Polyaminocarboxylate ligands, effect

Polyaminocarboxylate ligands, effect on water exchange, trivalent lanthides, 42 60-61... 

D. B. Rorabacher, W. J. MacKellar, F. R. Shu, and S. M. Bonavita, Anal. Chem., 43, 561 (1971). Solvent effects on protonation constants, NH4OH, acetate, polyamine, and polyaminocarboxylate ligands in CH3OH—HjO mixtures. 

Gd + complexes with macrocyclic and acyclic polyaminocarboxylic acid ligands 78-80, 8 are typical MRI contrast agents (Caravan et al., 1999). Although they effectively encapsulate the Gd + cation and form stable complexes in water (log K = 16-25), their metal centers have free coordination sites for water molecules and their unpaired electrons reduce the relaxation times Ti and T2 (fig. 29) (Rulofif et al., 1998 Aukmst et al., 2001 Dubost et al., 1991 Kumar et al., 1994). The exchange processes of the coordinated water molecules (inner-sphere water) and hydrogen-bonded water molecules (2nd-sphere water) with bulk water molecules have a significant influence on the reduction of the relaxation times (fig. 30). Therefore, the structural and electronic factors of the Gd + complex should be controlled to attain dynamic water exchange. 

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