Phosphodiester cleavage by yttrium(III) peroxide complexes

Potentiometric titrations of hydrogen peroxide in the presence of Y(III) revealed formation of dinuclear Y2(O2)2 2+ and Y2(O2)2(OH)2 complexes. Kinetics of the cleavage of bis(4-nitrophenyl) phosphate (BNPP) in the presence of Y(III) and H2O2 was studied at 25 °C in pH range 6–8 and at variable metal and H2O2 concentrations. Comparison of the pH-dependence of the reaction rate with the species distribution diagram shows that Y2(O2)2(OH)2 is the reactive species. The reaction kinetics is second-order in Y(III) at low metal concentration, but is of a ‘saturation’ type at high metal concentrations. A reaction mechanism, which agrees with such kinetics, involves intermediate reversible dimerization of Y2(O2)2(OH)2 to a tetranuclear complex capable to bind BNPP anion and to cleave it intramolecularly.