Fullerene oxides and ozonides

Laboratory IR Spectra of the Ionic Oxidized Fullerenes C60O+ and C60OH. J Phys Chem A 2022;126:2928-2935. [PMID: 35533303 PMCID: PMC9125688 DOI: 10.1021/acs.jpca.2c01329]

We present the first experimental vibrational spectra of gaseous oxidized derivatives of C₆₀ in protonated and radical cation forms, obtained through infrared multiple-photon dissociation spectroscopy using the FELIX free-electron laser. Neutral C₆₀O has two nearly iso-energetic isomers: the epoxide isomer in which the O atom bridges a CC bond that connects two six-membered rings and the annulene isomer in which the O atom inserts into a CC bond connecting a five- and a six-membered ring. To determine the isomer formed for C₆₀O⁺ in our experiment—a question that cannot be confidently answered on the basis of the DFT-computed stabilities alone—we compare our experimental IR spectra to vibrational spectra predicted by DFT calculations. We conclude that the annulene-like isomer is formed in our experiment. For C₆₀OH⁺, a strong OH stretch vibration observed in the 3 μm range of the spectrum immediately reveals its structure as C₆₀ with a hydroxyl group attached, which is further confirmed by the spectrum in the 400–1600 cm^–1 range. We compare the experimental spectra of C₆₀O⁺ and C₆₀OH⁺ to the astronomical IR emission spectrum of a fullerene-rich planetary nebula and discuss their astrophysical relevance.

Understanding phase-transfer catalytic synthesis of fullerenol and its interference from carbon dioxide and ozone

Phase-transfer catalytic reaction involving the use of tetrabutylammonium hydroxide (TBAH) as catalyst and sodium hydroxide (NaOH) solution as the source of hydroxide ions is among the popular choices for synthesis of fullerenol, the polyhydroxylated fullerene. To further understand the process, two experiments were conducted to preliminarily explore the influences of the amount of TBAH and NaOH, respectively, in terms of the achieved level of hydroxylation (i.e. number of hydroxyl groups per fullerenol molecule). The process responded to the variation of the amount of TBAH (over a twofold series of 3–192 drops, average volume 0.0223 ± 0.0004 ml per drop) in a nonlinear manner with a local maximum achieved from 24 drops TBAH (giving 13 OH groups) and a local minimum from 48 drops (giving 8 groups). To the variation of the amount of NaOH (over the range of 0.5–8.0 ml NaOH), the fitted function of the process response resembled Freundlich adsorption isotherm, with an initially increasing trend before levelling off at 4.0 ml NaOH (giving 15 OH groups). It is therefore suggested that fullerene hydroxylation could be explained by liquid–solid adsorption. In addition, it was found that ambient carbon dioxide led to the existence of sodium carbonate in the bulk of the collected product (although not chemically bound). It was also discovered that ambient ozone adversely affected fullerenol synthesis by converting C60 fullerene into fullerene epoxide (C60O). The affected syntheses thus produced epoxide-containing fullerenol instead.

The mechanism of the ozonolysis on the surface of C70 fullerene: the electron localizability indicator study

The formation of C₇₀O from C₇₀O₃ monomolozonide is a three-step process with the isomer dependent last step leading either to c,c-C₇₀O epoxide or d,d-C₇₀O oxidoannulene. The process involves the open intermediate (first O-O then C_c-C_c/C_d-C_d bonds broken), oxidoannulene-like structure intermediate (new C_c-O/C_d-O bond formed) and finally the oxide product. On the formation of c,c-C₇₀O isomer, the final release of O₂ is followed by the restoration of C_c-C_c bond, which stabilizes the product. Neither C_d-C_d bond is restored nor the total energy essentially lowered upon d,d-C₇₀O formation. At all steps of the studied process, the four CC bonds adjacent to C_c-C_c or C_d-C_d bond, respectively, play a crucial role donating or withdrawing the necessary electron density. C₇₀(O)O₂ products, with O₂ bridging one of the bonds adjacent to the parent C_c-C_c/C_d-C_d one, may compete with the oxide products. The OO bond in such structures is weak as suggested by its low electron population. For both c,c-C₇₀O₃ and d,d-C₇₀O₃, the shape of the potential energy surfaces (0 K) and the related, reported earlier, room temperature-free energy surfaces differ. Graphical abstract.

Direct observation of C60− nano-ion gas phase ozonation via ion mobility-mass spectrometry

Atmospheric pressure differential mobility analysis-mass spectrometry facilitates determination of nano-ion-neutral reaction rates approaching the collision controlled limit.

Spectromicroscopy of C60 and azafullerene C59N: Identifying surface adsorbed water

C60 fullerene crystals may serve as important catalysts for interstellar organic chemistry. To explore this possibility, the electronic structures of free-standing powders of C60 and (C59N)2 azafullerenes are characterized using X-ray microscopy with near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, closely coupled with density functional theory (DFT) calculations. This is supported with X-ray photoelectron spectroscopy (XPS) measurements and associated core-level shift DFT calculations. We compare the oxygen 1s spectra from oxygen impurities in C60 and C59N, and calculate a range of possible oxidized and hydroxylated structures and associated formation barriers. These results allow us to propose a model for the oxygen present in these samples, notably the importance of water surface adsorption and possible ice formation. Water adsorption on C60 crystal surfaces may prove important for astrobiological studies of interstellar amino acid formation.

A theoretical study of the ozonolysis of C60: primary ozonide formation, dissociation, and multiple ozone additions

We present an investigation of the reaction of ozone with C60 fullerene using electronic structure methods. Motivated by recent experiments of ozone exposure to a C60 film, we have characterized stationary points in the potential energy surface for the reactions of O3 with C60 that include both the formation of primary ozonide and subsequent dissociation reactions of this intermediate that lead to C-C bond cleavage. We have also investigated the addition of multiple O3 molecules to the C60 cage to explore potential reaction pathways under the high ozone flux conditions used in recent experiments. The lowest-energy product of the reaction of a single ozone molecule with C60 that results in C-C bond breakage corresponds to an open-cage C60O3 structure that contains ester and ketone moieties at the seam. This open-cage product is of much lower energy than the C60O + O2 products identified in prior work, and it is consistent with IR experimental spectra. Subsequent reaction of the open-cage C60O3 product with a second ozone molecule opens a low-energy reaction pathway that results in cage degradation via the loss of a CO2 molecule. Our calculations also reveal that, while full ozonation of all bonds between hexagons in C60 is unlikely even under high ozone concentration, the addition of a few ozone molecules to the C60 cage is favorable at room temperature.

Polarizability as a landmark property for fullerene chemistry and materials science

The review summarizes data on dipole polarizability of fullerenes and their derivatives, covering the most widespread classes of fullerene-containing molecules (fullerenes, fullerene exohedral derivatives, fullerene dimers, endofullerenes, fullerene ions, and derivatives with ionic bonds).

Formation and reinforcement of clusters composed of C60 molecules

We carry out two experiments: (1) the formation of clusters composed of C60 molecules via self-assembly and (2) the reinforcement of the clusters. Firstly, clusters such as fibres and helices composed of C60 molecules are produced via self-assembly in supercritical carbon dioxide. However, C60 molecules are so weakly bonded to each other in the clusters that the clusters are broken by the irradiation of electron beams during scanning electron microscope observation. Secondly, UV photons are irradiated inside a chamber in which air is filled at 1 atm and the above clusters are placed, and it was found that the clusters are reinforced; that is, they are not broken by electron beams any more. C60 molecules located at the surface of the clusters are oxidised, i.e. C60On molecules, where n = 1, 2, 3 and 4, are produced according to time-of-flight mass spectroscopy. It is supposed that oxidised C60 molecules at the surface of the clusters may have an important role for the reinforcement, but the actual mechanism of the reinforcement of the clusters has not yet been clearly understood and therefore is an open question.

Strategies for quantifying C(60) fullerenes in environmental and biological samples and implications for studies in environmental health and ecotoxicology

Fullerenes are sphere-like molecules with unique physico-chemical properties, which render them of particular interest in biomedical research, consumer products and industrial applications. Human and environmental exposure to fullerenes is not a new phenomenon, due to a long history of hydrocarbon-combustion sources, and will only increase in the future, as incorporation of fullerenes into consumer products becomes more widespread for use as anti-aging, anti-bacterial or anti-apoptotic agents.An essential step in the determination of biological effects of fullerenes (and their surface-functionalized derivatives) is establishment of exposure-assessment techniques. However, in ecotoxicological studies, quantification of fullerenes is performed infrequently because robust, uniformly applicable analytical approaches have yet to be identified, due to the wide variety of sample types. Moreover, the unique physico-chemistry of fullerenes in aqueous matrices requires reassessment of conventional analytical approaches, especially in more complex biological matrices (e.g., urine, blood, plasma, milk, and tissue).Here, we present a review of current analytical approaches for the quantification of fullerenes and propose a consensus approach for determination of these nanomaterials in a variety of environmental and biological matrices.

C(70) oxides and ozonides and the mechanism of ozonolysis on the fullerene surface. A theoretical study

A series of ab initio calculations have been carried out to determine why the a,b- and c,c-isomers are the most commonly observed mono-oxides of C(70) in ozonolysis reactions, when existing calculations in the literature report that these structures are not the most stable conformations. We show that the a,b- and c,c-isomers are the two most stable structures on the C(70)O(3) potential energy surface, which suggests that the reaction pathway toward oxide formation must proceed via the corresponding ozonide structure. From our calculations, we offer a mechanism for the thermally induced dissociation of C(70)O(3) that share the first two steps with the general mechanism for ozonolysis of alkenes proposed by Criegee. We suggest further steps that involve C(70)O(3) losing O(2) in its triplet or singlet state, thus leaving C(70)O in its triplet or singlet state, respectively. A pair of products in their singlet states seems to be more likely for the decomposition of a,b-C(70)O(3), which ultimately leads to the closed a,b-C(70)O epoxide structure. For c,c-C(70)O(3), the more thermodynamically favorable route is the triplet channel, resulting in the triplet open c,c-C(70)O oxidoannulene structure, which may subsequently decay to the singlet ground state c,c-C(70)O epoxide form. This finding offers an alternative interpretation of the experimental observations which reported an open d,d-C(70)O oxidoannulene structure as the metastable intermediate.