Concerning the denticity of the dimethylsulfinyl anion in Meisenheimer complexation

The denticity (O-, S-, and C-nucleophilic reactivity) of the dimethylsulfinyl carbanion ("dimsyl") toward 1,3,5-trinitrobenzene (TNB) has been studied by NMR spectroscopy, and structures of adducts have been assigned. Three dimsyl adducts are observed for the first time and have been ascribed to the O-adduct 15, the S-adduct 16, and the C-adduct 17. The kinetic (15 > 16 > 17) and thermodynamic preference (17 > 16 > 15) for the reactivity of dimsyl toward TNB is compared to the known O- and C-reactivity of enolate anions and the O- and S-reactivity of dimethyl sulfoxide. Thus, dimsyl apparently represents a unique system in which three adjacent atoms having unshared electron pairs can utilize these in covalent bond formation.     

A trimethylsulfonium salt with a novel polymeric cadmate anion

The title salt, catena‐poly[trimethylsulfonium [μ₂‐chlorido‐di‐μ₂‐thiocyanato‐cadmate(II)]] {(C₃H₉S)[CdCl(NCS)₂]}_n, consists of trimethylsulfonium cations sandwiched between layers of a two‐dimensional polyanion. The Cd^II centre displays a distorted octahedral environment coordinated by two bridging Cl atoms, two thiocyanate N atoms and two thiocyanate S atoms. The thiocyanate groups adopt the μ‐1,3‐coordination mode and bridge the Cd^II centres into a one‐dimensional zigzag chain extended along the [110] direction. The Cd^II centres of the zigzag chains are crosslinked by bridging Cl atoms, forming a two‐dimensional polyanion. The two‐dimensional anions are linked to layers of trimethylsulfonium cations by weak intermolecular C—H...Cl hydrogen bonds, forming the three‐dimensional structure.     

Anion binding vs. deprotonation in colorimetric pyrrolylamidothiourea based anion sensors

A pyrrolylamidothiourea deprotonates in the presence of one equivalent of not only fluoride, but also acetate, benzoate or dihydrogen phosphate in DMSO solution with structural studies using synchrotron radiation confirming thiourea deprotonation in the solid state.     

Ab initio MO study of the solvent effect on the SN2 reaction of the trimethylsulfonium cation with chloride anion

A recently developed ab initio MO theory including solvent effects has been applied to a typical cation-anion reaction, the S_N2 reaction of the trimethylsulfonium cation with the chloride anion. In the gas phase, the trimethylsulfonium and chloride ions are unstabilized, and the reaction is expected to proceed rapidly. In aqueous solution, the reactant ions are largely stabilized, and the reaction has been predicted to be endothermic, with an activation energy of 30–40 kcal/mol. This potential energy profile, which agrees with experimental results, has been well elucidated by differential solvation at several stages of the reaction path. At the transition state of this reaction, the C and H atoms in the transferring CH₃ group are almost in a plane that is perpendicular to the Cl(SINGLE BOND)C(SINGLE BOND)S line, reflecting the concerted nature of the reaction. The population analysis has shown that the electrons in the C(SINGLE BOND)S bond are mostly withdrawn by the sulfur atom at the transition state and that the electron transfer from Cl to CH₃ occurs after the transition state. The calculated activation energy for the reaction in ethanol is smaller than that in water. This agrees with experiments. © 1996 John Wiley & Sons, Inc.     

New block-grafted anion exchanger for environmental water analysis by ion chromatography

The IonPac AS14A is a recently developed stationary phase that was produced using a new block-grafting technique, which enables the preparation of high-water-content anion exchangers with excellent peak shape and good chromatographic efficiency. The performance of this column for the analysis of inorganic anions was compared to that obtained using an IonPac AS4A column, which is specified in US Environmental Protection Agency Method 300.0, in addition to another commonly used alternative; the AS14 column. The AS14A column is available in two different formats; 250×4 mm I.D. (7.0 μm diameter particle) and 150×3 mm I.D. (5.5 μm diameter particle). The IonPac AS14A (in 4 mm I.D. format) was found to provide similar performance to the AS14 column with increased peak efficiency and better pH stability and is a suitable alternative for the analysis of anions in moderate- to high-ionic-strength samples. The IonPac AS14A (in 3 mm I.D. format) provides comparable run times to the AS4A column with better overall peak selectivity and improved fluoride resolution, hence this column would be a suitable column to substitute in place of either the AS4A or AS14 columns for the analysis of inorganic anions in low- to moderate-ionic-strength environmental waters. The AS14A column used with an Atlas electrolytic suppressor provides equivalent method detection limits to those obtained when using a micromembrane suppressor but with the operational convenience of a self-regenerating suppressor.     

Metal ion interaction with dimethyl phosphate anion

The influence of metal ions on the conformation of dimethyl phosphate anion around its O-P bonds, has been studied theoretically. The perturbation caused due to metal ions like Na⁺ and Mg²⁺ seems to affect the free dimethyl phosphate anion conformation to a considerable extent. In particular, the fully extended conformation becomes much more favourable in the metal ion dimethyl phosphate complex.     

膜处理-离子色谱法测定碳酸钡中的杂质阴离子

建立了一种膜处理-离子交换色谱测定碳酸钡中痕量杂质阴离子(F^-、SO₄^2-和NO₃^-)的方法。碳酸钡是一种难溶于水的固体,因此选用酸对其进行溶解。为了减少酸根离子的影响,利用阳离子膜只能通过阳离子而阻碍阴离子交换的特点,用质量分数为7%的盐酸溶解阳离子交换膜内的碳酸钡样品,稀释100倍,过0.22 μ m滤膜,进样分析,进样体积为25 μ L。经流速为1 mL/min的20 mmol/L KOH淋洗液淋洗,目标离子经过Ion Pac AG11-HC保护柱(50 mm×4 mm)和Ion Pac AS11-HC阴离子交换色谱柱(250 mm×4 mm)进行分离,最后由抑制电导进行检测。在优化的色谱条件下,该方法在0.01~5.00 mg/L范围内线性关系良好,相关系数R²≥0.9996。相对标准偏差(RSD)为1.87%~2.19%,检出限(S/N=3)为1.37~9.45 μ g/L。将该方法应用于实际样品的检测中,得到样品的加标回收率为84.0%~106.2%。该方法实现了固体碳酸钡中杂质阴离子含量的测定,为水不溶性固体物质中的离子检测提供了依据,具有较好的应用前景。     

Nitrophenyl derivatives of pyrrole 2,5-diamides: structural behaviour,anion binding and colour change signalled deprotonation

Two new pyrrole 2,5-diamide clefts have been synthesized containing 4-nitrophenyl or 3,5-dinitrophenyl groups appended to the amide positions. The 3,5-dinitrophenyl derivative has been shown to deprotonate in the presence of fluoride, which in acetonitrile solution, gives rise to a deep blue colour.     

Effect of anion coordination upon radiationless transitions of the uranyl ion

At 80 K, where the deactivation processes in uranyl luminescence in solutions are temperature independent, the radiationless transition rate depends upon the presence of H₂O in the first coordination sphere of the uranyl ion, UO₂²⁺. It is found that such radiationless transitions are due to a photophysical intramolecular process.     

Fast ion chromatography using short anion exchange columns

A fast ion chromatographic system is described which uses shorter column lengths and compares various eluent profiles in order to maximise the performance without sacrificing the chromatographic resolution. Both isocratic and gradient elution profiles were considered to find the most efficient mode of separation. The separation and determination of seven target anions (chloride, chlorate, nitrate, chromate, sulfate, thiocyanate and perchlorate) was achieved using a short (4 mm ID, 50 mm long) column packed with Dionex AS20 high-capacity anion exchange material. A hydroxide eluent was used at an initial concentration of 25 mM (at a flow-rate of 1.0 mL/min) and two performance maxima were found. The maximum efficiency occurred at a normalised gradient ramp rate of 5 mM/t₀, resulting in a peak capacity of 16, while the fastest separation (<3 min) occurred at a normalised ramp rate of 30 mM/t₀. The retention time, peak width and resolution using the different eluent profiles on varying column lengths is also compared. Further investigations in this study determined that the highest peak capacity separation under gradient conditions could be approximated using an isocratic separation. The advantage of using this novel approach to approximate the maximum efficiency separation removes the need for column re-equilibration that is required for gradient elution resulting in faster analyses and enhanced sample throughput, with benefits in particular for multidimensional chromatography.     

离子色谱法测定PM_(2.5)中可溶性阴离子含量不确定度评议

准确测定大气颗粒物中水溶性组分对分析污染物来源及身体健康具有重要意义。本文采用离子色谱法测定PM2.5中水溶性阴离子(氯离子、硝酸根离子、硫酸根离子)含量,并对测定的不确定度进行分析。分析过程不确定度来源是样品重复性测量引入不确定度,样品测量准确性引入不确定度和标准曲线的不确定度。应用不确定度评定理论,分别计算氯离子、硝酸根离子和硫酸根离子的合成不确定度。结果表明,滤膜质量与取样环节是不确定度的主要来源。为了提高分析准确性,建议使用本底低的滤膜,取全样分析。     

Simple naphthalimide based anion sensors: deprotonation induced colour changes and CO2 fixation

The 4-amino-1,8-naphthalimide based chemosensors 2, 4 and 6 show striking green-to-purple colour changes due to the deprotonation of the 4-amino moiety on interaction with strongly basic anions such as F⁻: these colour changes reverse gradually with time due to the fixation of atmospheric CO₂ (as HCO₃⁻) yielding 1:1 adducts as demonstrated by X-ray crystallography.     

Premicellar and micelle formation behavior of dye surfactant ion pairs in aqueous solutions: deprotonation of dye in ion pair micelles

The premicellar and micelle formation behavior of dye surfactant ion pairs in aqueous solutions monitored by surface tension and spectroscopic measurements has been described. The measurements have been made for three anionic sulfonephthalein dyes and cationic surfactants of different chain lengths, head groups, and counterions. The observations have been attributed to the formation of closely packed dye surfactant ion pairs which is similar to nonionic surfactants in very dilute concentrations of the surfactant. These ion pairs dominate in the monolayer at the air-water interface of the aqueous dye surfactant solutions below the CMC of the pure surfactant. It has been shown that the dye in the ion pair deprotonates on micelle formation by the ion pair surfactants at near CMC but submicellar surfactant concentrations. The results of an equilibrium study at varying pH agree with the model of deprotonated 1:1 dye-surfactant ion pair formation in the near CMC submicellar solutions. At concentrations above the CMC of the cationic surfactant the dye is solubilized in normal micelles and the monolayer at the air-water interface consists of the cationic surfactant alone even in the presence of the dyes.     

An investigation of the deprotonation of hydrazone-based receptors on interaction with anion: develop a colorimetric system distinguishing cyanide from anions

Hydrazone-based receptors, containing fluorene-skeleton substituents, in a THF solution, in the presence of fluoride or cyanide, do not only form H-bond complexes, but mainly undergo deprotonation of the N–H fragments, an event, which is signaled by the color change, the ability of the deprotonation is associated with the fluorene skeleton. The deprotonation process is also reversible by the addition of metal ions, while cyanide from fluoride could be distinguished by the addition of copper (II).     

Asymmetric deprotonation of N-Boc-piperidines

A selection of chiral ligands was screened for the asymmetric deprotonation of N-Boc-piperidine. The asymmetric deprotonation of this compound is notoriously difficult and reasonable yields are obtained only with non-hindered ligands, such as tetramethylethylene diamine (TMEDA). Chiral versions of TMEDA were investigated but even small increases in steric bulk of the ligand caused significant reduction in the yields of the product after electrophilic quench. The ligands studied focused on diamines or amino-alcohols with one or two stereocentres, including C₂-symmetric ligands. In general these promoted low levels of enantioselectivity in this transformation; however a C₂-symmetric ligand first reported by Alexakis et al. gave a high enantiomer ratio but a low yield of the product. The substrate N-Boc-piperidine is therefore much more sensitive to steric factors in comparison with the related and highly enantioselective deprotonation of N-Boc-pyrrolidine. The application of the chemistry to two 4-substituted piperidines was also investigated and variable enantiomer ratios were obtained.     

Local structure around chloride ion in anion exchange resin

Neutron diffraction measurements on 35Cl/37Cl isotopically substituted anion exchange resins were carried out in order to obtain direct information on the local structure around the chloride ion absorbed in the resin. Structural parameters concerning the first nearest-neighbor interaction of chloride ions were determined through a least-squares fitting procedure of the observed first-order difference function, DeltaCl(Q). It has been revealed that the chloride ion is neighboring an ion exchange group (-CH2(CH3)3N+) with a Cl-...N distance of 3.10(3) A, and simultaneously bonded with 2.4(1) D2O molecules with a Cl-...D distance of 2.25(2) A. The second and third nearest water molecules around Cl- have also been observed. These results indicate that the direct ionic interaction between Cl- and -CH2(CH3)3N+ drastically reduces the number of first-neighbor water molecules around Cl- but enhances the long-distance structuring of the remaining water molecules in the environment surrounded by a hydrophobic polymer matrix.