A new macrocycle, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methyleneethylphosphinate) (DOTEP), has been synthesized, and its protonation constants and metal ion binding properties have been examined. The first two chelate protonations occur at nitrogens (log K1 and log K2: 10.94 and 8.24, respectively) while the pendant phosphinate groups are protonated only below pH 4. DOTEP forms less stable complexes with the alkaline-earth-metal cations, Cu2+, Zn2+, and Cd2+, and the trivalent lanthanides (Ln3+) than does the tetraacetate analogue, DOTA, largely due to the lower basicity of the nitrogen and oxygen donor atoms of DOTEP. Like DOTA, DOTEP forms complexes with the trivalent lanthanide ions rather slowly in the pH range 6-7 but, once formed, the Ln(DOTEP)- complexes release free Ln3+ slowly in strong acid.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry