Barrierless Photoisomerization of 11-cis Retinal Protonated Schiff Base in Solution
Giovanni Bassolino1, Tina Sovdat2, Alex Soares Duarte1
1Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford , South Parks Road, Oxford OX1 3QZ, U.K.
Abstract:
A hallmark of the primary visual event is the barrierless, ultrafast, and efficient 11-cis to all-trans photoisomerization of the retinal protonated Schiff base (RPSB) chromophore. The remarkable reactivity of RPSB in the visual pigment rhodopsin has been attributed to potential energy surface modifications enabled by evolution-optimized chromophore-protein interactions. Here, we use a combined synthetic and ultrafast spectroscopic approach to show that barrierless photoisomerization is an intrinsic property of 11-cis RPSB, suggesting that the protein may merely adjust the ratio between fast reactive and slow unreactive decay channels. These results call for a re-evaluation of our understanding and theoretical description of RPSB photochemistry.
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