Chiral recognition in aqueous solutions between enantiomeric α-amino acids bearing substituted alkyl chains at 25°C: The peferential configuration model

Calorimetric, densimetric, and nuclear relaxation time measurements were carried out at 25°C on binary and ternary aqueous solutions containing L and D forms of the following amino acids bearing substituted alkyl chains: lysine, glutamine, arginine, asparagine, serine, and homoserine. For three of them (lysine, glutamine, and arginine), very high differences were found between the values of the homochiral and heterochiral pairwise enthalpic interaction coefficients. Volume and spectroscopic data showed that it is possible to detect chiral recognition by techniques other than calorimetric. The role of the zwitterionic interaction and of the substituted side chain is discussed to explain the enhanced chiral recognition of these -aminoacids in respect to those bearing unsubstituted alkyl chains (alanine, -aminobutyric acid, valines and leucines).     

Thermoanalytical and spectroscopic characterization ofβ-cyclodextrin/ketoprofen inclusion complexes

A method to determine the composition and hydration state of the complexes formed in aqueous solution by cyclodextrins (CD) is presented and applied to the -CD/ketoprofen system; it is based on a combination of spectroscopic, calorimetric, and thermogravimetric analyses. The complexes have, on average and per -CD mole, more than eleven water molecules, which are present in completely different bound states.     

Efficient access to 5-substituted thiazoles by a novel metallotropic rearrangement

A novel rearrangement process involving the migration of trimethylstannanyl or trimethylsilanyl groups around the thiazole ring provides access to either 2- or 5-metallated thiazoles by tuning the reaction conditions. The proposed mechanism, based on experimental evidence, is characterized by the catalytic role of thiazole bisadducts as metal-transfer agents.     

Free surface flow impact on a vertical wall: a numerical assessment

The sudden impact of a free surface flow upon a solid wall is a common occurrence in many situations in nature and technology. The design of marine structures is probably the most obvious example, but also river and dam hydraulics as well as the necessity of understanding flood and debris flow-induced damage have led to theoretical and experimental work on the mechanism of fluid slamming loads. This is therefore a very old and rich research field, which has not yet reached full maturity, so that semi-empirical methods in design practice are still the rule in many sectors. Up-to-date CFD technology with both Eulerian and Lagrangian approaches is employed to investigate highly non-stationary fluid impact on a solid wall. The development of the pressure wave produced by the impact is examined as it propagates and interacts with the fluid boundaries, as well as the subsequent build-up of high-pressure gradients of high fluid velocities. The geometry and the velocity field of the problem considered are very simple, but the results seem to provide new insight, in particular, into the connection between phenomena with different timescales.     

Characteristics of a gold-doped electrode for application in high-performance lithium-sulfur battery

Bulk sulfur incorporating 3 wt% gold nano-powder is investigated as possible candidate to maximize the fraction of active material in the Li-S battery cathode.The material is prepared via simple mixing of gold with molten sulfur at 120℃,quenching at room temperature,and grinding.Our comprehensive study reports relevant electrochemical data,advanced X-ray computed tomography(CT)imaging of the positive and negative electrodes,and a thorough structural and morphological characterization of the S:Au 97:3 w/w composite.This cathode exhibits high rate capability within the range from C/10 to 1C,a maximum capacity above 1300 mAh gs^-1,and capacity retention between 85%and 91%after 100 cycles at 1C and C/3 rates.The novel formulation enables a sulfur fraction in the composite cathode film as high as 78 wt%,an active material loading of 5.7 mg cm^-2,and an electrolyte/sulfur(E/S)ratio of 5μL mg^-1,which lead to a maximum areal capacity of 5.4 mAh cm^-2.X-ray CT at the micro-and nanoscale reveals the microstructural features of the positive electrode that favor fast conversion kinetics in the battery.Quantitative analysis of sulfur distribution in the porous cathode displays that electrodeposition during the initial cycle may trigger an activation process in the cell leading to improved performance.Furthermore,the tomography study reveals the characteristics of the lithium anode and the cell separator upon a galvanostatic test prolonged over 300 cycles at a 2C rate.     

Picosecond timescale carrier dynamics of InAs quantum dots: The role of a continuum background

We have investigated the ultrafast carrier dynamics in Molecular Beam Epitaxy (MBE)-grown InAs/InGaAs/GaAs quantum dots emitting at 1.3 μm by means of time resolved photoluminescence upconversion measurements with a time resolution of about 200 fs. The detection energies scan the spectral region from the energy of the quantum dot excitonic transition up to the barrier layer absorption edge. We found, under high excitation intensity, that the intrinsic electronic states are populated mainly by carriers directly captured from the barrier.     

Transitions involving conical magnetic phases in a model with bilinear and biquadratic interactions

In a previous work a model was proposed for the phase transitions of crystals with localized magnetic moments which at low temperature have a “conical” arrangement that at higher T transforms into a more symmetrical structure (depending on the compound) before becoming totally disordered. The model assumes bilinear and biquadratic interactions between magnetic moments up to the fifth neighbours, and for any given T the structure with the least free energy is obtained by a mean-field approximation (MFA). The interaction constants are derived from ab initio   energy calculations. In this work we improve upon that model modifying the MFA in such a way that a continuous (instead of discontinuous) spectrum of excited states is available to the system. In the previous work, which dealt with _LaMn2Ge2${\mathrm{LaMn}}_2{\mathrm{Ge}}_2$ and _LaMn2Si2${\mathrm{LaMn}}_2{\mathrm{Si}}_2$, we found that transitions to different structures can be obtained for increasing T, in good qualitative agreement with experiment. The critical temperatures, however, were exaggeratedly high. With the new MFA we obtain essentially the same behaviour concerning the phase transitions, and critical temperatures much closer to the experimental ones.     

Telescoped,Divergent, Chemoselective C1 and C1‐C1 Homologation of Imine Surrogates: Access to Quaternary Chloro‐ and Halomethyl‐Trifluoromethyl Aziridines

A conceptually novel, high‐yielding, mono‐ or bis‐homologation was realized with lithium halocarbenoids and enables the one‐step, fully chemocontrolled assembly of a new class of quaternary trifluoromethyl aziridines. Trifluoroacetimidoyl chlorides (TFAICs) act as convenient electrophilic platforms, enabling the addition of either one or two homologating elements by simply controlling the stoichiometry of the process. Mechanistic studies highlighted that the homologation event, carried out with two different carbenoids (LiCH₂Cl and LiCH₂F), leads to fluoromethyl analogues in which the first nucleophile is employed for constructing the cycle and the second for decorating the resulting molecular architecture.