Pristine C60 Research Articles

Molecular dynamics and structural phase transition in C60 nanowhiskers

Nanowhiskers of C60 (C60 NWs) have been formed by a liquid-liquid interfacial precipitation method which uses an interface of the concentrated toluene solution of C60/2-propanol. In order to study the motion of C60 molecules in nanowhiskers, we have performed measurements of low-temperature X-ray diffraction, magnetic susceptibility, specific heat and 13C-NMR for C60 NWs. The temperature dependence of lattice constant for C60 NWs is in good agreement with that for pristine C60 powder, which demonstrates the large discontinuity at Tc ∼ 265 K caused by the structural phase transition. However, the temperature dependence of magnetic susceptibility for C60 NWs exhibits a faint anomaly at Tc. The temperature dependence of specific heat for C60 NWs shows two small anomalies at 232 K and 254 K. High resolution 13C-NMR measurements of the C60 NWs indicate that both of toluene and 2-propanol molecules interact with the C60 NW molecules in the suspension and the precipitate states obtained from the LLIP method. The broader linewidth of 13C-NMR in the dried C60 NWs compared with that in the pristine C60 powder indicates that the slower molecular reorientation in the dried C60 NWs compared with that in the pristine C60 powder. Since a rapid rotation of C60 molecules could be directly detected by 13C-NMR, polymer formation between C60 molecules is unlikely in C60 NWs at room temperature.

Conversion of single-crystallineC60 nanodisks and nanorods into graphitic nanostructures via hydrogen thermal annealing

We have developed a process to convertC60 nanostructures into graphitic nanostructures. Disk-shaped and wire-shapedC60 nanostructures synthesized by the liquid–liquid interfacial precipitationmethod, the vapor–solid process, and solvent evaporation were successfullyconverted into graphitic structures by thermal annealing in hydrogen at900 °C. Scanning electron and tunneling electron microscopic studies confirmed that the convertednanostructures were composed of multi-graphitic structures such as multi-walled carbonnanotubes, carbon nanofibers, and carbon onions. Fourier transform Raman spectroscopyand conductance measurements were carried out to further confirm the successful formationof graphitic layers. In the Raman spectra, the nanostructures converted fromC60 disks showed signature D,G, and G′ bands of graphiticstructures, while the Ag mode (1469 cm−1) of theoriginal C60 moleculedisappeared. C60 nanowire devices fabricated for the conductance measurements ofthe converted structures showed dramatically decreased resistance(R≈100 kΩ) comparedto the pristine C60 wire (R>100 MΩ). Further manipulation of the reaction environment, including the gas and the annealingtemperature, may reveal a new way to attain diverse graphitic nanostructures economically.

Structure and properties of fullerite C60 intercalated with CH2F2

AbstractWe have obtained fullerite intercalated with CH2F2 by precipitation of C60 from the solution in 1,2‐dichlorobenzene saturated by CH2F2. The chemical composition was identified as (CH2F2)x C60 (x = 1.03 ± 0.21). The fcc lattice parameter (14.28 Å) was found to increase significantly for (CH2F2)C60 in comparison with that for pristine C60 (14.16 Å). The IR absorption peak attributed to the stretching vibration of the C–F bond in (CH2F2)C60 was 30 cm–1 shifted to lower wave numbers in comparison with the gas phase CH2F2 spectrum. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modest vasomotor dysfunction induced by low doses of C60 fullerenes in apolipoprotein E knockout mice with different degree of atherosclerosis

BackgroundExposure to small size particulate matter in urban air is regarded as a risk factor for cardiovascular effects, whereas there is little information about the impact on the cardiovascular system by exposure to pure carbonaceous materials in the nano-size range. C60 fullerenes are nano-sized particles that are expected to have a widespread use, including cosmetics and medicines.MethodsWe investigated the association between intraperitoneal injection of pristine C60 fullerenes and vasomotor dysfunction in the aorta of 11–13 and 40–42 weeks old apolipoprotein E knockout mice (apoE-/-) with different degree of atherosclerosis.ResultsThe aged apoE-/-mice had lower endothelium-dependent vasorelaxation elicited by acetylcholine in aorta segments mounted in myographs and the phenylephrine-dependent vasoconstriction response was increased. One hour after an intraperitoneal injection of 0.05 or 0.5 mg/kg of C60 fullerenes, the young apoE-/- mice had slightly reduced maximal endothelium-dependent vasorelaxation. A similar tendency was observed in the old apoE-/- mice. Hampered endothelium-independent vasorelaxation was also observed as slightly increased EC50 of sodium nitroprusside-induced vasorelaxation response in young apoE-/- mice.ConclusionTreatment with C60 fullerenes affected mainly the response to vasorelaxation in young apoE-/- mice, whereas the vasomotor dysfunction in old apoE-/- mice with more advanced atherosclerosis was less affected by acute C60 fullerene treatment. These findings represent an important step in the hazard characterization of C60 fullerenes by showing that intraperitoneal administration is associated with a moderate decrease in the vascular function of mice with atherosclerosis.

Metal-to-insulator transition in thin-film polymeric AC60

We present an electron spectroscopy study of phase-pure AC60 thin films (A= Rb, Cs) in their monomer (face-centred cubic (fcc)) and polymer phases. A surface electronic reconstruction is observed in polymeric RbC60, analogous to that reported for the fcc phase. As for pristine C60, the occupied electronic states of AC60 fullerides are not dramatically affected by polymerization. The energy separation between the leading feature in photoemission and inverse photoemission is similar in both stable AC60 phases. These observations suggest that electron correlation effects are similar in the two phases, and that their different electronic behaviour is mainly related to the reduction of degeneracy of the polymer frontier states. Photoemission and electron-energy loss spectroscopy data show that the thin-film form of the RbC60 polymer is metallic at room temperature, and that it undergoes a metal–insulator transition at around 100 K. This transition temperature is much higher than that reported for the corresponding bulk phase and signals a poorer screening of Coulomb interactions at the film surface.

Water-soluble nanorods self-assembled via pristine C60 and porphyrin moieties

A novel water-soluble nanorod is discussed, which is prepared via the self-assembly of pristine C60 and a double-sided porphyrin projecting four beta-cyclodextrins from each face.

Antimicrobial Activity of Fullerenes and Their Hydroxylated Derivatives

The antimicrobial activities of fullerene C60 and its derivatives against 6 kinds of bacteria and 2 kinds of fungi were evaluated. The tested samples were water-soluble fullerenes (polyvinylpyrrolidone (PVP)/C60, gamma-cyclodextrin (gamma-CD)/C60, and nano-C60) and 3 types of fullerenols (C60(OH)12, C60(OH)36.8H2O, and C60(OH)44.8H2O). Their activities were compared with those of (+)-catechin and hinokitiol from the viewpoint of future application to cosmetics. Although pristine C60 demonstrated no antimicrobial activity, fullerenols exhibited good antimicrobial activity against Propionibacterium acnes, Staphylococcus epidermidis, Candida albicans, and Malassezia furfur. In particular, C60(OH)44 exhibited a strong and wide-ranging antimicrobial activity comparable to that of catechin. This compound exhibits antimicrobial activity via inhibition of microbial cell growth and not via bactericidal activity.

A comparative study of ion-induced damages in C60 and C70 fullerenes

The stability of fullerenes (C60 and C70) under swift heavy ion irradiation is investigated. C60 and C70 thin films were irradiated with 120 MeV Ag ions at fluences from 1×1012 to 3×1013 ions/cm2. The damage cross-section and radius of damaged cylindrical zone were found to be higher for C60 than C70 as evaluated by Raman spectroscopy, which shows that the C70 molecule is more stable under energetic ion impact. The higher damage cross-section of the C60 molecule compared with that of the C70 molecule is explained on the basis of thermal conductivity in the framework of the thermal spike model. The surface morphology of pristine C60 and C70 films is studied by atomic force microscopy. UV-visible absorption studies revealed that band gap for C60 and C70 fullerenes thin films decreases with increasing ion fluence. Resistivity of C60 and C70 thin films decreases with increasing ion fluence but the decrease is faster for C60 than C70, indicating higher damage in C60. Irradiation at a fluence of 3×1013 ions/cm2 results in complete damage of fullerenes (C60 and C70) into amorphous carbon.

Time dependence of the electronic structure of an electron-beam-irradiated C60 film

Time dependence of the electronic structure of an electron-beam (EB) irradiated C60 film (20–30 nm thick) has been examined using in situ high-resolution ultraviolet photoelectron spectroscopy. It is found that the electronic states of the C60 film have been changed continuously from an insulator (pristine C60 films) to a semiconductor and finally to a metal as EB-irradiation time increased. This can be explained by the increase in polymerization degree of a C60 polymer with a given cross-linked structure derived from the general Stone–Wales rearrangement from [Beu et al.,Phys. Rev. B 72, 155416 (2005)]. In addition, this finding suggests that the electronic properties of the C60 film can be controlled only in the EB-irradiated region by varying the irradiation time, which is interesting when applied to electronic devices.

Oxidatively Damaged DNA in Rats Exposed by Oral Gavage to C 60 Fullerenes and Single-Walled Carbon Nanotubes

BackgroundC60 fullerenes and single-walled carbon nanotubes (SWCNT) are projected to be used in medicine and consumer products with potential human exposure. The hazardous effects of these particles are expected to involve oxidative stress with generation of oxidatively damaged DNA that might be the initiating event in the development of cancer.ObjectiveIn this study we investigated the effect of a single oral administration of C60 fullerenes and SWCNT.MethodsWe measured the level of oxidative damage to DNA as the premutagenic 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) in the colon mucosa, liver, and lung of rats after intragastric administration of pristine C60 fullerenes or SWCNT (0.064 or 0.64 mg/kg body weight) suspended in saline solution or corn oil. We investigated the regulation of DNA repair systems toward 8-oxodG in liver and lung tissue.ResultsBoth doses of SWCNT increased the levels of 8-oxodG in liver and lung. Administration of C60 fullerenes increased the hepatic level of 8-oxodG, whereas only the high dose generated 8-oxodG in the lung. We detected no effects on 8-oxodG in colon mucosa. Suspension of particles in saline solution or corn oil yielded a similar extent of genotoxicity, whereas corn oil per se generated more genotoxicity than the particles. Although there was increased mRNA expression of 8-oxoguanine DNA glycosylase in the liver of C60 fullerene-treated rats, we found no significant increase in repair activity.ConclusionsOral exposure to low doses of C60 fullerenes and SWCNT is associated with elevated levels of 8-oxodG in the liver and lung, which is likely to be caused by a direct genotoxic ability rather than an inhibition of the DNA repair system.

Fullerene C60–Silver Nanoparticles Hybrid Structures: Optical and Photoelectric Characterization

A detailed optical and photoelectric characterization of pristine fullerene C60 films deposited onto n-silicon substrates (C60/Si), C60 films crosslinked by means of the solvent-free chemical functionalization with 1,8-diaminooctane (C60-DA/Si), and the pristine and crosslinked films decorated with silver nanoparticles (C60-Ag/Si and C60-DA-Ag/Si), was carried out. The reflectance spectra obtained allowed to calculate the absorption coefficient (alpha = 4pik/lamda) spectral dependencies and the spectra of light transmittance in layered barrier structures metal(Au)/fullerene/Si. Photoelectric properties of the films were investigated as well. The experimentally measured values of band gap were in a good agreement with mobility gap values (2.3 +/- 0.1 eV). The decoration of fullerene films (both pristine and chemically crosslinked) with silver nanoparticles did not change the photocurrent spectra as compared to those for undecorated fullerene films, but lowered the values of internal quantum efficiency Qint. The photocurrent generated in fullerene/Si heterostructure, showed a maximum value at lamda to appromimately 450 nm (Qint max approximately = 0.25 for decorated and undecorated C60-DA/Si films), and it was higher for the samples based on pristine C60 films, in accordance with their higher absorption coefficient. Diminishing of Qint for C60-DA/Si and C60-DA-Ag/Si films was observed for the spectral range of photocurrent generated in Si layer. The analysis of dark current-voltage characteristics showed that the barrier properties differ insignificantly, though a certain increase of series resistance was observed for the C60-DA/Si samples.

Orientational Ordering and Intermolecular Interactions in the Rotor-Stator Compounds C60·C8H8 and C70·C8H8 Studied under Pressure

Pressure-dependent transmittance measurements on C60·C8H8 and C70·C8H8 at room temperature were performed for pressures up to 10 GPa in the mid- and near-infrared frequency range, in order to monitor the vibrational modes of the fullerene and cubane molecules as a function of external pressure. Furthermore, the position of the absorption edge related to intramolecular electronic excitations on the fullerene molecules was studied with increasing pressure. For C60·C8H8, the anomaly at 0.5 GPa in the pressure dependence of the vibrational modes indicates a pressure-induced orientational ordering transition of the fullerene molecules and the anomaly at 1.3 GPa can be related to fullerene−cubane interaction. In C70·C8H8, the pressure-induced changes are more pronounced, with a splitting of the cubane modes at the pressures 0.8 and 1.75 GPa. This finding indicates stronger intermolecular interactions in C70·C8H8 compared to C60·C8H8, leading to larger distortions of cubane molecules. The energy position of the absorption edge in C60·C8H8 and C70·C8H8 shows a nonlinear decrease with increasing pressure. The zero-pressure value of the absorption edge in C60·C8H8 is larger than that of pristine C60 indicating that the cubane molecules reduce the overlap of the C60 molecular orbitals. In C70·C8H8, no shift of the optical absorption edge relative to C70 is found, in agreement with this compound being closer to a host−guest system than C60·C8H8.

Uniformly dimerized C60 film prepared by deposition under in situ photoirradiation

C60 films with thicknesses of 100–480 nm were deposited on Si reed substrates under in situ photoirradiation. In anelasticity measurements, no internal friction peaks associated with rotational motions of the C60 molecules were observed, and Young’s modulus was 1.5 times larger than that of a pristine C60 material. X-ray diffraction patterns suggested that the face-centered cubic lattice was contracted by about 3% and locally distorted from the pristine C60 material. Raman spectra very similar to those reported for dimerized C60 were also obtained. These characteristics recovered to those of the pristine C60 materials after annealing the C60 films at 523 K. These results indicate uniform dimerization in C60 films deposited under in situ photoirradiation.

Photo-and pressure-induced transformations in the linear orthorhombic polymer of C60

Stability of the linear orthorhombic polymer of C60 under pressure and laser irradiation is studied by Raman scattering and X-ray diffraction measurements. The Raman spectrum at ambient pressure remains unchanged, in the time scale of the experiment, up to an intensity of 3200 W/cm2 of the 514.5 nm line of an Ar+ laser, but irreversible changes are observed at higher intensities. The Raman spectra recorded at increased pressure show similar irreversible changes even at the laser intensity as low as 470 W/cm2. The X-ray diffraction and Raman measurements of the pressure-treated samples, performed after pressure release, show that the nonirradiated material does not exhibit any changes in the crystal structure and phonon spectra. This behavior indicates a pressure-enhanced photo-induced transformation to a new polymeric phase characterized by a Raman spectrum that differs from those of the other known polymeric phases of C60. The Raman spectra of the phototransformed linear orthorhombic polymer of C60 were measured at a pressure of up to 29 GPa. The pressure dependence of the Raman mode frequencies show singularities near 4 GPa and 15 GPa, respectively, related to a reversible phase transition and an irreversible transformation to a metastable disordered phase. The diffuse Raman spectrum of the disordered phase does not exhibit substantial changes with an increase in pressure up to 29 GPa. The high-pressure phase transforms to a mixture of pristine and dimerized C60, after pressure release and exposure to ambient conditions for 30 h.

Synthesis and Surface Self-Assembly of [3]Rotaxane−Porphyrin Conjugates: Toward the Development of a Supramolecular Surface Tweezer for C60

Surface immobilization of pristine C60 by supramolecular interactions is an attractive way to introduce C60 on surfaces since the pi-electron network and the electronic properties of C60 remain intact. Several hosts have been developed for surface complexation of C60. With few exceptions, the hosts reported to date are "electronically inert", limiting the potential applications of pristine C60-based devices. In this study, we present the synthesis and self-assembly of a potential tweezer-like host for C60 having a light-harvesting moiety and an electron-donating unit. More precisely, an azide-containing [3]rotaxane scaffold having ferrocene moieties as blocking group and thioctic acid as anchoring group for a gold surface has been synthesized. This [3]rotaxane has been self-assembled on gold in its protonated (NH2+) (1p) and neutral (NH) (1n) forms and characterized using electrochemistry, XPS, and contact angle measurements. The SAMs were functionalized with free-base and zinc porphyrin using copper-catalyzed 1,3-dipolar cycloaddition in optimized conditions. In combination with C60, this new host is expected to form a triad that could potentially be used as active building block in the preparation of nanostructured electrodes for photoelectrochemical application.

C60/PVP complex — No Toxicity after Introperitoneal Injection to Rats

The absence of acute toxicity of pristine fullerene C60 (3.5–8.9 mg/kg) after intraperitoneal injection of water soluble C60/PVP complex to rats was shown.

Effects of C60fullerene nanoparticles on soil bacteria and protozoans

Nanotechnology should produce numerous new materials in the coming years. Because of the novel design of nanomaterials with new physicochemical characteristics, their potential adverse impact on the environment and human health must be addressed. In the present study, agglomerates of pristine C60 fullerenes (50 nm to microm-size) were applied to soil at 0, 5, 25, and 50 mg/kg dry soil to assess their effect on the soil microbiota by measuring total respiration; biomass, number, and diversity of bacteria; and total number and diversity of protozoans during 14 d. Respiration and microbial biomass were unaffected by the fullerenes at any time, whereas the number of fast-growing bacteria was decreased by three- to fourfold just after incorporation of the nanomaterial. Protozoans seemed not to be very sensitive to C60, because their number decreased only slightly in the beginning of the experiment. With polymerase chain reaction and denaturing gradient gel electrophoresis analysis of eubacteria and kinetoplastids from the soil, however, a difference between the fullerene treatments and nonamended controls was demonstrated. The fullerenes did not induce more than 20 to 30% of relative dissimilarity (with both bacteria and protozoans) between treatments, but this effect was persistent throughout the experiment. It therefore is recommended that fullerene nanomaterial not be spread deliberately in the environment and that their ecotoxicology be further clarified.

How We Can Change the Biological Effects of Pristine C60

not Available.

Pristine (C60) and Hydroxylated [C60(OH)24] Fullerene Phototoxicity towards HaCaT Keratinocytes: Type I vs Type II Mechanisms

The increasing use of fullerene nanomaterials has prompted widespread concern over their biological effects. Herein, we have studied the phototoxicity of gamma-cyclodextrin bicapped pristine C 60 [(gamma-CyD) 2/C 60] and its water-soluble derivative C 60(OH) 24 toward human keratinocytes. Our results demonstrated that irradiation of (gamma-CyD) 2/C 60 or C 60(OH) 24 in D 2O generated singlet oxygen with quantum yields of 0.76 and 0.08, respectively. Irradiation (>400 nm) of C 60(OH) 24 generated superoxide as detected by the EPR spin trapping technique; superoxide generation was enhanced by addition of the electron donor nicotinamide adenine dinucleotide (reduced) (NADH). During the irradiation of (gamma-CyD) 2/C 60, superoxide was generated only in the presence of NADH. Cell viability measurements demonstrated that (gamma-CyD) 2/C 60 was about 60 times more phototoxic to human keratinocytes than C 60(OH) 24. UVA irradiation of human keratinocytes in the presence of (gamma-CyD) 2/C 60 resulted in a significant rise in intracellular protein-derived peroxides, suggesting a type II mechanism for phototoxicity. UVA irradiation of human keratinocytes in the presence of C 60(OH) 24 produced diffuse intracellular fluorescence when the hydrogen peroxide probe Peroxyfluor-1 was present, suggesting a type I mechanism. Our results clearly show that the phototoxicity induced by (gamma-CyD) 2/C 60 is mainly mediated by singlet oxygen with a minor contribution from superoxide, while C 60(OH) 24 phototoxicity is mainly due to superoxide.

Ab Initio Study of SO2 Molecules Interacting with Pristine and Transition Metal Covered Fullerenes as a Possible Route for Nanofilters

In this work, a systematic study of SO2 molecules interacting with pristine and transition metal (TM) covered C60 is presented by means of first principles calculations. It is observed that the SO2 molecule interacts weakly with the pristine C60 fullerene, although the resulting interaction is largely increased when the C60 structure is covered with Fe, Mn, or Ti atoms and the SO2 molecules are bounded through the TM atoms. The number of bounded SO2 molecules per TM atoms, in addition to the elevated binding energies per molecules, allows us to conclude that such composites can be used as a template for efficient devices to remove SO2 molecules or, alternatively, as SO2 gas sensor.