Synthesis and Evaluation of an Azo Dye for the Chromogenic Detection of Metal Cations

Great efforts have been focused on developing selective and sensitive signaling probes for detecting metal ions because they are indispensable in most biological processes, but in abnormal levels these analytes may cause severe effects on human health and the environment. Among chromogenic probes, azo dyes are widely used as optical chemosensors due to their ease of synthesis, structural variability and color recognition with naked eye. A very popular azo dye is 4-[[4′-(N,N-dimethylamino)phenyl]diazenyl]benzoic acid, known as Dabcyl, a push−pull azobenzene functionalized at the para positions of the phenyl rings. Besides its biomolecular applications as a quencher in FRET-based probes, Dabcyl has also been used as a precursor in colorimetric probes for cation recognition. Following the research group´s work on optical chemosensors, we report herein the synthesis of Dabcyl, by an azocoupling reaction, as well as its evaluation as a potential colorimetric chemosensor for metal cations. Therefore, interaction studies of Dabcyl in the presence of environmentally and biologically important metal ions were performed in acetonitrile solutions. It was found that this receptor has potential application as a colorimetric chemosensor for Hg²⁺, Fe²⁺, Pd²⁺, Sn²⁺ and Al³⁺ with remarkable sensitivity and a marked color change from light yellow to pink in the presence of these cations.