A novel biphenolic ligand for selective Mg2+ and Zn2+ ions sensing followed by colorimetric, spectroscopic and cell imaging methods

The (E)-2-((2-hydrohy-5-methylphenylimino) methyl) phenol ligand was synthesized. The receptor was characterized by IR, H-1 and C-13 NMR and CHN analysis. The ligand exhibits colorimetric and fluorometric sensing of Zn2+ and Mg2+ ions in semi-aqueous medium (DMSO-H2O). The receptor was tested with series of transition metal ions (Cr2+, Fe2+, Ni2+, Co2+, Cu2+, Zn2+) and heavy metal ions (Sn2+, Pd2+, Ce2+, Hg2+, Cd2+) and the essential human body elements like Ca2+, Mg2+, Na+ and K+ ions. The naked eye colorimetric sensing was absorbed only for Zn2+ and Mg2+. Both ions (ZnCl2 and MgCl2 in H2O), when added to the colorless solutions of the receptor of about 1 equivalence in incremental additions turn the solution into bright turmeric yellow. All other ions remain inactive, in colorimetric sensing. Further the Zn2+ and Mg2+ ions were probed by absorption and emission spectroscopy through incremental addition of respective metal ions. The in-situ deprotonation of the ligand on both Mg2+ and Zn2+ ions binding was confirmed by H-1 NMR titration studies. The imino nitrogen of the receptor is not coordinated to the metal ions. The Job's plot studies reveal the 1:2 binding ratio of metal ions to the receptor. The high fold fluorescence output on metal ions binding was positively used to sense the Zn2+ and Mg2+ ions, separately and together in HeLa cancer cells through cell imaging.