On-column complexation capillary electrophoretic separation of Fe2+ and Fe3+ using 2,6-pyridinedicarboxylic acid coupled with large-volume sample stacking

On-column complexation of Fe2+ and Fe3+ with 2,6-pyridinedicarboxylic acid (2,6-PDCA) formed anionic complexes, which were then separated by capillary zone electrophoresis with direct UV detection at 214 nm. To achieve reasonable separation selectivity and on-column complexation, the conditions such as pH, the concentration of 2,6-PCDA and the EOF modifiers in the electrolyte were examined. The electrolyte contained 5.0 mM 2,6-PDCA, 0.25 mM tetradecyltrimethlammonium bromide (TTAB) and 5% (v/v) acetonitrile at pH 4.0 was optimised for on-column complexation and the separation of Fe[PCDA]2(2-) and Fe[PCDA]2(-). To enhance the detection sensitivity, large-volume sample stacking (LVSS) was used for the on-line preconcentration of Fe[PCDA]2(2-) and Fe[PCDA]2(-). Under the optimised conditions, satisfactory working ranges (0.5-50 microM), lower detection limits (less than 0.1 microM) and good repeatability of the peak areas (R.S.D.: 5.2-7.8%, n = 5) was achieved using LVSS (300 s). With LVSS, the detection sensitivity was enhanced more than 50-fold compared to conventional hydrodynamic injection. The proposed method was used successfully for the determination of Fe2+ and Fe3+ in water samples.     

Structural studies of DMβCD/dihalogenated norcarane inclusion complexes

Inclusion complexes of 7,7-dibromonorcarane (1) and 7,7-dichloronorcarane (2) with 2,6-dimethyl--cyclodextrin (DMCD) have been synthesized. Their structures have been studied by chemical analysis, thermal behavior, IR spectra, UV absorptions and¹³C NMR spectra in DMSO solutions. The studies show that the orientation of (1) is different from that of (2) in the DMCD cavity.Presented at the 6th International Symposium on Molecular Recognition and Inclusion, Berlin, Germany, 10–14 September 1990.     

Binding of ferrocene by cyclic trimeric perfluoro-<Emphasis Type="Italic">o</Emphasis>-phenylenemercury. Synthesis and structure of the first double-decker sandwich complex of a sandwich

The first double-decker sandwich complex of a sandwich was synthesized and fully characterized. The complex was prepared by the reaction of cyclic trimeric perfluoro-o-phenylene-mercury (o-C₆F₄Hg)₃ (1) with ferrocene in an ethereal solution at 20 °C and has the composition {[(o-C₆F₄Hg)₃]₂(Cp₂Fe)} (2). The ferrocene sandwich in 2 is located between the planes of two mercury-containing macrocycles and is coordinated to each of them through donation of the -electrons of the ⁵-Cp ligands to vacant orbitals of the mercury atoms of the adjacent molecule 1. It was concluded that all carbon atoms of the ⁵-Cp rings in complex 2 are involved in the bonding to the macrocycles. Complexation with 1 leads to considerable shifts of the (C-H) and (C-H) bands of ferrocene in the IR spectrum to high frequencies. The structure of complex 2 was determined by X-ray diffraction.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2754–2756, December, 2004.     

Factors Contributing to Solubility Synergism of Some Basic Drugs with β-Cyclodextrin in Ternary Molecular Complexes

Ternary complexes exploiting solubility synergism (SSn) between basic drugs and β-cyclodextrin (β-CD) in the presence of an organic hydoxy acid have been reported to provide the pharmaceutical technology with highly soluble ternary complexes, even with the least soluble β-CD. In this work, phase solubility techniques were used to study factors affecting SSn in aqueous solution, which may help in understanding the mechanism involved in ternary complex formation in solution, under equilibrium conditions. The equilibrium solubility of both β-CD and each of 8 structurally unrelated drugs were measured in tandem in the presence of different acid types at low and high pHs, and at different time intervals over a period of 1–40 days. The results indicate that SSn is evident regardless of acid type (organic and inorganic) at low pH, but the extent of SSn is acid type dependant and is limited by the drug salt solubility product constant (pK _sp). Among different drugs, no apparent trend exists between drug salt solubility and the extent of SSn, but lowering drug salt solubility by increasing pH depresses SSn. The results also reveal no apparent trend between the magnitude of the complex formation constant (K _ij) and SSn. For example, drugs of low K _ij values such as astemizole, cisapride and sildenafil do not show any SSn, yet ketotifen and pizotifen, which also have low K _ij values, exhibit substantial SSn. However, the solublizing power of β-CD represented by the slope of phase solubility diagram can be used as a marker for SSn (slopes exceeding 0.4 induce SSn).     

f-Element/crown ether complexes: 21. Conformational changes in metal complexed versus hydrogen bonded benzo-15-crown-5 in the structure of [Y(OH2)3(NCMe)-(benzo-15-crown-5)][ClO4]3·benzo-15-crown-5·CH3CN

Crystalline [Y(OH₂)₃(NCMe)(benzo-15-crown-5)][ClO₄]₃·benzo-15-crown-5-CH₃CN can be obtained by slowly cooling a reaction mixture of Y(ClO₄)₃·n H₂O with benzo-15-crown-5 in a solution of acetonitrile and methanol (3 : 1) from 60°C to room temperature. The crystal structure of this complex has been determined at –150 and 20°C. The complex is triclinic,P . At –150°C the cell parameters area = 11.986(4),b = 12.071(7),c = 16.364(5) Å, = 93.56(3), = 98.68(3), = 109.68(4)°, vol = 2187 ų, andD _calc = 1.61 g cm^–3 forZ = 2 formula units. 3633 independently observed [F _o 5(F _o)] reflections were used in the final least-squares refinement leading to an agreement index ofR = 0.048. The Y(III) ion coordination geometry approximates a tricapped trigonal prism with three water molecules and three benzo-15-crown-5 oxygen atoms forming the prism, with the two remaining benzo-15-crown-5 oxygen atoms and the acetonitrile molecule completing the coordination as capping atoms. The three water molecules hydrogen bond a second crown ether molecule and two of the perchlorate anions. The two acetonitrile molecules have contacts with perchlorate oxygen atoms close enough for some weak interaction. One perchlorate is ordered, one is partially disordered as is the coordinated solvent molecule, and the third anion is totally disordered. The two unique crown ether molecules have distinctively different conformations.For Part 20, see reference [1].     

Spectroscopic Study of Azo- and Azoxycrowns Binding with Cations of Similar Ionic Radius

The complexation of 13- and 16-memberedazo- and azoxycrowns with metal cations of similarionic diameter (Na⁺ and Ca²⁺; and K⁺,Ba²⁺, Ag⁺ and Pb²⁺) was studied byuv/visible spectroscopic titration in acetonitrile andMeOH. In MeOH the 13-membered azo- and azoxycrowns 1 and 2 are weakly and non-selectively bound tohard cations of similar ionic diameter, but differentcharge (Na⁺ and Ca²⁺). At the same time thebinding to the soft cation Ag⁺ of larger sizethan the macrocycle cavity is considerably stronger.In contrast to solutions in acetonitrile no bindingwith the small Li⁺ cation was found.The 16-membered azocrowns 3 and 4 alsodiscriminate silver cation in MeOH withlog K = 3.65 ± 0.1 for both compounds.Unexpectedly low bindingwith the hard barium divalent cation of similar size(log K = 1.55 ± 0.4 and 1.95 ± 0.2, respectively)was found for these compounds. Similarly to13-membered compounds no binding with the smallLi⁺ cation was detected. A reverse order ofselectivity was observed for these crowns inacetonitrile with binding constant for association of3 with Ba²⁺ (log K 5.3) considerablyhigher than for other cations. The previously observedstrong binding with the smaller Li⁺ and Na⁺cations is confirmed.     

Synthesis and Complexation Studies of Various Precursors Based on Calix[4]arene-crown-5 and -6 for the Immunoanalysis of Potassium and Caesium Ions

In an attempt to generate antibodies for the development of an immunoanalysis method for potassium and caesium ions, new 1,3-alternate calix[4]arenes-crown-5 and -6 bearing either carboxylic or hydroxyl functions were synthesized in good yields. Their complexation properties towards potassium and caesium ions were investigated using ¹H NMR spectroscopy and the usual properties proved to be preserved in the presence of the anchoring arms.     

Tautomerism,protonation regioselectivity of 2-pyrrolidone and its complexation with palladium(II): an insight from the viewpoint of quantum chemistry

It has been established (AM1, PM3, RHF/6-31G**, MP2/6-31G**//RHF/6-31G**) that in the gaseous phase and in aqueous solution, the most thermodynamically stable tautomer of 2-pyrrolidone is lactame. According to PM3 evaluations with an explicit accounting for aqueous medium, the state of tautomeric equilibrium serves as a prerequisite to participation of 2-pyrrolidone's lactime tautomer (pyrroline-2-ol) in complexation with palladium(II) in aqueous solution. 2-Pyrrolidone protonation in the gaseous phase and in aqueous medium has been shown to proceed via the oxygen atom, corresponding to expectations on mesomeric displacement of electron density in the amide fragment. The aqueous medium stabilizes 2-pyrrolidone's lactime tautomer to a greater extent than for lactame, and an O-protonated cyclic amide compared to an N-protonated one. The stereodirective character of palladium(II) complexation with chloride ion and pyrroline-2-ol has been explained. The initially formed tetragonal–pyramidal adduct with an axial organic ligand rearranges into a precursor of the cis product, an intermediate with an extra coordinated axial chlorine atom. The less thermodynamically stable cis isomer of [PdCl₂(pyrroline-2-ol)₂] appears because its precursor is a lower energy intermediate of associative nucleophilic substitution. At a supramolecular level, cis product is capable of being stabilized by means of intermolecular dipole–dipole association in a crystal.     

地球化学模拟在高放废物地质处置中的应用与发展

随着核能事业的发展,高放废物的处理和处置问题日益突出.其中,研究高放废物在环境介质中的吸附、扩散和迁移行为是获取放射性核素对周围环境和人群健康影响的基础参数的最重要和最直接的途径.近年来,人们利用已有的实验数据及核素的基础热力学和动力学数据,附以相应的数学模型,建立了一些地球化学模拟软件,用于分析核素在地质介质中可能发生的连续性和长期性变化.目前,国内外常用的地球化学模拟软件有十多种.本文从热力学平衡计算原理、种态分布计算方法和表面配位模型假设等几个方面对地球化学模拟软件进行了简要介绍,对近年来地球化学模拟软件在核素种态分布计算和表面配位模型模拟两方面的应用进行了举例分析,并以Ca-U-CO3配合物为例,说明完备的热力学数据对地球化学模拟软件发展的重要性,以期促进我国地球化学模型的应用和发展.