Tuning of the Anion Affinity and Selectivity of Tripyrromethane-Based Receptors by Simple Structural Modification

초록

Tripyrromethane-based tripodal compounds 1-3 were synthesized as anion receptors. It was revealed by 1H NMR spectroscopic analyses carried out in CDCl3 that tripyrromethane 1 with an ester group was capable of recognizing F-, Cl-, Br-, and H2PO4- with relatively high selectivity for F-. By contrast, receptor 2 having an additional hydrogen bond donor of an amide group binds F- and H2PO4- with much improved affinity relative to receptor 1. On the other hand, receptor 3 bearing formyl groups on its two pyrrole subunits showed markedly enhanced selectivity for F- presumably due to the increased acidity of the pyrrolic NHs and the resulting strengthened intermolecular hydrogen bonds. In addition, tripodal receptors 1-3 were found to bind H2PO4-, a tetrahedral oxyanion, more efficiently than 2-dimensional macrocyclic calix[4]pyrrole 4. Selectivity and affinity for anions of pyrrole-based tripodal receptors can be modulated by their simple structural changes.+image

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