Hydrolysis of 8-quinolyl phosphate monoester: kinetic and theoretical studies of the effect of lanthanide ions.

8-Quinolyl phosphate (8QP) in the presence of the trivalent lanthanide ions (Ln = La, Sm, Eu, Tb, and Er) forms a [Ln x 8QP]+ complex where the lanthanide ion catalyzes hydrolysis of 8QP. In reactions with Tb3+ or Er3+, there is evidence of limited intervention by a second lanthanide ion. Rate constants are increased by more than 10(7)-fold, and kinetic data and B3LYP/ECP calculations indicate that the effects are largely driven by leaving group and metaphosphate ion stabilization. The lanthanides favor a single-step D(N)A(N) mechanism with a dissociative transition state, with limited nucleophilic assistance, consistent with the low hydroxide ion dependence and the small kinetic effect of Ln3+ radii.