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Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides

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Title: Energy dissipative photoprotective mechanism of carotenoid spheroidene from the photoreaction center of purple bacteria Rhodobacter sphaeroides
Authors: Arulmozhiraja, Sundaram Browse this author
Nakatani, Naoki Browse this author
Nakayama, Akira Browse this author →KAKEN DB
Hasegawa, Jun-ya Browse this author
Issue Date: 4-Aug-2015
Publisher: Royal Society of Chemistry
Journal Title: Physical chemistry chemical physics
Volume: 17
Issue: 36
Start Page: 23468
End Page: 23480
Publisher DOI: 10.1039/c5cp03089g
PMID: 26292635
Abstract: Carotenoid spheroidene (SPO) functions for photoprotection in the photosynthetic reaction centers (RCs) and effectively dissipates its triplet excitation energy. Sensitized cis-to-trans isomerization was proposed as a possible mechanism for a singlet-triplet energy crossing for the 15,15'-cis-SPO; however, it has been questioned recently. To understand the dissipative photoprotective mechanism of this important SPO and to overcome the existing controversies on this issue, we carried out a theoretical investigation using density functional theory on the possible triplet energy relaxation mechanism through the cis-to-trans isomerization. Together with the earlier experimental observations, the possible mechanism was discussed for the triplet energy relaxation of the 15,15'-cis-SPO. The result shows that complete cis-to-trans isomerization is not necessary. Twisting the C15-C15' bond leads to singlet-triplet energy crossing at phi(14,15,15',14') = 77 degrees with an energy 32.5 kJ mol(-1) (7.7 kcal mol(-1)) higher than that of the T-1 15,15'-cis minimum. Further exploration of the minimum-energy intersystem crossing (MEISC) point shows that triplet relaxation could occur at a less distorted structure (phi = 58.4 degrees) with the energy height of 26.5 KJ mol(-1) (6.3 kcal mol(-1)). Another important reaction coordinate to reach the MEISC point is the bond-length alternation. The model truncation effect, solvent effect, and spin-orbit coupling were also investigated. The singlet-triplet crossing was also investigated for the 13,14-cis stereoisomer and locked-13,14-cis-SPO. We also discussed the origin of the natural selection of the cis over trans isomer in the RC.
Type: article (author version)
Appears in Collections:触媒科学研究所 (Institute for Catalysis) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 長谷川 淳也

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