Synthesis, Characterization and Computational Investigation of the Phosphatase Activity of a Dinuclear Zinc(II) Complex Containing a New Heptadentate Asymmetric Ligand

We report the synthesis of a new asymmetric heptadentate ligand based on the 1,3-diaminopropan-2-ol backbone. The ligand 3-[[3-(bis-pyridin-2-ylmethyl-amino)-2-hydroxy-propyl]-(2-carbamoyl-ethyl)-amino]-propionamide (HL1) contains two amide and two pyridine groups attached to the 1,3-diaminopropan-2-ol core. Reaction between HL1 and Zn(ClO).6HO resulted in the formation of the dinuclear [Zn(L1)(μ-OAc)](ClO) complex, characterized by single crystal X-ray diffraction, H, C and N NMR, ESI-(+)-MS, CHN elemental analysis as well as infrared spectroscopy. The phosphatase activity of the complex was studied in the pH range 6-11 employing pyridinium bis(2,4-dinitrophenyl)phosphate (py(BDNPP)) as substrate. The complex exhibited activity dependent on the pH, presenting an asymmetric bell shape profile with the highest activity at pH 9; at high pH ligand exchange is rate-limiting. The hydrolysis of BDNPP at pH 9 displayed behavior characteristic of Michaelis-Menten kinetics, with k = 5.06 × 10 min and K = 5.7 ± 1.0 mM. DFT calculations map out plausible reaction pathways and identify a terminal, Zn(II)-bound hydroxide as likely nucleophile.