title: Excitonic energy level structure and pigment-protein interactions in the recombinant water-soluble chlorophyll protein. II. Spectral hole-burning experiments.
abstract: Persistent spectral hole burning at 4.5 K has been used to investigate the excitonic energy level structure and the excited state dynamics of the recombinant class-IIa water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The hole-burned spectra are composed of four main features: (i) a narrow zero-phonon hole (ZPH) at the burn wavelength, (ii) a number of vibrational ZPHs, (iii) a broad low-energy hole at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, and (iv) a second satellite hole at ~658 and ~673 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The doublet of broad satellite holes is assigned to an excitonically coupled chlorophyll dimer. The lower-energy holes at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, represent the lower exciton states. Taking into account the parameters of electron-phonon coupling, the lower exciton state can be assigned as the fluorescence origin. The lower exciton state is populated by two processes: (i) exciton relaxation from the higher exciton state and (ii) vibrational relaxation within the lower exciton state. Assuming identical site energies for the two excitonically coupled chlorophyll molecules, the dipole-dipole interaction energy J is directly determined to be 85 and 100 cm(-1) for chlorophyll b- and chlorophyll a-WSCP, respectively, based on the positions of the satellite holes. The Gaussian low-energy absorption band identified by constant fluence hole burning at 4.5 K has a width of ~150 cm(-1) and peaks at 664.9 and 682.7 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The action spectrum is broader and blue-shifted compared to the fluorescent lower exciton state. This finding can be explained by a slow protein relaxation between energetically inequivalent conformational substates within the lowest exciton state in agreement with the results of Schmitt et al. (J. Phys. Chem. B2008, 112, 13951).
authors.affiliation: Max-Volmer-Laboratories for Biophysical Chemistry, Berlin Institute of Technology, Berlin, Germany. joerg.pieper@tu-berlin.de
authors.forename: J
authors.initials: J
authors.lastname: Pieper
authors.forename: M
authors.initials: M
authors.lastname: Rätsep
authors.forename: I
authors.initials: I
authors.lastname: Trostmann
authors.forename: F-J
authors.initials: FJ
authors.lastname: Schmitt
authors.forename: C
authors.initials: C
authors.lastname: Theiss
authors.forename: H
authors.initials: H
authors.lastname: Paulsen
authors.forename: H J
authors.initials: HJ
authors.lastname: Eichler
authors.forename: A
authors.initials: A
authors.lastname: Freiberg
authors.forename: G
authors.initials: G
authors.lastname: Renger
mesh_terms: D001937:Brassica / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D004583:Electrons; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014732:Vibration; D014867:Water / Q000737:chemistry
chemical_list: D045342:Light-Harvesting Protein Complexes; D011994:Recombinant Proteins; D014867:Water; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A