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UMR 5182

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You are here: Home / News / Seminars / Baptiste DEMOULIN


Soutenance de Thèse, laboratoire de Chimie, ENSL

Sep 21, 2017 à 09:00 AM


Amphi Schrödinger

QM/MM modeling of the retinal chromophore in complex environments.

We have used our QM/MM interface to model the photochemical and photophysical proper-
ties of the retinal chromophore in several environments.
First, we proved that methylation of the retinal backbone, which converts a slow photochemistry to an ultra-fast protein-like behaviour in methanol solution, modifies the interplay between the retinal excited states, favouring the formation of a photo-active transient intermediate. Then, we have studied the direct effect of the environment in the case of rhodopsin mimics, where point mutations of a few amino-acids lead to systems that can absorb in the wide visible range. Combined with ultra-fast pump-probe spectroscopy, our method has shown that the electrostatic potential around the retinal can affect the shape of the excited potential energy surface, and is able to tune the excited state lifetime as well as the location of the photoisomerization. Next, we showed that the currently accepted protonation state of amino-acids in the vicinity of the retinal in bacteriorhodopsin leads to a strongly blue shifted absorption, while the protonation of Asp212 leads to accurate results; we now aim toward a validation of this protonation by computation of fluorescence and excited state lifetime. Finally, we have modeled the photophysics of the unprotonated Schiff base in a UV-pigment, where an original an previously unreported photochemistry takes place, especially with the direct involvement of a doubly excited state.
These studies have shown the reliability of our QM/MM potential for modeling a wide range of
different environments.