Cation complexation with p-tert-butylcalix[5]arene pentacarboxylic acid derivative: An allosteric regulation of the first metal ion for stepwise extraction of the second ion

Abstract

A calix[5]arene based solvent extraction reagent 3, appending carboxylic acid groups at the lower rim, has been developed and its complexation behavior towards some transition metal ions has been studied. The host 3 can selectively and quantitatively extract Pb(II) ions above pH 1.8 while other divalent ions such as Cu(II), Zn(II), Co(II), Ni(II) are extracted quantitatively only above pH 3.0. The outstanding Pb(II) selectivity of 3 comes from the size fit complementarity effect of the Pb(II) ion in the calix[5]arene cavity. One molecule of 3 extracts two Pb(II) ions in a stepwise manner. The first Pb(II) ion is extracted into the deep cavity of the calix[5]arene defined by phenoxy oxygen atoms. The first complexed Pb(II) ion acts as a template to bring the host into a cone conformation and induces a positive allosteric effect for the extraction of the second Pb(II) ion at an oxygen rich coordinating site composed of carboxyl groups. Both the Pb(II) ions are extracted through an ion exchange mechanism and the electroneutral complex in the organic phase is formed by the release of an equivalent number of hydrogen ions into aqueous solution. The loaded Pb(II) is easily back-extracted from Pb(II)-complexed 3 using dilute acid solution.

Selected applications of calixarene derivatives

“…41 It was found that p-t-butylcalix [5]arene pentacarboxylic acid forms with Pb(II) a very strong complex of a cone conformation. 42 To investigate the behavior of the higher order calix [6]arene, the complexation properties of p-t-butylcalix [6]arene hexacarboxylic acid 10a have been studied. The data of 1 H NMR analysis indicate for 10a the cone conformation in CHCl 3 , due to the presence of four hydrogen bond interactions among six carboxylic groups.…”

Synthesis, crystal structures and competitive binding property of a family of calix[4]arene-biscrown-5/6 and their application in extraction of alkali metal ions from sea bittern

“…It may be noted that substantial changes in chemical shifts were observed in both aliphatic and aromatic regions and also a new peak appeared around δ = 8.6, which is due to picrate anion [15,24]. It is interesting to note that upon addition of metal ion, a few new peaks generated at the expense of the original signals, indicating that the size of the metal ion fits well in the calix-crown cavity making strong interaction with the donor atoms forming stable complex [25,27,58]. The NMR data therefore, clearly supports the high selectivity for these ionophores towards K + .…”

Extraction Property of p-tert-Butylsulfonylcalix[4]arene Possessing Irradiation Stability towards Cesium(I) and Strontium(II)

“…The OH stretching bands of the extracted species were shifted to lower frequencies, which implied that hydroxyl groups were coordinated with metal ions. Previously examined complexes of p-tert-butylcalix [5]arene hexacarboxylic acid ligand with Cu(II) ion [38] showing that C=O stretching band of ligand-Cu(II) changed intensely and positively. In this experiment, the absorption bands at 1313 and 1156 cm´1 correspond to asymmetrical and symmetrical sulfonyl stretching vibrations of SC4A, respectively.…”