Gd3N@C84(OH)x: a new egg-shaped metallofullerene magnetic resonance imaging contrast agent.

Water-soluble derivatives of gadolinium-containing metallofullerenes have been considered to be excellent candidates for new magnetic resonance imaging (MRI) contrast agents because of their high relaxivity and characteristic encapsulation of the lanthanide ions (Gd3+), preventing their release into the bioenvironment. The trimetallic nitride template endohedral metallofullerenes (TNT EMFs) have further advantages of high stability, high relative yield, and encapsulation of three Gd3+ ions per molecule as illustrated by the previously reported nearly spherical, Gd3N@Ih-C80. In this study, we report the preparation and functionalization of a lower-symmetry EMF, Gd3N@Cs-C84, with a pentalene (fused pentagons) motif and an egg-shaped structure. The Gd3N@C84 derivative exhibits a higher 1H MR relaxivity compared to that of the Gd3N@C80 derivative synthesized the same way, at low (0.47 T), medium (1.4 T), and high (9.4 T) magnetic fields. The Gd3N@Cs-C84 derivative exhibits a higher hydroxyl content and aggreg...