Rediscovering Medicinal Amazonian Aromatic Plants: Piper carpunya (Piperaceae) Essential Oil as Paradigmatic Study.

Piper carpunya Ruiz & Pav. (Piperaceae) is a perennial aromatic shrub of Amazonian area of Ecuador and Peru, belonging to the ethnomedicine of these countries. The traditional preparations of the crude drug (fresh leaves used topically as is, and dried leaves in infusions or decoctions) are known for anti-inflammatory, antiulcer, antidiarrheal, antiparasitic effects, and wound healing properties. In light of this traditional evidence, chemical composition (GC-MS) and biological activity, i.e., antioxidant, antifungal (yeast) capacities, and genotoxicity, of Amazonian P. carpunya leaf essential oil (EO) have been investigated in order to valorize some of the putative ethnomedical effects. The EO was obtained through steam distillation of fresh leaves (yield: 7.6 g/kg [0.76%]; refractive index at 20°C: 1.49; density: 0.928 g/mL). Chemical characterization performed through GC-MS evidenced the presence of 21 compounds (96.2% of the total). The most abundant constituents were piperitone (26.2%), limonene (9.5%), elemicin (7.2%), and ß-phellandrene (5.6%). In vitro DPPH antioxidant assay showed a weak radical scavenging ability (IC50) if compared to positive control. Low bioactivity of the EO was also demonstrated against yeast, but it showed an interesting synergistic activity (FIC index of EO+fluconazole) against Candida sp. strains. Ames test evidenced the safety of the EO concerning genotoxicity.

Direct evidence of atomic-scale structural fluctuations in catalyst nanoparticles.

Rational catalyst design requires an atomic scale mechanistic understanding of the chemical pathways involved in the catalytic process. A heterogeneous catalyst typically works by adsorbing reactants onto its surface, where the energies for specific bonds to dissociate and/or combine with other species (to form desired intermediate or final products) are lower. Here, using the catalytic growth of single-walled carbon nanotubes (SWCNTs) as a prototype reaction, we show that the chemical pathway may in-fact involve the entire catalyst particle, and can proceed via the fluctuations in the formation and decomposition of metastable phases in the particle interior. We record in situ and at atomic resolution, the dynamic phase transformations occurring in a Cobalt catalyst nanoparticle during SWCNT growth, using a state-of-the-art environmental transmission electron microscope (ETEM). The fluctuations in catalyst carbon content are quantified by the automated, atomic-scale structural analysis of the time-resolved ETEM images and correlated with the SWCNT growth rate. We find the fluctuations in the carbon concentration in the catalyst nanoparticle and the fluctuations in nanotube growth rates to be of complementary character. These findings are successfully explained by reactive molecular dynamics (RMD) simulations that track the spatial and temporal evolution of the distribution of carbon atoms within and on the surface of the catalyst particle. We anticipate that our approach combining real-time, atomic-resolution image analysis and molecular dynamics simulations will facilitate catalyst design, improving reaction efficiencies and selectivity towards the growth of desired structure.

Structure of Supported and Unsupported Catalytic Rh Nanoparticles: Effects on Nucleation of Single-Walled Carbon Nanotubes.

Achieving a better control of the nucleation and growth of single-walled carbon nanotubes requires understanding of the changes in the catalyst structure and the interfacial phenomena occurring at the solid surface and the gaseous phase from the early stages of the synthesis process. Carbon nanotubes produced by chemical vapor deposition typically use carbon-philic metal catalysts such as Fe, Ni, and Co, in which both surface C and dissolved C atoms contribute to the nanotube formation. We use density functional theory to investigate the interactions of Rh, a noble metal, with carbon both as individual atoms gradually deposited on the catalyst surface from the precursor gas decomposition and as a nucleating seed adhered to the catalyst. Adsorption and limited dissolution of carbon atoms in the subsurface are found to be favorable in unsupported clusters of various sizes (Rh38, Rh55, and Rh68) and in Rh32 clusters supported on MgO(100) and MgO(111) surfaces. Changes in solubility, electron density transfer, and interactions of the Rh clusters with the support and the nascent nanotube are explored for increasing contents of carbon adsorbed on or dissolved inside the particles. The adhesion energy of small Rh38 clusters on the different MgO surfaces studied can differ by as much as 1 eV compared with the same-sized Rh2C particles. Also, the adhesion of graphene differs on the Rh particles by as much as 5.7 eV with respect to Rh2C supported nanoparticles. This demonstrates the influence that the presence of dissolved carbon can have on the catalyst interactions with the support and nucleating nanotube. A discussion on how such factors affect the lattice and electronic structure of the catalyst particles is presented in the interest of obtaining insight that will allow the design of improved catalysts for controlled nanotube synthesis.

Reduction of Electrolyte Components on a Coated Si Anode of Lithium-Ion Batteries.

Surface modification of Si anodes in Li-ion batteries by deposition of a thin alucone coating has demonstrated an effective way to help maintain a stable anode/electrolyte interface and good battery performance. In this work, we investigate the interactions and reactivity of the film with electrolyte components using ab initio molecular dynamics simulations. Adsorption of solvent molecules (ethylene carbonate, EC) and salt (LiPF6) and reduction by two mechanisms depending on the Li content of the film (yielding open EC adsorbed on the film or C2H4 + CO32-) take place near the film/electrolyte and film/anode interfaces. Reaction products incorporate into the structure of the film and create a new kind of solid-electrolyte interphase layer.

Structure and dynamics of metallic and carburized catalytic Ni nanoparticles: effects on growth of single-walled carbon nanotubes.

Understanding the evolution of the catalyst structure and interactions with the nascent nanotube under typical chemical vapor deposition (CVD) conditions for the synthesis of single-walled carbon nanotubes is an essential step to discover a way to guide growth toward desired chiralities. We use density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations on model metallic and carburized Ni clusters to explore changes in the fundamental features of the nanocatalyst: geometric and electronic structure, dynamics and stability of the carburized nanocatalyst, and interactions with nascent nanotube caps at two different temperatures (750 and 1000 K) and different carbon composition ratios. This allows us to gain insight about the evolution of these aspects during the pre-growth and growth stages of CVD synthesis of single-walled carbon nanotubes and their implications for reactivity and control of the nanotube structure.

Nanocatalyst shape and composition during nucleation of single-walled carbon nanotubes.

The dynamic evolution of nanocatalyst particle shape and carbon composition during the initial stages of single-walled carbon nanotube growth by chemical vapor deposition synthesis is investigated. Classical reactive and ab initio molecular dynamics simulations are used, along with environmental transmission electron microscope video imaging analyses. A clear migration of carbon is detected from the nanocatalyst/substrate interface, leading to a carbon gradient showing enrichment of the nanocatalyst layers in the immediate vicinity of the contact layer. However, as the metal nanocatalyst particle becomes saturated with carbon, a dynamic equilibrium is established, with carbon precipitating on the surface and nucleating a carbon cap that is the precursor of nanotube growth. A carbon composition profile decreasing towards the nanoparticle top is clearly revealed by the computational and experimental results that show a negligible amount of carbon in the nanoparticle region in contact with the nucleating cap. The carbon composition profile inside the nanoparticle is accompanied by a well-defined shape evolution of the nanocatalyst driven by the various opposing forces acting upon it both from the substrate and from the nascent carbon nanostructure. This new understanding suggests that tuning the nanoparticle/substrate interaction would provide unique ways of controlling the nanotube synthesis.

Nucleation of graphene and its conversion to single-walled carbon nanotubes.

We use an environmental transmission electron microscope to record atomic-scale movies showing how carbon atoms assemble together on a catalyst nanoparticle to form a graphene sheet that progressively lifts-off to convert into a nanotube. Time-resolved observations combined with theoretical calculations confirm that some nanoparticle facets act like a vice-grip for graphene, offering anchoring sites, while other facets allow the graphene to lift-off, which is the essential step to convert into a nanotube.

Necrotic mature ovarian teratoma associated with anti-N-methyl-D-aspartate receptor encephalitis.

A 20-year-old female with a diagnosis of autoimmune encephalitis against N-methyl-D-aspartate receptor was found to have a 13 mm teratoma in the left ovary. The tumor had undergone massive coagulative necrosis within a normal ovary, a previously unreported feature. Necrosis of a mature cystic teratoma is very rare in the absence of ovarian torsion. It is proposed that necrosis may have induced a massive liberation of neuronal antigens. The vast majority of the tumors associated with this newly described condition are ovarian teratomas containing neural tissues. In this paper, we review their different histopathological aspects that may explain the relative incidence of various tumor types associated to this form of encephalitis. Anti N-methyl-D-aspartate receptor encephalitis has now become the most frequent autoimmune disorder associated with ovarian teratoma.