Studies of Catalysis of Hydrolysis of Phosphate Esters by Zinc(II) Complexes

This paper seeks to contribute to the development of synthetic complexes that mimic the catalytic properties of hydrolysis of metalloenzymes. Metalloenzymes catalyze hydrolytic reactions of various functional groups such as amide bonds (nucleases) and phosphate esters (phosphatases). A large number of these enzymes contain one or more Zn (II) ions at their active centers. [2] In this work we have synthesized and studied the catalytic properties of some Zinc (II) complexes for the hydrolysis of phosphate esters. We studied complexes in order to determine the features of complexes that exhibit high efficiency of catalysis of hydrolysis of phosphate ester bonds. We report the rates of catalysis by these zinc complexes of chelating ligands with nitrogen donors in the hydrolysis of phosphate esters.;Zn(II) complexes of the ligands 1,3-Bis[(2-pyridylethyl)iminomethyl] benzene (1), 1,3-Bis(2-pyridyliminomethyl)m-xylene (2), and 1,3-Bis[(2-pyridylaminomethyl)m-xylene(3) were synthesized. The complexes were characterized by Infrared, UV-visible, H-NMR, and Atomic Absorption spectroscopic analysis. Their catalytic activities for the hydrolysis of bis(4-nitrophenyl)phosphate were studied. The complexes and the substrate were dissolved in a buffer solution of tris(hydroxymethyl)aminomethane (THAM) of a range of pH values (6 -- 10). The rates of hydrolysis were studied at various pH, temperatures and complex and substrate concentration ratios by monitoring the progress of the hydrolysis of the substrate bis(4-nitrophenyl)phosphate by measurement of the absorbance at 400 nm on a UV-visible spectrophotometer.;Complexes 1, 2, and 3 showed optimum rates of hydrolysis at pH 8.96, 8.98, and 8.67 respectively. Complexes 1 and 2 were studied under the same conditions at pH 7.4, 72°C, [complex]=3.5x10-4M, and [BNPP]=5.0x10 -3M. Under these conditions, the rate of reaction associated with complexes 1 and 2 are 4.5x10-8 (M/s) and 3.4x10-8 (M/s). The variation of the rates of hydrolysis by each complex as a function of pH showed that the catalytic species in the hydrolysis of the substrate is Zn2+-L-OH entity.