title: Dihydrogen phosphate as a hydrogen-bonding donor element: anion receptors based on acylhydrazone.
abstract: 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 (H2PO4(-)). Both showed strong association constants with H2PO4(-) even in polar solvents. Receptor 1 was found to recognize H2PO4(-) 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 H2PO4(-) through two types of H-bonding donors. Despite this seemingly different number of H-bonding elements, the binding constants of receptors 1 and 2 with H2PO4(-) were almost equal. To understand this puzzling result, we investigated the binding poses of complexes using density functional theory. The proposed 2·H2PO4(-) 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 H2PO4(-) 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 H2PO4(-) acting as a H-bonding donor during an anion-recognition event.
authors.affiliation: Department of Chemistry, Sejong University , Seoul 143-747, South Korea.
authors.forename: T Senthil
authors.initials: TS
authors.lastname: Pandian
authors.forename: Seung Joo
authors.initials: SJ
authors.lastname: Cho
authors.forename: Jongmin
authors.initials: J
authors.lastname: Kang
mesh_terms: D000838:Anions / Q000138:chemical synthesis / Q000737:chemistry; D006835:Hydrazones / Q000138:chemical synthesis / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D010710:Phosphates / Q000737:chemistry*
chemical_list: D000838:Anions; D006835:Hydrazones; D010710:Phosphates; D006859:Hydrogen