Femtosecond Exciton Relaxation in Chlorosomes of the Photosynthetic Green Bacterium Chloroflexus aurantiacus

Process of photosynthesis in the green bacteria Chloroflexus (Cfx.) aurantiacus starts from absorption of light by chlorosomes, peripheral antennas consisting of thousands of bacteriochlorophyll  c (BChl  c ) molecules combined into oligomeric structures. In this case, the excited states are formed...

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Bibliographic Details
Published in:Biochemistry (Moscow) 2023-05, Vol.88 (5), p.704-715
Main Authors: Yakovlev, Andrei G., Taisova, Alexandra S., Fetisova, Zoya G.
Format: Article
Language:English
Subjects:
Absorption
Analysis
Bacteria
Bacteria, Photosynthetic
Bacteriochlorophyll
Biochemistry
Biomedical and Life Sciences
Biomedicine
Bioorganic Chemistry
Chlorophyll
Chlorosomes
Coordination compounds
Cryogenic temperature
Electromagnetic absorption
Energy charge
Exciton theory
Excitons
Genetic aspects
Identification and classification
Kinetic equations
Life Sciences
Light
Mathematical analysis
Microbiology
Microscopy
Photosynthesis
Properties
Proteins
Solar energy
Spectroscopy
Spectrum analysis
Structure
Wavelength
Wavelengths
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Summary:Process of photosynthesis in the green bacteria Chloroflexus (Cfx.) aurantiacus starts from absorption of light by chlorosomes, peripheral antennas consisting of thousands of bacteriochlorophyll  c (BChl  c ) molecules combined into oligomeric structures. In this case, the excited states are formed in BChl  c , energy of which migrates along the chlorosome towards the baseplate and further to the reaction center, where the primary charge separation occurs. Energy migration is accompanied by non-radiative electronic transitions between the numerous exciton states, that is, exciton relaxation. In this work, we studied dynamics of the exciton relaxation in Cfx. aurantiacus chlorosomes using differential femtosecond spectroscopy at cryogenic temperature (80 K). Chlorosomes were excited by 20-fs light pulses at wavelengths in the range from 660 to 750 nm, and differential (light-dark) absorption kinetics were measured at a wavelength of 755 nm. Mathematical analysis of the obtained data revealed kinetic components with characteristic times of 140, 220, and 320 fs, which are responsible for exciton relaxation. As the excitation wavelength decreased, the number and relative contribution of these components increased. Theoretical modelling of the obtained data was carried out based of the cylindrical model of BChl  c . Nonradiative transitions between the groups of exciton bands were described by a system of kinetic equations. The model that takes into account energy and structural disorder of chlorosomes turned out to be the most adequate.
ISSN:0006-2979
1608-3040
DOI:10.1134/S0006297923050139