title: A study of molecular interactions in light-harvesting complexes LHCIIb, CP29, CP26 and CP24 by Stark effect spectroscopy.
abstract: Electric field-induced absorption changes (electrochromism or Stark effect) of the light-harvesting PSII pigment-protein complexes LHCIIb, CP29, CP26 and CP24 were investigated. The results indicate the lack of strong intermolecular interactions in the chlorophyll a (Chl a) pools of all complexes. Characteristic features occur in the electronic spectrum of Chl b, which reflect the increased values of dipole moment and polarizability differences between the ground and excited states of interacting pigment systems. The strong Stark signal recorded for LHCIIb at 650-655 nm is much weaker in CP29, where it is replaced by a unique Stark band at 639 nm. Electrochromism of Chl b in CP26 and CP24 is significantly weaker but increased electrochromic parameters were also noticed for the Chl b transition at 650 nm. The spectra in the blue region are dominated by xanthophylls. The differences in Stark spectra of Chl b are linked to differences in pigment content and organization in individual complexes and point to the possibility of electron exchange interactions between energetically similar and closely spaced Chl b molecules.
authors.affiliation: Institute of Physics, Maria Curie-Skłodowska University, P1. M. Curie-Skl?odowskiej 1, 20-031 Lublin, Poland.
authors.forename: Dorota
authors.initials: D
authors.lastname: Olszówka
authors.forename: Stanisław
authors.initials: S
authors.lastname: Krawczyk
authors.forename: Waldemar
authors.initials: W
authors.lastname: Maksymiec
mesh_terms: D002734:Chlorophyll / Q000737:chemistry* / Q000528:radiation effects; D000077194:Chlorophyll A; D004563:Electrochemistry / Q000379:methods*; D004574:Electromagnetic Fields; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000528:radiation effects; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000528:radiation effects; D011485:Protein Binding; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A