Identificatin and quantiative analysis of amyrins in Humulus lupulus L.

ABSTRACT In the paper, the identification and quantification of α- and β-amyrin in five varieties of Humulus lupulus is described. The plant samples were extracted with ethyl acetate and analyzed using of high performance liquid chromatography (HPLC) with PAD detection. The separation was achieved on RP 18 column, at 2 mL/min flow rate and at temperature of 35°C. Acetonitrile was used as a mobile phase. The established calibration curves and the other validation parameters: linearity (correlation coefficient r > 0.9988) and precision (RSD values ranged from 0.14 to 1.81%) were found to be satisfactory for the proposed method. The content of α- and β-amyrin strongly depended on varieties of H. lupulus and amounted from 72.7 to 232.5 μg/g and from 77.9 to 176.9 μg/g of dry plant material, respectively.

PHOTOLUMINESCENE PROPERTIES AND LOCAL STRUCTURE OF POLYMER-LIKE A-C:H FILMS

In order to understand better the electronic properties of π-bonded materials, some optical and photoluminescence properties of amorphous carbon films have been investigated as a function of film density (0.9 to 1.7 g.cm-3). This study gives an overview of the radiative recombination properties in relation with local structure characterizations (in situ infrared ellipsometry and Raman spectroscopies) for a series of dual-plasma deposited polymer-like a-C:H films. Medium range topology has consequences in the hyperconjugation effects seen on infrared bands, as well as in optical and resonant Raman characteristics. Photoluminescence (PL) excitation spectroscopy reveals resonance features which are attributed to exciton-like electron-hole pairs in close Coulomb interaction. The PL efficiency shows a sharp quenching for densities above 1.3 g.cm -3 where a clear transition also occurs in the Raman "fingerprint". In addition, quantiative analysis of IR ellipsometry and Elastic Recoil Detection give evidence of a strong decrease of both the effective dynamical charge e*(C-H) and the bandwidth of sp 3 C-H vibrations; this is interpreted as being a result of the increase of local strains in the carbon skeleton, meaning that matrix distortions already appear at H content values as high as 46 H at .% due to film densification. An expected consequence is the mixing between π and σ molecular orbitals and the enhancement of the dissociation rate of confined electron-hole pairs. PL quenching would thus result form both a decrease of exciton confinement and an increase of the density of accessible nonradiative centers.

Quantiative analysis of grain boundaries in YBa2Cu3O7-δ using a 20Å high-resolution probe

One challenge for high Tc superconductor research is to overcome the low intergranular transport currents which hinder practical applications. Evidence shows that lattice mismatch at the boundaries contributes to the depletion in charge carriers (holes), while the strain fields surrounding the cores of boundary dislocations suppress the superconducting order parameter. Using high-spatialresolution EDX, EELS and CBED techniques with a 20 Å field emission probe, we studied cation segregation, variations in oxygen/hole content, and lattice parameters at and across grain boundaries for various Σ and near-Σ boundaries in bulk YBa2Cu3O7-δ. The geometry of those arbitrary grain boundaries was modeled using the constrained Coincidence Site Lattice (cCSL) theory, which requires c2/a2 being rational for coincidence boundaries in non-cubic crystals.In this presentation, we report our quantitative and simultaneous measurements of lattice parameters, and of oxygen/hole content at the boundary regions. The oxygen/hole density was quantified by guassian fitting to the observed oxygen K-edge spectra and comparing them with those from the same batch which had undergone oxygen reduction process (Fig.1).