Strongly exciton-coupled BChle chromophore system in the chlorosomal antenna of intact cells of the green bacteriumChlorobium phaeovibrioides: A spectral hole burning study

Abstract

Spectral hole burning studies of intact cells of the green bacteriumChlorobium phaeovibrioides have proven that the Qy-absorption system of antenna bacteriochlorophylle (BChle) should be interpreted in terms of the delocalized exciton level structure of an aggregate. For the first time the 0-0 band of the lowest exciton state of BChle aggregates has been directly detected as the lowest energy inhomogeneously broadened band (FWHM ∼ 100 cm(-1); position of maximum, at ∼ 739 nm) of the near-infrared BChle band in the 1.8 K excitation spectrum (FWHM=750 cm(-1); position of maximum, at 715 nm). The comparative analysis of the hole spectra, measured for the three species of BChlc- ande-containing green bacteria, has shown that the 0-0 transition bands of the lowest exciton state of BChlc ande aggregates display fundamentally similar spectral features: (1) the magnitude of inhomogeneous broadening of these bands is about 100 cm(-1); (2) at the wavelength of the maximum of each band, the amplitude of the preburnt excitation spectrum makes up 20% of the maximum amplitude of the spectrum; (3) the spectral position of each band coincides with the spectral position of the longest wavelength band of the circular dichroism spectrum; (4) the width of these bands is ∼ 2.3-times less than that of monomeric BChl in vitro.

Theoretical characterization of excitation energy transfer in chlorosome light-harvesting antennae from green sulfur bacteria

“…The chlorosome pigments should be distinguished from ideal J-aggregates where the J-band with the largest oscillator strength is also the lowest exciton state (LES) [23,43]. Pšenčík et al [23] has shown that LESs in chlorosomes from C. tepidum are distributed within 760-800 nm range, while the absorption maximum is at 750 nm.…”

Structure of bacteriochlorophyll aggregates in chlorosomes of green bacteria: A spectral hole burning study

“…lA). The Hamiltonian can be written as (13) + ~ ~ We consider low-temperature optical spectra assuming a weak exclton-phonon coupling (3)(4)(5). In this case the perturbation theory for…”

“…One of the structural optlmizlng factors is oligomerization of antenna pigments [2). The chlorosome of green bacteria contalning several thousands of antenna bacteriochlorophyll (BChl) c,d or e molecules in an aggregated state is the most convincing example of natural antenna of oligomeric type (3)(4)(5). The discovered strong orientational ordering of the near-infrared transition dipoles of BChl c in situ (6) suggested that an elementary BChl aggregate has the form of a linear chain.…”

“…Information about the exciton level structure of in vivo BChl aggregates is available due to recent spectral hole-burning studies performed on three species of intact cells from both families of green bacteria, Chlorobiaceae and Chloroflexaceae (3)(4)(5). The experiments have…”

“…Only the models of exciton-coupled BChl chains with a low packing density, approximating that in vivo, can provide the exciton level structure revealed by hole-burning experiments on intact cells (3)(4)(5).…”