Energetics of Primary Charge Separation in Bacterial Photosynthetic Reaction Center Mutants:  Triplet Decay in Large Magnetic Fields†

2003 ◽  
Vol 107 (18) ◽  
pp. 3341-3350 ◽  
Author(s):  
Alex de Winter ◽  
Steven G. Boxer
Keyword(s):  
Magnetic Fields ◽  
Reaction Center ◽  
Charge Separation ◽  
Photosynthetic Reaction Center ◽  
Primary Charge Separation ◽  
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.

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