The effect of hemiketals on the relaxivity of endohedral gadofullerenols

Abstract

Gadofullerenols have received much attention due to their high relaxivities and low-toxicity as magnetic resonance imaging (MRI) contrast agents. However, the relaxivities of gadofullerenols vary in different reports. In this study, Gd@C₈₂(OH)_xO_y with different hemiketal content were synthesized and the influence of this factor on water proton relaxation was investigated. The results show that Gd@C₈₂(OH)_xO_y with more hemiketals exhibit much higher relaxivities than those with fewer hemiketals. The hemiketal structure is supposed to promote the formation of intermolecular hydrogen bonds, and finally lead to large aggregates. This is consistent with a previous report that the relaxivities of endohedral gadofullerene derivatives are strongly associated with the aggregate size. Hence, this work provides an important strategy for the manipulation of the relaxivities of gadofullerene based MRI contrast agents by controlling the quantity of hemiketals on the carbon cage.