29 research outputs found
Structure and cytotoxic activity of sesquiterpene glycoside esters from Calendula officinalis L.: studies on the conformation of viridiflorol
Topic applications of Calendula officinalis L. lipophilic extracts are used in phytotherapy to relieve skin
inflammatory conditions whereas infusions are used as a remedy for gastric complaints. Such a different
usage might be explained by some cytotoxicity of lipophilic extracts at gastric level but little is known
about this. Therefore, we screened the CH2Cl2 extract from the flowers of C. officinalis by MTT and LDH
assays in human epithelial gastric cells AGS. This bioassay-oriented approach led to the isolation of several
sesquiterpene glycosides which were structurally characterized by spectroscopic measurements,
chemical reactions and MM calculations. The conformational preferences of viridiflorol fucoside were
established and a previously assigned stereochemistry was revised. The compounds 1a, 2a and 3f showed
comparably high cytotoxicity in the MTT assays, whereas the effect on LDH release was lower. Our study
provides new insights on the composition of C. officinalis extracts of medium polarity and identifies the
main compounds that could be responsible for cytotoxic effects at gastric level
SI methane hydrate confined in C8-grafted SBA-15: A highly efficient storage system enabling ultrafast methane loading and unloading
Confinement of water and methane in mesopores of hydrophobized SBA-15 is
demonstrated to promote methane hydrate formation. In comparison to
as-synthesized SBA-15, hydrophobization by C8 grafting accelerates the kinetics
of methane storage in and delivery from the hydrate. C8 grafting density was
determined at 0.5 groups nm-2 based on TGA and quantitative NMR spectroscopy.
Multinuclear 1H-1H DQSQ and 1H-1H RFDR NMR provided spectroscopic evidence for
the occurrence of C8 chains inside the mesopores of SBA-15, by showcasing close
spatial proximity between the grafted C8 chains and pore-intruded water
species. X-ray diffraction demonstrates formation of Structure I hydrate on
SBA-15 C8. At 7.0 MPa and 248 K, the water-to-hydrate conversion on
hydrophobized SBA-15 C8 reaches 96 pct. as compared to only 71 pct. on a
pristine SBA-15 sample with comparable pore size, pore volume and surface area.
The clathrate loading amounted to 14.8 g g-1. 2D correlation NMR spectroscopy
(1H-13C CP-HETCOR, 1H-1H RFDR) reveals hydrate formation occurs within pores of
SBA-15 C8 as well as in interparticle volumes. Following the initial
crystallization of SBA-15 C8-supported methane hydrate taking several hours, a
pressure swing process at 248 K allows to desorb and re-adsorb methane from the
structure within minutes and without thawing the frozen water structure. Fast
loading and unloading of methane was achieved in 19 subsequent cycles without
losses in kinetics. The ability to harvest the gas and regenerate the structure
without the need to re-freeze the water represents a 50 pct. energy gain with
respect to melting and subsequently recrystallizing the hydrate at 298 K and
248 K, respectively. After methane desorption, a small amount of residual
methane hydrate in combination with an amorphous yet locally ordered ice phase
is observed using 13C and 2H NMR spectroscopy
First atom lifetime and scattering length measurements
The results of a search for hydrogen-like atoms consisting of
mesons are presented. Evidence for atom production
by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen
in terms of characteristic pairs from their breakup in the same target
() and from Coulomb final state interaction (). Using
these results the analysis yields a first value for the atom lifetime
of fs and a first model-independent measurement of
the S-wave isospin-odd scattering length
( for isospin ).Comment: 14 pages, 8 figure
Determination of scattering lengths from measurement of atom lifetime
The DIRAC experiment at CERN has achieved a sizeable production of
atoms and has significantly improved the precision on its lifetime
determination. From a sample of 21227 atomic pairs, a 4% measurement of the
S-wave scattering length difference
has been attained, providing an important test of Chiral Perturbation Theory.Comment: 6 pages, 6 figure
Evidence for -atoms with DIRAC
We present evidence for the first observation of electromagnetically bound
-pairs (-atoms) with the DIRAC experiment at the CERN-PS.
The -atoms are produced by the 24 GeV/c proton beam in a thin Pt-target
and the and -mesons from the atom dissociation are analyzed in
a two-arm magnetic spectrometer. The observed enhancement at low relative
momentum corresponds to the production of 173 54 -atoms. The mean
life of -atoms is related to the s-wave -scattering lengths, the
measurement of which is the goal of the experiment. From these first data we
derive a lower limit for the mean life of 0.8 fs at 90% confidence level.Comment: 15 pages, 9 figure
An ultra-high gain and efficient amplifier based on Raman amplification in plasma
Raman amplification arising from the excitation of a density echelon in plasma could lead to amplifiers that significantly exceed current power limits of conventional laser media. Here we show that 1-100 J pump pulses can amplify picojoule seed pulses to nearly joule level. The extremely high gain also leads to significant amplification of backscattered radiation from "noise", arising from stochastic plasma fluctuations that competes with externally injected seed pulses, which are amplified to similar levels at the highest pump energies. The pump energy is scattered into the seed at an oblique angle with 14 J sr(-1), and net gains of more than eight orders of magnitude. The maximum gain coefficient, of 180 cm(-1), exceeds high-power solid-state amplifying media by orders of magnitude. The observation of a minimum of 640 J sr(-1) directly backscattered from noise, corresponding to approximate to 10% of the pump energy in the observation solid angle, implies potential overall efficiencies greater than 10%. © The Author(s) 20174
The role of the gas/plasma plume and self-focusing in a gas-filled capillary discharge waveguide for high-power laser-plasma applications
The role of the gas/plasma plume at the entrance of a gas-filled capillary discharge plasma waveguide in increasing the laser intensity has been investigated. Distinction is made between neutral gas and hot plasma plumes that, respectively, develop before and after discharge breakdown. Time-averaged measurements show that the on-axis plasma density of a fully expanded plasma plume over this region is similar to that inside the waveguide. Above the critical power, relativistic and ponderomotive self-focusing lead to an increase in the intensity, which can be nearly a factor of 2 compared with the case without a plume. When used as a laser plasma wakefield accelerator, the enhancement of intensity can lead to prompt electron injection very close to the entrance of the waveguide. Self-focusing occurs within two Rayleigh lengths of the waveguide entrance plane in the region, where the laser beam is converging. Analytical theory and numerical simulations show that, for a density of 3.0 × 1018 cm−3, the peak normalized laser vector potential, a 0, increases from 1.0 to 1.85 close to the entrance plane of the capillary compared with a 0 = 1.41 when the plume is neglected