title: Unified analysis of ensemble and single-complex optical spectral data from light-harvesting complex-2 chromoproteins for gaining deeper insight into bacterial photosynthesis.
abstract: Bacterial light-harvesting pigment-protein complexes are very efficient at converting photons into excitons and transferring them to reaction centers, where the energy is stored in a chemical form. Optical properties of the complexes are known to change significantly in time and also vary from one complex to another; therefore, a detailed understanding of the variations on the level of single complexes and how they accumulate into effects that can be seen on the macroscopic scale is required. While experimental and theoretical methods exist to study the spectral properties of light-harvesting complexes on both individual complex and bulk ensemble levels, they have been developed largely independently of each other. To fill this gap, we simultaneously analyze experimental low-temperature single-complex and bulk ensemble optical spectra of the light-harvesting complex-2 (LH2) chromoproteins from the photosynthetic bacterium Rhodopseudomonas acidophila in order to find a unique theoretical model consistent with both experimental situations. The model, which satisfies most of the observations, combines strong exciton-phonon coupling with significant disorder, characteristic of the proteins. We establish a detailed disorder model that, in addition to containing a C_{2}-symmetrical modulation of the site energies, distinguishes between static intercomplex and slow conformational intracomplex disorders. The model evaluations also verify that, despite best efforts, the single-LH2-complex measurements performed so far may be biased toward complexes with higher Huang-Rhys factors.
authors.affiliation: Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu, Estonia.
authors.forename: Mihkel
authors.initials: M
authors.lastname: Pajusalu
authors.affiliation: Experimental Physics IV and Bayreuth Institute for Macromolecular Research, University of Bayreuth, 95440 Bayreuth, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Kunz
authors.affiliation: Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu, Estonia.
authors.forename: Margus
authors.initials: M
authors.lastname: Rätsep
authors.affiliation: Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu, Estonia.
authors.forename: Kõu
authors.initials: K
authors.lastname: Timpmann
authors.affiliation: Experimental Physics IV and Bayreuth Institute for Macromolecular Research, University of Bayreuth, 95440 Bayreuth, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Köhler
authors.affiliation: Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu, Estonia.|Institute of Molecular and Cell Biology, University of Tartu, Riia 23, 51010 Tartu, Estonia.
authors.forename: Arvi
authors.initials: A
authors.lastname: Freiberg
mesh_terms: D005454:Fluorescence Polarization; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D009010:Monte Carlo Method; D010788:Photosynthesis; D011487:Protein Conformation; D012241:Rhodopseudomonas / Q000201:enzymology / Q000378:metabolism*
chemical_list: D045342:Light-Harvesting Protein Complexes