STRONGLY EXCITON-COUPLED BCHL-E CHROMOPHORE SYSTEM IN THE CHLOROSOMAL ANTENNA OF INTACT-CELLS OF THE GREEN BACTERIUM CHLOROBIUM PHAEOVIBRIOIDES - A SPECTRAL HOLE-BURNING STUDY

Spectral hole burning studies of intact cells of the green bacterium Chlorobium phaeovibrioides have proven that the Q(y)-absorption system of antenna bacteriochlorophyll e (BChl e) 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 BChl e aggregates has been directly detected as the lowest energy inhomogeneously broadened band (FWHM similar to 100 cm(-1). position of maximum, at similar to 739 nm) of the near-infrared BChl e 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 BChl c- and e-containing green bacteria, has shown that the 0-0 transition bands of the lowest exciton state of BChl c and e 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 similar to 2.3-times less than that of monomeric BChl in vitro.