Novel fluorescent Schiff bases as Al3+ sensors with high selectivity and sensitivity, and their bioimaging applications

A short set of three new Schiff base chemosensors with high selectivity and sensitivity towards Al3+ over other metal cations in aqueous solution were developed and fully characterized. Compounds (E)-1-((L-glutamineimino)methyl)naphthalen-2-ol (A), (E)-1-((glucosamine-imino)methyl)naphthalen-2-ol (B), and (E)-3-hydroxy-4-(((2-hydroxynaphthalen-1-yl)methylene)amino)benzoic acid (C) exhibited a significant fluorescence enhancement in the presence of Al3+ over other competitive metal ions with a low detection limit of 0.103, 0.317 and 0.091 mu M respectively, much lower than the WHO acceptable limit (0.05 mg/L or 1.85 mu M of Al3+) in drinking water. The Schiff base C, shows high sensitivity in aqueous media (Limit of detection, LOD: 0.091 mu M) and with a 38-fold (phi=1.64% for Schiff free base; phi = 63.91% for Aluminium complex) fluorescence enhancement in the presence of Al3+. The theoretical research has enabled us to rationalize the behaviours of the three selective sensors to Al3+ synthesized in this work. Based on the design, the amino acid Schiff bases (A) showed good solubility and compatibility with and without Al3+ and some fluorescent bioimaging (FBI) are reported in human epithelial cells Hs27.