title: Broadband 2D electronic spectroscopy reveals a carotenoid dark state in purple bacteria.
abstract: Although the energy transfer processes in natural light-harvesting systems have been intensively studied for the past 60 years, certain details of the underlying mechanisms remain controversial. We performed broadband two-dimensional (2D) electronic spectroscopy measurements on light-harvesting proteins from purple bacteria and isolated carotenoids in order to characterize in more detail the excited-state manifold of carotenoids, which channel energy to bacteriochlorophyll molecules. The data revealed a well-resolved signal consistent with a previously postulated carotenoid dark state, the presence of which was confirmed by global kinetic analysis. The results point to this state's role in mediating energy flow from carotenoid to bacteriochlorophyll.
authors.affiliation: Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada.
authors.forename: Evgeny E
authors.initials: EE
authors.lastname: Ostroumov
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Mulvaney
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Scholes
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry*; D004735:Energy Transfer; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D012242:Rhodobacter sphaeroides / Q000201:enzymology* / Q000528:radiation effects; D012241:Rhodopseudomonas / Q000201:enzymology* / Q000528:radiation effects
chemical_list: C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D002338:Carotenoids