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Quantum Mechanics/Molecular Mechanics Study on the Photoreactions of Dark‐ and Light‐Adapted States of a Blue‐Light YtvA LOV Photoreceptor
Author(s) -
Chang XuePing,
Gao YuanJun,
Fang WeiHai,
Cui Ganglong,
Thiel Walter
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201703487
Subject(s) - intersystem crossing , photochemistry , dark state , chemistry , qm/mm , diradical , photoexcitation , excited state , triplet state , chemical physics , conical intersection , computational chemistry , atomic physics , physics , molecular dynamics , singlet state
The dark‐ and light‐adapted states of YtvA LOV domains exhibit distinct excited‐state behavior. We have employed high‐level QM(MS‐CASPT2)/MM calculations to study the photochemical reactions of the dark‐ and light‐adapted states. The photoreaction from the dark‐adapted state starts with an S 1 →T 1 intersystem crossing followed by a triplet‐state hydrogen transfer from the thiol to the flavin moiety that produces a diradical intermediate, and a subsequent internal conversion that triggers a barrierless C−S bond formation in the S 0 state. The energy profiles for these transformations are different for the four conformers of the dark‐adapted state considered. The photochemistry of the light‐adapted state does not involve the triplet state: photoexcitation to the S 1 state triggers C−S bond cleavage followed by recombination in the S 0 state; both these processes are essentially barrierless and thus ultrafast. The present work offers new mechanistic insights into the photoresponse of flavin‐containing blue‐light photoreceptors.