STABILITY-CONSTANTS AND H-1 RELAXATION EFFECTS OF TERNARY COMPLEXES FORMED BETWEEN GD-DTPA, GD-DTPA-BMA, GD-DOTA, AND GD-EDTA AND CITRATE, PHOSPHATE, AND CARBONATE IONS

Formation of ternary complexes between Gd-DTPA, Gd-DTPA-BMA, and Gd-DO TA, used as contrast enhancement agents in MRI and the endogenously av ailable carbonate and phosphate ions, has been demonstrated. The exten t of ternary complex formation and its effect on the proton relaxation , measured at 9 MHz, rates is negligible at around pH < 8. The complex Gd-EDTA forms more stable ternary complexes with carbonate and phosph ate and it also strongly coordinates the terdentate citrate ligand, Th e formation of ternary complexes Gd-EDTA(X) (X = CO32-, Cit(3-)) resul ts in a significant decrease in the proton relaxation rates under phys iological conditions.