title: Strategies to enhance the excitation energy-transfer efficiency in a light-harvesting system using the intra-molecular charge transfer character of carotenoids.
abstract: Fucoxanthin is a carotenoid that is mainly found in light-harvesting complexes from brown algae and diatoms. Due to the presence of a carbonyl group attached to polyene chains in polar environments, excitation produces an excited intra-molecular charge transfer. This intra-molecular charge transfer state plays a key role in the highly efficient (∼95%) energy-transfer from fucoxanthin to chlorophyll a in the light-harvesting complexes from brown algae. In purple bacterial light-harvesting systems the efficiency of excitation energy-transfer from carotenoids to bacteriochlorophylls depends on the extent of conjugation of the carotenoids. In this study we were successful, for the first time, in incorporating fucoxanthin into a light-harvesting complex 1 from the purple photosynthetic bacterium, Rhodospirillum rubrum G9+ (a carotenoidless strain). Femtosecond pump-probe spectroscopy was applied to this reconstituted light-harvesting complex in order to determine the efficiency of excitation energy-transfer from fucoxanthin to bacteriochlorophyll a when they are bound to the light-harvesting 1 apo-proteins.
authors.affiliation: Department of Applied Chemistry for Environment, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337, Japan. hideki-hassy@kwansei.ac.jp.
authors.forename: Nao
authors.initials: N
authors.lastname: Yukihira
authors.forename: Yuko
authors.initials: Y
authors.lastname: Sugai
authors.forename: Masazumi
authors.initials: M
authors.lastname: Fujiwara
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kosumi
authors.forename: Masahiko
authors.initials: M
authors.lastname: Iha
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Sakaguchi
authors.forename: Shigeo
authors.initials: S
authors.lastname: Katsumura
authors.forename: Alastair T
authors.initials: AT
authors.lastname: Gardiner
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
mesh_terms: D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008958:Models, Molecular; D008968:Molecular Conformation; D012247:Rhodospirillum rubrum / Q000201:enzymology; D024341:Xanthophylls / Q000737:chemistry / Q000378:metabolism*
chemical_list: D045342:Light-Harvesting Protein Complexes; D024341:Xanthophylls; C025164:fucoxanthin