Kristof Kimpe

Interaction of [Ln(DO2A)(H2O)2-3]+ and [Ln(DO2P)(H2O)2-3]- with phosphate, acetate and fluoride anions in aqueous solution

Abstract Mixed complexation of the lanthanide(III) chelates of the 1,7-disubstituted tetraazacyclododecane macrocycles DO2A and DO2P with phosphate, acetate and fluoride anions was studied in aqueous solutions using high resolution 1 H and 31 P NMR spectroscopy. The [La(DO2A)(H 2 O) 2−3 ] + and [Ce(DO2A)(H 2 O) 2−3 ] + chelates readily decompose in aqueous solutions containing phosphate anions. [Nd(DO2A)(H 2 O) 2−3 ] + and [Eu(DO2A)(H 2 O) 2−3 ] + chelates remain stable in an acetate environment. Association constants for the 1:1 adduct were obtained via 1 H NMR titrations. In a fluoride environment, [La(DO2A)(H 2 O) 2−3 ] + was found to be unstable, in contrast to [Eu(DO2A)(H 2 O) 2−3 ] + , for which the association constant for the 1:1 adduct was calculated. Chelate formation, as well as mixed complexation with fluoride and phosphate was studied for [Eu(DO2P)(H 2 O) 2−3 ] − . The 31 P chemical shifts of [Eu(DO2P)(H 2 O) 2−3 ] − indicate that the DO2P macrocycle forms an ‘in-cage’ complex with binding through all four nitrogens. The [Eu(DO2P)(H 2 O) 2−3 ] − chelate gradually decomposes in a phosphate environment, but remains stable in an fluoride environment.