Synthesis and spectroscopic characterization of zinc(II) and copper(II) complexes of N,N-bis(2-picolyl)glycine as structural phosphotriestrase models: The catalyzed detoxification of paraoxon

The reaction of the tetradentate ligand N,N-bis(2-picolyl)glycine, BPG-H, which was successfully synthesized in its free state, with the nitrate or perchlorate salts of both zinc(II) and copper(II) ions yielded the aqua complexes [BPG-Zn(H2O)2]X 1, 2 and [BPG-Cu(H2O)2]X 3, 4 (X = NO3- for 1 and 3 and X = ClO4- for 2 and 4). Two intermediate complex species, namely the bridged copper(II) hydroxo {[(BPG)Cu]2(μ-OH)2} 5 and zinc(II)-bound diethylphosphate ([BPG-Zn(OPO(C2H5)2] 6 were successfully isolated in good yields and pure forms. The ligand and its complexes were characterized by using elemental analyses, FT-IR, and thermal analyses as well as in solution by using conductometric, UV–visible, pH, and 1H NMR titrations. All complexes have basically similar coordination chromophor (N3O3) through the coordination of the ligand with both zinc(II) and copper(II) metal ions. The hydrolase biomimetic catalytic activity of complexes 1 and 3 were examined towards the toxic organophosphate, paraoxon (p-NPDEP). The results indicate that the obtained bell-shaped curves of pH-rate below pH 8.6 mirrors the ionization curves of the coordinated water molecules to give the hydroxoaqua complexes and provide strong evidence that these are the catalytically active species in the hydrolysis reactions.