Study on the Stability of Polyazamacrocycle-Eu (Tb) by Potentiometry and Catalytic Hydrolysis on Phosphate Diester of BDBPH-Tb Complexes

The stability constants and species distributions of complexes of two lanthanide ions, Eu(III) and Tb(III), with a macrocyclic ligand, BDBPH in 1:1 and 2:1 systems, were determined potentiometrically in 50% ethanol solution, at 35.0 °C and I = 0.100 mol/L (KCl). The two metal ions could form de-protonated mono- or di- nuclear complexes with BDBPH with high stability. At higher pH values, Eu(III) could not form hydroxo complexes with BDBPH, while Tb(III) could form hydroxo complexes in the type of M2L(OH), M2L(OH)2, and M2L(OH)3. The kinetic study on the hydrolysis reaction of bis (4-nitrophenyl) phosphate (BNPP) catalyzed by Tb-BDBPH system (2:1) was carried out in 50% ethanol solution (pH 7.0-10.0) at 35°C with I = 0.1000 mol/L (KCl). The second-order rate constant, kBNPP (2.3×10−3 mol−1·L·S−1) was determined. The dinuclear monohydroxo species, L-2Tb-OH, is kinetically active species. The hydrolysis rate of BNPP by the complex is increased almost 2.6×106- fold compared with the background hydroxide rate at the same condition. The results obtained will provide some information for the further research on the nucleic acid cleavage.