Acetate binding induces fluorescence enhancement in tryptophan ligands

The anion coordination properties of bis-tryptophan dicarboxamide ligands 1–3 were investigated using fluorescence and 1H NMR spectroscopy. It was observed that the coordination of acetate anions to these ligands produced emissions at 381 nm with gradual enhancement of fluorescence. In comparison, fluoride produced minor enhancement, the addition of chloride, bromide and nitrate anions caused quenching of ligand fluorescence. 1H NMR studies revealed that the ligands coordinated to the acetate anions through the indole and amide NH groups.