141 research outputs found
Potent Antioxidant and Anti-Tyrosinase Activity of Butein and Homobutein Probed by Molecular Kinetic and Mechanistic Studies â€
Butein (BU) and homobutein (HB) are bioactive polyhydroxylated chalcones widespread in dietary plants, whose antioxidant properties require mechanistic definition. They were investigated by inhibited autoxidation kinetic studies of methyl linoleate in TritonTM X-100 micelles at pH 7.4, 37 °C. Butein had kinh = (3.0 ± 0.9) × 104 M−1s−1 showing a chain-breaking mechanism with higher antioxidant activity than reference α-tocopherol (kinh = (2.2 ± 0.6) × 104 M−1s−1), particularly concerning the stoichiometry or peroxyl radical trapping n = 3.7 ± 1.1 vs. 2.0 for tocopherol. Homobutein had kinh = (2.8 ± 0.9) × 103 M−1s−1, pairing the relative BDEOH measured by radical equilibration EPR as 78.4 ± 0.2 kcal/mol for BU and estimated as 82.6 kcal/mol for HB. The inhibition of mushroom tyrosinase (mTYR) by HB and BU was also investigated. BU gives a reversible uncompetitive inhibition of monophenolase reaction with KI′ = 9.95 ± 2.69 μM and mixed-type diphenolase inhibition with KI = 3.30 ± 0.75 μM and KI′ = 18.75 ± 5.15 μM, while HB was nearly competitive toward both mono- and diphenolase with respective KI of 2.76 ± 0.70 μM and 2.50 ± 1.56 μM. IC50 values (monophenolase/diphenolase at 1 mM substrate) were 10.88 ± 2.19 μM/15.20 ± 1.25 μM, 14.78 ± 1.05 μM/12.36 ± 2.00 μM, and 33.14 ± 5.03 μM/18.27 ± 3.42 μM, respectively, for BU, HB, and reference kojic acid. Molecular docking studies confirmed the mechanism. Results indicate very potent antioxidant activity for BU and potent anti-tyrosinase activity for both chalcones, which is discussed in relation to bioactivity toward protection from skin disorders and food oxidative spoilage
Star-forming dwarf galaxies in the Virgo cluster: the link between molecular gas, atomic gas, and dust
We present CO(1-0) and CO(2-1) observations of a sample of 20
star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with
oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is
observed in ten galaxies and marginally detected in another one. CO fluxes
correlate with the FIR 250 m emission, and the dwarfs follow the same
linear relation that holds for more massive spiral galaxies extended to a wider
dynamical range. We compare different methods to estimate H2 molecular masses,
namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on
H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant
at stellar masses <~ 10 M, contrary to the atomic hydrogen
fraction, M/M, which increases inversely with M. The flattening
of the M/M ratio at low stellar masses does not seem to be related
to the effects of the cluster environment because it occurs for both
HI-deficient and HI-normal dwarfs. The molecular-to-atomic ratio is more
tightly correlated with stellar surface density than metallicity, confirming
that the interstellar gas pressure plays a key role in determining the balance
between the two gaseous components of the interstellar medium. Virgo dwarfs
follow the same linear trend between molecular gas mass and star formation rate
as more massive spirals, but gas depletion timescales, , are not
constant and range between 100 Myr and 6 Gyr. The interaction with the Virgo
cluster environment is removing the atomic gas and dust components of the
dwarfs, but the molecular gas appears to be less affected at the current stage
of evolution within the cluster. However, the correlation between HI deficiency
and the molecular gas depletion time suggests that the lack of gas
replenishment from the outer regions of the disc is lowering the star formation
activity.Comment: 19 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
HST Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution
The optical expansion parallax of NGC 6543 has been detected and measured
using two epochs of HST images separated by a time baseline of only three
years. We have utilized three separate methods of deriving the angular
expansion of bright fiducials, the results of which are in excellent agreement.
We combine our angular expansion estimates with spectroscopically obtained
expansion velocities to derive a distance to NGC 6543 of 1001269 pc. The
deduced kinematic age of the inner bright core of the nebula is 1039259
years; however, the kinematic age of the polar caps that surround the core is
larger - perhaps the result of deceleration or earlier mass ejection. The
morphology and expansion patterns of NGC 6543 provide insight into a complex
history of axisymmetric, interacting stellar mass ejections.Comment: Accepted for publication in AJ. 18 pages. 6 figure
An Atlas of Monte Carlo Models of Dust Extinction in Galaxies for Cosmological Applications
We present an extensive study of the radiative transfer in dusty galaxies
based on Monte Carlo simulations. The main output of these simulations are the
attenuation curves (i.e. the ratio between the observed,
dust extinguished, total intensity to the intrinsic unextinguished one of the
galaxy as a function of wavelength). We have explored the dependence of on a conspicuous set of quantities (Hubble type, inclination, dust
optical thickness, dust distribution and extinction properties) for a large
wavelength interval, ranging from 1250\AA to the K band, thus finally providing
a comprehensive atlas of dust extinction in galaxies, which is electronically
available. This study is particularly suitable for inclusion into galaxy
formation evolution models and to directly interpret observational data on high
redshift galaxies.Comment: 29 pages, aasms4.sty, LaTeX, 5 figures. ApJSS, accepte
State of the art and perspectives on the use of planktonic communities as indicators of environmental status in relation to the EU Marine Strategy Framework Directive
State of the art and perspectives on the use of planktonic communities as indicators of environmental status in relation to the EU Marine Strategy FD
Mantle Xenoliths from Huanul Volcano (Central-West Argentina): A Poorly Depleted Mantle Source under Southern Payenia
Huanul is a shield volcano with several lava flows hosting mantle xenoliths erupted during the Pleistocene (0.84 ± 0.05 Ma). It is located in the southern part of the Payenia Volcanic Province, which is among the largest Neogene-Quaternary volcanic provinces of South America. The vol-canism here has been ascribed as the northernmost expression of the back-arc volcanism of the Andean Southern Volcanic Zone. We present the first petrographic and mineral chemistry study of mantle xenoliths collected from Huanul lavas with the aim of reconstructing directly the mantle source of the Payenia Volcanic Province. Xenoliths are commonly small (<5 cm in radius) but scarcely crossed by basaltic veins. All xenoliths have a fertile lherzolitic modal composition and are equilibrated in the spinel-facies. Most of them exhibit an almost primitive-mantle geochemical affinity, characterized by slightly depleted clinopyroxene REE patterns reproducible by partial melting degrees between 0 and 4% of a PM source. Geothermobarometric P-T estimates of cli-nopyroxene-orthopyroxene couples form a linear trend between 10 and 24 kbar with constant increase of T from 814 to 1170 °C along a 50–60 mW/m2 geotherm. Evidences of interaction with the host basalts occur as spongy textures in clinopyroxene and reacted spinel, which tend to became more restitic in composition and show chromatographic or complete overprinting of the trace element compositions. The presence of plagioclase and calculated P-T values constrain this melt/rock reaction process between 6 and 14 kbar, during magma ascent, and fit the mantle ad-iabat model. Calculated melts in equilibrium with the primary clinopyroxenes do not fit the composition of the host basalt and, together with the geothermobarometric estimations, point to an asthenospheric mantle source for the magmatism in southern Payenia. The PM geochemical affinity of the xenoliths of Huanul is an extremely rare finding in the South America lithospheric mantle, which is commonly extensively refertilized by subduction-derived melts
The Herschel Virgo Cluster Survey: IV. Resolved dust analysis of spiral galaxies
We present a resolved dust analysis of three of the largest angular size
spiral galaxies, NGC 4501 and NGC 4567/8, in the Herschel Virgo Cluster Survey
(HeViCS) Science Demonstration field. Herschel has unprecedented spatial
resolution at far-infrared wavelengths and with the PACS and SPIRE instruments
samples both sides of the peak in the far infrared spectral energy distribution
(SED).We present maps of dust temperature, dust mass, and gas-to-dust ratio,
produced by fitting modified black bodies to the SED for each pixel. We find
that the distribution of dust temperature in both systems is in the range ~19 -
22 K and peaks away from the centres of the galaxies. The distribution of dust
mass in both systems is symmetrical and exhibits a single peak coincident with
the galaxy centres. This Letter provides a first insight into the future
analysis possible with a large sample of resolved galaxies to be observed by
Herschel.Comment: Letter accepted for publication in A&A (Herschel special issue
The far-infrared view of M87 as seen by the Herschel Space Observatory
The origin of the far-infrared emission from the nearby radio galaxy M87
remains a matter of debate. Some studies find evidence of a far-infrared excess
due to thermal dust emission, whereas others propose that the far-infrared
emission can be explained by synchrotron emission without the need for an
additional dust emission component. We observed M87 with PACS and SPIRE as part
of the Herschel Virgo Cluster Survey (HeViCS). We compare the new Herschel data
with a synchrotron model based on infrared, submm and radio data to investigate
the origin of the far-infrared emission. We find that both the integrated SED
and the Herschel surface brightness maps are adequately explained by
synchrotron emission. At odds with previous claims, we find no evidence of a
diffuse dust component in M87.Comment: 4 pages, 2 figures, proceedings IAU Symposium 275 (Jets at all
scales
The Herschel Virgo Cluster Survey: I. Luminosity functions
We describe the Herschel Virgo Cluster Survey (HeViCS) and the first data
obtained as part of the Science Demonstration Phase (SDP). The data cover a
central 4x4 sq deg region of the cluster. We use SPIRE and PACS photometry data
to produce 100, 160, 250, 350 and 500 micron luminosity functions (LFs) for
optically bright galaxies that are selected at 500 micron and detected in all
bands. We compare these LFs with those previously derived using IRAS, BLAST and
Herschel-ATLAS data. The Virgo Cluster LFs do not have the large numbers of
faint galaxies or examples of very luminous galaxies seen previously in surveys
covering less dense environments.Comment: Letter accepted for publication in A&A (Herschel special issue
- …