Enantioselective transport by a steroidal guanidinium receptor

The cationic steroidal receptors 9 and 11 have been synthesized from cholic acid 3. Receptor 9 extracts N-acetyl-alpha-amino acids from aqueous media into chloroform with enantioselectivities (L:D) of 7-10:1. The lipophilic variant 11 has been employed for the enantioselective transport of N-acetylphenylalanine, a) through dichloromethane (DCM) and dichloroethane (DCE) bulk liquid membranes (U-tube apparatus), and b) through 2.5% (v/v) octanol/hexane via hollow fibre membrane contactors. Significant enantioselectivities and multiple turnovers were observed for both types of apparatus.     

Modeling nanoparticle uptake and intracellular distribution using stochastic process algebras

Intermolecular energy decomposition analysis (EDA) is reported for the binding of CO₂ with zeolitic imidazole frameworks (ZIF) to provide a molecular level interpretation of the recent capacity and selectivity measurements of several ZIFs and to suggest a theoretical guideline to improve their performance further, using 1?nm size of organic linker fragment of the ZIFs as a target molecule. The EDA suggests that the local electronic interaction of CO₂ and the substituent groups, mainly frozen density and polarization interactions with little charge transfer, is the primary binding interaction, but the electron correlation effects can be equally or more important depending on the binding geometry and functional groups. The present correlated calculations identify the preferred ZIF binding sites for various gases including CO₂ to be mostly near the benzene substituent groups rather than the plane of imidazole rings. We predict that the NH₂-substituted ZIF would have an enhanced capacity of CO₂ as compared to the NO₂-substituted ZIF that was recently synthesized and reported to be one of the materials with the best capacity results along with high gas selectivity. The present calculations may imply that the local functionality of the linking organics, rather than detailed framework structures, may be of primary importance in designing certain high capacity MOF or ZIF materials.     

Smooth driving of M?ssbauer electromechanical transducers

Quality of Mössbauer spectra is strongly related to the performance of source velocity modulator. Traditional electromechanical driving techniques demand hard-edged square or triangular velocity waveforms that introduce long settling times and demand careful driver tuning. For this work, the behavior of commercial velocity transducers and drive units was studied under different working conditions. Different velocity reference waveforms in constant-acceleration, constant-velocity and programmable-velocity techniques were tested. Significant improvement in spectrometer efficiency and accuracy was achieved by replacing triangular and square hard edges with continuous smooth-shaped transitions. A criterion for best waveform selection and synchronization is presented and attainable enhancements are evaluated. In order to fully exploit this driving technique, a compact microprocessor-based architecture is proposed and a suitable data acquisition system implementation is presented. System linearity and efficiency characterization are also shown.     

Fast and reliable determination of antioxidant capacity based on the formation of gold nanoparticles

Microchimica Acta - We demonstrate that the formation of gold nanoparticles (AuNPs) can be exploited in a well-defined and reliable electron-transfer assay for antioxidant capacity (AOxC). The AOxC...     

Phase transition in multiferroic YMnO3 and its solid solution YMn(0.93)Fe(0.07)O3

Ceramics of YMnO₃ and its Fe substituted YMn_(0.93)Fe_(0.07)O₃ solid solution were synthesized by solid state reaction of the oxides at 1200 °C. Hexagonal phase was identified in both cases by X-ray powder diffraction. Rietveld refinement of cell parameters showed an increase of the parameter values for the solid solution. Dielectric permittivity measurements versus temperature showed a phase transition at 655 °C for yttrium manganite, however, for the solid solution no phase transition was detected on heating up to 700 °C. Dielectric loss measurements showed higher slope changes and better defined local maxima for the solid solution than for the pure phase.     

Orientational dependence of the potential of mean force for a discotic liquid crystal near a substrate

In this work we calculate the potential of mean force for a discotic liquid crystal (DLC) confined in a slab geometry. We have set the reaction coordinate as the distance between a DLC test particle with a fixed orientation and a wall with face-on anchoring. Five different orientations of the DLC test particle are explored, which correspond to parallel and perpendicular orientations with regard to the anchoring promoted by the walls, and three intermediate orientations between the parallel and perpendicular configurations. The potential of mean force reflects the strong effect of the system's anisotropy: particles with the wrong orientation are energetically penalised whilst the particles with the correct orientation are favoured.