Francisco J. Martin-Martinez

Electronic structure and aromaticity of graphene nanoribbons.

We analyse the electronic structure and aromaticity of graphene nanoribbons and carbon nanotubes through a series of delocalisation and geometry analysis methods. In particular, the six-centre index (SCI) is found to be in good agreement with the mean bond length (MBL) and ring bond dispersion (RBD) geometry descriptors. Based on DFT periodic calculations, three distinct classes of aromaticity patterns have been found for armchair graphene nanoribbons, appearing periodically as the width of the ribbon is increased. The periodicity in the band gap is found to be related to these aromaticity patterns. Also, the appearance of such distinct aromaticity distribution is explained within the framework of the Clars sextet theory. Both delocalisation and geometry analysis methods are shown to be very fast and reliable tools for easily analysing the aromaticity in carbon nanosystems.

Reversible attachment of platinum alloy nanoparticles to nonfunctionalized carbon nanotubes.

The formation of monodisperse, tunable sized, alloyed nanoparticles of Ni, Co, or Fe with Pt and pure Pt nanoparticles attached to carbon nanotubes has been investigated. Following homogeneous nucleation, nanoparticles attach directly to nonfunctionalized single-walled and multi-walled carbon nanotubes during nanoparticle synthesis as a function of ligand nature and the nanoparticle work function. These ligands not only provide a way to tune the chemical composition, size, and shape of the nanoparticles but also control a strong reversible interaction with carbon nanotubes and permit controlling the nanoparticle coverage. Raman spectroscopy reveals that the sp(2) hybridization of the carbon lattice is not modified by the attachment. In order to better understand the interaction between the directly attached nanoparticles and the nonfunctionalized carbon nanotubes, we employed first-principles calculations on model systems of small Pt clusters and both zigzag and armchair single-walled carbon nanotubes. The detailed comprehension of such systems is of major importance since they find applications in catalysis and energy storage.

Clar-Kekule structuring in armchair carbon nanotubes.

Geometrical patterns on armchair nanotubes and their dependence on length (up to 10 nm) have been studied using first-principles methods. The results indicate that finite nanotubes do not show a uniform bond structure. The previous structural classification of armchair nanotubes in Clar, Kekule, and incomplete-Clar types becomes unified with lengthening, not in a bond-uniform structure, as PBC models report, but into an alternated sequence of Clar and Kekule domains in all cases, with possible mechanical and electronic consequences.

CoNTub v2.0 - Algorithms for Constructing C3-Symmetric Models of Three-Nanotube Junctions

Here, a method is described for easily building three-carbon nanotube junctions. It allows the geometry to be found and bond connectivity of C(3) symmetric nanotube junctions to be established. Such junctions may present a variable degree of pyramidalization and are composed of three identical carbon nanotubes with arbitrary chirality. From the indices of the target nanotube, applying the formulas of strip algebra, the possible positions of the six defects (heptagonal rings) needed can be found. Given the multiple possibilities that arise for a specific pair of indices, the relation between the macroscopic geometry (interbranch angles, junction size, and pyramidalization) and each specific solution is found. To automate the construction of these structures, we implemented this algorithm with CoNTub software, version 2.0, which is available at ( http://www.ugr.es/local/gmdm/contub2 ). In addition, a classification of three-nanotube junctions, 3TJ, in seven types based on the location of defects has been proposed, i.e. 3TJ(0:0:6), 3TJ(0:1:5), 3TJ(0:2:4), 3TJ(0:3:3), 3TJ(1:1:4), 3TJ(1:2:3), and 3TJ(2:2:2) types.

Ion Effect and Metal-Coordinated Cross-Linking for Multiscale Design of Nereis Jaw Inspired Mechanomutable Materials

The Nvjp-1 protein is a key component in the jaws of Nereis virens, a species of marine worm. It contains over 25 mol % of histidine, which is believed to play a key role in the metal-coordinated cross-linking responsible for the structural stability and exceptional mechanical performance of the worm jaw. Understanding the nanoscale mechanism behind this cross-linking and its pathway in affecting the macroscopic mechanical behavior of the material is crucial to develop bioinspired mechanomutable materials based on Nvjp-1. Here, we use a combination of multiscale modeling and experimental synthesis to understand the behavior of this heterologous-expressed protein from the nano- to the macroscale. We have built a bottom-up molecular-based model, which includes electronic-based density functional theory calculations, atomistic simulation of the nanoscale properties with replica exchange molecular dynamics, and an elastic network model for describing the macroscale behavior at different pHs. This multiscale modeling supports the experimental synthesis of a photo-cross-linked Nvjp-1 hydrogel by proving both the nanoscale mechanisms and mechanical behavior predictions. Our theoretical results agree well with the experimental observations, showing that Nvjp-1 forms a more compact structure in the presence of Zn2+ ions with a suitable pH environment, leading to the formation of more stable intramolecular metal-coordinated cross-links. These metal-coordinated cross-links induce nanoscale aggregation of Nvjp-1, which is responsible for the hydrogel contraction observed in experiments and predicted by the model.