Addition of sulfur radicals to fullerenes

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 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.

Thiophene adsorption on Single Wall Carbon Nanotubes and graphene

“…The methodology applied herein is the same as the one we applied to successfully study sulfur doped graphene [18], thiolated [19] and hydrogenated [20] graphene, thioepoxidated [21] and thiolated [22][23] SWCNTs, hydrogenated DWCNTs [24], the addition of azomethine ylides to carbon nanostructures [25] and the adsorption of CH 4 on SWCNTs [26]. Briefly, we performed Density Functional (DFT) calculations employing the VDW-DF [14] and LDA [15] functionals, as implemented in SIESTA [27,28], which performs SCF calculations using numerical basis sets.…”

“…We have checked the convergence of the Mesh cut-off; using a value of 200 Ry we obtained converged binding energies (within 0.02 eV). It is important to note that in our previous studies [18][19][20][21][22][23][24][25][26] we performed methodology calibration against mesh cut-off and orbital confining cut-off values. By doing so, we were able to reproduce the results obtained without the use of pseudopotentials.…”

On the applicability of cluster models to study the chemical reactivity of carbon nanotubes

“…The methodology used herein is the same as the one we applied to successfully study phosphorous 17 and sulfur 18 doped graphene, thiolated graphene, 14 nitrene functionalized graphene, 16 hydrogenated graphene, 15 thioepoxidated SWCNTs, 19 thiolated SWCNTs, 8,9 hydrogenated DWCNTs, 20 the addition of sulfur centered radicals to fullerenes, 21 the addition of azomethine ylides to carbon nanostructures, 22 the adsorption of CH 4 on SWCNTs, 23 and thiophene onto graphene and nanotubes. 24 Briefly, we performed density functional calculations using the UPBE functional 25 for all carbon nanostructures.…”

Modulation of the exfoliated graphene work function through cycloaddition of nitrile imines

“…41 One of these approaches involves the description of graphene as a two dimensional infinite superstructure by ab initio methods within periodic boundary conditions. 42,43 This approach is employed in order to determine the electronic properties of graphene and its derivatives and it allows the study of the organized monolayer adsorption of molecules on the surface. The description of graphene as a 'finite' structure is an approach that is widely used in the recent literature on graphene and it correctly describes the interaction with isolated molecules.…”