Capture and displacement-based release of the bicarbonate anion by calix[4]pyrroles with small rigid straps |
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| Authors: | Nam Jung Heo Ju Ho Yang Vincent M Lynch Byoung Joon Ko Jonathan L Sessler Sung Kuk Kim |
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| Institution: | Department of Chemistry, Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701 Korea.; Department of Chemistry, The University of Texas at Austin, 105 E. 24th Street-Stop A5300, Austin Texas 78712-1224 USA.; New Drug Development Center, Osong Medical Innovation Foundation, Chungbuk Korea 28160, |
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| Abstract: | Two-phenoxy walled calix4]pyrroles 1 and 2 strapped with small rigid linkers containing pyridine and benzene, respectively, have been synthesized. 1H NMR spectroscopic analyses carried out in CDCl3 revealed that both of receptors 1 and 2 recognize only F− and HCO3− among various test anions with high preference for HCO3− (as the tetraethylammonium, TEA+ salt) relative to F− (as the TBA+ salt). The bound HCO3− anion was completely released out of the receptors upon the addition of F− (as the tetrabutylammonium, TBA+ salt) as a result of significantly enhanced affinities and selectivities of the receptors for F− once converted to the TEAHCO3 complexes. Consequently, relatively stable TEAF complexes of receptors 1 and 2 were formed via anion metathesis occurring within the receptor cavities. By contrast, the direct addition of TEAF to receptors 1 and 2 produces different complexation products initially, although eventually the same TEAF complexes are produced as via sequential TEAHCO3 and TBAF addition. These findings are rationalized in terms of the formation of different ion pair complexes involving interactions both inside and outside of the core receptor framework.The inherent selectivity of anion receptors can be reversed by ion pairing occurring both inside and outside of the receptor cavity. |
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