Effects of Concentration of Some Lanthanide(III) Complexes of 1,7-Bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane on Bis(p-nitrophenyl)-phosphate Hydrolysis

Abstract

A detailed study of the effects of the concentration of some lanthanide(III) complexes [LnDO2A(+); DO2A = 1,7-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane] on the hydrolysis of the phosphodiester bond of the compound BNPP [sodium bis(4-nitrophenyl)phosphate] is reported at 25 degrees C and pH 7.90 (Ln = Eu), 9.35 (Ln = Eu), and 9.90 (Ln = Eu, Er and Yb). The reaction is found to be first order with respect to BNPP concentration at pH 7.90 and 9.35 and to increase to 1.78 +/- 0.09, 1.64 +/- 0.07, and 1.63 +/- 0.09 with respect to [EuDO2A(+)] concentration at pH 7.90, 9.35, and 9.90, respectively, thereby indicating that dinuclear species are involved in the reactions. Similar observations were found for the other two LnDO2A(+) complexes at pH 9.90 [1.63 +/- 0.11 (Er) and 1.49 +/- 0.09 (Yb)]. The k(obs) data obtained by the initial rate method could be fitted to a monomer-dimer reaction model for all LnDO2A(+) complexes at pH 7.90, 9.35, and 9.90 in the [LnDO2A(+)] concentration range 1.0-20.0 mM. The dinuclear species, namely the mono-hydroxo-bridged complexes [Ln(2)(DO2A)(2)(mu-OH)(OH)(H(2)O)(n=1-3)] and the di-hydroxo-bridged complexes [Ln(2)(DO2A)(2)(mu-OH)(OH)(H(2)O)(n=0.2)] are found to be more reactive, with reactivities in the order Eu > Yb > Er. The overall formation constants for [Ln(2)(DO2A)(2)(mu-OH)(OH)(H(2)O)(n)]-BNPP are around 10(4)M(-1). The EuDO2A(+)-promoted BNPP hydrolysis rates are similar to, or up to two orders of magnitude faster than, most of those reported for other lanthanide and transition-metal complexes. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)