A Novel C3v-Symmetrical Calix(aza)cryptand with a Remarkably High and Selective Affinity for Small Ammoniums
journal contributionposted on 23.07.2004, 00:00 by Ulrich Darbost, Michel Giorgi, Olivia Reinaud, Ivan Jabin
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The three-step synthesis of a calixarene capped with a TAC unit is presented. The novel C3v-symmetrical calix(aza)cryptand displayed an exceptionally high affinity for small ammoniums. NMR and X-ray diffraction analyses demonstrated the formation of endo-complexes. These complexes are stabilized thanks to (i) hydrogen bonding to both the aza cap and one phenolic unit of the calixarene and to (ii) cationic and CH−π interactions between the ammonium and the aromatic walls of the host. Combined extraction and competitive binding experiments yielded the free energies of bindings ΔG° in chloroform. The values are the highest ever obtained with a calixarene-type host. CalixTAC displayed the best affinity for EtNH3+. Comparison with other small ammoniums emphasizes the high selectivity of the recognition process.