Über Oxocuprate. XVII. Zur Kenntnis von Ca2CuO2Cl2 und Ca2CuO2Br2

About Oxocuprates. XVII. Ca₂CuO₂Cl₂ and Ca₂CuO₂Br₂ The so far unkown compounds Ca₂CuO₂Cl₂ (I) and Ca₂CuO₂Br₂ (II) were prepared and examined by X-ray single crystal methods. They are isotypic with Sr₂CuO₂Cl₂ ((I) a = 386.6, c = 1 497.5; (II) a = 387.5, c = 1 726.4 pm, space group d–I4/mmm). A discussion of the distances in respect to the structure shows that the stretching of octahedron around Cu²⁺ is no evidence for a Jahn-Teller-effect.     

Structure, Stoichiometry, and Phase Purity of Calcium Substituted Lanthanum Manganite Powders

Calcium-doped lanthanum manganite La_1−xCa_xMnO₃, synthesized by the glycine/nitrate method, was characterized by high resolution synchrotron X-ray powder diffraction, electron diffraction, and infrared spectroscopy. A strong correlation was observed between the cooling rate from the calcination temperature and the powder quality, indicating the importance of a homogeneous oxygen stoichiometry. The structure refinement reveals that La_1−xCa_xMnO₃withx=0.2, 0.3, 0.4, and 0.6 has orthorhombic symmetry with space groupPnma. The MnO₆octahedra are fairly symmetrical, but the octahedra are tilted about 20° relative to the ideal perovskite structure. Infrared spectroscopy revealed that only the O–Mn–O bending mode is significantly influenced by the substitution of La with Ca. In La_0.8Ca_0.2MnO₃we found diffraction evidence of a superstructure in domains in some of the grains. We propose that the superstructure in La_0.8Ca_0.2MnO₃is due to ordering of Ca²⁺ions onA(La³⁺) sites in the perovskiteABO₃structure.     

New pi-complexation adsorbents for propane-propylene separation

New adsorbents were prepared and tested for the separation of propane-propylene mixtures by adsorption. The ordered mesoporous material SBA-15 was used as the starting material for silver-ion deposition for pi-complexation with propylene. Two different loadings of silver were evaluated. Adsorption equilibrium and kinetic measurements of propane and propylene in the matrix (pure SBA-15) and the silver-modified adsorbents were performed at 323, 343, and 373 K. In this temperature range, the selectivity of propylene in one of the materials (Ag/SBA-15 = 0.5) is in the range 13-22 because the amount of propane adsorbed is very small, 0.095 mmol/g of propane versus 1.12 mmol/g of propylene at 100 kPa and 343 K. The diffusivity of both hydrocarbons is not seriously affected by the introduction of silver into the mesoporous structure.     

Development of a rapid method based on solid-phase extraction and liquid chromatography with ultraviolet absorbance detection for the determination of polyphenols in alcohol-free beers

An analytical method based on solid-phase extraction (SPE) and followed by liquid chromatographic separation and ultraviolet detection (HPLC-UV) is proposed for the determination of 10 phenolic compounds which participate on beer stability and sensory properties in alcohol-free beers. Acetonitrile was found to be the most appropriate solvent for the elution of polyphenolic compounds adsorbed on C18 cartridges. The performance of the method was assessed by the evaluation of parameters such as absolute recovery (generally higher than 60%), repeatability (lower than 10%), linearity (r2 higher than 0.993) and limits of quantitation (ranging from 1 to 37 microg/L); no matrix effects were observed. The polyphenol content of different Spanish alcohol-free beers is presented. Five phenolic compounds such as protocatechuic, p-coumaric, ferulic, caffeic acids, and (+)-catechin were identified at levels lower than 10 mg/L.     

Rapid,metal‐free room temperature vulcanization produces silicone elastomers

Silicone room temperature vulcanization elastomers are usually formed through either a platinum‐catalyzed hydrosilylation or tin‐catalyzed moisture cure. In this article, we show that it is possible to create robust, transparent silicone elastomers without the need for metal catalysts. Hydrogen‐terminated silicone polymers are crosslinked by tri‐ or tetraalkoxysilane crosslinkers in a condensation process catalyzed by the presence of trispentafluorophenylborane catalyst to give elastomers and alkane by‐products. This procedure allows for very fast cure times (< 30 s to a tack free state): the process is more conveniently controlled with the addition of a small amount of solvent. Physical and mechanical properties are readily modified by control of the chain length of the starting polymer, the functionality and nature of the alkoxy group on the crosslinker. Organofunctional groups, useful for further polymer modification, can optionally be incorporated by judicious choice of readily available starting materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Al-K-Auger energy spectra: Probing the electron dynamics in ion-solid interactions

K-Auger electron emission has been investigated for incident electrons and for different types of heavy ions interacting with mono-crystalline aluminum (100) targets at specific kinetic energies of 3 to 5 MeV/u. In an effort to gain a profound knowledge about the ionization and vacancy-decay dynamics for the K-shell in Al, spectra have been measured with different energy resolutions and angular distributions have been taken as well. Here we concentrate on the energy spectra — we identify the measured peak structures and we investigate different line intensities and mean target charge-states quantitatively, in comparison with theoretical results.     

Novel routes to epoxy functionalization of PHA‐based electrospun scaffolds as ways to improve cell adhesion

Straightforward and versatile routes to functionalize the surface of poly(3‐hydroxyalkanoate) (PHA) electrospun fibers for improving cell compatibility are reported under relatively mild conditions. The modification of nanofibrous PHAs is implemented through two different methodologies to introduce epoxy groups on the fiber surface: (1) preliminary chemical conversion of double bonds of unsaturated PHAs into epoxy groups, followed by electrospinning of epoxy‐functionalized PHAs blended with nonfunctionalized PHAs, (2) electrospinning of nonfunctionalized PHAs, followed by glycidyl methacrylate grafting polymerization under UV irradiation. The latter approach offers the advantage to generate a higher density of epoxy groups on the fiber surface. The successful modification is confirmed by ATR‐FTIR, Raman spectroscopy, and TGA measurements. Further, epoxy groups are chemically modified via the attachment of a peptide sequence such as Arg‐Gly‐Asp (RGD), to obtain biomimetic scaffolds. Human mesenchymal stromal cells exhibit a better adhesion on the latter scaffolds than that on nonfunctionalized PHA mats. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 816–824     

Dimorphism SmA-B2 in bent-core mesogens with perfluorinated terminal chains

Several banana-shaped liquid crystal materials with perfluorinated terminal chains have been synthesized. A dimorphism SmA-B₂ was proved by X-ray studies and electro-optical measurements. The unusual ratio d/L (d = layer spacing, L = molecular length) and the unexpected behaviour of the layer spacing at the phase transition SmA > B2 can be interpreted by a change of the packing of the bent molecules.