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A Novel C3v-Symmetrical Calix[6](aza)cryptand with a Remarkably High and Selective Affinity for Small Ammoniums

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journal contribution
posted on 23.07.2004, 00:00 by Ulrich Darbost, Michel Giorgi, Olivia Reinaud, Ivan Jabin
The three-step synthesis of a calix[6]arene capped with a TAC unit is presented. The novel C3v-symmetrical calix[6](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. Calix[6]TAC displayed the best affinity for EtNH3+. Comparison with other small ammoniums emphasizes the high selectivity of the recognition process.

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