SOLUTION KINETIC-BEHAVIOR OF LANTHANIDE(III) POLYAMINOCARBOXYLATES FROM O-17 NMR-STUDIES

We review O-17 NMR studies of water exchange kinetics on the lanthanid e(III) ions and their complexes with a series of polyaminocarboxylate ligands. The complexes show a wide range of water exchange rates. Vari able pressure measurements yield the activation volume for the water e xchange process, and allow these variations to be rationalised in term s of reaction mechanism and the accessibility of transition states of different coordination number. The results have special significance f or the use of gadolinium complexes as contrast agents in medical magne tic resonance imaging, since the slow water exchange observed on these complexes will in some cases limit their proton relaxivity.