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

[摘要]：Kinetics and thermodn. of lanthanide complexation with 8-quinolinyl phosphate ROPO32- (8QP, R = 8-quinolinyl), and lanthanide-catalyzed hydrolysis of 8QP, yielding 8-quinolinol, were explored by kinetic measurements, potentiometric titrn., attenuated total reflectance IR (ATR-FTIR) spectra and B3LYP/ECP calcns. 8-Quinolyl phosphate (8QP) in the presence of the trivalent lanthanide ions (Ln = La, Sm, Eu, Tb, and Er) forms a [Ln?QP]+ complex, in which lanthanide ion is coordinated to the phosphate oxygens and heterocyclic nitrogen. The complexes [Ln?QP]+ undergo smooth hydrolysis with liberation of inorg. phosphate. In reactions with Tb3+ or Er3+, there is evidence of limited intervention by a second lanthanide ion. Rate consts. are increased by more than 107-fold, and kinetic data and B3LYP/ECP calcns. indicate that the effects are largely driven by leaving group and metaphosphate ion stabilization. The lanthanides favor a single-step DNAN 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.

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