Ultrafast photoreactions in biomolecules studied by femtosecond laser spectroscopy

by Stefan Haacke, University of Strasbourg

Thursday 22 Apr 2010, 11:00 → 12:00 Europe/Berlin

AER 19 3.11 (AER 19)

Light is used by bacteria as energy source (photo-synthesis) or for orientation (photo-taxis). On the molecular level, proteins are driving the underlying often complex bio-chemical machinery, and an ultrafast photochemical process is the starting point of these processes. In photo-sensory proteins, like the visual photo-receptor rhodopsin, this involves photo isomerisation, but more and more examples are known where photo-induced charge transfer is the energy-converting process. The present talk will review the recent progress made in understanding the ultrafast photo-physics of bacteriorhodopsin, the key element of archaebacterial photo-synthesis. Our focus is on the light-induced dipole moment change, and how this can be measured via the response of tryptophan amino acids [1,2]. When the photo-physics of rhodopsin's retinal is mimicked in artificial, computer-designed molecules, interesting new model systems are obtained, the so-called indanone-pyrollene photo switches. Isomerisation occurs within 0.3 ps and more remarkably, a vibrational coherence is observed, i.e. in concert among the ensemble of molecules, within half a torsional period [3,4]. This could open new perspectives for probing the "optically dark" S0/S1 crossing by ultrafast XPS spectroscopy. [1] “Probing the Ultrafast Charge Translocation of Photoexcited Retinal in Bacteriorhodopsin”, S. Schenkl, F.van Mourik, G. van der Zwan, S. Haacke, M. Chergui, Science 309, 917-921 (2005). [2]“Functional electric field changes in photo-activated proteins revealed by ultrafast Stark spectroscopy of the Trp residues”, J. Léonard, et al., Proc. Nat. Acad. Sci. USA, 7718-7723 (2009). [3] “An artificial molecular switch that mimics the visual pigment and completes its photocycle in picoseconds”, A. Sinicropi, et al., Proc. Nat. Acad. Sci. USA, 105,17642-17647 (2008). [4]"Ultrafast Coherent Torsional Motion and Isomerisation in a Dipolar Photoswitch", J. Briand et al., PCCP, in press (2010).