10,829 research outputs found
Redox thermodynamics of mutant forms of the rubredoxin from Clostridiumpasteurianum: identification of a stable Fe-III(S-Cys)(3)(OH) centre in the C6S mutant
No full textRedox thermodynamic data provide a detailed insight into control of the reduction potential E-o' of the [Fe(S-Cys)(4)] site in rubredoxin. Mutant forms were studied in which specific structural changes were made in both the primary and secondary coordination spheres. Those changes have been probed by resonance Raman spectroscopy. The decrease of similar to 200mV in E-o' observed for the [Fe(S-Cys)(3)(O-Ser)](-/2-) couples in the surface ligand mutants C9S and S42S is essentially enthalpic in origin and associated with the substitution of ligand thiolate by ligand elate. However, the pH dependence of the potentials below characteristic pK(a)(red)approximate to7 is an entropic contribution, plausibly associated with increased conformational flexibility induced by a longer Fe-II-O(H)-Ser bond in the reduced form. The presence of a second surface Ser ligand in the new double mutant protein C9S/C42S affects the enthalpic term primarily for pH>pK(a)(red)greater than or equal to9.3, but for pHpK(a)similar to9: [Fe-III(S-Cys)(3)(OH)](-) + e(-) --> [Fe-II(S-Cys)(3)(OH>)](2-) pH [Fe-II(S-Cys)(3)(OH2)](-)
Advances in Azorella glabra Wedd. Extract research: In vitro antioxidant activity, antiproliferative effects on acute myeloid leukemia cells and bioactive compound characterization
No full textAzorella glabra Wedd. (AG) is traditionally used to treat gonorrhea or kidney's problems. The antioxidant, antidiabetic, anticholinesterase and in vitro antitumor activities of AG extracts were recently reported. The aim of this work was to investigate anti-leukemic properties of AG chloroform fraction (AG CHCl3) and of its ten sub-fractions (I-X) and to identify their possible bioactive compounds. We determined their in vitro antioxidant activity using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), nitric oxide (NO) and superoxide anion (SO) assays, and their phytochemical profile by spectrophotometric and LC-MS/MS techniques. I-X action on two acute myeloid leukemia (AML) cell lines viability, apoptosis and cell cycle were evaluated by MTS, western blotting and cytofluorimetric assays. Different polyphenol, flavonoid and terpenoid amount, and antioxidant activity were found among all samples. Most of I-X induced a dose/time dependent reduction of cell viability higher than parent extract. IV and VI sub-fractions showed highest cytotoxic activity and, of note, a negligible reduction of healthy cell viability. They activated intrinsic apoptotic pathway, induced a G0/G1 block in leukemic cells and, interestingly, led to apoptosis in patient AML cells. These activities could be due to mulinic acid or azorellane terpenoids and their derivatives, tentatively identified in both IV and VI. In conclusion, our data suggest AG plant as a source of potential anti-AML agents
Antioxidant activity and phytochemical characterization of senecio clivicolus wedd
No full textAntioxidant phytochemicals play a key role in oxidative stress control and in the prevention of related disorders, such as premature aging, degenerative diseases, diabetes, and cancer. The aim of this study was to investigate the potential antioxidant activity and the phytochemical profile of Senecio clivicolus Wedd., a perennial shrub, belonging to the Asteraceae family. Despite the wide interest of this family, this specie has not been investigated yet. S. clivicolus aerial parts were extracted with 96% ethanol. Then, the ethanol extract was fractionated by liquid/liquid extraction using an increasing solvents polarity. Total polyphenol and terpenoid contents were measured. Moreover, the antioxidant activity was evaluated by six different complementary in vitro assays. The Relative Antioxidant Capacity Index (RACI) was used to compare data obtained by different tests. The sample showing the highest RACI was subjected to characterization and quantitation of its phenolic composition using LC-MS/MS analysis. The ethyl acetate fraction, investigated by LC-MS/MS analysis, showed 30 compounds, most of them are chlorogenic acid and flavonoid derivatives. To the best of our knowledge, this is the first report about the evaluation of antioxidant activity and phytochemical profile of S. clivicolus, underlying the importance of this species as a source of health-promoting phytochemicals
Polarization dependence of the light coupling to surface plasmons in an Ag nanoparticle & Ag nanowire system
No full textPolarization dependence of the coupling of excitation light to surface plasmon polaritons (SPPs) was investigated in a Ag nanoparticle-nanowire waveguide system (a Ag nanoparticle attached to a Ag nanowire). It was found that under the illumination of excitation light on the nanoparticle-nanowire junction, the coupling efficiency of light to SPPs depends on the polarization of the excitation light. Theoretical simulations revealed that it is the local near-field coupling between the nanoparticle and the nanowire that enhances the incident light to excite the nanowire SPPs. Because the shapes of the Ag nanoparticles differ, the local field intensity, and thus the excitement of the nanowire SPPs, vary with the polarization of the excitation light.Physics, MultidisciplinarySCI(E)EI中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)[email protected]
Effects of shell thickness on the thermal stability of Cu-Ag core-shell nanoparticles: A molecular dynamics study
No full textCu-Ag core-shell (CS) nanoparticle (NP) is considered as a cost-effective alternative material to nano silver sintering material in die attachment application. To further reduce the cost, the thickness of the Ag shell can be adjusted. Whereas the shell thickness will also affect the thermal stability of the Cu-Ag CSNPs. In this study, molecular dynamics simulation was applied to study the thickness effect on the thermal behavior of Cu-Ag CSNPs. The melting points of CSNPs and Pure NPs can be determined by the evolutions of Potential Energy (PE), and the Lindemann index (LI) of the system. The results indicated that the melting points of CS NPs were lower than monometallic NP and the melting point of CS NP is influenced by the size of the Cu core and the number of lattice mismatches. Moreover, the distribution of atoms’ LI showed that the premelting point is independent of shell thickness. However, the fraction of atoms that occurred premelting is increased with the decrease of the shell thickness. Otherwise, we also simulated the sintering process of double CS NPs with equal size.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Voltammetric Detection of Urea on an Ag-Modified Zeolite- Expanded Graphite-Epoxy Composite Electrode
No full textIn this paper, a modified expanded graphite composite electrode based on natural zeolitic volcanic tuff modified with silver (EG-Ag-Z-Epoxy) was developed. Cyclic voltammetry measurements revealed a reasonably fast electron transfer and a good stability of the electrode in 0.1 M NaOH supporting electrolyte. This modified electrode exhibited moderate electrocatalytic effect towards urea oxidation, allowing its determination in aqueous solution. The linear dependence of the current versus urea concentration was reached using square-wave voltammetry in the concentrations range of urea between 0.2 to 1.4 mM, with a relatively low limit of detection of 0.05 mM. A moderate enhancement of electroanalytical sensitivity for the determination of urea at EG-Ag-Z-Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric/amperometric quantification.ChemE/Chemical EngineeringApplied Science
Ore mineralogy and trace element (re)distribution at the metamorphosed Lappberget Zn-Pb-Ag-(Cu-Au) deposit, Garpenberg, Sweden
No full textQualitative and quantitative mineralogical and textural investigations were undertaken for the different sulfide minerals in the 1.89 Ga Lappberget deposit, with a focus on sphalerite and pyrite. Three sphalerite types were identified and associated with: (1) main massive sulfide mineralization, (2) Fe-Mn skarn ore, and (3) Ag-rich fissure veins. Sphalerite-1 contained a relatively higher amount of trace elements (Fe, Co, Ge, Cu, Sn, and Au) but is lower in Mn/Fe, Ga, and Hg compared to sphalerite-2. Evidence of tectono-metamorphic modification of sulfides is observed throughout the deposit, such as the formation of growth twins and deformation twins in sulfides, the development of high-angled triple-point junctions in recrystallized pyrite and sphalerite, and the formation of â??ball oreâ?? or â??durchbewegungâ?? textures within mineralized shear zones. The recrystallization of pyrite and galena may have led to the re-distribution of fluid-mobile elements (As, Cu, Zn, Pb, Ag, and Au), some of which were deposited in discordant Ag-rich fissure veins peripheral to the main massive sulfide lenses. Trace element signatures of sulfides in Lappberget are compatible with the other metamorphosed and deformed, subseafloor volcanogenic carbonate replacement (SVALS)-type deposits in the Bergslagen mining district. © 2021 The Author(s)</p
Ore mineralogy and trace element (re)distribution at the metamorphosed Lappberget Zn-Pb-Ag-(Cu-Au) deposit, Garpenberg, Sweden
No full textQualitative and quantitative mineralogical and textural investigations were undertaken for the different sulfide minerals in the 1.89 Ga Lappberget deposit, with a focus on sphalerite and pyrite. Three sphalerite types were identified and associated with: (1) main massive sulfide mineralization, (2) Fe-Mn skarn ore, and (3) Ag-rich fissure veins. Sphalerite-1 contained a relatively higher amount of trace elements (Fe, Co, Ge, Cu, Sn, and Au) but is lower in Mn/Fe, Ga, and Hg compared to sphalerite-2. Evidence of tectono-metamorphic modification of sulfides is observed throughout the deposit, such as the formation of growth twins and deformation twins in sulfides, the development of high-angled triple-point junctions in recrystallized pyrite and sphalerite, and the formation of â??ball oreâ?? or â??durchbewegungâ?? textures within mineralized shear zones. The recrystallization of pyrite and galena may have led to the re-distribution of fluid-mobile elements (As, Cu, Zn, Pb, Ag, and Au), some of which were deposited in discordant Ag-rich fissure veins peripheral to the main massive sulfide lenses. Trace element signatures of sulfides in Lappberget are compatible with the other metamorphosed and deformed, subseafloor volcanogenic carbonate replacement (SVALS)-type deposits in the Bergslagen mining district. © 2021 The Author(s)</p
Advances in Azorella glabra Wedd. Extract Research: In Vitro Antioxidant Activity, Antiproliferative Effects on Acute Myeloid Leukemia Cells and Bioactive Compound Characterization
No full textAzorella glabra Wedd. (AG) is traditionally used to treat gonorrhea or kidney’s problems. The antioxidant, antidiabetic, anticholinesterase and in vitro antitumor activities of AG extracts were recently reported. The aim of this work was to investigate anti-leukemic properties of AG chloroform fraction (AG CHCl3) and of its ten sub-fractions (I-X) and to identify their possible bioactive compounds. We determined their in vitro antioxidant activity using 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), nitric oxide (NO) and superoxide anion (SO) assays, and their phytochemical profile by spectrophotometric and LC-MS/MS techniques. I-X action on two acute myeloid leukemia (AML) cell lines viability, apoptosis and cell cycle were evaluated by MTS, western blotting and cytofluorimetric assays. Different polyphenol, flavonoid and terpenoid amount, and antioxidant activity were found among all samples. Most of I-X induced a dose/time dependent reduction of cell viability higher than parent extract. IV and VI sub-fractions showed highest cytotoxic activity and, of note, a negligible reduction of healthy cell viability. They activated intrinsic apoptotic pathway, induced a G0/G1 block in leukemic cells and, interestingly, led to apoptosis in patient AML cells. These activities could be due to mulinic acid or azorellane terpenoids and their derivatives, tentatively identified in both IV and VI. In conclusion, our data suggest AG plant as a source of potential anti-AML agents
A comparative study in CCl4 reaction on Ag/Si(111) surfaces: PEEM and PES investigations
No full textA comparative study in CCl4 reaction on Ag/Si(111) surfaces: PEEM and PES investigations
Yunxi Yao, Qiang Fu, Xinhe Bao
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P.R. China
We report a comparative study in the reactivity of bulk Ag(111), monolayer Ag film on Si(111), and Si(111)-77 surfaces via X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), photoemission electron microscopy (PEEM), and scanning tunneling microscopy (STM). The monolayer Ag film grown on Si(111), which is known as √3×√3-Ag-Si surface structure, was obtained by depositing one monolayer Ag on the Si(111)-77 surface at 550 K. The most simple halogen methane, CCl4, was chosen as the probe molecule to study the surface reactivity of the bulk Ag(111) surface, the monolayer Ag film, and the Si(111) surface. XPS and UPS data indicate that the monolayer Ag film presents unique reactivity to CCl4 in comparison to the other two surfaces. For the PEEM study, a dedicated sample consisting of bulk Ag particles supported on the monolayer Ag film was prepared as shown in the schematics in Fig. 1. In situ PEEM imaging of the surface reaction in presence of CCl4 shows a gradual change in the grey intensity from bright to totally dark on the Ag particles but little change on the √3×√3-Ag-Si surface. The grey intensity decrease is due to local work function increase from the dissociated Cl atoms. The experiments suggest that monolayer Ag is inert toward dissociation of CCl4 compared to the Ag(111) and Si(111) surface. It has proposed that the confinement of 5sp electron of Ag atoms in the √3×√3-Ag-Si surface, which is delocalized in the bulk Ag(111) surface, is decisive to the different reactivity.
Figure 1: (a) Schematic representation of the √3×√3-Ag-Si surface supported Ag islands; (b) PEEM image of the Ag islands/√3×√3-Ag-Si sample before CCl4 exposure. Field of view (FoV) is 27 μm; (c) PEEM image shows the same area in (b) but after 24 L (5.2×10-9 mbar × 6000 s) CCl4 exposure; (d) the work function change (ΔΦ) of the Ag(111) and √3×√3-Ag-Si surfaces when exposed to different amount of CCl4 at RT, measured from PES results.
References:
[1] Y.X. Yao, X. Liu, Q. Fu, W.X. Li, D.L. Tan, X.H. Bao, ChemPhysChem 2008, 9: 975-979.
*Corresponding author: Fax: +86-411-84694447, E-mail: [email protected], [email protected]
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