Per-6-ammonium-β-cyclodextrin/p-nitrophenol complex as a colorimetric sensor for phosphate and pyrophosphate anions in water

Using per-6-ammonium-β-cyclodextrin (per-6-NH3+-β-CD) as an anion binding site and p-nitrophenol as a spectroscopic probe, a colorimetric sensor is developed for phosphate and pyrophosphate anions in water. Per-6-NH3+-β-CD forms a 1:2 inclusion complex with p-nitrophenol as characterized by NOESY and ESI-MS spectra and it undergoes a distinct color change from colorless to intense yellow upon exposure to phosphate or pyrophosphate anions over other anions including perchlorate, ATP2−, ADP2− and AMP2−. The seven ammonium groups of 1, bind phosphate (characterized by ESI-MS) or pyrophosphate anions specifically by electrostatic interaction. This naked eye sensing is significant for very low concentration (5 × 10−5 M) of anion with 1:2 ratio of host and guest.