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Dihydrogen phosphate selective anion receptors 1, 2, and 3 that utilize amide N H, and C H for anion recognition have been designed and synthesized. For 1 and 2, aromatic C H hydrogen bonding element is present on naphthyl rings (H a ). In addition, for receptor 1, this aromatic hydrogen bonding element is further polarized by the nitro groups, which would enhance the hydrogen bonding ability. Partial charges derived from Natural Population Analysis also supported the existence of this polarization. That is, positive partial charge of H a in receptor 1 was more positive than that in receptor 2. As expected from the partial charge values, receptor 1 consistently showed highest affinity among three receptors, followed by receptor 2 regardless of the anions tested in this study. Therefore, we have shown that affinity modulation of a receptor was possible by changing the nature of the aromatic C H hydrogen. In addition, the receptors showed selectivity toward dihydrogen phosphate among various anions including acetate and chloride.

We have developed new symmetric receptors 1 and 2, which bind selectively to oxoanions of phosphorus such as phosphinates and dihydrogen phosphate. Among the phosphinates and dihydrogen phosphate, we have investigated the orders of binding affinities to receptors 1 and 2 are Me2PO2− > H2PO4− > PhHPO2− and Me2PO2− > H2PO4−, respectively. We further investigated the physicochemical reasons for this order by theoretical calculations. Calculation results were in good agreement with experimental results. The order of affinity for the anions seemed to depend on the magnitude of the partial charge of oxygen (hydrogen bond acceptor) present in the anion.

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