Two-Dimensional Electronic Spectroscopy of the D1-D2-cyt b559 Photosystem II Reaction Center Complex

Myers, Jeffrey A.; Lewis, Kristin; Fuller, Franklin D.; Tekavec, Patrick F.; Yocum, Charles F.; Ogilvie, Jennifer P.

doi:10.1021/jz100972z

Cited by 121 publications

(143 citation statements)

References 45 publications

(119 reference statements)

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“…Such a background signal cannot be completely excluded, but at short times we see no sharp features that could account for a π∕2 radians phase shift, and we do not see phase evolution during the beating from population dynamics. Supporting this assumption, prior works on LH3 and other similar photosynthetic complexes consistently show broad, featureless excited state absorption in the upper diagonal region of the spectra (40)(41)(42). We also observe beating between the two states in the B850 band at the expected difference frequency as shown in Fig.…”

Section: Discussionsupporting

confidence: 84%

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

Harel

Engel

2012

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

179

213

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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...

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Section: Discussionsupporting

confidence: 84%

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

Harel

Engel

2012

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

179

213

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“…The extension of two-dimensional (2D) spectroscopy to the visible range [4] has allowed light-harvesting complexes to be investigated in great detail [5,6], revealing electronic energy transfer between the coupled pigments [5,7]. The observation of long-lasting oscillatory features in 2D spectra of the Fenna-Matthews-Olson (FMO) complex [8] has stimulated the hypothesis that this transfer happens coherently.…”

Section: Introductionmentioning

confidence: 99%

Laser-Limited Signatures of Quantum Coherence

et al. 2015

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The observation of persistent oscillatory signals in multidimensional spectra of proteinpigment complexes has spurred a debate on the role of coherence-assisted electronic energy transfer as a key operating principle in photosynthesis. Vibronic coupling has recently been proposed as an explanation for the long lifetime of the observed spectral beatings. However, photosynthetic systems are inherently complicated, and tractable studies on simple molecular compounds are in demand to fully understand the underlying physics. In this work, we present measurements and calculations on a solvated molecular homodimer with clearly resolvable oscillations in the corresponding twodimensional spectra. Through analysis of the various contributions to the nonlinear response, we succeed in isolating the signal due to inter-exciton coherence. We find that while calculations predict a prolongation of this coherence due to vibronic coupling, the combination of dynamic disorder and vibrational relaxation leads to a coherence decay on a timescale comparable to the electronic dephasing time.

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“…Possible complexities in primary photochemistry for the bacterial RC multicofactor core have been suggested by findings of excitation energy-dependent variation photochemical pathways (13,14), including those that do not involve P* (15,16) that are analogous to the primary processes identified in Photosystem I and II reaction centers in oxygenic photosynthesis. (17)(18)(19)(20). Analysis of a broad range of spectroscopic, excitation energy transfer, and electron transfer properties based on modeling the electronic structure of RCs have led to the concept that the hexameric cofactor core should be considered as a supermolecule with a ladder of exciton states composed of various contributions from each of the individual cofactors (21)(22)(23).…”

mentioning

confidence: 99%

Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

Huang

Ponomarenko

Wiederrecht

et al. 2012

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

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High-resolution mapping of cofactor-specific photochemistry in photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides was achieved by polarization selective ultrafast spectroscopy in single crystals at cryogenic temperature. By exploiting the fixed orientation of cofactors within crystals, we isolated a single transition within the multicofactor manifold, and elucidated the sitespecific photochemical functions of the cofactors associated with the symmetry-related active A and inactive B branches. Transient spectra associated with the initial excited states were found to involve a set of cofactors that differ depending upon whether the monomeric bacteriochlorophylls, BChl A , BChl B , or the special pair bacteriochlorophyll dimer, P, was chosen for excitation. Proceeding from these initial excited states, characteristic photochemical functions were resolved. Specifically, our measurements provide direct evidence for an alternative charge separation pathway initiated by excitation of BChl A that does not involve P*. Conversely, the initial excited state produced by excitation of BChl B was found to decay by energy transfer to P. A clear sequential kinetic resolution of BChl A and the A-side bacteriopheophytin, BPh A , in the electron transfer proceeding from P* was achieved. These experiments demonstrate the opportunity to resolve photochemical function of individual cofactors within the multicofactor RC complexes using single crystal spectroscopy.photosynthesis | transient absorption | light-harvesting

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Two-Dimensional Electronic Spectroscopy of the D1-D2-cyt b559 Photosystem II Reaction Center Complex

Cited by 121 publications

References 45 publications

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

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

Laser-Limited Signatures of Quantum Coherence

Cofactor-specific photochemical function resolved by ultrafast spectroscopy in photosynthetic reaction center crystals

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