Anion Complexation Studies of 3-Nitrophenyl-Substituted Tripodal Thiourea Receptor: A Naked-Eye Detection of Sulfate via Fluoride Displacement Assay.

A thiourea-based tripodal receptor substituted with 3-nitrophenyl groups has been synthesized, and the binding affinity for a variety of anions has been studied by H NMR titrations and nuclear Overhauser enhancement spectroscopy experiments in dimethyl sulfoxide-. As investigated by H NMR titrations, the receptor binds an anion in a 1:1 binding mode, showing the highest binding and strong selectivity for sulfate anion. A competitive colorimetric assay in the presence of fluoride suggests that the sulfate is capable of displacing the bound fluoride, showing a sharp visible color change.