Use of the interaction of a boronic acid with a merocyanine to develop an anionic colorimetric assay

A displacement assay based on the interaction of Brooker's merocyanine (BM), a merocyanine dye, with an excess of phenylboronic acid (BA) was studied in acetonitrile. BM is colored in solution, but its reaction with BA yields a colorless covalently linked BA-BM species. This strategy was studied in the presence of different anions (F−, Cl−, Br−, I−, H2PO4-, HSO4-, CH3COO−, and NO3-), but only fluoride, a strongly nucleophilic anion, and to a much lesser extent acetate, reacted with BA-BM, displacing BM through a bimolecular nucleophilic substitution mechanism, and coloring the solution. Experimental data were collected and are shown here in order to gain a better understanding of this chromogenic sensor.