Berlin 2012 – scientific programme

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BP: Fachverband Biologische Physik

BP 7: Posters: Proteins

BP 7.10: Poster

Monday, March 26, 2012, 17:30–19:30, Poster A

Many-Body study of the excited-state properties of the Retinal Protonated Schiff Base of Rhodopsin — •Adriano Mosca Conte¹, Leonardo Guidoni², Daniele Varsano³, and Olivia Pulci¹ — ¹MIFP, NAST, ETSF,CNR INFM-SMC, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, Roma, Italy — ²University of L'Aquila, Dipartimento di Chimica, Ingegneria Chimica e Materiali, Via Campo di Pile, 67100, L'Aquila, Italy — ³University of Rome "La Sapienza" , P.le Aldo Moro 2, Rome, Italy

The first step of the mechanism of vision in living creatures is the photo-isomerization of the rhodopsin chromophore: the protonated Schiff base of the 11-cis retinal. We investigate the optical properties of the tZt-penta-3,5-dieniminium cation, a simplified model for the retinal, along the isomerization pathway by ab-initio calculations based on Many-Body Perturbation Theory (GW method and the Bethe-Salpeter equation), and by TDDFT. Our excitation energies are qualitatively in agreement with previous Quantum Monte Carlo and Post-Hartree Fock calculations. We then investigate the effect of the protein environment on the optical absorption spectra of the 11-cis retinal, in gas phase and in the rhodopsin. We follow a Quantum-Mechanics/Molecular-Mechanics scheme in which the retinal is treated by quantum Many-Body methods (DFT+GW+BSE), while the surrounding atoms of the protein are treated according to a classical model. Our results show that the effect of the rhodopsin on the retinal produces a geometrical distorsion of the retinal and a blueshift on the absorption spectrum in good agreement with the experiments.