Mapping the ultrafast vibrational dynamics of all- trans and 13- cis retinal isomerization in Anabaena Sensory Rhodopsin

Partha Pratim Roy (1) , Youshitoka Kato (2) , Rei Abe-Yoshizumi (2) , Elisa Pieri (3) , Nicolas Ferré (3) , Hideki Kandori (2) , Tiago Buckup (1)

1 Universität Heidelberg [Heidelberg] = Heidelberg University
2 NIT - Nagoya Institute of Technology
3 ICR - Institut de Chimie Radicalaire

Discrepancies in the isomerization dynamics and quantum yields of the trans and cis retinal protonated Schiff base is a well-known issue in the context of retinal photochemistry. Anabaena Sensory Rhodopsin (ASR) is a microbial retinal protein that comprises a retinal chromophore in two ground state (GS) conformations: all-trans, 15-anti (AT) and 13-cis, 15-syn (13C). In this work, we apply impulsive vibrational spectroscopic techniques (DFWM, pump-DFWM and pump-IVS) to ASR to shed more light on how the structural changes take place in the excited state within the same protein environment. Our findings point to distinct features in the ground state structural conformations as well as to drastically different evolutions in the excited state manifold. The ground state vibrational spectra show stronger Raman activity of the C14-H out-of-plane wag (at about 805 cm-1) for 13C than for AT isomer, which hints at a pre-distortion of the 13C in the ground state. Evolution of the Raman frequency after interaction with actinic pulse shows a blue shift for the C=C stretching and CH3 rocking mode for both isomers. For AT, however, the blue shift is not instantaneous as observed for the 13C isomer, rather it takes more than 200 fs to reach the maximum frequency shift. This frequency blue shift is rationalized by a decrease of the effective conjugation length during the isomerization reaction, which further confirms a slower formation of the twisted state for the AT isomer and corroborates the presence of a barrier in the excited state trajectory previously predicted by quantum chemical calculations.

Mots clés: Anabaena/chemistry; Bacterial Proteins/chemistry; Retinaldehyde/chemistry; Sensory Rhodopsins/chemistry; Stereoisomerism; Vibration

Domaines: Chimie théorique et/ou physique

Partha Pratim Roy, Youshitoka Kato, Rei Abe-Yoshizumi, Elisa Pieri, Nicolas Ferré, et al.. Mapping the ultrafast vibrational dynamics of all- trans and 13- cis retinal isomerization in Anabaena Sensory Rhodopsin. Physical Chemistry Chemical Physics, 2018, 20 (48), pp.30159-30173. ⟨10.1039/c8cp05469j⟩. ⟨hal-02053137⟩