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

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 (H-5ccdp) 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 degrees C and 37 degrees C and different pH (7-10) conditions. The kinetic studies revealed that the turnover rate (k(cat)) values among the PNPP hydrolysis systems, the highest and the lowest k(cat) values were displayed by [Cu-2(ccdp)(mu-OAc)](2-) at 2.34 x 10(-6) s(-1) (pH 8 and 37 degrees C) and 2.13 x 10(-8) s(-1) (pH 8 and 25 degrees C), respectively. However, similar comparisons among the BNPP hydrolysis revealed that highest and the lowest kcat values were displayed by [Zn-2(ccdp)(mu-OAc)](2-) at 4.64 x 10(-8) s(-1) (pH 9 and 37 degrees C) and 2.38 x 10(-9) (pH 9 and 25 degrees 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.

Automated summary

This study describes the synthesis, characterization, and catalytic activities of two homodinuclear Cu(II) and Zn(II) complexes of a carboxylate-rich ligand towards hydrolysis of substrates in aqueous systems. Kinetic investigations show different turnover rates for the complexes under various conditions.