The nature of the lower excited state of the special pair of bacterial photosynthetic reaction center of Rhodobacter Sphaeroides and the dynamics of primary charge separation

2016 ◽  
Vol 121 (2) ◽  
pp. 181-189 ◽  
Author(s):  
N. V. Ivashin ◽  
E. E. Shchupak
Keyword(s):  
Excited State ◽  
Reaction Center ◽  
Rhodobacter Sphaeroides ◽  
Charge Separation ◽  
Photosynthetic Reaction Center ◽  
Lower Excited State ◽  
Primary Charge Separation ◽  
Special Pair ◽  
Bacterial Photosynthetic Reaction Center

scholarly journals Switching sides—Reengineered primary charge separation in the bacterial photosynthetic reaction center

2019 ◽  
Vol 117 (2) ◽  
pp. 865-871 ◽  
Author(s):  
Philip D. Laible ◽  
Deborah K. Hanson ◽  
James C. Buhrmaster ◽  
Gregory A. Tira ◽  
Kaitlyn M. Faries ◽  
...  
Keyword(s):  
Reaction Center ◽  
Charge Separation ◽  
Internal Conversion ◽  
Photosynthetic Reaction Center ◽  
Primary Electron ◽  
Primary Electron Donor ◽  
Primary Charge Separation ◽  
Bacteriochlorophyll Dimer ◽  
Initial Charge ◽  
Bacterial Photosynthetic Reaction Center

We report 90% yield of electron transfer (ET) from the singlet excited state P* of the primary electron-donor P (a bacteriochlorophyll dimer) to the B-side bacteriopheophytin (HB) in the bacterial photosynthetic reaction center (RC). Starting from a platform Rhodobacter sphaeroides RC bearing several amino acid changes, an Arg in place of the native Leu at L185—positioned over one face of HB and only ∼4 Å from the 4 central nitrogens of the HB macrocycle—is the key additional mutation providing 90% yield of P+HB−. This all but matches the near-unity yield of A-side P+HA− charge separation in the native RC. The 90% yield of ET to HB derives from (minimally) 3 P* populations with distinct means of P* decay. In an ∼40% population, P* decays in ∼4 ps via a 2-step process involving a short-lived P+BB− intermediate, analogous to initial charge separation on the A side of wild-type RCs. In an ∼50% population, P* → P+HB− conversion takes place in ∼20 ps by a superexchange mechanism mediated by BB. An ∼10% population of P* decays in ∼150 ps largely by internal conversion. These results address the long-standing dichotomy of A- versus B-side initial charge separation in native RCs and have implications for the mechanism(s) and timescale of initial ET that are required to achieve a near-quantitative yield of unidirectional charge separation.

Synthesis of two cyanine dyes as potential artificial antennas for the bacterial photosynthetic Reaction Center

MRS Advances ◽  
2019 ◽  
Vol 4 (22) ◽  
pp. 1293-1298 ◽  
Author(s):  
R. Ragni ◽  
G. Leone ◽  
G. Rizzo ◽  
S. la Gatta ◽  
F. Milano ◽  
...  
Keyword(s):  
Reaction Center ◽  
Cross Section ◽  
Rhodobacter Sphaeroides ◽  
Spectral Region ◽  
Photophysical Properties ◽  
Photosynthetic Reaction Center ◽  
Visible Spectral Region ◽  
Absorption Cross ◽  
Conversion Yield ◽  
Bacterial Photosynthetic Reaction Center

ABSTRACT:Particular attention has been recently devoted to the development of biohybrid photoconverters based on the bacterial Reaction Center (RC) of Rhodobacter sphaeroides. This highly efficient photoenzyme has a conversion yield close to unit that makes it extremely appealing in the field of artificial photosynthesis. Isolated RCs suffer of a limited absorption cross-section in the visible spectral region that limits their applicative employment. Here we report the synthesis of two heptamethine cyanine molecules, whose photophysical properties make them potentially suitable as light harvesting antennas for the RC.

scholarly journals Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy

2018 ◽  
Vol 115 (14) ◽  
pp. 3563-3568 ◽  
Author(s):  
Andrew Niedringhaus ◽  
Veronica R. Policht ◽  
Riley Sechrist ◽  
Arkaprabha Konar ◽  
Philip D. Laible ◽  
...  
Keyword(s):  
Excited State ◽  
Reaction Center ◽  
Charge Separation ◽  
Purple Bacteria ◽  
Electronic Spectroscopy ◽  
Reaction Centers ◽  
Purple Bacterium ◽  
Absorption Bands ◽  
Sequential Reaction ◽  
Special Pair

In the initial steps of photosynthesis, reaction centers convert solar energy to stable charge-separated states with near-unity quantum efficiency. The reaction center from purple bacteria remains an important model system for probing the structure–function relationship and understanding mechanisms of photosynthetic charge separation. Here we perform 2D electronic spectroscopy (2DES) on bacterial reaction centers (BRCs) from two mutants of the purple bacterium Rhodobacter capsulatus, spanning the Qy absorption bands of the BRC. We analyze the 2DES data using a multiexcitation global-fitting approach that employs a common set of basis spectra for all excitation frequencies, incorporating inputs from the linear absorption spectrum and the BRC structure. We extract the exciton energies, resolving the previously hidden upper exciton state of the special pair. We show that the time-dependent 2DES data are well-represented by a two-step sequential reaction scheme in which charge separation proceeds from the excited state of the special pair (P*) to P+HA− via the intermediate P+BA−. When inhomogeneous broadening and Stark shifts of the B* band are taken into account we can adequately describe the 2DES data without the need to introduce a second charge-separation pathway originating from the excited state of the monomeric bacteriochlorophyll BA*.

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