Potentiometric Selectivities of Dibenzo-16-crown-5 Compounds for Alkali and Alkaline Earth Metal Cations and Ammonium Ions

Potentiometric selectivities toward alkali and alkaline earth metal cations and ammonium ions are utilized to probe the complexation of these cationic species by dibenzo-16-crown-5 lariat ethers. Attachment of one or two pendant groups to the central carbon of the three-carbon bridge in dibenzo-16-crown-5 markedly alters the potentiometric responses of the ionophores when incorporated in solvent polymeric membrane electrodes. Results obtained for dibenzo-16-crown-5 compounds with coordinating side arms containing ether, carboxylic acid, ester, and amide groups provide insight into the role of the side arm in metal ion complexation by lariat ether compounds.     

Modeling of metal-humate complexation based on the mean molecular weight and charge of humic substances: Application to Eu(III) humate complexes using ion exchange

A general model, the so called Mean Molecular Weight Model (MMWM), of complexation of metal cations (Me^z+) with macromolecular polyanions of humic acid (HA^p-) is proposed. The model is based on the results of previous studies of the electrophoretic mobility of humate complexes and assumes that the complexation proceeds by consecutive neutralization of the dissociated carboxyl groups of the central polyanion HA^p- with Me^z+ cations. It reflects the macromolecular character of humic acid, applies molar concentrations of reacting components with equations for stability constants and incorporates also the mean charge of humic macromolecules. The model has been verified with experimental data obtained in the study of complexation of Eu(III) with Aldrich humic acid using ion exchange (Amberlite IR-120), over a broad range of [Eu] to [HA] ratio, at pH 4 and 7.     

Comparison of upper and lower rim-functionalized,di-ionizable calix[4]arene-crown-6 structural isomers in divalent metal ion extraction

Upper rim-functionalized, di-ionizable calix[4]arene-crown-6 ligands are synthesized and compared with structural isomers having the two acidic side arms attached to the lower rim. Solvent extractions of selected divalent metal cations (alkaline earth metal cations, Pb²⁺, and Hg²⁺) from aqueous solutions into chloroform by the upper and lower rim-functionalized, di-ionizable calix[4]arene-crown-6 isomers are utilized to assess the effects of this structural modification on metal ion complexation abilities of the ligands. The observed effects are compared with those reported for analogous di-ionizable calix[4]arene-crown-5 structural isomers.     

Metal ion extraction by cone p-tert-butylcalix[4]arene-1,3-crown-5 with two N-(X)sulfonyl carbamoylmethoxy side arms and -1,3-monothiacrown-5 analogues

Four cone p-tert-butylcalix[4]arene-1,3-monothiacrown-5 ligands each with two N-(X)sulfonyl carbamoylmethoxy side arms are synthesized for comparison with analogs having only oxygen heteroatoms in the crown ether ring. Solvent extractions of hard alkali metal and alkaline earth metal cations, intermediate Pb²⁺, and soft Hg²⁺ from aqueous solutions into chloroform by these ligands are utilized to probe the effects of sulfur replacement in the crown ether ring on metal ion complexation.     

Synthesis and Inclusion Properties of a Novel Thiacalix[4]arene-Based Hard–Soft Receptor with 1,3-Alternate Conformation

A novel ditopic receptor possessing two complexation sites and bearing 1,3-alternate conformation based on thiacalix[4]arene was prepared. The binding behaviors with alkali metals and silver ion have been examined by ¹H NMR titration experiment. Although the formation of the heterogeneous dinuclear complexes was not observed, the exclusive formation of mononuclear complexes of 1,3-alternate-3 with metal cations is of particular interest in negative allosteric effect in the thiacalix[4]arene family. These findings demonstrate that preorganization, subtle conformational changes and affinity have a pronounced effect on the complexation process between the two different arms placed at the two edges of the thiacalix[4]arene cavity.     

Metal ion complexation by acyclic polyethers with lipophilic amide, thioamide, and amine end groups

A series of acyclic polyethers with lipophilic amide, thioamide, and amine end groups was synthesized. Metal ion transport across bulk liquid membranes and measurement of thermodynamic parameters for ligand-metal ion complexation by titration calorimetry show strong selectivity for complexation of lead ion over other metal ion species for the diamide ligand. Lead ion complexation by the acyclic polyether diamide involves the amide oxygens and silver ion coordination by a dithioamide analog involves the thioamide sulfurs. With a proper length of the ethereal linkage, the ligand wraps around the metal ion in a pseudocyclic fashion.     

A new calix[4]pyrrole derivative and its anion (fluoride)/cation (mercury and silver) recognition

A new calix[4]pyrrole-based macrocycle, meso-tetramethyl-tetrakis{4-[2-(ethylthio)ethoxy]phenyl}calix[4]pyrrole, 7, has been synthesized and fully characterized. Unlike other calixpyrrole derivatives that show selective interaction with anions, calixpyrrole 7 described in the present work forms stable complexes with both metal cations and anions. The thermodynamics of complexation of this ditopic calixpyrrole derivative with metal cations (Hg2+ and Ag+) and the fluoride anion in nonaqueous solutions have been determined by titration calorimetry, and the host-guest composition has been investigated by using conductance measurements at 298.15 K. 1H NMR studies provide clear evidence about the sites of complexation of 7 with the ionic species, which show that the NH groups are taking part in the complexation of this ligand with the fluoride anion while the sulfur donor atoms are responsible for the interaction with metal cations. Using the present data on 7 and structurally related analogues (1-6), the complexation behavior is discussed comparatively from the thermodynamic point of view. Possessing four sulfur-containing pendent arms, 7 displays an enhanced hosting ability for Hg2+ in acetonitrile. As compared with 1, the calixpyrrole derivative, 7, shows a unique interaction with fluoride among the anions investigated in acetonitrile and dimethyl sulfoxide. As far as the fluoride complex is concerned, the medium effect is assessed in terms of the thermodynamics of the transfer of reactants and product from acetonitrile (reference solvent) to dimethyl sulfoxide.     

Heterogeneity and liability of Pb(II) complexation by humic substances: practical interpretation tools

The complexation of Pb(II) by natural organic matter (NOM) is better described by taking into account the dependence of the strength of binding on metal loading conditions. The utility of a linear differential equilibrium function for interpretation of metal ion binding data is demonstrated. This approach considers the binding intensity (log K*) as a function of metal ion loading (theta = bound metal/binding site concentration). Three methods for calculating this function are presented: -direct calculation from metal titration curves, -direct calculation from polarograms, and -compilation of data derived from interpretation of complexation in terms of one- or two- binding sites (e.g. Scatchard analysis), i.e. Cc (complexation capacity = effective site concentration)-K pairs. Heterogeneity also impacts on the apparent lability of complexes; complexes formed at the lowest metal loadings are the least labile.     

螯合物离子色谱

螯合物离子色谱是一种利用螯合物进行不同方式分离和检测的离子色谱模式，目前已经被痕量金属分析广泛采用，本文对一些螯合物阳离子交换色谱、螯合物色谱、阴离子交换色谱和离子对色谱最新进展进行了综述，并采用基本螯合物化学理论（金属螯合物稳定性、金属原子有效电荷、螯合剂能力等）对保留和分离机理进行了讨论。     

Complexation ion chromatography —an overview of developments and trends in trace metal analysis

Complexation ion chromatography (IC), including all ion chromatographic modes in which complexation is exploited for the separation and detection of metal ions in different ways, is now a widely accepted method of trace metal analysis. Some of the significant advances in the theoretical aspects and practical applications of complexation IC modifications (non-suppressed cation chromatography with complex- forming mobile phases, coordination chromatography with chelate-forming bonded phases, ion-exchange and ion-pair chromatography of anionic metal chelates) recently developed in the authors' laboratories are reviewed. The retention behaviour and separation mechanism of non-complexed and completed metal analytes are discussed from the point of view of basic coordination chemistry (stability of metal complexes, effective charge of metal atom, ligand completing ability, etc.). Comparisons and contrasts between various metal complexation IC techniques and their common features and advantages relative to other methods used in analyses for transition and heavy metal ions are evaluated.     

Investigation of Metal Ion Complexation of π-Coordinate Calixarene Derivatives by Electrospray-Ionization Mass Spectrometry

Complexation of π-coordinate calix[4]arene derivatives toward soft metal ions, silver and thallium (I) ions, has been studied by electrospray-ionization mass spectrometry. Competitive metal–ion complexation of three calix[4]arene derivatives demonstrates a significant effect of olefinic substituents and its location on the silver ion complexation, but there was no effect of them on the thallium ion complexation. The stability constants for the metal ion complexes of the calixarene derivatives in methanol have been successfully determined by a mass-spectrometric method using 18-crown-6 as the reference ligand.     

Structural control of Schiff base ligands for selective extraction of copper(II).

Structural control of Schiff base ligands for selective extraction of copper(II) was investigated by changing pendant arms and the distance between two imine-N donor atoms in ligands. Di-Schiff base ligands, N,N'-bis(2-quinolylmethylidene)-1,2-diiminoethane (BQIE), N,N'-bis(2-pyridylmethylidene)-1,3-diimino-2,2-dimethylpropane (BPMP) and N,N'-bis(2-quinolylmethylidene)-1,3-diimino-2,2-dimethylpropane (BQMP), were used as complexation reagents for ion-pair extraction of divalent transition metal cations into nitrobenzene with picrate anion. The pendant arms affected the lipophilicity of ligand to nitrobenzene, due to their polarity. The distance between two imine-N atoms, on the contrary, was a factor of controlling the extraction selectivity. BQMP has both 2-quinolyl pendant arms and trimethylene backbone structure; use of BQMP as a complexation reagent led to the selective extraction of Cu2+ in the system.     

Alkali cation attachment to derivatized fullerenes studied by matrix-assisted laser desorption/ionization

The complexation of alkali metal ions with amphiphilic fullerene derivatives has been investigated by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The formation of analyte ions occurs via two competing mechanisms including electron transfer from matrix-derived ions and metal ion attachment. The interplay of these processes has been examined by laser fluence dependent sample activation and by variation of the target composition. The attachment of metal ions has been established as the gentler and thus more efficient route towards the formation of intact analyte ions. Investigations into the metal ion complexation have been conducted to reveal the reactivity order of the alkali metals in these reactions and to elucidate the influence of structural differences of the analytes, as well as to unravel effects caused by the anionic counter ion of the metal. The experimental data have been derived by two complementary approaches. Competing reactants were either studied simultaneously, so that the product distribution would provide direct insight into the reactivity pattern, and/or product distributions were obtained in a large variety of separate experiments and normalized for reliable comparison. It has been found that the extent to which complexation is observed follows the charge density order of the alkali metal ions. The structural features of the fullerene-attached ligands were of profound influence on the attachment of the metal ion, inducing enhanced selectivity for the complexation with less reactive metals. The metal ion attachment is reduced with the use of smaller anionic counter ions. Rationalization of these findings is provided within the framework of the mechanisms of ion formation in MALDI.     

Fluorometric sensing of alkaline Earth metal cations by new lariat ethers having plural pyrenylmethyl groups on the electron-donating sidearms

[structure: see text] New fluorescent compounds (1), lariat ethers having plural pyrenylmethyl groups on the sidearms, were prepared, and their complexation behavior with alkaline earth metal cations was examined by fluorescence spectrometry. The pyrene excimer emission decreased accompanied with an increase in the monomer emission upon complexation with the metal ion. This finding is ascribed to the cooperative participation of one of the two sidearms in the complexation of the crown ring with the metal ion.     

Complexation amplified pH oscillation in metal involved systems

A novel mechanism of amplifying pH oscillations by pH-dependent EDTA-metal ion complexation is proposed. If there is a metal ion involved in the H(+) consuming reactions in the pH oscillator and the metal's complex formation constant is big enough, the nonlinear coupling of the original oscillator with the complexation induced metal ion oscillation can finally amplify the pH oscillation. This effect is demonstrated in H(2)O(2)-S(2)O(3)(2-)-Cu(2+) system and further discussed in three other systems. Since pH oscillation is widely used in many areas as a spontaneous periodical driving force at the molecular level, this work may help to broaden the driving range of pH oscillators.     

Kinetic studies of complexation reactions of water-soluble hydrazones with nickel(II) and palladium(II) ions

The kinetics of complexation reactions of five water-soluble heterocyclic hydrazones with nickel(II) and palladium(II) ions have been investigated by stopped-flow spectrophotometry. Rates of complexations with nickel(II) and palladium(II) in the absence of chloride ion were found to be proportional to the first order of the ligand and metal ion concentrations and to the inverse first order of the hydrogen ion concentration except for the complexation of alpha-(2-benzimidazolyl)-alpha-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid with palladium(II). Rates of complexation with palladium(II) in the presence of chloride ion were best described by a two-term expression, both terms being first order in the palladium ion and ligand concentrations and inverse first order in the hydrogen ion concentration. The first term has zero dependence of the chloride ion concentration, whereas the second is first order with respect to the chloride ion concentration. The rate constant for each complexation reaction was determined. The complexation of the hydrazones with nickel(II) was estimated to go according to an Eigen mechanism and that with palladium (II) according to the associative mechanism.     

Heterogeneity and lability of Pb(II) complexation by humic substances: practical interpretation tools

The complexation of Pb(II) by natural organic matter (NOM) is better described by taking into account the dependence of the strength of binding on metal loading conditions. The utility of a linear differential equilibrium function for interpretation of metal ion binding data is demonstrated. This approach considers the binding intensity (log K*) as a function of metal ion loading (ı = bound metal/binding site concentration). Three methods for calculating this function are presented: – direct calculation from metal titration curves, – direct calculation from polarograms, and – compilation of data derived from interpretation of complexation in terms of one- or two- binding sites (e.g. Scatchard analysis), i.e. Cc (complexation capacity = effective site concentration)–K pairs. Heterogeneity also impacts on the apparent lability of complexes; complexes formed at the lowest metal loadings are the least labile. Received: 28 December 2000 / Revised: 23 February 2001 / Accepted: 28 February 2001     

Cation-π interactions of curved polycyclic systems: M (M=Li and Na) ion complexation with buckybowls

B3LYP/6-311+G** calculations on alkali metal ion (Li⁺ and Na⁺) complexation with corannulene and sumanene indicate stronger binding compared to [5]-radialene or benzene. The dependence of binding to the convex and concave site is marginal, albeit the preference was consistent for convex binding in the range of 1-4 kcal/mol. The bowl-to-bowl inversion barriers are only marginally affected, below 2 kcal/mol, by metal ion complexation.     

Use of Two-Column Ion Chromatography for the Separation of Transition Metal Complexes of 1,2-Cyclohexanediaminetetraacetic Acid and Study of Complexation in Alkaline Solutions

The ion-chromatographic behavior of anionic transition metal complexes of 1,2-cyclohexanediaminetetraacetic acid (CHDTA) on polymeric anion exchangers was studied. It was demonstrated that two-column ion chromatography can be used for studying the complexation of CHDTA with transition metal ions in alkaline solutions. A method was proposed for the calculation of equilibrium constants of complexation reactions and stability constants from the data of ion-chromatographic measurements.