-H elimination, single electron oxidation, two-electron oxidation, etc.) provides an additional level of control that ultimately enables A-ring functionalizations that are orthogonal to the cyclase cascade. We particularly focus on

  10. Oxidation of thioanisole and p-methoxythioanisole by lignin peroxidase: kinetic evidence of a direct reaction between compound II and a radical cation.

    PubMed Central

    Brück, Thomas B; Gerini, Maria Francesca; Baciocchi, Enrico; Harvey, Patricia J

    2003-01-01

    The reaction of H2O2 with thioanisole and p-methoxythioanisole catalysed by lignin peroxidase from Phanerochaete chrysosporium has been studied spectrophotometrically under turnover and single turnover conditions with a stopped-flow apparatus. Pre-formed lignin peroxidase compounds I and II are each able to react with the sulphides to form a sulphide radical cation. The radical cation is then converted into the sulphoxide either by reaction with the medium or by reaction with compound II. This is the first report of a direct reaction between compound II and the substrate radical cation. With thioanisole, significant enantiomeric selectivity and high oxygen incorporation in the sulphoxide are obtained because compound II is preferentially reduced by the enzyme-bound thioanisole radical cation compared with the neutral substrate. By contrast, with p-methoxythioanisole, the data imply formation of an intermediate ternary complex comprising compound II, radical cation and neutral substrate, such that a chain of electron transfer reactions starting from neutral molecule and progressing to oxidized haem via substrate radical cation is facilitated, yielding the native enzyme and two molecules of p-methoxythioanisole radical cation as products. The reactions of compounds I and II with sulphides imply flexing of the apoprotein moiety during catalysis. PMID:12803544

  11. Non-photochemical Fluorescence Quenching in Photosystem II Antenna Complexes by the Reaction Center Cation Radical.

    PubMed

    Paschenko, V Z; Gorokhov, V V; Grishanova, N P; Korvatovskii, B N; Ivanov, M V; Maksimov, E G; Mamedov, M D

    2016-06-01

    In direct experiments, rate constants of photochemical (kP) and non-photochemical (kP(+)) fluorescence quenching were determined in membrane fragments of photosystem II (PSII), in oxygen-evolving PSII core particles, as well as in core particles deprived of the oxygen-evolving complex. For this purpose, a new approach to the pulse fluorometry method was implemented. In the "dark" reaction center (RC) state, antenna fluorescence decay kinetics were measured under low-intensity excitation (532 nm, pulse repetition rate 1 Hz), and the emission was registered by a streak camera. To create a "closed" [P680(+)QA(-)] RC state, a high-intensity pre-excitation pulse (pump pulse, 532 nm) of the sample was used. The time advance of the pump pulse against the measuring pulse was 8 ns. In this experimental configuration, under the pump pulse, the [P680(+)QA(-)] state was formed in RC, whereupon antenna fluorescence kinetics was measured using a weak testing picosecond pulsed excitation light applied to the sample 8 ns after the pump pulse. The data were fitted by a two-exponential approximation. Efficiency of antenna fluorescence quenching by the photoactive RC pigment in its oxidized (P680(+)) state was found to be ~1.5 times higher than that of the neutral (P680) RC state. To verify the data obtained with a streak camera, control measurements of PSII complex fluorescence decay kinetics by the single-photon counting technique were carried out. The results support the conclusions drawn from the measurements registered with the streak camera. In this case, the fitting of fluorescence kinetics was performed in three-exponential approximation, using the value of τ1 obtained by analyzing data registered by the streak camera. An additional third component obtained by modeling the data of single photon counting describes the P680(+)Pheo(-) charge recombination. Thus, for the first time the ratio of kP(+)/kP = 1.5 was determined in a direct experiment. The mechanisms of higher

  12. Modelling exchange kinetics of copper at the water-aquatic moss (Fontinalis antipyretica) interface: influence of water cationic composition (Ca, Mg, Na and pH).

    PubMed

    Ferreira, Daniel; Ciffroy, Philippe; Tusseau-Vuillemin, Marie-Hélène; Garnier, Cédric; Garnier, Jean-Marie

    2009-02-01

    The present study investigated the effect of water cationic composition (Ca, Mg, Na, pH) on the bioaccumulation and elimination rates of copper by an aquatic moss (Fontinalis antipyretica), under laboratory conditions. For this purpose, mosses were exposed to copper at an environmentally relevant and usually non-toxic concentration (5 microg L(-1)) in natural waters where cationic composition and concentrations were varied. To describe copper bioaccumulation by aquatic mosses, a two-compartment model was the first-order kinetics, was developed and calibrated under a wide range of water cationic composition. Bioaccumulation rates of Cu in mosses were significantly reduced as the concentrations of competitive cations in solution increased. Hence, in hard-water, Ca and Mg cations play a protective role as they compete with Cu2+ ions for the absorption on transport sites at the organism-water interface. Based on the relationships between each major cation concentration and the exchange kinetics on mosses, the binding constants (K(Ci)(BL)) of each competing cations to the biological surfaces were derived. Using the present cationic-dependent kinetic model, it is now feasible to incorporate water cationic composition in the (re)interpretation of bryophytes contamination levels and in the (re)definition of Water Quality Criteria (WQC) as illustrated through two selected examples of biomonitoring programmes. In the framework of future national water quality guidelines revisions, a such flexible and mechanistic biomonitoring tool (integrating the protective effects of competing cations) may greatly improve the ability of regulators to derive site-specific Cu (metal) guidelines for protecting aquatic biota, while limiting the use of conservative assumptions. PMID:19042004

  13. NOVEL CONTINUOUS PH/SALT GRADIENT AND PEPTIDE SCORE FOR STRONG CATION EXCHANGE CHROMATOGRAPHY IN 2D-NANO-LC/MSMS PEPTIDE IDENTIFICATION FOR PROTEOMICS

    EPA Science Inventory

    Tryptic digests of human serum albumin (HSA) and human lung epithelial cell lysates were used as test samples in a novel proteomics study. Peptides were separated and analyzed using 2D-nano-LC/MSMS with strong cation exchange (SCX) and reverse phase (RP) chromatography and contin...

  14. Knockout of multiple arabidopsis Cation/H+ exchangers suggest isoform-specific roles in metal stress response, germinatin and seed mineral nutrition

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cation/H(+) exchangers encoded by CAX genes play an important role in the vacuolar accumulation of metals including Ca(2+) and Mn(2+). Arabidopsis thaliana CAX1 and CAX3 have been previously shown to differ phylogenetically from CAX2 but the physiological roles of these different transporters are st...

  15. Sea cucumber-like hydroxyapatite: cation exchange membrane-assisted synthesis and its application in ultra-sensitive heavy metal detection.

    PubMed

    Zhang, Ying; Liu, Yong; Ji, Xiaobo; Banks, Craig E; Zhang, Wei

    2011-04-14

    Sea cucumber-like hydroxyapatite fabricated with the aid of a Nafion N-117 cation exchange membrane was applied to the detection of lead(II) and cadmium(II) in ultra-trace concentration levels. The proposed HAp-modified carbon paste electrode has significantly lower linear ranges and exhibits a larger sensitivity than those reported previously.

  16. Reactivity of Cations and Zwitterions Formed in Photochemical and Acid-Catalyzed Reactions from m-Hydroxycycloalkyl-Substituted Phenol Derivatives.

    PubMed

    Cindro, Nikola; Antol, Ivana; Mlinarić-Majerski, Kata; Halasz, Ivan; Wan, Peter; Basarić, Nikola

    2015-12-18

    Three m-substituted phenol derivatives, each with a labile benzylic alcohol group and bearing either protoadamantyl 4, homoadamantyl 5, or a cyclohexyl group 6, were synthesized and their thermal acid-catalyzed and photochemical solvolytic reactivity studied, using preparative irradiations, fluorescence measurements, nanosecond laser flash photolysis, and quantum chemical calculations. The choice of m-hydroxy-substitution was driven by the potential for these phenolic systems to generate m-quinone methides on photolysis, which could ultimately drive the excited-state pathway, as opposed to forming simple benzylic carbocations in the corresponding thermal route. Indeed, thermal acid-catalyzed reactions gave the corresponding cations, which undergo rearrangement and elimination from 4, only elimination from 5, and substitution and elimination from 6. On the other hand, upon photoexcitation of 4-6 to S1 in a polar protic solvent, proton dissociation from the phenol, coupled with elimination of the benzylic OH (as hydroxide ion) gave zwitterions (formal m-quinone methides). The zwitterions exhibit reactivity different from the corresponding cations due to a difference in charge distribution, as shown by DFT calculations. Thus, protoadamantyl zwitterion has a less nonclassical character than the corresponding cation, so it does not undergo 1,2-shift of the carbon atom, as observed in the acid-catalyzed reaction. PMID:26595342

  17. Exchangeable sodium induced changes in yield, water relation and cation composition of fennel (Foeniculum vulgare Mill).

    PubMed

    Garg, V K; Singh, P K; Pushpangadan, P

    2005-06-01

    A pot experiment was conducted with the objectives to assess the adaptation potential of fennel crop grown at 10, 20, 25, 35 and 40 ESP (exchangeable sodium percentage) levels. Results showed that the rate of seed germination, plant growth including branching pattern, umbels per plant and 1000 test seed weight were adversely affected by sodic soils. Assuming that fifty percent reduction in seed yield and Na+/K+ ratio in leaf tissue as an index of alkali tolerance revealed that fennel was tolerant up to 25 ESP. The cell sap pH and EC reflected optimum osmoticum maintenance to withstand sodicity stress at this level and beyond this leaf water potential decreased (negatively) more to impede water uptake.

  18. Theoretical investigation of isotope exchange reaction in tritium-contaminated mineral oil in vacuum pump.

    PubMed

    Dong, Liang; Xie, Yun; Du, Liang; Li, Weiyi; Tan, Zhaoyi

    2015-04-28

    The mechanism of the isotope exchange reaction between molecular tritium and several typical organic molecules in vacuum pump mineral oil has been investigated by density functional theory (DFT), and the reaction rates are determined by conventional transition state theory (TST). The tritium-hydrogen isotope exchange reaction can proceed with two different mechanisms, the direct T-H exchange mechanism and the hyrogenation-dehydrogenation exchange mechanism. In the direct exchange mechanism, the titrated product is obtained through one-step via a four-membered ring hydrogen migration transition state. In the hyrogenation-dehydrogenation exchange mechanism, the T-H exchange could be accomplished by the hydrogenation of the unsaturated bond with tritium followed by the dehydrogenation of HT. Isotope exchange between hydrogen and tritium is selective, and oil containing molecules with OH and COOH groups can more easily exchange hydrogen for tritium. For aldehydes and ketones, the ability of T-H isotope exchange can be determined by the hydrogenation of T2 or the dehydrogenation of HT. The molecules containing one type of hydrogen provide a single product, while the molecules containing different types of hydrogens provide competitive products. The rate constants are presented to quantitatively estimate the selectivity of the products.

  19. Design of a fixed-bed ion-exchange process for the treatment of rinse waters generated in the galvanization process using Laminaria hyperborea as natural cation exchanger.

    PubMed

    Mazur, Luciana P; Pozdniakova, Tatiana A; Mayer, Diego A; Boaventura, Rui A R; Vilar, Vítor J P

    2016-03-01

    In this study, the removal of zinc from galvanization wastewaters was performed in a fixed bed column packed with brown macro-algae Laminaria hyperborea, acting as a natural cation exchanger (resin). The rinse wastewater presents a zinc concentration between 9 and 22 mg/L, a high concentration of light metals (mainly Na and Ca), a high conductivity (0.5-1.5 mS/cm) and a low organic content (DOC = 7-15 mg C/L). The zinc speciation diagram showed that approximately 80% of zinc is in the form of Zn(2+) and ≅20% as ZnSO4, considering the effluent matrix. From all operational conditions tested for zinc uptake (17 < bed height<27 cm, 4.5 < flow rate<18.2 BV/h, 0.8 < particle equivalent diameter<2.0 mm), the highest useful capacity (7.1 mg Zn/g algae) was obtained for D/dp = 31, L/D = 11, 9.1 BV/h, τ = 6.4 min, corresponding to a service capacity of 124 BV (endpoint of 2 mg Zn/L). Elution was faster and near to 100% effective using 10 BV of HCl (1 M, 3.0%, 363 g HCl/L of resin), for flow rates higher than 4.5 BV/h. Calcium chloride solution (0.1 M) was selected as the best regenerant, allowing the reuse of the natural resin for more than 3 saturation/elution/regeneration cycles. The best operation conditions were scaled-up and tested in a pre-pilot plant. The scale-up design of the cation exchange process was proposed for the treatment of 2.4 m(3)/day of galvanization wastewater, resulting in an estimated reactants cost of 2.44 €/m(3).

  20. Design of a fixed-bed ion-exchange process for the treatment of rinse waters generated in the galvanization process using Laminaria hyperborea as natural cation exchanger.

    PubMed

    Mazur, Luciana P; Pozdniakova, Tatiana A; Mayer, Diego A; Boaventura, Rui A R; Vilar, Vítor J P

    2016-03-01

    In this study, the removal of zinc from galvanization wastewaters was performed in a fixed bed column packed with brown macro-algae Laminaria hyperborea, acting as a natural cation exchanger (resin). The rinse wastewater presents a zinc concentration between 9 and 22 mg/L, a high concentration of light metals (mainly Na and Ca), a high conductivity (0.5-1.5 mS/cm) and a low organic content (DOC = 7-15 mg C/L). The zinc speciation diagram showed that approximately 80% of zinc is in the form of Zn(2+) and ≅20% as ZnSO4, considering the effluent matrix. From all operational conditions tested for zinc uptake (17 < bed height<27 cm, 4.5 < flow rate<18.2 BV/h, 0.8 < particle equivalent diameter<2.0 mm), the highest useful capacity (7.1 mg Zn/g algae) was obtained for D/dp = 31, L/D = 11, 9.1 BV/h, τ = 6.4 min, corresponding to a service capacity of 124 BV (endpoint of 2 mg Zn/L). Elution was faster and near to 100% effective using 10 BV of HCl (1 M, 3.0%, 363 g HCl/L of resin), for flow rates higher than 4.5 BV/h. Calcium chloride solution (0.1 M) was selected as the best regenerant, allowing the reuse of the natural resin for more than 3 saturation/elution/regeneration cycles. The best operation conditions were scaled-up and tested in a pre-pilot plant. The scale-up design of the cation exchange process was proposed for the treatment of 2.4 m(3)/day of galvanization wastewater, resulting in an estimated reactants cost of 2.44 €/m(3). PMID:26766159

  1. Separation of Cinchona alkaloids on a novel strong cation-exchange-type chiral stationary phase-comparison with commercially available strong cation exchanger and reversed-phase packing materials.

    PubMed

    Hoffmann, Christian V; Lämmerhofer, Michael; Lindner, Wolfgang

    2009-02-01

    A recently reported chiral strong cation exchanger (cSCX) type stationary phase was investigated for the LC separation of a series of Cinchona alkaloids and synthetic derivatives thereof to test its usefulness as alternative methodology for the separation of those important pharmaceuticals. The cSCX column-packing material was qualitatively compared on the one hand against a commercially available non-enantioselective SCX-material, PolySulfoethyl-A, and, on the other hand, against a modern C18 reversed-phase stationary phase which is commonly employed for Cinchona alkaloid analysis. Both SCX columns showed no pronounced peak-tailing phenomena which typically hamper Cinchona alkaloid RP analysis and require specific optimization. Thus, the cSCX-based assay provided new feasibilities for the separation of the Cinchona alkaloids in polar organic mode as opposed to conventional reversed-phase methodologies. In particular, a method for the simultaneous determination of eight Cinchona alkaloids (quinine, quinidine, cinchonine, cinchonidine, and their corresponding dihydro analogs) using the cSCX column in HPLC has been developed and exemplarily applied to impurity profiling of a commercial alkaloid sample. Furthermore, both SCX materials allowed successful separation of C9-epi and 10,11-didehydro derivatives from their respective educts in an application in synthetic Cinchona alkaloid chemistry. PMID:19107468

  2. Dithioacetal Exchange: A New Reversible Reaction for Dynamic Combinatorial Chemistry.

    PubMed

    Orrillo, A Gastón; Escalante, Andrea M; Furlan, Ricardo L E

    2016-05-10

    Reversibility of dithioacetal bond formation is reported under acidic mild conditions. Its utility for dynamic combinatorial chemistry was explored by combining it with orthogonal disulfide exchange. In such a setup, thiols are positioned at the intersection of both chemistries, constituting a connecting node between temporally separated networks. PMID:26990904

  3. Dithioacetal Exchange: A New Reversible Reaction for Dynamic Combinatorial Chemistry.

    PubMed

    Orrillo, A Gastón; Escalante, Andrea M; Furlan, Ricardo L E

    2016-05-10

    Reversibility of dithioacetal bond formation is reported under acidic mild conditions. Its utility for dynamic combinatorial chemistry was explored by combining it with orthogonal disulfide exchange. In such a setup, thiols are positioned at the intersection of both chemistries, constituting a connecting node between temporally separated networks.

  4. Iron-copper cooperative catalysis in the reactions of alkyl Grignard reagents: exchange reaction with alkenes and carbometalation of alkynes.

    PubMed

    Shirakawa, Eiji; Ikeda, Daiji; Masui, Seiji; Yoshida, Masatoshi; Hayashi, Tamio

    2012-01-11

    Iron-copper cooperative catalysis is shown to be effective for an alkene-Grignard exchange reaction and alkylmagnesiation of alkynes. The Grignard exchange between terminal alkenes (RCH═CH(2)) and cyclopentylmagnesium bromide was catalyzed by FeCl(3) (2.5 mol %) and CuBr (5 mol %) in combination with PBu(3) (10 mol %) to give RCH(2)CH(2)MgBr in high yields. 1-Alkyl Grignard reagents add to alkynes in the presence of a catalyst system consisting of Fe(acac)(3), CuBr, PBu(3), and N,N,N',N'-tetramethylethylenediamine to give β-alkylvinyl Grignard reagents. The exchange reaction and carbometalation take place on iron, whereas copper assists with the exchange of organic groups between organoiron and organomagnesium species through transmetalation with these species. Sequential reactions consisting of the alkene-Grignard exchange and the alkylmagnesiation of alkynes were successfully conducted by adding an alkyne to a mixture of the first reaction. Isomerization of Grignard reagents from 2-alkyl to 1-alkyl catalyzed by Fe-Cu also is applicable as the first 1-alkyl Grignard formation step. PMID:22128888

  5. Development of high-productivity, strong cation-exchange adsorbers for protein capture by graft polymerization from membranes with different pore sizes

    PubMed Central

    Chenette, Heather C.S.; Robinson, Julie R.; Hobley, Eboni; Husson, Scott M.

    2012-01-01

    This paper describes the surface modification of macroporous membranes using ATRP (atom transfer radical polymerization) to create cation-exchange adsorbers with high protein binding capacity at high product throughput. The work is motivated by the need for a more economical and rapid capture step in downstream processing of protein therapeutics. Membranes with three reported nominal pore sizes (0.2, 0.45, 1.0 μm) were modified with poly(3-sulfopropyl methacrylate, potassium salt) tentacles, to create a high density of protein binding sites. A special formulation was used in which the monomer was protected by a crown ether to enable surface-initiated ATRP of this cationic polyelectrolyte. Success with modification was supported by chemical analysis using Fourier-transform infrared spectroscopy and indirectly by measurement of pure water flux as a function of polymerization time. Uniformity of modification within the membranes was visualized with confocal laser scanning microscopy. Static and dynamic binding capacities were measured using lysozyme protein to allow comparisons with reported performance data for commercial cation-exchange materials. Dynamic binding capacities were measured for flow rates ranging from 13 to 109 column volumes (CV)/min. Results show that this unique ATRP formulation can be used to fabricate cation-exchange membrane adsorbers with dynamic binding capacities as high as 70 mg/mL at a throughput of 100 CV/min and unprecedented productivity of 300 mg/mL/min. PMID:23175597

  6. Cation exchange synthesis of uniform PbSe/PbS core/shell tetra-pods and their use as near-infrared photodetectors.

    PubMed

    Mishra, N; Mukherjee, B; Xing, G; Chakrabortty, S; Guchhait, A; Lim, J Y

    2016-08-01

    In this work we explore the preparation of complex-shaped semiconductor nanostructures composed of different materials via a cationic exchange process in which the cations of the original semiconductor nanostructure are replaced by cations of different metals with preservation of the shape and the anionic framework of the nanocrystals. Utilizing this cation exchange method, we synthesized two new tetrapods for the first time: Cu2-xSe/Cu2-xS and PbSe/PbS, both prepared from CdSe/CdS tetrapods as 'templates'. We also fabricated near-infrared (NIR) photodetectors with a very simple architecture comprising a PbSe/PbS tetrapod layer between two Au electrodes on a glass substrate. When illuminated by a NIR laser, these devices are capable of achieving a responsivity of 11.9 A W(-1) without the use of ligand-exchange processes, thermal annealing or hybrid device architecture. Transient absorption spectroscopy was carried out on these PbSe/PbS tetrapods, the results of which suggest that the branched morphology contributes in part to device performance. Investigation of the charge dynamics of the PbSe/PbS tetrapods revealed an extremely long-lived exciton recombination lifetime of ∼17 ms, which can result in enhanced photoconductive gain. Overall, these heterostructured tetrapods showcase simultaneously the importance of nanoparticle shape, band structure, and surface chemistry in the attainment of NIR photodetection. PMID:27387963

  7. Method development for the separation of monoclonal antibody charge variants in cation exchange chromatography, Part I: salt gradient approach.

    PubMed

    Fekete, Szabolcs; Beck, Alain; Fekete, Jenő; Guillarme, Davy

    2015-01-01

    Ion exchange chromatography (IEX) is a historical technique widely used for the detailed characterization of therapeutic proteins and can be considered as a reference and powerful technique for the qualitative and quantitative evaluation of charge variants. When applying salt gradient IEX approach for monoclonal antibodies (mAbs) characterization, this approach is described as time-consuming to develop and product-specific. The goal of this study was to tackle these two bottle-necks. By modeling the retention of several commercial mAbs and their variants in IEX, we proved that the mobile phase temperature was not relevant for tuning selectivity, while optimal salt gradient program can be easily found based on only two initial gradients of different slopes. Last but not least, the dependence of retention vs. pH being polynomial, three initial runs at different pH were required to optimize mobile phase pH. Finally, only 9h of initial experiments were necessary to simultaneously optimize salt gradient profile and pH in IEX. The data can then be treated with commercial modeling software to find out the optimal conditions to be used, and accuracy of retention times prediction was excellent (less than 1% variation between predicted and experimental values). Second, we also proved that generic IEX conditions can be applied for the characterization of mAbs possessing a wide range of pI, from 6.7 to 9.1. For this purpose, a strong cation exchange column has to be employed at a pH below 6 and using a proportion of NaCl up to 0.2M. Under these conditions, all the mAbs were properly eluted from the column. Therefore, salt gradient CEX can be considered as a generic multi-product approach. PMID:25240157

  8. Synthesis and characterization of a novel hybrid nano composite cation exchanger poly-o-toluidine Sn(IV) tungstate: Its analytical applications as ion-selective electrode

    NASA Astrophysics Data System (ADS)

    Khan, Asif Ali; Shaheen, Shakeeba

    2013-02-01

    A novel organic-inorganic nano composite cation exchanger poly-o-toluidine Sn(IV) tungstate has been synthesized by incorporation of a polymer material into inorganic precipitate. The material is a class of hybrid ion-exchanger with good ion-exchange properties, reproducibility, stability and good selectivity for heavy metals. The physico-chemical properties of this nano composite material were characterized by using XRD, TGA, FTIR, SEM and TEM. The ion-exchange capacity, pH titrations, elution behavior and chemical stability were also carried out to study ion-exchange properties of the material. Distribution studies for various metal ions revealed that the nano composite is highly selective for Cd(II). An ion-selective membrane electrode was fabricated using this material for the determination of Cd(II) ions in solutions. The analytical utility of this electrode was established by employing it as an indicator electrode in electrometric titrations.

  9. Proteomics-based, multivariate random forest method for prediction of protein separation behavior during cation-exchange chromatography.

    PubMed

    Swanson, Ryan K; Xu, Ruo; Nettleton, Dan; Glatz, Charles E

    2012-08-01

    The most significant cost of recombinant protein production lies in the optimization of the downstream purification methods, mainly due to a lack of knowledge of the separation behavior of the host cell proteins (HCP). To reduce the effort required for purification process development, this work was aimed at modeling the separation behavior of a complex mixture of proteins in cation-exchange chromatography (CEX). With the emergence of molecular pharming as a viable option for the production of recombinant pharmaceutical proteins, the HCP mixture chosen was an extract of corn germ. Aqueous two phase system (ATPS) partitioning followed by two-dimensional electrophoresis (2DE) provided data on isoelectric point, molecular weight and surface hydrophobicity of the extract and step-elution fractions. A multivariate random forest (MVRF) method was then developed using the three characterization variables to predict the elution pattern of individual corn HCP. The MVRF method achieved an average root mean squared error (RMSE) value of 0.0406 (fraction of protein eluted in each CEX elution step) for all the proteins that were characterized, providing evidence for the effectiveness of both the characterization method and the analysis approach for protein purification applications.

  10. [Preparation of a strong cation-exchange polymer monolith and its application in determination of melamine in milk products].

    PubMed

    Ma, Qiao; Hu, Xizhou; Huang, Jincui; Feng, Yuqi

    2009-09-01

    A poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-ethylene dimethacrylate) (AMPS-co-EDMA) monolith was prepared in a fused-silica capillary (530 microm i.d.) and applied for polymer monolith microextraction (PMME). With the optimal ratio of N, N-dimethyl-formamide (DMF, porogen) and polyethylene glycol (PEG, co-porogen), the resulting monolith exhibited satisfactory permeability, high mechanical strength and good stability in aqueous buffer. The effects of several parameters to PMME were investigated, such as pH value, inorganic salt and organic phase concentration of the sample matrix. It demonstrated that the melamine was captured on the poly (AMPS-co-EDMA) monolith mainly through strong cation-exchange and hydrophobic interactions. A novel approach is presented for the determination of melamine in milk products by coupling PMME to high performance liquid chromatography with ultraviolet detection. Because of the high extraction capacity of the monolith towards melamine, low detection limits (S/N = 3, 0.9 mg/kg) and quantification limits (S/N = 10, 0.3 mg/kg) were obtained. The method showed good linearity ranging from 0.5 to 80 mg/kg. Excellent reproducibility of the method was exhibited by intraday and interday precisions, yielding the relative standard deviations not larger than 7.5%. The proposed method is simple, rapid, sensitive, and low cost.

  11. Proteomics-based, multivariate random forest method for prediction of protein separation behavior during cation-exchange chromatography.

    PubMed

    Swanson, Ryan K; Xu, Ruo; Nettleton, Dan; Glatz, Charles E

    2012-08-01

    The most significant cost of recombinant protein production lies in the optimization of the downstream purification methods, mainly due to a lack of knowledge of the separation behavior of the host cell proteins (HCP). To reduce the effort required for purification process development, this work was aimed at modeling the separation behavior of a complex mixture of proteins in cation-exchange chromatography (CEX). With the emergence of molecular pharming as a viable option for the production of recombinant pharmaceutical proteins, the HCP mixture chosen was an extract of corn germ. Aqueous two phase system (ATPS) partitioning followed by two-dimensional electrophoresis (2DE) provided data on isoelectric point, molecular weight and surface hydrophobicity of the extract and step-elution fractions. A multivariate random forest (MVRF) method was then developed using the three characterization variables to predict the elution pattern of individual corn HCP. The MVRF method achieved an average root mean squared error (RMSE) value of 0.0406 (fraction of protein eluted in each CEX elution step) for all the proteins that were characterized, providing evidence for the effectiveness of both the characterization method and the analysis approach for protein purification applications. PMID:22748375

  12. Enhanced photocatalytic activity of chromium(VI) reduction and EDTA oxidization by photoelectrocatalysis combining cationic exchange membrane processes.

    PubMed

    Hsu, Hung-Te; Chen, Shiao-Shing; Tang, Yi-Fang; Hsi, Hsing-Cheng

    2013-03-15

    A novel technology of photoelectrocatalysis (PEC) combining with cationic exchange membrane (CEM) was proposed for simultaneous reduction of chromium(VI) and oxidization of EDTA. The application of CEM was used to enhance the efficiency for prevention of the re-oxidation of reduced chromium with the electron-hole pairs. In this study, effects of current density, pH, TiO2 dosage, hydraulic retention time (HRT), light intensity and EDTA/Cr(VI) molar ratio were all investigated. The results showed that the optimum conversion efficiency occurred at 4mA/cm(2) with the presence of CEM. Higher conversion efficiencies were observed at lower pH due to the electrostatic attractions between positive charged TiOH2(+), and negatively charged Cr(VI) and EDTA. The optimum TiO2 loading of 1g/L was depended mainly on the acidic pH range, especially at higher HRT and irradiation intensity. In addition, higher EDTA/Cr(VI) molar ratio enhanced the reduction efficiency of Cr(VI), indicating EDTA plays the role of hole scavenger in this system. Moreover, incomplete EDTA decomposition contributes to the occurrence of intermediates, including nitrilotriacetic acid, iminodiacetic acid, glycine, oxamic acid, lyoxylic acid, oxalic acid, acetic acid and formic acid, as identified by GC/MS. Consequently, transformation pathway was determined from these analyzed byproducts and molecular orbital package analysis.

  13. Solution-Membrane Equilibrium at Metal-Deposited Cation-Exchange Membranes: Chronopotentiometric Characterization of Metal-Modified Membranes.

    PubMed

    Shahi; Prakash; Ramachandraiah; Rangarajan; Vasudevan

    1999-08-01

    Copper- and lead-deposited interpolymer cationic membranes have been prepared by electroless plating by an ion-exchange method and characterized by chronopotentiometry and cyclic voltammetry. The parameters such as transition time (tau), Itau1/2, the potential drop (E0) across these membranes immediately after the application of constant current (I), and the height of the potential jump (DeltaE) across the membrane at tau have been measured by chronopotentiometry and compared with those of plain membranes. The approximate percentage of metal coverage and the number of ionic sites masked by the deposited metal in terms of NaCl concentration have been estimated from the differences in Itau1/2 values of plain and metal-deposited membranes. The quantity of metal deposited in a unit area of the membrane surface was measured by differential pulse polarography. The oxidation and reduction peak potentials corresponding to Cu(0)/Cu(II) and Pb(0)/Pb(II) couples were identified by cyclic voltammetry at pH 2.8 and 4.5 of 0.2 M CH3COONa-H2SO4. Copyright 1999 Academic Press. PMID:10395776

  14. Cation exchange capacity (Qv) estimation in shaly sand reservoirs: case studies in the Junggar Basin, northwest China

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Mao, Zhi-Qiang; Sun, Zhong-Chun; Luo, Xing-Ping; Deng, Ren-Shuang; Zhang, Ya-Hui; Ren, Bing

    2015-10-01

    Cation exchange capacity (Qv) is a key parameter in resistivity-based water saturation models of shaly sand reservoirs, and the accuracy of Qv calculation is crucial to the prediction of saturations of oil and gas. In this study, a theoretical expression of Qv in terms of shaly sand permeability (Kshaly-sand), total porosity (ϕt), and salinity of formation water (S) is deduced based on the capillary tube model and the physics volume model. Meanwhile, the classical Schlumberger-Doll research (SDR) model has been introduced to estimate Kshaly-sand. On this basis, a novel technique to estimate Qv from nuclear magnetic resonance (NMR) logs is proposed, and the corresponding model is also established, whose model parameters are calibrated by laboratory Qv and NMR measurements of 15 core samples from the Toutunhe formation of the Junggar Basin, northwest China. Based on the experimental data sets, this technique can be extended to reservoir conditions to estimate continuous Qv along the intervals. The processing results of field examples illustrate that the Qv calculated from field NMR logs are consistent with the analyzed results, with the absolute errors within the scope of  ±0.1 mmol cm-3 for the majority of core samples.

  15. Spectrophotometric study of the effect of cationic micelles on the reaction between gallein and TH(IV)

    SciTech Connect

    Mori, I.; Fujita, Y.; Fujita, K.; Koshiyama, Y.; Nakahashi, Y.

    1987-01-01

    The acid dissociation equilibria of gallein (pyrogallolphthalein, gall), as a xanthene dye, in the presence of various surfactants--cationic, anionic, nonionic, are discussed. The coexistence of a cationic surfactant, such as hexadecyltrimethylammonium chloride (HTAC) slightly enhanced the acid dissociation, and led to a chromogenic reaction between metal ions and gall in weakly acidic media. The ternary complex between gall and Th(IV), in weakly acidic media and in the presence of N-hexadecylpyridinium chloride(HPC), was very stable with definitive spectra. However, the complex was easily decomposed in proportion to the concentration of citrate ion. Therefore, simple and rapid spectrophotometric methods for the determination of Th(IV) and citrate ion were respectively established, by using the gall-Th(IV)-HPC ternary complex in the cationic surfactant micelle. Beer's law was obeyed over the range 0 to 90..mu..g of Th(IV) and 12 to 35..mu..g of citrate ion, in a final volume of 10 ml. The Sandell sensitivities were estimated to be 0.0013 ..mu..g/cm/sup 2/ Th(IV) and 0.0005 ..mu..g/cm/sup 2/ citrate ion at 600 nm. The analytical procedures were simple and did not require any organic solvent extraction.

  16. Gas-Phase Reactions of Doubly Charged Lanthanide Cations with Alkanes and Alkenes. Trends in Metal(2+) Reactivity

    SciTech Connect

    Gibson, John K.; Marcalo, Joaquim; Santos, Marta; Pires de Matos, Antonio; Haire, Richard G.

    2008-12-08

    The gas-phase reactivity of doubly-charged lanthanide cations, Ln2+ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), with alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) was studied by Fourier transform ion cyclotron resonance mass spectrometry. The reaction products consisted of different combinations of doubly-charged organometallic ions?adducts or species formed via metal-ion-induced hydrogen, dihydrogen, alkyl, or alkane eliminations from the hydrocarbons?and singly-charged ions that resulted from electron, hydride, or methide transfers from the hydrocarbons to the metal ions. The only lanthanide cations capable of activating the hydrocarbons to form doubly-charged organometallic ions were La2+, Ce2+, Gd2+, and Tb2+, which have ground-state or low-lying d1 electronic configurations. Lu2+, with an accessible d1 electronic configuration but a rather high electron affinity, reacted only through transfer channels. The remaining Ln2+ reacted via transfer channels or adduct formation. The different accessibilities of d1 electronic configurations and the range of electron affinities of the Ln2+ cations allowed for a detailed analysis of the trends for metal(2+) reactivity and the conditions for occurrence of bond activation, adduct formation, and electron, hydride, and methide transfers.

  17. Exchange of Silicon by Trivalent Cations of Iron or Aluminium in Calcium Silicate Perovskite

    NASA Astrophysics Data System (ADS)

    Bläß, U. W.; Boffa-Ballaran, T.; Frost, D. J.; Langenhorst, F.; McCammon, C. A.; Seifert, F.; van Aken, P. A.

    2003-04-01

    Based on experiments it is widely accepted that calcium silicate perovskite is an important constituent of the Earth's transition zone and the lower mantle as a host mineral for calcium as well as for trace elements. In addition the incorporation of Fe3+ or Al3+ and the associated creation of oxygen vacancies could lead to drastic changes in physical and structural properties. In other perovskites such effects are well known: In MgSiO3 perovskite the incorporation of even a few percent of these elements strongly affects the elastic and transport properties. At higher concentrations of vacancies ordering may occur, as in the model system Ca(FexTi1-x)O3-x/2, in which a complete ordering of oxygen vacancies in pseudocubic \\{100\\} planes causes the formation of several intermediate phases. Multianvil experiments in the system Ca(FexSi1-x)O3-x/2 were run at several P-T conditions and a buffered oxygen fugacity of Re-ReO2, and have shown that the maximum exchange of silicon by trivalent iron in CaSiO3 - perovskite is limited to 4% at 16 GPa. This probably disordered phase is clearly separated by a solvus from an ordered perovskite phase with the composition Ca(Fe0.4Si0.6)O2.8. No further oxygen deficient perovskites exist at more iron rich compositions, except the endmember CaFeO2.5, which we observed to be stable at less than 5 GPa only. The unique Ca(Fe0.4Si0.6)O2.8 phase could be examined in detail by optical microscopy, X-ray diffraction, M&{uml;o}ssbauer spectroscopy, electron microprobe, transmission electron microscopy and electron energy loss spectroscopy. All observations indicate that the structure can be characterised by oxygen deficient tetrahedral double layers perpendicular to pseudocubic <111> directions, alternating with eight octahedral perovskite layers, which are one half each occupied by silicon and iron. With aluminium an analogous phase exists with the composition Ca(Al0.4Si0.6)O2.8, where a similar diffraction pattern suggests the same type of

  18. Invited Parallel Talk: Forward pion-nucleon charge exchange reaction and Regge constraints

    NASA Astrophysics Data System (ADS)

    Huang, Fei; Sibirtsev, A.; Krewald, S.; Hanhart, C.; Haidenbauer, J.; Meißner, U.-G.

    2009-12-01

    We present our recent study of pion-nucleon charge exchange amplitudes above 2 GeV. We analyze the forward pion-nucleon charge exchange reaction data in a Regge model and compare the resulting amplitudes with those from the Karlsruhe-Helsinki and George-Washington-University partial-wave analyses. We explore possible high-energy constraints for theoretical baryon resonance analyses in the energy region above 2 GeV. Our results show that for the pion-nucleon charge exchange reaction, the appropriate energy region for matching meson-nucleon dynamics to diffractive scattering should be around 3 GeV for the helicity flip amplitude.

  19. A DFT study on the mechanisms for the cycloaddition reactions between 1-aza-2-azoniaallene cations and acetylenes.

    PubMed

    Wang, Jing-mei; Li, Zhi-ming; Wang, Quan-rui; Tao, Feng-gang

    2013-01-01

    The mechanisms of cycloaddition reactions between 1-aza-2-azoniaallene cations 1 and acetylenes 2 have been investigated using the global electrophilicity and nucleophilicity of the corresponding reactants as global reactivity indexes defined within the conceptual density functional theory. The reactivity and regioselectivity of these reactions were predicted by analysis of the energies, geometries, and electronic nature of the transition state structures. The theoretical results revealed that the reaction features a tandem process: an ionic 1,3-dipolar cycloaddition to produce the cycloadducts 3 H-pyrazolium salts 3 followed by a [1,2]-shift affording the thermodynamically more stable adducts 4 or 5. The mechanism of the cycloaddition reactions can be described as an asynchronous concerted pathway with reverse electron demand. The model reaction has also been investigated at the QCISD/6-31++G(d,p) and CCSD(T)/6-31++G(d,p)//B3LYP/6-31++G(d,p) levels as well as by the DFT. The polarizable continuum model, at the B3LYP/6-31++G(d,p) level of theory, was used to study solvent effects on all the studied reactions. In solvent dichloromethane, all the initial cycloadducts 3 were obtained via direct ionic process as the result of the solvent effect. The consecutive [1,2]-shift reaction, in which intermediates 3 are rearranged to the five-membered heterocycles 4/5, is proved to be a kinetically controlled reaction, and the regioselectivity can be modulated by varying the migrant. The LOL function and RDG function based on localized electron analysis were used to analysis the covalent bond and noncovalent interactions in order to unravel the mechanism of the title reactions. PMID:22810049

  20. Effects of Forest Succession on Exchangeable Cation Concentrations and Nitrogen Mineralization Rates in Soils Following Logging of Eastern Hemlock Forest, Whately, Massachusetts

    NASA Astrophysics Data System (ADS)

    Rhodes, A. L.; Sweezy, T.; Zukswert, J. M.; Dwyer, C. H.

    2012-12-01

    Ecological forest successions associated with invasive species and human disturbance may alter biogeochemical cycles within New England forests. Spread of the invasive insect hemlock woolly adelgid (Adelges tsugae) to eastern North America is causing mortality of the eastern hemlock (Tsuga canadensis), prompting salvage logging. Regrowth by deciduous hardwood trees is often observed. To evaluate whether changes in nutrient cycling could be altered by forest succession, we investigated exchangeable cation chemistry and nitrogen mineralization rates for soil in a mature, eastern hemlock forest and in a juvenile black birch (Betula lenta) forest in western MA. Eastern hemlock on this property was selectively logged 20 years ago, with black birch regrowth succeeding hemlock. We measured soil pH, exchangeable acidity (Al3+ and H+), exchangeable base cations (Ca2+, Mg2+, Na+, and K+), and nitrogen mineralization rates of organic and mineral horizons for 7 incubation periods between May 2011 - July 2012. We also measured the cation exchange capacity and nitrogen mineralization rates of soils from May - July 2012 (2 incubations) in a mature deciduous forest composed primarily of black birch. At each field site, 7 soil cores were collected. Soil horizons (organic and mineral) were separated and homogenized, and 3 replicates of each composite sample were analyzed for soil geochemistry. Organic soils within the juvenile black birch plot (BB) exhibit a low pH (4.3) similar to hemlock organic soils (HEM, pH=4.2). Surprisingly, exchangeable Al3+—the dominant cation in both plots—is significantly greater in organic soils at BB than at HEM (p<.001), and base saturation is less at BB (29%) than at HEM (46%, p<0.001) due to less Ca2+. There are no significant differences in the exchangeable cation chemistry of the mineral horizons at both sites, suggesting that the acidity difference of organic matter is not due to different soil mineralogy. In comparison, organic soil at the

  1. Multi-cycle recovery of lactoferrin and lactoperoxidase from crude whey using fimbriated high-capacity magnetic cation exchangers and a novel "rotor-stator" high-gradient magnetic separator.

    PubMed

    Brown, Geoffrey N; Müller, Christine; Theodosiou, Eirini; Franzreb, Matthias; Thomas, Owen R T

    2013-06-01

    Cerium (IV) initiated "graft-from" polymerization reactions were employed to convert M-PVA magnetic particles into polyacrylic acid-fimbriated magnetic cation exchange supports displaying ultra-high binding capacity for basic target proteins. The modifications, which were performed at 25 mg and 2.5 g scales, delivered maximum binding capacities (Qmax ) for hen egg white lysozyme in excess of 320 mg g(-1) , combined with sub-micromolar dissociation constants (0.45-0.69 µm) and "tightness of binding" values greater than 49 L g(-1) . Two batches of polyacrylic acid-fimbriated magnetic cation exchangers were combined to form a 5 g pooled batch exhibiting Qmax values for lysozyme, lactoferrin, and lactoperoxidase of 404, 585, and 685 mg g(-1) , respectively. These magnetic cation exchangers were subsequently employed together with a newly designed "rotor-stator" type HGMF rig, in five sequential cycles of recovery of lactoferrin and lactoperoxidase from 2 L batches of a crude sweet bovine whey feedstock. Lactoferrin purification performance was observed to remain relatively constant from one HGMF cycle to the next over the five operating cycles, with yields between 40% and 49% combined with purification and concentration factors of 37- to 46-fold and 1.3- to 1.6-fold, respectively. The far superior multi-cycle HGMF performance seen here compared to that observed in our earlier studies can be directly attributed to the combined use of improved high capacity adsorbents and superior particle resuspension afforded by the new "rotor-stator" HGMS design.

  2. {sup 1}H and {sup 23}Na MAS NMR spectroscopy of cationic species in CO{sub 2} selective alkaline earth metal porous silicoaluminophosphates prepared via liquid and solid state ion exchange

    SciTech Connect

    Arevalo-Hidalgo, Ana G.; Dugar, Sneha; Fu, Riqiang; Hernandez-Maldonado, Arturo J.

    2012-07-15

    The location of extraframework cations in Sr{sup 2+} and Ba{sup 2+} ion-exchanged SAPO-34 was estimated by means of {sup 1}H and {sup 23}Na MAS NMR spectroscopy and spectral deconvolution. Incorporation of the alkaline earth metal cations onto the SAPO framework was achieved via liquid state ion exchange, coupled partial detemplation/solid-state ion exchange, and combination of both techniques. MAS NMR revealed that the level of ion exchange was limited by the presence of protons and sodium cations near hexagonal prisms (site SI), which are relatively difficult to exchange with the alkaline earth metal due to steric and charge repulsion criteria. In addition, the presence of ammonium cations in the supercages facilitated the exchange of otherwise tenacious hydrogen as corroborated by unit cell compositional data as well as enhanced CO{sub 2} adsorption at low partial pressures. The extraframework ammonium species were produced from partial detemplation of the structure-directing agent employed for the SAPO-34 synthesis, tetraethylammonium. - Graphical abstract: MAS NMR was used to elucidate the position the cationic species in alkaline earth metal exchanged silicoaluminophosphates. These species played a significant role during the ion exchange process and, therefore, the materials ultimate CO{sub 2} adsorption performance. Highlights: Black-Right-Pointing-Pointer Location of extraframework Sr{sup 2+} or Ba{sup 2+} cations was estimated by means of {sup 1}H and {sup 23}Na MAS NMR. Black-Right-Pointing-Pointer Level of Sr{sup 2+} or Ba{sup 2+} ion exchange was limited by the presence of protons and sodium cations. Black-Right-Pointing-Pointer Presence of ammonium cations in the supercages facilitated the exchange. Black-Right-Pointing-Pointer Sr{sup 2+} and Ba{sup 2+} ion exchanged SAPOs are outstanding CO{sub 2} adsorbents.

  3. An index of the literature for bimolecular gas phase cation-molecule reaction kinetics

    NASA Technical Reports Server (NTRS)

    Anicich, V. G.

    2003-01-01

    This is an index to the literature for gas phase bimolecular positive ionmolecule reactions. Over 2300 references are cited. Reaction rate coefficients and product distributions of the reactions are abstracted out of the original citations where available. This index is intended to cover the literature from 1936 to 2003. This is a continuation of several surveys: the original (Huntress Astrophys. J. Suppl. Ser., 33, 495 (1977)), an expansion (Anicich and Huntress, Astrophys. J. Suppl. Ser. 62, 553 (1986)), a supplement (Anicich, Astrophys. J. Suppl. Ser. 84, 215 (1993)), and an evaluation (Anicich, V. G. J. Phys. Chem. Ref. Data 22,1469 (1993b). The Table of reactions is listed by reactant ion.

  4. Why Seemingly Trivial Events Sometimes Evoke Strong Emotional Reactions: The Role of Social Exchange Rule Violations

    PubMed Central

    Leary, Mark R.; Diebels, Kate J.; Jongman-Sereno, Katrina P.; Fernandez, Xuan Duong

    2015-01-01

    ABSTRACT People sometimes display strong emotional reactions to events that appear disproportionate to the tangible magnitude of the event. Although previous work has addressed the role that perceived disrespect and unfairness have on such reactions, this study examined the role of perceived social exchange rule violations more broadly. Participants (N = 179) rated the effects of another person’s behavior on important personal outcomes, the degree to which the other person had violated fundamental rules of social exchange, and their reactions to the event. Results showed that perceptions of social exchange rule violations accounted for more variance in participants’ reactions than the tangible consequences of the event. The findings support the hypothesis that responses that appear disproportionate to the seriousness of the eliciting event are often fueled by perceived rule violations that may not be obvious to others. PMID:26331429

  5. Why Seemingly Trivial Events Sometimes Evoke Strong Emotional Reactions: The Role of Social Exchange Rule Violations.

    PubMed

    Leary, Mark R; Diebels, Kate J; Jongman-Sereno, Katrina P; Fernandez, Xuan Duong

    2015-01-01

    People sometimes display strong emotional reactions to events that appear disproportionate to the tangible magnitude of the event. Although previous work has addressed the role that perceived disrespect and unfairness have on such reactions, this study examined the role of perceived social exchange rule violations more broadly. Participants (N = 179) rated the effects of another person's behavior on important personal outcomes, the degree to which the other person had violated fundamental rules of social exchange, and their reactions to the event. Results showed that perceptions of social exchange rule violations accounted for more variance in participants' reactions than the tangible consequences of the event. The findings support the hypothesis that responses that appear disproportionate to the seriousness of the eliciting event are often fueled by perceived rule violations that may not be obvious to others.

  6. Selective enrichment of sulfides, thiols and methylthiophosphates from water samples on metal-loaded cation-exchange materials for gas chromatographic analysis.

    PubMed

    Beiner, K; Popp, P; Wennrich, R

    2002-08-30

    The suitability of using metal-loaded sorbents for solid-phase extraction to enrich organic sulfur compounds from water samples was studied. To test the retention behavior of a number of sulfides, thiols and methylthiophosphates, a cation-exchanger was loaded with various metal ions. The elution behavior of sulfur compounds was investigated with different solvents. A combination of Pb2+-modified cation-exchanger as sorbent and CS2 (1%, v/v) in toluene proved to be the most suitable approach for the given problem. Using GC with a pulsed flame photometric detector yielded detection limits of between 0.6 and 2.9 microg/l. The results showed good reproducibility with relative standard deviations of 2-11%. PMID:12236501

  7. Application of mixed-mode, solid-phase extraction in environmental and clinical chemistry. Combining hydrogen-bonding, cation-exchange and Van der Waals interactions

    USGS Publications Warehouse

    Mills, M.S.; Thurman, E.M.; Pedersen, M.J.

    1993-01-01

    Silica- and styrene-divinylbenzene-based mixed-mode resins that contain C8, C18 and sulphonated cation-exchange groups were compared for their efficiency in isolation of neutral triazine compounds from water and of the basic drug, benzoylecgonine, from urine. The triazine compounds were isolated by a combination of Van der Waals and hydrogen-bonding interactions, and benzoylecgonine was isolated by Van der Waals interactions and cation exchange. All analytes were eluted with a polar organic solvent contaning 2% ammonium hydroxide. Larger recoveries (95%) were achieved on copolymerized mixed-mode resins where C18 and sulfonic acid are in closer proximity than on 'blended' mixed-mode resins (60-70% recovery).

  8. Dynamics of the separation of amino acid and mineral salt in the stationary dialysis of solutions with an MK-40 profiled sulfo group cation exchange membrane

    NASA Astrophysics Data System (ADS)

    Vasil'eva, V. I.; Vorob'eva, E. A.

    2012-11-01

    The conjugated diffusion transport of amino acid and mineral salt through a profiled sulfo group cation exchange membrane that simulates the extraction of amino acid from wash waters of microbiological production containing mineral components not used in synthesis is studied. The competitive nature of the conjugation of flows resulting in a decrease in the rate of the mass transfer of components and their separation factor is established from a comparative analysis of experimental data on the diffusion transfer of phenylalanine and sodium chloride in the form of hydrogen from individual and mixed solutions through a profiled sulfo group cation exchange membrane. The range of concentrations and the ratio of components in solution corresponding to the effective separation of phenylalanine and sodium chloride are determined.

  9. Hydrogen exchange kinetics and the mechanism of reaction B of yeast tryptophan synthase.

    PubMed

    Turner, P D; Loughrey, H C; Bailey, C J

    1985-12-20

    It has been shown that yeast tryptophan synthase (L-serine hydro-lyase (adding indoleglycerol-phosphate) EC 4.2.1.20) catalyses tritium exchange reactions between protons on the alpha-carbon of L-serine of L-tryptophan, and water. The absolute rates of these reactions and indole-serine condensation (reaction B), all of which are pyridoxal phosphate-dependent, were measured. L-Serine exchange was resolved into two components, a high-affinity, slow, Michaelian reaction (KmS,H = 0.06 mM, kcats,H 3 X 10(-3) s-1) and a faster reaction (kcat greater than 2.5 S-1) which was not saturated even at 100 mM L-serine. Hydrogen exchange by tryptophan was a Michaelian process (KmT,H = 2.9 mM; kcatT,H = 0.6 s-1). Indole did not inhibit either exchange reaction. A plausible explanation of the results, that reaction B has a ping-pong mechanism with serine as first substrate and water and L-tryptophan as first and second products, respectively, was inadequate because of the observations that L-tryptophan is as first and second products, respectively, was inadequate because of the observations that L-tryptophan is synthesised with less than 1 mol of exchanged proton per mol amino acid, and that the ratio kcat/Km for serine changes between enzyme reactions. A branched modification with two enzyme-serine complexes, only one of which will exchange protons with water, will fit all the results. PMID:3935173

  10. Does Nature Know Best? Pericyclic Reactions in the Daphniphyllum Alkaloid-Forming Cation Cascade.

    PubMed

    Tantillo, Dean J

    2016-09-16

    Heathcock's classic cyclization/rearrangement cascade for formation of Daphniphyllum alkaloids is subjected to analysis using density functional theory calculations. The results of these calculations are consistent with a two-step pathway involving two pericyclic reactions, a Diels-Alder cycloaddition and an ene reaction. PMID:27559932

  11. Impact of 1 mmol dm(-3) concentrations of small molecules containing nitrogen-based cationic groups on the oxygen reduction reaction on polycrystalline platinum in aqueous KOH (1 mol dm(-3)).

    PubMed

    Ong, Ai Lien; Whelligan, Daniel K; Fox, Michael L; Varcoe, John R

    2013-11-21

    Alkaline anion-exchange membranes (AAEMs) containing cationic head-groups (e.g. involving quaternary ammonium and imidazolium groups) are of interest with regard to application in alkaline polymer electrolyte fuel cells (APEFCs). This initial ex situ study evaluated the effect of 1 mmol dm(-3) concentrations of model molecules containing (AAEM-relevant) cationic groups on the oxygen reduction reaction on a polycrystalline platinum disk (Ptpc) electrode in aqueous KOH (1 mol dm(-3)). The cationic molecules studied were tetramethylammonium (TMA), benzyltrimethylammonium (BTMA), 1-benzyl-3-methylimidazolium (BMI), 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane (BAABCO) and 6-(benzyloxy)-N,N,N-trimethylhexan-1-aminium (BOTMHA). Both cyclic and hydrodynamic linear sweep rotating disk electrode voltammetry techniques were used. The resulting voltammograms, derived estimates of apparent electrochemically active surface areas, Tafel slopes, apparent exchange-current densities and the number of electrons transferred (per O2 molecule) were compared. The results strongly suggest that 1 mmol dm(-3) concentrations of BTMA, BAABCO, and (especially) BMI seriously inhibit the catalytic activities of Ptpc in an aqueous KOH electrolyte at 25 °C. The negative influence of (benzene-ring-free) TMA and Cl(-) anions (KCl control experiment) appeared to be less severe. The separation of the trimethylammonium group from the benzene ring via a hexyloxy spacer chain (in BOTMHA) also produced a milder negative effect. PMID:24100347

  12. Impact of 1 mmol dm(-3) concentrations of small molecules containing nitrogen-based cationic groups on the oxygen reduction reaction on polycrystalline platinum in aqueous KOH (1 mol dm(-3)).

    PubMed

    Ong, Ai Lien; Whelligan, Daniel K; Fox, Michael L; Varcoe, John R

    2013-11-21

    Alkaline anion-exchange membranes (AAEMs) containing cationic head-groups (e.g. involving quaternary ammonium and imidazolium groups) are of interest with regard to application in alkaline polymer electrolyte fuel cells (APEFCs). This initial ex situ study evaluated the effect of 1 mmol dm(-3) concentrations of model molecules containing (AAEM-relevant) cationic groups on the oxygen reduction reaction on a polycrystalline platinum disk (Ptpc) electrode in aqueous KOH (1 mol dm(-3)). The cationic molecules studied were tetramethylammonium (TMA), benzyltrimethylammonium (BTMA), 1-benzyl-3-methylimidazolium (BMI), 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane (BAABCO) and 6-(benzyloxy)-N,N,N-trimethylhexan-1-aminium (BOTMHA). Both cyclic and hydrodynamic linear sweep rotating disk electrode voltammetry techniques were used. The resulting voltammograms, derived estimates of apparent electrochemically active surface areas, Tafel slopes, apparent exchange-current densities and the number of electrons transferred (per O2 molecule) were compared. The results strongly suggest that 1 mmol dm(-3) concentrations of BTMA, BAABCO, and (especially) BMI seriously inhibit the catalytic activities of Ptpc in an aqueous KOH electrolyte at 25 °C. The negative influence of (benzene-ring-free) TMA and Cl(-) anions (KCl control experiment) appeared to be less severe. The separation of the trimethylammonium group from the benzene ring via a hexyloxy spacer chain (in BOTMHA) also produced a milder negative effect.

  13. Novel ultra stable silica-based stationary phases for reversed phase liquid chromatography--study of a hydrophobically assisted weak acid cation exchange phase.

    PubMed

    Zhang, Yu; Carr, Peter W

    2011-02-11

    A mixed-mode reversed-phase/weak cation exchange (RP/WCX) phase has been developed by introducing a small amount of carboxylate functionality into a hydrophobic hyper-crosslinked (HC) platform. This silica-based HC platform was designed to form an extensive polystyrene network completely confined to the particle's surface. The fully connected polymer network prevents the loss of bonded phase, which leads to superior hydrolytic stability of the new phase when compared to conventional silica-based phases. Compared to previously introduced HC phases the added carboxylic groups impart a new weak cation exchange selectivity to the base hydrophobic HC platform. The phase thus prepared shows a mixed-mode retention mechanism, allowing for both neutral organic compounds and bases of a wide polarity range to be simultaneously separated on the same phase under the same conditions. In addition, the new phase offers the flexibility that gradients in organic modifier, pH or ionic competitors can be used to affect the separation of a wide range of solutes. Moreover, the inherent weak acid cation exchange groups allow formic and acetic acid buffers to be used as eluents thereby avoiding the mass spectrometric ionization suppression problems concomitant to the use of non-volatile additives such as strong amine modifiers (e.g. triethylamine) or salts (e.g. NaCl) to elute basic solutes from the strong cation exchange phase which was previously developed in this lab. The use of the new phase for achieving strong retention of rather hydrophilic neurotransmitters and drugs of abuse without the need for ion pairing agents is demonstrated.

  14. Core-Shell MnSe@Bi2 Se3 Fabricated via a Cation Exchange Method as Novel Nanotheranostics for Multimodal Imaging and Synergistic Thermoradiotherapy.

    PubMed

    Song, Guosheng; Liang, Chao; Gong, Hua; Li, Meifang; Zheng, Xianchuang; Cheng, Liang; Yang, Kai; Jiang, Xiqun; Liu, Zhuang

    2015-10-28

    MnSe@Bi2 Se3 core-shell nanostructures with highly integrated imaging and therapy functions are fabricated by a simple cation exchange method. Using those nanoparticles as a theranostic agent, a promise concept is further demonstrated to enhance conventional radiotherapy by: i) using X-ray absorbing agents to locally concentrate radiation energy and ii) employing near-infrared-light-triggered photothermal therapy to overcome hypoxia-associated radioresistance. PMID:26331476

  15. Controllable conversion of plasmonic Cu2-xS nanoparticles to Au2S by cation exchange and electron beam induced transformation of Cu2-xS-Au2S core/shell nanostructures.

    PubMed

    Wang, Xianliang; Liu, Xin; Zhu, Dewei; Swihart, Mark T

    2014-08-01

    Self-doped Cu2-xS nanocrystals (NCs) were converted into monodisperse Cu2-xS-Au2S NCs of tunable composition, including pure Au2S, by cation exchange. The near-infrared (NIR) localized surface plasmon resonance (LSPR) was dampened and red-shifted with increasing Au content. Cation exchange was accompanied by elimination of cation vacancies and a change in crystal structure. Partially exchanged Cu2-xS-Au2S core/shell structures evolved to dumbbell-like structures under electron irradiation in the transmission electron microscope (TEM).

  16. Unfolding and aggregation of monoclonal antibodies on cation exchange columns: effects of resin type, load buffer, and protein stability.

    PubMed

    Guo, Jing; Carta, Giorgio

    2015-04-01

    The chromatographic behavior of a monoclonal antibody (mAb) that exhibits a pronounced two-peak elution behavior is studied for a range of strong cation exchange resins and with varying load buffer pH and composition. Six stationary phases are considered, including two tentacle-type resins (Fractogel EMD SO3-(M) and Eshmuno S), a resin with grafted polymeric surface extenders (Nuvia S), a resin with a bimodal pore size distribution (POROS HS 50), and two macroporous resins without polymer grafts (Source 30S and UNOsphere Rapid S). The two-peak elution behavior is very pronounced for the tentacle and polymer-grafted resins and for POROS HS 50, but is essentially absent for the two macroporous resins. The extent of this behavior decreases as the buffer pH and concentration increase and, consequently, mAb binding becomes weaker. Replacing sodium with arginine as the buffer counterion, which is expected to decrease the mAb binding strength, nearly completely eliminates the two-peak behavior, while replacing sodium with tetra-n-butylammonium hydroxide, which is expected to increase the mAb binding strength, dramatically exacerbate the effect. As shown by hydrogen-deuterium exchange mass spectrometry (HX-MS), the two-peak elution behavior is related to conformational changes that occur when the mAb binds. These changes result in increased solvent exposure of specific peptides in the Fc-region for either the Fractogel or the Nuvia resin. No significant conformational changes were seen by HX-MS when the mAb was bound to the UNOsphere resin or on the Fractogel resin when arginine was used in lieu of sodium as the load buffer counterion. Experiments with two additional mAbs on the Fractogel resin show that the two-peak elution behavior is dependent on the particular antibody. Circular dichroism suggests that the propensity of different mAbs to either precipitate directly or to form stabilizing intermolecular structures upon exposure to thermal stress can be related to their

  17. The effect of geometrical presentation of multimodal cation-exchange ligands on selective recognition of hydrophobic regions on protein surfaces.

    PubMed

    Woo, James; Parimal, Siddharth; Brown, Matthew R; Heden, Ryan; Cramer, Steven M

    2015-09-18

    The effects of spatial organization of hydrophobic and charged moieties on multimodal (MM) cation-exchange ligands were examined by studying protein retention behavior on two commercial chromatographic media, Capto™ MMC and Nuvia™ cPrime™. Proteins with extended regions of surface-exposed aliphatic residues were found to have enhanced retention on the Capto MMC system as compared to the Nuvia cPrime resin. The results further indicated that while the Nuvia cPrime ligand had a strong preference for interactions with aromatic groups, the Capto MMC ligand appeared to interact with both aliphatic and aromatic clusters on the protein surfaces. These observations were formalized into a new set of protein surface property descriptors, which quantified the local distribution of electrostatic and hydrophobic potentials as well as distinguishing between aromatic and aliphatic properties. Using these descriptors, high-performing quantitative structure-activity relationship (QSAR) models (R(2)>0.88) were generated for both the Capto MMC and Nuvia cPrime datasets at pH 5 and pH 6. Descriptors of electrostatic properties were generally common across the four models; however both Capto MMC models included descriptors that quantified regions of aliphatic-based hydrophobicity in addition to aromatic descriptors. Retention was generally reduced by lowering the ligand densities on both MM resins. Notably, elution order was largely unaffected by the change in surface density, but smaller and more aliphatic proteins tended to be more affected by this drop in ligand density. This suggests that modulating the exposure, shape and density of the hydrophobic moieties in multimodal chromatographic systems can alter the preference for surface exposed aliphatic or aromatic residues, thus providing an additional dimension for modulating the selectivity of MM protein separation systems. PMID:26292626

  18. Estimation of soil cation exchange capacity using Genetic Expression Programming (GEP) and Multivariate Adaptive Regression Splines (MARS)

    NASA Astrophysics Data System (ADS)

    Emamgolizadeh, S.; Bateni, S. M.; Shahsavani, D.; Ashrafi, T.; Ghorbani, H.

    2015-10-01

    The soil cation exchange capacity (CEC) is one of the main soil chemical properties, which is required in various fields such as environmental and agricultural engineering as well as soil science. In situ measurement of CEC is time consuming and costly. Hence, numerous studies have used traditional regression-based techniques to estimate CEC from more easily measurable soil parameters (e.g., soil texture, organic matter (OM), and pH). However, these models may not be able to adequately capture the complex and highly nonlinear relationship between CEC and its influential soil variables. In this study, Genetic Expression Programming (GEP) and Multivariate Adaptive Regression Splines (MARS) were employed to estimate CEC from more readily measurable soil physical and chemical variables (e.g., OM, clay, and pH) by developing functional relations. The GEP- and MARS-based functional relations were tested at two field sites in Iran. Results showed that GEP and MARS can provide reliable estimates of CEC. Also, it was found that the MARS model (with root-mean-square-error (RMSE) of 0.318 Cmol+ kg-1 and correlation coefficient (R2) of 0.864) generated slightly better results than the GEP model (with RMSE of 0.270 Cmol+ kg-1 and R2 of 0.807). The performance of GEP and MARS models was compared with two existing approaches, namely artificial neural network (ANN) and multiple linear regression (MLR). The comparison indicated that MARS and GEP outperformed the MLP model, but they did not perform as good as ANN. Finally, a sensitivity analysis was conducted to determine the most and the least influential variables affecting CEC. It was found that OM and pH have the most and least significant effect on CEC, respectively.

  19. Evaluation of strong cation exchange versus isoelectric focusing of peptides for multidimensional liquid chromatography-tandem mass spectrometry.

    PubMed

    Slebos, Robbert J C; Brock, Jonathan W C; Winters, Nancy F; Stuart, Sarah R; Martinez, Misti A; Li, Ming; Chambers, Mathew C; Zimmerman, Lisa J; Ham, Amy J; Tabb, David L; Liebler, Daniel C

    2008-12-01

    Shotgun proteome analysis platforms based on multidimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS) provide a powerful means to discover biomarker candidates in tissue specimens. Analysis platforms must balance sensitivity for peptide detection, reproducibility of detected peptide inventories and analytical throughput for protein amounts commonly present in tissue biospecimens (< 100 microg), such that platform stability is sufficient to detect modest changes in complex proteomes. We compared shotgun proteomics platforms by analyzing tryptic digests of whole cell and tissue proteomes using strong cation exchange (SCX) and isoelectric focusing (IEF) separations of peptides prior to LC-MS/MS analysis on a LTQ-Orbitrap hybrid instrument. IEF separations provided superior reproducibility and resolution for peptide fractionation from samples corresponding to both large (100 microg) and small (10 microg) protein inputs. SCX generated more peptide and protein identifications than did IEF with small (10 microg) samples, whereas the two platforms yielded similar numbers of identifications with large (100 microg) samples. In nine replicate analyses of tryptic peptides from 50 microg colon adenocarcinoma protein, overlap in protein detection by the two platforms was 77% of all proteins detected by both methods combined. IEF more quickly approached maximal detection, with 90% of IEF-detectable medium abundance proteins (those detected with a total of 3-4 peptides) detected within three replicate analyses. In contrast, the SCX platform required six replicates to detect 90% of SCX-detectable medium abundance proteins. High reproducibility and efficient resolution of IEF peptide separations make the IEF platform superior to the SCX platform for biomarker discovery via shotgun proteomic analyses of tissue specimens.

  20. Aromatic C-H Bond Functionalization Induced by Electrochemically in Situ Generated Tris(p-bromophenyl)aminium Radical Cation: Cationic Chain Reactions of Electron-Rich Aromatics with Enamides.

    PubMed

    Li, Long-Ji; Jiang, Yang-Ye; Lam, Chiu Marco; Zeng, Cheng-Chu; Hu, Li-Ming; Little, R Daniel

    2015-11-01

    An effective Friedel-Crafts alkylation reaction of electron-rich aromatics with N-vinylamides, induced by electrochemically in situ-generated TBPA radical cation, has been developed; the resulting adducts are produced in good to excellent yields. In the "ex-cell" type electrolysis, TBPA is transformed to its oxidized form in situ and subsequently employed as an electron transfer reagent to initiate a cationic chain reaction. An easily recoverable and reusable polymeric ionic liquid-carbon black (PIL-CB) composite was also utilized as a supporting electrolyte for the electrochemical generation of TBPA cation radical, without sacrificing efficiency or stability after four electrolyses. Cyclic voltammetry analysis and the results of control experiments demonstrate that the reaction of electron-rich aromatics and N-vinylamides occurs via a cationic chain reaction, which takes place though an oxidative activation of a C-H bond of electron-rich aromatics instead of oxidation of the N-vinylamide as previously assumed.

  1. Aromatic C-H Bond Functionalization Induced by Electrochemically in Situ Generated Tris(p-bromophenyl)aminium Radical Cation: Cationic Chain Reactions of Electron-Rich Aromatics with Enamides.

    PubMed

    Li, Long-Ji; Jiang, Yang-Ye; Lam, Chiu Marco; Zeng, Cheng-Chu; Hu, Li-Ming; Little, R Daniel

    2015-11-01

    An effective Friedel-Crafts alkylation reaction of electron-rich aromatics with N-vinylamides, induced by electrochemically in situ-generated TBPA radical cation, has been developed; the resulting adducts are produced in good to excellent yields. In the "ex-cell" type electrolysis, TBPA is transformed to its oxidized form in situ and subsequently employed as an electron transfer reagent to initiate a cationic chain reaction. An easily recoverable and reusable polymeric ionic liquid-carbon black (PIL-CB) composite was also utilized as a supporting electrolyte for the electrochemical generation of TBPA cation radical, without sacrificing efficiency or stability after four electrolyses. Cyclic voltammetry analysis and the results of control experiments demonstrate that the reaction of electron-rich aromatics and N-vinylamides occurs via a cationic chain reaction, which takes place though an oxidative activation of a C-H bond of electron-rich aromatics instead of oxidation of the N-vinylamide as previously assumed. PMID:26444498

  2. Cationic polymers for DNA origami coating - examining their binding efficiency and tuning the enzymatic reaction rates

    NASA Astrophysics Data System (ADS)

    Kiviaho, Jenny K.; Linko, Veikko; Ora, Ari; Tiainen, Tony; Järvihaavisto, Erika; Mikkilä, Joona; Tenhu, Heikki; Nonappa, Affc; Kostiainen, Mauri A.

    2016-06-01

    DNA origamis are fully tailored, programmable, biocompatible and readily functionalizable nanostructures that provide an excellent foundation for the development of sophisticated drug-delivery systems. However, the DNA origami objects suffer from certain drawbacks such as low cell-transfection rates and low stability. A great deal of studies on polymer-based transfection agents, mainly focusing on polyplex formation and toxicity, exists. In this study, the electrostatic binding between a brick-like DNA origami and cationic block-copolymers was explored. The effect of the polymer structure on the binding was investigated and the toxicity of the polymer-origami complexes evaluated. The study shows that all of the analyzed polymers had a suitable binding efficiency irrespective of the block structure. It was also observed that the toxicity of polymer-origami complexes was insignificant at the biologically relevant concentration levels. Besides brick-like DNA origamis, tubular origami carriers equipped with enzymes were also coated with the polymers. By adjusting the amount of cationic polymers that cover the DNA structures, we showed that it is possible to control the enzyme kinetics of the complexes. This work gives a starting point for further development of biocompatible and effective polycation-based block copolymers that can be used in coating different DNA origami nanostructures for various bioapplications.DNA origamis are fully tailored, programmable, biocompatible and readily functionalizable nanostructures that provide an excellent foundation for the development of sophisticated drug-delivery systems. However, the DNA origami objects suffer from certain drawbacks such as low cell-transfection rates and low stability. A great deal of studies on polymer-based transfection agents, mainly focusing on polyplex formation and toxicity, exists. In this study, the electrostatic binding between a brick-like DNA origami and cationic block-copolymers was explored. The

  3. The role of monovalent cations in the ATPase reaction of DNA gyrase

    PubMed Central

    Hearnshaw, Stephen James; Chung, Terence Tsz-Hong; Stevenson, Clare Elizabeth Mary; Maxwell, Anthony; Lawson, David Mark

    2015-01-01

    Four new crystal structures of the ATPase domain of the GyrB subunit of Escherichia coli DNA gyrase have been determined. One of these, solved in the presence of K+, is the highest resolution structure reported so far for this domain and, in conjunction with the three other structures, reveals new insights into the function of this domain. Evidence is provided for the existence of two monovalent cation-binding sites: site 1, which preferentially binds a K+ ion that interacts directly with the α-phosphate of ATP, and site 2, which preferentially binds an Na+ ion and the functional significance of which is not clear. The crystallographic data are corroborated by ATPase data, and the structures are compared with those of homologues to investigate the broader conservation of these sites. PMID:25849408

  4. Enzyme-substrate complementarity governs access to a cationic reaction manifold in the P450(BM3)-catalysed oxidation of cyclopropyl fatty acids.

    PubMed

    Cryle, Max J; Hayes, Patricia Y; De Voss, James J

    2012-12-01

    The products of cytochrome P450(BM3)-catalysed oxidation of cyclopropyl-containing dodecanoic acids are consistent with the presence of a cationic reaction intermediate, which results in efficient dehydrogenation of the rearranged probes by the enzyme. These results highlight the importance of enzyme-substrate complementarity, with a cationic intermediate occurring only when the probes used begin to diverge from ideal substrates for this enzyme. This also aids in reconciling literature reports supporting the presence of cationic intermediates with certain cytochrome P450 enzyme/substrate pairs. PMID:23109039

  5. Development and validation of S-allyl-L-cysteine in rat plasma using a mixed-mode reversed-phase and cation-exchange LC-ESI-MS/MS method: application to pharmacokinetic studies.

    PubMed

    Lee, Sanghee; Chang, Nae In; Yoo, Miyoung; Choi, Jung Hoon; Shin, Dongbin

    2015-01-01

    S-Allyl-L-cysteine (SAC), the most abundant organosulfur compound derived from garlic, has multifunctional biological activities that occur via different mechanisms. A sensitive, rapid and simple LC-ESI-MS/MS method using a mixed-mode reversed-phase and cation-exchange column containing C18 silica particles and sulfonic acid cation-exchange particles has been developed and validated for the analysis of SAC in rat plasma. The mobile phase was optimized at 2 mM ammonium acetate buffer (pH = 3.5) and acetonitrile (75:25, v/v). The assay utilized 0.6% acetic acid in methanol to achieve simple and rapid deproteinization. Quantification was conducted using multiple reaction monitoring (MRM) of the transitions of m/z 162.0 → 145.0 for SAC. The standard curve for SAC was linear (r(2) ≥ 0.999) over a range from 5 to 2,500 ng/mL. The intra- and interday precision (relative standard deviation) of the method was not >6.0% at three quality control levels. The limit of quantification (LOQ) was 5.0 ng/mL. After being fully validated, the method was successfully applied to the pharmacokinetic monitoring of SAC in rat plasma. PMID:24668040

  6. Functionalized alkynyl-chlorogermanes: hydrometallation, Ge-Cl bond activation, Ge-H bond formation and chlorine-tert-butyl exchange via a transient germyl cation.

    PubMed

    Honacker, Christian; Qu, Zheng-Wang; Tannert, Jens; Layh, Marcus; Hepp, Alexander; Grimme, Stefan; Uhl, Werner

    2016-04-14

    Treatment of alkynyl-arylchlorogermanes ArylnGe(Cl)(C[triple bond, length as m-dash]C-(t)Bu)3-n (n = 1, 2) with HM(t)Bu2 (M = Al, Ga) yielded mixed Al or Ga alkenyl-alkynylchlorogermanes via hydrometallation reactions. Intramolecular interactions between the Lewis-basic Cl atoms and the Lewis-acidic Al or Ga atoms afforded MCGeCl heterocycles. The endocyclic M-Cl distances were significantly lengthened compared to the starting compounds and indicated Ge-Cl bond activation. Dual hydrometallation succeeded only with HGa(t)Bu2. One Ga atom of the product was involved in a Ga-Cl bond, while the second one had an interaction to a C-H bond of a phenyl group. In two cases treatment of chlorogermanes with two equivalents of HAl(t)Bu2 resulted in hydroalumination of one alkynyl group and formation of unprecedented Ge-H functionalized germanes, Aryl-Ge(H)(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2)[double bond, length as m-dash]C(H)-(t)Bu] (Aryl = mesityl, triisopropylphenyl). The Al atoms of these compounds interacted with the α-C atoms of the alkynyl groups. Ph(Cl)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C(Al(t)Bu2}[double bond, length as m-dash]C(H)-(t)Bu] reacted in an unusual Cl/(t)Bu exchange to yield the tert-butylgermane Ph((t)Bu)Ge(C[triple bond, length as m-dash]C-(t)Bu)[C{Al((t)Bu)(Cl)}[double bond, length as m-dash]C(H)-(t)Bu]. Quantum chemical calculations suggested the formation of a germyl cation as a transient intermediate.

  7. Development and application of a new method to extract bacterial DNA from soil based on separation of bacteria from soil with cation-exchange resin.

    PubMed

    Jacobsen, C S; Rasmussen, O F

    1992-08-01

    A new method for the extraction of bacterial DNA from soil has been developed. Soil samples of 50 g were dispersed, and bacteria were released by use of a cation-exchange resin; subsequently, bacteria were separated from soil particles by low-speed centrifugation and lysed with lysozyme and ionic detergent, and the DNA was then purified by CsCl-ethidium bromide equilibrium density centrifugation. The extracted DNA was of high molecular weight and sufficiently pure for restriction enzyme digestion, DNA-DNA hybridization, and amplification by the polymerase chain reaction. The advantages of the new method are that the separation of bacteria from soil is considerably faster than by repeated blending, more samples can be handled, and furthermore no aerosols are formed during separation. Also, we investigated whether the CsCl-ethidium bromide equilibrium density centrifugation could be replaced by purification using Gene-Clean. However, this method produced DNAs which were insufficiently pure for several types of analysis. The new method was used to study survival of a 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading Pseudomonas cepacia DBO1 (pRO101) in unamended soil and in soil amended with 2,4-D. We found that the degrading strain, irrespective of inoculation level, was able to grow to the same high numbers in soil amended with 2,4-D, while the strain in nonamended soil were maintained at the inoculation level. Detection based on DNA extraction and subsequent dot blot DNA-DNA hybridization was in accordance with detection by plating on selective medium. PMID:16348750

  8. NN-->NNπ reaction near threshold in a covariant one-boson-exchange model

    NASA Astrophysics Data System (ADS)

    Shyam, R.; Mosel, U.

    1998-04-01

    We calculate the cross sections for the p(p,nπ+)p and p(p,pπ0)p reactions for proton beam energies near threshold in a covariant one-boson-exchange model, which incorporates the exchange of π, ρ, σ and ω mesons, treats both nucleon and delta isobar as intermediate states. The final state interaction effects are included within the Watson's theory. Within this model the ω and σ meson exchange terms contribute significantly at these energies, which, along with other meson exchanges, make it possible to reproduce the available experimental data for the total as well as differential cross sections for both the reactions. The cross sections at beam energies <=300 MeV are found to be almost free from the contributions of the Δ isobar excitation.

  9. Role of the aerosol phase state in ammonia/amines exchange reactions.

    PubMed

    Chan, Lap P; Chan, Chak K

    2013-06-01

    The exchange reaction of ammonia in (NH4)2SO4 with an amine and the corresponding reverse reaction of amines in aminium sulfates with ammonia were investigated using an electrodynamic balance coupled with a Raman spectrometer. The temporal changes in particle mass, chemical composition, and phase state were simultaneously monitored. When the salt particles were in an aqueous state at elevated relative humidities (RHs), the exchange of ammonia/amine vapors in the particle phase was reversible. The exchange rates of aqueous particles were in general higher than those of their corresponding solid counterparts. An aqueous phase was essential for the effective displacement of ammonia and amines. Aminium salts in different phase states and with different evaporation characteristics showed remarkably different reaction behaviors in ammonia vapor. The less compact amorphous aminium sulfate solids were more susceptible to ammonia exchange than the crystalline solids. The aminium salts in a liquid state exhibited substantial amine evaporation at <3% RH and formed acidic bisulfate. Under ammonia exposure, these acidic aminium droplets underwent both neutralization and displacement reactions. Stable solid salts containing ammonium, aminium, sulfate, and bisulfate were formed and hindered further reactions. The result suggests that ambient aminium sulfates may be acidic. Overall, the phase states of the ammonium and aminium salt particles crucially determine the heterogeneous reaction rates and final product properties and identities. PMID:23668831

  10. EXFOR BASICS A SHORT GUIDE TO THE NEUTRON REACTION DATA EXCHANGE FORMAT.

    SciTech Connect

    MCLANE,V.; NUCLEAR DATA CENTER NETWORK

    2000-05-19

    This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear reaction data between the Nuclear Reaction Data Centers. In addition to storing the data and its' bibliographic information, experimental information is also compiled. The status (e.g., the source of the data) and history (e.g., date of last update) of the data set is also included. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear reaction data centers. It was originally conceived for the exchange of neutron data and was developed through discussions among personnel from centers situated in Saclay, Vienna, Livermore and Brookhaven. It was accepted as the official exchange format of the neutron data centers at Saclay, Vienna, Brookhaven and Obninsk, at a meeting held in November 1969. As a result of two meetings held in 1975 and 1976 and attended by several charged-particle data centers, the format was further developed and adapted to cover all nuclear reaction data. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center's own sphere of responsibility. The EXFOR format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in a format: that is machine-readable (for checking and indicating possible errors); that can be read by personnel (for passing judgment on and correcting errors). The data presently included in the EXFOR exchange file include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle-induced reaction data, a selected compilation of photon-induced reaction data.

  11. EXFOR BASICS A SHORT GUIDE TO THE NEUTRON REACTION DATA EXCHANGE FORMAT.

    SciTech Connect

    MCLANE,V.; NUCLEAR DATA CENTER NETWORK

    2000-05-19

    This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear reaction data between the Nuclear Reaction Data Centers. In addition to storing the data and its' bibliographic information, experimental information is also compiled. The status (e.g., the source of the data) and history (e.g., date of last update) of the data set is also included. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear reaction data centers. It was originally conceived for the exchange of neutron data and was developed through discussions among personnel from centers situated in Saclay, Vienna, Livermore and Brookhaven. It was accepted as the official exchange format of the neutron data centers at Saclay, Vienna, Brookhaven and Obninsk, at a meeting held in November 1969.3 As a result of two meetings held in 1975 and 1976 and attended by several charged-particle data centers, the format was further developed and adapted to cover all nuclear reaction data. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center's own sphere of responsibility. The EXFOR format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in a format: l that is machine-readable (for checking and indicating possible errors); l that can be read by personnel (for passing judgment on and correcting errors). The data presently included in the EXFOR exchange file include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle-induced reaction data, a selected compilation of photon-induced reaction data.

  12. Reaction chemistry and ligand exchange at cadmium selenide nanocrystal surfaces

    SciTech Connect

    Owen, Jonathan; Park, Jungwon; Trudeau, Paul-Emile; Alivisatos, A. Paul

    2008-12-02

    Chemical modification of nanocrystal surfaces is fundamentally important to their assembly, their implementation in biology and medicine, and greatly impacts their electrical and optical properties. However, it remains a major challenge owing to a lack of analytical tools to directly determine nanoparticle surface structure. Early nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) studies of CdSe nanocrystals prepared in tri-n-octylphosphine oxide (1) and tri-n-octylphosphine (2), suggested these coordinating solvents are datively bound to the particle surface. However, assigning the broad NMR resonances of surface-bound ligands is complicated by significant concentrations of phosphorus-containing impurities in commercial sources of 1, and XPS provides only limited information about the nature of the phosphorus containing molecules in the sample. More recent reports have shown the surface ligands of CdSe nanocrystals prepared in technical grade 1, and in the presence of alkylphosphonic acids, include phosphonic and phosphinic acids. These studies do not, however, distinguish whether these ligands are bound datively, as neutral, L-type ligands, or by X-type interaction of an anionic phosphonate/phosphinate moiety with a surface Cd{sup 2+} ion. Answering this question would help clarify why ligand exchange with such particles does not proceed generally as expected based on a L-type ligand model. By using reagents with reactive silicon-chalcogen and silicon-chlorine bonds to cleave the ligands from the nanocrystal surface, we show that our CdSe and CdSe/ZnS core-shell nanocrystal surfaces are likely terminated by X-type binding of alkylphosphonate ligands to a layer of Cd{sup 2+}/Zn{sup 2+} ions, rather than by dative interactions. Further, we provide spectroscopic evidence that 1 and 2 are not coordinated to our purified nanocrystals.

  13. Cation exchange synthesis of uniform PbSe/PbS core/shell tetra-pods and their use as near-infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Mishra, N.; Mukherjee, B.; Xing, G.; Chakrabortty, S.; Guchhait, A.; Lim, J. Y.

    2016-07-01

    In this work we explore the preparation of complex-shaped semiconductor nanostructures composed of different materials via a cationic exchange process in which the cations of the original semiconductor nanostructure are replaced by cations of different metals with preservation of the shape and the anionic framework of the nanocrystals. Utilizing this cation exchange method, we synthesized two new tetrapods for the first time: Cu2-xSe/Cu2-xS and PbSe/PbS, both prepared from CdSe/CdS tetrapods as `templates'. We also fabricated near-infrared (NIR) photodetectors with a very simple architecture comprising a PbSe/PbS tetrapod layer between two Au electrodes on a glass substrate. When illuminated by a NIR laser, these devices are capable of achieving a responsivity of 11.9 A W-1 without the use of ligand-exchange processes, thermal annealing or hybrid device architecture. Transient absorption spectroscopy was carried out on these PbSe/PbS tetrapods, the results of which suggest that the branched morphology contributes in part to device performance. Investigation of the charge dynamics of the PbSe/PbS tetrapods revealed an extremely long-lived exciton recombination lifetime of ~17 ms, which can result in enhanced photoconductive gain. Overall, these heterostructured tetrapods showcase simultaneously the importance of nanoparticle shape, band structure, and surface chemistry in the attainment of NIR photodetection.In this work we explore the preparation of complex-shaped semiconductor nanostructures composed of different materials via a cationic exchange process in which the cations of the original semiconductor nanostructure are replaced by cations of different metals with preservation of the shape and the anionic framework of the nanocrystals. Utilizing this cation exchange method, we synthesized two new tetrapods for the first time: Cu2-xSe/Cu2-xS and PbSe/PbS, both prepared from CdSe/CdS tetrapods as `templates'. We also fabricated near-infrared (NIR) photodetectors

  14. A molecular dynamics study of bond exchange reactions in covalent adaptable networks.

    PubMed

    Yang, Hua; Yu, Kai; Mu, Xiaoming; Shi, Xinghua; Wei, Yujie; Guo, Yafang; Qi, H Jerry

    2015-08-21

    Covalent adaptable networks are polymers that can alter the arrangement of network connections by bond exchange reactions where an active unit attaches to an existing bond then kicks off its pre-existing peer to form a new bond. When the polymer is stretched, bond exchange reactions lead to stress relaxation and plastic deformation, or the so-called reforming. In addition, two pieces of polymers can be rejoined together without introducing additional monomers or chemicals on the interface, enabling welding and reprocessing. Although covalent adaptable networks have been researched extensively in the past, knowledge about the macromolecular level network alternations is limited. In this study, molecular dynamics simulations are used to investigate the macromolecular details of bond exchange reactions in a recently reported epoxy system. An algorithm for bond exchange reactions is first developed and applied to study a crosslinking network formed by epoxy resin DGEBA with the crosslinking agent tricarballylic acid. The trace of the active units is tracked to show the migration of these units within the network. Network properties, such as the distance between two neighboring crosslink sites, the chain angle, and the initial modulus, are examined after each iteration of the bond exchange reactions to provide detailed information about how material behaviors and macromolecular structure evolve. Stress relaxation simulations are also conducted. It is found that even though bond exchange reactions change the macroscopic shape of the network, microscopic network characteristic features, such as the distance between two neighboring crosslink sites and the chain angle, relax back to the unstretched isotropic state. Comparison with a recent scaling theory also shows good agreement.

  15. Scaling Hydrologic Exchange Flows and Biogeochemical Reactions from Bedforms to Basins

    NASA Astrophysics Data System (ADS)

    Harvey, J. W.; Gomez-Velez, J. D.

    2015-12-01

    River water moves in and out of the main channel along pathways that are perpendicular to the channel's main axis that flow across or beneath the ground surface. These hydrologic exchange flows (HEFs) are difficult to measure, yet no less important than a river's downstream flow, or exchanges with the atmosphere and deeper groundwater (Harvey and Gooseff, 2015, WRR). There are very few comprehensive investigations of exchange fluxes to understand patterns with river size and relative importance of specific types of exchanges. We used the physically based model NEXSS to simulate multiple scales of hyporheic flow and their cumulative effects on solute reaction in large basins (on the order of Chesapeake Bay basin or larger). Our goal was to explain where and when particular types of hyporheic flow are important in enhancing key biogeochemical reactions, such as organic carbon respiration and denitrification. Results demonstrate that hyporheic flux (expressed per unit area of streambed) varies surprisingly little across the continuum of first-order streams to eighth-order rivers, and vertical exchange beneath small bedforms dominates in comparison with lateral flow beneath gravel bars and meanders. Also, the river's entire volume is exchanged many times with hyporheic flow within a basin, and the turnover length (after one entire river volume is exchanged) is strongly influenced by hydrogeomorphic differences between physiographic regions as well as by river size. The cumulative effects on biogeochemical reactions were assessed using a the reaction significance factor, RSF, which computes the cumulative potential for hyporheic reactions using a dimensionless index that balances reaction progress in a single hyporheic flow path against overall processing efficiency of river turnover through hyporheic flow paths of that type. Reaction significance appears to be strongly dominated by hydrologic factors rather than biogeochemical factors, and seems to be dominated by

  16. Arrhenius' law in turbulent media and an equivalent tunnel effect. [in binary exchange chemical reactions

    NASA Technical Reports Server (NTRS)

    Tsuge, S.; Sagara, K.

    1978-01-01

    The indeterminacy inherent to the formal extension of Arrhenius' law to reactions in turbulent flows is shown to be surmountable in the case of a binary exchange reaction with a sufficiently high activation energy. A preliminary calculation predicts that the turbulent reaction rate is invariant in the Arrhenius form except for an equivalently lowered activation energy. This is a reflection of turbulence-augmented molecular vigor, and causes an appreciable increase in the reaction rate. A similarity to the tunnel effect in quantum mechanics is indicated. The anomaly associated with the mild ignition of oxy-hydrogen mixtures is discussed in this light.

  17. Effect of cation-exchange pretreatment of aqueous soil extracts on the gas chromatographic-mass spectrometric determination of nerve agent hydrolysis products after tert.-butyldimethylsilylation.

    PubMed

    Kataoka, M; Tsunoda, N; Ohta, H; Tsuge, K; Takesako, H; Seto, Y

    1998-10-23

    The efficiency of pretreatment of aqueous soil extracts using a cation-exchange resin has been investigated by gas chromatographic-mass spectrometric (GC-MS) determination of nerve agent hydrolysis products after tert.-butyldimethylsilyl (TBDMS) derivatization. An aqueous solution containing methylphosphonic acid (MPA) and its monoalkyl esters, ethyl methylphosphonic acid, isopropyl methylphosphonic acid and pinacolyl methylphosphonic acid, was dried, and these phosphonic acids were derivatized with N-methyl-N-(tert.-butyldimethylsilyl)trifluoro-acetamide and analyzed by GC-MS. The yields of TBDMS derivatives were significantly decreased by the addition of calcium and magnesium ions to an aqueous solution (approximately 0.5 mM) before derivatization. The extent of lowered yields was related to the hydrophilicity of phosphonic acids. MPA and its monoalkyl esters were spiked into soil samples (sand, alluvial soil and volcanic ash soil), extracted with distilled water, dried, silylated and applied to GC-MS. The yields of TBDMS derivatives of monoalkyl esters from soil samples were low (3-42%) and MPA derivative was scarcely detected (yield: < 0.7%). By desalting the aqueous soil extract by passage through a strong cation-exchange resin, the yields of TBDMS derivatives of monoalkyl esters were significantly improved (12-69%) and MPA derivative was detected (yield: 2-36%). The extent of improved yields was related to the concentrations of divalent metal cations in aqueous soil extracts. In combination with desalting by the cation-exchange resin, GC-MS after TBDMS derivatization enables detection of nerve agent hydrolysis products in soils at sub-ppm (0.2 microgram/g) concentrations. PMID:9818434

  18. Cationic aluminum hydride complexes: reactions of carbene-alane adducts with trityl-borate.

    PubMed

    Cao, Levy L; Daley, Erika; Johnstone, Timothy C; Stephan, Douglas W

    2016-04-18

    Reaction of (Idipp)AlH3 with [Ph3C][B(C6F5)4] in toluene affords the dimeric aluminum dication [((Idipp)AlH(μ-H))2][B(C6F5)4]22. In contrast, the reaction of (IBn)AlH3 with [Ph3C][B(C6F5)4] in bromobenzene gives a redistribution product, the salt of a monomeric dication [(IBn)2AlH][B(C6F5)4]24. PMID:27001908

  19. Competition between abstraction and exchange channels in H + HCN reaction: Full-dimensional quantum dynamics

    SciTech Connect

    Jiang, Bin; Guo, Hua

    2013-12-14

    Dynamics of the title reaction is investigated on an ab initio based potential energy surface using a full-dimensional quantum wave packet method within the centrifugal sudden approximation. It is shown that the reaction between H and HCN leads to both the hydrogen exchange and hydrogen abstraction channels. The exchange channel has a lower threshold and larger cross section than the abstraction channel. It also has more oscillations due apparently to quantum resonances. Both channels are affected by long-lived resonances supported by potential wells. Comparison with experimental cross sections indicates underestimation of the abstraction barrier height.

  20. Competition between abstraction and exchange channels in H + HCN reaction: Full-dimensional quantum dynamics

    NASA Astrophysics Data System (ADS)

    Jiang, Bin; Guo, Hua

    2013-12-01

    Dynamics of the title reaction is investigated on an ab initio based potential energy surface using a full-dimensional quantum wave packet method within the centrifugal sudden approximation. It is shown that the reaction between H and HCN leads to both the hydrogen exchange and hydrogen abstraction channels. The exchange channel has a lower threshold and larger cross section than the abstraction channel. It also has more oscillations due apparently to quantum resonances. Both channels are affected by long-lived resonances supported by potential wells. Comparison with experimental cross sections indicates underestimation of the abstraction barrier height.

  1. Effects of cationic species on visual color formation in model Maillard reactions of pentose sugars and amino acids.

    PubMed

    Rizzi, George P

    2008-08-27

    Effects of cationic species on Maillard browning were examined after heating (ca. 100 degrees C) aqueous pH 7.2 buffered solutions of amino acids and pentose sugars. Metallic ions of Group I metals (Li, Na, K, Rb and Cs) produced a small increase in browning (A420), but somewhat greater effects were observed with ions of Group II metals Ca and Mg. Browning was suppressed by triethylammonium ion, but unaffected by a salt of the stronger base, guanidine. The quaternary amine salt choline chloride produced enhanced browning and served as a model for phospholipid involvement in Maillard reactions. With alpha,omega-diamino acids increases in browning were observed which related to lowered pK2 values resulting from positively charged omega-substituents in these molecules. PMID:18611025

  2. The partitioning of sulfur and chlorine between andesite melts and magmatic volatiles and the exchange coefficients of major cations

    NASA Astrophysics Data System (ADS)

    Zajacz, Zoltán; Candela, Philip A.; Piccoli, Philip M.; Sanchez-Valle, Carmen

    2012-07-01

    Andesite melts were equilibrated with an H-O-S-bearing volatile phase to determine the partition coefficients for S and Cl as a function of melt composition and oxygen fugacity. The experiments were conducted in rapid-quench MHC vessel assemblies at 200 MPa and 1000 °C, and over a range of imposed fO2 between NNO-1.2 and NNO+1.8. High fluid/melt mass ratios (∼15) were employed, allowing precise and accurate partition coefficients to be obtained by mass balance calculations. Chlorine exhibits Henrian behavior at ClO-0.5 activities typical for arc magmas, with D Cl volatile/melt = 1.36 ± 0.06 (1σ) below 0.2 wt.% Cl in the melt; at higher ClO-0.5 activities, D Cl volatile/melt increases linearly to 2.11 ± 0.02 at 1 wt.% Cl in the melt. In the volatile phase: FeCl2 ∼ NaCl > KCl ∼ HCl. The determination of cation exchange coefficients for major cations yielded: K K,Na volatile/melt = 1.23 ± 0.10 (1σ) and ∗K Fe,Na volatile/melt = D Fe volatile/melt / D Na volatile/melt = 1.08 ± 0.16 (1σ). Under these conditions, the concentration of HCl in the vapor is negatively correlated with the (Na + K)/(Al + Fe3+) ratio in the melt. Reduced sulfur (S2-) appears to obey Henry's law in andesite melt-volatile system at fH2S below pyrrhotite saturation. The partition coefficient for S at fO2 = NNO-0.5 correlates negatively with the FeO concentration in the melt, changing from 254 ± 25 at 4.0 wt.% FeO to 88 ± 6 at 7.5 wt.% FeO. Pyrrhotite saturation is reached when approximately 3.2 mol% S is present in the volatile phase at fO2 = NNO-0.5. At the sulfide/sulfate transition, the partition coefficient of S drops from 171 ± 23 to 21 ± 1 at a constant FeO content of ∼6 wt.% in the melt. At fO2 = NNO+1.8, anhydrite saturation is reached at ∼3.3 mol% S present in the volatile phase. Aqueous volatiles exsolving from intermediate to mafic magmas can efficiently extract S, and effect its

  3. (Pentamethylcyclopentadienyl)ruthenium complexes. 6. (Pentamethylcyclopentadienyl)(polyarene)ruthenium cations. Synthesis and electrochemical reaction

    SciTech Connect

    Koelle, U.; Wang, Maja Hong )

    1990-01-01

    By treatment of the alkoxo complex (Cp{sup *}Ru(OMe)){sub 2} with acid or trimethylsilyl trifluoromethanesulfonate in the presence of a polycyclic arene, the monocations Cp{sup *}Ru(arene){sup +} (arene = naphthalene ((1){sup +}), phenanthrene ((2){sup +}), pyrene ((3){sup +}), anthracene ((4){sup +})) and dications (Cp{sup *}Ru){sub 2}(arene){sup 2+} (arene = phenanthrene ((5){sup 2+}), pyrene ((6){sup 2+}), and anthracene ((7){sup 2+})) were synthesized. Electrochemistry (cyclic voltammetry) in dichloromethane or propylene carbonate shows all these complexes, in contrast to the case for (Cp or Cp{sup *})Ru(arene) (Cp = {eta}{sup 5}-C{sub 5}H{sub 5}, Cp{sup *} = {eta}{sup 5}-C{sub 5}Me{sub 5}) cations featuring an unfused aromatic ligand, to be reducible. Some of the electron couples are chemically reversible. Potentials and peak current ratios are discussed in terms of interaction of the Cp{sup *}Ru units and of stabilization of the reduction products.

  4. Energetics and Control of Ultracold Isotope-Exchange Reactions between Heteronuclear Dimers in External Fields

    NASA Astrophysics Data System (ADS)

    Tomza, Michał

    2015-08-01

    We show that isotope-exchange reactions between ground-state alkali-metal, alkaline-earth-metal, and lanthanide heteronuclear dimers consisting of two isotopes of the same atom are exothermic with an energy change in the range of 1-8000 MHz, thus resulting in cold or ultracold products. For these chemical reactions, there are only one rovibrational and at most several hyperfine possible product states. The number and energetics of open and closed reactive channels can be controlled by the laser and magnetic fields. We suggest a laser-induced isotope- and state-selective Stark shift control to tune the exothermic isotope-exchange reactions to become endothermic, thus providing the ground for testing models of the chemical reactivity. The present proposal opens the way for studying the state-to-state dynamics of ultracold chemical reactions beyond the universal limit with a meaningful control over the quantum states of both reactants and products.

  5. Energetics and Control of Ultracold Isotope-Exchange Reactions between Heteronuclear Dimers in External Fields.

    PubMed

    Tomza, Michał

    2015-08-01

    We show that isotope-exchange reactions between ground-state alkali-metal, alkaline-earth-metal, and lanthanide heteronuclear dimers consisting of two isotopes of the same atom are exothermic with an energy change in the range of 1-8000 MHz, thus resulting in cold or ultracold products. For these chemical reactions, there are only one rovibrational and at most several hyperfine possible product states. The number and energetics of open and closed reactive channels can be controlled by the laser and magnetic fields. We suggest a laser-induced isotope- and state-selective Stark shift control to tune the exothermic isotope-exchange reactions to become endothermic, thus providing the ground for testing models of the chemical reactivity. The present proposal opens the way for studying the state-to-state dynamics of ultracold chemical reactions beyond the universal limit with a meaningful control over the quantum states of both reactants and products.

  6. Catalysis in a Cage: Condition-Dependent Speciation and Dynamics of Exchanged Cu Cations in SSZ-13 Zeolites.

    PubMed

    Paolucci, Christopher; Parekh, Atish A; Khurana, Ishant; Di Iorio, John R; Li, Hui; Albarracin Caballero, Jonatan D; Shih, Arthur J; Anggara, Trunojoyo; Delgass, W Nicholas; Miller, Jeffrey T; Ribeiro, Fabio H; Gounder, Rajamani; Schneider, William F

    2016-05-11

    The relationships among the macroscopic compositional parameters of a Cu-exchanged SSZ-13 zeolite catalyst, the types and numbers of Cu active sites, and activity for the selective catalytic reduction (SCR) of NOx with NH3 are established through experimental interrogation and computational analysis of materials across the catalyst composition space. Density functional theory, stochastic models, and experimental characterizations demonstrate that within the synthesis protocols applied here and across Si:Al ratios, the volumetric density of six-membered-rings (6MR) containing two Al (2Al sites) is consistent with a random Al siting in the SSZ-13 lattice subject to Löwenstein's rule. Further, exchanged Cu(II) ions first populate these 2Al sites before populating remaining unpaired, or 1Al, sites as Cu(II)OH. These sites are distinguished and enumerated ex situ through vibrational and X-ray absorption spectroscopies (XAS) and chemical titrations. In situ and operando XAS follow Cu oxidation state and coordination environment as a function of environmental conditions including low-temperature (473 K) SCR catalysis and are rationalized through first-principles thermodynamics and ab initio molecular dynamics. Experiment and theory together reveal that the Cu sites respond sensitively to exposure conditions, and in particular that Cu species are solvated and mobilized by NH3 under SCR conditions. While Cu sites are spectroscopically and chemically distinct away from these conditions, they exhibit similar turnover rates, apparent activation energies and apparent reaction orders at the SCR conditions, even on zeolite frameworks other than SSZ13. PMID:27070199

  7. Insights in understanding aggregate formation and dissociation in cation exchange chromatography for a structurally unstable Fc-fusion protein.

    PubMed

    Chen, Zhiqiang; Huang, Chao; Chennamsetty, Naresh; Xu, Xuankuo; Li, Zheng Jian

    2016-08-19

    Cation-exchange chromatography (CEX) of a structurally unstable Fc-fusion protein exhibited multi-peak elution profile upon a salt-step elution due to protein aggregation during intra-column buffer transition where low pH and high salt coexisted. The protein exhibited a single-peak elution behavior during a pH-step elution; nevertheless, the levels of soluble aggregates (i.e. high molecular weight species, HMW) in the CEX eluate were still found up to 12-fold higher than that for the load material. The amount of the aggregates formed upon the pH-step elution was dependent on column loading with maximum HMW achieved at intermediate loading levels, supporting the hypothesis that the aggregation was the result of both the conformational changes of the bound protein and the solution concentration of the aggregation-susceptible proteins during elution. Factors such as high load pH, short protein/resin contact time, hydrophilic resin surface, and weak ionizable ligand were effective, to some extent, to reduce aggregate formation by improving the structural integrity of the bound protein. An orthogonal technique, differential scanning fluorimetry (DSF) using Sypro Orange dye confirmed that the bound protein exposed more hydrophobic area than the native molecule in free solution, especially in the pH 4-5 range. The Sypro Orange dye study of resin surface property also demonstrated that the poly[styrene-divinylbenzene]-based Poros XS with polyhydroxyl surface coating is more hydrophobic compared to the agarose-based CM Sepharose FF and SP Sepharose FF. The hydrophobic property of Poros XS contributed to stronger interactions with the partially unfolded bound protein and consequently to the higher aggregate levels seen in Poros XS eluate. This work also investigates the aggregation reversibility in CEX eluate where up to 66% of the aggregates were observed to dissociate into native monomers over a period of 120h, and links the aggregate stability to such conditions as resin

  8. Energy-loss cross sections for inclusive charge-exchange reactions at intermediate energies

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.; Townsend, Lawrence W.; Dubey, Rajendra R.

    1993-01-01

    Charge-exchange reactions for scattering to the continuum are considered in a high-energy multiple scattering model. Calculations for (p,n) and (He-3,H-3) reactions are made and compared with experimental results for C-12, O-16, and Al-27 targets. Coherent effects are shown to lead to an important role for inelastic multiple scattering terms when light projectiles are considered.

  9. Total synthesis of cephalosporolide E via a tandem radical/polar crossover reaction. The use of the radical cations under nonoxidative conditions in total synthesis.

    PubMed

    Cortezano-Arellano, Omar; Quintero, Leticia; Sartillo-Piscil, Fernando

    2015-03-01

    The present work reports the first example of the use of the chemistry of radical cations under nonoxidative conditions in total synthesis. Using a late-stage tandem radical/polar crossover reaction, a highly stereoselective total synthesis of cephalosporolide E (which is typically obtained admixed with cephalosporolide F) was accomplished. The reaction of a phthalimido derivative with triphenyltin radical in refluxing toluene engenders a contact ion-pair (radical cation) that leads, in the first instance, to the cephalosporolide F, which is transformed into the cephalosporolide E via a stereocontrolled spiroketal isomerization promoted by the diphenylphosphate acid that is formed during the tandem transformation.

  10. Effect of nickel hexaaluminate mirror cation on structure-sensitive reactions during n-tetradecane partial oxidation

    SciTech Connect

    Gardner, T H; Shekhawat, D; Berry, D A; Smith, M W; Salazar, M; Kugler, E L

    2007-04-30

    Reforming studies were conducted on nickel-substituted hexaaluminate catalysts, ANi0.4Al11.6O19-δ (A = La, Sr and Ba), to reform liquid hydrocarbon fuels into H2-rich synthesis gas for fuel cell applications. The reaction conditions studied were the partial oxidation of n-tetradecane (I) and n-tetradecane with 50 ppmw sulfur as dibenzothiophene (II). Hexaaluminate catalyst activity toward reaction conditions (I) and (II) as well as the surface Ni concentration and dispersion was shown to correlate with the type of mirror cation substituted into the lattice. The Ni surface concentration was determined by XPS to be 5.3, <0.1 and 0.7 wt.% for LaNi0.4Al11.6O19-δ, BaNi0.4Al11.6O19-δ and SrNi0.4Al11.6O19-δ, respectively. SrNi0.4Al11.6O19-δ and BaNi0.4Al11.6O19-δ catalysts exhibited stable performance for reaction condition (I), while the loss in activity exhibited over time by LaNi0.4Al11.6O19-δ suggested site blocking by carbon deposition. Under reaction condition (II), additional activity loss was experienced by both LaNi0.4Al11.6O19-δ and Al11.6O19-δ catalysts due to the presence of dibenzothiophene. However, LaNi0.4Al11.6O19-δ experienced more severe and partially reversible site blocking where SrNi0.4Al11.6O19-δ experienced a less severe loss of activity, selectivity and irreversible site blocking. The behavior observed in nickel-substituted hexaaluminate catalysts suggests that the different mirror cations influenced the coordination of Ni sites within the lattice and adsorption of hydrocarbons to the surface of the catalysts.

  11. Properties of ionic liquids on Au surfaces: non-conventional anion exchange reactions with carbonate.

    PubMed

    Ratel, Mathieu; Branca, Mathieu; Breault-Turcot, Julien; Zhao, Sandy Shuo; Chaurand, Pierre; Schmitzer, Andreea R; Masson, Jean-Francois

    2011-10-14

    A simple anion metathesis in diluted aqueous carbonate at room temperature affords 1-(12-mercaptododecyl)-3-methyl-imidazolium carbonate (MDMI-HCO(3)) from MDMI salts self-assembled on gold films and nanoparticles. The properties of MDMI-SAM differ from MDMI in solution, for which the anion exchange reaction does not proceed. PMID:21879044

  12. An anionic zeolite-like metal-organic framework (AZMOF) with a Moravia network for organic dye absorption through cation-exchange.

    PubMed

    Shen, Yu; Fan, Cong-Cong; Wei, Yu-Zhen; Du, Jie; Zhu, Hai-Bin; Zhao, Yue

    2016-07-01

    An anionic zeolite-like metal-organic framework (AZMOF) with a twisted partially augmented the net, known as the "Moravia" net, [(CH3)2NH2]6[Sr13(O)3()8(OH)2(H2O)16]·xS (, where S represents non-coordinated solvent molecules, and is the abbreviation of benzo-(1,2;3,4;5,6)-tris-(thiophene-2'-carboxylic acid)), has been solvothermally synthesized and characterized, which possesses an anionic framework and nano-sized sodalite cage. Through cation-exchange, is capable of uptaking large organic cationic dyes including Rhodamine B (RB), Basic Red 2 (BR2), Crystal Violet (CV) and Methylene Blue (MB), amongst which the adsorption capability for RB (up to 545 mg g(-1)), and BR2 (up to 675 mg g(-1)) is the highest for reported absorbants to date. PMID:27301344

  13. Use of a new tandem cation/anion exchange system with clinical-scale generators provides high specific volume solutions of technetium-99m and rhenium-188

    SciTech Connect

    Knapp, F.R. Jr.; Beets, A.L.; Mirzadeh, S.; Guhlke, S. |

    1998-03-01

    In this paper the authors describe the first application of a simple and inexpensive post elution tandem cation-anion exchange column system which is based on generator elution with salts of weak acids such as ammonium acetate instead of saline solution to provide very high specific volume solutions of technetium-99m and rhenium-188 from clinical scale molybdenum-99/technetium-99m generator prepared from low specific activity (n,y) molybdenum-99, and tungsten-188/rhenium-188 generators, respectively. Initial passage of the bolus through a strong cation exchange cartridge converts the ammonium acetate to acetic acid which is essentially not ionized at the acidic pH, allowing specific subsequent amine type (QMA SepPak{trademark}) anion exchange cartridge column trapping of the microscopic levels of the pertechnetate or perrhenate. Subsequent elution of the anion cartridge with a small volume (< 1 mL) of saline then provides high specific volume solutions of technetium-99m by concentration of the high eluant volumes obtained by elution of clinical-scale (1 Ci) generators. This new approach also works very effectively to obtain high specific volume solutions of rhenium-188 (> 500 mCi/mL) from the alumina-based tungsten-188/rhenium-188 generator.

  14. Solvation of exchangeable Cu/sup 2 +/ cations by primary alcohols in montmorillonite clay studied by electron spin resonance and electron spin echo modulation spectroscopies

    SciTech Connect

    Brown, D.R.; Kevan, L.

    1988-04-07

    A montmorillonite clay (STx-1), with Mg/sup 2 +/ as the major exchangeable cation and Cu/sup 2 +/ exchanged into 5% of the Mg/sup 2 +/ sites, is used to study the interaction between the exchangeable cations and adsorbed primary alcohols, methanol, ethanol, and 1-propanol, in the clay interlayer region. Electron spin resonance (ESR) shows that, on saturation of the clay with methanol, a freely rotating Cu/sup 2 +/ center is formed in the clay interlayer. Electron spin echo modulation (ESEM) spectroscopy indicates that the center is a four-coordinate Cu/sup 2 +/ solvate, in which the methanol ligands are in a square-planar configuration. On adsorption of ethanol into the interlayer region, a rotationally restricted Cu/sup 2 +/ center is detected. ESEM again indicates a four-coordinate, square-planar solvate, and ESR of oriented clay films reveals that the major symmetry axis of the ethanol-solvated Cu/sup 2 +/ center is perpendicular to the plane of the clay lattice. Similar ESP data are reported for 1-propanol-saturated montmorillonite, and a four-coordinate, square-planar Cu/sup 2 +/ solvate, similar to that described for ethanol, is proposed.

  15. Enrichment and low-level determination of glyphosate, aminomethylphosphonic acid and glufosinate in drinking water after cleanup by cation exchange resin.

    PubMed

    Küsters, Markus; Gerhartz, Michael

    2010-04-01

    For the determination of glyphosate, aminomethylphosphonic acid and glufosinate in drinking water, different procedures of enrichment and cleanup were examined using anion exchange or SPE. In many cases interactions of, e.g. alkaline earth metal ions especially calcium could be observed during enrichment and cleanup resulting in loss of analytes. For that reason, a novel cleanup and enrichment procedure for the determination of these phosphonic acid herbicides has been developed in drinking water using cation-exchange resin. In summary, the cleanup procedure with cation-exchange resin developed in this study avoids interactions as described above and is applicable to calcium-rich drinking water samples. After derivatization with 9-fluorenylmethylchloroformate followed by LC with fluorescence detection, LOD of 12, 14 and 12 ng/L and mean recoveries from real-world drinking water samples of 98+/-9, 100+/-16 and 101+/-11% were obtained for glyphosate, aminomethylphosphonic acid and glufosinate, respectively. The low LODs and the high precision permit the analysis of these phosphonic acid herbicides according to the guidelines of the European Commission.

  16. Analysis of Native-Like Proteins and Protein Complexes Using Cation to Anion Proton Transfer Reactions (CAPTR).

    PubMed

    Laszlo, Kenneth J; Bush, Matthew F

    2015-12-01

    Mass spectra of native-like protein complexes often exhibit narrow charge-state distributions, broad peaks, and contributions from multiple, coexisting species. These factors can make it challenging to interpret those spectra, particularly for mixtures with significant heterogeneity. Here we demonstrate the use of ion/ion proton transfer reactions to reduce the charge states of m/z-selected, native-like ions of proteins and protein complexes, a technique that we refer to as cation to anion proton transfer reactions (CAPTR). We then demonstrate that CAPTR can increase the accuracy of charge state assignments and the resolution of interfering species in native mass spectrometry. The CAPTR product ion spectra for pyruvate kinase exhibit ~30 peaks and enable unambiguous determination of the charge state of each peak, whereas the corresponding precursor spectra exhibit ~6 peaks and the assigned charge states have an uncertainty of ±3%. 15+ bovine serum albumin and 21+ yeast enolase dimer both appear near m/z 4450 and are completely unresolved in a mixture. After a single CAPTR event, the resulting product ions are baseline resolved. The separation of the product ions increases dramatically after each subsequent CAPTR event; 12 events resulted in a 3000-fold improvement in separation relative to the precursor ions. Finally, we introduce a framework for interpreting and predicting the figures of merit for CAPTR experiments. More generally, these results suggest that CAPTR strongly complements other mass spectrometry tools for analyzing proteins and protein complexes, particularly those in mixtures. Graphical Abstract ᅟ.

  17. Analysis of Native-Like Proteins and Protein Complexes Using Cation to Anion Proton Transfer Reactions (CAPTR)

    NASA Astrophysics Data System (ADS)

    Laszlo, Kenneth J.; Bush, Matthew F.

    2015-12-01

    Mass spectra of native-like protein complexes often exhibit narrow charge-state distributions, broad peaks, and contributions from multiple, coexisting species. These factors can make it challenging to interpret those spectra, particularly for mixtures with significant heterogeneity. Here we demonstrate the use of ion/ion proton transfer reactions to reduce the charge states of m/ z-selected, native-like ions of proteins and protein complexes, a technique that we refer to as cation to anion proton transfer reactions (CAPTR). We then demonstrate that CAPTR can increase the accuracy of charge state assignments and the resolution of interfering species in native mass spectrometry. The CAPTR product ion spectra for pyruvate kinase exhibit ~30 peaks and enable unambiguous determination of the charge state of each peak, whereas the corresponding precursor spectra exhibit ~6 peaks and the assigned charge states have an uncertainty of ±3%. 15+ bovine serum albumin and 21+ yeast enolase dimer both appear near m/ z 4450 and are completely unresolved in a mixture. After a single CAPTR event, the resulting product ions are baseline resolved. The separation of the product ions increases dramatically after each subsequent CAPTR event; 12 events resulted in a 3000-fold improvement in separation relative to the precursor ions. Finally, we introduce a framework for interpreting and predicting the figures of merit for CAPTR experiments. More generally, these results suggest that CAPTR strongly complements other mass spectrometry tools for analyzing proteins and protein complexes, particularly those in mixtures.

  18. Conferring specificity in redox pathways by enzymatic thiol/disulfide exchange reactions.

    PubMed

    Netto, Luis Eduardo S; de Oliveira, Marcos Antonio; Tairum, Carlos A; da Silva Neto, José Freire

    2016-01-01

    Thiol-disulfide exchange reactions are highly reversible, displaying nucleophilic substitutions mechanism (S(N)2 type). For aliphatic, low molecular thiols, these reactions are slow, but can attain million times faster rates in enzymatic processes. Thioredoxin (Trx) proteins were the first enzymes described to accelerate thiol-disulfide exchange reactions and their high reactivity is related to the high nucleophilicity of the attacking thiol. Substrate specificity in Trx is achieved by several factors, including polar, hydrophobic, and topological interactions through a groove in the active site. Glutaredoxin (Grx) enzymes also contain the Trx fold, but they do not share amino acid sequence similarity with Trx. A conserved glutathione binding site is a typical feature of Grx that can reduce substrates by two mechanisms (mono and dithiol). The high reactivity of Grx enzymes is related to the very acid pK(a) values of reactive Cys that plays roles as good leaving groups. Therefore, although distinct oxidoreductases catalyze similar thiol–disulfide exchange reactions, their enzymatic mechanisms vary. PDI and DsbA are two other oxidoreductases, but they are involved in disulfide bond formation, instead of disulfide reduction, which is related to the oxidative environment where they are found. PDI enzymes and DsbC are endowed with disulfide isomerase activity, which is related with their tetra-domain architecture. As illustrative description of specificity in thiol-disulfide exchange, redox aspects of transcription activation in bacteria, yeast, and mammals are presented in an evolutionary perspective. Therefore, thiol-disulfide exchange reactions play important roles in conferring specificity to pathways, a required feature for signaling.

  19. Stationary phase-related investigations of quinine-based zwitterionic chiral stationary phases operated in anion-, cation-, and zwitterion-exchange modes.

    PubMed

    Hoffmann, Christian V; Reischl, Roland; Maier, Norbert M; Lämmerhofer, Michael; Lindner, Wolfgang

    2009-02-13

    The concept of recently introduced Cinchona alkaloid-type zwitterionic chiral stationary phases (CSPs) is based on fusing key cation- and anion-exchange (CX, AX) moieties in one single low-molecular mass chiral selector (SO) with the resulting CSPs allowing enantiomer separations of a wide range of chiral ionizable analytes comprising acids, bases, and zwitterionic compounds. Herein, we report principal, systematic investigations of the ion-exchange-type retention mechanisms available with the novel zwitterionic CSPs in nonaqueous polar organic mode. Typical CX and AX processes, corresponding to the parent single ion exchangers, are confirmed also for zwitterionic CSPs. Also the mechanism leading to recognition and retention of zwitterions was found to be ion exchange mediated in a zwitterion-exchange (ZX) mode. In both AX and CX modes the additional ionizable group within the SO besides the site responsible for the respective ion-exchange process could be characterized as an intramolecular counterion (IMCI) that effectively participates in the ion-exchange equilibria and thus, contributes to solute elution. In the ZX mode both oppositely charged groups of the zwitterionic SO were found not only to be the sites for simultaneous ion pairing with the analyte but also functioned as IMCIs at the same time. The main practical consequences of the IMCI feature were significant reduction of the amounts and even elimination of acidic and basic additives required in the eluent systems to afford analyte elution while still providing faster analysis than the parent single ion-exchanger-type CSPs. The set of ten structurally different zwitterionic CSPs employed in this study facilitated the establishment of correlations between chromatographic behavior of the CSPs with particular SO elements, thereby supporting the understanding of the working principles of these novel packing materials on a molecular level.

  20. Competition between charge exchange and chemical reaction - The D2/+/ + H system

    NASA Technical Reports Server (NTRS)

    Preston, R. K.; Cross, R. J., Jr.

    1973-01-01

    Study of the special features of molecular charge exchange and its competition with chemical reaction in the case of the D2(+) + H system. The trajectory surface hopping (TSH) model proposed by Tully and Preston (1971) is used to study this competition for a number of reactions involving the above system. The diatomics-in-molecules zero-overlap approximation is used to calculate the three adiabatic surfaces - one triplet and two singlet - which are needed to describe this system. One of the significant results of this study is that the chemical reaction and charge exchange are strongly coupled. It is also found that the number of trajectories passing into the chemical regions of the three surfaces depends very strongly on the surface crossings.-

  1. Distinct reaction pathway promoted by non-divalent-metal cations in a tertiary stabilized hammerhead ribozyme

    PubMed Central

    Roychowdhury-Saha, Manami; Burke, Donald H.

    2007-01-01

    Divalent ion sensitivity of hammerhead ribozymes is significantly reduced when the RNA structure includes appropriate tertiary stabilization. Therefore, we investigated the activity of the tertiary stabilized “RzB” hammerhead ribozyme in several nondivalent ions. Ribozyme RzB is active in spermidine and Na+ alone, although the cleavage rates are reduced by more than 1,000-fold relative to the rates observed in Mg2+ and in transition metal ions. The trivalent cobalt hexammine (CoHex) ion is often used as an exchange-inert analog of hydrated magnesium ion. Trans-cleavage rates exceeded 8 min−1 in 20 mM CoHex, which promoted cleavage through outersphere interactions. The stimulation of catalysis afforded by the tertiary structural interactions within RzB does not require Mg2+, unlike other extended hammerhead ribozymes. Site-specific interaction with at least one Mg2+ ion is suggested by CoHex competition experiments. In the presence of a constant, low concentration of Mg2+, low concentrations of CoHex decreased the rate by two to three orders of magnitude relative to the rate in Mg2+ alone. Cleavage rates increased as CoHex concentrations were raised further, but the final fraction cleaved was lower than what was observed in CoHex or Mg2+ alone. These observations suggest that Mg2+ and CoHex compete for binding and that they cause misfolded structures when they are together. The results of this study support the existence of an alternate catalytic mechanism used by nondivalent ions (especially CoHex) that is distinct from the one promoted by divalent metal ions, and they imply that divalent metals influence catalysis through a specific nonstructural role. PMID:17456566

  2. Bandgap and Structure Engineering via Cation Exchange: From Binary Ag2S to Ternary AgInS2, Quaternary AgZnInS alloy and AgZnInS/ZnS Core/Shell Fluorescent Nanocrystals for Bioimaging.

    PubMed

    Song, Jiangluqi; Ma, Chao; Zhang, Wenzhe; Li, Xiaodong; Zhang, Wenting; Wu, Rongbo; Cheng, Xiangcan; Ali, Asad; Yang, Mingya; Zhu, Lixin; Xia, Ruixiang; Xu, Xiaoliang

    2016-09-21

    Attention on semiconductor nanocrystals have been largely focused because of their unique optical and electrical properties, which can be applied as light absorber and luminophore. However, the band gap and structure engineering of nanomaterials is not so easy because of their finite size. Here we demonstrate an approach for preparing ternary AgInS2 (AIS), quaternary AgZnInS (AZIS), AgInS2/ZnS and AgZnInS/ZnS nanocompounds based on cation exchange. First, pristine Ag2S quantum dots (QDs) with different sizes were synthesized in one-pot, followed by the partial cation exchange between In(3+) and Ag(+). Changing the initial ratio of In(3+) to Ag(+), reaction time and temperature can control the components of the obtained AIS QDs. Under the optimized conditions, AIS QDs were obtained for the first time with a cation disordered cubic phase and high photoluminescence (PL) quantum yield (QY) up to 32% in aqueous solution, demonstrating the great potential of cation exchange in the synthesis for nanocrystals with excellent optical properties. Sequentially, Zn(2+) ions were incorporated in situ through a second exchange of Zn(2+) to Ag(+)/In(3+), leading to distinct results under different reaction temperature. Addition of Zn(2+) precursor at room temperature produced AIS/ZnS core/shell NCs with successively enhancement of QY, while subsequent heating could obtain AZIS homogeneous alloy QDs with a successively blue-shift of PL emission. This allow us to tune the PL emission of the products from 483 to 675 nm and fabricate the chemically stable QDs core/ZnS shell structure. Based on the above results, a mechanism about the cation exchange for the ternary nanocrystals of different structures was proposed that the balance between cation exchange and diffusion is the key factor of controlling the band gap and structure of the final products. Furthermore, photostability and in vitro experiment demonstrated quite low cytotoxicity and remarkably promising applications in the

  3. Bandgap and Structure Engineering via Cation Exchange: From Binary Ag2S to Ternary AgInS2, Quaternary AgZnInS alloy and AgZnInS/ZnS Core/Shell Fluorescent Nanocrystals for Bioimaging.

    PubMed

    Song, Jiangluqi; Ma, Chao; Zhang, Wenzhe; Li, Xiaodong; Zhang, Wenting; Wu, Rongbo; Cheng, Xiangcan; Ali, Asad; Yang, Mingya; Zhu, Lixin; Xia, Ruixiang; Xu, Xiaoliang

    2016-09-21

    Attention on semiconductor nanocrystals have been largely focused because of their unique optical and electrical properties, which can be applied as light absorber and luminophore. However, the band gap and structure engineering of nanomaterials is not so easy because of their finite size. Here we demonstrate an approach for preparing ternary AgInS2 (AIS), quaternary AgZnInS (AZIS), AgInS2/ZnS and AgZnInS/ZnS nanocompounds based on cation exchange. First, pristine Ag2S quantum dots (QDs) with different sizes were synthesized in one-pot, followed by the partial cation exchange between In(3+) and Ag(+). Changing the initial ratio of In(3+) to Ag(+), reaction time and temperature can control the components of the obtained AIS QDs. Under the optimized conditions, AIS QDs were obtained for the first time with a cation disordered cubic phase and high photoluminescence (PL) quantum yield (QY) up to 32% in aqueous solution, demonstrating the great potential of cation exchange in the synthesis for nanocrystals with excellent optical properties. Sequentially, Zn(2+) ions were incorporated in situ through a second exchange of Zn(2+) to Ag(+)/In(3+), leading to distinct results under different reaction temperature. Addition of Zn(2+) precursor at room temperature produced AIS/ZnS core/shell NCs with successively enhancement of QY, while subsequent heating could obtain AZIS homogeneous alloy QDs with a successively blue-shift of PL emission. This allow us to tune the PL emission of the products from 483 to 675 nm and fabricate the chemically stable QDs core/ZnS shell structure. Based on the above results, a mechanism about the cation exchange for the ternary nanocrystals of different structures was proposed that the balance between cation exchange and diffusion is the key factor of controlling the band gap and structure of the final products. Furthermore, photostability and in vitro experiment demonstrated quite low cytotoxicity and remarkably promising applications in the

  4. "Abnormal" salt and solvent effects on anion/cation electron-transfer reactions: an interpretation based on Marcus-Hush treatment.

    PubMed

    Garcia-Fernandez, E; Prado-Gotor, R; Sanchez, F

    2005-08-11

    Salt and solvent effects on the kinetics of the reactions [Fe(CN)6]3- + [Ru(NH3)5pz](2+) right arrow over left arrow [Fe(CN)6]4- + [Ru(NH3)5pz]3+ (pz = pyrazine) have been studied through T-jump measurements. The forward and reverse reactions show different behaviors: "abnormal" salt and solvent effects in the first case and normal effects in the second one. These facts imply an asymmetric behavior of anion/cation reactions depending on the charge of the oxidant. The results can be rationalized by using the Marcus-Hush treatment for electron-transfer reactions.

  5. Hydraulic controls of in-stream gravel bar hyporheic exchange and reactions

    NASA Astrophysics Data System (ADS)

    Trauth, Nico; Schmidt, Christian; Vieweg, Michael; Oswald, Sascha E.; Fleckenstein, Jan H.

    2015-04-01

    Hyporheic exchange transports solutes into the subsurface where they can undergo biogeochemical transformations, affecting fluvial water quality and ecology. A three-dimensional numerical model of a natural in-stream gravel bar (20 m × 6 m) is presented. Multiple steady state streamflow is simulated with a computational fluid dynamics code that is sequentially coupled to a reactive transport groundwater model via the hydraulic head distribution at the streambed. Ambient groundwater flow is considered by scenarios of neutral, gaining, and losing conditions. The transformation of oxygen, nitrate, and dissolved organic carbon by aerobic respiration and denitrification in the hyporheic zone are modeled, as is the denitrification of groundwater-borne nitrate when mixed with stream-sourced carbon. In contrast to fully submerged structures, hyporheic exchange flux decreases with increasing stream discharge, due to decreasing hydraulic head gradients across the partially submerged structure. Hyporheic residence time distributions are skewed in the log-space with medians of up to 8 h and shift to symmetric distributions with increasing level of submergence. Solute turnover is mainly controlled by residence times and the extent of the hyporheic exchange flow, which defines the potential reaction area. Although streamflow is the primary driver of hyporheic exchange, its impact on hyporheic exchange flux, residence times, and solute turnover is small, as these quantities exponentially decrease under losing and gaining conditions. Hence, highest reaction potential exists under neutral conditions, when the capacity for denitrification in the partially submerged structure can be orders of magnitude higher than in fully submerged structures.

  6. Kinetics of esterification of acidified oil with different alcohols by a cation ion-exchange resin/polyethersulfone hybrid catalytic membrane.

    PubMed

    Zhang, Honglei; Ding, Jincheng; Qiu, Yanli; Zhao, Zengdian

    2012-05-01

    Hybrid catalytic membranes consisting of cation ion-exchange resin particles (CERP) and polyethersulfone (PES) were prepared by immersion phase inversion and used as heterogeneous catalysts for the esterification of acidified oil with methanol, ethanol, propanol and butanol. The membranes were characterized by ion exchange capacity and swelling degree tests. The membranes were annealed at different temperatures to improve catalytic activity and membranes annealed at 393 K had the highest catalytic activity. Butanol allowed the highest free fatty acids (FFAs) conversion of 95.28% since it has better miscibility than the other alcohols which strengthened mass and heat transfer. Furthermore, pseudo-homogeneous kinetic models of the esterification of acidified oil with the four alcohols were established according to the experimental data. The kinetic models can well predict the FFA conversion. PMID:22424925

  7. Tandem anion and cation exchange solid phase extraction for the enrichment of micropollutants and their transformation products from ozonation in a wastewater treatment plant.

    PubMed

    Deeb, Ahmad A; Schmidt, Torsten C

    2016-06-01

    The presence of organic micropollutants and their transformation products (TPs) from biotic and abiotic processes in aquatic environments is receiving intense public and scientific attention. Yet a suitable sample preparation method that would enable extraction and enrichment of a wide range of such compounds from water is missing. The focus of this paper was to develop an enhanced solid phase extraction (SPE) protocol which enabled isolation of parent compounds and low molecular weight transformation products (that are produced after treatment of water with ozone) from different water matrices. Ten SPE sorbents were evaluated with regard to their ability to extract acidic, neutral, and basic compounds from water at several pH values. Highest recoveries (91-99 %) for all analytes in pure water were obtained by combining strong anion and cation exchangers of two manufacturers in a tandem mode without pH adjustment. Tandem Oasis (MAX+MCX) was finally applied to extract the spiked analytes from tap water, surface water, and several wastewater samples. The efficiency of the used SPE procedure was examined using an optimized liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method using multiple reaction monitoring (MRM) mode. The occurrence of some of the investigated TPs in environmental water matrices was proven for the first time in this study. Method quantification limits (MQLs) for all compounds ranged from 3.7 to 15.3 ng/L in all matrices. Recoveries (%RE) were between 90 and 110 %. Intraday and interday precision, expressed as relative standard deviation, varied from 0.7 to 5.9 % and 1.8 to 10.3 %, respectively. Matrix effect (%ME) evaluation demonstrated that even complex sample matrices did not show significant ion suppression or enhancement. The applicability of the method was shown during two sampling campaigns at Ruhr river and a wastewater treatment plant (WWTP) equipped with an ozonation step after regular

  8. Quantification of Site-Specific Cation Exchange in Metal-Organic Frameworks Using Multi-Wavelength Anomalous X-ray Dispersion

    SciTech Connect

    Brozek, Carl K.; Cozzolino, Anthony F.; Teat, Simon J.; Chen, Yu-Sheng; Dinc,; #259; Mircea,

    2013-09-23

    We employed multiwavelength anomalous X-ray dispersion to determine the relative cation occupation at two crystallographically distinct metal sites in Fe2+-, Cu2+-, and Zn2+-exchanged versions of the microporous metal–organic framework (MOF) known as MnMnBTT (BTT = 1,3,5-benzenetristetrazolate). By exploiting the dispersive differences between Mn, Fe, Cu, and Zn, the extent and location of cation exchange were determined from single crystal X-ray diffraction data sets collected near the K edges of Mn2+ and of the substituting metal, and at a wavelength remote from either edge as a reference. Comparing the anomalous dispersion between these measurements indicated that the extent of Mn2+ replacement depends on the identity of the substituting metal. We contrasted two unique methods to analyze this data with a conventional approach and evaluated their limitations with emphasis on the general application of this method to other heterometallic MOFs, where site-specific metal identification is fundamental to tuning catalytic and physical properties.

  9. Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions

    PubMed Central

    2015-01-01

    We demonstrate that, via controlled anion exchange reactions using a range of different halide precursors, we can finely tune the chemical composition and the optical properties of presynthesized colloidal cesium lead halide perovskite nanocrystals (NCs), from green emitting CsPbBr3 to bright emitters in any other region of the visible spectrum, and back, by displacement of Cl– or I– ions and reinsertion of Br– ions. This approach gives access to perovskite semiconductor NCs with both structural and optical qualities comparable to those of directly synthesized NCs. We also show that anion exchange is a dynamic process that takes place in solution between NCs. Therefore, by mixing solutions containing perovskite NCs emitting in different spectral ranges (due to different halide compositions) their mutual fast exchange dynamics leads to homogenization in their composition, resulting in NCs emitting in a narrow spectral region that is intermediate between those of the parent nanoparticles. PMID:26214734

  10. Neutrino nuclear responses for double beta decays and astro neutrinos by charge exchange reactions

    NASA Astrophysics Data System (ADS)

    Ejiri, Hiroyasu

    2014-09-01

    Neutrino nuclear responses are crucial for neutrino studies in nuclei. Charge exchange reactions (CER) are shown to be used to study charged current neutrino nuclear responses associated with double beta decays(DBD)and astro neutrino interactions. CERs to be used are high energy-resolution (He3 ,t) reactions at RCNP, photonuclear reactions via IAR at NewSUBARU and muon capture reactions at MUSIC RCNP and MLF J-PARC. The Gamow Teller (GT) strengths studied by CERs reproduce the observed 2 neutrino DBD matrix elements. The GT and spin dipole (SD) matrix elements are found to be reduced much due to the nucleon spin isospin correlations and the non-nucleonic (delta isobar) nuclear medium effects. Impacts of the reductions on the DBD matrix elements and astro neutrino interactions are discussed.

  11. Cationic ruthenium alkylidene catalysts bearing phosphine ligands.

    PubMed

    Endo, Koji; Grubbs, Robert H

    2016-02-28

    The discovery of highly active catalysts and the success of ionic liquid immobilized systems have accelerated attention to a new class of cationic metathesis catalysts. We herein report the facile syntheses of cationic ruthenium catalysts bearing bulky phosphine ligands. Simple ligand exchange using silver(i) salts of non-coordinating or weakly coordinating anions provided either PPh3 or chelating Ph2P(CH2)nPPh2 (n = 2 or 3) ligated cationic catalysts. The structures of these newly reported catalysts feature unique geometries caused by ligation of the bulky phosphine ligands. Their activities and selectivities in standard metathesis reactions were also investigated. These cationic ruthenium alkylidene catalysts reported here showed moderate activity and very similar stereoselectivity when compared to the second generation ruthenium dichloride catalyst in ring-closing metathesis, cross metathesis, and ring-opening metathesis polymerization assays.

  12. Scaling hyporheic exchange and its influence on biogeochemical reactions in aquatic ecosystems

    NASA Astrophysics Data System (ADS)

    O'Connor, Ben L.; Harvey, Judson W.

    2008-12-01

    Hyporheic exchange and biogeochemical reactions are difficult to quantify because of the range in fluid-flow and sediment conditions inherent to streams, wetlands, and nearshore marine ecosystems. Field measurements of biogeochemical reactions in aquatic systems are impeded by the difficulty of measuring hyporheic flow simultaneously with chemical gradients in sediments. Simplified models of hyporheic exchange have been developed using Darcy's law generated by flow and bed topography at the sediment-water interface. However, many modes of transport are potentially involved (molecular diffusion, bioturbation, advection, shear, bed mobility, and turbulence) with even simple models being difficult to apply in complex natural systems characterized by variable sediment sizes and irregular bed geometries. In this study, we synthesize information from published hyporheic exchange investigations to develop a scaling relationship for estimating mass transfer in near-surface sediments across a range in fluid-flow and sediment conditions. Net hyporheic exchange was quantified using an effective diffusion coefficient (De) that integrates all of the various transport processes that occur simultaneously in sediments, and dimensional analysis was used to scale De to shear stress velocity, roughness height, and permeability that describe fluid-flow and sediment characteristics. We demonstrated the value of the derived scaling relationship by using it to quantify dissolved oxygen (DO) uptake rates on the basis of DO profiles in sediments and compared them to independent flux measurements. The results support a broad application of the De scaling relationship for quantifying coupled hyporheic exchange and biogeochemical reaction rates in streams and other aquatic ecosystems characterized by complex fluid-flow and sediment conditions.

  13. Scaling hyporheic exchange and its influence on biogeochemical reactions in aquatic ecosystems

    USGS Publications Warehouse

    O'Connor, B.L.; Harvey, J.W.

    2008-01-01

    Hyporheic exchange and biogeochemical reactions are difficult to quantify because of the range in fluid-flow and sediment conditions inherent to streams, wetlands, and nearshore marine ecosystems. Field measurements of biogeochemical reactions in aquatic systems are impeded by the difficulty of measuring hyporheic flow simultaneously with chemical gradients in sediments. Simplified models of hyporheic exchange have been developed using Darcy's law generated by flow and bed topography at the sediment-water interface. However, many modes of transport are potentially involved (molecular diffusion, bioturbation, advection, shear, bed mobility, and turbulence) with even simple models being difficult to apply in complex natural systems characterized by variable sediment sizes and irregular bed geometries. In this study, we synthesize information from published hyporheic exchange investigations to develop a scaling relationship for estimating mass transfer in near-surface sediments across a range in fluid-flow and sediment conditions. Net hyporheic exchange was quantified using an effective diffusion coefficient (De) that integrates all of the various transport processes that occur simultaneously in sediments, and dimensional analysis was used to scale De to shear stress velocity, roughness height, and permeability that describe fluid-flow and sediment characteristics. We demonstrated the value of the derived scaling relationship by using it to quantify dissolved oxygen (DO) uptake rates on the basis of DO profiles in sediments and compared them to independent flux measurements. The results support a broad application of the De scaling relationship for quantifying coupled hyporheic exchange and biogeochemical reaction rates in streams and other aquatic ecosystems characterized by complex fluid-flow and sediment conditions.

  14. Isolation of carboxyl-termini and blocked amino-termini of viral proteins by high-performance cation-exchange chromatography.

    PubMed

    Gorman, J J; Shiell, B J

    1993-08-27

    The strong cation-exchanger, PolySulfoethyl Aspartamide, has been assessed as a medium for isolation of carboxyl-terminal and blocked amino-terminal peptides from tryptic digests of small quantities of viral proteins. Peptides with a single positive charge, the blocked amino-terminal peptides of ovalbumin and the Newcastle disease virus (NDV) matrix protein and carboxyl-terminal peptides of ovalbumin and the NDV nucleocapsid protein, eluted in early ion-exchange fractions and were readily isolated in homogeneous form by subsequent reversed-phase HPLC. Some early ion-exchange fractions also contained singly charged peptides derived by "chymotryptic-like" cleavage, whilst other peptides eluted in these fractions due to their highly acidic character. Terminal sequences with additional basic residues were isolated from later eluting ion-exchange fractions. Peptides with this property included the blocked amino-terminus of the NDV nucleocapsid protein and a portion of the carboxyl-terminus of the NDV matrix protein. Hitherto undescribed polymorphism in the amino-terminal region of ovalbumin was revealed in this study. Truncated peptides from the carboxyl-terminus of the NDV matrix protein were also detected. The presence of these peptides could be a reflection of carboxyl-terminal processing of the matrix protein. The strategy described herein should be of general utility for selective microisolation of carboxyl-terminal peptides and blocked amino-terminal peptides from tryptic digests of proteins. PMID:8408428

  15. Many-body exchange-repulsion in polarizable molecular mechanics. I. Orbital-based approximations and applications to hydrated metal cation complexes.

    PubMed

    Chaudret, Robin; Gresh, Nohad; Parisel, Olivier; Piquemal, Jean-Philip

    2011-11-15

    We have quantified the extent of the nonadditivity of the short-range exchange-repulsion energy, E(exch-rep), in several polycoordinated complexes of alkali, alkaline-earth, transition, and metal cations. This was done by performing ab initio energy decomposition analyses of interaction energies in these complexes. The magnitude of E(exch-rep(n-body, n > 2)) was found to be strongly cation-dependent, ranging from close to zero for some alkali metal complexes to about 6 kcal/mol for the hexahydrated Zn(2+) complex. In all cases, the cation-water molecules, E(exch-rep(three-body)), has been found to be the dominant contribution to many-body exchange-repulsion effects, higher order terms being negligible. As the physical basis of this effect is discussed, a three-center exponential term was introduced in the SIBFA (Sum of Interactions Between Fragments Ab initio computed) polarizable molecular mechanics procedure to model such effects. The three-body correction is added to the two-center (two-body) overlap-like formulation of the short-range repulsion contribution, E(rep), which is grounded on simplified integrals obtained from localized molecular orbital theory. The present term is computed on using mostly precomputed two-body terms and, therefore, does not increase significantly the computational cost of the method. It was shown to match closely E(three-body) in a series of test cases bearing on the complexes of Ca(2+), Zn(2+), and Hg(2+). For example, its introduction enabled to restore the correct tetrahedral versus square planar preference found from quantum chemistry calculations on the tetrahydrate of Hg(2+) and [Hg(H(2)O)(4)](2+). PMID:21793002

  16. Water-Chemistry Evolution and Modeling of Radionuclide Sorption and Cation Exchange during Inundation of Frenchman Flat Playa

    SciTech Connect

    Hershey, Ronald; Cablk, Mary; LeFebre, Karen; Fenstermaker, Lynn; Decker, David

    2013-08-01

    Atmospheric tests and other experiments with nuclear materials were conducted on the Frenchman Flat playa at the Nevada National Security Site, Nye County, Nevada; residual radionuclides are known to exist in Frenchman Flat playa soils. Although the playa is typically dry, extended periods of winter precipitation or large single-event rainstorms can inundate the playa. When Frenchman Flat playa is inundated, residual radionuclides on the typically dry playa surface may become submerged, allowing water-soil interactions that could provide a mechanism for transport of radionuclides away from known areas of contamination. The potential for radionuclide transport by occasional inundation of the Frenchman Flat playa was examined using geographic information systems and satellite imagery to delineate the timing and areal extent of inundation; collecting water samples during inundation and analyzing them for chemical and isotopic content; characterizing suspended/precipitated materials and archived soil samples; modeling water-soil geochemical reactions; and modeling the mobility of select radionuclides under aqueous conditions. The physical transport of radionuclides by water was not evaluated in this study. Frenchman Flat playa was inundated with precipitation during two consecutive winters in 2009-2010 and 2010-2011. Inundation allowed for collection of multiple water samples through time as the areal extent of inundation changed and ultimately receded. During these two winters, precipitation records from a weather station in Frenchman Flat (Well 5b) provided information that was used in combination with geographic information systems, Landsat imagery, and image processing techniques to identify and quantify the areal extent of inundation. After inundation, water on the playa disappeared quickly, for example, between January 25, 2011 and February 10, 2011, a period of 16 days, 92 percent of the areal extent of inundation receded (2,062,800 m2). Water sampling provided

  17. EXFOR basics: A short guide to the nuclear reaction data exchange format

    SciTech Connect

    McLane, V.

    1996-07-01

    This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear data between the Nuclear Reaction Data Centers. In addition to storing the data and its` bibliographic information, experimental information, including source of uncertainties, is also compiled. The status and history of the data set is also included, e.g., the source of the data, any updates which have been made, and correlations to other data sets. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear data compilation centers. This format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center`s own sphere of responsibility. The exchange format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in an easily machine-readable format (for checking and indicating possible errors) and a format that can be read by personnel (for passing judgment on and correcting any errors indicated by the machine). The data presently included in the EXFOR exchange include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle induced reaction data, a selected compilation of photon-induced reaction data.

  18. Magnetic graphene - polystyrene sulfonic acid nano composite: A dispersive cation exchange sorbent for the enrichment of aminoalcohols and ethanolamines from environmental aqueous samples.

    PubMed

    Chinthakindi, Sridhar; Purohit, Ajay; Singh, Varoon; Tak, Vijay; Dubey, D K; Pardasani, Deepak

    2015-12-01

    Present study aimed at graphene surface modification to achieve selective analyte binding in dispersive solid phase extraction. Magnetic graphene - polystyrene sulfonic acid (MG-PSS) cation exchange nano-composite was prepared by non-covalent wrapping method. Composite was characterized by FT-IR and zeta potential. Material exhibited good dispersion in water and high exchange capacity of 1.97±0.16mMg(-1). Prepared nano-sorbent was then exploited for the cation exchange extraction and gas chromatography mass spectrometric analysis of Chemical Weapons Convention relevant aminoalcohols and ethanolamines from aqueous samples. Extraction parameters such as sorbent amount, extraction time, desorption conditions and sample pH were optimized and effect of common matrix interferences such as polyethylene glycol and metal salts was also studied. Three milligram of sorbent per mL of sample with 20min of extraction time at room temperature afforded 70-81% recoveries of the selected analytes spiked at concentration level of 1μgmL(-1). Method showed good linearity in the studied range with r(2)≥0.993. The limits of detection and limits of quantification ranged from 23 to 54ngmL(-1) and 72 to 147ngmL(-1), respectively. The relative standard deviation for intra- and inter-day precision ranged from 4.6 to 10.2% and 7.4 to 14.8% respectively. Applicability of the method to different environmental samples as well as the proficiency tests conducted by the Organization for the Prohibition of Chemical Weapons (OPCW) was also ascertained.

  19. Selective removal of alkali metal cations from multiply-charged ions via gas-phase ion/ion reactions using weakly coordinating anions.

    PubMed

    Luongo, Carl A; Bu, Jiexun; Burke, Nicole L; Gilbert, Joshua D; Prentice, Boone M; Cummings, Steven; Reed, Christopher A; McLuckey, Scott A

    2015-03-01

    Selective removal of alkali metal cations from mixed cation multiply-charged peptide ions is demonstrated here using gas-phase ion/ion reactions with a series of weakly coordinating anions (WCAs), including hexafluorophosphate (PF6 (-)), tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BARF), tetrakis(pentafluorophenyl)borate (TPPB), and carborane (CHB11Cl11 (-)). In all cases, a long-lived complex is generated by dication/anion condensation followed by ion activation to compare proton transfer with alkali ion transfer from the peptide to the anion. The carborane anion was the only anion studied to undergo dissociation exclusively through loss of the metallated anion, regardless of the studied metal adduct. All other anions studied yield varying abundances of protonated and metallated peptide depending on the peptide sequence and the metal identity. Density functional theory calculations suggest that for the WCAs studied, metal ion transfer is most strongly favored thermodynamically, which is consistent with the experimental results. The carborane anion is demonstrated to be a robust reagent for the selective removal of alkali metal cations from peptide cations with mixtures of excess protons and metal cations. PMID:25560986

  20. Selective Removal of Alkali Metal Cations from Multiply-Charged Ions via Gas-Phase Ion/Ion Reactions Using Weakly Coordinating Anions

    NASA Astrophysics Data System (ADS)

    Luongo, Carl A.; Bu, Jiexun; Burke, Nicole L.; Gilbert, Joshua D.; Prentice, Boone M.; Cummings, Steven; Reed, Christopher A.; McLuckey, Scott A.

    2015-03-01

    Selective removal of alkali metal cations from mixed cation multiply-charged peptide ions is demonstrated here using gas-phase ion/ion reactions with a series of weakly coordinating anions (WCAs), including hexafluorophosphate (PF6 -), tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BARF), tetrakis(pentafluorophenyl)borate (TPPB), and carborane (CHB11Cl11 -). In all cases, a long-lived complex is generated by dication/anion condensation followed by ion activation to compare proton transfer with alkali ion transfer from the peptide to the anion. The carborane anion was the only anion studied to undergo dissociation exclusively through loss of the metallated anion, regardless of the studied metal adduct. All other anions studied yield varying abundances of protonated and metallated peptide depending on the peptide sequence and the metal identity. Density functional theory calculations suggest that for the WCAs studied, metal ion transfer is most strongly favored thermodynamically, which is consistent with the experimental results. The carborane anion is demonstrated to be a robust reagent for the selective removal of alkali metal cations from peptide cations with mixtures of excess protons and metal cations.

  1. Retention of the Cluster Core Structure during Ligand Exchange Reactions of Carboxylato-Substituted Metal Oxo Clusters

    PubMed Central

    Kreutzer, Johannes; Puchberger, Michael; Artner, Christine; Schubert, Ulrich

    2015-01-01

    The exchange of the carboxylato ligands of Zr4O2(methacrylato)12 in reactions with carboxylic acids proceeds with retention of the composition and structure of the cluster core. This was concluded from exchange/re-exchange experiments and from comparison of the IR bands of the cluster core of the original and ligand-exchanged clusters. The IR bands were assigned on the basis of DFT calculations. Scrambling reactions between two Zr4O2(OOCR)12 clusters with different carboxylato ligands are a new way to prepare mixed-ligand oxo clusters. PMID:26113799

  2. Hydroxide Degradation Pathways for Imidazolium Cations. A DFT Study

    SciTech Connect

    Long, H.; Pivovar, B.

    2014-05-15

    Imidazolium cations are promising candidates as covalently tetherable cations for application in anion exchange membranes. They have generated specific interest in alkaline membrane fuel cell applications where ammonium-based cations have been the most commonly applied but have been found to be susceptible to hydroxide attack. In the search for high stability cations, a detailed understanding of the degradation pathways and reaction barriers is required. In this work, we investigate imidazolium and benzimidazolium cations in the presence of hydroxide using density functional theory calculations for their potential in alkaline membrane fuel cells. Moreover, the dominant degradation pathway for these cations is predicted to be the nucleophilic addition–elimination pathway at the C-2 atom position on the imidazolium ring. Steric interferences, introduced by substitutions at the C-2, C-4, and C-5 atom positions, were investigated and found to have a significant, positive impact on calculated degradation energy barriers. Benzimidazolium cations, with their larger conjugated systems, are predicted to degrade much faster than their imidazolium counterparts. Our results provide important insight into designing stable cations for anion exchange membranes. Some of the molecules studied have significantly increased degradation energy barriers suggesting that they could possess significantly improved (several orders of magnitude) durability compared to traditional cations and potentially enable new applications.

  3. Methane activation by cobalt cluster cations, Con+ (n=2-16): Reaction mechanisms and thermochemistry of cluster-CHx (x=0-3) complexes

    NASA Astrophysics Data System (ADS)

    Citir, Murat; Liu, Fuyi; Armentrout, P. B.

    2009-02-01

    The kinetic energy dependences of the reactions of Con+ (n =2-16) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0-10 eV. The main products are hydride formation, ConD+, dehydrogenation to form ConCD2+, and double dehydrogenation yielding ConC+. These primary products decompose to form secondary and higher order products, ConCD+, Con-1D+, Con-1C+, Con-1CD+, and Con-1CD2+ at higher energies. Adduct formation of ConCD4+ is also observed for the largest cluster cations, n ≥10. In general, the efficiencies of the single and double dehydrogenation processes increase with cluster size, although the hexamer cation shows a reduced reactivity compared to its neighbors. All reactions exhibit thresholds, and cross sections for the various primary and secondary reactions are analyzed to yield reaction thresholds from which bond energies for cobalt cluster cations to D, C, CD, CD2, and CD3 are determined. The relative magnitudes of these bond energies are consistent with simple bond order considerations. Bond energies for larger clusters rapidly reach relatively constant values, which are used to estimate the chemisorption energies of the C, CD, CD2, and CD3 molecular fragments to cobalt surfaces.

  4. Understanding chemical reactions of CO2 and its isoelectronic molecules with 1-butyl-3-methylimidazolium acetate by changing the nature of the cation: the case of CS2 in 1-butyl-1-methylpyrrolidinium acetate studied by NMR spectroscopy and density functional theory calculations.

    PubMed

    Cabaço, M Isabel; Besnard, Marcel; Chávez, Fabián Vaca; Pinaud, Noël; Sebastião, Pedro J; Coutinho, João A P; Danten, Yann

    2014-06-28

    NMR spectroscopy ((1)H, (13)C, (15)N) shows that carbon disulfide reacts spontaneously with 1-butyl-1-methylpyrrolidinium acetate ([BmPyrro][Ac]) in the liquid phase. It is found that the acetate anions play an important role in conditioning chemical reactions with CS2 leading, via coupled complex reactions, to the degradation of this molecule to form thioacetate anion (CH3COS(-)), CO2, OCS, and trithiocarbonate (CS3 (2-)). In marked contrast, the cation does not lead to the formation of any adducts allowing to conclude that, at most, its role consists in assisting indirectly these reactions. The choice of the [BmPyrro](+) cation in the present study allows disentangling the role of the anion and the cation in the reactions. As a consequence, the ensemble of results already reported on CS2-[Bmim][Ac] (1), OCS-[Bmim][Ac] (2), and CO2-[Bmim][Ac] (3) systems can be consistently rationalized. It is argued that in system (1) both anion and cation play a role. The CS2 reacts with the acetate anion leading to the formation of CH3COS(-), CO2, and OCS. After these reactions have proceeded the nascent CO2 and OCS interact with the cation to form imidazolium-carboxylate ([Bmim] CO2) and imidazolium-thiocarboxylate ([Bmim] COS). The same scenario also applies to system (2). In contrast, in the CO2-[Bmim] [Ac] system a concerted cooperative process between the cation, the anion, and the CO2 molecule takes place. A carbene issued from the cation reacts to form the [Bmim] CO2, whereas the proton released by the ring interacts with the anion to produce acetic acid. In all these systems, the formation of adduct resulting from the reaction between the solute molecule and the carbene species originating from the cation is expected. However, this species was only observed in systems (2) and (3). The absence of such an adduct in system (1) has been theoretically investigated using DFT calculations. The values of the energetic barrier of the reactions show that the formation of [Bmim

  5. Understanding chemical reactions of CO{sub 2} and its isoelectronic molecules with 1-butyl-3-methylimidazolium acetate by changing the nature of the cation: The case of CS{sub 2} in 1-butyl-1-methylpyrrolidinium acetate studied by NMR spectroscopy and density functional theory calculations

    SciTech Connect

    Cabaço, M. Isabel; Besnard, Marcel; Danten, Yann; Chávez, Fabián Vaca; Pinaud, Noël; Sebastião, Pedro J.; Coutinho, João A. P.

    2014-06-28

    NMR spectroscopy ({sup 1}H, {sup 13}C, {sup 15}N) shows that carbon disulfide reacts spontaneously with 1-butyl-1-methylpyrrolidinium acetate ([BmPyrro][Ac]) in the liquid phase. It is found that the acetate anions play an important role in conditioning chemical reactions with CS{sub 2} leading, via coupled complex reactions, to the degradation of this molecule to form thioacetate anion (CH{sub 3}COS{sup −}), CO{sub 2}, OCS, and trithiocarbonate (CS{sub 3}{sup 2−}). In marked contrast, the cation does not lead to the formation of any adducts allowing to conclude that, at most, its role consists in assisting indirectly these reactions. The choice of the [BmPyrro]{sup +} cation in the present study allows disentangling the role of the anion and the cation in the reactions. As a consequence, the ensemble of results already reported on CS{sub 2}-[Bmim][Ac] (1), OCS-[Bmim][Ac] (2), and CO{sub 2}-[Bmim][Ac] (3) systems can be consistently rationalized. It is argued that in system (1) both anion and cation play a role. The CS{sub 2} reacts with the acetate anion leading to the formation of CH{sub 3}COS{sup −}, CO{sub 2}, and OCS. After these reactions have proceeded the nascent CO{sub 2} and OCS interact with the cation to form imidazolium-carboxylate ([Bmim] CO{sub 2}) and imidazolium-thiocarboxylate ([Bmim] COS). The same scenario also applies to system (2). In contrast, in the CO{sub 2}-[Bmim] [Ac] system a concerted cooperative process between the cation, the anion, and the CO{sub 2} molecule takes place. A carbene issued from the cation reacts to form the [Bmim] CO{sub 2}, whereas the proton released by the ring interacts with the anion to produce acetic acid. In all these systems, the formation of adduct resulting from the reaction between the solute molecule and the carbene species originating from the cation is expected. However, this species was only observed in systems (2) and (3). The absence of such an adduct in system (1) has been theoretically

  6. Atmospheric deposition and canopy exchange of anions and cations in two plantation forests under acid rain influence

    NASA Astrophysics Data System (ADS)

    Shen, Weijun; Ren, Huili; Darrel Jenerette, G.; Hui, Dafeng; Ren, Hai

    2013-01-01

    Acid deposition as a widely concerned environmental problem in China has been less studied in plantation forests compared to urban and secondary forests, albeit they constitute 1/3 of the total forested areas of the country. We measured the rainwater amount and chemistry outside and beneath the canopies of two widely distributed plantations (Acacia mangium and Dimocarpus longan) in the severe acid rain influenced Pearl River Delta region of southeastern China for two years. Our results showed that the frequency of acid rain was 96% on the basis of pH value <5.6. The volume-weighted mean (vwm) pH was 4.62 and higher in the dry (Oct.-Mar.) than in the wet (Apr.-Sep.) seasons. The major acidic anion was sulfate with vwm concentration of 140 μeq l-1 and annual deposition flux of 110.3 kg ha-1 yr-1. The major neutralizing cations were calcium (94.8 μeq l-1 and 28 kg ha-1 yr-1) and ammonium (41.2 μeq l-1 and 11.7 kg ha-1 yr-1). Over 95% of these major acidic anions and neutralizing cations were derived from anthropogenic and terrestrial sources as a result of industrial, agricultural and forestry activities. Plantation canopy had marked impacts on rainwater chemistry, with the measured anion and cation concentrations being significantly enriched in throughfall (TF) and stemflow (SF) rainwater by 1.4 (for NO) to 20-fold (for K+) compared to those in bulk precipitation (BP). Dry deposition generally contributed about 13-22% of the total deposition while canopy leaching mainly occurred for K+ (>88%) and NH (10-38%). The two tree species showed distinct impacts on rainfall redistribution and rainwater chemistry due to their differences in canopy architecture and leaf/bark texture, suggesting that species-specific effects should not be overlooked while assessing the acid deposition in forested areas.

  7. Applying reactive models to column experiments to assess the hydrogeochemistry of seawater intrusion: Optimising ACUAINTRUSION and selecting cation exchange coefficients with PHREEQC

    NASA Astrophysics Data System (ADS)

    Boluda-Botella, N.; Valdes-Abellan, J.; Pedraza, R.

    2014-03-01

    Three sets of laboratory column experimental results concerning the hydrogeochemistry of seawater intrusion have been modelled using two codes: ACUAINTRUSION (Chemical Engineering Department, University of Alicante) and PHREEQC (U.S.G.S.). These reactive models utilise the hydrodynamic parameters determined using the ACUAINTRUSION TRANSPORT software and fit the chloride breakthrough curves perfectly. The ACUAINTRUSION code was improved, and the instabilities were studied relative to the discretisation. The relative square errors were obtained using different combinations of the spatial and temporal steps: the global error for the total experimental data and the partial error for each element. Good simulations for the three experiments were obtained using the ACUAINTRUSION software with slight variations in the selectivity coefficients for both sediments determined in batch experiments with fresh water. The cation exchange parameters included in ACUAINTRUSION are those reported by the Gapon convention with modified exponents for the Ca/Mg exchange. PHREEQC simulations performed using the Gains-Thomas convention were unsatisfactory, with the exchange coefficients from the database of PHREEQC (or range), but those determined with fresh water - natural sediment allowed only an approximation to be obtained. For the treated sediment, the adjusted exchange coefficients were determined to improve the simulation and are vastly different from those from the database of PHREEQC or batch experiment values; however, these values fall in an order similar to the others determined under dynamic conditions. Different cation concentrations were simulated using two different software packages; this disparity could be attributed to the defined selectivity coefficients that affect the gypsum equilibrium. Consequently, different calculated sulphate concentrations are obtained using each type of software; a smaller mismatch was predicted using ACUAINTRUSION. In general, the presented

  8. Gas-phase reactions of aryl radicals with 2-butyne: experimental and theoretical investigation employing the N-methyl-pyridinium-4-yl radical cation.

    PubMed

    Lam, A K Y; Li, C; Khairallah, G; Kirk, B B; Blanksby, S J; Trevitt, A J; Wille, U; O'Hair, R A J; da Silva, G

    2012-02-21

    Aromatic radicals form in a variety of reacting gas-phase systems, where their molecular weight growth reactions with unsaturated hydrocarbons are of considerable importance. We have investigated the ion-molecule reaction of the aromatic distonic N-methyl-pyridinium-4-yl (NMP) radical cation with 2-butyne (CH(3)C≡CCH(3)) using ion trap mass spectrometry. Comparison is made to high-level ab initio energy surfaces for the reaction of NMP and for the neutral phenyl radical system. The NMP radical cation reacts rapidly with 2-butyne at ambient temperature, due to the apparent absence of any barrier. The activated vinyl radical adduct predominantly dissociates via loss of a H atom, with lesser amounts of CH(3) loss. High-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry allows us to identify small quantities of the collisionally deactivated reaction adduct. Statistical reaction rate theory calculations (master equation/RRKM theory) on the NMP+2-butyne system support our experimental findings, and indicate a mechanism that predominantly involves an allylic resonance-stabilized radical formed via H atom shuttling between the aromatic ring and the C(4) side-chain, followed by cyclization and/or low-energy H atom β-scission reactions. A similar mechanism is demonstrated for the neutral phenyl radical (Ph˙)+2-butyne reaction, forming products that include 3-methylindene. The collisionally deactivated reaction adduct is predicted to be quenched in the form of a resonance-stabilized methylphenylallyl radical. Experiments using a 2,5-dichloro substituted methyl-pyridiniumyl radical cation revealed that in this case CH(3) loss from the 2-butyne adduct is favoured over H atom loss, verifying the key role of ortho H atoms, and the shuttling mechanism, in the reactions of aromatic radicals with alkynes. As well as being useful phenyl radical analogues, pyridiniumyl radical cations may form in the ionosphere of Titan, where they could undergo rapid

  9. Towards rotationally state-resolved differential cross sections for the hydrogen exchange reaction

    SciTech Connect

    Vrakking, M.J.J.

    1992-11-01

    The hydrogen exchange reaction H + H{sub 2} {yields} H{sub 2} + H (and its isotopic variants) plays a pivotal role in chemical reaction dynamics. It is the only chemical reaction for which fully converged quantum scattering calculations have been carried out using a potential energy surface which is considered to be chemically accurate. To improve our ability to test the theory, a `perfect experiment`, measuring differential cross sections with complete specification of the reactant and product states, is called for. In this thesis, the design of an experiment is described that aims at achieving this goal for the D + H{sub 2} reaction. A crossed molecular beam arrangement is used, in which a photolytic D atom beam is crossed by a pulsed beam of H{sub 2} molecules. DH molecules formed in the D + H{sub 2} reaction are state-specifically ionized using Doppler-free (2+1) Resonance-Enhanced Multi-Photon Ionization (REMPI) and detected using a Position-sensitive microchannel plate detector. This detection technique has an unprecedented single shot detection sensitivity of 6.8 10{sup 3} molecules/cc. This thesis does not contain experimental results for the D + H{sub 2} reaction yet, but progress that has been made towards achieving this goal is reported. In addition, results are reported for a study of the Rydberg spectroscopy of the water molecule.

  10. Towards rotationally state-resolved differential cross sections for the hydrogen exchange reaction

    SciTech Connect

    Vrakking, M.J.J.

    1992-11-01

    The hydrogen exchange reaction H + H[sub 2] [yields] H[sub 2] + H (and its isotopic variants) plays a pivotal role in chemical reaction dynamics. It is the only chemical reaction for which fully converged quantum scattering calculations have been carried out using a potential energy surface which is considered to be chemically accurate. To improve our ability to test the theory, a 'perfect experiment', measuring differential cross sections with complete specification of the reactant and product states, is called for. In this thesis, the design of an experiment is described that aims at achieving this goal for the D + H[sub 2] reaction. A crossed molecular beam arrangement is used, in which a photolytic D atom beam is crossed by a pulsed beam of H[sub 2] molecules. DH molecules formed in the D + H[sub 2] reaction are state-specifically ionized using Doppler-free (2+1) Resonance-Enhanced Multi-Photon Ionization (REMPI) and detected using a Position-sensitive microchannel plate detector. This detection technique has an unprecedented single shot detection sensitivity of 6.8 10[sup 3] molecules/cc. This thesis does not contain experimental results for the D + H[sub 2] reaction yet, but progress that has been made towards achieving this goal is reported. In addition, results are reported for a study of the Rydberg spectroscopy of the water molecule.

  11. Ae4 (Slc4a9) is an electroneutral monovalent cation-dependent Cl−/HCO3− exchanger

    PubMed Central

    Peña-Münzenmayer, Gaspar; George, Alvin T.; Shull, Gary E.; Melvin, James E.

    2016-01-01

    Ae4 (Slc4a9) belongs to the Slc4a family of Cl−/HCO3− exchangers and Na+-HCO3− cotransporters, but its ion transport cycle is poorly understood. In this study, we find that native Ae4 activity in mouse salivary gland acinar cells supports Na+-dependent Cl−/HCO3− exchange that is comparable with that obtained upon heterologous expression of mouse Ae4 and human AE4 in CHO-K1 cells. Additionally, whole cell recordings and ion concentration measurements demonstrate that Na+ is transported by Ae4 in the same direction as HCO3− (and opposite to that of Cl−) and that ion transport is not associated with changes in membrane potential. We also find that Ae4 can mediate Na+-HCO3− cotransport–like activity under Cl−-free conditions. However, whole cell recordings show that this apparent Na+-HCO3− cotransport activity is in fact electroneutral HCO3−/Na+-HCO3− exchange. Although the Ae4 anion exchanger is thought to regulate intracellular Cl− concentration in exocrine gland acinar cells, our thermodynamic calculations predict that the intracellular Na+, Cl−, and HCO3− concentrations required for Ae4-mediated Cl− influx differ markedly from those reported for acinar secretory cells at rest or under sustained stimulation. Given that K+ ions share many properties with Na+ ions and reach intracellular concentrations of 140–150 mM (essentially the same as extracellular [Na+]), we hypothesize that Ae4 could mediate K+-dependent Cl−/HCO3− exchange. Indeed, we find that Ae4 mediates Cl−/HCO3− exchange activity in the presence of K+ as well as Cs+, Li+, and Rb+. In summary, our results strongly suggest that Ae4 is an electroneutral Cl−/nonselective cation–HCO3− exchanger. We postulate that the physiological role of Ae4 in secretory cells is to promote Cl− influx in exchange for K+(Na+) and HCO3− ions. PMID:27114614

  12. Chemistry of (and on) transition metal clusters: a Fourier transform ion cyclotron resonance study of the reaction of niobium cluster cations with nitric oxide.

    PubMed

    Harding, Daniel J; Oliver, Thomas A A; Walsh, Tiffany R; Drewello, Thomas; Woodruff, D Phil; Derrick, Peter J; Mackenzie, Stuart R

    2009-01-01

    The reactions of niobium cluster cations, Nb(+)(n) (n = 2-19), with nitric oxide have been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The overall reaction rate constants are found to be in reasonable agreement with collision rates calculated using the surface charge capture model. The dominant reaction for small clusters (n <9) involves reaction-induced fragmentation resulting in the loss of either NbO or NbN. By contrast, the main reaction observed for the larger clusters (n> 11) is sequential NO chemisorption. Clusters n = 9, 10 exhibit both extremes of behaviour and are the only clusters upon which there is evidence of NO decomposition with N(2) loss observed whenever multiple NO molecules are co-adsorbed. The rate constants for each process have been determined as a function of cluster size.

  13. Double-regge exchange limit for the γp→ K⁺K⁻p reaction

    DOE PAGES

    Shi, M.; Danilkin, I. V.; Fernández-Ramírez, C.; Mathieu, V.; Pennington, M. R.; Schott, D.; Szczepaniak, A. P.

    2015-02-01

    We apply the generalized Veneziano model (B₅ model) in the double-Regge exchange limit to the γp→K⁺K⁻p reaction. Four different cases defined by the possible combinations of the signature factors of leading Regge exchanges ((K*,a₂/f₂), (K*,ρ/ω), (K*₂,a₂/f₂), and (K*₂,ρ/ω)) have been simulated through the Monte Carlo method. Suitable event candidates for the double-Regge exchange high-energy limit were selected employing Van Hove plots as a better alternative to kinematical cuts in the K⁺K⁻p Dalitz plot. In this way we predict and analyze the double-Regge contribution to the K⁺K⁻p Dalitz plot, which constitutes one of the major backgrounds in the search for strangeonia,more » hybrids and exotics using γp→K⁺K⁻p reaction. We expect that data currently under analysis, and that to come in the future, will allow verification of the double-Regge behavior and a better assessment of this component of the amplitude.« less

  14. Double-regge exchange limit for the γp→ K⁺K⁻p reaction

    SciTech Connect

    Shi, M.; Danilkin, I. V.; Fernández-Ramírez, C.; Mathieu, V.; Pennington, M. R.; Schott, D.; Szczepaniak, A. P.

    2015-02-01

    We apply the generalized Veneziano model (B₅ model) in the double-Regge exchange limit to the γp→K⁺K⁻p reaction. Four different cases defined by the possible combinations of the signature factors of leading Regge exchanges ((K*,a₂/f₂), (K*,ρ/ω), (K*₂,a₂/f₂), and (K*₂,ρ/ω)) have been simulated through the Monte Carlo method. Suitable event candidates for the double-Regge exchange high-energy limit were selected employing Van Hove plots as a better alternative to kinematical cuts in the K⁺K⁻p Dalitz plot. In this way we predict and analyze the double-Regge contribution to the K⁺K⁻p Dalitz plot, which constitutes one of the major backgrounds in the search for strangeonia, hybrids and exotics using γp→K⁺K⁻p reaction. We expect that data currently under analysis, and that to come in the future, will allow verification of the double-Regge behavior and a better assessment of this component of the amplitude.

  15. EXFOR systems manual: Nuclear reaction data exchange format. Revision 97/1

    SciTech Connect

    McLane, V.

    1997-07-01

    This document describes EXFOR, the exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Center Network. In addition to storing the data and its` bibliographic information, experimental information, including source of uncertainties, is also compiled. The status and history of the data set is also included, e.g., the source of the data, any updates which have been made, and correlations to other data sets. EXFOR is designed for flexibility rather than optimization of data processing in order to meet the diverse needs of the nuclear reaction data centers. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center`s own sphere of responsibility. The exchange format, as outlined, is designed to allow a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in an easily machine-readable format (for checking and indicating possible errors) and a format that can be read by personnel (for passing judgment on and correcting any errors indicated by the machine).

  16. Controlling plasmonic "hot spots" in nanoparticle assemblies using ligand place-exchange reactions

    NASA Astrophysics Data System (ADS)

    Bao, Lanlan

    This thesis describes the 1) selective attachment of Au nanoparticles (NPs) to the edges of Au nanoplates via ligand place-exchange reactions, 2) preparation of coupled Au nanoplates via ligand place-exchange reactions, 3) attachment of Au NPs to Au nanorods via ligand place-exchange reactions, 4) study of the dynamics of ligand place-exchange reactions on Au nanoplates, 5) study of the changes in the optical properties of Au nanoplates upon attachment of Au NPs by observing the shift in the localized surface plasmon resonance (LSPR) band, and 6) study of the surface-enhanced Raman spectroscopy (SERS) enhancement of analyte molecules located in the "hot-spots" of coupled Au nanoplate-Au NP structures. We regio-selectively attached 20 nm Au NPs to Au nanoplates by first assembling hexanethiol (HT) onto Au nanoplates, then exchanging HT with 4-aminothiophenol (4-ATP) using different reaction times, and finally electrostatically attaching the negatively-charged Au NPs to the positively-charged 4-ATP ligands bound to the Au nanoplates. We prepared nanoplate-NP assemblies with 100% of the NPs attached to vertex sites or 100% attached to vertex and edge sites using 1 h and 2 h exchange times, respectively. The location and number of bound Au NPs to the nanoplates as a function of exchange time provided information about the mechanism of the ligand place-exchange reaction on the Au nanoplate surface. Ligand place-exchange starts from the vertex sites, then proceeds at the edge sites and finally occurs at smooth terrace sites for longer times. Direct exchange at terraces is possible but the data suggests it occurs mostly through lateral migration of the 4-ATP ligands from vertex/edge sites to the terrace. The data also suggests that phase segregation of 4-ATP ligands and HT ligands occurs on the terrace sites for longer times. The ligand place-exchange strategy also leads to interesting coupled Au nanoplate-Au nanoplate and Au nanorod-Au NP assemblies. The optical

  17. Huge Quantum Symmetry Effect in the O + O2 Exchange Reaction.

    PubMed

    Rao, Tammineni Rajagopala; Guillon, Grégoire; Mahapatra, Susanta; Honvault, Pascal

    2015-02-19

    We report extensive, full quantum-mechanical calculations for the (16)O + (16)O(16)O → (16)O(16)O + (16)O collisions, for both inelastic and atom exchange processes, using a time-independent method based on hyperspherical coordinates. The rates obtained in the present study are much larger than the previously reported ones for this system. The discrepancy is attributed to a huge symmetry effect that was missing in the studies so far. This effect differs from the well-known isotope effect. Importance of this quantum effect is further confirmed by comparison with results for the (16)O + (18)O(18)O → (16)O(18)O + (18)O, exchange reaction.

  18. A method to buffer the concentrations of free Zn and Cd ions using a cation exchange resin in bacterial toxicity studies

    SciTech Connect

    Knight, B.; McGrath, S.P.

    1995-12-01

    The chemical form or species of metal present in a growth system is crucial to the toxicity of that metal. A growth medium is described in which the free metal concentration of either Zn or Cd is known. A method using a cation exchange resin as a buffer to maintain free metal ion concentrations during microbial growth is discussed. Using a buffered system, free concentrations of 3.4 {micro}g Cd L{sup {minus}1} and 57 {micro}g Zn L{sup {minus}1} reduced the growth rate of a sensitive isolate of Rhizobium leguminosarum biovar trifolii. The results demonstrate that to assess the true toxicity of Cd and Zn, the free ion concentration must be considered and that small free concentrations must be buffered.

  19. Role of competitive cation exchange on chromatographic displacement of cesium in the vadose zone beneath the Hanford S/SX tank farm

    SciTech Connect

    Lichtner, Peter C.; Yabusaki, Steve; Pruess, Karsten; Steefel, Carl I.

    2003-10-01

    Migration of radionuclides under the SX-tank farm at the Hanford nuclear waste complex involves interaction of variably water saturated sediments with concentrated NaOH-NaNO3-NaNO2 solutions that have leaked from the tanks. Constant Kd models for describing radionuclide retardation are not valid under these conditions because of strong competition for sorption sites by abundant Na+ ions, and because of dramatically changing solution compositions with time as the highly concentrated tank fluid becomes diluted as it mixes with infiltrating rainwater. A mechanistic multicomponent sorption model is required that can account for effects of competition and spatially and temporally variable solution compositions. To investigate the influence of the high ionic strength tank fluids on Cs+ migration, numerical calculations are performed using the multiphase-multicomponent reactive transport code FLOTRAN. The computer model describes reactive transport in nonisothermal, variably saturated porous media including both liquid and gas phases. Pitzer activity coefficient corrections are used to describe the high ionic strength solutions. The calculations take into account multicomponent cation exchange based on measured selectivity coefficients specific to the Hanford sediments. Solution composition data obtained from Well 299-W23-19, documenting a moderately concentrated leak from the SX-115 tank, are used to calibrate the model. In addition to exchange of cations Na+, K+, Ca2+, and Cs+, aqueous complexing and a kinetic description of precipitation and dissolution of calcite are also included in the calculations. The fitted infiltration rate of 0.08 m yr-1, and fitted cation exchange capacity of 0.05 mol kg-1 are consistent with measured values for the Hanford sediments. A sensitivity analysis is performed for Na+ concentrations ranging from 5 to 20 m to investigate the mobility of Cs+ interacting with a highly concentrated background electrolyte solution believed to have been

  20. Role of Competitive Cation Exchange on Chromatographic Displacement of Cesium in the Vadose Zone beneath the Hanford S/SX Tank Farm

    SciTech Connect

    Lichtner, Peter C.; Yabusaki, Steven B.; Pruess, Karsten; Steefel, Carl

    2004-01-12

    Migration of radionuclides under the SX-tank farm at the Hanford nuclear waste complex involves interaction of variably water saturated sediments with concentrated NaOH-NaNO{sub 3}-NaNO{sub 2} solutions that have leaked from the tanks. Constant K{sub d} models for describing radionuclide retardation are not valid under these conditions because of strong competition for sorption sites by abundant Na{sup +} ions, and because of dramatically changing solution compositions with time as the highly concentrated tank fluid becomes diluted as it mixes with infiltrating rainwater. A mechanistic multicomponent sorption model is required that can account for effects of competition and spatially and temporally variable solution compositions. To investigate the influence of the high ionic strength tank fluids on Cs{sup +} migration, numerical calculations are performed using the multiphase-multicomponent reactive transport code FLOTRAN. The computer model describes reactive transport in nonisothermal, variably saturated porous media including both liquid and gas phases. Pitzer activity coefficient corrections are used to describe the high ionic strength solutions. The calculations take into account multicomponent cation exchange based on measured selectivity coefficients specific to the Hanford sediments. Solution composition data obtained from Well 299-W23-19, documenting a moderately concentrated leak from the SX-115 tank, are used to calibrate the model. In addition to exchange of cations Na{sup +}, K{sup +}, Ca{sup 2+}, and Cs{sup +}, aqueous complexing and a kinetic description of precipitation and dissolution of calcite are also included in the calculations. The fitted infiltration rate of 0.08 m yr{sup -1}, and fitted cation exchange capacity of 0.05 mol kg{sup -1} are consistent with measured values for the Hanford sediments. A sensitivity analysis is performed for Na{sup +} concentrations ranging from 5 to 20 m to investigate the mobility of Cs{sup +} interacting with

  1. Investigation of the swelling behavior of cationic exchange resins saturated with Na{sup +} ions in a C{sub 3}S paste

    SciTech Connect

    Lafond, E.; Cau Dit Coumes, C.; Gauffinet, S.; Chartier, D.; Le Bescop, P.; Stefan, L.; Nonat, A.

    2015-03-15

    Ion exchange resins (IERs) are widely used by the nuclear industry to decontaminate radioactive effluents. Spent products are usually encapsulated in cementitious materials. However, the solidified waste form can exhibit strong expansion, possibly leading to cracking, if the appropriate binder is not used. In this work, the interactions between cationic resins in the Na{sup +} form and tricalcium silicate are investigated during the early stages of hydration in order to gain a better understanding of the expansion process. It is shown that the IERs exhibit a transient swelling of small magnitude due to the decrease in the osmotic pressure of the external solution. This expansion, which occurs just after setting, is sufficient to damage the material which is poorly consolidated for several reasons: low degree of hydration, precipitation of poorly cohesive sodium-bearing C–S–H, and very heterogeneous microstructure with zones of high porosity.

  2. Sequential Determination of Total Arsenic and Cadmium in Concentrated Cadmium Sulphate Solutions by Flow-Through Stripping Chronopotentiometry after Online Cation Exchanger Separation

    PubMed Central

    Cacho, Frantisek; Lauko, Lukas; Manova, Alena; Dzurov, Jan; Beinrohr, Ernest

    2012-01-01

    Flow-through stripping chronopotentiometry with a gold wire electrode was used for the determination of total arsenic and cadmium in cadmium sulphate solutions for cadmium production. The analysis is based on the online separation of arsenic as arsenate anion from cadmium cations by means of a cation exchanger. On measuring arsenate in the effluent, the trapped cadmium is eluted by sodium chloride solution and determined in a small segment of the effluent by making use of the same electrode. The elaborated protocol enables a full automatic measurement of both species in the same sample solution. The accuracy of the results was confirmed by atomic absorption spectrometry. The LOD and LOQ for Arsenic were found to be 0.9 μg dm−3 and 2.7 μg dm−3, respectively. A linear response range was observed in the concentration range of 1 to 300 μg dm−3 for sample volumes of 4 mL. The repeatability and reproducibility were found to be 2.9% and 5.2%, respectively. The linear response range for cadmium was found to be 0.5 to 60 g/L. The method was tested on samples from a cadmium production plant. PMID:22448343

  3. LA-ICP-MS of rare earth elements concentrated in cation-exchange resin particles for origin attribution of uranium ore concentrate.

    PubMed

    Asai, Shiho; Limbeck, Andreas

    2015-04-01

    Rare earth elements (REE) concentrated on cation-exchange resin particles were measured with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to obtain chondrite-normalized REE plots. The sensitivity of REE increased in ascending order of the atomic number, according to the sensitivity trend in pneumatic nebulization ICP-MS (PN-ICP-MS). The signal intensities of REE were nearly proportional to the concentrations of REE in the immersion solution used for particle-preparation. Minimum measurable concentration calculated from the net signals of REE was approximately 1 ng/g corresponding to 0.1 ng in the particle-preparation solution. In LA analysis, formation of oxide and hydroxide of the light REE and Ba which causes spectral interferences in the heavy REE measurement was effectively attenuated due to the solvent-free measurement capability, compared to conventional PN-ICP-MS. To evaluate the applicability of the proposed method, the REE-adsorbed particles prepared by immersing them in a U-bearing solution (commercially available U standard solution) were measured with LA-ICP-MS. Aside from the LA analysis, each concentration of REE in the same U standard solution was determined with conventional PN-ICP-MS after separating REE by cation-exchange chromatography. The concentrations of REE were ranging from 0.04 (Pr) to 1.08 (Dy) μg/g-U. The chondrite-normalized plot obtained through LA-ICP-MS analysis of the U standard sample exhibited close agreement with that obtained through the PN-ICP-MS of the REE-separated solution within the uncertainties.

  4. Ion-neutral reaction of the C2H2N+ cation with C2H2: An experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Fathi, P.; Geppert, W. D.; Kaiser, A.; Ascenzi, D.

    2016-03-01

    The ion-neutral reactions of the C2H2N+ cation with C2H2 have been investigated using a Guided Ion Beam Mass Spectrometer (GIB-MS). The following ionic products were observed: CH3+, C2H2+, C2H3+, HNC+ /HCN+ , HCNH+, C3H+ , C2N+ , C3H3+, HCCN+ and C4H2N+ . Theoretical calculations have been carried out to propose reaction pathways leading to the observed products. These processes are of relevance for the generation of long chain nitrogen-containing species and they may be of interest for the chemistry of Titan's ionosphere or circumstellar envelopes.

  5. Barrier Height for the Exchange Reaction F + HF → FH + F

    PubMed Central

    O'Neil, Stephen V.; Schaefer, Henry F.; Bender, Charles F.

    1974-01-01

    There exists a body of conflicting data as to the existence or nonexistence of FHF, ClHCl, BrHBr, and IHI as chemically bound molecular species. Ab initio quantum mechanical electronic structure calculations are presented which predict linear symmetric FHF to be unstable. The barrier height for the F + HF exchange reaction is suggested to be no less than 18 kcal/mol, much larger than expected either intuitively or on the basis of certain experiments on related systems. The expected reliability of the calculations is based upon comparable results for diatomic molecules and the F + H2 and H + F2 potential energy surfaces. PMID:16592128

  6. Catalytic Activity of Cationic and Neutral Silver(I)-XPhos Complexes with Nitrogen Ligands or Tolylsulfonate for Mannich and Aza-Diels-Alder Coupling Reactions.

    PubMed

    Grirrane, Abdessamad; Álvarez, Eleuterio; García, Hermenegildo; Corma, Avelino

    2016-01-01

    Cationic and neutral silver(I)-L complexes (L=Buchwald-type biaryl phosphanes) with nitrogen co-ligands or organosulfonate counter ions have been synthesised and characterised through their structural and spectroscopic properties. At room temperature, both cationic and neutral silver(I)-L complexes are extremely active catalysts in the promotion of the single and double A(3) coupling of terminal (di)alkynes, pyrrolidine and formaldehyde. In addition, the aza-Diels-Alder two- and three-component coupling reactions of Danishefsky's diene with an imine or amine and aldehyde are efficiently catalysed by these cationic or neutral silver(I)-L complexes. The solvent influences the catalytic performance due to limited complex solubility or solvent decomposition and reactivity. The isolation of new silver(I)-L complexes with reagents as ligands lends support to mechanistic proposals for such catalytic processes. The activity, stability and metal-distal arene interaction of these silver(I)-L catalysts have been compared with those of analogous cationic gold(I) and copper(I) complexes. PMID:26598792

  7. Identification of a critical intermediate in galvanic exchange reactions by single-nanoparticle-resolved kinetics.

    PubMed

    Smith, Jeremy G; Yang, Qing; Jain, Prashant K

    2014-03-10

    The realization of common materials transformations in nanocrystalline systems is fostering the development of novel nanostructures and allowing a deep look into the atomistic mechanisms involved. Galvanic corrosion is one such transformation. We studied galvanic replacement within individual metal nanoparticles by using a combination of plasmonic spectroscopy and scanning transmission electron microscopy. Single-nanoparticle reaction trajectories showed that a Ag nanoparticle exposed to Au³⁺ makes an abrupt transition into a nanocage structure. The transition is limited by a critical structural event, which we identified by electron microscopy to comprise the formation of a nanosized void. Trajectories also revealed a surprisingly strong nonlinearity of the reaction kinetics, which we explain by a model involving the critical coalescence of vacancies into a growing void. The critical void size for galvanic exchange to spontaneously proceed was found to be 20 atomic vacancies.

  8. Selective sorption of lead, cadmium and zinc ions by a polymeric cation exchanger containing nano-Zr(HPO3S)2.

    PubMed

    Zhang, Qingrui; Pan, Bingcai; Pan, Bingjun; Zhang, Weiming; Jia, Kun; Zhang, Quanxing

    2008-06-01

    A novel polymeric hybrid sorbent, namely ZrPS-001, was fabricated for enhanced sorption of heavy metal ions by impregnating Zr(HPO3S)2 (i.e., ZrPS) nanoparticles within a porous polymeric cation exchanger D-001. The immobilized negatively charged groups bound to the polymeric matrix D-001 would result in preconcentration and permeation enhancement of target metal ions prior to sequestration, and ZrPS nanoparticles are expected to sequester heavy metals selectively through an ion-exchange process. Highly effective sequestration of lead, cadmium, and zinc ions from aqueous solution can be achieved by ZrPS-001 even in the presence of competing calcium ion at concentration several orders of magnitude greater than the target species. The exhausted ZrPS-001 beads are amenable to regeneration with 6 M HCI solution for repeated use without any significant capacity loss. Fixed-bed column treatment of simulated waters containing heavy metals at high or trace levels was also performed. The content of heavy metals in treated effluent approached or met the WHO drinking water standard.

  9. Rapid method of separating Am(VI) from transplutonium and rare-earth elements on a cation exchanger in phosphoric acid

    SciTech Connect

    Tikhomirova, G.S.; Guseva, L.I.

    1988-07-01

    Measurements have been made on cation-exchanger sorption of americium, other actinoids, and certain rare-earth elements from 0.1-2.0 M H/sub 3/PO/sub 4/ when the elements have been oxidized with ammonium persulfate alone or mixed with silver phosphate. There are considerable differences in behavior between the americium and the other elements on account of its being oxidized to a higher valency state. Measurements have been made on the effects of acid and oxidant concentrations and of the oxidation and elution conditions on the americium yield when the exchanger is treated with H/sub 3/PO/sub 4/. Optimum oxidation conditions have been chosen, and a rapid method has been devised for separating americium(VI) from other transplutonium elements and REE on Dowex 50 /times/ 8, where the eluent is 0.1-1.0 M H/sub 3/PO/sub 4/ plus 0.05 M (NH/sub 4/)/sub 2/S/sub 2/O/sub 8/.

  10. Selective sorption of lead, cadmium and zinc ions by a polymeric cation exchanger containing nano-Zr(HPO3S)2.

    PubMed

    Zhang, Qingrui; Pan, Bingcai; Pan, Bingjun; Zhang, Weiming; Jia, Kun; Zhang, Quanxing

    2008-06-01

    A novel polymeric hybrid sorbent, namely ZrPS-001, was fabricated for enhanced sorption of heavy metal ions by impregnating Zr(HPO3S)2 (i.e., ZrPS) nanoparticles within a porous polymeric cation exchanger D-001. The immobilized negatively charged groups bound to the polymeric matrix D-001 would result in preconcentration and permeation enhancement of target metal ions prior to sequestration, and ZrPS nanoparticles are expected to sequester heavy metals selectively through an ion-exchange process. Highly effective sequestration of lead, cadmium, and zinc ions from aqueous solution can be achieved by ZrPS-001 even in the presence of competing calcium ion at concentration several orders of magnitude greater than the target species. The exhausted ZrPS-001 beads are amenable to regeneration with 6 M HCI solution for repeated use without any significant capacity loss. Fixed-bed column treatment of simulated waters containing heavy metals at high or trace levels was also performed. The content of heavy metals in treated effluent approached or met the WHO drinking water standard. PMID:18589978

  11. Preparation and evaluation of differently sulfonated styrene-divinylbenzene cross-linked copolymer cationic exchange resins as novel carriers for drug delivery.

    PubMed

    Akkaramongkolporn, Prasert; Ngawhirunpat, Tanasait; Opanasopit, Praneet

    2009-01-01

    The differently sulfonated styrene-divinylbenzene cross-linked copolymer cationic exchange resins were prepared by oil-in-water polymerization and varied degrees of sulfonation. Several characteristics of the obtained resins were evaluated, i.e., Fourier transform infrared spectra, the ion-exchange capacity, microscopic morphology, size, and swelling. The resin characteristics were altered in relation to the degree of sulfonation, proving that differently sulfonated resins could be prepared. The behavior of chlorpheniramine (CPM) loading and in vitro release in the USP simulated gastric (SGF) and intestinal fluids (SIF) of the obtained resins were also evaluated. The CPM loaded in the resinates (drug-loaded resins) increased with the increasing degree of sulfonic group and hence the drug binding site in the employed resins. The CPM release was lower from the resins with the higher degree of sulfonic group due to the increase in the diffusive path depth. The CPM release was obviously lower in SGF than SIF because CPM, a weak base drug, ionized to a greater extent in SGF and then preferred binding with rather than releasing from the resins. In conclusion, the differently sulfonated resins could be utilized as novel carriers for drug delivery.

  12. Does Size Really Matter? The Steric Isotope Effect in a Supramolecular Host?Guest Exchange Reaction

    SciTech Connect

    Mugridge, Jeffrey; Bergman, Robert; Raymond, Kenneth

    2010-01-29

    Isotope effects (IEs), which arise from differences in zero point energies (ZPEs) between a parent and isotopically substituted bond, have been used extensively by chemists to probe molecular interactions and reactivity. Due to the anharmonicity of the C-H/D vibrational potential energy function and the lower ZPE of a C-D bond, the average C-D bond length is typically {approx}0.005 {angstrom} shorter than an equivalent C-H bond. It is this difference in size that is often invoked to explain the observation of secondary, inverse kinetic isotope effects (KIEs) in chemical processes which proceed through a sterically strained transition state. This so-called 'steric isotope effect' (SIE) has been observed in processes such as the racemization of ortho-substituted biphenyls[6] and phenanthrenes, ring flipping of cyclophanes, and more recently in the deslipping of rotaxanes, where substitution of the sterically less demanding deuterium for protium results in rate accelerations for these processes. Herein, we use deuterium substitution in a cationic guest molecule to probe the sensitivity limits of the guest exchange process from a highly-charged supramolecular host.

  13. O2 activation by binuclear Cu sites: Noncoupled versus exchange coupled reaction mechanisms

    NASA Astrophysics Data System (ADS)

    Chen, Peng; Solomon, Edward I.

    2004-09-01

    Binuclear Cu proteins play vital roles in O2 binding and activation in biology and can be classified into coupled and noncoupled binuclear sites based on the magnetic interaction between the two Cu centers. Coupled binuclear Cu proteins include hemocyanin, tyrosinase, and catechol oxidase. These proteins have two Cu centers strongly magnetically coupled through direct bridging ligands that provide a mechanism for the 2-electron reduction of O2 to a µ-2:2 side-on peroxide bridged species. This side-on bridged peroxo-CuII2 species is activated for electrophilic attack on the phenolic ring of substrates. Noncoupled binuclear Cu proteins include peptidylglycine -hydroxylating monooxygenase and dopamine -monooxygenase. These proteins have binuclear Cu active sites that are distant, that exhibit no exchange interaction, and that activate O2 at a single Cu center to generate a reactive CuII/O2 species for H-atom abstraction from the C-H bond of substrates. O2 intermediates in the coupled binuclear Cu enzymes can be trapped and studied spectroscopically. Possible intermediates in noncoupled binuclear Cu proteins can be defined through correlation to mononuclear CuII/O2 model complexes. The different intermediates in these two classes of binuclear Cu proteins exhibit different reactivities that correlate with their different electronic structures and exchange coupling interactions between the binuclear Cu centers. These studies provide insight into the role of exchange coupling between the Cu centers in their reaction mechanisms.

  14. Identification of a Critical Intermediate in Galvanic Exchange Reactions by Single-Nanoparticle Resolved Kinetics

    NASA Astrophysics Data System (ADS)

    Smith, Jeremy George; Jain, Prashant

    2014-06-01

    The realization of common materials transformations in nanocrystalline systems is fostering the development of novel nanostructures and allowing a deep look into the atomistic mechanisms involved. Galvanic corrosion is one such transformation. We studied galvanic replacement within individual metal nanoparticles by using plasmonic spectroscopy. This proved to be a powerful approach to studying materials transformations in the absence of ensemble averaging. Individual nanoscale units act as domains that can be interrogated optically in isolation, whereas the averaging of all such domains provides a bulk reaction trajectory. Single-nanoparticle reaction trajectories showed that a Ag nanoparticle exposed to Au3+ makes an abrupt transition into a nanocage structure. The transition is limited by a critical structural event, which we identified by electron microscopy to comprise the formation of a nanosized void, similar to the pitting process commonly observed in the corrosion of metals. Trajectories also revealed a surprisingly strong nonlinearity of the reaction kinetics, which we explain by a model involving the critical coalescence of vacancies into a growing void. The critical void size for galvanic exchange to spontaneously proceed was found to be 20 atomic vacancies. In the future we hope to extend this approach to examine a wide variety of materials transformations and chemical reactions.

  15. Evolution with time of hydrophobicity and microrelief of a cation-exchange membrane surface and its impact on overlimiting mass transfer.

    PubMed

    Pismenskaya, Natalia D; Nikonenko, Victor V; Melnik, Nadezhda A; Shevtsova, Kseniya A; Belova, Elena I; Pourcelly, Gérald; Cot, Didier; Dammak, Lasâad; Larchet, Christian

    2012-02-23

    Surface properties were measured together with electrochemical characteristics of a CMX (Neosepta, Tokuyama Corp.) cation-exchange membrane. Relative hydrophobicity was controlled by the contact angle; XPS and SEM were used for characterizing chemical composition and microrelief of the surface, respectively. Voltammetry, chronopotentiometry, and mass transfer rate measurements were made as well. A "fresh" membrane and samples after 10, 25, 100, and 150 h of operation in an electrodialysis cell at an overlimiting current equal to 3 theoretical limiting currents, in a 0.02 M NaCl solution, were characterized. Some electrochemical properties were also measured for a Neosepta cation-exchange membrane, aged 2 years, in an industrial food process. It was found that the hydrophobicity of the CMX membrane has increased after the first 10 h of operation; more and more cavities of the dimension of the order of 1 μm have appeared with time testifying electrochemical erosion of the surface. The limiting current density (i(lim)) and the overlimiting transfer rate through the CMX membrane increased with time of its operation under overlimiting current. In the case of new CMX, i(lim) was very close to the theoretical value i(lim)(theor) calculated by the Lévêque equation. After 10 h of operation, i(lim) increased by 5%, and after 25, 100, and 150 h, the increase was by 30%, 70%, and 100%, respectively. Similarly, the mass transfer rate was found to increase up to 5 times (when desalting 0.005 M NaCl under 3 V) in comparison with the theoretical value. The ensemble of data was explained by the hypothesis that the passage of intensive current produces erosion of the ion-exchange polymer forming a continuous phase in CMX. This erosion results in exposure at the surface of the other constituent of CMX: small (about 100 nm) particles of relatively hydrophobic polyvinylchloride. Increasing surface hydrophobicity facilitates the slip of electroconvective vortexes along the surface

  16. Evolution with time of hydrophobicity and microrelief of a cation-exchange membrane surface and its impact on overlimiting mass transfer.

    PubMed

    Pismenskaya, Natalia D; Nikonenko, Victor V; Melnik, Nadezhda A; Shevtsova, Kseniya A; Belova, Elena I; Pourcelly, Gérald; Cot, Didier; Dammak, Lasâad; Larchet, Christian

    2012-02-23

    Surface properties were measured together with electrochemical characteristics of a CMX (Neosepta, Tokuyama Corp.) cation-exchange membrane. Relative hydrophobicity was controlled by the contact angle; XPS and SEM were used for characterizing chemical composition and microrelief of the surface, respectively. Voltammetry, chronopotentiometry, and mass transfer rate measurements were made as well. A "fresh" membrane and samples after 10, 25, 100, and 150 h of operation in an electrodialysis cell at an overlimiting current equal to 3 theoretical limiting currents, in a 0.02 M NaCl solution, were characterized. Some electrochemical properties were also measured for a Neosepta cation-exchange membrane, aged 2 years, in an industrial food process. It was found that the hydrophobicity of the CMX membrane has increased after the first 10 h of operation; more and more cavities of the dimension of the order of 1 μm have appeared with time testifying electrochemical erosion of the surface. The limiting current density (i(lim)) and the overlimiting transfer rate through the CMX membrane increased with time of its operation under overlimiting current. In the case of new CMX, i(lim) was very close to the theoretical value i(lim)(theor) calculated by the Lévêque equation. After 10 h of operation, i(lim) increased by 5%, and after 25, 100, and 150 h, the increase was by 30%, 70%, and 100%, respectively. Similarly, the mass transfer rate was found to increase up to 5 times (when desalting 0.005 M NaCl under 3 V) in comparison with the theoretical value. The ensemble of data was explained by the hypothesis that the passage of intensive current produces erosion of the ion-exchange polymer forming a continuous phase in CMX. This erosion results in exposure at the surface of the other constituent of CMX: small (about 100 nm) particles of relatively hydrophobic polyvinylchloride. Increasing surface hydrophobicity facilitates the slip of electroconvective vortexes along the surface

  17. Ion-pairing ability, chemical stability, and selectivity behavior of halogenated dodecacarborane cation exchangers in neutral carrier-based ion-selective electrodes.

    PubMed

    Peper, Shane; Qin, Yu; Almond, Philip; McKee, Michael; Telting-Diaz, Martin; Albrecht-Schmitt, Thomas; Bakker, Eric

    2003-05-01

    Recently, it has been discovered that carba-closo-dodecaborates can be used as cation exchangers in neutral carrier-based ion-selective chemical sensors. Because of their inherent chemical stability and versatile functionalization chemistries, they offer many advantages that may potentially be exploited for ion analyses that require nontraditional sample conditions, including strongly acidic media. In this work, trimethylammonium salts of undecachlorinated (UCC), undecabrominated (UBC), hexabrominated (HBC), and undecaiodinated (UIC) carborane anions were prepared and evaluated for their potential use in solvent polymeric membrane-based sensors. Computational methods including Natural population analysis and electrostatic mapping were used to predict the ion-exchanging ability of each lipophilic anion. In addition, the sandwich membrane technique was used to evaluate the ion-pairing ability of each carborane anion in situ (i.e., within bis(2-ethylhexyl) sebacate (DOS)- and 2-nitrophenyl octyl ether (o-NPOE)-plasticized ISE membranes). The results of the computational and potentiometric studies found that binding affinity of the anions followed the generalized trend HBC > UCC > UBC > UIC. PVC-DOS bulk optode thin films containing the chromoionophore ETH 5315 and a respective anion were used to determine the chemical stability/lipophilicity of the carboranes and tetrakis[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) in acidic media (0.2 M HOAc) under flowing conditions. The studies found that in terms of stability/lipophilicity UIC > UBC > TFPB approximately UCC > HBC. Electrodes containing a Pb(2+)-selective ionophore, tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide)(lead IV), were used to evaluate the functionality of each cation exchanger. An evaluation of response characteristics such as slope and selectivity found that UIC and UBC were quite comparable to the behavior of TFPB. Interestingly, both UIC and UBC showed a marked selectivity improvement

  18. TraML—A Standard Format for Exchange of Selected Reaction Monitoring Transition Lists*

    PubMed Central

    Deutsch, Eric W.; Chambers, Matthew; Neumann, Steffen; Levander, Fredrik; Binz, Pierre-Alain; Shofstahl, Jim; Campbell, David S.; Mendoza, Luis; Ovelleiro, David; Helsens, Kenny; Martens, Lennart; Aebersold, Ruedi; Moritz, Robert L.; Brusniak, Mi-Youn

    2012-01-01

    Targeted proteomics via selected reaction monitoring is a powerful mass spectrometric technique affording higher dynamic range, increased specificity and lower limits of detection than other shotgun mass spectrometry methods when applied to proteome analyses. However, it involves selective measurement of predetermined analytes, which requires more preparation in the form of selecting appropriate signatures for the proteins and peptides that are to be targeted. There is a growing number of software programs and resources for selecting optimal transitions and the instrument settings used for the detection and quantification of the targeted peptides, but the exchange of this information is hindered by a lack of a standard format. We have developed a new standardized format, called TraML, for encoding transition lists and associated metadata. In addition to introducing the TraML format, we demonstrate several implementations across the community, and provide semantic validators, extensive documentation, and multiple example instances to demonstrate correctly written documents. Widespread use of TraML will facilitate the exchange of transitions, reduce time spent handling incompatible list formats, increase the reusability of previously optimized transitions, and thus accelerate the widespread adoption of targeted proteomics via selected reaction monitoring. PMID:22159873

  19. Experimental and theoretical study on gas-phase ion/molecule reactions of silver trimer cation, Ag{sub 3}{sup