74 research outputs found
Conception de nouveaux matériaux hybrides types MOFs bio-inspirés à fonctionnalités avancées pour la catalyse
Metal Organic Frameworks, MOFs, are porous crystalline solid based on metal clusters and organic ligands, investigated for numerous applications such as catalysis, drug delivery, gas storage and, more recently, biosensors. The work presented in this thesis focuses on functionalizing MOFs through different strategies, such as covalent grafting or surface coordination chemistry, through chemical reactions, such as peptide coupling or synthesis of urea. In particular, a new method to very quickly graft chiral peptides into the nanopores of MOFs is reported. A large library of MOF-peptides has thus been obtained and characterized. These novel compounds have also been used for grafting organometallics in the cavities of MOFs. Following a post-synthetic ligand exchange, it was also possible to integrate a photocatalytic complex in the structure of a MOF, improving its activities and selectivities for the photocatalytic CO2 reduction. In general, the catalytic performances of these materials were superior to those of their homogeneous counterparts, thus further expanding the potential of MOFs as well-defined heterogeneous catalysts for fine chemistryLes MOFs sont des solides à la structure cristalline poreuse à base de clusters métalliques et de ligands organiques qui font l'objet de très nombreuses études, dans des champs d'applications très variés, qui vont de la catalyse au « drug delivery », en passant par le stockage de gaz et, plus récemment, en tant que senseurs biologiques. Les ligands organiques, qui les constituent, peuvent lorsqu'ils possèdent un point d'ancrage, comme des groupements amino, être fonctionnalisés grâce à des réactions chimiques. Les travaux présentés dans cette thèse reportent la fonctionnalisation de MOFs, via différentes stratégies, comme des greffages covalent et issues de la chimie de coordination, tel que le couplage peptidique ou encore la synthèse d'urée. Dans cette thèse, est notamment présentée une nouvelle méthode permettant de greffer très rapidement des peptides chiraux dans les nanopores des MOFs. Une large bibliothèque MOF-peptides a ainsi été obtenue et caractérisée. Ces nouveaux composés ont également été utilisés pour l'ancrage de complexes organométalliques dans les cavités des MOFs. Suivant un échange de ligands post-synthétique, il a aussi été possible d'intégrer un complexe organométallique photo-catalytique dans la structure d'un MOF, améliorant ainsi ses activités et sélectivités pour la photo-réduction de CO2. Enfin, les performances catalytiques de ces derniers matériaux MOFs se sont révélées supérieures aux versions homogènes des complexes, ce qui offre de nouvelles opportunités pour la catalyse fin
Structure and Assembly Properties of the N-Terminal Domain of the Prion Ure2p in Isolation and in Its Natural Context
Background: The aggregation of the baker’s yeast prion Ure2p is at the origin of the [URE3] trait. The Q- and N-rich N-terminal part of the protein is believed to drive Ure2p assembly into fibrils of amyloid nature and the fibrillar forms of fulllength Ure2p and its N-terminal part generated in vitro have been shown to induce [URE3] occurrence when introduced into yeast cells. This has led to the view that the fibrillar form of the N-terminal part of the protein is sufficient for the recruitment of constitutive Ure2p and that it imprints its amyloid structure to full-length Ure2p. Results: Here we generate a set of Ure2p N-terminal fragments, document their assembly and structural properties and compare them to that of full-length Ure2p. We identify the minimal region critical for the assembly of Ure2p N-terminal part into amyloids and show that such fibrils are unable to seed the assembly of full length Ure2p unlike fibrils made of intact Ure2p. Conclusion: Our results clearly indicate that fibrillar Ure2p shares no structural similarities with the amyloid fibrils made of Ure2p N-terminal part. Our results further suggest that the induction of [URE3] by fibrils made of full-length Ure2p is likely the consequence of fibrils growth by depletion of cytosolic Ure2p while it is the consequence of de novo formation of prion particles following, for example, titration within the cells of a specific set of molecular chaperones when fibrils made o
The Agentcities Network Architecture
Agentcities is a worldwide initiative designed to help realize the commercial and research potential of agent-based applications by constructing an open distributed network of platforms hosting diverse agents and services. The ultimate aim of the Agentcities initiative is to enable the dynamic, intelligent and autonomous composition of services to achieve user and business goals, thereby creating compound services to address changing needs. In this paper, we present the progress and current status of the Agentcities Network, six months after the launch of the project. The architecture of the Network, consisting of agents, services and platforms, is described. Finally, the plans and challenges for enhancing the Agentcities Network in the next phase of development are also discussed
High contrast imaging at the LBT: the LEECH exoplanet imaging survey
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began
its 130-night campaign from the Large Binocular Telescope (LBT) atop Mt
Graham, Arizona. This survey benefits from the many technological achievements
of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual
adaptive secondary mirrors for high Strehl performance, and a cold beam
combiner to dramatically reduce the telescope's overall background emissivity.
LEECH neatly complements other high-contrast planet imaging efforts by
observing stars at L' (3.8 m), as opposed to the shorter wavelength
near-infrared bands (1-2.4 m) of other surveys. This portion of the
spectrum offers deep mass sensitivity, especially around nearby adolescent
(0.1-1 Gyr) stars. LEECH's contrast is competitive with other extreme
adaptive optics systems, while providing an alternative survey strategy.
Additionally, LEECH is characterizing known exoplanetary systems with
observations from 3-5m in preparation for JWST.Comment: 12 pages, 5 figures. Proceedings of the SPIE, 9148-2
The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions
We present the results of the largest (m) direct
imaging survey for exoplanets to date, the Large Binocular Telescope
Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98
stars with spectral types from B to M. Cool planets emit a larger share of
their flux in compared to shorter wavelengths, affording LEECH an
advantage in detecting low-mass, old, and cold-start giant planets. We
emphasize proximity over youth in our target selection, probing physical
separations smaller than other direct imaging surveys. For FGK stars, LEECH
outperforms many previous studies, placing tighter constraints on the hot-start
planet occurrence frequency interior to au. For less luminous,
cold-start planets, LEECH provides the best constraints on giant-planet
frequency interior to au around FGK stars. Direct imaging survey
results depend sensitively on both the choice of evolutionary model (e.g., hot-
or cold-start) and assumptions (explicit or implicit) about the shape of the
underlying planet distribution, in particular its radial extent. Artificially
low limits on the planet occurrence frequency can be derived when the shape of
the planet distribution is assumed to extend to very large separations, well
beyond typical protoplanetary dust-disk radii ( au), and when
hot-start models are used exclusively. We place a conservative upper limit on
the planet occurrence frequency using cold-start models and planetary
population distributions that do not extend beyond typical protoplanetary
dust-disk radii. We find that of FGK systems can host a 7 to 10
planet from 5 to 50 au. This limit leaves open the
possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A
Global Climate and Atmospheric Composition of the Ultra-Hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations
We present thermal phase curve measurements for the hot Jupiter WASP-103b
observed with Hubble/WFC3 and Spitzer/IRAC. The phase curves have large
amplitudes and negligible hotspot offsets, indicative of poor heat
redistribution to the nightside. We fit the phase variation with a range of
climate maps and find that a spherical harmonics model generally provides the
best fit. The phase-resolved spectra are consistent with blackbodies in the
WFC3 bandpass, with brightness temperatures ranging from K on the
nightside to K on the dayside. The dayside spectrum has a
significantly higher brightness temperature in the Spitzer bands, likely due to
CO emission and a thermal inversion. The inversion is not present on the
nightside. We retrieved the atmospheric composition and found the composition
is moderately metal-enriched ( solar)
and the carbon-to-oxygen ratio is below 0.9 at confidence. In
contrast to cooler hot Jupiters, we do not detect spectral features from water,
which we attribute to partial HO dissociation. We compare the phase curves
to 3D general circulation models and find magnetic drag effects are needed to
match the data. We also compare the WASP-103b spectra to brown dwarfs and young
directly imaged companions and find these objects have significantly larger
water features, indicating that surface gravity and irradiation environment
play an important role in shaping the spectra of hot Jupiters. These results
highlight the 3D structure of exoplanet atmospheres and illustrate the
importance of phase curve observations for understanding their complex
chemistry and physics.Comment: 25 pages, 17 figures, 7 tables; accepted to A
LEECH: A 100 Night Exoplanet Imaging Survey at the LBT
In February 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began
its 100-night campaign from the Large Binocular Telescope atop Mount Graham in
Arizona. LEECH nearly complements other high-contrast planet imaging efforts by
observing stars in L' band (3.8 microns) as opposed to the shorter wavelength
near-infrared bands (1-2.3 microns). This part of the spectrum offers deeper
mass sensitivity for intermediate age (several hundred Myr-old) systems, since
their Jovian-mass planets radiate predominantly in the mid-infrared. In this
proceedings, we present the science goals for LEECH and a preliminary contrast
curve from some early data.Comment: IAUS 299 Proceeding
LEECH: A 100 Night Exoplanet Imaging Survey at the LBT
In February 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its 100-night campaign from the Large Binocular Telescope atop Mount Graham in Arizona. LEECH neatly complements other high-contrast planet imaging efforts by observing stars in L' band (3.8 microns) as opposed to the shorter wavelength near-infrared bands (1-2.3 microns). This part of the spectrum offers deeper mass sensitivity for intermediate age (several hundred Myr-old) systems, since their Jovian-mass planets radiate predominantly in the mid-infrared. In this proceedings, we present the science goals for LEECH and a preliminary contrast curve from some early dat
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b
We present the highest fidelity spectrum to date of a planetary-mass object.
VHS 1256 b is a 20 M widely separated (8\arcsec, a =
150 au), young, planetary-mass companion that shares photometric colors and
spectroscopic features with the directly imaged exoplanets HR 8799 c, d, and e.
As an L-to-T transition object, VHS 1256 b exists along the region of the
color-magnitude diagram where substellar atmospheres transition from cloudy to
clear. We observed VHS 1256~b with \textit{JWST}'s NIRSpec IFU and MIRI MRS
modes for coverage from 1 m to 20 m at resolutions of 1,000 -
3,700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium
are observed in several portions of the \textit{JWST} spectrum based on
comparisons from template brown dwarf spectra, molecular opacities, and
atmospheric models. The spectral shape of VHS 1256 b is influenced by
disequilibrium chemistry and clouds. We directly detect silicate clouds, the
first such detection reported for a planetary-mass companion.Comment: Accepted ApJL Iterations of spectra reduced by the ERS team are
hosted at this link:
https://github.com/bemiles/JWST_VHS1256b_Reduction/tree/main/reduced_spectr
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems IV: NIRISS Aperture Masking Interferometry Performance and Lessons Learned
We present a performance analysis for the aperture masking interferometry
(AMI) mode on board the James Webb Space Telescope Near Infrared Imager and
Slitless Spectrograph (JWST/NIRISS). Thanks to self-calibrating observables,
AMI accesses inner working angles down to and even within the classical
diffraction limit. The scientific potential of this mode has recently been
demonstrated by the Early Release Science (ERS) 1386 program with a deep search
for close-in companions in the HIP 65426 exoplanetary system. As part of ERS
1386, we use the same dataset to explore the random, static, and calibration
errors of NIRISS AMI observables. We compare the observed noise properties and
achievable contrast to theoretical predictions. We explore possible sources of
calibration errors, and show that differences in charge migration between the
observations of HIP 65426 and point-spread function calibration stars can
account for the achieved contrast curves. Lastly, we use self-calibration tests
to demonstrate that with adequate calibration, NIRISS AMI can reach contrast
levels of mag. These tests lead us to observation planning
recommendations and strongly motivate future studies aimed at producing
sophisticated calibration strategies taking these systematic effects into
account. This will unlock the unprecedented capabilities of JWST/NIRISS AMI,
with sensitivity to significantly colder, lower mass exoplanets than
ground-based setups at orbital separations inaccessible to JWST coronagraphy.Comment: 20 pages, 12 figures, submitted to AAS Journal
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