Darmstadt 2008 – scientific programme

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MO: Fachverband Molekülphysik

MO 18: Femtosekundenspektroskopie

MO 18.1: Poster

Tuesday, March 11, 2008, 14:00–19:00, Poster C1

Femtosecond Optical and Vibrational Spectroscopy of Flavins and Flavoproteins — •Alexander Weigel and Luis Perez Lustres — Institute for Chemistry, Brook-Taylor-Str. 2, 12489 Berlin

Flavin photreceptors form a newly discovered class of blue-light sensing proteins which bind flavin chromophores as cofactors. Excitation of the chromophore leads to long living conformational changes in the protein, which trigger multiple biological responses. Contrary to the other known photoreceptor families, photactivation of flavoproteins does not occur by E/Z isomerization but displays unusual activation mechanisms which remain largely unknown. We apply femtosecond broadband transient absorption and report here on riboflavin and the phototropin mutant LOV1C57S. In the latter a critical cysteine residue was substituted by serine to hinder signalling state formation. Ultrafast loss of oscillator strength in riboflavin on a ∼10 fs timescale is assigned to vibronic coupling between the optically active ππ^* state and the dark nπ^* state. In the LOV1 mutant we were able to resolve spectral hole-burning at early time and its development on a 100 fs time scale. Weak spectral evolution with 1 ps time constant reflects structural reorganisation of the cofactor in the protein pocket. Vibrational wavepackets give rise to strong oscillations with frequencies ranging from 40 to 500 cm⁻¹. Remarkably, a 190 ps time constant and a series of oscillations with zero phase over the 20,000 cm⁻¹ spectral window exhibit similar spectral amplitudes, which may reflect coherent oscillations from vibronic coupling in the mutant. We present first results from broadband femtosecond stimulated Raman spectroscopy.