Design of conformationally rigid dimeric MRI agents

The conformational flexibility of the linkage mechanism or tether between paramagnetic metal centers is explored to assess optimal structural characteristics of multimeric MRI contrast agents. Two dimeric paramagnetic chelates differing in linkage flexibility but similar in symmetry are compared. Relaxivity, water hydration number, and reorientational times of the chelate groups are obtained, and the results demonstrate that greater linkage flexibility reduces overall relaxivity.