Tuning ligand vicinity towards development of “turn-on” fluorescence for cadmium(II) ions under physiological pH and bio-imaging.

A supramolecular ligand for the specific detection of Cd 2+ ions, [pyridine-2,6-diylbis (methyleneimino-2,1-phenylene)]bis(phenyl methanone) ( L ) was synthesized, and characterized by various spectral techniques and single crystal X-ray crystallography. The L exhibits “turn-on” fluorescence and excellent selectivity towards Cd 2+ ions in acetonitrile/HEPES buffer medium (1:5 v/v). The lowest quantum yield and shorter emission lifetime of L (Φ = 0.0293, τ = 9.98 ns) was corroborated by the operation of PET process. This PET is quenched during the complex formation between L and Cd 2+ leads to high quantum yield and longer emission lifetime (Φ = 0.1770, τ = 13.46 ns). The L forms 1:1 complex with Cd 2+ is confirmed by Job’s plot and ESI-Mass techniques. The binding of L with Cd 2+ was studied by UV–vis and NMR. The reversible of L.Cd 2+ with EDTA establishes the reuse of L. The lower detection limit of L was found to be 10.21 nM. The impact of fluorescence with respect to pH, time, temperature and solvent concentrations was investigated to find its practical applications. The sensor was applied for the determination of Cd 2+ ions in water samples. DFT studies explain the binding mechanism between the L and Cd 2+ . The cell imaging studies established that L has been used to detect the intracellular Cd 2+ ions in HeLa cells. [ABSTRACT FROM AUTHOR]