Exploiting 1,4-naphthoquinone and 3-iodo-1,4-naphthoquinone motifs as anion binding sites by hydrogen or halogen-bonding interactions

Abstract

We describe here the utilization of 1,4-naphthoquinone and 3-iodo-1,4-naphthoquinone motifs as new anion binding sites by hydrogen- or halogen-bonding interactions, respectively. These binding sites have been integrated in bidentate ester based receptors. Emission experiments reveal that both receptors selectively recognize sulfate anions, which induced a remarkable increase of a new emission band attributed to the formation of π-stacking interactions between two 1,4-naphthoquinone units. Absorption spectroscopy and mass spectrometry indicate the disruption of the ester group of the 1,4-naphthoquinone based receptor in the presence of HP₂O₇³⁻, H₂PO₄⁻, F⁻, AcO⁻ and C₆H₅CO₂⁻ and in the halogenated receptor with HP₂O₇³⁻, F⁻ and AcO⁻ anions, while the presence of sulfate anions showed the clasical complexation behaviour. The ¹H-NMR experiment showed a slow exchange process of the receptors with their sulfate complexes. The binding mode of the receptors with sulfate has been studied by DFT calculations along with the Molecular Electrostatic Potential (MEP) surface computational tool that reveals those parts of the receptors which are more suitable for interacting with anions.