Nanoparticles of [Fe(NH2‐trz)3]Br2⋅3 H2O (NH2‐trz=2‐Amino‐1,2,4‐triazole) Prepared by the Reverse Micelle Technique: Influence of Particle and Coherent Domain Sizes on Spin‐Crossover Properties

By changing the surfactant/water ratio , nanoparticles of the iron(II) spin crossover material, [Fe(NH₂‐trz)₃]Br₂ ? 3 H₂O (with NH₂‐trz=4‐amino‐1,2,4‐triazole), have been synthesised from 1 μm down to 30 nm (see figure). Magnetic and reflectivity experiments indicate that the critical size for observing a thermal hysteresis in this 1D polymer family is around 50 nm, and powder X‐ray diffraction shows that particles of about 30 nm are constituted by about one coherent domain.

     

Time for telling stories: narrative thinking with dynamic geometry

In his work on human cognition, Bruner (The culture of education, Harvard University Press, Cambridge, 1996) distinguishes between narrative and paradigmatic modes of thinking. While the latter is closely associated with mathematics, Bruner’s writings suggest that the former contributes non-trivially to the learning of mathematics. In this paper, we argue that the very nature of dynamic mathematical representations—being intrinsically temporal, occurring over time—offer very different opportunities for narrative thinking than do the static diagrams and pictures traditionally available to learners. Using examples from our research, we analyse these opportunities both in terms of their potential for enhancing understanding and for their relation to the kind of paradigmatic thinking that usually constitutes mathematical knowledge.     

Atomic dynamics of the α-(Al,Si)CuFe alloy: A crystalline approximant of a quasicrystal...

The atomic dynamics of the Al_0.550Si_0.070Cu_0.255Fe_0.125 alloy with the structure that approximates the structure of an icosahedral quasicrystal with a similar chemical composition has been investigated using inelastic neutron scattering. The partial vibrational spectra of copper, iron, and aluminum atoms and the total spectrum of thermal vibrations of the compound have been directly reconstructed from the experimental data for the first time. A combined analysis of the results obtained and the data on the atomic dynamics of the i-AlCuFe icosahedral quasicrystal has been performed.     

Perfluorinated surfactants as model charged systems for understanding the effect of confinement on proton transport and water mobility in fuel cell membranes. A study by QENS

We have investigated the dynamical properties of water confined in mesomorphous phases of perfluorinated sulfonic surfactants. These systems mimic the physico-chemical properties of the perfluorinated Nafion membranes which are used as electrolyte in fuel cells. As the surfactants offer the advantage to self-assemble in well defined organized phases (such as hexagonal and lamellar phases), they could be used as model charged systems to understand the structure-transport relationship in complex real materials. Indeed, the geometry as well as the typical confinement size can be easily controlled and tuned through water concentration and temperature. A QENS study of hexagonal and lamellar phases has been performed on both time-of-flight and backscattering spectrometers to cover a dynamic range from picoseconds to nanoseconds. Analysis of the data with localized translational diffusion models shows the existence of a strong confinement effect that depends on the geometry. Typical confinement sizes and diffusion coefficients can be extracted from the QENS analysis and compared to the Nafion membrane.     

Effects of Ulva sp. Extracts on the Growth,Biofilm Production,and Virulence of Skin Bacteria Microbiota: Staphylococcus aureus,Staphylococcus epidermidis,and Cutibacterium acnes Strains

Ulva sp. is known to be a source of bioactive compounds such as ulvans, but to date, their biological activity on skin commensal and/or opportunistic pathogen bacteria has not been reported. In this study, the effects of poly- and oligosaccharide fractions produced by enzyme-assisted extraction and depolymerization were investigated, for the first time in vitro, on cutaneous bacteria: Staphylococcus aureus, Staphylococcus epidermidis, and Cutibacterium acnes. At 1000 μg/mL, poly- and oligosaccharide fractions did not affect the growth of the bacteria regarding their generation time. Polysaccharide Ulva sp. fractions at 1000 μg/mL did not alter the bacterial biofilm formation, while oligosaccharide fractions modified S. epidermidis and C. acnes biofilm structures. None of the fractions at 1000 μg/mL significantly modified the cytotoxic potential of S. epidermidis and S. aureus towards keratinocytes. However, poly- and oligosaccharide fractions at 1000 μg/mL induced a decrease in the inflammatory potential of both acneic and non-acneic C. acnes strains on keratinocytes of up to 39.8%; the strongest and most significant effect occurred when the bacteria were grown in the presence of polysaccharide fractions. Our research shows that poly- and oligosaccharide Ulva sp. fractions present notable biological activities on cutaneous bacteria, especially towards C. acnes acneic and non-acneic strains, which supports their potential use for dermo-cosmetic applications.     

Optimization of preparation of thermally stable cellulose nanofibrils via heat‐induced conversion of ionic bonds to amide bonds

Improving the thermal stability of nanocelluloses is important for practical applications such as melt compounded nanocellulose‐reinforced polymer composites and flexible substrates for nanocellulose‐containing electronic devices. Here, we report optimum conditions for a straightforward surface modification strategy for improving the thermal stability of 2,2,6,6‐tetramethypiperidine‐1‐oxyl (TEMPO)‐oxidized cellulose nanofibrils (TOCNs); the heat‐induced conversion of TOCN alkyl ammonium carboxylates to amides. Different amine‐terminated compounds (R‐NH₂) were grafted onto the surface of TOCNs under aqueous conditions. The influences of R‐NH₂ molecular weight, R‐NH₂/TOCN‐COOH molar ratio, and thermal stability of R‐NH₂ on the properties of the grafted TOCN films were investigated through infrared spectroscopy and thermogravimetric analysis. For maximum thermal improvement of up to 90 °C, complete ionic bonding of TOCN carboxy groups with R‐NH₂ was required, as well as proper selection of the R‐NH₂ compound. A controlled heating process was also needed to achieve effective ionic‐to‐amide bond conversion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1750–1756     

Donor/Acceptor‐Stabilized 1‐Silaketene: Reversible [2+2] Cycloaddition with Pyridine and Evolution by an Olefin Metathesis Reaction

The reaction of silacyclopropylidene 1 with benzaldehyde generates a 1‐silaketene complex 2 by a formal atomic silicon insertion into the C=O bond of the aldehyde. The highly reactive 1‐silaketene 2 undergoes a reversible [2+2] cycloaddition with pyridine to give sila‐β‐lactam 3 . Of particular interest, in the presence of 4‐dimethylaminopyridine (DMAP), 1‐silaketene complex 2 evolves through an intramolecular olefin metathesis reaction, generating a new 1‐silaketene complex 8 and cis‐stilbene. Theoretical studies suggest that the reaction proceeds through the formation of a transient silacyclobutanone, a four‐membered‐ring intermediate, similar to that proposed by Chauvin and co‐workers for the transition‐metal‐based olefin metathesis.