Lanthanoid Endohedral Metallofullerenols for MRI Contrast Agents

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Abstract
Water-soluble multi-hydroxyl lanthanoid (La, Ce, Gd, Dy, and Er) endohedral metallofullerenes (metallofullerenols, [email protected]82(OH)n) have been synthesized and characterized for the use of magnetic resonance imaging (MRI) contrast agents. The observed longitudinal and transverse relaxivities for water protons, r1 and r2, of the metallofullerenols are in the range 0.8−73 and 1.2−80 (sec-1mM-1), respectively, which are significantly higher than those of the corresponding lanthanoid-DTPA chelate complexes. Among these Gd-metallofullerenols, [email protected]82(OH)n has exhibited the highest r1 and r2 values in consistent with our previous results. The observed large r1 of the current metallofullerenols can mainly be ascribed to the dipole−dipole relaxation together with a substantial decrease of the overall molecular rotational motion. The large r2, except for the Gd-metallofullerenols, have been attributed to the so-called Curie spin relaxation. The MRI phantom studies are also performed and are consistent with these results. The metallofullerenols will be an ideal model for future MRI contrast agents with higher proton relaxivities.