Chromogenic anion receptors based on acylhydrazone are designed and synthesized. UV−vis and 1 H NMR titration showed that receptors 1 and 2 are selective receptors for dihydrogen phosphate (H 2 PO 4 − ). Both showed strong association constants with H 2 PO 4 − even in polar solvents. Receptor 1 was found to recognize H 2 PO 4 − through three types of hydrogen-bonding (H-bonding) donors: indole N−H, amide N−H, and imine C−H hydrogens. However, receptor 2 seemed to sense H 2 PO 4 − through two types of Hbonding donors. Despite this seemingly different number of H-bonding elements, the binding constants of receptors 1 and 2 with H 2 PO 4− were almost equal. To understand this puzzling result, we investigated the binding poses of complexes using density functional theory. The proposed 2•H 2 PO 4 − complex structure revealed another possible H-bonding element involving an aromatic nitrogen acting as a H-bonding acceptor. To confirm this, we synthesized receptor 3, which is devoid of this nitrogen. The binding constant of receptor 3 for H 2 PO 4 − was 2 orders of magnitude lower than those of receptors 1 and 2. This decreased binding affinity strongly supports the existence of a N(aromatic)•••H−O(phosphate) interaction. These results provide a rare opportunity to identify H 2 PO 4 − acting as a H-bonding donor during an anion-recognition event.

A novel chromogenic anion receptor 1 based on acylhydrazone and pyrazole has been designed and synthesized. Receptor 1 forms stable 1 : 1 complexes with dihydrogen phosphate and other halide anions in DMSO solution.

No abstract

No abstract

No abstract