Pyrene‐Based Dyad and Triad Leading to a Reversible Chemical and Redox Optical and Magnetic Switch

Two new pyrene–polychlorotriphenylmethyl (PTM) dyads and triads have been synthesized and characterized by optical, magnetic, and electrochemical methods. The interplay between the different electronic states of the PTM moiety in the dyads and triads and the optical and magnetic properties of the molecules have been studied. The electronic spectra of the radicals 5 ^. and 6 ^. show the intramolecular charge‐transfer transition at around 700 nm due to the acceptor character of the PTM radical. In the diamagnetic protonated derivatives 3 and 4 the fluorescence due to the pyrene is maintained, whereas in the radicals 5 ^. and 6 ^. and the corresponding anions 5 ^? and 6 ^? there is a clear quenching of the fluorescence, which is more efficient in the case of radicals. The redox activity of PTM radicals that are easily reduced to the corresponding carbanion has been exploited to fabricate electrochemical switches with optical and magnetic response.     

Oxidative homocoupling of arylboronic acids catalyzed by a 4‐aminoantipyrine–Pd(II)complex

A one‐step synthesis of symmetric biaryls is reported under very mild conditions via the homocoupling reaction of substituted arylboronic acids using an air‐ and moisture‐stable 4‐aminoantipyrine–Pd(II) complex as catalyst. The reaction is conducted at a low catalyst loading of 0.1 mol% at room temperature in methanol in the presence of K₂CO₃ as the base and KMnO₄ as the oxidant. The catalytic methodology is shown to be compatible with diverse functional groups and affords the desired biphenyls in good to excellent yields. Copyright © 2015 John Wiley & Sons, Ltd.     

A highly accurate GPU Lattice Boltzmann method with directional interpolation for the probability distribution functions

In this article, a highly accurate and graphics processing unit (GPU)-accelerated Lattice Boltzmann Method (LBM) is presented. The methodology is derived from a combination of conventional and recent LBM algorithms, mainly focusing on reducing the computational time, memory allocation, and complexity of existing algorithms. The general implementation focuses on accelerating the overall methodology using GPGPU technology based on Compute Shaders from OpenGL and avoids the storage of the distribution function components to reduce the memory allocation size. Furthermore, an efficient spatial interpolation of the probability distribution function components is described, based on a directional interpolation, without unnecessary control points for the reconstruction of virtual nodes data. The present methodology, tested for spatial accuracy via two- and three-dimensional Lid-Driven Cavity benchmark cases, shows excellent agreement with the results reported in the literature. Additionally, time efficiency is analyzed by comparing different configurations for the construction of virtual streaming points.     

Conceptual model of coalescence and break-up in the presence of external agitation

A Markovian probabilistic cellular automaton with the capability to capture the essential phenomenology of coalescence and break-up processes in the presence of external agitation is introduced. The existence of homogeneous stationary states of the model which admit large cluster formation for a range of agitation speeds is analytically predicted by mean field calculations. Through mean field analysis it is possible to obtain formulas that link experimental and model parameters on the base of simple measurable quantities. In this way, the experimental conditions for which a desirable stationary particle size distribution should be expected can be derived.     

Light-scattering methods for modelling algal particles as a collection of coated and/or nonspherical scatterers

Ocean reflectance or ocean colour measurements are an important tool for oceanographic studies of phytoplankton dynamics. Theoretical models based on homogeneous, spherical particles underestimate algal backscattering and thus reflectance values. It is our understanding that more advanced light-scattering methods must be employed, both for refractive index retrieval (Mie, Aden–Kerker) with inverse models, and for backscattering calculations (Extended Boundary Condition Method, EBCM). The measured optical properties of a monospecific bloom of the marine brown tide pelagophyte Aureococcus anophagefferens are used to compare the effects of assuming various simulated particle geometries. Computational results from polydisperse, coated spherical particles show results that compare better to experimental reflectance values than calculations based on homogeneous spheres. No noticeable change in simulated reflectance values is observed when a randomly oriented coated spheroidal (rather than spherical) geometry is assumed for the particle population. Our results suggest that a layered spherical geometry, based on Aden–Kerker theory, can adequately reproduce experimentally determined light-scattering properties even supposedly shape-sensitive properties such as the backscattering coefficient.     

Turbulent drag reduction by spanwise wall oscillations

In the present work a technique is numerically investigated, which is aimed at reducing the friction drag in turbulent boundary layers and channel flows. A cyclic spanwise oscillation of the wall with a proper frequency and amplitude is imposed, allowing a reduction of the turbulent drag of up to 40%. The present work is based on the numerical simulation of the Navier-Stokes equations in the simple geometry of a plane channel flow. The frequency of the oscillations is kept fixed at the most efficient value determined in previous studies, while the choice of the best value for the amplitude of the oscillations is evaluated not only in terms of friction reduction, but also by taking into consideration the overall energy balance and the power spent for the motion of the wall. The analysis of turbulence statistics allows to shed some light on the way oscillations interact with wall turbulence, as illustrated by visual inspection of some instantaneous flow fields. Finally, a simple explanation is proposed for this interaction, which leads to a rough estimate of the most efficient value for the frequency of the oscillations.     

Calix[4]arene‐Functionalised Silver Nanoparticles as Hosts for Pyridinium‐Loaded Gold Nanoparticles as Guests

A series of lipophilic gold nanoparticles (AuNPs) circa 5 nm in diameter and having a mixed organic layer consisting of 1‐dodecanethiol and 1‐(11‐mercaptoundecyl) pyridinium bromide was synthesised by reacting tetraoctylammonium bromide stabilised AuNPs in toluene with different mixtures of the two thiolate ligands. A bidentate ω‐alkylthiolate calix[4]arene derivative was instead used as a functional protecting layer on AgNPs of approximately 3 nm. The functionalised nanoparticles were characterised by transmission electron microscopy (TEM), and by UV/Vis and X‐ray photoelectron spectroscopy (XPS). Recognition of the pyridinium moieties loaded on the AuNPs by the calix[4]arene units immobilised on the AgNPs was demonstrated in solution of weakly polar solvents by UV/Vis titrations and DLS measurements. The extent of Au‐AgNPs aggregation, shown through the low‐energy shift of their surface plasmon bands (SPB), was strongly dependent on the loading of the pyridinium moieties present in the organic layer of the AuNPs. Extensive aggregation between dodecanethiol‐capped AuNPs and the Ag calix[4]arene‐functionalised NPs was also promoted by the action of a simple N‐octyl pyridinium difunctional supramolecular linker. This linker can interdigitate through its long fatty tail in the organic layer of the dodecanethiol‐capped AuNPs, and simultaneously interact through its pyridinium moiety with the calix[4]arene units at the surface of the modified AgNPs.     

Temperature-dependent optical band structure and defect mode in a one-dimensional photonic liquid crystal

We analysed the propagation of an electromagnetic wave in a one-dimensional periodic system composed of a finite set of E7 liquid crystal mixture slabs in a twisted configuration alternated by homogeneous and isotropic dielectric layers. For different incident angles of the circularly polarised wave, we studied the optical band structure for reflectance and transmittance considering that the dielectric matrix of the device depends on temperature and wavelength. We demonstrated that the position of the band can be moved from visible to short-infrared spectrum region by increasing the thickness of the layers. We found that for a fixed incident angle, the band spectrum shifts towards the short-wavelength region as the temperature gets increasing, whereas, for a constant temperature, such a spectrum moves towards larger frequencies as the incident angle increases. We show that when one of the homogeneous and isotropic slabs has a different size compared with the remaining ones, a defect mode is induced in the band structure whose frequency can be thermally tuned.     

Integration of Mesoporous Bioactive Glass Nanoparticles and Curcumin into PHBV Microspheres as Biocompatible Composite for Drug Delivery Applications

Bioactive glasses (BGs) are being increasingly considered for biomedical applications. One convenient approach to utilize BGs in tissue engineering and drug delivery involves their combination with organic biomaterials in order to form composites with enhanced biocompatibility and biodegradability. In this work, mesoporous bioactive glass nanoparticles (MBGN) have been merged with polyhydroxyalkanoate microspheres with the purpose to develop drug carriers. The composite carriers (microspheres) were loaded with curcumin as a model drug. The toxicity and delivery rate of composite microspheres were tested in vitro, reaching a curcumin loading efficiency of over 90% and an improving of biocompatibility of different concentrations of MBGN due to its administrations through the composite. The composite microspheres were tested in terms of controlled release, biocompatibility and bioactivity. Our results demonstrate that the composite microspheres can be potentially used in biomedicine due to their dual effects: bioactivity (due to the presence of MBGN) and curcumin release capability.