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Ascension vibrationnelle dans les hémoprotéines à l'aide d'impulsions infrarouges intenses à dérive de fréquence

Abstract : Understanding the details of biochemical reactions which take place inside proteins is a central goal of molecular biology. In this work, we are interested in the first steps of such reactions, which occur on a time scale of a few hundreds of femtoseconds. The typical approach consists of using ultrashort pulses in the visible or UV range to excite the molecule to an upper electronic state, which rapidly triggers the reaction with high efficiency.
In this work, we have studied another way to excite proteins: namely, by using infrared pulses to deposit energy directly in the vibration of the molecule. In theory, this technique allows one to explore the protein potential surface far from the harmonic region, and even to approach the transition state of the reaction catalysed by the protein. To maximise the energy transfered to the molecule, we used intense and negatively chirped infrared pulses, which allows efficient climbing of the vibrational energy ladder.

In a first step, I generated intense infrared pulses whose energy is several microjoules and whose spectral width is roughly 170 cm-1. We then characterized these pulses using several methods: in particular, we measured their spectral phase using time-domain HOT SPIDER, resulting in the first self-referenced spectral phase measurement for infrared pulses centred around 10 µm.

In a second step, we used these infrared pulses to excite the vibration of a CO molecule bound to myoglobin and hemoglobin. In the latter case, we demonstrated vibrational climbing of the CO molecule up to the 7th step of the ladder, thus realising the first vibrational climbing experiment in a biological molecule, or more generally in a macromolecule. This technique gave new spectroscopic insight into carboxy-hemoglobin, such as the position and width of the absorption lines, the excited states lifetimes, and the presence of a significant electrical anharmonicity.
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Contributor : Cathie Ventalon <>
Submitted on : Thursday, February 17, 2005 - 12:43:57 AM
Last modification on : Wednesday, January 23, 2019 - 10:29:00 AM
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Cathie Ventalon. Ascension vibrationnelle dans les hémoprotéines à l'aide d'impulsions infrarouges intenses à dérive de fréquence. Biophysique [physics.bio-ph]. Ecole Polytechnique X, 2004. Français. ⟨tel-00008323⟩

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