Synthesis and study of allosteric effects on extraction behaviour of novel calixarene-based dichromate anion receptors

In this study the selective derivatization of p-tert-butylcalix[4]arene was carried out and two new calix[4]arene-based azacrown ionophores, 5,17-di-tert-butyl-11,23-di-(methyl-3,5-dioxaoctane-1,8-diimine)-25,26,27,28-tetrahydroxycalix[4]arene (6), and 5,17-di-tertbutyl-11,23-di-(methyl-3,5-dioxaoctane-1,8-diimine)-25,27-diethoxyformyl-methoxy-26,28-dihydroxycalix[4]arene (7) have been synthesized. Treatment of 5,17-di-tert-butyl-11,23-diformylcalix[4]arene-25,26,27,28-tetrol (5) with 1,8-diamino-3,6-dioxaoctane gave the ionophore 6 which was converted to its diester derivative 7 by reaction with ethylbromoacetate in the presence of potassium carbonate. In the synthesis, the upper and lower rims of p-tert-butylcalix[4]arene were modified in order to acquire binding sites for the recognition of metal cations and dichromate anions. It was observed that receptor 7 is a better extractant for Cr2O72- anions than receptors 6. The protonated alkylinium form of 7 is an effective extractant for transferring the Cr2O72- anions from aqueous into a dichloromethane layer and failed in transferring Na+ cations due to the allosteric effect produced by the crown part of the calix moiety present at the p-position. (C) 2002 Elsevier Science Ltd. All rights reserved.