Addition of sulfur radicals to fullerenes

The addition of oxygen‐centered radicals to fullerenes has been intensively studied due to their role in cell protection against against hydrogen peroxide induced oxidative damage. However, the analogous reaction of sulfur‐centered radicals has been largely overlooked. Herein, we investigate the addition of S‐centered radicals to C 50 , C 60 , C 70 , and C 100 fullerenes by means of DFT calculations. The radicals assayed were: S, SH, SCH 3 , SCH 2 CH 3 , SC 6 H 5 , SCH 2 C 6 H 5 , and the open‐disulfide SCH 2 CH 2 CH 2 CH 2 S. Sulfur, the most reactive species, prefers to be attached to a 66‐bond of C 60 with a binding energy ( E bind ) of 2.4 eV. For the SR radicals the electronic binding energies to C 60 are 0.77, 0.74, 0.58, 0.67, and 0.35 eV for SH, SCH 3 , SCH 2 CH 3 , SCH 2 C 6 H 5 , and SC 6 H 5 , respectively. The reactivity of C 60 toward SR radicals can be increased by lithium doping. For Li@C 60 , the E bind is increased by 0.65 eV with respect to C 60 , but only by 0.33 eV for the exohedral doping. Fullerenes act like free radical sponges. Indeed, the C 60 ‐SR E bind can be duplicated if two radicals are added in ortho or para positions. The enhanced reactivity because of multiple additions is mostly a local effect, although the addition of one radical makes the whole cage more reactive. Therefore, as observed for hydroxylated fullerenes, they should protect cells from oxidative damage. However, the thiolated fullerenes have one advantage, they can be easily attached to gold nanoparticles. For the addition on pentagon junctions smaller fullerenes like C 50 are more reactive than C 60 . Interestingly, C 70 is as reactive as C 60 , even for the addition on the equatorial belt. For larger fullerenes like C 100 , reactivity decreases for the carbon atoms belonging to hexagon junctions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010