Homodinuclear copper(II) and zinc(II) complexes of a carboxylate-rich ligand as synthetic mimics of phosphoester hydrolase in aqueous solutions

Abstract

The synthesis, characterization and catalytic activities of two homodinuclear Cu(II) and Zn(II) complexes of a carboxylate-rich ligand, N,N′-Bis[2-carboxybenzomethyl]-N,N′ -Bis[carboxymethyl]-1,3-diaminopropan-2-ol (H5ccdp) ligand towards the hydrolysis of (p-nitrophenyl phosphate) (PNPP) and bis(p-nitrophenyl) phosphate (BNPP) substrates in aqueous systems are described. Kinetic investigations were carried out using UV–Vis spectrophotometric techniques at 25 °C and 37 °C and different pH (7–10) conditions. The kinetic studies revealed that the turnover rate (kcat) values among the PNPP hydrolysis systems, the highest and the lowest kcat values were displayed by [Cu2(ccdp)(μ-OAc)]2− at 2.34 × 10−6 s−1 (pH 8 and 37 °C) and 2.13 × 10−8 s−1 (pH 8 and 25 °C), respectively. However, similar comparisons among the BNPP hydrolysis revealed that highest and the lowest kcat values were displayed by [Zn2(ccdp)(μ-OAc)]2− at 4.64 × 10−8 s−1 (pH 9 and 37 °C) and 2.38 × 10−9 (pH 9 and 25 °C). Significantly enough, the catalyst−substrate adduct species containing a metal bound PNPP and BNPP have been detected by ESI-MS techniques. Additionally, a PNPP-bound copper complex has been isolated and crystalized using single crystal X-ray diffraction technique. Based on the structural and activity information obtained in this study, reaction mechanisms for the hydrolysis of PNPP have been proposed.