Interactions of Fullerene (C60) and its Hydroxyl Derivatives with Lipid Bilayer: A Coarse-Grained Molecular Dynamics Simulation

Coarse-grained molecular dynamic simulations were employed to study the interactions of fullerene (C₆₀) and its hydroxyl derivatives (C₆₀(OH)_n, n?=?4, 5, 6, 8, 12, and 16) with a lipid bilayer composed of dipalmitoylphosphatidylcholine molecules. It was found that the C₆₀ moves towards the center of the bilayer and laid between central and peripheral regions of the bilayer. The potential mean force was calculated to estimate free energy profile when pulling the fullerene from its initial position to the center of the bilayer using an umbrella sampling method. Results showed that the hydrophobic region of the membrane acts as a barrier to transport a nonpolar C₆₀ molecule through the bilayer. This makes a deep minimum in the free energy profile between the center and head regions of membrane. Various numbers of polar functional groups (–OH) were then used to make derivatives of fullerene and change the hydrophilic of the molecule. It was found that optimal number of hydroxyl groups to facilitate the transportation of C₆₀(OH)_n through the bilayer is 4.     

Effect of C60 fullerene, fullerene-containing soot, and other carbon materials on the sliding edge friction of metals

A comparative study of different carbon materials (C₆₀ fullerene; soot, both with and without fullerenes; graphite; and industrial carbon black) as additives to industrial lubricating oils has been carried out for copper-steel and steel-steel sliding couples. The soot containing fullerene and the powder of pure fullerene produce a noticeable improvement in the antifriction and antiwear properties of steel-steel and steel-copper couples, especially under heavy loads and pressures at the contact. The greatest improvement was observed for the steel-steel couple. Structural-mechanical studies were carried out for copper riders and it has been demonstrated by several methods that the addition of the C₆₀ fullerene (pure fullerene or as a fullerene-containingsoot) creates a fullerene-polymer film on the frictional surface about 1000 Å thick, which has a protective effect.     

Experimental investigation of C60/NMP/toluene solutions by UV-Vis spectroscopy and small-angle neutron scattering

The transformation of the C₆₀ fullerene cluster state into C₆₀/N-methylpyrrolidone (NMP) solution after the addition of a nonpolar solvent (toluene, electric permittivity ?= 2.4) is studied. The results of ultraviolet-visible spectroscopy and small-angle neutron scattering measurements are used for comparison of the C₆₀/NMP/toluene system with C₆₀/NMP mixtures with a high-polar solvent (water, ? = 80). As to the observed reorganization of the cluster state, the C₆₀/NMP/toluene system is similar to the C₆₀/NMP/water system. This effect is explained by the formation of charge-transfer complexes in the initial C₆₀/NMP solution. These complexes are thought to be soluble in both binary mixtures. The connection between the cluster-reorganization effect and solvatochromism is discussed.     

Specific features of the formation of defects in fullerene C46

The initial stage of the formation of defects in the fullerene C₄₆ has been investigated using the atomistic computer simulation. It has been found that the relatively low symmetry of this fullerene leads to the emergence of channels of defect formation, which have not been revealed in the fullerenes C₂₀, C₃₆, and C₆₀. These channels consist in breaking a single C-C bond (in contrast to the simultaneous breaking of two bonds in the course of the Stone-Wales transformation, which is characteristic of high-symmetry fullerenes). For some typical channels, the paths of transformation of the C₄₆ fullerene into the corresponding defect isomers have been determined and the heights of the potential barriers encountered in these paths have been calculated.     

Fullerene C60 formation in partially ionized carbon vapor

The assembling rate of a fullerene C₆₀ molecule has been theoretically studied as a function of electron concentration and temperature in partially ionized carbon vapor. For C⁶⁰ formation via one or two intermediate stages of cluster collisions, it has been shown that there is a region of plasma parameters (the temperature and electron concentration) in which fullerene C₆₀ is formed more efficiently. The C₆₀ formation rate versus temperature and electron concentration relationships have been found to correlate with the trends in the collision cross-section of carbon clusters as functions of these parameters.     

Intercalation of C60 fullerene crystals with alkali and alkaline-earth metals through self-propagating high-temperature synthesis

A method for rapidly intercalating C₆₀ fullerene crystals has been implemented using self-propagating high-temperature synthesis. The method has been used to intercalate C₆₀ fullerene crystals with alkali (K, Rb) and alkaline-earth (Ca, Ba) metals. The superconducting transition temperatures of the prepared compounds have been measured. The C₆₀ fullerene crystals intercalated with calcium have been investigated using X-ray diffraction.     

ELECTRON SPIN RESONANCE CHARACTERISTICS OF NITROGEN-DOPED FULLERENE

The nitrogen-doped fullerene has been obtained by arc discharge between two high-purity graphite rods in the atmosphere of N₂ and He, The electron spin resonance(ESR) characteristics of N-doped fullerene have been investigated. The results show that the ESR spectra of N-doped fallerene axe composed of two parts, a paramagnetic signal of N-center and a paramagnetic signal of C-center, For comparing with N-doped fullerene, we have also studied ESR spectra of C₆₀ powder, C₆₀ sublimed film and H-doped C₆₀ film. For C₆₀ powder and H-doped C₆₀ film, their in situ ESR. measurements are carried out at various temperatures, and reasonable explanations are proposed.     

Electron paramagnetic and muon spin resonance studies in fullerenes

This article reviews the various EPR (CW, pulsed and time-resolved) and μSR studies reported in C₆₀/C₇₀/C₈₂ fullerenes. Different techniques for preparing paramagnetic C₆₀/C₇₀ species giving an EPR signal have been included. This literature survey is complete from the beginning of fullerene research (1985) up to middle 1994.     

New property of the fullerenes: the anomalously effective quenching of electronically excited states owing to energy transfer to the C<Subscript>70</Subscript> and C<Subscript>60</Subscript> molecules

The quenching of the electronically excited states of various energy donors—Tb³⁺; 9,10-anthracene dibromide; and adamantanone—by C₇₀ fullerene has been detected and analyzed. The quenching is characterized by anomalously high biomolecular quenching rate constants, which are obtained from the Stern-Volmer dependences of the energy-donor photoluminescence intensity on the concentration of the C₇₀ molecules. It has been shown that the high efficiency of quenching by the C₇₀ fullerene as compared to the C₆₀ fullerene is due to the higher polarizability of the C₇₀ molecule and large overlap integrals of the energy-donor photoluminescence spectra with the absorption spectrum of the C₇₀ fullerene.     

Investigation of the possibility of functionalization of C20 fullerene by benzene via Diels–Alder reaction

C₂₀ fullerene, this novel species with all its pentagonal faces has displayed some unique operations in making fast pericyclic reactions. As an example, the high dienophile character of the C₂₀ fullerene and the ability of this species in making an ultra-fast Diels–Alder reaction with 1,3-butadiene, has been recently reported. Moreover, new experimental reports claim that the C₆₀ fullerene, one of the fullerene family, could make a Diels–Alder reaction with the central ring of anthracene and make the ring non-aromatic. These reports may encourage researchers to do more studies on the properties of this small carbon cage.To address this question, the present research has discussed all the reaction channels of the Diels–Alder cycloaddition of benzene molecule as a 1,3-diene with the C₂₀ fullerene in order to answer this question: “Is C₂₀ fullerene able to make a Diels–Alder reaction with this molecule?”.     

Specifics of C<Subscript>60</Subscript> Fullerene Cluster Formation in a Solvent Mixture of Toluene and <Emphasis Type="Italic">N</Emphasis>-Methyl-2-Pyrollidone

The two-level organization of C₆₀ fullerene clusters in solutions of C₆₀ in pure toluene and toluene/N-methyl-2-pyrrolidone solvent mixtures is studied by small-angle X-ray scattering (SAXS). The SAXS data for freshly prepared solutions are compared with the data obtained by dynamic light scattering, a technique we use to assess the temporal stability of the prepared solutions. For all solutions in the mixed solvent, regardless of the ratio between the polar and nonpolar components, the UV?Vis absorption spectra tend to become featureless with time. We attribute this behavior primarily to the presence of the polar component in the molecular environment of fullerene molecules.     

Phase transition in C60-2-thioxo-l, 3dithiole cycloadduct

Quadratic electrooptic coefficient (QEOC) measurements have been made for fullerene C₆₀) and its derivative C₆₀-2-thioxo-l,3-dithiole. An anomaly in C_p has been revealed at about — 60°C that corresponds to the appearance of a structural phase transition. Correlation with a temperature anomaly in the QEOC is revealed. This leads to the conclusion that the QEOC for fullerene depends mainly on vibrational and rotational contributions. The contribution arising from charge distribution asymmetry is most important in the fullerene derivative. The observed temperature anomalies of the QEOC result in the possibility of using the QEOC as a sensitive tool for observing low-temperature phase transitions in the fullerene derivatives.     

Specific features of the stone-wales transformation in the C20 and C36 fullerenes

The initial stage of the defect formation in the C₂₀ and C₃₆ fullerenes has been investigated by the ab initio method and in terms of tight-binding models. A comparison with the Stone-Wales transformation in the C₆₀ fullerene has revealed the presence of two independent stages in this process, the first of which is an “incomplete” Stone-Wales transformation. At this stage, the C₂₀ and C₃₆ fullerenes transform into metastable defect configurations with two adjacent “windows” on their surface, whereas a similar configuration of the C₆₀ fullerene is unstable and corresponds to a saddle stationary point of the potential energy of the cluster. A new mechanism of plastic deformation due to the Stone-Wales transformation has been predicted for the (C₃₆) _n fullerites.     

Junction characteristics of C60/polycarbonate blend on Si substrate

We report a study of the interface between fullerene (C₆₀) doped polycarbonate (PC) blends and n-type Si substrate. C₆₀ is usually an electron acceptor in interpenetrated networks and an electron transport in photovoltaic cells. We have studied that the guest-host approach to prepare C₆₀ doped polycarbonate blend. In this article, we report the I-V characteristics of C₆₀ doped polycarbonate/n-type Si junction and the annealing effect on these characteristics. In this junction, a nanocomposite of organic semiconductor fullerene (C₆₀), used as the active medium, with an inert polycarbonate matrix was spin coated on n-type Si substrate. We found that the C₆₀ shows the junction characteristics with n-type Si substrate. The knee voltage and dynamic resistance varies with concentration of C₆₀ as well as temperature. Ellipsometry studies showed the annealing effect on the refractive index and thickness of C₆₀ doped polycarbonate blend on n-type Si substrate. The optical micrographs show that fullerene (C₆₀) is spherical molecule and it is blend in the form of crystallites having size of micron order.     

Nanoemitter of giga- and terahertz ranges based on a carbon peapod: Numerical simulation

A mathematical model of a nanoemitter for the giga- and terahertz ranges based on a carbon nanopeapod formed by a (10, 10) nanotube with encapsulated C₆₀ fullerenes has been proposed. The fundamental possibility of the generation of giga- and terahertz radiation by a charged free fullerene oscillating in the potential well created by the atomic framework of the nanotube and several fullerenes polymerized with its walls and with each other has been proven. The radiation frequency is controlled by means of an external electric field. The dependence of the amplitude and frequency of oscillations on the charge of C₆₀ and on the external field strength has been revealed by the molecular dynamics method. If the fullerene has a charge of +1e or +2e, it emits electromagnetic waves only in the gigahertz range in strong external fields. At the same time, the physical conditions under which the frequency of radiation can be 0.36 GHz have been established: the charge of the fullerene must be +3e, the tube should be oriented strictly along the external field lines, and the strength should be 0.1 V/nm.     

EPR evidence of the low temperature phase transition in C60

A standard EPR technique has been applied to perform temperature studies of polycrystalline samples of C₆₀ fullerene. A comparison of the three main parameters of EPR spectra obtained for a C₆₀ sample before and after (solvent free) purification has been made in temperatures from 4 to 300 K. When compared to the spectrum of the as-obtained (crude) sample the spectrum of the purified sample revealed considerable changes i.e. an increase in the EPR signal intensity and evidence of a phase transition at about 90 K. This transition is proved to be related to the two processes: freezing of the orientational motion of C₆₀ molecules and redistribution of the positive and negative charge observed as paramagnetic centres localized on C₆₀ molecules.     

Phase Transitions in a Mixture of Amorphous C<Subscript>60</Subscript> and C<Subscript>70</Subscript> Fullerene Phases at High Temperatures and Pressures

Phase transitions in two types of amorphous fullerene phases (C₆₀–C₇₀ (50/50) mixtures and an amorpous C₇₀ fullerene phase) are studied via neutron diffraction at pressures of 2–8 GPa and temperatures of 200–1100°C. Fullerenes are amorphized by grinding in a ball mill and sintered under quasi-hydrostatic pressure in a toroidal-type chamber. Diffraction studies are performed ex situ. It is shown that the amorphous phase of fullerenes retains its structure at temperatures of 200–500°C, and amorphous graphite is formed at 800–1100°C with a subsequent transition to crystalline graphite. This process is slow in a mixture of fullerenes, compared to C₇₀ fullerene. According to neutron diffraction data, the amorphous graphite formed from amorphous fullerene phases has anisotropy that is much weaker in a fullerene mixture.     

Collision dynamics of He@C<Subscript>60</Subscript>+He@C<Subscript>60</Subscript> at low energies

A semi-empirical molecular dynamics model is developed. The central collisions of C₆₀+C₆₀ and He@C₆₀+He@C₆₀ at different incident energies are investigated based on this model. It is found that the dimer structures have been produced at proper incident energies and these fullerene dimers could be formed by a self-assembly of C₆₀ fullerene and He@C₆₀. The He atom has a significant effect at higher incident energy and this embedded He atom can enhance the stability of the dimer structure.     

A close look at the motion of C60 on gold

In this paper, we have studied the motion of buckminsterfullerene (C₆₀) on a gold surface by analyzing its potential energy and using classical molecular dynamics method. The results can be employed to investigate the motion of C₆₀-based nanocars which have been made in recent years. For this purpose, we have studied the translational and rotational motions of C₆₀ molecule independently. First, we have calculated the potential energy of a C₆₀ molecule on a gold surface in different orientations and positions and employed this data to predict fullerene motion by examining its potential energy. Then we have simulated the motion of C₆₀ at different temperatures using classical molecular dynamics methods. Specifying the regime of the motion at different temperatures is one of main goals of this paper. We have found that the rotational motion of C₆₀ molecule on the gold substrate, was easier than its sliding (translational) motion. Also, the regime of motion of fullerene depended on temperature. The results demonstrate that three different regimes of motion, dependent on temperature, could be observed: rare jumps to adjacent cells, frequent jumps, and continuous motion. Employing the results of this paper not only helps to understand the C₆₀ motion on the gold surface but also provides an appropriate tool for realizing motion of the thermally-driven fullerene-based nanocars.