Manuel Melle-Franco

Supramolecular self-assembled fullerene nanostructures

Four ionic fullerene derivatives, which are relatively soluble in polar solvents, are shown to organize into morphologically different nanoscale structures. Spheres, nanorods, and nanotubules form in water depending on the side chain appendage of the fullerene spheroid. Images at different nanoscale structures were obtained via transmission electron microscopy. Also, computer simulations were used for investigating the relative spatial arrangements. The efficient method to fabricate almost perfect and uniformly shaped nanotubular crystals, which order spontaneously by self-assembly, opens the way to the possibility of exploiting the fullerene properties at the nanometer scale.

Graphene Can Wreak Havoc with Cell Membranes

Molecular dynamics--coarse grained to the level of hydrophobic and hydrophilic interactions--shows that small hydrophobic graphene sheets pierce through the phospholipid membrane and navigate the double layer, intermediate size sheets pierce the membrane only if a suitable geometric orientation is met, and larger sheets lie mainly flat on the top of the bilayer where they wreak havoc with the membrane and create a patch of upturned phospholipids. The effect arises in order to maximize the interaction between hydrophobic moieties and is quantitatively explained in terms of flip-flops by the analysis of the simulations. Possible severe biological consequences are discussed.

Stable hydrogenated graphene edge types: Normal and reconstructed Klein edges

Hydrogenated graphene edges are assumed to be either armchair, zigzag, or a combination of the two. We show that the zigzag is not the most stable fully hydrogenated edge structure along the ⟨21⎯⎯1⎯⎯0⟩ direction. Instead hydrogenated Klein and reconstructed Klein based edges are found to be energetically more favorable, with stabilities approaching that of armchair edges. These new structures “unify” graphene edge topology, the most stable flat hydrogenated graphene edges always consisting of pairwise bonded C2H4 edge groups, irrespective of the edge orientation. When edge rippling is included, CH3 edge groups are most stable. These new fundamental hydrogen-terminated edges have important implications for graphene edge imaging and spectroscopy, as well as mechanisms for graphene growth, nanotube cutting, and nanoribbon formation and behavior.

A computational analysis of the insertion of carbon nanotubes into cellular membranes

Carbon nanotubes have been proposed to serve as nano-vehicles to deliver genetic or therapeutic material into the interior of cells because of their capacity to cross the cell membrane. A detailed picture of the molecular mode of action of such a delivery is, however, difficult to obtain because of the concealing effects of the cell membrane. Here we report a systematic computational study of membrane insertion of individual carbon nanotubes and carbon nanotube bundles using two entirely different and unrelated techniques. First a static scan of the environmental free energy is carried out based on a membrane mimicry approach and different insertion geometries are assessed. Then the dynamics is investigated with a coarse-grained approach that was previously used in the study of the integration dynamics of nanoparticles into the bilayer. The results of both models point, for unfunctionalized carbon nanotubes, at a preference for the horizontal orientation inside the internal hydrophobic layer of the cell membrane. Finally, the energetics of the formation of bundles of carbon nanotubes is studied. The cellular membrane promotes aggregation of carbon nanotubes in its hydrophobic core and modifies the structural stability of the bundles.

A Carbon Nano-Onion–Ferrocene Donor–Acceptor System: Synthesis, Characterization and Properties

We describe the synthesis and characterization of a novel ferrocene-carbon onion derivative, where ferrocene acts as an electron-donating moiety, while the carbon nano-onion (CNO) serves as the electron acceptor. CNOs were functionalized by 1,3-dipolar cycloaddition and the resulting products were characterized by transmission electron microscopy, thermogravimetric analysis, Raman and energy dispersive spectroscopies. The electronic properties of the Fc-CNO derivative were investigated by electrochemical and photophysical techniques, complemented by quantum chemical calculations. On average, the CNOs have a spherical appearance with six shells. Functionalization saturates one carbon atom in 36 carbon atoms on the outer cage of the CNO. Through-space interactions between the Fc moiety and the CNO core were detected electrochemically. Fluorescence was observed at low and high energies with an intrinsic decay that is faster at lower energies. Based on theory and experiment, we conclude that, after absorption of a photon at low energy, there is emission from CNOs characterized by larger external shells and a lower degree of functionalization. At high energy, emission comes from CNOs with smaller external shells and a higher degree of functionalization.

Hexaazatrinaphthylenes with Different Twists

A synthetic strategy that allows the induction of twist angles of different sizes in 5,6,11,12,17,18-hexaazatrinaphthylene (HATNA) chromophores is reported. The different twist angles are accompanied by measurable changes in the emission and electrochemical characteristics of HATNA.

Solutions of fully exfoliated individual graphene flakes in low boiling point solvents

Graphenide solutions (solutions of negatively charged graphene flakes) have been prepared in low boiling point solvents such as tetrahydrofuran (THF) by dissolution of the graphite intercalation compound (GIC) KC8. The presence of two-dimensional objects in solution, with an average lateral size of over one micron, is evidenced by light scattering analysis. High resolution transmission electron microscopy analysis shows that the solubilized graphene flakes are exclusively single and double layers with no evidence for thicker species. Molecular dynamics simulations support the graphene folding, observed in TEM, and suggest it is triggered by solvent nanodrops.

Polyarene‐Functionalized Fullerenes in Carbon Nanotubes: Towards Controlled Geometry of Molecular Chains

Mechanisms for controlling the assembly of molecular arrays in carbon nanotubes via alteration of the size and geometry of the functional groups attached to the molecules inserted into the nanotubes are studied. As model compounds, a series of structurally related fullerenes functionalized with polyaryl groups (C(60)X, where X is a polyaryl group) of various lengths are synthesized to explore this effect. These molecules are inserted into single-walled carbon nanotubes (SWNTs) under mild conditions to prevent their decomposition and to form C(60)X@SNWT structures. The molecular chains thus formed are studied by high-resolution transmission electron microscopy, X-ray diffraction, and Raman spectroscopy, revealing that the functional groups increase the interfullerene separation proportionally with the size of X. However, the functional groups themselves appear to adopt various orientations with respect to each other and exhibit intermolecular pi-pi interactions within the cavities of the carbon nanotubes. All these effects create a distribution of observed interfullerene separations in nanotubes, which are examined by theoretical simulations and interpreted in terms of molecular geometries and intermolecular interactions.

Twisted Aromatic Frameworks: Readily Exfoliable and Solution-Processable Two-Dimensional Conjugated Microporous Polymers

Abstract Twisted two‐dimensional aromatic frameworks have been prepared by overcrowding the nodes with bulky and rigid substituents. The highly distorted aromatic framework with alternating out‐of‐plane substituents results in diminished interlayer interactions that favor the exfoliation and dispersion of individual layers in organic media.

Carbon nanotubes accelerate methane production in pure cultures of methanogens and in a syntrophic coculture

Carbon materials have been reported to facilitate direct interspecies electron transfer (DIET) between bacteria and methanogens improving methane production in anaerobic processes. In this work, the effect of increasing concentrations of carbon nanotubes (CNT) on the activity of pure cultures of methanogens and on typical fatty acid-degrading syntrophic methanogenic coculture was evaluated. CNT affected methane production by methanogenic cultures, although acceleration was higher for hydrogenotrophic methanogens than for acetoclastic methanogens or syntrophic coculture. Interestingly, the initial methane production rate (IMPR) by Methanobacterium formicicum cultures increased 17 times with 5 g·L-1 CNT. Butyrate conversion to methane by Syntrophomonas wolfei and Methanospirillum hungatei was enhanced (∼1.5 times) in the presence of CNT (5 g·L-1 ), but indications of DIET were not obtained. Increasing CNT concentrations resulted in more negative redox potentials in the anaerobic microcosms. Remarkably, without a reducing agent but in the presence of CNT, the IMPR was higher than in incubations with reducing agent. No growth was observed without reducing agent and without CNT. This finding is important to re-frame discussions and re-interpret data on the role of conductive materials as mediators of DIET in anaerobic communities. It also opens new challenges to improve methane production in engineered methanogenic processes.