Synthesis and complexation of Gd3+, Ca2+, Cu2+ and Zn2+ by 3,6,10-tri(carboxymethyl)-3,6,10-triazadodecanedioic acid

3,6,10-Tri(carboxymethyl)-3,6,10-triazadodecanedioic acid (H5L), was synthe sized and its protonation constants were determined by potentiometric titra tion in 0.10 mol dm(-3) Me4NNO3 and by NMR pH titration at 25.0 +/- 0.1 deg rees C. Stability and selectivity constants have been measured to evaluate the possibility of using the corresponding gadolinium(III) complex as a mag netic resonance imaging contrast agent. The formations of gadolinium(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitati vely by potentiometry. The stability constant for the gadolinium(III) compl ex is larger than those of Ca-II, Zn-II and Cu-II for this octadentate liga nd. The selectivity constants and modified selectivity constants of the lig and for Gd3+ over endogenously available metal ions were calculated. The sp in-lattice relaxivity R-1 for the gadolinium(III) complex was also determin ed. It was found to decrease with increasing pH below 4 and became invarian t with respect to pH over the range 4-10. Oxygen-17 NMR shifts showed that the [DyL](2-) complex had one inner-sphere water molecule. The water proton spin-lattice relaxation rate for the [GdL](2-) complex was also consistent with one inner-sphere co-ordination position.