Energy transfer dynamics of the B800—B850 antenna complex of Rhodobacter sphaeroides: a hole burning study

Reddy, N. R. S.; Small, Gerald J.; Seibert, Michael; Picorel, Rafael

doi:10.1016/0009-2614(91)90369-k

Cited by 129 publications

(193 citation statements)

References 43 publications

Supporting

Mentioning

174

Contrasting

Order By: Relevance

“…[13][14][15] Hole-burning measurements have shown that in the B800 band of LH-2, narrow holes can be burnt over the whole absorption band (at 4.2 K), suggesting that most of the width of this band (170 cm -1 ) is due to inhomogeneous broadening. 15 From site-selected fluorescence measurements on the B820 subunit, 16 and spectral modeling of the absorption and fluorescence spectra, 45,46 it was concluded that the width of the inhomogeneous distribution function (IDF) of this subunit is approximately 250-350 cm -1 . From modeling of pump probe measurements an estimate of 400 cm -1 at room temperature and 200 cm -1 at 4 K for the LH-1 antenna of Rs.…”

Section: Discussionmentioning

confidence: 99%

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

et al. 1997

View full text Add to dashboard Cite

We present temperature-dependent fluorescence quantum yield and lifetime measurements on the LH-1 and LH-2 complexes of Rhodobacter sphaeroides and on the isolated B820 subunit of Rhodospirillum rubrum. From these measurements the superradiance is calculated, which is related to the delocalization of excitations in these complexes. In the B820 preparation we find a radiative rate that is 30% higher than that of monomeric bacteriochlorophyll, in agreement with a dimer model of this subunit. At room temperature both LH-1 and LH-2 are superradiant relative to monomeric Bchl-a with enhancement factors of 3.8 and 2.8, respectively. In LH-2 the radiative rate does not change significantly upon lowering the temperature to 4 K. LH-1 however exhibits a strong temperature dependence, giving rise to a 2.4 times higher radiative rate at 4 K relative to room temperature. From modeling of the superradiance using a Hamiltonian based on the LH-2 structure and including site inhomogeneity, we conclude that the ratio of inhomogeneity over the coupling between the pigments is around 1 for LH-1 and 2-3 for LH-2. From the Monte Carlo simulations we estimate the delocalization length in LH-1 and LH-2 to be on the order of 3-4 pigments at room temperature.

show abstract

Section: Discussionmentioning

confidence: 99%

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

et al. 1997

View full text Add to dashboard Cite

show abstract

“…Reddy et al (12,13) have studied the dynamics of the B850 complex of chromatophores of Rb. sphaeroides by nonphotochemical hole burning and have concluded that even at 4.2 K, where pure dephasing of the ground and excited-state electronic coherence is negligible, the absorption band is almost entirely homogeneously broadened.…”

Section: Discussionmentioning

confidence: 99%

Ultrafast exciton relaxation in the B850 antenna complex ofRhodobacter sphaeroides

Nagarajan

Alden

Williams

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

100

101

View full text Add to dashboard Cite

Spectral changes were measured with femtosecond resolution following low-intensity, broad-band excitation of the peripheral antenna complex of the purple photosynthetic bacterium Rhodobacter sphaeroides. Absorption anisotropy decays also were measured. We identified a 35-fs relaxation of the absorption and emission spectra of the excited state, as well as a 20-fs anisotropy decay. We interpret these results as interlevel relaxation and dephasing, respectively, of extensively delocalized exciton states of the circular bacteriochlorophyll aggregate.Photosynthetic organisms contain pigment-protein antenna complexes that absorb light and transfer energy rapidly to the reaction centers where charge separation occurs. The crystal structures of the peripheral light-harvesting complexes (LH2) from two species of photosynthetic purple bacteria have been determined recently by McDermott et al. (1) and Koepke et al. (2). With these structures in hand, it now is possible to evaluate the intermolecular interactions that give rise to the multiple excited states of an antenna complex and to explore the roles of these states in energy transfer. The LH2 complex of Rhodopseudomonas acidophila (1) contains 27 molecules of bacteriochlorophyll-a (BChl). Eighteen of these molecules are arranged in a ring with their Q y transition dipoles (N1-N3 molecular axes) oriented approximately in the membrane plane. These BChls are termed the B850 pigments because they probably account for the strong absorption band of the complex in the region of 850 nm (3). A similar ring of 16 BChls occurs in the complex from Rhodospirillum molischianum (2). The short distances between the B850 BChls would be expected to bring about relatively strong exciton interactions, which could lead to extensively delocalized excited states. The remaining BChl molecules in the LH2 complex form a larger ring that probably accounts for an absorption band at 800 nm. Here the intermolecular interactions are weaker and the excited states may be more localized (4). In this paper we use femtosecond pump-probe spectroscopy to investigate the dynamics of the excited states of B850 in Rhodobacter sphaeroides. Our results support the notion of delocalized exciton states involving the entire B850 ring. EXPERIMENTALFemtosecond Spectrometer. The pump and probe pulses were derived from a femtosecond Ti͞sapphire laser of Murnane-Kapteyn design (5). The laser delivered pulses centered at 850 nm with a spectral range as broad as 120 nm and a pulse width as short as 12 fs. The pulse spectrum and the width were adjustable by varying the placement of the intracavity, fusedsilica prisms. The repetition rate of the pulses was reduced from 96 MHz to 200 kHz by focusing the light on a Bragg cell outside the laser cavity and collecting the acoustooptically diffracted light after a single pass. The diffraction efficiency was about 30% per pulse. The diffracted beam was split into pump and probe beams with an intensity ratio of 9:1; the two beams were sent through separate sets of LaKL2...

show abstract

“…Numerous time-resolved experiments have measured energy transfer from the B800 ring to the B850 ring in under a picosecond at room temperature (3)(4)(5)(6)(7). Förster resonance energy transfer (FRET) theory (8) estimates a slower transfer time by approximately a factor of five (9)(10)(11)(12)(13).…”

mentioning

confidence: 99%

Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2)

Harel

Engel

2012

Proc. Natl. Acad. Sci. U.S.A.

186

213

View full text Add to dashboard Cite

Light-harvesting antenna complexes transfer energy from sunlight to photosynthetic reaction centers where charge separation drives cellular metabolism. The process through which pigments transfer excitation energy involves a complex choreography of coherent and incoherent processes mediated by the surrounding protein and solvent environment. The recent discovery of coherent dynamics in photosynthetic light-harvesting antennae has motivated many theoretical models exploring effects of interference in energy transfer phenomena. In this work, we provide experimental evidence of long-lived quantum coherence between the spectrally separated B800 and B850 rings of the light-harvesting complex 2 (LH2) of purple bacteria. Spectrally resolved maps of the detuning, dephasing, and the amplitude of electronic coupling between excitons reveal that different relaxation pathways act in concert for optimal transfer efficiency. Furthermore, maps of the phase of the signal suggest that quantum mechanical interference between different energy transfer pathways may be important even at ambient temperature. Such interference at a product state has already been shown to enhance the quantum efficiency of transfer in theoretical models of closed loop systems such as LH2.quantum biology | photosynthesis | ultrafast spectroscopy | biophysics | excitonic dynamics L ight-harvesting complex 2 (LH2) is the peripheral antenna pigment-protein complex of purple non-sulfur bacteria. LH2 contains two rings of BChl a pigments known as the B800 and B850 rings according to their respective room-temperature absorption bands in the infrared region of the spectrum (Fig. 1). These pigments are held in place by noncovalent interactions with pairs of low-molecular weight apoproteins. In most bacterial species, the LH2 complex consists of eight or nine of these protein heterodimers (αβ) organized in a highly symmetric ring (1). LH2 increases the effective cross-section for photon absorption from the solar spectrum in the membrane of purple bacteria. The energy absorbed by LH2 passes to another light-harvesting complex (LH1) tightly associated with the photosynthetic reaction center (2), wherein a stable charge separated state forms that ultimately drives the production of ATP.The energy transfer dynamics in LH2 has been studied for many years. Numerous time-resolved experiments have measured energy transfer from the B800 ring to the B850 ring in under a picosecond at room temperature (3-7). Förster resonance energy transfer (FRET) theory (8) estimates a slower transfer time by approximately a factor of five (9-13). Close examination of electronic coupling between pigments within each ring reveals, in part, the origin of this discrepancy. Studies on the excitation of the B850 ring (14-17) indicate the existence of Frenkel excitons (18,19), delocalized excitations that persist across several pigment molecules depending on the degree of structural symmetry present. In one limiting case, excitation is delocalized across the entire ring, invalidating a fundamen...

show abstract

Energy transfer dynamics of the B800—B850 antenna complex of Rhodobacter sphaeroides: a hole burning study

Cited by 129 publications

References 43 publications

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

Ultrafast exciton relaxation in the B850 antenna complex ofRhodobacter sphaeroides

Quantum coherence spectroscopy reveals complex dynamics in bacterial light-harvesting complex 2 (LH2)

Contact Info

Product

Resources

About