Radical-Specific Kinetics of Hydroxylated Fullerenes and Endohedral Metallofullerenols: Distinct Reactivity toward Alkylperoxyl and Hydroperoxyl Radicals

Endohedral metallofullerenols represent a unique class of carbon nanomaterials in which encapsulated metal species modify the electronic properties of the fullerene cage while preserving the hydroxylated surface required for aqueous compatibility. Here, the radical reactivity of the hydroxylated fullerene C 70 (OH) 12 , and three endohedral metallofullerenols, Sc 3 N@C 80 (OH) 18 , Lu 3 N@C 80 (OH) 18 , and Gd@C 82 (OH) 22 , was quantitatively evaluated using inhibited autoxidation kinetics. Oxygen uptake measurements were used to determine second-order inhibition rate constants ( k inh ) for reactions with alkylperoxyl radicals (ROO • ) generated during cumene and tetrahydrofuran oxidation and hydroperoxyl radicals (HOO • ) generated during 1,4-cyclohexadiene oxidation. The investigated endohedral metallofullerenols exhibited higher apparent inhibition rate constants than C 70 (OH) 12 . In the cumene/chlorobenzene system, k inh increased from 61 M -1 s -1 for C 70 (OH) 12 to 520 M -1 s -1 for Sc 3 N@C 80 (OH) 18 . During oxidation of aqueous THF the k inh enhancement was substantially larger, reaching 5.1 × 10 5 M -1 s -1 for Gd@C 82 (OH) 22 compared to 1.0 × 10 4 M -1 s -1 for C 70 (OH) 12 . In peroxidation mediated by HOO • a distinct kinetic behavior was observed, indicating that fullerene-based antioxidants cannot be characterized by a single intrinsic activity parameter. These findings establish radical-specific kinetic analysis as an essential approach for understanding structure–reactivity relationships in metallofullerene-based carbon nanomaterials.