First principles calculation of L21+A2 coherent equilibria in the Fe–Al–Ti system

By combining first-principles density functional total energy calculations and statistical mechanics the ground state and the phase equilibria at finite temperatures of the ternary system Fe–Al–Ti have been investigated. Total energy calculations have been performed by means of the Wien 2k code to establish the ground state energetic. A cluster expansion method was therewith used to describe solid solutions. At several chosen finite temperatures the cluster variation method in the irregular tetrahedron approximation was employed in order to calculate the iron rich ternary bcc equilibria. It is confirmed that there are two kinds of phase separations of the bcc phase, A2+L2₁ and B2+L2₁.     

Plant-Derived Pesticides as an Alternative to Pest Management and Sustainable Agricultural Production: Prospects,Applications and Challenges

Pests and diseases are responsible for most of the losses related to agricultural crops, either in the field or in storage. Moreover, due to indiscriminate use of synthetic pesticides over the years, several issues have come along, such as pest resistance and contamination of important planet sources, such as water, air and soil. Therefore, in order to improve efficiency of crop production and reduce food crisis in a sustainable manner, while preserving consumer’s health, plant-derived pesticides may be a green alternative to synthetic ones. They are cheap, biodegradable, ecofriendly and act by several mechanisms of action in a more specific way, suggesting that they are less of a hazard to humans and the environment. Natural plant products with bioactivity toward insects include several classes of molecules, for example: terpenes, flavonoids, alkaloids, polyphenols, cyanogenic glucosides, quinones, amides, aldehydes, thiophenes, amino acids, saccharides and polyketides (which is not an exhaustive list of insecticidal substances). In general, those compounds have important ecological activities in nature, such as: antifeedant, attractant, nematicide, fungicide, repellent, insecticide, insect growth regulator and allelopathic agents, acting as a promising source for novel pest control agents or biopesticides. However, several factors appear to limit their commercialization. In this critical review, a compilation of plant-derived metabolites, along with their corresponding toxicology and mechanisms of action, will be approached, as well as the different strategies developed in order to meet the required commercial standards through more efficient methods.     

Microwave irradiation and COMU: a potent combination for solid-phase peptide synthesis

Here we demonstrate the compatibility of Oxyma-based uronium-type coupling reagent COMU with microwave-assisted peptide synthesizers. Consistent with previous reports, COMU displayed higher efficiency than benzotriazole classical immonium salts HATU and HBTU in the demanding synthesis of the Aib derivative of Leu-Enkephalin pentapeptide and did not yield Oxyma-based byproducts. Thus, the combination of microwave irradiation and COMU resulted in a similar performance in considerably shorter time to that achieved by manual synthesis.     

Surface films of short fluorocarbon-hydrocarbon diblocks studied by molecular dynamics simulations: Spontaneous formation of elongated hemimicelles

Using grazing incidence small-angle X-ray scattering (GISAXS), and atomic force microscopy (AFM) it has been recently demonstrated that linear fluorocarbon-hydrocarbon diblocks (FnHm) self-assemble in water/air interfaces forming elongated and circular hemimicelles. Those structures have been observed for diblocks with at least eight fluorinated carbons. Based on the lack of a collapse pressure for F6H16, and due to the fact that no stable surface pressure values are reached under compression, it has been concluded that these molecules do not form stable monolayers. It has been also suggested that F6H16 and shorter diblocks desorb from the water surface under compression. It is not easy to accept that a significant concentration of so hydrophobic molecules can be stable in aqueous solution even when the employed experimental techniques were not able to clearly detect a well defined structure on the interface. In the present work the adsorption and arrangement of F6H16 and F6H10 at the water surface are studied by molecular dynamics (MD) simulations as a function of the available area per molecule. Starting from a random mixture, the spontaneous formation of elongated hemimicelles is observed for both systems when the area per molecule is higher than approximately 50 A(2). For intermediate areas two pseudo-phases, one rich in hydrocarbons and the other with higher fluorocarbon concentration, are formed. For the systems with less than approximately 30 A(2) available per molecule the formation of multilayers is observed. This is the first time that the dynamics and structure of perfluoroalkane (PFA) films, and in particular of hemimicelles on a liquid surface, are observed and characterized at atomic level.     

Weakly driven anomalous diffusion in non-ergodic regime: an analytical solution

We derive the probability density of a diffusion process generated by nonergodic velocity fluctuations in presence of a weak potential, using the Liouville equation approach. The velocity of the diffusing particle undergoes dichotomic fluctuations with a given distribution ψ(τ) of residence times in each velocity state. We obtain analytical solutions for the diffusion process in a generic external potential and for a generic statistics of residence times, including the non-ergodic regime in which the mean residence time diverges. We show that these analytical solutions are in agreement with numerical simulations.     

Graphene functionalisation with a conjugated poly(fluorene) by click coupling: striking electronic properties in solution

Graphene flakes covalently modified with a conjugated polymer, poly[(9,9-dihexylfluorene)-co-alt-(9,9-bis-(6-azidohexyl)fluorene)] (PFA), were efficiently synthesised by a Cu-catalysed Huisgen 1,3-dipolar cycloaddition between alkyne-modified graphene and an azide-functionalised polymer. Two approaches for the modification of graphene with alkyne groups were investigated (coupling with a diazonium salt generated in situ or an amidation reaction) and the optimum conditions determined. The success of the click-coupling approach was confirmed by FTIR, (1)H?NMR, Raman, and X-ray photoelectron spectroscopy (XPS). The absorption and emission spectra of the click product show a strong solvent dependency.