Excited State Energy Transfer Pathways in Photosynthetic Reaction Centers. 1. Structural Symmetry Effects

Stanley, Robert J.; King, Brett; Boxer, Steven G.

doi:10.1021/jp9614916

Cited by 89 publications

(193 citation statements)

References 49 publications

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“…The fluorescence decay of P* was measured by fluorescence upconversion essentially as described. 94 Emission was detected at 890 nm at the magic angle relative to the excitation at 800 nm. RC samples had an OD of 0.6 at 800 nm in a 1 mm path length and contained 1 mM dithionite and terbutryn at 30 times the RC concentration to reduce Q A and displace Q B , respectively.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Between 10 and 40 scans were averaged for each sample. Each average was fit to the convolution of the pumpprobe cross correlation as determined the same day (typically between 150 and 170 fs) and a sum of exponentials, which included a fixed rise time of 150 fs due to the energy transfer from B* to P. 94 Picosecond Transient Absorption Spectroscopy. The transient absorption measurements were conducted basically as described previously 95 and utilized a regeneratively amplified Ti:sapphire laser pumping an OPA (Spectra Physics) to generate 130 fs excitation and white-light probe flashes at 10 Hz.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Temperature Dependence of Electron Transfer to the M-Side Bacteriopheophytin in Rhodobacter capsulatus Reaction Centers

et al. 2008

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-lauryl-N,N-dimethylamine-N-oxide (LDAO) is used to suspend the RCs, the excited state of the primary electron donor (P*) decays to the ground state with an average lifetime at 77 K of 330 or 170 ps, respectively; however, in both cases the time constant obtained from single-exponential fits varies markedly as a function of the probe wavelength. These findings on the D LL RC are most easily explained in terms of a heterogeneous population of RCs. Similarly, the complex results for D LL -FY L F M in Deriphatglycerol glass at 77 K are most simply explained using a model that involves (minimally) two distinct populations of RCs with very different photochemistry. Within this framework, in 50% of the D LL -FY L F M RCs in Deriphat-glycerol glass at 77 K, P* deactivates to the ground state with a time constant of ∼400 ps, similar to the deactivation of P* in the D LL mutant at 77 K. In the other 50% of D LL -FY L F M RCs, P* has a 35 ps lifetime and decays via electron transfer to the M branch, giving P + H M -in high yield (g80%). This result indicates that P* f P + H M -is roughly a factor of 2 faster at 77 K than at 295 K. In alternative homogeneous models the rate of this M-side electron-transfer process is the same or up to 2-fold slower at low temperature. A 2-fold increase in rate with a reduction in temperature is the same behavior found for the overall L-side process P* f P + H L -in wild-type RCs. Our results suggest that, as for electron transfer on the L side, the M-side electron-transfer reaction P* f P + H M -is an activationless process.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Temperature Dependence of Electron Transfer to the M-Side Bacteriopheophytin in Rhodobacter capsulatus Reaction Centers

et al. 2008

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“…Energy transfer from 1 B to P as measured by the rise of emission from 1 P at 940 nm for 804 nm excitation is 163 ( 54 fs. 5 That the decay of emission at 850 nm matches the rise of emission from 1 P suggests that the excited state probed at 850 nm transfers energy to P. 15 Emission between 800 and 850 nm is observed for excitation in the H band at 760 nm in WT RCs at 85 K ( Figure 3B shows emission at 815 nm). The emitting state is populated with a lifetime of 85 ( 17 fs ( 1 H f B) and decays with a lifetime of 199 ( 16 fs ( 1 B f P).…”

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confidence: 91%

Excited State Energy Transfer Pathways in Photosynthetic Reaction Centers. 3. Ultrafast Emission from the Monomeric Bacteriochlorophylls

et al. 2000

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Ultrafast singlet excited state energy transfer occurs from the monomeric bacteriopheophytin (H) and bacteriochlorophyll (B) chromophores to the primary electron donor or special pair (P) in bacterial photosynthetic reaction centers. Because of rapid quenching of the singlet excited state of B by energy transfer to P, 1 B emission has not previously been observed in functional reaction centers. Using fluorescence upconversion, spontaneous fluorescence associated with the monomeric bacteriochlorophylls is observed for excitation of the monomeric bacteriochlorophylls and bacteriopheophytins at 85 K. The decay kinetics of the fluorescence match the kinetics of the rise of emission from 1 P, the ultimate acceptor of singlet energy. Together with measurements of the time-resolved fluorescence anisotropy, the data suggest that 1 B is populated in the energy transfer pathway from 1 H to P. By exciting H in wild-type and in the reaction center mutant M182HL, where contributions from the chromophores in the B sites on the L and M sides are spectrally resolved, the amplitudes of the kinetic traces at several wavelengths between 790 and 825 nm can be used to construct the time-resolved emission spectrum of 1 B. The Stokes shift of the accessory bacteriochlorophylls in wild-type on the femtosecond time scale is close to zero, while for the monomeric bacteriopheophytin in the B M binding site in the M182HL mutant, the Stokes shift is less than 100 cm -1 . These results have significant implications for the mechanism of ultrafast energy transfer in the reaction center.The bacterial photosynthetic reaction center (RC) is responsible for the initial light-driven charge separation events in photosynthesis. Light energy absorbed by antenna complexes is funneled to the special pair in the RC, and 1 P transfers an electron to an electron acceptor, rapidly trapping the excitation energy in a transient charge-separated species. In isolated RCs, excitation of the special pair can be achieved by rapid singlet excited state energy transfer from the monomeric bacteriopheophytins and bacteriochlorophylls. 1-3 A schematic diagram illustrating the arrangement of the chromophores that are relevant to both the energy and electron-transfer processes is shown in Figure 1 (top panel) based on the X-ray structure, 4 and a putative singlet excitation energy transfer scheme paralleling the structure is shown in Figure 1 (bottom panel). The chromophores labeled B L and B M are monomeric bacteriochlorophylls on the functional and nonfunctional sides, respectively, of the RC; the chromophores labeled H L and H M are monomeric bacteriopheophytins on the functional and nonfunctional sides, respectively. Functional is used here to denote the electrontransfer process 1 P f P + H L -which is found to occur almost exclusively in wild-type RCs at all temperatures, despite the structural symmetry of the RC that suggests that 1 P f P + H M -might be equally likely to occur.It is possible to study the rate of singlet energy transfer from the B and H chromophore...

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“…At room temperature P ϩ B A Ϫ is formed as a short-lived, intermediate with a lifetime of 0.9-1.5 ps (7)(8)(9)(10)(11). Charge separation is completed by electron transfer from P Until recently it generally was accepted that excitation of the RC bacteriopheophytins or monomeric Bchls resulted in downhill energy transfer to P within a few hundreds of femtoseconds, forming P* that drives charge separation (12)(13)(14)(15). However, steady-state fluorescence excitation experiments conducted at 77 K on mutant RCs in which P* has a very long lifetime have shown that, despite their rapidity, the efficiency of this energy transfer is not 100% (16,17).…”

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Multiple pathways for ultrafast transduction of light energy in the photosynthetic reaction center of Rhodobacter sphaeroides

Brederode

Mourik

Stokkum

et al. 1999

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

112

107

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A pathway of electron transfer is described that operates in the wild-type reaction center (RC) of the photosynthetic bacterium Rhodobacter sphaeroides. The pathway does not involve the excited state of the special pair dimer of bacteriochlorophylls (P*), but instead is driven by the excited state of the monomeric bacteriochlorophyll (B A *) present in the active branch of pigments along which electron transfer occurs. Pump-probe experiments were performed at 77 K on membrane-bound RCs by using different excitation wavelengths, to investigate the formation of the charge separated state P ؉ H A ؊ . In experiments in which P or B A was selectively excited at 880 nm or 796 nm, respectively, the formation of P ؉ H A ؊ was associated with similar time constants of 1.5 ps and 1.7 ps. However, the spectral changes associated with the two time constants are very different. Global analysis of the transient spectra shows that a mixture of P ؉ B A ؊ and P* is formed in parallel from B A * on a subpicosecond time scale. In contrast, excitation of the inactive branch monomeric bacteriochlorophyll (B B ) and the high exciton component of P (P ؉ ) resulted in electron transfer only after relaxation to P*. The multiple pathways for primary electron transfer in the bacterial RC are discussed with regard to the mechanism of charge separation in the RC of photosystem II from higher plants.

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Excited State Energy Transfer Pathways in Photosynthetic Reaction Centers. 1. Structural Symmetry Effects

Cited by 89 publications

References 49 publications

Temperature Dependence of Electron Transfer to the M-Side Bacteriopheophytin in Rhodobacter capsulatus Reaction Centers

Temperature Dependence of Electron Transfer to the M-Side Bacteriopheophytin in Rhodobacter capsulatus Reaction Centers

Excited State Energy Transfer Pathways in Photosynthetic Reaction Centers. 3. Ultrafast Emission from the Monomeric Bacteriochlorophylls

Multiple pathways for ultrafast transduction of light energy in the photosynthetic reaction center of Rhodobacter sphaeroides

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