A. Cheminal, M. Gueye, J. Léonard, S. Haacke
Photo-isomerization allows the conversion of light energy into mechanical energy via molecular motion. This phenomenon triggers vertebrate vision with the fast (150fs) and efficient (60% quantum yield) photosiomerization of retinal in the Rhodopsin protein. Deciphering the key parameters controlling optically triggered molecular motion is of major interest to design efficient molecular switches, motors or nano-manipulators.
In our group, we study the ultrafast isomerization of retinal proteins such as Bacteriorhodopsin [1, 2] and Anabaena Sensory Rhodopsin  (see fig. 1), as well as synthetic “biomimetic” photoswitching molecules [4-7] which were designed to mimic in a synthetic molecule the photoreaction properties of retinal in its natural protein environment.
Combining UV-vis transient absorption spectroscopy with <50fs time resolution and theoretical modeling performed by our partners (Prof. M. Olivucci, Siena, Italy, and Bowling Green, USA), we explore the parameters likely to rule the efficiency and dynamics of photoisomerization. By changing amino acids surrounding retinal in proteins through mutations, or substitutions on the molecules, we observe changes in the yield, speed and the presence of coherent, vibrational wavepackets during isomerization (see fig. 2).
Funding: ANR project IPQCS (2012-15); Labex NIE, Labex CSC, Equipex UNION, Région Alsace.
Collaborations: H. Kandori (Nagoya, Japan); M. Olivucci (Siena, Italy and Bowling Green USA); E. Gindensperger (Uni. Strasbourg, France); G. Cerullo (Politecnico Milano, Italy); Diego Sanpedro (La Rioja, Spain)
1. Leonard, J., et al., Functional electric field changes in photoactivated proteins revealed by ultrafast Stark spectroscopy of the Trp residues. Proceedings of the National Academy of Sciences of the United States of America, 2009. 106(19): p. 7718-7723.
3. Cheminal, A., et al., Steady state emission of the fluorescent intermediate of Anabaena Sensory Rhodopsin as a function of light adaptation conditions. Chemical Physics Letters, 2013. 587: p. 75-80.
4. Sinicropi, A., et al., An artificial molecular switch that mimics the visual pigment and completes its photocycle in picoseconds. Proceedings of the National Academy of Sciences of the United States of America, 2008. 105(46): p. 17642-17647.