Stability of Highly OH-Covered C₆₀ Fullerenes:  Role of Coadsorbed O Impurities and of the Charge State of the Cage in the Formation of Carbon-Opened Structures

Abstract

We have performed both semiempirical as well as ab initio density functional theory calculations in order to investigate the structural stability of highly hydroxylated C60(OH)32 fullerenes, so-called fullerenols. Interestingly, we have found that low-energy atomic configurations are obtained when the OH groups are covering the C60 in the form of small hydroxyl islands. The previous formation of OH molecular domains on the carbon surface, stabilized by hydrogen bonds between neighboring OH groups, defines the existence of C60(OH)32 fullerene structures with some elongated C-C bonds, closed electronic shells, and large highest occupied-lowest unoccupied molecular orbital energy gaps, with the latter two being well-known indicators of high chemical stability in these kind of carbon compounds. The calculated optical absorption spectra show that the location of the first single dipole-allowed excitation strongly depends on the precise distribution of the OH groups on the surface, a result that, combined with optical spectroscopy experiments, might provide an efficient way to identify the structure of these kinds of fullerene derivatives. We found that the presence of a few coadsorbed oxygen species on the fullerene surface leads in general to the existence of C60(OH)32O(x) (x = 1-4) compounds in which some of the C-C bonds just below the O impurities are replaced by C-O-C bridge bonds, leading to the formation of stable carbon-opened structures in agreement with the recent experimental work of Xing et al. (J. Phys. Chem. B 2004, 108, 11473). Actually, a more dramatic cage destruction is obtained when considering multiply charged C60(OH)32O(x)(+/-m) (m = 2, 4, 6) species (that can exist in both gas-phase and aqueous environments), where now sizable holes made of 9- and 10-membered rings can exist in the carbon network. We believe that our results are important if the controlled opening of carbon cages is needed and it should be taken into account also in several technological applications where the permanent encapsulation of atomic or molecular species in these types of fullerene derivatives is required.

Modifying the endohedral La-ion location in both neutral and positively charged polyhydroxylated metallofullerenes

“…3, ͑i͒ the La-ion changes its endohedral location but now when the q value increases and that, as already found in Ref. 23, ͑ii͒ the charging of the fullerene compound ͑up to q = +8͒ induces the rupture of various C-C bonds of the carbon network, leading to the formation of sizable holes in the C 60 cavity made of nine-membered rings ͓see Figs. 5͑c͒ and 5͑d͔͒.…”

Reactivity Indexes and Structure of Fullerenes

“…As our work group has studied fullerenes and their reactivity [7,16,[62][63][64][65] and it has been proposed that C 60 might be an ideal candidate for trapping nitrogen by a polymer [53,54], the intention now is to show that C 70 might also be an alternative way of storing polynitrogenous species, contributing to the development of new materials in the future.…”

Exploring the chemical bonding, infrared and UV–vis absorption spectra of OH radicals adsorption on the smallest fullerene

“…For example, Xu et al [15,16] studied the water-soluble derivatives C 60 (OH) x (x = 22,24), and found that the derivatives have the potential usage as an inhaled drug delivery, in which the hydroxyl radicals play key roles in asthma and chronic obstructive pulmonary diseases, the physical behavior of fullerenol products was observed to significantly differ from the parent materials [17]. In fact, there is a great challenge to find the global minima of the fullerenols, and the derivatives present a strong structural flexibility due to the rotation of the OH groups around the C-O bonds which are distributed differently on fullerene surface.…”

“…Using molecular dynamics simulations, Radic et al [21] found that the more hydrophilic nanoparticles with a higher number of hydroxyl groups bound to the surface of the protein via hydrogen bonds, which stabilize the protein structure. Additionally, some other polyhydroxylated derivatives, e.g., C 60 (OH) 32 [22], C 70 (OH) n (n = 14, 16, 18 and 20) [23], and C 82 (OH) n (n = 0-12) [24], have also been studied systematically.…”