STABILITY ASSESSMENT OF GADOLINIUM COMPLEXES BY P-31 AND H-1 RELAXOMETRY

Longitudinal P-31 relaxation rate enhancements of phosphate groups hav e been measured at pH 7-7.2 and 310-degrees-K on aqueous solutions con taining adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (P(i)) and some lanthanide complexes (Gd-DOTA, Gd-HPDO3A, G d-DO3A, Gd-DTPA, Gd-DTPA-BMA). The macrocyclic complexes induce linear enhancements of the relaxation rates of all phosphorus nuclei. For Gd -DOTA and Gd-HPD03A, the mechanism of the interaction with the P-31 nu clei seems to be of the outer sphere type and a better efficiency is n oted for the ''neutral'' Gd-HPD03A. A short-lived ternary complex betw een Gd-DO3A and the phosphorylated metabolites appears to be formed en abling an inner sphere interaction. In solutions containing the open c hain complexes, Gd-DTPA and Gd-DTPA-BMA, P-31 relaxation rates of ATP exhibit significant and nonlinear enhancements that are much larger th an those observed for PCr and P(i). A ternary complex involving the la nthanide ion, its original chelator, and the ATP molecule is precluded by various experiments which confirm that the lanthanide ion shifts f rom the original complexes to the ATP phosphate groups.