Abstract

A zwitterionic compound (L) as a specific detector for aluminum ion in methanol/HEPES buffer (5mM, pH 7.2; 1:5v/v) by fluorescence “turn on” was synthesized by the condensation of propargylated 2,4-dihydroxybenzophenone with ethanolamine. The compound L was characterized by various spectral methods and also crystalographically. L was found to be in equilibrium with the deprotonated form with a pKa value of 8.63. During photophysical process, L exhibits weak fluorescence with low quantum yield (Φ=0.069) at 440nm due to the quick conversion of excited keto-form into the excited enol-form by transfer of a proton (ESIPT). The interaction of L with Al3+ inhibits the ESIPT process and the emission enhanced band (20 fold) appears at shorter wavelength (427nm) with increased quantum yield (Φ=0.217). The binding of L with Al3+ and stoichiometry (1:1) has been established by UV–vis, NMR, emission and ESI–MS spectral methods L.Al3+ is reversible with EDTA and can be reused. The effect of pH, time, temperature and solvent concentrations on fluorescence intensity were studied. Fascinatingly, the fluorescence microscopic studies established that L could be used as an efficient probe for detection of intracellular Al3+ ions in HeLa cells without any toxicity.

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