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Moreno Marcellini

From Time Resolved Small/Wide Angle X-rays Scattering to Microscopy

jeudi 7 décembre 2017, 15h

salle de conférences de l’observatoire

Moreno MARCELLINI

chercheur associé à l’Institut UTINAM, ancien post-doctorant au Ceramic Synthesis and Functionalization Lab,
UMR3080 CNRS/Saint-Gobain, Cavaillon

Résumé :

X-rays scattering is a basic and powerful tool to investigate objects at several length scales. For example, crystal structures (atom-atom distribution), protein conformations (few nm), and colloidal crystal (tens of nm). Albeit it yields an average measurement of the ensemble, we can extract fine details. To extract fine structural changes in dynamic processes, for example the action mechanism of a protein after being triggered, Time Resolved X-rays Scattering yields information about the overall structural changes between the excited and the ground state of the ensemble. These changes are observable both at simple molecule scale, such as small molecules carrying heavy scatterer, and at large molecule (proteins, polymers) scale. Here, we show few examples of what we wanted to do by Time Resolved X-rays scattering (mechanism of the water oxidation cluster in PS II) and what we achieved (uncovering the transient isomer in a photoreaction).

The identification of the reaction path by X-rays scattering can be aided by molecular dynamic simulations. On the one hand, molecular dynamic simulation can generate, under certain conditions for the virtual experiments, several conformers which can then be used as basic structures to compute the X-rays scattering and fit the latter to the experimental one. We will show that we can determine the best conformers during an unfolding process. On the other hand, we can guide the molecular dynamic simulations toward conformations that agree with experimental data.

Can we imagine how does water freeze ? Confocal laser scanning microscopy allows us to image growing ice crystals in Zirconium acetate solution. Such compound has been shown to behave, under certain restrict conditions, like an ice-shaping protein. With the same optical method, we can observe the unidirectional drying of a colloidal suspension. By following the motion of the single particle, we find out that the particle velocity is the key-factor to obtain either ordered or disordered dense regions.

Numéro ORCID de l’auteur orcid.org/0000-0002-1434-5611
La présentation peut être téléchargée dès maintenant au DOI :10.6084/m9.figshare.5612779