Effects of Hofmeister anions on the aggregation behavior of PEO-PPO-PEO triblock copolymers

The effects of a series of Hofmeister anions on the phase behaviors of a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer were investigated with an automated melting point system. Well hydrated anions and poorly hydrated anions interacted with the polymer differently and further affected the phase transition of the polymer. Poorly hydrated anions worked through changing the interfacial tension at the polymer/aqueous interface and in enhancing the polymer hydration by ion binding. The phase transition of the polymer in the presence of well hydrated anions correlated directly to the hydration entropy of the anions. As a consequence, the polymer showed a two-step phase transition in solutions containing poorly hydrated anions while displayed a single-step phase transition in the presence of well hydrated anions. The mechanisms of how ions interact with the polymer and further modulate its phase behaviors were discussed.     

Disproportionation of dipyrrolylquinoxaline radical anions via the internal protons of the pyrrole moieties

Disproportionation of dipyrrolylquinoxaline radical anions occurs via hydrogen atom transfer from the pyrrole moiety to the quinoxaline moiety to produce monodeprotonated dipyrrolylquinoxaline anions and monohydrodipyrrolylquinoxaline anions. In contrast, simple quinoxaline radical anions without pyrrole moieties are stable, and disproportionation occurs only in the presence of external protons.     

Electron photodetachment from aqueous anions. 3. Dynamics of Geminate pairs derived from photoexcitation of mono- vs polyatomic anions

Photostimulated electron detachment from aqueous inorganic anions is the simplest example of solvent-mediated electron transfer reaction. As such, this photoreaction became the subject of many ultrafast studies. Most of these studied focused on the behavior of halide anions, in particular, iodide, that is readily accessible in the UV. In this study, we contrast the behavior of these halide anions with that of small polyatomic anions, such as pseudohalide anions (e.g., HS(-)) and common polyvalent anions (e.g., SO(3)(2-)). Geminate recombination dynamics of hydrated electrons generated by 200 nm photoexcitation of aqueous anions (I(-), Br(-), OH(-), HS(-), CNS(-), CO(3)(2-), SO(3)(2-), and Fe(CN)(6)(4-)) have been studied. Prompt quantum yields for the formation of solvated, thermalized electrons and quantum yields for free electrons were determined. Pump-probe kinetics for 200 nm photoexcitation were compared with kinetics obtained at lower photoexcitation energy (225 or 242 nm) for the same anions, where possible. Free diffusion and mean force potential models of geminate recombination dynamics were used to analyze these kinetics. These analyses suggest that for polyatomic anions (including all polyvalent anions studied) the initial electron distribution has a broad component, even at relatively low photoexcitation energy. There seems to be no well-defined threshold energy below which the broadening of this electron distribution does not occur, as is the case for halide anions. The constancy of (near-unity) prompt quantum yields vs the excitation energy as the latter is scanned across the lowest charge-transfer-to-solvent band of the anion is observed for halide anions but not for other anions: the prompt quantum yields are considerably less than unity and depend strongly on the excitation energy. Our study suggests that halide anions are in the class of their own; electron photodetachment from polyatomic, especially polyvalent, anions exhibits qualitatively different behavior.     

The evaluation and comparison of trigonal and linear tricationic ion-pairing reagents for the detection of anions in positive mode ESI-MS

A general and sensitive method for detecting divalent anions by ESI-MS and LC/ESI-MS as positive ions has been developed. The anions are paired with tricationic reagents to form positively charged complexes. In this study, four tricationic reagents, 2 trigonal and 2 linear, were used to study a wide variety of anions, such as disulfonates, dicarboxylates, and inorganic anions. The limits of detection for many of the anions studied were often improved by tandem mass spectrometry. Tricationic pairing agents can also be used with chromatography to enhance the detection of anions. The tricationic reagents were also used to detect monovalent anions by monitoring the doubly charged positive complex. The limits of detection for some of the divalent anions by this method are substantially lower than by other current analytical techniques.     

Effect of temperature on retention and selectivity in ion chromatography of anions

The temperature dependence of retention of a wide range of inorganic anions is studied on two commercially available ion exchangers (Dionex AS11 and AS14 columns). Anion retention exhibited both exothermic and endothermic behavior, such that varying the temperature from ambient to 60°C produced selectivity changes. The anions displayed three groupings of temperature dependence: weakly retained singly charged anions (e.g., iodate, bromate, nitrite, bromide and nitrate); multiply charged anions (sulfate, oxalate, phosphate and thiosulfate); and strongly retained singly charged anions (iodide, thiocyanate and perchlorate). Temperature was ineffective at changing the selectivity of retention between anions of the same grouping. However, significant selectivity changes, including elution order reversal, could be achieved between anions from different groupings.     

邻-二(吡咯-2-甲酰胺基)亚苯的合成、晶体结构及阴离子识别

设计合成了邻-二(吡咯-2-甲酰胺基)亚苯.用X射线单晶衍射研究了该化合物的固态构象,发现其可以通过氢键与DMSO发生络合.¹HNMR研究发现该化合物即使在强极性的DMSO溶液中也可对F^-,Cl^-和H₂PO₄^-常见阴离子产生一定的识别,其中对F-的识别为最优.     

Simultaneous separation of 17 anions by capillary electrophoresis with the addition of an organic solvent

Seventeen inorganic and organic anions, that normally are insufficiently separated via ion chromatography, were completely separated by the addition of an organic solvent to a solution of BGE combined with an adjustment of the apparent pH via CE in combination with indirect UV absorbance detection. Methanol, ethanol, and acetonitrile were examined for their utility in manipulating the selective separation of anions. Methanol and acetonitrile were better modifiers than ethanol at enhancing the resolution of anions comigrating in an aqueous solution of BGE. Methanol was selected as the modifier that provided the largest separation window that could achieve a complete separation of the target analytes. Via the use of methanol, manipulation of the selectivity between inorganic anions and that between inorganic and organic anions was enhanced, but the separation between organic anions remained difficult when only methanol was used. By varying the apparent pH of the BGE in the presence of 10% v/v methanol, however, the separation selectivity between organic anions was substantially improved. Eventually, 7 inorganic and 10 organic anions were simultaneously separated using BGE at a pH of 6.3 in the presence of 10% v/v methanol.     

C60负离子化学的研究进展

中性的C60是很强的缺电子体,主要和亲核试剂进行化学反应.与之不同的是C60经还原生成负离子后,由缺电子变为富含电子,具有很强的亲核性质,可与亲电试剂进行反应.由于这种电子结构的变化,C60负离子进行的反应从机理至产物均有可能与中性富勒烯不同.从而丰富了富勒烯的反应方式和富勒烯产物的类型.结合我们的工作综述了C60负离子化学的研究进展,对丰富富勒烯化学、扩展富勒烯衍生物的种类及制备方法具有一定意义.     

Gradient chromatographic elution of sulphur anions

The distribution coefficient of sulphide, sulphite, sulphate and thiosulphate anions between different concentrations of aqueous alkali metal chloride solutions and the anion exchanger Dowex 1X8 is studied. The obtained distribution deportment of these anions is explained in the light of water-water, anion-cation and ion-ion interactions as well as the different tendencies of the alkali ions to hydration. Based on the separation factors encountered between adjacent anions, a chromatographic method is adopted for isolation of the sulphur anions by gradient elution. This method is further compared with the chromatographic procedures so far reported for separation of the investigated anions.     

Solubilities of salts of cobalt(III), chromium(III), and iron(II) complexes in aqueous methanol; transfer chemical potentials of anions

Summary We report solubilities of a variety of salts of cobalt(III), chromium(III), and iron(II) complexes in methanol-water mixtures at 298.2K. From these solubilities and published transfer chemical potentials for the complex cations we are able to derive transfer chemical potentials for such anions as nitrate, thiosulphate, peroxodisulphate, dithionate, thiocyanate, and antimonyl tartrate. Transfer chemical potentials for several hexahalogenometallate anions, and tetrachloroplatinate(II), are derived from published solubilities. A comparative picture of transfer chemical potentials for anions is thus available, with the transition metal complex anions in the overall context of anions and their solvation characteristics in methanol-water mixtures.On leave from the Faculty of Science, Sohag, Egypt.     

A new and selective capillary column coated with cationic diazacrown ether for separation of organic and inorganic anions by capillary electrophoresis

A new coated capillary has been introduced for capillary electrophoretic separation of anions by using a positively charged diazacrown ether with a 12-membered ring. A positive charge spread over the inner capillary surface led to a substantial anodic electroosmotic flow (EOF) over the range of migrating buffer of pH 2-11. Under the optimum conditions of 25 mM phosphate buffer at pH 7, the diazacrown-coated capillary showed a successful simultaneous separation of 7 inorganic anions and 13 aromatic anions (including positional isomers) in less than 15 min. The migration times of the sample anions and EOF marker for consecutive runs on a single column were highly reproducible, giving a relative standard deviation of 1%. Theoretical treatment of the migration behavior clearly demonstrated that ion association between the diazacrown and analyte anions is strongly dependent on the nature of the functional groups of anions (e.g., sulfonate groups > carboxyl groups) and the number of negative charges (e.g., trivalent anions > divalent anions > monovalent anions) on the analyte.     

Determination of anions in landfill leachates by ion chromatography

Ion chromatography has been used to determine inorganic and organic anions within landfill leachates. Two procedures are operated on split samples which have multiple dilutions and vary in sample treatment: gradient ion-exchange chromatography for inorganic anions and isocratic ion-exclusion chromatography for organic anions. Interference between carbonate and organic acid anions using ion-exclusion chromatography is avoided by treatment with octanesulphonic acid eluent. Using ion-exchange chromatography, the presence of valerate, hexanoate and heptanoate is checked (but not quantified) for a subsample which has been treated to remove chloride; these species are then determined by ion-exclusion chromatography. Analysis of certified standards (10 mg/1 certified VFA standard; Supelco, Bellefonte, PA, USA; 20–150 mg/l inorganic anions, ICMIX1-100, Glen Spectra Reference Materials, Middlesex, UK) gives good agreement (within 5% for organic anions except formate, and within 1% for inorganic anions), with R.S.D. values for all anionic species varying from 0.44–2.23.     

离子色谱中高质量浓度的Cl-对痕量NO2-，Br-和NO3-测定的影响

 在3支不同性质的离子色谱柱上,研究了高质量浓度的Cl-对痕量NO2-,Br-和NO3-分离分析的影响,提出在分离过程中同时存在自身洗脱效应和在柱流动相变化两种洗脱机理。当Cl-与待测离子色谱峰重叠时,在抑制器处置换出的H+使弱酸型阴离子分子化,给定量测定带来偏差,而对于强酸型阴离子则没有影响。由实验得到用峰高法测定NO-2,Br-和NO3-等3种阴离子时在不同Cl-质量浓度下的线性范围以及能够准确定量的Cl-的最大质量浓度。     

Simultaneous Ion Chromatographic Determination of Weakly and Strongly Retained Inorganic Anions using Aminoacids as Eluents

Abstract

At present eluents that are most widely used in ion chromatography of inorganic anions are salts with carbonate and hydroxyl eluting ions. But these eluents appear to be of no efficiency when samples containing both weakly and strongly retained inorganic anions are to be analyzed. In this case, one should use either expensive and complicated gradient elution technique or double injection with different eluents separately for weakly and strongly retained anions.

In this work, the simultaneous ion chromatographic determination of weakly and strongly retained inorganic anions without gradient elution is considered. The most common eluent for ion chromatography of anions, carbonate and aminoacids are compared. Dependence of the chromatographic behaviour of the strongly retained inorganic anions upon the concentration of the organic components in the eluent is shown.     

Valence- and dipole-bound anions of the thymine-water complex: ab initio characterization of the potential energy surfaces

The potential energy surfaces of the neutral and anionic thymine-water complexes are investigated using high-level ab initio calculations. Both dipole-bound (DB) and valence-bound (VB) anionic forms are considered. Four minima and three first-order stationary points are located, and binding energies are computed. All minima, for both anions, are found to be vertically and adiabatically stable. The binding energies are much higher for valence-bound than for dipole-bound anions. Adiabatic electron affinities are in the 66-287 meV range for VB anions and the 4-60 meV range for DB anions, and vertical detachment energies are in the 698-977 meV and 10-70 meV range for VB and DB anions, respectively. For cases where literature data are available, the computed values are in good agreement with previous experimental and theoretical studies. It is observed that electron attachment modifies the shape of the potential energy surfaces of the systems, especially for the valence-bound anions. Moreover, for both anions the size of the energy barrier between the two lowest energy minima is strongly reduced, rendering the coexistence of different structures more probable.     

Effect of low-molecular-weight organic anions on electrokinetic properties of variable charge soils

It is known that some inorganic anions can be adsorbed by variable-charge soils specifically, resulting in the lowering of the zeta potential of the clay particle. Reasoning similarly, organic anions should also have such an effect. In this article, the effect of the anions of five low-molecular-weight (LMW) organic acids existing widely in soils on the zeta potentials of two variable-charge soils was examined. The results showed that the presence of organic anions led to a decrease in zeta potential. The effect of different anions on zeta potential followed the order oxalate>citrate>malate>maleate>acetate. The effect increased with the increase in anion concentration and decreased with the increase in pH. The extent of the effect on different soils was apparently related to their iron oxide content. The presence of organic anions also led to a decrease in the isoelectric point (IEP) of the soil. The IEPs of two soils in organic anion systems followed the order acetate>maleate>malate>citrate. No IEP was detected for the oxalate system.     

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.     

Separation of inorganic anions by liquid chromatography with crown ether as eluent additive

Inorganic anions were separated on a reversed-phase stationary phase dynamically modified with crown ether as a selector in capillary ion chromatography. The eluent contained crown ether, acetonitrile and a salt. Free and cation-trapped crown ether molecules in the eluent were adsorbed on a hydrophobic stationary phase such as triacontyl-functionalized silica (C30). The eluent cations trapped on crown ether worked as the ion-exchange sites, where the eluent anions and the analyte anions were competing for electrostatic interaction. The sizes of crown ether and the salt cation affected the retention of analyte anions. The concentrations of acetonitrile and crown ether as well as the eluent anion also affected the retention of analyte anions. An aqueous solution containing 18-crown-6-ether, potassium salt and acetonitrile achieved larger retention for analyte anions. Effects of the eluent conditions on the retention of analyte anions were examined in detail.     

Equilibrium analysis of reactions between aromatic anions and nonionic surfactant micelles by capillary zone electrophoresis.

Separability of some positional isomers of aromatic anions by capillary zone electrophoresis was improved by adding nonionic surfactants to a migrating solution. Eleven kinds of aromatic anions, including positional isomers, were used as analytes, and Brij-35, Brij-58 and Brij-78 were investigated as nonionic surfactants to form micelles, where hydrophobicities are different from each other. Increasing the concentration of the surfactants developed the separability of the anionic isomers. The interaction between the anions and the nonionic surfactant micelles is also investigated through the change in the electrophoretic mobility, and the binding constants are determined. Apparent electrophoretic mobility of the anions decreased with increasing concentrations of the nonionic surfactants. The decrease in the mobility, as well as the binding constant, was larger in the monovalent anions than in the divalent anions, which indicates that the interaction or reactivity of the monovalent analytes is higher than that of the divalent analytes. The reactivity of each anion was almost identical even when the kinds of the surfactants were changed, suggesting that the hydrophobicity of the polyoxyethylene group in the surfactant would have the main role for binding the analytes. The reactivity tendency among the positional isomers was almost similar to that in ion association-capillary zone electrophoresis using tertabutylammonium ion as a pairing ion. The results obtained in this work suggest that the anions are bound to the micelles by the hydrophobic interaction between analyte anions and the polyoxyethylene moiety of the surfactant micelles. Changes in the fluorescence intensity of the anions were also investigated; the results can explain well the mobility changes of the analytes.     

Influence of acidic eluent for retention behaviors of common anions and cations by ion-exclusion/cation-exchange chromatography on a weakly acidic cation-exchange resin in the H+ -form

Influence of acidic eluent on retention behaviors of common anions and cations by ion-exclusion/cation-exchange chromatography (ion-exclusion/CEC) were investigated on a weakly acidic cation-exchange resin in the H(+)-form with conductivity. Sensitivities of analyte ions, especially weak acid anions (F(-) and HCOO(-)), were affected with degree of background conductivity level with pK(a1) (first dissociation constant) of acid in eluent. The retention behaviors of anions and cations were related to that of elution dip induced after eluting acid to separation column and injecting analyte sample. These results were largely dependent on the natures of acid as eluent. Through this study, succinic acid as the eluent was suitable for simultaneous separation of strong acid anions (SO(4)(2-), Cl(-), NO(3)(-) and I(-)), weak acid anions (F(-), HCOO(-) and CH(3)COO(-)), and cations (Na(+), K(+), NH(4)(+), Mg(2+) and Ca(2+)). The separation was achieved in 20 min under the optimum eluent condition, 20 mM succinic acid/2 mM 18-crown-6. Detection limits at S/N=3 ranged from 0.10 to 0.51 microM for strong acid anions, 0.20 to 5.04 microM for weak acid anions and 0.75 to 1.72 microM for cations. The relative standard deviations of peak areas in the repeated chromatographic runs (n=10) were in the range of 1.1-2.9% for anions and 1.8-4.5% for cations. This method was successfully applied to hot spring water containing strong acid anions, weak acid anions and cations, with satisfactory results.