"Photochemical Z &rarr E Isomerization of a Hemithioindigo/Hemistilbene omega-Amino Acid"T. Cordes, B. Heinz, N. Regner, C. Hoppmann, T. E. Schrader, W. Summerer, K. Rück-Braun, and W. Zinth
ChemPhysChem 8 (2007) 1713 - 1721
The molecule HTI which combines a hemithioindigo and hemistilbene molecular part allows reversible switching between two isomeric states. The photochromic behaviour of the HTI-molecule is observed by irradiation with UV/VIS light. The photochemical reaction, a Z/E isomerization around the central double bond connecting the two
molecular parts, is investigated by transient absorption and emission spectroscopy. For a special HTI-molecule, an &omega-amino acid, the Z &rarr E isomerization process occurs on the time scale of 30 ps. In the course of the reaction fast processes on the 1-10 ps time scale are observed
which point to motions of the molecule on the excited state potential energy surface. The combination of transient absorption experiments
in the visible spectral range with time-resolved fluorescence and infrared measurements allows to reveal the photochemical pathway with three intermediate states. Together with a theoretical modelling procedure the experiments point to a sequential reaction scheme and give indications on the nature of the involved intermediates.
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Peptide and protein folding