The anthraquinone profile, antioxidant and antimicrobial activities as well as the total phenol and total flavonoid contents were determined in methanol extracts of the barks of Rhamnus catharticus L. and R. orbiculatus Bornm. The most abundant anthraquinone derivatives in R. catharticus were physcion (67.8%) and emodin (26.2%), while R. orbiculatus contained mostly physcion (81.3%) and chrysophanol (14.6%). R. catharticus displayed better activity in the beta-carotene-linoleic acid assay, as well as chelating activity, whereas its activity in the reducing power assay was significantly lower than that of R. orbiculatus. Both methanol extracts showed antimicrobial activity against all microbial species tested (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, Aspergillus niger, Microsporum gypseum) with MIC values either equal to or lower than 2.50 mg/mL. R. catharticus and R. orbiculatus contained several anthranoid aglycones and their bark extracts demonstrated notable antioxidant and antimicrobial properties. The results obtained indicate the medicinal potential of these two species. 相似文献
The onset of instability in autonomous dynamical systems (ADS) of ordinary differential equations is investigated. Binary, ternary and quaternary ADS are taken into account. The stability frontier of the spectrum is analyzed. Conditions necessary and sufficient for the occurring of Hopf, Hopf–Steady, Double-Hopf and unsteady aperiodic bifurcations—in closed form—and conditions guaranteeing the absence of unsteady bifurcations via symmetrizability, are obtained. The continuous triopoly Cournot game of mathematical economy is taken into account and it is shown that the ternary ADS governing the Nash equilibrium stability, is symmetrizable. The onset of Hopf bifurcations in rotatory thermal hydrodynamics is studied and the Hopf bifurcation number (threshold that the Taylor number crosses at the onset of Hopf bifurcations) is obtained.
1H longitudinal relaxation time profiles (T1) at different proton Larmor frequencies were registered for a solid-state plant tissue by using fast field cycling (FFC) nuclear magnetic resonance (NMR) spectroscopy. T1 distributions were obtained and the curves deconvoluted in order to differentiate among the different T1 components. Among the components, two were assigned to hydrophobic (e.g., fatty acid) and hydrophilic (e.g., saccharide) molecular systems, whereas the others were attributed to bulk and bound water. This paper shows for the first time solid-state FFC-NMR spectroscopy applied to plant tissue and reveals that relaxometry is a very promising technique for studying plant systems. 相似文献
For each admissiblev we exhibit a path designP(v, 3, 1) with a spanning set of minimum cardinality and aP(v, 3, 1) with a scattering set of maximum cardinality. Moreover, we study maximal independent sets (or complete arcs in the geometric terminology) having the minimum number of secants, i.e. sets which are both spanning and scattering, and complete arcs with the maximum number of secants.The research for this paper was supported by MURST and GNSAGA-CNR. 相似文献
Erbium doping of silicon has recently emerged as a promising method to tailor the optical properties of Si towards the achievement of a light emission at 1.54 μm. In this paper we will review our recent work on this subject. In particular a detailed investigation of the non-radiative processes, competing with the radiative emission of Er in Si will be presented. Among these processes, an Auger de-excitation with the energy released to free carriers will be demonstrated to be extremely efficient, with an Auger coefficient CA4.4×10−13 cm3/s. Moreover, at temperatures above 100 K a phonon-assisted back-transfer decay process, characterized by an activation energy of 0.15 eV is seen to set in. This understanding of the physical properties competing with the radiative light emission allowed us to control them and obtain efficient room temperature luminescence. Two examples will be reported. It will be shown that by exciting Er within the depletion region of reverse biased p+–n+ Si diodes in the breakdown regime it is possible to avoid Auger quenching and to achieve high efficiency. Moreover, at the switch off of the diode, when the depletion region shrinks, the excited Er ions become suddenly embedded within the neutral heavily doped region of the device. In this region Auger de-excitation with free carriers sets in and quenches rapidly the luminescence. This allows to modulate the light signal at frequencies as high as a few MHz. Furthermore, the introduction of Er within Si nanocrystals is demonstrated to be a promising way to eliminate back-transfer processes by a widening of the bandgap while maintaining the full advantage of the efficient electron-hole mediated excitation present in Si. These data are presented and future perspective discussed. 相似文献
A mild and improved method for the synthesis of thioethers has been developed. In the presence of cesium carbonate, tetrabutylammonium iodide, and DMF, various alkyl and aryl thiols underwent S-alkylation to afford structurally diverse sulfides in high yield. Unprotected mercaptoalcohols and thioamines reacted chemoselectively at the sulfur moiety exclusively. An example of a one-pot, solid-phase synthesis of a thioether is also described. 相似文献