The oxidative dehydrogenation of a coumarinyl scaffold with copper ion and metal ion detection in human liver cancer cells (HepG2)

An unsymmetrical o-phenylenediamine derivative, L (7-hydroxy-4-methyl-8-(1-(phenyl- (pyridin-2-yl)methyl)-1H-benzo[d]imidazol-2-yl)-2H-chromen-2-one), has been synthesized from (E)-N-1-(phenyl(pyridine-2-yl)methylene)benzene-1,2-diamine with 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde and characterized by X-ray, IR, H-1 NMR and ESI-MS spectral analyses. The X-ray structure shows L as a cyclic benzimidazole derivative, but it undergoes ring-opening upon reaction with transition metal ions. L is non-emissive in 9:1 (v/v) EtOH/H2O (HEPES buffer, pH 7.4) but becomes highly fluorescent upon Zn2+ coordination, and the emissive Zn(ii) complex undergoes transmetallation in the presence of Cu2+ ions specifically, followed by amine to imine oxidation, i.e. an oxidative dehydrogenation (OD) reaction -(2e + 2H(+)) occurs. The transmetallation of Zn2+ from the complex by Cu2+ (CuCl2) separated the non-emissive X-ray diffractable crystal of [Cu(L")Cl] (L" = amine oxidized form of L). A square pyramidal [Cu(L")][ClO4] complex was also isolated from the reaction of L with Cu(CH3CN)(4)(ClO4) in the presence of air, and in this complex the amine is also oxidized to the imine. Here, copper ions in the presence of air play an important role in the OD reaction of L as determined by EPR and cyclic voltammetry studies. The ligand, L, is used for Zn2+ ion recovery from a municipally supplied water sample. A paper strip detection kit for Zn2+ and Cu2+ is designed using L. The ligand is also used for intracellular Zn2+ detection in a human liver cancer cell line (HepG2).