Picoline Based Fluorescence ‘Turn-On’ Chemosensor for Zinc(II) Ion Recognition, Cell Imaging and Cytotoxicity Study: Synthesis, Crystal Structure, Spectroscopy and DFT

Abstract

A new picoline based ligand, namely 2-hydroxy-5-methyl-3-[{(6-methylpyridin-2-yl)imino}methyl]benzaldehyde ( L ) and it’s zinc(II) complex, Zn(L) 2 ( 1 ) have been synthesized and structurally characterized. The ligand ( L ) selectively interacts with Zn 2+ ion in presence of series of cations in CH 3 CN-H 2 O (v/v 1:1) in 1 mM HEPES buffer (pH 7.2). The fluorescence intensity of L is significantly enhanced, and it is increased to 52 times on coordination with Zn(II) ion. The fluorescence intensity value of the L does not show any significant change in the pH range 5 to 9, while the extent of emission phenomenon with Zn(II) ions is observed in the said pH range. The detection limit (0.36 µM) and association constant (log K app = 13.25) are evaluated by the fluorescence emission experiment. The probe shows reversibility in addition of dihydrogen phosphate (H 2 PO 4 – ) ion to the 1 . Additionally, the ‘turn-on’ fluorescence probe has sufficient cell permeability and intracellular Zn(II) sensing property as envisaged from the microscopic imaging in HEK293T cells. Both L and ZnL 2 ( 1) are innocuous against PBMC (peripheral blood mononuclear cells) but effective antitumor agents against U-937 cancer cells.