A coumarin based visual and fluorometric probe for selective detection of Al(III), Cr(III) and Fe(III) ions through turn-on response and its biological application

A Schiff base (L) containing coumarin and pyrene moieties was synthesized and characterized. It showed excellent selective recognition of M(III) ions (M = Al, Cr and Fe) in presence of monovalent, divalent and other trivalent metal ions. Sensor L itself is non-fluorescent upon excitation with 353 nm light (lambda ex = 353) but a very large enhancement in fluorescence intensity was observed during the addition of these three trivalent metal ions into a CH3OH/aqueous HEPES buffer (5 mM, pH = 7.4, 6:4, v/v) solution of L. This prominent OFF-ON fluorescence switching can be observed with naked eye, in which OFF is due to operation of PET process in free L but PET is inhibited upon complexation thereby allowing CHEF (chelation enhanced fluorescence) process to operate. Detection limits of Al3+, Cr3+ and Fe3+ using L have been found to be 0.79 nM, 1.15 mu M, and 1.28 mu M respectively in the pH range of 6-10. Additionally, OFF-ON fluorescence can be reversed by sequestering M(III) ions using [EDTA]4- solutions. Analysis of mass spectra and Job's plot revealed a binding ratio of 1:1 for all three metal ions with L. The imine nitrogen and carbonyl oxygen atoms of L are involved in binding with Al3+, Cr3+ and Fe3+ ions, as revealed by NMR titration and IR spectroscopic analysis. Results of quantum yield (phi), time resolved photoluminescence (TRPL) and computational studies (DFT/TDDFT) studies were also reported. Fluorescence intensity of these M(III) bound L complexes is quenched by fluoride ions. From cytotoxicity analysis, 7.5 mu M of probe L was selected to analyze its fluorescence attributes in cellular imaging. Using human breast cancer cell line (MDA-MB-231) and primary human dermal fibroblasts (HDF), the potentiality of the probe L was confirmed through fluorescence cell imaging experiments.

Automated summary

A Schiff base sensor containing coumarin and pyrene moieties was synthesized and characterized for selective recognition of M(III) ions. The sensor exhibited a significant fluorescence enhancement upon the addition of trivalent metal ions, with potential applications demonstrated in cellular imaging experiments. The study also included analyses of binding mechanisms, fluorescence quenching by fluoride ions, and cytotoxicity assessment.