Organophosphonate Functionalized Gd@C₈₂ as a Magnetic Resonance Imaging Contrast Agent

A new magnetic resonance imaging contrast agent containing organophosphonate functional groups was synthesized in high yield by a simple synthesis procedure. This molecule exhibits much higher longitudinal water proton relaxivity (37.0 mM −1 s −1 ) than commercial Omniscan (Gd-DTPA BMA, 5.7 mM −1 s −1 ) at 0.35 T. Notably, the relaxivity is larger than that of carboxylated Gd@C 82 (16.0 mM −1 s −1 ) under the same conditions, indicating that the functional groups have an important role on the image contrast enhancement. In addition, the introduction of phosphonate substituents may provide bone-targeting MRI contrast agents.