A Water-Soluble Schiff Base Turn-on Fluorescent Chemosensor for the Detection of Al and Zn Ions at the Nanomolar Level: Application in Live-Cell Imaging.

A water-soluble Schiff base, 2,3-bis((E)-(2-hydroxy-3-methoxybenzylidene)amino) propanoic acid (ODA) prepared by condensing o-vanillin and DL-2,3-diaminopropionic acid was evaluated as an efficient "turn on" fluorescent chemosensor for the selective recognition of Al and Zn ions in presence of several interfering metal ions (detection limit; for Al = 1.82 nM, Zn = 7.06 nM). The probe also shows a selective chromogenic behavior towards Al and Zn ions that the naked eye can view. The binding stoichiometry was determined using H-NMR titration and ESI-MS spectrometry. The sensing mechanism is due to the inhibition of ESIPT and isomerization of -C=N of ODA on complexation with Al/Zn. The intramolecular hydrogen bonding energy and the critical bond energy in ODA-Al/Zn were calculated using QTAIM analysis. The Thin Layer Chromatography (TLC) plates and strip papers loaded with ODA were used to test the practical applications for sensing Al and Zn ions. Moreover, the probe has been used for live-cell imaging to detect Al and Zn ions in hepatoma C3A and human glioblastoma U87 cells.