Exciton (De)Localization in the LH2 Antenna of <i>Rhodobacter sphaeroides </i>As Revealed by Relative Difference Absorption Measurements of the LH2 Antenna and the B820 Subunit

Novoderezhkin, P.; Monshouwer, R.; Grondelle, Rienk van

doi:10.1021/jp9844415

Cited by 103 publications

(103 citation statements)

References 50 publications

(167 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…84,85 Very close estimates for these couplings were also obtained from the analysis of the relative difference absorption of the B820 subunit and B850 antenna. 86 This also agrees with the results reported in (46) (column k in Table 2) where the nearest to the Bchl-a chromophores proteins were explicitly taken into INDO/S/CIS calculations to model the dielectric medium effect. This effect could be attributed in part to the reduction of the Q y transition dipole due to solvent: the ∼ 1.2 decrease of the transition dipole roughly leads to the reduction of couplings by factor 1.2 2 ) 1.44.…”

Section: Frenkel Exciton Hamiltonian In a Dielectric Mediumsupporting

confidence: 90%

Bacteriochlorophyll and Carotenoid Excitonic Couplings in the LH2 System of Purple Bacteria

et al. 2000

View full text Add to dashboard Cite

An effective Frenkel-exciton Hamiltonian for the entire LH2 photosynthetic complex (B800, B850, and carotenoids) from Rhodospirillum molischianum is calculated by combining the crystal structure with the Collective Electronic Oscillators (CEO) algorithm for optical response. Electronic couplings among all pigments are computed for the isolated complex and in a dielectric medium, whereby the protein environment contributions are incorporated using the Self-Consistent Reaction Field approach. The absorption spectra are analyzed by computing the electronic structure of the bacteriochlorophylls and carotenoids forming the complex. Interchromophore electronic couplings are then calculated using both a spectroscopic approach, which derives couplings from Davydov's splittings in the dimer spectra, and an electrostatic approach, which directly computes the Coulomb integrals between transition densities of each chromophore. A comparison of the couplings obtained using these two methods allows for the separation of the electrostatic (Förster) and electron exchange (Dexter) contributions. The significant impact of solvation on intermolecular interactions reflects the need for properly incorporating the protein environment in accurate computations of electronic couplings. The Förster incoherent energy transfer rates among the weakly coupled B800-B800, B800-B850, Lyc-B850, and Lyc-B850 molecules are calculated, and the effects of the dielectric medium on the LH2 light-harvesting function are analyzed and discussed.

show abstract

Section: Frenkel Exciton Hamiltonian In a Dielectric Mediumsupporting

confidence: 90%

Bacteriochlorophyll and Carotenoid Excitonic Couplings in the LH2 System of Purple Bacteria

et al. 2000

View full text Add to dashboard Cite

show abstract

“…Generally, in LH2, quenching is performed by intramolecular and protein vibrations. Because LH2 has a fluorescence quantum yield of only 10%, these vibrations dissipate most photoenergy (28,29). A conformational change might increase vibronic coupling or coupling between intramolecular and protein vibrations to facilitate this dissipation.…”

Section: Discussionmentioning

confidence: 99%

Single-molecule spectroscopy reveals photosynthetic LH2 complexes switch between emissive states

Schlau‐Cohen¹,

Wang

Southall

et al. 2013

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

126

View full text Add to dashboard Cite

Photosynthetic organisms flourish under low light intensities by converting photoenergy to chemical energy with near unity quantum efficiency and under high light intensities by safely dissipating excess photoenergy and deleterious photoproducts. The molecular mechanisms balancing these two functions remain incompletely described. One critical barrier to characterizing the mechanisms responsible for these processes is that they occur within proteins whose excited-state properties vary drastically among individual proteins and even within a single protein over time. In ensemble measurements, these excited-state properties appear only as the average value. To overcome this averaging, we investigate the purple bacterial antenna protein light harvesting complex 2 (LH2) from Rhodopseudomonas acidophila at the single-protein level. We use a room-temperature, single-molecule technique, the antiBrownian electrokinetic trap, to study LH2 in a solution-phase (nonperturbative) environment. By performing simultaneous measurements of fluorescence intensity, lifetime, and spectra of single LH2 complexes, we identify three distinct states and observe transitions occurring among them on a timescale of seconds. Our results reveal that LH2 complexes undergo photoactivated switching to a quenched state, likely by a conformational change, and thermally revert to the ground state. This is a previously unobserved, reversible quenching pathway, and is one mechanism through which photosynthetic organisms can adapt to changes in light intensities.photosynthesis | purple bacteria | fluorescence spectroscopy I n photosynthetic light harvesting, networks of antenna pigmentprotein complexes (PPCs) absorb sunlight, then efficiently transport the excitation through these networks to the reaction center, a PPC dedicated to charge separation (1, 2). Photosynthetic systems can complete this process both with near unity quantum efficiency and also function at light levels that provide photoenergy in excess of the capacity of downstream photochemistry. This is accomplished through mechanisms that dissipate harmful by-products produced by unused photoenergy (2, 3). The absorption, energy transport, and dissipation properties are governed by the balance of pigment-pigment and pigment-protein couplings (4). However, the molecular machinery responsible for this balance, and for the couplings themselves, is still poorly understood. This is because the couplings are highly sensitive to intermolecular distances. As a result of this sensitivity, the light-harvesting properties vary drastically among individual PPCs, because of small differences in protein conformation, and vary drastically even within a single PPC over time, because of protein fluctuations (2). In ensemble measurements, these drastic variations appear solely as a static, average value. Therefore, only through single-molecule spectroscopy can we investigate the photodynamics of individual PPCs, specifically how the absorption, energy transport, and dissipation of each change with time. We ...

show abstract

“…16. However, somewhat larger values for both the reorganization energy and disorder have also been used to fit experimental data, 14,28 , as well as in studies of artificial circular excitonic systems. 44 For simplicity, we assume that each bath is characterized by the same spectral density.…”

Section: Model Systemsmentioning

confidence: 99%

“…[23][24][25][26] However, the influence of thermal noise on the coherence length is much more difficult to treat, and is generally either completely neglected or included only approximately. 8,9,27,28 Notable exceptions include the exact calculations of Ray and Makri in which they used the size of the bead from imaginary time path integral calculations as yet another estimate for the coherence length in LH2. 15 Similarly, Ishizaki and Fleming have used the exact hierarchy equations of motion simulations to study the concurrence and its time-dependence in a two-site model for LHCII.…”

Section: Introductionmentioning

confidence: 99%

Equilibrium-reduced density matrix formulation: Influence of noise, disorder, and temperature on localization in excitonic systems

2012

View full text Add to dashboard Cite

An exact method to compute the entire equilibrium reduced density matrix for systems characterized by a system-bath Hamiltonian is presented. The approach is based upon a stochastic unraveling of the influence functional that appears in the imaginary time path integral formalism of quantum statistical mechanics. This method is then applied to study the effects of thermal noise, static disorder, and temperature on the coherence length in excitonic systems. As representative examples of biased and unbiased systems, attention is focused on the well-characterized light harvesting complexes of FMO and LH2, respectively. Due to the bias, FMO is completely localized in the site basis at low temperatures, whereas LH2 is completely delocalized. In the latter, the presence of static disorder leads to a plateau in the coherence length at low temperature that becomes increasingly pronounced with increasing strength of the disorder. The introduction of noise, however, precludes this effect. In biased systems, it is shown that the environment may increase the coherence length, but only decrease that of unbiased systems. Finally it is emphasized that for typical values of the environmental parameters in light harvesting systems, the system and bath are entangled at equilibrium in the single excitation manifold. That is, the density matrix cannot be described as a product state as is often assumed, even at room temperature. The reduced density matrix of LH2 is shown to be in precise agreement with the steady state limit of previous exact quantum dynamics calculations. * Electronic address: jianshu@mit.edu 2

show abstract

Exciton (De)Localization in the LH2 Antenna of Rhodobacter sphaeroides As Revealed by Relative Difference Absorption Measurements of the LH2 Antenna and the B820 Subunit

Cited by 103 publications

References 50 publications

Bacteriochlorophyll and Carotenoid Excitonic Couplings in the LH2 System of Purple Bacteria

Bacteriochlorophyll and Carotenoid Excitonic Couplings in the LH2 System of Purple Bacteria

Single-molecule spectroscopy reveals photosynthetic LH2 complexes switch between emissive states

Equilibrium-reduced density matrix formulation: Influence of noise, disorder, and temperature on localization in excitonic systems

Contact Info

Product

Resources

About