Pristine C60 Research Articles

On the Thermal Stability of [60]Fullerene Cycloadducts: Retro-Cycloaddition Reaction of 2-Pyrazolino[4,5:1,2][60]fullerenes

2-Pyrazolino[4,5:1,2][60]fullerenes undergo a thermally induced retro-cycloaddition process whose efficiency is influenced by the nature of the C-substituent. C-Aryl-N-Aryl-2-pyrazolino[60]fullerenes (2a-d) poorly undergo a thermal retro-cycloaddition reaction even in the presence of a strong dipolarophile or a metal Lewis acid which, in contrast to other fullerene derivatives, shows their remarkable thermal stability. C-Alkyl-N-Aryl-2-pyrazolino[60]fullerenes (2e-f) show a different behavior, being more vulnerable to the presence of copper triflate and leading to the retro-cycloaddition product (pristine C60) in good yield.

Femtosecond carrier dynamics in electron-beam-irradiated C60 film

Time-resolved temperature-dependent transmission changes were measured for both pristine C60 and electron-beam-irradiated C60 polymer films using an optical pump-probe technique. Only the signals obtained for the C60 polymer show a temperature-dependent slow decay, which appears in the low temperature region below ∼60K. This slow decay component exhibits a monotonic increase in both relaxation time and amplitude with decreasing temperature, providing evidence of gap formation associated with ordering fluctuations.

Low-temperature optical studies of C60-cubane rotor-stator compound

We present here low-temperature Raman and photoluminescence spectra of the C60-cubane rotor-stator compound. We show the continuous evolution of Raman spectra between 77 K and room temperature, with no sharp transition visible at 140 K, the orientational ordering temperature. Low-temperature luminescence spectra of C60 in C60-cubane compound are found to be shifted and better resolved then spectra for pristine C60 at the corresponding temperatures, showing relatively weaker intermolecular interactions. In fact, the solid-state luminescence of C60-cubane is similar to free-molecule C60 luminescence spectra.

Synthesis of Buckminsterfullerene C60 functionalised core cross-linked star polymers

Buckminsterfullerene C60 core functionalised core cross-linked star (CCS) polymers have been prepared for the first time, using atom transfer radical polymerisation and the arms-first approach. A simple and efficient method is presented which allows the construction of star polymers consisting of a large number of arms and multiple units of C60 per core, far in excess of that obtained previously. The C60 CCS polymers were characterised by gel permeation chromatography (GPC), UV–vis spectroscopy and cyclic voltammetry (CV). GPC revealed that the C60 CCS polymers possess weight average molecular weights (Mw) ranging from 172–411kDa and up to 30 arms per macromolecule. The average number of molecules of C60 per CCS polymer core was found to be dependent on the C60/PMMA ratio employed and was determined by UV–vis spectroscopy to range up to 6.2. CV revealed that, like pristine C60, the C60 CCS polymers possessed three reversible one electron reductions. However, the reduction potentials were positively shifted, implying that the electron affinity of these macromolecules is higher than pristine C60.

Photodynamic properties of supramolecular assembly constructed by magnesium complex of hypocrellin A and fullerene C60

A supramolecular assembly, composed of magnesium complex of hypocrellin A (Mg2+–HA) and pristine C60 with a molar ratio of 2 : 1, is constructed and characterized. The supramolecular assembly (Mg2+–HA/C60) shows moderate solubility in polar solvents and strong absorption in visible region. EPR studies demonstrate that one-electron transfer from N,N-diethylaniline (DEA) to excited-state Mg2+–HA induces the generation of the reduced form of Mg2+–HA (Mg2+–HA−˙ radical), followed by electron transfer from the Mg2+–HA−˙ radical to C60, forming the corresponding anion radical C60−˙ under anaerobic conditions. In aerobic media, the generation of reactive oxygen species, including superoxide anion radical (O2−˙) and singlet oxygen (1O2), by Mg2+–HA/C60 photosensitization is observed. Mg2+–HA/C60 exhibits much stronger photodamage ability on pBR322 plasma DNA than Mg2+–HA and HA under both aerobic and anaerobic conditions.

Unilamellar composite vesicles and Y-junctions from pristine fullerene C60

We report here the first structurally defined aqueous phase nanovesicles and Y-junctions from a pristine C(60) dispersion at a strictly defined [C(60)]/[TX-100] concentration ratio, bearing a temporal dependence.

Cytotoxic and radiosensitizing effects of nano-C60 on tumor cells in vitro

There is growing evidence in recent years that the pristine fullerene may be endowed with strong pro-oxidant capacity to biological samples. In this investigation we tested the hypothesis that water-soluble fullerene-C60 (nano-C60) may interact with ionizing radiation enhancing its antiproliferative effects. The two tumor cell lines with different radiosensitivity B16 and SMMU-7721 were treated by a combination of pristine fullerene and 60Co γ irradiation. We measured cell survival rates, apoptotic characteristics, reactive oxygen species (ROS) production and alteration of cell diameter with or without γ-irradiation. There was reduced survival with B16 and SMMU-7721 cells exposed to nano-C60, with the inhibitory concentrations reducing the viability by 50% to 65 part per billion (ppb) and 150 ppb respectively. For cells exposed to nano-C60 prior to γ-irradiation, damage to cell membranes and increased numbers of apoptotic cells were detected by morphologic Hoechst-staining analysis and Annexin V/propidium iodide double-staining. In cells exposed to nano-C60, there were increased levels of ROS, as measured by fluorescence detection under laser confocal microscopy. Preincubation with non-toxic pristine C60 before γ-ray caused enlargement of cells with increased diameter. The results show that nano-C60 inhibits the growth of tumor cells at certain concentrations and increases the effects of 60Co γ-irradiation, possibly through the elevated production of cellular ROS and the membrane disruption. Data in this study indicates a possible consideration of using C60 as a candidate of sensitization modifier in tumor radiation biology.

Cross-Linking of C<SUB>60</SUB> Films with 1,8-Diaminooctane and Further Decoration with Silver Nanoparticles

We applied the direct solvent-free functionalization of fullerene C60 with aliphatic bifunctional amine, 1,8-diaminooctane, to prepare chemically cross-linked C60 thin films capable of binding silver nanoparticles. The gas-phase diamine treatment of C60 reduced dramatically the fullerene solubility in toluene, indicating the transformation of pristine C60 into a different solid phase with cross-linked fullerene molecules. Compared to the spectra of pristine C60 film and powder samples, Fourier-transform infrared, UV-Visible, Raman, and 13C nucleic magnetic resonance spectra of the functionalization products exhibited new features, which point to a breaking of C60 ideal structure during the formation of new covalent bonds and to the appearance of sp3 hibridization. The covalent functionalization with 1,8-diaminooctane allowed for a stable and homogeneous deposition of silver nanoparticles of ca. 5-nm diameter onto the functionalized films through the coordination bonding between metal atoms and nitrogen donor atoms of the fullerene derivatives. The proposed mechanism of Ag nanoparticle binding was supported by density functional theory calculations using the hybrid BLYP functional in conjunction with the double numerical basis set DND.

Thermal Stability of Deuterated C60 Films

The thermal stability and electronic structure of deuterated C60 films were studied by temperature-resolved mass spectroscopy and ultraviolet photoionization/photoelectron spectroscopy, UPS. The films were prepared by exposing C60 layers predeposited onto HOPG to a flux of thermal energy atomic deuterium. The initial stage of on-top deuteration at room temperature is associated with the formation of a capping layer that exhibits a higher thermal stability than pristine C60 films. The sublimation heat of the capping layer increases with the deuterium dose applied and levels off at a value of 2.15 ± 0.05 eV/cage at deuterium exposures in the range of 1016 D/cm-2. Capping layers appear to kinetically hinder further deuteration of subsurface C60. This hindrance can be reduced by performing the initial (and subsequent) deuteration at elevated sample temperatures. Further deuterium exposure leads to the formation of higher deuterofullerenes (e.g., C60D36). These exhibit sublimation enthalpies of 1.39 ± 0.1 eV/cage, considerably lower than the capping layers but comparable to pristine C60 films. Capping layers are air-resistant and amenable to the fabrication of stable multilayered [C60/C60Dx]m structures.

Olive Oil as a Biocompatible Solvent for Pristine C60

Olive oil is suggested a new solvent for C60 which offers the possibility to deliver in a biocompatible from this compound to biosystems and living organisms. This allows investigating for the first time the true biocompatibility and toxicity of C60.

Electronic Spectra of the Crystalline Polymers of C60: Photoluminescence Study at High Pressure

Specific details of the electronic spectra of perfect crystalline polymers of C60 were studied by means of the photoluminescence spectra measurements at normal conditions and at high pressure up to 4 GPa. The structure of the photoluminescence spectra, the intensity distribution between the principal bands and the pressure-induced shift of the bands differ considerably among the pristine C60, linear orthorhombic and planar tetragonal and rhombohedral polymeric phases of C60. Unlike the planar polymers of C60, the linear orthorhombic polymer exhibits irreversible changes in the photoluminescence spectrum under simultaneous application of high pressure and laser irradiation. The changes observed in the photoluminescence spectra of the planar polymeric phases of C60, as compared to the pristine material, are discussed in relation to the corresponding changes in the calculated electronic structure of the pristine C60 and its polymeric phases. The observed photoluminescence spectral structure along with the pressure behavior of the photoluminescence spectra are very sensitive to the structure of the polymers as well as to the C60 cage deformations and can be used to effectively characterize the various polymeric phases of C60.

Structure and Dynamics in Self-Organized C60 Fullerenes

This manuscript on 'structure and dynamics in self-organized C60 fullerenes' has three sections dealing with: (A) pristine C60 aggregate structure and geometry in solvents of varying dielectric constant. Here, using positronium (Ps) as a fundamental probe which maps changes in the local electron density of the microenvironment, the onset concentration for stable C60 aggregate formation and its phase behavior is deduced from the specific interactions of the Ps atom with the surrounding. (B) A novel methanofullerene dyad, based on a hydrophobic (acceptor C60 moiety)-hydrophilic (bridge with benzene and ester functionalities)-hydrophobic (donor didodecyloxybenzene) network is chosen for investigation of characteristic self-assembly it undergoes leading to supramolecular aggregates. The pi-electronic amphiphile, necessitating a critical dielectric constant epsilon > or = 30 in binary THF-water mixtures, dictated the formation of bilayer vesicles as precursors for spherical fractal aggregates upon complete dyad extraction into a more polar water phase. (C) While the molecular orientation is dependent on the packing density, the ordering of the molecular arrangement, indispensable for self-assembly depends on the balance between the structures demanded by inter-molecular and molecule-substrate interactions. The molecular orientation in a monolayer affects the orientation in a multilayer, formed on the monolayer, suggesting the possibility of the latter to act as a template for controlling the structure of the three dimensionally grown self-assembled molecular aggregation. A systematic study on the electronic structure and orientation associated with C60 functionalized aminothiol self-assembled monolayers on Au(111) surface is presented using surface sensitive Ultra-Violet Photoelectron Spectroscopy (UPS) and C-K edge Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The results revealed drastic modifications to d-band structure of Au(111) and the electronic structure was found sensitive towards the S-Au interface and the C60 end functional moiety with formation of localized sigma-(S-Au) and sigma(N-C) bonds, respectively. Upon binding C60 to the amine-terminated alkanethiol SAM, a drastically reduced HOMO-LUMO gap of 2.7 eV as compared to a large electronic gap of approximately 8 eV in alkanethiols enables the SAM to be a potential electron transport medium.

Translocation of C60 and Its Derivatives Across a Lipid Bilayer

Obtaining an understanding, at the atomic level, of the interaction of nanomaterials with biological systems has recently become an issue of great research interest. Here we report on the molecular dynamics study of the translocation of fullerene C60 and its derivative C60(OH)20 across a model cell membrane (dipalmitoylphosphatidylcholine or DPPC bilayer). The simulation results indicate that, although a pristine C60 molecule can readily "jump" into the bilayer and translocate the membrane within a few milliseconds, the C60(OH)20 molecule can barely penetrate the bilayer. Indeed, the mean translocation time via diffusion for the C60(OH)20 molecule is several orders of magnitude longer than for the former. It was also determined that the two different forms of fullerenes, when adsorbed into/onto the bilayer, affected the membrane structure differently. This study offers a mechanistic explanation of that difference and for the reduced acute toxicity of functionalized fullerenes.

Ultrasonic pulverization of fullerene nanofibers

The liquid-liquid interfacial precipitation method can produce C60 nanotubes with a length of the order of millimeters. The C60 nanotubes dried in air showed a Raman profile close to that of pristine C60. The C60 nanotubes are expected to be very useful to include various catalytic materials inside. The ultrasonic pulverization of the C60 nanotubes was examined in order to prepare short C60 nanotubes with open ends which make it easy to incorporate chemical substances. It was found that the ultrasonication of a few minutes is enough to prepare short C60 nanotubes with open ends.

C60-Fullerenes: detection of intracellular photoluminescence and lack of cytotoxic effects

We have developed a new method of application of C60 to cultured cells that does not require water-solubilization techniques. Normal and malignant cells take-up C60 and the inherent photoluminescence of C60 is detected within multiple cell lines. Treatment of cells with up to 200 μg/ml (200 ppm) of C60 does not alter morphology, cytoskeletal organization, cell cycle dynamics nor does it inhibit cell proliferation. Our work shows that pristine C60 is non-toxic to the cells, and suggests that fullerene-based nanocarriers may be used for biomedical applications.

Photophysical properties of a 1,2,3,4,5,6-hexasubstituted fullerene derivative.

The photophysical properties of a novel 1,2,3,4,5,6-hexasubstituted fullerene derivative (1) are examined in this study. In addition to the ground state absorption spectrum of 1, we report its triplet-triplet absorption spectrum and molar extinction coefficient (Deltae(T-T)), as well as the triplet quantum yield (PhiT), lifetime (tauT), and energy (ET). The saturation of a single six-member ring on the fullerene cage results in significant changes in the triplet state properties as compared to that of pristine C60. The triplet-triplet absorption spectrum shows a hypsochromic shift in long wavelength absorption, and both the triplet state lifetime and the triplet quantum yield are decreased. The triplet energy was found to be similar to that of C60. In addition, the quantum yield (PHI(delta)) of singlet oxygen generated by 1 was calculated and is found to be significantly less than in the case of C60.

Room Temperature Liquid Fullerenes: An Uncommon Morphology of C60 Derivatives.

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Photoluminescence properties of high-pressure-polymerized C60 nanorods in the orthorhombic and tetragonal phases

C 60 nanorods in two polymeric phases have been synthesized under different high pressure and high temperature conditions. Orthorhombic and tetragonal phases have been identified from Raman spectra. The rod shape can be kept under quasihydrostatic pressure. The photoluminescence intensity of the polymeric C60 nanorods has been greatly enhanced compared with that of pristine C60 nanorods. The main fluorescence band shifted from 730nm in the unpolymeric phase to 748nm and near infrared 780nm in the orthorhombic and tetragonal phases, respectively. The enhanced photoluminescence with tunable frequency for different polymeric C60 nanorods suggests potential applications in luminescent nanomaterials.

Highly Enhanced Luminescence from Single-Crystalline C60·1m-xylene Nanorods

Single-crystalline C60·1m-xylene nanorods with a hexagonal structure were successfully synthesized by evaporating a C60 solution in m-xylene at room temperature. The ratio of the length to the diameter of the nanorods can be controlled in the range of ≈10 to over 1000 for different applications. The photoluminescence (PL) intensity of the nanorods is about 2 orders of magnitude higher than that for pristine C60 crystals in air. Both UV and Raman results indicate that there is no charge transfer between C60 and m-xylene. It was found that the interaction between C60 and m-xylene molecules is of the van der Waals type. This interaction reduces the icosahedral symmetry of C60 molecule and induces strong PL from the solvate nanorods.

Room Temperature Liquid Fullerenes: An Uncommon Morphology of C60 Derivatives

Room temperature liquid C60 derivatives bearing a 2,4,6-trialkyloxyphenyl branch show a dramatic decrease in viscosity with an increase in the length of the alkyl chains. This feature, when combined with electrochemical activities similar to those of pristine C60 and relatively high charge carrier mobility, makes them an extremely attractive novel carbon material for future applications in materials science.