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 Zn2+ ion in presence of series of cations in CH3CN-H2O (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 Kapp = 13.25) are evaluated by the fluorescence emission experiment. The probe shows reversibility in addition of dihydrogen phosphate (H2PO4−) 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 ZnL2 (1) are innocuous against PBMC (peripheral blood mononuclear cells) but effective antitumor agents against U-937 cancer cells.