Specific Cooperative Effect of a Macrocyclic Receptor for Metal Ion Transfer into an Ionic Liquid

Abstract

An intramolecular cooperative extraction system for the removal of strontium cations (Sr(2+)) from water by use of a novel macrocyclic receptor (H(2)βDA18C6) composed of diaza-18-crown-6 and two β-diketone fragments in ionic liquid (IL) is reported, together with X-ray spectroscopic characterization of the resulting extracted complexes in the IL and chloroform phases. The covalent attachment of two β-diketone fragments to a diazacrown ether resulted in a cooperative interaction within the receptor for Sr(2+) transfer, which remarkably enhanced the efficiency of Sr(2+) transfer relative to a mixed β-diketone and diazacrown system. The intramolecular cooperative effect was observed only in the IL extraction system, providing a 500-fold increase in extraction performance for Sr(2+) over chloroform. Slope analysis and potentiometric titration confirmed that identical extraction mechanisms operated in both the IL and chloroform systems. Extended X-ray absorption fine structure spectroscopy revealed that the average distance between Sr(2+) and O atoms in the Sr(2+) complex was shorter in IL than in chloroform. Consequently, Sr(2+) was held by H(2)βDA18C6 more rigidly in IL than in chloroform, representing an important factor dominating the magnitude of the intramolecular cooperative effect of H(2)βDA18C6 for Sr(2+). Furthermore, competitive extraction studies with alkaline earth metal ions revealed that the magnitude of the intramolecular cooperative effect depended on the suitability between metal ion size and the cavity size of H(2)βDA18C6. Sr(2+) was successfully recovered from IL by controlling the pH in the receiving phase, and the extraction performance of H(2)βDA18C6 in IL was maintained after five repeated uses.

Highly Efficient Extraction Separation of Lanthanides Using a Diglycolamic Acid Extractant

“…S1, Supporting Information). 32 The pKa value of DODGAA was estimated to be 4.11 ± 0.01 in H2O-C2H5OH (1:1, v/v). For comparison, it was confirmed that the pKa value of acetic acid was 5.51 ± 0.02 under the same conditions.…”

Highly Selective Synergism for the Extraction of Lanthanoid(III) Ions with β-Diketones and Trioctylphosphine Oxide in an Ionic Liquid

“…[10][11][12][13] Thus, the extractability and separability of metal ions in the IL extraction system are expected to differ from those of the usual organic solvent systems. 14,15 Recently, the present authors have reported on the synergistic ionic-liquid extraction of lanthanoids(III) (Ln(III)) with 2-thenoyltrifluoroacetone (Htta) as an acidic chelating extractant and several neutral ligands in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][Tf2N]). [16][17][18] In the Htta-18-crown-6 derivative (CE) systems, 17 a synergistic enhancement of the extractability was found for only light Ln(III) from La to Eu, leading to selective extraction of the lighter Ln, while in the Htta-trioctylphosphine oxide (TOPO) system, 18 the synergistic effect increased with an increase in the atomic number, leading to an improvement in the selectivity among Ln(III) ions.…”

Enhanced Retention of Chelating Reagents in Octadecylsilyl Silica Phase by Interaction with Residual Silanol Groups in Solid Phase Extraction of Divalent Metal Ions

“…1 The performances of a variety of extraction systems, each consisting of an extracting reagent and an extraction solvent, have been studied, so that a suitable extraction system is selectable for each general application. Extracting reagents with novel selectivities have been extensively developed, while alternative media for organic solvents such as ionic liquids [2][3][4][5] and supercritical fluids 6 have been lately studied by taking into account their harmful effects on the environment. Solid-phase extraction (SPE) of metal ions using octadecylsilyl silica (ODS) has also been developed in this respect.…”