A new hexacarboxylate uranophile derived from calix[6]arene

Abstract

A new hexacarboxylate uranophile has been synthesised from calix [6]arene: log K (stability constant for the complex with U022+) was estimated to be 18.7.The selective extraction of uranium from sea water has attracted extensive attention from chemists because of its importance in relation to energy problems. In order to design a ligand that can selectively extract the uranyl ion (U022+), one has to overcome a difficult problem: the ligand must strictly discriminate between U022+ and other metal ions present in great excess in sea water. It has been established that U022+ adopts a pseudoplanar six-co-ordinate structure,lJ which is quite different from the co-ordination structures of other metal ions. This suggests that a macrocyclic host having a nearly coplanar arrangement of six ligand groups would serve as a specific ligand for U022+. Tabushi et a l . s 5 have currently been interested in this approach and reported the macrocyclic host molecule (1) having six carboxylate groups in the ring.4 Although the stability constant for U022+ and (1) is large (log K 16.4 at pH 10.4 and 25 OC),4 compound (1) is not easy to synthesise.Recently, we have been interested in the functionalisation of calixarenes (cyclic oligomers made up of benzene units in a similar way to that in which cyclodextrins are made up of glucose units); they are expected to be useful in the design of enzyme mimics in totally synthetic systems.6.7 In the course of

Scavenging of UO2 2+ using 4-sulfonic calix[6]arene in the presence of goethite

“…2-5 It was shown that these macrocycles formed extremely stable uranyl complex, and the stability is attributed to the quasi-planar arrangement of the 5 or 6 binding groups on the lower calixarene rim. 4 This arrangement coincides with the preferred hexa-coordinate planar geometry occurring perpendicular to the U-O bonds of the linear uranyl ion. The calix[n]arene used in this work was 4-sulfonic calix [6]arene which have six hydroxyl groups on the lower rim and six sulfonate groups on the upper rim.…”

Removal of lindane from an aqueous solution by using aminopropyl silica gel-immobilized calix[6]arene

“…[6]arene and immobilization onto APS;C [6]APS p-tert-Butylcalix [6]arene is used as the basis for derivatization which is described in Sheme 1. The syntheses of compounds 1-3 were obtained according to the previously published procedures [33], while the reaction producing C [6]APS (see Scheme 1) was described by Tabakci [27]. The hexaacid derivative of p-tert-butylcalix [6]arene 3 was obtained by hydrolysis of ester moieties of p-tert-butylcalix [6]arene (2).…”

Extraction sélective des actinides : application à l'analyse radiotoxicologique

“…Des études cristallographiques par diffraction des rayons X (Araki et al, 1993) ont établi que les complexes de l'ion uranyle adoptent une structure pseudoplanaire hexacoordonnée, ce qui n'est pas le cas des autres cations métal-liques. Ceci suggère l'utilisation d'un macrocycle hôte ayant un arrangement coplanaire de six groupes ligands spécifiques pour l'ion uranyle (Shinkai et al, 1986(Shinkai et al, ,1987. Toutefois, des travaux concernant le calix [o]arène substitué par six fonctions acide carboxylique ont montré une diminution de la sélectivité lorsque UO$+ se trouve en compétition avec d'autres cations métalliques lors de l'extraction (Nagaski et Shinkai, 1991).…”