Characterization of excitation energy trapping in photosynthetic purple bacteria at 77 K

Bergström, Hans; Grondelle, Rienk van; Sundström, Villy

doi:10.1016/0014-5793(89)80785-9

Cited by 70 publications

(58 citation statements)

References 23 publications

(43 reference statements)

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“…sphaeroides complexes. As a reference energy transfer time, we have used the -35 ps measured for the trapping of energy from LH1 by the RC (23)(24)(25), which was inferred to correspond to a distance of 35-40 A between the B875 Bchls and the special pair of the RC.…”

Section: Methodsmentioning

confidence: 99%

Temporally and spectrally resolved subpicosecond energy transfer within the peripheral antenna complex (LH2) and from LH2 to the core antenna complex in photosynthetic purple bacteria.

Hess

Chachisvilis

Timpmann

et al. 1995

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

123

110

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We report studies ofenergy transfer from the 800-nm absorbing pigment (B800) to the 850-nm absorbing pigment (B850) of the LH2 peripheral antenna complex and from LH2 to the core antenna complex (LH1) in Rhodobacter (Rb.) sphaeroides. The B800 to B850 process was studied in membranes from a LH2-reaction center (no LH1) mutant of Rb. sphaeroides and the LH2 to LH1 transfer was studied in both the wild-type species and in LH2 mutants with blueshifted B850. The measurements were performed by using '100-fs pulses to probe the formation of acceptor excitations in a two-color pump-probe measurement. Our experiments reveal a B800 to B850 transfer time of -0.7 ps at 296 K and energy transfer from LH2 to LH1 is characterized by a time constant of -3 ps at 296 K and -5 ps at 77 K. In the blue-shifted B850 mutants, the transfer time from B850 to LH1 becomes gradually longer with increasing blue-shift of the B850 band as a result of the decreasing spectral overlap between the antennae. The results have been used to produce a model for the association between the ring-like structures that are characteristic of both the LH2 and LH1 antennae.Organization and function of the core antenna complex (LH1) and the peripheral antenna complex (LH2) of purple bacteria have been extensively studied in the past (1, 2, 29). A major step forward in this work was taken very recently when the threedimensional structure of a complex of the peripheral antenna absorbing at 800 nm (B800) and at 850 nm (B850) from Rhodopseudomonas (Rps.) acidophila was solved to high resolution showing a ninefold circular symmetry of a13 pairs (3). From this structure of LH2 and the similar circular structure of LH1 (4), it has become clear that the pigment density in these light harvesting pigments is very high, leading to short intermolecular distances and strong dipole-dipole interactions. Presently, two modes of energy transfer are considered, incoherent F6rster transfer or exciton state relaxation (5-8), and it is a challenge for future research to establish the levels of organization at which the two modes of energy transfer are operative. Until experiments and theory have produced a unified description of the energy transfer dynamics, we have chosen to describe the energy transfer steps within LH2 and LH1 and between the complexes as incoherent Forster hopping. Early work on energy transfer dynamics in photosynthetic purple bacteria (9-16) yielded information about the overall exciton lifetime in the antenna and provided a time scale for energy equilibration within individual complexes (9, 10) and over the whole antenna (11,16). In particular, the LH2 antenna is probably the most extensively studied complex. Picosecond absorption and fluorescence studies performed at room and low temperature on the LH2 pigmentprotein complex of Rhodobacter (Rb.) sphaeroides revealed that B800 -> B850 energy transfer is a very fast and temperature-The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereb...

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Section: Methodsmentioning

confidence: 99%

Temporally and spectrally resolved subpicosecond energy transfer within the peripheral antenna complex (LH2) and from LH2 to the core antenna complex in photosynthetic purple bacteria.

Hess

Chachisvilis

Timpmann

et al. 1995

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

123

110

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“…The S parameters tend to agree with experiment somewhat better than the R parameters, although not completely. For example, S parameters get the LH1 → RC transfer time approximately right (estimated at 20 ps at room temperature [57,67]), but the reverse rate (7-9 ps [68]) is much better captured by the R parameters. Measured transfer times involving LH2 (5 ps for LH2 → LH2 [69] and 3.3 ps for LH2 → LH1 [70]) also agree with those predicted from the S parameters at the separations we used.…”

Section: Geometrymentioning

confidence: 99%

Distinguishing the roles of energy funnelling and delocalization in photosynthetic light harvesting

Baghbanzadeh

Kassal

2016

Phys. Chem. Chem. Phys.

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Photosynthetic complexes improve the transfer of excitation energy from peripheral antennas to reaction centers in several ways. In particular, a downward energy funnel can direct excitons in the right direction, while coherent excitonic delocalization can enhance transfer rates through the cooperative phenomenon of supertransfer. However, isolating the role of purely coherent effects is difficult because any change to the delocalization also changes the energy landscape. Here, we show that the relative importance of the two processes can be determined by comparing the natural light-harvesting apparatus with counterfactual models in which the delocalization and the energy landscape are altered. Applied to the example of purple bacteria, our approach shows that although supertransfer does enhance the rates somewhat, the energetic funnelling plays the decisive role. Because delocalization has a minor role (and is sometimes detrimental), it is most likely not adaptive, being a side-effect of the dense chlorophyll packing that evolved to increase light absorption per reaction center.Photosynthetic organisms harvest light using antenna complexes containing many chlorophyll molecules [1]. The energy collected by the antennas is then transmitted, through excitonic energy transfer (EET) [2], to a reaction center (RC), where it drives the first chemical reactions of photosynthesis. The thorough study of EET in photosynthetic antennas has been motivated, in part, by the prospect of learning how to design more efficient artificial light-harvesting devices [3,4].It has long been recognized that excitons in many photosynthetic complexes are directed toward the RC energetically: if the antennas lie higher in energy than the RC, the excitons can spontaneously funnel to the RC. A more recent discovery is that coherent mechanisms can also enhance light-harvesting efficiency. In particular, excitonic eigenstates may be localized or delocalized over a number of molecules, depending on the strength of their couplings [2,[5][6][7][8]. Delocalization-i.e., coherence in the site basis-makes the aggregate behave differently than a single chlorophyll molecule, and phenomena such as superradiance [9,10], superabsorption [11], and supertransfer [12][13][14][15] can occur in densely packed aggregates. Specifically, supertransfer occurs when delocalization in the donor and/or the acceptor enhances the rate of the (incoherent) EET between them.The presence of both funnelling and supertransfer suggests that their contributions to the efficiency could be quantified. However, the two effects are too closely related for such a separation to be easily carried out; in particular, a change to the extent of delocalization requires changing excitonic couplings, which also determine the energy landscape. In other words, because delocalization and the energy landscape are intimately connected, it is not sufficient to alter one property to see what happens to the efficiency, because doing so also alters the other property as well.Here, we show that the ...

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“…As shown above the lifetime of P* in both mutants is much longer than in the wild type. The RC receives excitation via the light harvesting complexes and the transfer of this excitation to the RC occurs in approximately 20-30 ps (van Grondelle et al, 1987;Bergström et al, 1989). Since the lifetime of P* in wild type is short (3.5 ps) there is essentially no accumulation of P* and energy transfer is efficient.…”

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confidence: 99%

The Role of Tyrosine M210 in the Initial Charge Separation in the Reaction Center of Rhodobacter sphaeroides

Gray

Farchaus

Wachtveitl

et al. 1990

Reaction Centers of Photosynthetic Bacteria

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Characterization of excitation energy trapping in photosynthetic purple bacteria at 77 K

Cited by 70 publications

References 23 publications

Temporally and spectrally resolved subpicosecond energy transfer within the peripheral antenna complex (LH2) and from LH2 to the core antenna complex in photosynthetic purple bacteria.

Temporally and spectrally resolved subpicosecond energy transfer within the peripheral antenna complex (LH2) and from LH2 to the core antenna complex in photosynthetic purple bacteria.

Distinguishing the roles of energy funnelling and delocalization in photosynthetic light harvesting

The Role of Tyrosine M210 in the Initial Charge Separation in the Reaction Center of Rhodobacter sphaeroides

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