368 research outputs found
Recent developments in the rapid analysis of plants and tracking their bioactive constituents
Natural products chemistry has witnessed many new developments in the last 5 years like extractions with subcritical water and ionic liquids, LC/HRMS and LC/SPE/cryo-NMR, UHPLC, TLC/MS, MS-based preparative HPLC, comprehensive chromatography (GC × GC, LC × LC), high-throughput screening, introduction of monolithic columns, miniaturisation, and automated structure identification. Nevertheless identifying bioactive constituents in complex plant extracts remains a tedious process. The classical approach of bioassay guided fractionation is time-consuming while off-line screening of extracts does not provide information on individual compounds and sometimes suffers from false positives or negatives. One way out of this is by coupling chromatography with chemical or biochemical assays, so called high resolution screening. An example is the development of HPLC on-line assays for antioxidants. By the post-column addition of a relatively stable coloured radical like DPPH¿ or ABTS¿+, radical scavengers are detected as negative peaks because in a reaction coil they reduce the model radical to its reduced, non-coloured form. When combined with LC/DAD/MS and LC/SPE/NMR, reliable identification of active constituents becomes possible without the necessity of ever isolating them in a classical sense. Also for finding leads for new drugs, combining HPLC with biochemical assays is interesting but technically more difficult. Most enzymes do not work at the organic modifier concentrations commonly encountered in RP-HPLC and the reaction time is often longer requiring dilution and lengthy coils respectively. Therefore, new techniques have to be implemented to gain the required sensitivity for on-line enzyme assays. For stable analytes, high temperature LC offers a solution to the organic modifier problem. When enzymes are highly expensive, like those used in the screening for Cytochrome P450 inhibitors, miniaturisation to chip format may offer a way out. Microreactors (chips) are not only useful for miniaturising larger assays but also offer completely new prospects in phytochemical analysis. One such application is in the sample clean-up of acids and bases like alkaloids. In a lay-out of three parallel channels of 100 ¿m width with the middle one containing organic phase and the two outer ones water of high pH (feed phase) and low pH (trapping phase) such a chip replaces two classical LLE steps but is much faster and requires less solvents and less manpower input
The châine opératoire approach to prehistoric figurines : an example from Dolnoslav, Bulgaria.
Comparison of different spectral population models
We have compared simple stellar populations (SSPs) generated with different population synthesis tools: BC03, Vazdekis and Pegase.HR and different stellar libraries: ELODIE3.1, SteLib and MILES. We find that BC03/SteLib SSPs are biased toward solar metallicity, however Pegase.HR/ELODIE3.1 and Vazdekis/MILES are extremely consistent. The extensive coverage of the space of atmospheric parameters in the large stellar libraries allows precise synthesis for a large range of ages (0.1 .. 10 Gyr) and metallicities (-2 .. +0.4 dex) limited by the quality of the determination of stellar parameters (like temperature scale of the giants)
“Green” Synthesis of Sucrose Octaacetate and Characterization of Its Physicochemical Properties and Antimicrobial Activity
Sucrose octaacetate (octa-O-acetylsucrose) has been synthesized by esterification of sucrose with acetic anhydride using ultrasound-assisted irradiation. This sucrose ester is a white, water-insoluble substance with a bitter taste. The FT-IR and NMR spectra confirmed
acetylation and revealed the hydrophobic incorporation in sucrose molecule. Furthermore, the foamability, foam stability, emulsification and antimicrobial properties of octa-O-acetylsucrose were evaluated. Foams and 50 % (oil/water) model emulsions were prepared with 2 % (w/w) octa-O-acetylsucrose. The obtained results demonstrate the
formation of emulsions and foams with high stability (50–70 %). The antimicrobial activity of octa-O-acetylsucrose was evaluated against seventeen microorganisms (Gram-positive and Gram-negative bacteria, yeasts, and fungi). Octa-O-acetylsucrose inhibited
the growth of fungi Penicillium sp., Rhizopus sp. and Fusarium moniliforme at 5 mg cm–3, and yeasts Candida albicans at 1 mg cm–3. Inhibition against Gram-positive and Gram-negative bacteria was not observed. The obtained results demonstrate the potential
applications of octa-O-acetylsucrose as a foaming agent, oil-in-water emulsion stabilizer, and antifungal substance in pharmaceutical and cosmetic preparations.
This work is licensed under a Creative Commons Attribution 4.0 International License
Efficient Synthesis of Fluorescent Coumarins and Phosphorous-Containing Coumarin-Type Heterocycles via Palladium Catalyzed Cross-Coupling Reactions
Quantum-chemical calculations on the spectral properties of some aryl substituted 3-
phosphonocoumarins were performed, and the effect of the substituents in the aryl moiety was
evaluated. The structures possessing promising fluorescent properties were successfully synthesized via Suzuki and Sonogashira cross-coupling. The synthetic protocol was also applied for the
phosphorous chemoisomer of 3-phosphonocoumarin, 1,2-benzoxaphosphorin, and their carboxylate
analogues. The optical properties of the arylated and alkynylated products were experimentally
determined. The obtained quantum-chemical and experimental results give the possibility for a
fine tuning of the optical properties of phosphorous-containing coumarin systems by altering the
substituent at its C-6 position
A new method for reconstructing the density distribution of matter in the disks of spiral galaxies from the rotation velocity curve in it
In this paper we propose a new method for reconstructing the surface density
of matter in flat disks of spiral galaxies. The surface density is expressed
through observational rotation velocity curves of visible matter in the disks
of spiral galaxies. The new method is not based on quadrature of special
functions. The found solution is used for processing and analysis of
observational data from several spiral galaxies. The new method can be used to
more accurately estimate the amount of dark matter in spiral galaxies.Comment: 18 pages, 6 figure
Recovering star formation histories: Integrated-light analyses vs stellar colour-magnitude diagrams
Accurate star formation histories (SFHs) of galaxies are fundamental for
understanding the build-up of their stellar content. However, the most accurate
SFHs - those obtained from colour-magnitude diagrams (CMDs) of resolved stars
reaching the oldest main sequence turnoffs (oMSTO) - are presently limited to a
few systems in the Local Group. It is therefore crucial to determine the
reliability and range of applicability of SFHs derived from integrated light
spectroscopy, as this affects our understanding of unresolved galaxies from low
to high redshift.
To evaluate the reliability of current full spectral fitting techniques in
deriving SFHs from integrated light spectroscopy by comparing SFHs from
integrated spectra to those obtained from deep CMDs of resolved stars.
We have obtained a high signal--to--noise (S/N 36.3 per \AA)
integrated spectrum of a field in the bar of the Large Magellanic Cloud (LMC)
using EFOSC2 at the 3.6 meter telescope at La Silla Observatory. For this same
field, resolved stellar data reaching the oMSTO are available. We have compared
the star formation rate (SFR) as a function of time and the age-metallicity
relation (AMR) obtained from the integrated spectrum using {\tt STECKMAP}, and
the CMD using the IAC-star/MinnIAC/IAC-pop set of routines. For the sake of
completeness we also use and discuss other synthesis codes ({\tt STARLIGHT} and
{\tt ULySS}) to derive the SFR and AMR from the integrated LMC spectrum.
We find very good agreement (average differences 4.1 ) between the
SFR(t) and the AMR obtained using {\tt STECKMAP} on the integrated light
spectrum, and the CMD analysis. {\tt STECKMAP} minimizes the impact of the
age-metallicity degeneracy and has the advantage of preferring smooth solutions
to recover complex SFHs by means of a penalized . [abridged]Comment: 23 pages, 24 figures. Accepted for publication in A&A (6 Sep 2015
Subsurface carbon: a general feature of noble metals
Carbon moieties on late transition metals are regarded as poisoning agents in heterogeneous catalysis. Recent studies show the promoting catalytic role of subsurface C atoms in Pd surfaces and their existence in Ni and Pt surfaces. Here energetic and kinetic evidence obtained by accurate simulations on surface and nanoparticle models shows that such subsurface C species are a general issue to consider even in coinage noble-metal systems. Subsurface C is the most stable situation in densely packed (111) surfaces of Cu and Ag, with sinking barriers low enough to be overcome at catalytic working temperatures. Low-coordinated sites at nanoparticle edges and corners further stabilize them, even in Au, with negligible subsurface sinking barriers. The malleability of low-coordinated sites is key in the subsurface C accommodation. The incorporation of C species decreases the electron density of the surrounding metal atoms, thus affecting their chemical and catalytic activity
Charting the Atomic C Interaction with Transition Metal Surfaces
Carbon interaction with transition metal (TM) surfaces is a relevant topic in heterogeneous catalysis, either for its poisoning capability, for the recently attributed promoter role when incorporated in the subsurface, or for the formation of early TM carbides, which are increasingly used in catalysis. Herein, we present a high-throughput systematic study, adjoining thermodynamic plus kinetic evidence obtained by extensive density functional calculations on surface models (324 diffusion barriers located on 81 TM surfaces in total), which provides a navigation map of these interactions in a holistic fashion. Correlation between previously proposed electronic descriptors and ad/absorption energies has been tested, with the d-band center being found the most suitable one, although machine learning protocols also underscore the importance of the surface energy and the site coordination number. Descriptors have also been tested for diffusion barriers, with ad/absorption energies and the difference in energy between minima being the most appropriate ones. Furthermore, multivariable, polynomial, and random forest regressions show that both thermodynamic and kinetic data are better described when using a combination of different descriptors. Therefore, looking for a single perfect descriptor may not be the best quest, while combining different ones may be a better path to follow
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses IX. Time delays, lens dynamics and baryonic fraction in HE 0435-1223
We present accurate time delays for the quadruply imaged quasar HE 0435-1223.
The delays were measured from 575 independent photometric points obtained in
the R-band between January 2004 and March 2010. With seven years of data, we
clearly show that quasar image A is affected by strong microlensing variations
and that the time delays are best expressed relative to quasar image B. We
measured Delta_t(BC) = 7.8+/-0.8 days, Delta_t(BD) = -6.5+/-0.7 days and
Delta_t_CD = -14.3+/-0.8 days. We spacially deconvolved HST NICMOS2 F160W
images to derive accurate astrometry of the quasar images and to infer the
light profile of the lensing galaxy. We combined these images with a stellar
population fitting of a deep VLT spectrum of the lensing galaxy to estimate the
baryonic fraction, , in the Einstein radius. We measured f_b =
0.65+0.13-0.10 if the lensing galaxy has a Salpeter IMF and f_b =
0.45+0.04-0.07 if it has a Kroupa IMF. The spectrum also allowed us to estimate
the velocity dispersion of the lensing galaxy, sigma_ap = 222+/-34 km/s. We
used f_b and sigma_ap to constrain an analytical model of the lensing galaxy
composed of an Hernquist plus generalized NFW profile. We solve the Jeans
equations numerically for the model and explored the parameter space under the
additional requirement that the model must predict the correct astrometry for
the quasar images. Given the current error bars on f_b and sigma_ap, we did not
constrain H0 yet with high accuracy, i.e., we found a broad range of models
with chi^2 < 1. However, narrowing this range is possible, provided a better
velocity dispersion measurement becomes available. In addition, increasing the
depth of the current HST imaging data of HE 0435-1223 will allow us to combine
our constraints with lens reconstruction techniques that make use of the full
Einstein ring that is visible in this object.Comment: 12 pages, 10 figures, final version accepted for publication by A&
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