The incorporation of four carboxylic acids or four amino groups to the upper rim of an aryl extended calix[4]pyrrole produces water-soluble receptors which are able to effectively bind aromatic N-oxides in water by a combination of hydrogen bonding, π-π, CH-π, and hydrophobic interactions.
![Molecular recognition of pyridine N-oxides in water using calix[4]pyrrole receptors](https://www.iciq.org/wp-content/uploads/2014/03/Molecular-recognition_3178.gif)