Simultaneous separation of inorganic anions and cations by using anion-exchange and cation-exchange columns connected in tandem in ion chromatography

Inorganic anions and cations in environmental waters were determined by ion chromatography. Stationary and mobile phases were examined for the simultaneous separation of both anions and cations. Cations detection by UV detection requires a mobile phase with a UV absorbing additive, which indirectly visualizes cations as negative peaks. Simultaneous separation of anions and cations were achieved when using an eluent that consists of inorganic acid with weak basic amino acid as additives. It was convenient to separate both anions and cations by coupling anion-exchange and cation-exchange columns in tandem. The order of the separation columns connected affected the elution profiles. When the eluent comprises of multiple anions and a single cation, the anion-exchange column should be connected in the upper stream, whereas when the eluent comprises multiple cations and a single anion, the cation-exchange column should be connected in the upper stream. Use of switching valves also allowed simultaneous separation of anions and cations in a single chromatographic run. In the present work, operating conditions were optimized for the simultaneous separation of anions and cations.     

Rheological and DSC studies of mixtures of gellan gum and konjac glucomannan

The interaction between gellan gum (GELL) and konjac glucomannan (KGM) with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride has been monitored using mechanical spectroscopy and differential scanning calorimetry (DSC). The rheological results indicated that the synergism occurred at sufficient low temperatures where individual helices of GELL molecules were sufficiently aggregated. With progressive addition of monovalent cations, storage shear modulus G' and loss shear modulus G” for mixtures gradually increased, and not only the helix-coil transition temperature of GELL molecules in mixtures but also the sol-gel transition temperature for mixtures shifted to higher temperatures with increasing concentration of salts. Moreover, in the presence of sufficient monovalent cations, mixtures formed an elastic gel with large thermal hysteresis. In the presence of divalent cations, the synergistic interaction was promoted up to a certain concentration, however, with more progressive addition of divalent cations, the main structure formed by aggregates of GELL helices would be smaller, so that mixtures could not form a gel in the presence of excessive divalent cations. DSC results indicated that the intermolecular binding complexes between GELL and KGM molecules would not occur, but KGM markedly influenced the disorder-order transition of GELL molecules. We have suggested that KGM was attached to the surface of large aggregates of GELL helices, and since cations promote GELL self-aggregation by a screening effect, the synergistic interaction between GELL and KGM was promoted with increasing concentration of salts. However, excessive divalent cations formed various aggregates of GELL helices with different thermal stabilities, so that the phase-separation in GELL/KGM mixtures was promoted in the presence of excessive divalent cations.     

High-pressure and -temperature ion exchange of aluminosilicate and gallosilicate natrolite

The simultaneous application of high pressure and high temperature has been used to achieve direct ion exchange of large cesium cations for the small sodium cations found in the zeolite natrolite by putting it into a superhydrated state with increased pore size. The larger cations remain trapped upon pressure release, and thus, this method is a means of producing new cationic forms of zeolites.     

Construction and control of plasmid DNA network

The influences of different cations on plasmid DNA network structures on a mica substrate were investigated by atomic force microscopy (AFM). Interactions between the DNA strands and mica substrate, and between the DNA strands themselves were more strongly influenced by the complex cations (Fe(phen)3(2+), Ni(phen)3(2+), and Co(phen)3(3+)) than by the simple cations (Mg2+, Mn2+, Ni2+, Ca2+, Co3+). The mesh height of the plasmid DNA network was higher when the complex cations were added to DNA samples. The mesh size decreased with increasing DNA concentration and increased with decreasing DNA concentration in the same cation solution sample. Hence, plasmid DNA network height can be controlled by selecting different cations, and the mesh size can be controlled by adjusting plasmid DNA concentration.     

Design and preparation of a novel temperature-responsive ionic gel. 3. Valence selective control of transport modes of ions in response to temperature

We propose a novel model dialysis system that can valence-selectively control the transport modes of ions in response to temperature change. In a dialysis system consisting of an anionic gel membrane and mixed solutions containing a driving electrolyte and electrolytes with uni-, bi-, and trivalent cations, the dependence of the charge density of the gel and the valence of the ions on the transport modes of the ions through the gel membrane was investigated by computer simulations. The simulations show that the system has four transport types in the transport modes of the cations according to their valence [downhill (transport along their own concentration gradient in the system) and uphill (transport against their own concentration gradient)] in response to the charge density changes: (A) downhill transport of all the cations; (B) uphill transport of trivalent cations, downhill transport of the other cations; (C) uphill transport of bi- and trivalent cations, downhill transport of univalent cations; and (D) uphill transport of all the cations except for the driving cations. To examine the prediction of the simulations, a temperature-responsive anionic gel membrane was prepared from a modified poly(vinyl alcohol) (PVA) containing 2 mol % of sulfonic acid groups and another modified PVA prepared by in situ polymerization of N-isopropylacrylamide in a PVA solution. Permeation experiments in a dialysis system consisting of the membrane and mixed electrolyte solutions of NaCl, LiCl, CaCl2, and LaCl3 indicate that the system valence-selectively controls the transport modes of the cations in response to temperature change as predicted in our simulations.     

Synthesis and isolation of polytrityl cations by utilizing hexaphenylbenzene and tetraphenylmethane scaffolds

The successful isolation of stable (and soluble) hexa- and tetratrityl cations based on hexaphenylbenzene and tetraphenylmethane scaffold has been accomplished by using readily available starting materials. These robust polytrityl cations can be isolated in crystalline form and stored indefinitely at 0 degrees C. Their structures have been established by (1)H/(13)C NMR spectroscopy and by UV-vis spectroscopy. The structures of these polytrityl cations were further confirmed by quantitative transformations to the reduced (poly)triphenylmethyl derivatives by hydride transfer from triethylsilane, cycloheptatriene, or a borane-dimethyl sulfide complex.     

Adsorptive bubble separation of zinc and cadmium cations in presence of ferric and aluminum hydroxides

The adsorptive bubble separation of zinc and cadmium cations from solution in the presence of ferric and aluminum hydroxides was carried out by means of Tween 80 (nonionic surfactant), and sodium laurate and stearate (anionic surfactants). The mechanism of metal removal is different depending on the nature of the surfactant used. The removal of zinc cations by adsorbing colloid flotation is higher than that of cadmium cations. It increases with increases in the amount of hydroxide precipitate and the concentration of Tween 80. The removal of zinc cations by ion flotation is lower than that of cadmium cations. It does not change with increases in the hydroxide amount. It increases, however, with increased sodium laurate or stearate concentration. Both separation methods turned out to be helpful for studying both the solution's structure and the interactions at the solution-solid interface.     

OFF沸石中锂离子在骨架外的分布及可接近性

对OFF沸石进行离子交换制备出NH4-OFF沸石,然后通过Li2CO3/NH4-OFF体系的固态反应制备了不同锂离子交换度的Li-OFF沸石。对吸附氮气和氧气的Li-OFF样品进行了7Li MAS NMR表征。研究发现,所有吸附氧气样品的部分7Li MAS NMR共振峰均发生了顺磁位移。通过对实验谱的拟合,得知Li-OFF沸石中的锂离子可分布在三类阳离子位置（A、B和C）上,对应于三个不同位移的谱峰。Li+离子并非等比例地进入三个可交换的位置,而是优先占据主孔道中的A位置,随着交换度的升高,位能较高的C和B位置上的Li离子占有率逐渐增加。在100％固态交换度样品中,Li+离子在不同离子位的占有率分别为17％(位置B)、29％(位置C)和54％(位置A)。其中,位置B是O2分子不可接近的,所以Li-OFF沸石中有83％的阳离子是可以接近的。     

On the nature of gallium species in gallium-modified mordenite and MFI zeolites. A comparative DRIFT study of carbon monoxide adsorption and hydrogen dissociation

The results of a DRIFT study of carbon monoxide molecular adsorption and hydrogen dissociative adsorption on gallium-modified mordenite and MFI (ZSM-5) zeolites are presented. It was found that in the reduced gallium-modified mordenite (Ga-MOR) both Ga(3+) and Ga(+) exchanged cations are present and can be detected by CO adsorption. Ga(3+) cations in Ga-MOR dissociatively adsorb molecular hydrogen at elevated temperatures, resulting in the formation of gallium hydride species and acidic hydroxyl groups. In the reduced Ga-MFI evacuated at 823 K under medium vacuum conditions only Ga(+) exchanged intrazeolite cations were detected. It was found, however, that Ga(3+) intrazeolite exchanged cations which form upon high-temperature disproportionation of Ga(+) cations in the reduced Ga-MFI and Ga-MOR can be stabilized by high-temperature oxidation of these zeolites.     

Radical cations of branched alkanes in solutions: time-resolved magnetic field effect and quantum chemical studies

Radical cations of heptane and octane isomers, as well as several longer branched alkanes, were detected in irradiated n-hexane solutions at room temperature by the method of time-resolved magnetic field effect (TR MFE). To identify radical cations, the hyperfine coupling constants as determined by simulation of the TR MFE curves were compared to the constants calculated using the density functional theory (DFT) approach. The g-values of the observed radical cations were close to that of the 2,2,3,3-tetramethylbutane radical cation studied earlier by optically detected electron spin resonance (ESR) and TR MFE techniques. No evidence of the decay of the radical cations of branched alkanes to produce olefin radical cations was found, which was further supported by the observation of positive charge transfer from the observed radical cations to cycloalkane molecules. The lifetimes of the radical cations of the branched alkanes were found to be longer than tens of nanoseconds.     

Cleavage of Multiple Disulfide Bonds in Insulin via Gold Cationization and Collision-induced Dissociation

Intact bovine insulin, with its two chains linked via two disulfide linkages, has been used as a model system to study the incorporation of one or more gold cations as means for facilitating the cleavage of multiple disulfide bonds in a tandem mass spectrometry experiment. Gas-phase ion/ion reactions involving Au(I)Cl(2) (-) or Au(III)Cl(4) (-) were used to incorporate either one or two gold cations into multiply-protonated insulin cations, followed by ion trap collision-induced dissociation (CID) of the products. The incorporation of a single gold cation followed by CID showed little evidence for disulfide bond cleavage. Rather, the CID spectra were similar to those acquired for the same charge state with only excess protons present. However, the incorporation of two gold cations, regardless of oxidation state, resulted in efficient cleavage of the disulfide bonds connecting the two chains of insulin. Furthermore, ion trap CID of the insulin complexes containing two gold cations showed more sequence information compared to the complexes containing only one gold cation or no gold cations. The partitioning of the gold cations between the two chains upon CID proved to be largely asymmetric, as both gold cations tended to stay together. There appeared to be a slight preference for both gold cations to partition into the B-chain. However, the relatively low contribution from single chain ions with only one gold ion suggests a degree of cooperativity in the overall mechanism for separation of the two chains.     

Gas-phase reactions of carbon dioxide with atomic transition-metal and main-group cations: room-temperature kinetics and periodicities in reactivity

The chemistry of carbon dioxide has been surveyed systematically with 46 atomic cations at room temperature using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The atomic cations were produced at ca. 5500 K in an ICP source and allowed to cool radiatively and to thermalize by collisions with Ar and He atoms prior to reaction downstream in a flow tube in helium buffer gas at 0.35 +/- 0.01 Torr and 295 +/- 2 K. Rate coefficients and products were measured for the reactions of first-row atomic ions from K(+) to Se(+), of second-row atomic ions from Rb(+) to Te(+) (excluding Tc(+)), and of third-row atomic ions from Cs(+) to Bi(+). CO(2) was found to react in a bimolecular fashion by O atom transfer only with 9 early transition-metal cations: the group 3 cations Sc(+), Y(+), and La(+), the group 4 cations Ti(+), Zr(+), and Hf(+), the group 5 cations Nb(+) and Ta(+), and the group 6 cation W(+). Electron spin conservation was observed to control the kinetics of O atom transfer. Addition of CO(2) was observed for the remaining 37 cations. While the rate of addition was not measurable some insight was obtained into the standard free energy change, DeltaG(o), for CO(2) ligation from equilibrium constant measurements. A periodic variation in DeltaG(o) was observed for first row cations that is consistent with previous calculations of bond energies D(0)(M(+)-CO(2)). The observed trends in D(0) and DeltaG(o) are expected from the variation in electrostatic attraction between M(+) and CO(2) which follows the trend in atomic-ion size and the trend in repulsion between the orbitals of the atomic cations and the occupied orbitals of CO(2). Higher-order CO(2) cluster ions with up to four CO(2) ligands also were observed for 24 of the atomic cations while MO(2)(+) dioxide formation by sequential O atom transfer was seen only with Hf(+), Nb(+), Ta(+), and W(+).     

Generation and reactions of radical cations from the photolysis of aromatic compounds with tetranitromethane in 1,1,1,3,3,3-hexa-fluoropropan-2-ol

The generation and reactions of aromatic radical cations by photolysis of ArH-tetranitromethane in 1,1,1,3,3,3-hexfluoropropan-2-ol (HFP) at room temperature has been investigated. The primary radical cations (ArH^⊙?) were detectable by EPR spectroscopy in most cases where E ^o(Ar^⊙?/ArH) 1.5 V (vs. Ag/AgCl). Secondary radical cations were obtained from pentamethylbenzene and durene (1,2,3,4,5,6,7,8-octamethyl- and 1,2,4,5,6,8-hexamethyl-anthraceneradical cation), from certain naphthalenes (dehydrodimer radical cations, Ar?Ar^⊙?) and from 2,3-dimethylanisole (the radical of a nitroso derivative). The persistence of the radical cations in the presence of trinitromethanide ion is seen as a consequence of the stabilization of the nucleophile by HFP. This assumption was supported by preparative results on 1-methoxynaphthalene and 1,4-dimethylnaphthalene, where the trinitromethanide ion initiated pathway was completely eliminated in HFP, contrary to results earlier obtained in dichloromethane.     

Synthesis and pulse radiolytic studies of mono- and polyfluorinated biphenyls

The polyfluorinated biphenyls investigated were synthesized by reaction of fluorinated anilines with excess benzene and characterized by spectroscopic methods. Upon pulse radiolysis of the polyfluorinated biphenyls in dichloroethane radical cations are formed. By comparison with unsubstituted biphenyl the fluoro-substitution does not exert a strong effect on the optical absorption spectra or the first half-lives of the biphenyl radical cations.     

The effect of the secondary structure on dissociation of peptide radical cations: fragmentation of angiotensin III and its analogues

Fragmentation of protonated RVYIHPF and RVYIHPF-OMe and the corresponding radical cations was studied using time- and collision energy-resolved surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Peptide radical cations were produced by gas-phase fragmentation of Co (III)(salen)-peptide complexes. Both the energetics and the mechanisms of dissociation of even-electron and odd-electron angiotensin III ions are quite different. Protonated molecules are much more stable toward fragmentation than the corresponding radical cations. RRKM modeling of the experimental data suggests that this stability is largely attributed to differences in threshold energies for dissociation, while activation entropies are very similar. Detailed analysis of the experimental data obtained for radical cations demonstrated the presence of two distinct structures separated by a high free-energy barrier. The two families of structures were ascribed to the canonical and zwitterionic forms of the radical cations produced in our experiments.     

Separation and determination of pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection

A method for rapid and simultaneous determination of multiple pyrrolidinium ionic liquid cations by ion chromatography with direct conductivity detection was developed.Chromatographic separations were performed on a cation exchange column using ethylenediamine-acetonitrile as the mobile phase.The effects of chromatographic column and the mobile phase,as well as the column temperature on the retention of the cations were investigated.The retention rules of the cations under different chromatographic conditions were formulated.The retention of the cations followed the carbon number rule.The method has been successfully applied to the determination of three ionic liquids synthesized by a chemical laboratory.     

Adsorption of Thiophene Vapor on Sodium and Polyhydroxoaluminum Montmorillonites

Changes in the surface properties and pore structure of montmorillonite in substitution of inorganic exchange cations by polyhydroxoaluminum cations were studied by measuring the adsorption of thiophene vapor.     

Synthesis and complexing properties of bis-crown ethers incorporating benzo-15-crown-5 and metallocene

Bis-crown ethers in which the benzo-15-crown-5 units were linked to 1,1′-positions of metallocene (M = Fe or Ru) with amide, ester, or ? C? C? bonds were synthesized. Complexing ability of the compounds with alkali, alkali earth, and transition metal cations were measured by the solvent extraction method. The results showed that these crown ethers had high affinity toward alkali metal cations (Li⁺, Na⁺, K⁺, and Rb⁺) and heavy-metal cations (Ag⁺ and Tl⁺). The difference of complexing ability for metal cations between ferrocene and ruthenocene derivatives could not be detected significantly. The extractability of metallocene-bis-crown ethers for metal cations was more larger than that of the corresponding mono-crown ethers, and irregular increments of extractability were explained by assuming the existence of a mixture of 1:1 and 2:1 complexes.     

Use of styrene radical cations as probes for the complexation dynamics of charged guests with alpha- and beta-cyclodextrins

The complexation dynamics of radical cations with cyclodextrins (CD) was studied using photophysical techniques. Radical cations of 4-vinylanisole and trans-anethole were formed within alpha- and beta-CD cavities by two-photon photolysis of the respective styrene precursors. Exit of the radical cations from alpha-CD complexes with 1: 1 and 1:2 (guest: CD) stoichiometries and beta-CD complexes with 1:1 stoichiometries occurred with lifetimes shorter than 100 ns. Most of the radical cations formed escape from the CD cavities, but a small portion do react with alpha-CD when this host is present in high concentrations.     

Synthesis and Alkaline Metal Ion Binding Ability of New Steroid Dimers Derived from Cholic and Lithocholic Acids

The synthesis and NMR spectra of steroid dimers being derivatives of cholic and lithocholic acid methyl esters, in which the steroid residues are linked by the terephthaloyl spacer, are described. The complexing ability of the dimers towards alkaline metal cations has been studied by the electrospray mass spectrometry. Cholic acid derivatives show affinity toward metal cations and anions. Binding of metal cations by methyl lithocholate dimer has not been detected.