Structures of MRI contrast agents in solution

Contrast agents for magnetic resonance imaging are mainly Gd3+ complexes of octadentate polyaminopolycarboxylates and one water molecule in the first coordination sphere of the metal ion. Both the Ln(3+) ion and the nitrogen atoms in these complexes may be chiral. Therefore, various isomers may occur for these complexes, which interconvert in aqueous solution. Here studies on the configurations and conformations of Ln(3+) complexes of acyclic and cyclic ligands are reviewed. Furthermore, the structures of new generations of contrast agents that are able to target organs or to sense their biochemical environment are discussed. Molecular recognition is an important issue for these compounds.