Fullerene Clusters Research Articles

Interaction of Fullerene with Model Cell Membranes: a Computer Simulation Study

Nano-sized fullerene aggregates can enter cells and alter their functions, but the mechanisms of cell damage is unclear. In our previous work [1] we used coarse-grained molecular dynamics simulations to characterize the thermodynamics and kinetics of permeation of fullerene clusters through a model membrane. We also showed that high fullerene concentrations induce changes in the structural and elastic properties of the lipid bilayer, but these are not sufficient to cause a direct mechanical damage to the membrane. Now we explore the effect of fullerene on model membranes including an ion channel protein, Kv1.2, using computer simulations with both a coarse-grained and an atomistic representation. We also investigate the effects of a naturally abundant organic compound, gallic acid, on fullerene-membrane interactions. Recent work [2] has shown that gallic acid-coated fullerenes cause cell contraction. We use computer simulations to describe possible mechanisms of cell damage.[1] Wong-ekkabut et al., Nature Nanotech (2008), 3, 363.[2] Salonen et al., Small, in press.

The influence of polymer architecture on the assembly of poly(ethylene oxide) grafted C60 fullerene clusters in aqueous solution: a molecular dynamics simulation study

The effect of polymer architecture on the aggregation behavior of C60 fullerenes tethered with a single chain of poly(ethylene oxide) (PEO) in aqueous solution has been investigated using coarse-grained, implicit solvent molecular dynamics simulations. The PEO-grafted fullerenes were comprised of a single tether of 60 repeat units represented as a linear polymer, a three-arm star (20 repeat units/arm) or a six-arm star (10 repeat units/arm). Additionally, the influence of arm length on self-assembly of the PEO-fullerene conjugates was investigated for the three-arm stars. Self-assembly is driven by favorable fullerene-fullerene and fullerene-PEO interactions. Our simulations reveal that it should be possible to control the size and geometry of the self-assembled fullerene aggregates in water through variation of PEO architecture and PEO molecular weight. We found that aggregate size and shape could be understood qualitatively in terms of the packing parameter concept that has been employed for diblock polymer and surfactant self-assembly. Higher molecular weight PEO (longer arms) and more compact PEO (more arms for the same molecular weight) resulted in greater steric repulsion between fullerenes, engendering greater aggregate surface curvature and hence the formation of smaller, more spherically shaped aggregates. Finally, weak attractive interactions between PEO and the fullerenes were found to play an important role in determining aggregate shape, size and the dynamics of self-assembly.

Formation of fullerene clusters in carbon disulfide: Data on small-angle neutron scattering and molecular dynamics

Fullerene solutions in carbon disulfide are studied by small-angle neutron scattering (SANS). In addition to earlier experiments on the given system, the range of measured transmitted impulses is extended and the influence of solution preparation methods on C60 cluster formation in these solutions is studied. It is shown that the formation of large C60 clusters (with a size of about 10 nm) is due to nonequilibrium methods of solution preparation. For nonequilibrium dissolution, there is a 10% excess of the observed fullerene size in the solution over the calculated value. It has been established by simulation of the C60/CS2 interface by molecular dymanics methods that inclusion of how solvent molecules are organized on the C60 surface leads to a decrease in the fullerene size in the solution, observed by using SANS. In this paper, the effect of excess Rg is explained by the presence of small clusters in the solution (approximately 10% of dissolved C60 molecules). It is discovered that there is a time variation in the concentration of the saturated solution. The explanation of this effect using a model of formation and sedimentation of large clusters (with a size of 100 nm or more) is proposed.

MD Study of the Endohedral Potassium Ion Fullerene Cluster (K<sup>+</sup>@C<sub>60</sub>)<sub>7</sub>

The nanosystem composed of only as few as seven endohedral fullerene K+@C60 molecules was simulated using the MD method. The interaction was taken to be the full site-site pairwise additive Lennard-Jones (LJ) potential, which generates both translational and anisotropic rotational motions of each endohedral fullerene. The atomically detailed MD simulations allow the dynamics of the motion of K+@C60 molecule inside the cluster to be analysed. The radial distribution function, the mean square displacement, the translational velocity correlation functions and the Lindemann index of endohedral fullerene have been calculated for several energies of the nanosystem. The solid/liquid phase transition and the existence of the liquid phase in the endohedral potassium ion fullerene cluster was found.

First Principle Investigation of Structural Properties of Potassium Doped Fullerene Clusters – K<sub>n</sub>(C<sub>60</sub>)<sub>2</sub>

First principle simulations for the nanosystems Kn(C60)2, (n = 1, 2) composed of two fullerene (C60) molecules and one or two potassium (K) atoms have been undertaken. A very effective delocalization of the 4s1 valence electron of potassium was observed, the potassium atom in practice becomes an ion. The adsorption binding energy of potassium atom(s) is Ea = - 1.923 ± 0.04 eV, - 3.819 ± 0.04 eV for K(C60)2 and K2(C60)2, respectively. The reported large values of adsorption energy should cause a significant change in electronic properties of alkali doped fullerene clusters.

A Titanium-Decorated Fullerene Cluster – A Molecular Dynamics Simulation

A small titanium-decorated fullerene cluster (C60[TiH2]6)7 was studied by MD simulation over a wide range of energy, from the solid state to the vaporization of the nanosystem. The low energy, solid state structure of the cluster was obtained as a deformed pentagonal bipyramid. Several physical characteristics: the radial distribution function, the mean square displacement, the translational velocity autocorrelation function, translational diffusion coefficient, Lindemann index, etc., were calculated for a wide range of energy in the system.

Aggregation in C60/NMP, C60/NMP/water and C60/NMP/Toluene Mixtures

The solutions of C60 in N‐methyl‐2‐pyrrolidone (NMP) and in the binary mixtures NMP/water and NMP/toluene are investigated using UV‐Vis spectroscopy, small‐angle neutron scattering and mass‐spectroscopy. The decomposition of fullerene clusters after dilution of C60/NMP system with water and the effect of solvent polarity on fullerene aggregation in C60/NMP/toluene solutions are analyzed.

Computer simulation study of fullerene translocation through lipid membranes

Recent toxicology studies suggest that nanosized aggregates of fullerene molecules can enter cells and alter their functions, and also cross the blood-brain barrier. However, the mechanisms by which fullerenes penetrate and disrupt cell membranes are still poorly understood. Here we use computer simulations to explore the translocation of fullerene clusters through a model lipid membrane and the effect of high fullerene concentrations on membrane properties. The fullerene molecules rapidly aggregate in water but disaggregate after entering the membrane interior. The permeation of a solid-like fullerene aggregate into the lipid bilayer is thermodynamically favoured and occurs on the microsecond timescale. High concentrations of fullerene induce changes in the structural and elastic properties of the lipid bilayer, but these are not large enough to mechanically damage the membrane. Our results suggest that mechanical damage is an unlikely mechanism for membrane disruption and fullerene toxicity.

Hybride Nanomaterials Based on Silica Coated C60 Clusters Obtained by Microemulsion Technique

Currently, there is a major trend to produce nanostructures of a wide variety of materials by understanding their properties and their functionality in order to develop future nanotechnologies. In this article the silica coated fullerene C60 clusters have been produced by microemulsion technique. Firstly, the ternary phase diagrams in water/TX-114/tetraethylorthosilicate (TEOS) system at different temperatures were constructed, followed by establishing the influence of clusterization and solubilization agents in choosing the pseudoternary system. By using the phase diagram specific working conditions have been selected, in order to facilitate nanostructured templates for preparation of the silica coated fullerene nanoclusters.

Surface depth analysis for fluorinated block copolymer films by X-ray photoelectron spectroscopy using C 60 cluster ion beam

X-ray photoelectron spectroscopy (XPS) using fullerene (C 60) cluster ion bombardment was applied to films of a fluorinated block copolymer. Spectra so obtained were essentially different from those using Ar ion beam. Structure in the surface region with the depth down to 60 nm drawn on the basis of XPS with C 60 beam was essentially the same as the one drawn by the result using dynamic secondary ion mass spectrometry, which is a well-established method for the depth analysis of polymers. This implies that XPS using C 60 beam enables one to gain access to the depth analysis of structure in polymer films with the depth range over the analytical depth of conventional XPS, that is, three times inelastic mean-free path of photoelectrons.

Applications of fullerene beams in analysis of thin layers

Molecular dynamics computer simulations have been employed to model ejection of particles from Ag{1 1 1} metal substrate and thin benzene overlayer bombarded by fullerene cluster projectiles. The sputtering yields are analyzed depending on the size (from C 20 up to C 540) and the kinetic energy (5–20 keV) of a projectile. It has been found that for clean metal substrate bombarded by 15 keV projectiles the maximum ejection is stimulated by the impact of the C 60 cluster. However, the size of the cluster projectile maximizing the yield depends on the kinetic energy of the cluster, shifting towards larger clusters as the impact energy increases. For a thin benzene overlayer, the yield increases monotonically with the size of the cluster within investigated range of fullerene projectiles and kinetic energies.

Molecular Dynamics Simulation Study of the Influence of Cluster Geometry on Formation of C60 Fullerene Clusters in Aqueous Solution

We have performed atomistic molecular dynamics simulations of linear (1-dimensional), planar (2-dimensional), and icosahedral (3-dimensional) clusters of C60 fullerenes in aqueous solution in order to investigate the influence of cluster geometry on their free energy of formation. As was found in our previous study of the potential of mean force (PMF) as a function of separation for a single pair of fullerenes in aqueous solution, the interaction between fullerenes for all cluster geometries was dominated by direct fullerene-fullerene interactions and not by water-induced hydrophobic interactions. A coarse-grained implicit solvent (CGIS) potential, given by the PMF for the fullerene pair in water obtained from atomistic simulations, was found to describe well the free energy of formation of the linear cluster, indicating that many-body effects, i.e., the influence of neighboring fullerenes on the water-induced interaction between a fullerene pair, are negligible for the 1-dimensional geometry. For the 2-dimensional and particularly the 3-dimensional geometry, however, many-body effects were found to strongly influence hydration, leading to complete dehydration of the central fullerene at close fullerene-fullerene separations for the icosahedral cluster. This strong influence of geometry on hydration translates into water-induced interactions that, while remaining repulsive, as is found for the fullerene pair, are not well described by the two-body CGIS potential obtained from the isolated fullerene pair, particularly for the 3-dimensional geometry.

Competition between Fission and Intra‐Cluster Fusion in Highly Excited Fullerene Clusters

AbstractThe occurrence of intra‐cluster fusion of fullerene molecules inside van der Waals bound fullerene clusters can be observed following femtosecond laser excitation. We show that the fusion reaction competes with the fission of multiply charged clusters. Energetic barriers to the reaction of at least 85 eV have to be overcome, similar to the energetic barriers to molecular fusion observed in fullerene ion‐neutral fullerene collision experiments.

The Change of the State of an Endohedral Fullerene by Encapsulation into SWCNT: A Raman Spectroelectrochemical Study of Dy3N@C80 Peapods

Raman and in situ Raman spectroelectrochemical studies of Dy3N@C80@SWCNT peapods have been carried out for the first time. The formation of peapods by the encapsulation of gaseous Dy3N@C80 has been confirmed by HR-TEM microscopy and by the successful transformation of Dy3N@C80@SWCNT into double-walled carbon nanotubes. The Raman spectra of the endohedral fullerene cluster changed dramatically in the interior of the single-walled carbon nanotube (SWCNT). The electrochemical charging of the peapod indicates a slight reversible attenuation of the Raman intensities of fullerene features during anodic doping. The results support the assignment of Raman bands to the Dy3N@C80 moiety inside a SWCNT.

Unconventional magnetic properties of the icosahedral symmetry antiferromagnetic Heisenberg model

The antiferromagnetic Heisenberg model on icosahedral symmetry ${I}_{h}$ fullerene clusters exhibits unconventional magnetic properties despite the lack of anisotropic interactions. At the classical level, and for number of sites $n\ensuremath{\leqslant}720$, the magnetization has two discontinuities in an external magnetic field, except from the dodecahedron where it has three, emphasizing the role of frustration introduced by the pentagons in the unusual magnetic properties. For spin magnitude ${s}_{i}=\frac{1}{2}$, there is a discontinuity of quantum character close to saturation for $n\ensuremath{\leqslant}80$. This common magnetic behavior indicates that it is a generic feature of ${I}_{h}$ fullerene clusters, irrespective of $n$.

Stabilities of multiply charged dimers and clusters of fullerenes

The authors find even-odd variations as functions of r (<or=7) for multiple ionization of van der Waals dimers in slow Xe(30+)+[C60]2([C60C70])-->...+[C60]2(r+)([C60C70](r+)) electron-transfer collisions. This even-odd behavior is in sharp contrast to the smooth one for fullerene monomers and may be related to even-odd effects in dimer ionization energies in agreement with results from an electrostatic model. The kinetic energy releases for dimer dissociations [predominantly yielding intact fullerenes [C60]2(r+)-->C60(r1+)+C60(r2+) in the same (r1=r2) or nearby (r1=r2+/-1) charge states] are found to be low in comparison with the corresponding model results indicating that internal excitations of the separating (intact) fullerenes are important. Experimental appearance sizes for the heavier clusters of fullerenes [C60]n(r+) (n>3 and r=2-5) compare well with predictions from a new nearest-neighbor model assuming that r unit charges in [C60]n(r+) are localized to r C60 molecules such that the Coulomb energy of the system is minimized. The system is then taken to be stable if (i) two (singly) charged C60 are not nearest neighbors and (ii) the r C60(+) molecules have binding energies to their neutral nearest neighbors which are larger than the repulsive energies for the (r-1) C60(+)-C60(+) pairs. Essential ingredients in the nearest-neighbor model are cluster geometries and the present results on dimer stabilities.

Molecular fusion within fullerene clusters induced by femtosecond laser excitation

Molecular fusion is induced in clusters of fullerene molecules on excitation with fs laser pulses. The dependence of the mass distributions of the fused products on the initial cluster distribution are studied and results for (C60)N and (C70)N clusters are compared. The fused products decay by emitting C2 molecules and the fragmentation spectrum is used to determine the initial excitation energy of the fused species. The threshold excitation energy needed to induce fusion is consistent with the energetic thresholds for molecular fusion of fullerenes determined previously in single collision experiments.

Effect of the age of the C60/N-methyl-2-pyrrolidone solution on the structure of clusters in the C60/N-methyl-2-pyrrolidone/water system according to the small-angle neutron scattering data

Fullerene clusters in the C60/N-methyl-2-pyrrolidone (NMP)/water system have been investigated by small-angle neutron scattering. It is shown that the scattering cross section corresponding to the size range 10–100 nm depends on the water content in the mixture. Addition of water to a C60/NMP solution in an amount exceeding 40% leads to a sharp increase in the average scattering cross section. This effect depends on the interval between the times of preparation of a C60/NMP solution and its dilution with water: the size of the clusters formed as a result of adding water increases with increasing the age of the initial solution. The reasons for this effect are discussed.

Small-angle neutron scattering data on C60 clusters in weakly polar solutions of fullerenes

Solutions of fullerence C60 in carbon disulfide CS2 have been investigated by small-angle neutron scattering. Combination of solubility, contrast, and incoherent scattering make it possible to measure and analyze the relatively small scattering cross section of this system. Along with single fullerene molecules, a small amount of large fullerene clusters (more than 100 A in size) is found in these solutions. The formation of these clusters depends on the procedure of solution preparation. The size distribution functions of clusters are compared with the results of the phenomenological cluster model of fullerene solubility.

Organic solar cells. Supramolecular composites of porphyrins and fullerenes organized by polypeptide structures as light harvesters

We have constructed supramolecular solar cells composed of a series of porphyrin–peptide oligomers [porphyrin functionalized α-polypeptides, P(H2P)n or P(ZnP)n (n = 1, 2, 4, 8, 16)], and fullerenes assembled on a nanostructured SnO2 electrode using an electrophoretic deposition method. Remarkable enhancement in the photoelectrochemical performance as well as the broader photoresponse in the visible and near-infrared regions is seen with increasing the number of porphyrin units in α-polypeptide structures. Formation of supramolecular clusters of porphyrins and fullerenes prepared in acetonitrile–toluene = 3 : 1 has been confirmed by transmission electron micrographs (TEM) and the absorption spectra. The highly colored composite clusters of porphyrin–peptide oligomers and fullerenes have been assembled as three-dimensional arrays onto nanostructured SnO2 films using an electrophoretic deposition method. A high power conversion efficiency (η) of ∼1.6% and the maximum incident photon-to-photocurrent efficiency (IPCE = 56%) were attained using composite clusters of free base and zinc porphyrin–peptide hexadecamers [P(H2P)16 and P(ZnP)16] with fullerenes, respectively. Femtosecond transient absorption and fluorescence measurements of porphyrin–fullerene composite films confirm improved electron-transfer properties with increasing number of porphyrins in a polypeptide unit. The formation of molecular assemblies between porphyrins and fullerenes with a polypeptide structure controls the electron-transfer efficiency in the supramolecular complexes, meeting the criteria required for efficient light energy conversion.