Tönu Pullerits
Professor
Picosecond dynamics of directed excitation transfer in spectrally heterogeneous light-harvesting antenna of purple bacteria
Author
Summary, in English
Picosecond spectrally resolved fluorescence kinetics measurements,
together with model simulations of the obtained data, based on coupled
rate equations, have been employed to determine the rates and the
pathways of heterogeneous excitation transfer in Rhodobacter sphaeroides and Chromatium minutissimum.
The presence of a directed excitation flow from the short-wavelength
bacteriochlorophyll forms to the long-wavelength one and from the latter
to reaction centres has been revealed. As a result, the overall
excitation trapping time in the bacteria investigated has been found to
be about 60 ps both at 77 K and at room temperature, i.e. the same as in
Rhodospirillum rubrum, although the number of antenna
bacteriochlorophyll molecules per reaction centre is several times
larger. A comparison of the experimental and theoretical kinetic data
shows that, besides obvious spectral heterogeneity of the
bacteriochlorophyll antenna represented by well-resolved B800, B850 and
B875 spectra forms, an intrinsic spectral inhomogeneiry of these forms
is likely to play an essential role in the excitation transfer. The
obtained picture of the mutual arrangement of different complexes in
membranes is similar to the one suggested earlier, except that the
presence of at least two typesof B800-850 complexes, the ones closely
associated with B875 and the more remote ones,has been discovered. The
excitation transfer to B875 has been shown to take about 10 and 50 ps
for the first and the second type of B850 molecules, respectively. The
intracomplex B800 → B850 transfer time is an order of magnitude smaller,
about 1 ps. These three time constants seem to be practically
independent of the reaction centre state and the temperature in the 300
K-77 K interval. At high excitation intensities (more than 1 · 1010
photons per pulse) a shortening of the long-wavelength fluorescence
decay time and a short-wavelength shiftof the corresponding band maximum
have been observed. Both effects are due to the annihilation of singlet
and triplet excitations.
together with model simulations of the obtained data, based on coupled
rate equations, have been employed to determine the rates and the
pathways of heterogeneous excitation transfer in Rhodobacter sphaeroides and Chromatium minutissimum.
The presence of a directed excitation flow from the short-wavelength
bacteriochlorophyll forms to the long-wavelength one and from the latter
to reaction centres has been revealed. As a result, the overall
excitation trapping time in the bacteria investigated has been found to
be about 60 ps both at 77 K and at room temperature, i.e. the same as in
Rhodospirillum rubrum, although the number of antenna
bacteriochlorophyll molecules per reaction centre is several times
larger. A comparison of the experimental and theoretical kinetic data
shows that, besides obvious spectral heterogeneity of the
bacteriochlorophyll antenna represented by well-resolved B800, B850 and
B875 spectra forms, an intrinsic spectral inhomogeneiry of these forms
is likely to play an essential role in the excitation transfer. The
obtained picture of the mutual arrangement of different complexes in
membranes is similar to the one suggested earlier, except that the
presence of at least two typesof B800-850 complexes, the ones closely
associated with B875 and the more remote ones,has been discovered. The
excitation transfer to B875 has been shown to take about 10 and 50 ps
for the first and the second type of B850 molecules, respectively. The
intracomplex B800 → B850 transfer time is an order of magnitude smaller,
about 1 ps. These three time constants seem to be practically
independent of the reaction centre state and the temperature in the 300
K-77 K interval. At high excitation intensities (more than 1 · 1010
photons per pulse) a shortening of the long-wavelength fluorescence
decay time and a short-wavelength shiftof the corresponding band maximum
have been observed. Both effects are due to the annihilation of singlet
and triplet excitations.
Publishing year
1989-01
Language
English
Pages
93-104
Publication/Series
BBA - Bioenergetics
Volume
973
Issue
1
Document type
Journal article
Publisher
Elsevier
Keywords
- (Chr. minutissimum)
- (Rb. sphaeroides)
- Excitation annihilation
- Excitation transfer
- Fluorescence
- Light harvesting antenna
- Photosynthesis, bacterial
- Picosecond fluorescence
Status
Published
ISBN/ISSN/Other
- ISSN: 0005-2728