Exciton delocalization in the B808-866 antenna of the green bacterium Chloroflexus aurantiacus as revealed by ultrafast pump-probe spectroscopy.
A model of pigment organization in the B808-866 bacteriochlorophyll a antenna of the green photosynthetic bacterium Chloroflexus aurantiacus based on femtosecond pump-probe studies is proposed. The building block of the antenna was assumed to be structurally similar to that of the B800-850 light-harvesting 2 (LH2) antenna of purple bacteria and to have the form of two concentric rings of N strongly coupled BChl866 pigments and of N/2 weakly coupled BChl808 monomers, where N = 24 or 32. We have shown that the Qy transition dipoles of BChl808 and BChl866 molecules form the angles 43 degrees +/- 3 degrees and 8 degrees +/- 4 degrees, respectively, with the plane of the corresponding rings. Using the exciton model, we have obtained a quantitative fit of the pump-probe spectra of the B866 and B808 bands. The anomalously high bleaching value of the B866 band with respect to the B808 monomeric band provided the direct evidence for a high degree of exciton delocalization in the BChl866 ring antenna. The coherence length of the steady-state exciton wave packet corresponds to five or six BChl866 molecules at room temperature.
Novoderezhkin
V
V
A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia.
Fetisova
Z
Z
D016880:Anisotropy; D001426:Bacterial Proteins / Q000737:chemistry*; D001429:Bacteriochlorophylls / Q000737:chemistry*; D019414:Chlorobi / Q000737:chemistry*; D045342:Light-Harvesting Protein Complexes; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D010860:Pigments, Biological / Q000737:chemistry*; D013053:Spectrophotometry
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D010860:Pigments, Biological; C069404:protein complex B806-866, Chloroflexus aurantiacus