Les séminaires de l'UMET

My work explores the physical properties, chemical reactions, evolution, and characterization of particles or molecules involved in atmospheric processes or evolving in the interstellar medium, from a physico-chemical perspective and in utilizing both commercial and custom-built instrumentation. We developed a unique setup capable of micrometer-resolution analyses of microfossils using a laser-based, low-fragmentation scheme for organic compound identification (HR-L2MS). This novel instrument holds significant potential for the microanalysis of space-returned samples or microfossils. This instrument has been successfully used to explore sedimentary archives, and gain insights into the organic inventory and biomarkers that help constrain the co-evolution of life and the environment on early Earth. In the meantime, HR-L2MS was used to investigate the organic inventory of carbonaceous chondrite meteorites, while the combined application of HR-L2MS and vibrational spectroscopy yielded valuable insights into their thermal history and the properties of interstellar carbon dust analogs produced by dielectric barrier discharge.

The in situ and real-time detection of analytes in complex biological media demands robust, sensitive, and stable biosensors capable of signal amplification. Luminescent nanoparticles (LNPs) are promising candidates, offering exceptional brightness and photostability compared to traditional dyes.1 These LNPs fall into two main categories: intrinsically luminescent, such as Quantum Dots (QDs), or doped NPs, where dyes are encapsulated within a matrix. For imaging and sensing applications, LNPs aim to achieve excellent brightness, enhanced photostability, and strong colloidal stability in water, outperforming conventional organic dyes. Classical FRET nanosensors typically involve a donor LNP conjugated with bioreceptors that bind to a ligand labeled with an acceptor dye. While bioreceptors optimization has advanced detection limits and dynamic ranges, the roles of dye type and spatial configuration in these systems remained underexplored. In this talk, we will compare organic fluorophores (e.g., Cy5, Texas Red) and QDs as FRET donors or acceptors, identifying key molecular parameters that enhance sensor performance to provide guidelines for FRET-based assays and diagnostics.2-3 Additionally, Fluorescent Organic Nanoparticles (dFONs) will be introduced as metal-free alternatives to QDs, with comparable brightness per volume. Obtained via nanoprecipitation of hydrophobic dyes, dFONs remain underutilized as biosensors due to limited functionalization strategies.4 We demonstrate an innovative maleimide-thiol surface functionalization approach, enabling applications such as intracellular thiol sensing in the µM range5 and biotinylation for biomarker development. These advancements position dFONs as versatile, ultra-bright, and metal-free tools for next-generation diagnostics.

References : 

1. A. Ashoka, et al., Chem. Soc. Rev 2023, DOI : 10.1039/D2CS00464J

2. C. Grazon et al., Chemical Science 2022, DOI : 10.1039/D1SC06921G

3. C. Grazon, R. Baer et al., Nature Communications 2020, DOI : 10.1038/s41467-020-14942-5

4. J. Daniel et al., CRAS 2024, DOI : 10.5802/crchim.294

5. O. Dal Pra et al., Small Methods, DOI : 10.1002/smtd.202400716

The mineralogy of meteorites records evidence of parent bodies second processes providing constraints on aqueous alteration and geochemical environments. This seminar will focus on the characterization of secondary mineral phases in carbonaceous chondrites and ungrouped chondrites, as well as Martian meteorites, in order to investigate the traces of aqueous alteration. In contrast, micrometeorites offer insights into the diversity of parent bodies and the flux of cosmic material to Earth through time. Using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM), we analyze the mineralogy and petrography of meteorites and micrometeorites, identifying primary and secondary mineral phases to reconstruct parent body processes, assess post-atmospheric entry alteration, and refine current classification schemes.

Controlling the polymorphic forms of active pharmaceutical ingredients (APIs) is a major
challenge for both basic research and the pharmaceutical industry. Recent advances have
highlighted the crucial role played by the surface properties of different crystalline structures,
and in particular by the conformational distribution of API molecules at the solid interface, in
promoting polymorphism.
In this context, this thesis presents an in-depth study of the interface between curcumin
(CUR) and supercritical carbon dioxide (scCO2) using molecular dynamics (MD) simulations.
Curcumin, a molecule subject to growing interest in medicine, has been parametrized, based on
quantum chemical (QC) calculations, in order to accurately reproduce thermodynamic
differences between polymorphs as well as their conformational distributions.
We have developed new algorithms for sampling CUR conformations, as well as for
calculating various structural and dynamic properties at its interface. In order to reliably study
the CUR-scCO2 system, we have evaluated several force fields for the CO2 and identified the
one that most faithfully reproduces the critical point properties. We demonstrated how certain
local observables can be used to characterize the organization and dynamics of the supercritical
fluid near the critical point. This protocol was then applied to compare the structural and
dynamic behaviors of scCO2 with those of water and ammonia in their respective supercritical
regimes.
Finally, we characterized local structural changes at the CUR-vacuum and CUR-scCO2
interface under different thermodynamic conditions. A specific algorithm was used to identify
the CUR molecules belonging to each interfacial layer, allowing a fine analysis of the structural,
dynamic and energetic properties within these critical regions for the stability and evolution of
polymorphic forms.

Les propriétés des matériaux moléculaires pharmaceutiques et énergétiques sont étroitement liées à leur forme cristallographique. Les procédés de fabrication et de mise en forme utilisés depuis la poudre de départ jusqu’au produit final pouvant modifier la cristallographie de ces matériaux, il est crucial de détecter et maitriser ces éventuelles transformations pour éviter une dégradation de leurs propriétés. A l’inverse, il peut être intéressant de modifier volontairement la structure cristallographique de ces composés moléculaire pour améliorer leurs propriétés. La diffraction des rayons X est la principale technique utilisée dans ces travaux. Elle permet l’étude fine de la cristallographie de ces matériaux, depuis l’identification simple de phase qui peut être réalisée en laboratoire, jusqu’à la résolution d’une structure cristallographique encore inconnue, ce qui nécessite bien souvent l’utilisation du rayonnement synchrotron. Dans ce manuscrit, l’influence de plusieurs procédés de mise en forme sur la structure cristallographique de différents matériaux énergétiques est discutée dans un premier temps. Dans un second temps, les études sur la résolution de nouvelles structure cristallographiques sont présentées. Elles portent sur l’analyse de molécules simples pour explorer leur polymorphisme, ainsi que sur l’analyse de la structure de cocristaux et leur stabilité. Les travaux présentés dans la troisième partie montrent comment l’étude des cinétiques de transformations polymorphiques et les analyses Rietveld, qui permettent une quantification des phases en présence et des défauts structuraux, ont permis de mieux cerner les mécanismes de transformations polymorphique des matériaux moléculaires sous broyage. Les perspectives auxquelles conduisent ces travaux sur le broyage sont également exposées. Enfin, dans la dernière partie de ce manuscrit, je présenterai le nouvel axe de recherches que je souhaite mettre en place. Le but est de soumettre des principes actifs à de hautes pression dans le but d’obtenir de nouvelles formes cristallographiques afin d’améliorer leur biodisponibilité. Les hautes pressions permettront également de mieux comprendre les mécanismes physiques impliqués dans les transformations de phase des matériaux moléculaires sous sollicitations mécaniques

The three peridotite massifs in the Zabargad island (northern Red Sea) document the exhumation of the mantle during continental rifting and the rift to drift transition. Deformation evolved from pervasive at the massif scale to localized in metric shear zones. To characterize the active processes and the role of melts and aqueous fluids in the deformation, we performed a petrostructural study of 40 samples representative of the different stages of deformation in the three massifs. Microstructures recording synkinematic crystallization of plagioclase, clinopyroxene, and orthopyroxene in the southern and amphibole-bearing spinel-websterite layers in the central and northern massifs indicate that pervasive deformation occurred in the presence of melts, but at lower pressure in the south. In the shear zones, deformation was accommodated by concomitant dislocation and dissolution-precipitation creep. Evolution from protomylonites to ultramylonites produced increasing volumes of a fine-grained polymineralic matrix where amphibole progressively replaces plagioclase and clinopyroxene. Fluid-assisted deformation at all stages is attested by the interstitial shapes of pyroxene neoblasts intermixed with olivine in the matrix. Local deformation at the brittle-ductile transition is accompanied by the crystallization of scapolite. Thermobarometry and thermodynamic modelling constrained by the microstructural observations document shearing under decreasing pressure and temperature from near solidus conditions at >1 GPa in the north and central massifs and ~0.7 GPa in the southern massif to < 600°C and <0.3 GPa in all three massifs. These data also imply increasing hydration, indicating fluid focusing and local aqueous fluid saturation in the shear zones, with sea water ingression to10 km depth. However, fluid supply was spatially heterogeneous and probably intermittent, withequilibrium only achieved locally in the ultramylonites. The present study documents thereforehow progressive strain localization and fluid-focusing in extensional shear zones enable thinningand exhumation of the mantle during continental rift and rift-to-drift transition.

I will discuss the implications of early processes related to planet formation like ²⁶Al heating and magma ocean outgassing on the volatile content and the atmospheric evolution of terrestrial planets Earth and Venus and exoplanets beyond our solar system.

La modélisation des déformations de marée observées pour les planètes telluriques est une approche complémentaire aux éventuelles données sismologiques pour décrypter leur organisation interne.
Elle apporte des contraintes sur les hétérogénéités internes mais également des contraintes rhéologiques et de densité sur les matériaux permettant ainsi une « tomographie » tidale.
Ces contraintes couplées à des modèles thermodynamiques permettent d’établir la structure actuelle de ces objets et contribuent à comprendre leur évolution géodynamique.
Dans ce séminaire, nous aborderons l’organisation des noyaux lunaire et martien ; le processus de retournement mantellique lors de la cristallisation de l’océan magmatique lunaire ; la persistance d’une zone potentiellement fondue dans le manteau martien et celle d’un contraste de viscosité conséquent entre le manteau supérieur de Vénus et le manteau inférieur. Nous aborderons également les contrastes de viscosité entre la lithosphère et l’asthénosphère martienne. Les enjeux sur la caractérisation des propriétés rhéologiques (rigidité, viscosité) de matériaux haute pression (selon les textures, taux de fusion) seront abordés.