Urea and thiourea based efficient colorimetric sensors for oxyanions

Urea and thiourea based receptors 1 and 2 bind H2PO4−, OH−, CH3CO2−, and PhCO2− ions in an acetonitrile/DMSO (9:1, v/v) medium. Binding of these anions causes an appreciable change in the visible region of the spectrum, which can be detected by the naked eye. The affinity constant for H2PO4− is higher by about an order of magnitude as compared to the other oxyanions mentioned above. Ab initio calculations predicted tweezer-like binding modes for receptors 1 and 2 with these anions and a higher affinity toward H2PO4− was predicted in acetonitrile.