Rapid hydrolysis of phosphate monoesters by zirconium(IV) complexes in neutral solution

Abstract

Three zirconium(IV) complexes (1-3) with mono- and dinucleating tripodal ligands are reported that promote the hydrolysis of the phosphate monoesters p-nitrophenyl phosphate (NPP) and phenyl phosphate (PP) in neutral solution. At pH 7 up to 10(4)- and 10(6)-fold rate accelerations of the hydrolysis of NPP and PP are observed. A detailed kinetic study has been carried out for NPP. The complexes show Michaelis-Menten behavior, k(cat) and 1/K-m values at pH 7.0, 25 degrees C are 2.7 x 10(-5) s(-1) and 806 M-1 (1), 1.1 x 10(-4) s(-1) and 556 M-1 (2) and 1.1 x 10(-4) s(-1) and 565 M-1 (3). Entropies of activation of -92.0 J K-1 mol(-1) (1), -75.6 J K-1 mol(-1) (2) and -98.6 J K-1 mol(-1) (3) are consistent with an associative mechanism.