Exact relativistic models of conformastatic charged dust thick disks

We construct relativistic models of charged dust thick disks for a particular conformastatic spacetime through a Miyamoto–Nagai transformation used in Newtonian gravity to model disk like galaxies. Two simple families of thick disk models and a family of thick annular disks based on the field of an extreme Reissner–Nordström black hole and a Morgan–Morgan-like metric are considered. The electrogeodesic motion of test particles around the structures are analyzed. Also the stability of the particles against radial perturbation is studied using an extension of the Rayleigh criteria of stability of a fluid in rest in a gravitational field. The models built satisfy all the energy conditions.     

Chemoenzymatic Dynamic Kinetic Resolution of Primary Benzylic Amines using Pd0-CalB CLEA as a Biohybrid Catalyst

Herein, we report on the use a biohybrid catalyst consisting of palladium nanoparticles immobilized on cross-linked enzyme aggregates of lipase B of Candida antarctica (CalB CLEA) for the dynamic kinetic resolution (DKR) of benzylic amines. A set of amines were demonstrated to undergo an efficient DKR and the recyclability of the catalysts was studied. Extensive efforts to further elucidate the structure of the catalyst are presented.     

On the Coherent Description of Diffusion‐Influenced Fluorescence Quenching Experiments II: Early Events

In a previous article we showed how to perform and analyze steady‐state and nanosecond time‐resolved experiments on fluorescence quenching by electron transfer in a coherent manner. Now, by making use of a superior time resolution, we explore the first stages of this kind of reaction. The novel information gained enables us to merge the results on the viscosity and the driving‐force dependencies of the reaction rate. A unique set of parameters for a single reaction channel suffices to describe all the results in the frame of differential encounter theory for diffusion‐influenced, bimolecular, remote electron‐transfer reactions. The inclusion of the solvent structure is crucial for the understanding of the reaction kinetics. To the authors’ best knowledge, this is the first time that such a comprehensive set of data has been successfully and jointly explained in the field, with physically sound parameters for electron‐transfer reactions.     

Dielectric anomalous response of water at 60 °C

Recently, the paraelectric response of water was investigated in the range 0–100 °C. It showed an almost perfect Curie–Weiss behaviour up to 60 °C, but a slight change in slope of 1/ε_d versus T at 60 °C was overlooked. In this work, we report optical extinction measurements on metallic (gold and silver) nanoparticles dispersed in water, annealed at various temperatures in the range from 20 to 90 °C. An anomalous response at 60 °C is clearly detectable, which we associate to a subtle structural transformation in the water molecules at that temperature. This water anomaly is also manifested by means of a blue shift in the longitudinal surface plasmon resonance of the metallic nanoparticles for the solutions annealed at temperatures higher than about 60 °C. A reanalysis of 1/ε_d (T) for water in the whole temperature range leads us to conclude that the water molecule undergoes a subtle transformation from a low temperature (0–60 °C) configuration with a dipole moment μ₁ = 2.18 D (close to the molecular dipole moment of ice) to a high temperature (60–100 °C) configuration with μ₂ = 1.87 D (identical to the molecular dipole moment in water vapour).     

Ultrasonic solvent extraction and nonaqueous CE for the determination of herbicide residues in potatoes

In the present work we address the development of a simple and effective method for the determination of triazine herbicide residues in horticultural products by CE in nonaqueous media (NACE). Potato samples were selected as a representative matrix of such foods with a nonfatty content. Isolation of the analytes from the sample matrix was accomplished by extraction with organic solvents, assisted by ultrasound; a clean‐up step of the organic extracts was carried out with SPE, using an Oasis MCX® sorbent to retain the analytes directly from the organic medium. The detection limits achieved in spiked potatoes (1.7–4.0 μg/kg) were lower than the default value of maximum residue level (MRL) established by current EU legislation for pesticide residues in foodstuffs. The results obtained were compared with HPLC in order to evaluate the performance of the NACE procedure.     

Non-destructive method to determine halophenols and haloanisoles in cork stoppers by headspace sorptive extraction

The new solvent-free technique called headspace sorptive extraction (HSSE) was used to determine 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, 2,4,6-tribromoanisole, pentachloroanisole in cork stoppers, without grinding them, as these may be responsible for the cork taint off-flavour in wine. The best HSSE sorption kinetics for the target analytes were obtained after submitting the spiked corks to 100 degrees C for 1h, followed by a 30 min stabilization time at room temperature. The stir bar was desorbed in a thermal desorption system coupled to a gas chromatograph-mass spectrometer. The method proposed showed good linearity over the concentration range tested, 1-70 ngg(-1), and correlation coefficients ranged from 0.90 to 0.99 for all the analytes. The reproducibility and repeatability of the method were estimated between 4.91 and 12.67%. The effect of the different cork matrixes on the extraction recovery of the target compounds was studied, with the natural corks showing the higher recovery percentage in relation to agglomerate ones.