Femtosecond dynamics of energy transfer in B800-850 light-harvesting complexes of Rhodobacter sphaeroides (original) (raw)
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Photochemistry and Photobiology, 1993
,4-dihydrospheroidene a)1,d spheroidene, have been incorporated into the B850 light-harvesting complex of the carotenoidless mutant, photosynthetic bacterium, Rhodobacter sphaeroides R-26.1. The extent of 'If-electron conjugation in these molecules in,creases from 7 to 10 carbon-<:arbon double bonds. Carotenoid-to-bacteriochlorophyll singlet state energy transfer efliciencies were measured using steady-state fluorescence excitation spectroscopy to be 54 :t 2%, 66 :t 4%, 71 :t 611& and 56 :t 3% for the carotenoid series. These results are discussed with respect to the position of the energy levels and the magnitude of spectral overlap between the S, (2'AJ state emission from the isolated carotenoids and the bacteriochlorophyll absorption of the native complex. These studies provide a systematic approach to exploring the efl"ect of excited state energies, spectral overlap and excited state lifetimes on the efficiencies of carotenoid-tobacteriochlorophyll singlet energy transfer in photosynthetic systems.
Carotenoid-bacteriochlorophyll energy transfer in LH2 complexes studied with 10-fs time resolution
2006
In this report, we present a study of carotenoid-bacteriochlorophyll energy transfer processes in two peripheral light-harvesting complexes (known as LH2) from purple bacteria. We use transient absorption spectroscopy with 10 fs temporal resolution, which is necessary to observe the very fast energy relaxation processes. By comparing excited-state dynamics of the carotenoids in organic solvents and inside the LH2 complexes, it has been possible to directly evaluate their energy transfer efficiency to the bacteriochlorophylls. In the case of okenone in the LH2 complex from Chromatium purpuratum, we obtained an energy transfer efficiency of h ET2 ¼ 63 6 2.5% from the optically active excited state (S 2) and h ET1 ¼ 61 6 2% from the optically dark state (S 1); for rhodopin glucoside contained in the LH2 complex from Rhodopseudomonas acidophila these values become h ET2 ¼ 49.5 6 3.5% and h ET1 ¼ 5.1 6 1%. The measurements also enabled us to observe vibrational energy relaxation in the carotenoids' S 1 state and real-time collective vibrational coherence initiated by the ultrashort pump pulses. Our results are important for understanding the dynamics of early events of photosynthesis and relating it to the structural arrangement of the chromophores.
The Journal of Physical Chemistry B, 2004
The B808-866 light-harvesting complex of the filamentous anoxygenic phototrophic green bacterium Chloroflexus aurantiacus has characteristics of both the LH1 and LH2 antenna complexes found in purple photosynthetic bacteria. Energy transfer kinetics in this complex were studied using ultrafast transient absorption spectroscopy and time-resolved fluorescence spectroscopy, including the excited singlet states of the γ-carotene present in the B808-866 complex and energy transfer to the B866 Bchl a. Energy transfer from the carotenoid S 1 state to the B866 Bchl a was observed and found to be ∼12-15% efficient. A separate pathway, populating the previously described S* state, was also observed as a precursor to carotenoid triplet state formation. While the energy transfer efficiency is similar to what has been reported for LH1 complexes of Rhodospirillum rubrum, the kinetic scheme for energy relaxation and transfer is somewhat different than that seen in either LH1 from Rhodospirillum rubrum or LH2 of Rhodobacter sphaeroides.
Journal of Physical Chemistry B, 1998
Ultrafast fluorescence upconversion has been used to probe electronic excitation transfer within the B800-B820 light-harvesting antenna of Rhodopseudomonas acidophila strain 7050. Emission from the carotenoid S 2 band decays in 54 ( 8 fs, and the bacteriochlorophyll B820 Q y band rises in approximately 110 fs. The B820 Q y rise time is wavelength-dependent. Energy-transfer rates between the carotenoid and several neighboring bacteriochlorophyll are calculated. Coupling strengths are estimated through transition dipoletransition dipole, polarization, and higher-order Coulombic coupling along with a new transition density volume coupling calculation. Data are compared to calculated energy-transfer rates through the use of a four-state model representing direct carotenoid to B820 energy transfer. The carotenoid emission data bound the S 2 to Q x transfer time between 65 and 130 fs. The S 1 to Q y transfer is assumed to be mediated by polarization and Coulombic coupling rather than by exchange; the transfer time is estimated to be in the picosecond regime, consistent with fluorescence quantum yield data. † Present address:
Proceedings of the National Academy of Sciences, 1986
Reaction centers from the photosynthetic bacterium Rhodopseudomonas viridis have been excited within the near-infrared absorption bands of the dimeric primary donor (P), of the “accessory” bacteriochlorophylls (B), and of the bacteriopheophytins (H) by using laser pulses of 150-fsec duration. The transfer of excitation energy between H, B, and P occurs in slightly less than 100 fsec and leads to the ultrafast formation of an excited state of P. This state is characterized by a broad absorption spectrum and exhibits stimulated emission. It decays in 2.8 ± 0.2 psec with the simultaneous oxidation of the primary donor and reduction of the bacteriopheophytin acceptor, which have been monitored at 545, 675, 815, 830, and 1310 nm. Although a transient bleaching relaxing in 400 ± 100 fsec is specifically observed upon excitation and observation in the 830-nm absorption band, we have found no indication that an accessory bacteriochlorophyll is involved as a resolvable intermediary acceptor ...
Biochemistry, 1994
Rhodobacter sphaeroides and Rhodopseudomonas acidophila has been studied a t 77 K using tunable femtosecond and subpicosecond infrared pulses. The complexes examined include the wild-type B800-850 as well as three different specifically mutated complexes. The site-directed mutant strains were altered at positions 44 and 45 near the C-terminus of the a-subunit, which introduces a spectral blue-shift of the 850-nm absorption band. In addition to a constant band a t 800 nm, the mutations aTyr44,Tyr45-.Phe,Tyr; +Tyr,Phe; and +Phe,Leu have absorption peaks a t 838, 838, and 826 nm, respectively. As the spectral overlap between the B800 and the variable bands increases, the rate of energy transfer as measured by the lifetime of the B800 excited state also increases from 2.4 f 0.2 to 1.8 f 0.2, 1.6 f 0.2, and 0.8 f 0.1 ps. This correlation between energy-transfer rate and spectral blue-shift of the B850 absorption band is in qualitative agreement with the trend predicted from Forster spectral overlap calculations, although the variation of the experimentally determined rate through the series of mutants is somewhat wider than what is predicted by simulations. In addition to the decay time constants related to the B8004B850 energy transfer, the B800 excited state is seen to decay with a faster 150-500-fs component due to energy transfer between spectrally inhomogeneous B800 molecules and possibly also vibrational relaxation and cooling in the bacteriochlorophyll excited state.
Excited-state dynamics in light-harvesting complex of Rhodobacter sphaeroides
Chinese Science Bulletin, 2008
Temperature-induced dissociation reaction and dynamics of light-harvesting complex II isolated from purple photosynthetic bacterium Rps. palustris Chinese Science Bulletin 52, 1029 (2007); Ultrafast excitation relaxation in light-harvesting complex LH2 from Rb. sphaeroides 601 Science in China Series B-Chemistry 47, 192 (2004); Effects of pH on the peripheral light-harvesting antenna complex for Rhodopseudomonas palustris Science in China Series C-Life Sciences 51, 760 (2008); Excited-state solvation dynamics of meso-tetrakis (4-sulfonatophenyl) porphyrin in solid imidazolium-sulfonate-based ionic liquids Chinese Science Bulletin 59, 492 (2014); Determination of pKa values of perylenequinonoid photosensitizer in excited state
LAT 2010: International Conference on Lasers, Applications, and Technologies, 2010
The pathways of excitation energy transfer (EET) via pigments of the light-harvesting antenna are still in discussion. The bacteriochlorophyll fluorescence of peripheral light-harvesting complexes (LH2) from purple bacteria can be observed upon two-photon excitation (TPE) within 1200-1500 nm spectral range (a broad band near 1300 nm). Earlier the occurrence of this band was taken as an evidence for the participation of "dark" carotenoid S 1 state in EET processes (see [Walla et al., Proc. Nat. Acad. Sci. U.S.A. 97, 10808-10813 (2000)] and references in it). However we showed that TPE spectrum of LH2 fluorescence within 1200-1500 nm is not associated with carotenoids [Stepanenko et al., J. Phys. Chem. B. 113(34), 11720-11723 (2009)]. Here we present TPE spectra of fluorescence for chromatophores and lightharvesting complexes LH2 and LH1 from wild-type cells and from carotenoid-depleted or carotenoidless mutant cells of several purple bacteria. The broad band within 1300-1400 nm was found for all preparations. Absorption pump-probe femtosecond spectroscopy applied to LH2 complex from Rb. sphaeroides revealed the similar spectral and kinetic patterns for TPE at 1350 nm and one-photon excitation at 675 nm. Analysis of pigment composition of this complex by high-pressure liquid chromatography showed that even under mild isolation conditions some bacteriochlorophyll molecules were oxidized to 3-acetyl-chlorophyll molecules having the long-wavelength absorption peak in the 650-700 nm range. It is proposed that these 3-acetyl-chlorophyll molecules are responsible for the broad band in TPE spectra within the 1200-1500 nm region.