Addition of sulfur radicals to fullerenes

Authors

  • Pablo A. Denis,

    Corresponding author
    1. Computational Nanotechnology, DETEMA, Facultad de Química, UDELAR, CC 1157, 11800 Montevideo, Uruguay
    2. Centro Interdisciplinario en Nanotecnología y Química Física de Materiales, Espacios Intersiciplinarios, UDELAR
    • Computational Nanotechnology, DETEMA, Facultad de Química, UDELAR, CC 1157, 11800 Montevideo, Uruguay
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  • Federico Iribarne

    1. Laboratorio de Bioinformática y Farmacología Molecular, DETEMA, Facultad de Química, UDELAR, CC 1157, 11800 Montevideo-Uruguay
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Abstract

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 C50, C60, C70, and C100 fullerenes by means of DFT calculations. The radicals assayed were: S, SH, SCH3, SCH2CH3, SC6H5, SCH2C6H5, and the open-disulfide SCH2CH2CH2CH2S. Sulfur, the most reactive species, prefers to be attached to a 66-bond of C60 with a binding energy (Ebind) of 2.4 eV. For the SR radicals the electronic binding energies to C60 are 0.77, 0.74, 0.58, 0.67, and 0.35 eV for SH, SCH3, SCH2CH3, SCH2C6H5, and SC6H5, respectively. The reactivity of C60 toward SR radicals can be increased by lithium doping. For Li@C60, the Ebind is increased by 0.65 eV with respect to C60, but only by 0.33 eV for the exohedral doping. Fullerenes act like free radical sponges. Indeed, the C60-SR Ebind 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 C50 are more reactive than C60. Interestingly, C70 is as reactive as C60, even for the addition on the equatorial belt. For larger fullerenes like C100, reactivity decreases for the carbon atoms belonging to hexagon junctions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

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