title: Excitonic energy level structure and pigment-protein interactions in the recombinant water-soluble chlorophyll protein. I. Difference fluorescence line-narrowing.
abstract: Difference fluorescence line-narrowing spectroscopy at 4.5 K was employed to investigate electron-phonon and electron-vibrational coupling strengths of the lower exciton level of water-soluble chlorophyll-binding protein (WSCP) from cauliflower reconstituted with chlorophyll a or chlorophyll b, respectively. The electron-phonon coupling is found to be moderate with integral Huang-Rhys factors S in the order of 0.81-0.85. A weak dependence of S on excitation wavelength within the inhomogeneously broadened fluorescence origin band is attributed to a sizable contribution of nonresonant excitation that varies with excitation wavelength. The strongly asymmetric and highly structured one-phonon profile is characterized by a peak phonon frequency (ω(m)) of ~24 cm(-1) and further discernible peaks at 48 and 88 cm(-1), respectively. A structural assignment of this unusual one-phonon profile is proposed. As will be shown in the accompanying paper (part II) (DOI 10.1021/jp111457t), the parameters of electron-phonon coupling readily account for shape and position of the fluorescence origin bands at 666.1 and 683.8 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. A rich structure of S(1)→S(0) vibrational frequencies was resolved in the wavenumber range between 180 and 1665 cm(-1) for both chlorophyll a- and chlorophyll b-WSCP. The corresponding individual Huang-Rhys factors fall in the range between 0.0011 and 0.0500. To the best of our knowledge, this is the first report of S-factors for vibrational modes of chlorophyll b. Most remarkable is the presence of two additional modes at 228 and 327 cm(-1) compared with the vibrational spectrum of chlorophyll in solution. The additional modes can most likely be attributed to H-bond formation in the vicinity of the chlorophyll molecule bound by WSCP.
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: H
authors.initials: H
authors.lastname: Paulsen
authors.forename: G
authors.initials: G
authors.lastname: Renger
authors.forename: A
authors.initials: A
authors.lastname: Freiberg
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; D014867:Water / Q000737:chemistry
chemical_list: D045342:Light-Harvesting Protein Complexes; D011994:Recombinant Proteins; D014867:Water; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A