Kinetics of metal ion complex formation in micellar media. A comparison between normal and polymerized micelles

Micellar media can be used to investigate the rate of complex formation between hydrophobic extractants and metal ions. Acceleration or retardation effects may be obtained, depending on factors such as the nature of the surfactant, the hydrophilic/lipophilic character and ionization state of the extractant, etc. The present work was aimed at studying the influence of some specific parameters in producing retardation effects, which have potential application for performing separation of metal ions on a kinetic basis. The stopped-flow technique was used to measure the rate of complex formation between Cu²⁺ and complexing agents with varying alkyl chain length. Micelles made of the nonionic surfactants C₁₂EO₆, Triton X-100 and Brij 35 were first considered, which did not show any direct correlation between the rate of complex formation and the thickness of the hydrophilic layer constituted by the polar heads of the surfactant molecules.In a second approach, we have used polymerized micelles obtained from undec-10-enyltrimethyl ammonium bromide, which we assumed to be more rigid than normal micelles. Although the absence of CMC was confirmed, the rates measured in these polymerized micelles were larger than those obtained in micellar solutions of CTAB and DTAB. The results are discussed in relation with the nature of the hydrophobic domains in the different situations.Institut Nancéien de Chimie Moléculaire (I.N.C.M.), FU CNRS n=8     

GRAFTING OF HUMIC ACID ONTO COTTON CELLULOSE (Ⅱ)*

Cotton cellulose reacted with epichlorohydrin under the catalytic action of HClO_4 and H_2O to form 3-chloro-2-hydroxypropyl ether with a substitution degree of 0.61. The chlorine-containing product was treated with aliphatic diamines (ethylenediamine, propylenediamine, etc.) to produce nitrogen-containing cellulose which further reacted with humic acid to give black fiberous graft cellulose. This product contains 27—35% humic acid, 0.90 meq/g acidic groups, possesses 0.49 meq/g Cu~(2+)-complexing capacity and good mechanical strength, and can be used under pH12.     

冠醚聚合物的研究 Ⅱ.以聚硫醚为主链的硫杂冠醚聚合物的合成及其络合性能

本文报道了一种合成硫杂冠醚聚合物的新方法。以聚(2′-氯乙基-2,3-环硫丙基醚)为预聚物与二巯基化合物通过大分子反应直接环化,一步法合成了四种以聚硫醚为主链的新型硫杂冠醚聚合物(PD1-PD4)。并测定了它们对Ag~+、Au~(3+)、Pd~(2+)、Pt~(4+)、Cu~(2+)、Hg~(2+)、Zn~(2+)、Cd~(2+)、Pb~(2+)、Mg~(2+)、K~+、Ns~+等金属离子的络合性能。结果表明:它们除不络合K~+、Na~+、Mg~(2+)、Pb~(2+)外,对其它八种离子有不同程度的络合,其中对Ag~+、Au~(3+)、Pd~(2+)等贵金属离子的络合容量较高。     

Modeling of tracer diffusion in liquids when solute–solvent interactions are present

The linear solvation energy relationship (LSER) model is employed to correlate the tracer diffusion coefficients of 550 binary systems at 298.15 K. Among the selected solutes and solvents there exist apolar, polar and hydrogen-bonding substances that can interact with themselves (solvent polymerization) or with the other compound (solute–solvent complexes formation). The results of the proposed formulas are compared with those of other predictive equations.     

Influence of the nature of the metal ions on the complexation with chitosan.: Application to the treatment of liquid waste

The capacity of the chitosan to complex metallic ions is one of its most important potentialities. This polymer shows a selectivity according to the considered cation. In the case of divalent ions the capacity to fix the metallic ions increases from 0.02 mmol/g of chitosan for Co²⁺, Ca²⁺ to 1.2 for Cu²⁺ in the same external conditions. Considering trivalent ions this capacity is from 0.2 mmol/g of chitosan for Pr³⁺ and Cr³⁺ to 1.47 for Eu³⁺ and Nd³⁺. This selectivity seems to be independent on the size and the hardness of the ions. This order in the selectivity is confirmed using potentiometric and spectrophotometric methods and does not depend on the physical form of chitosan. Recovery tests of metals were carried out on real effluents. The first results obtained confirm the initial interest in using chitosan as a depolluting agent, especially as a film.     

Comparative study on the transition metal complexes of a novel thiacalix[4]arene derivative

A comparative study on Zn²⁺ and Cu²⁺ complexes of the novel compound 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycarbonyl)phenyl]methoxy}-2,8,14,20-tetrathiacalix[4]arene, that possesses potential as a core unit for the construction of molecular receptors, is presented using semiempirical AM1 calculation. The possible structures of each metal complex and their corresponding energetic data are compared with the parent 5,11,17,23-tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene. The complexation ability of both thiacalix[4]arenes towards the two metal ions is discussed on the basis of binding energies. Both thiacalix[4]arene 1:1 complexes show higher complexation ability towards Cu²⁺. However, 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycarbonyl)phenyl]methoxy}-2,8,14,20-tetrathiacalix[4]arene presents lower complexation ability when compared with the 5,11,17,23-tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene. The results of liquid–liquid extraction experiments of the thiacalix[4]arenes are in good agreement with the theoretical calculations.     

Study of the Complexation,Adsorption and Electrode Reaction Mechanisms of Chromium(VI) and (III) with DTPA Under Adsorptive Stripping Voltammetric Conditions

The complexation of Cr(III) and Cr(VI) with diethylenetriaminepentaacetic acid (DTPA), the redox behavior of these complexes and their adsorption on the mercury electrode surface were investigated by a combination of electrochemical techniques and UV/vis spectroscopy. A homogenous two‐step reaction was observed when mixing Cr(III), present as hexaquo complex, with DTPA. The first reaction product, the electroactive 1 : 1 complex, turns into an electroinactive form in the second step. The results indicate that the second reaction product is presumably a 1 : 2 Cr(III)/DTPA complex. The electroreduction of the DTPA‐Cr(III) complex to Cr(II) was found to be diffusion rather than adsorption controlled.The Cr(III) ion, generated in‐situ from Cr(VI) at the mercury electrode at about ?50 mV (vs. Ag|AgCl) (3 mol L^?1 KCl), was found to form instantly an electroactive and adsorbable complex with DTPA. By means of electrocapillary measurements its surface activity was shown to be 30 times higher than that of the complex built by homogenous reaction of DTPA with the hydrated Cr(III). Both components, DTPA and the in‐situ built complex Cr(III) ion were found to adsorb on the mercury electrode.The effect of nitrate, used as catalytic oxidant in the voltammetric determination method, on the complexation reaction and on the adsorption processes was found to be negligible.The proposed complex structures and an overall reaction scheme are shown.     

Yttrium(III) bonding to organic ligands: A comparison with the lanthanoid(III) cations

Summary The yttrium(III) bonding to organic substrates (oximes, -diketonates and (poly)amino-(poly)carboxylates) has been compared with that of the lanthanoid(III) cations. The complexation constants of Y³⁺ with the examined organic ligands are similar to those of some cations of the first half of the lanthanoid series, in contrast with the fact that the Y³⁺ ionic dimensions are similar to those of Ho³⁺. This has been explained by correlating the formation constants of the Y³⁺ and the lanthanoids(III) complexes by the equation logK ₁=C _AC_B+E _AE_B, where the parametersC andE indicate the tendency of each Lewis acidA and Lewis baseB to undergo covalent or ionic bonding, and where the ratioH=E/C indicates the charge control on the bond formation tendency of each speciesA orB. The results are commented in terms of the utility of Y³⁺ in assisting organic reactions.

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Bindung von Yttrium(III) an organische Liganden: Vergleich mit Lanthanoid(III)-Kationen

Zusammenfassung Es wurde die Bindung von Yttrium(III) an organische Substanzen [Oxime, -Diketonate und (Poly)Amino(poly)carboxylate] im Vergleich mit Lanthanoid(III)-Kationen behandelt. Die Komplexierungskonstanten von Y³⁺ sind ähnlich denen einiger Kationen der ersten Hälfte der Lanthanoidenserie; dies steht im Gegensatz zur Tatsache, daß die Dimensionen des Y³⁺-Ions denen des Ho³⁺ entsprechen. Die Erklärung wurde mittels der für die Bildungskonstanten der Y³⁺- und Lanthanoid(III)-Komplexe gültigen Gleichung logK ₁=C _AC_B+E _AE_B gefunden, wobeiC undE Parameter sind, die die Tendenz der Lewis-SäurenA und der Lewis-BasenB zum Eingehen von kovalenten oder ionischen Bindungen charakterisieren und wo das VerhältnisH=E/C den Steuerungseffekt der Ladung auf die Bindungstendenz der SpeziesA oderB beschreibt. Die Ergebnisse werden im Hinblick auf den Nutzen von Y³⁺ zur Unterstützung organischer Reaktionen diskutiert.

     

Modification of 4-(2-pyridylazo)-resorcinol postcolumn reagent selectivity through competitive equilibria with chelating ligands

Aminopolycar☐ylate ligands were added to the 4-(2-pyridylazo)-resorcinol (PAR) postcolumn reagent to alter the reagent selectivity towards transition metals. Addition of ethylenediaminetetraacetic acid (EDTA) completely suppressed the reaction between PAR and the metal ions. Addition of 0.1 mM nitrilotriacetic acid (NTA) to 1 mM PAR lowered the response to specific transition metal ions, but completely suppressed the PAR response to the lanthanides. Increasing the NTA concentration to 8 mM resulted in complete suppression of the PAR response to all metal ions except Cu²⁺ and Co²⁺ for which the detection limits were 3 and 1 ng, respectively. The observed selectivity results from the slow rate of conversion of metal ions from the M(NTA)₂⁴⁻ form to M(PAR)₂.     

Effect of Cu(II) on the electrochemically initiated reaction of thiols with<Emphasis Type="Italic"> N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethyl-<Emphasis Type="Italic">p</Emphasis>-phenylenediamine: methodology for the indirect voltammetric determination of Cu(II)

The effect of Cu(II) on the determination of homocysteine via its electrochemically initiated reaction with N,N-diethyl-p-phenylenediamine is examined. The presence of copper inhibited the detection process for homocysteine owing to a complexation reaction occurring. This provided an indirect route for the sensitive and selective determination of Cu(II), which produced a linear response over the range from 2.5 to 500 M and a limit of detection of 2.5 M. The detection pathway was examined in the presence of metallic and inorganic ions, with negligible interference observed.