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Title: Switching sides—Reengineered primary charge separation in the bacterial photosynthetic reaction center

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America

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 (H B ) 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 H B and only ∼4 Å from the 4 central nitrogens of the H B macrocycle—is the key additional mutation providing 90% yield of P + H B . This all but matches the near-unity yield of A-side P + H A charge separation in the native RC. The 90% yield of ET to H B 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 + B B intermediate, analogous to initial charge separation on the A side of wild-type RCs. In an ∼50% population, P* → P + H B conversion takes place in ∼20 ps by a superexchange mechanism mediated by B B . 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.

Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC02-06CH11357; SC0002036
OSTI ID:
1580676
Alternate ID(s):
OSTI ID: 1671638; OSTI ID: 1696796
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 2 Vol. 117; ISSN 0027-8424
Publisher:
National Academy of SciencesCopyright Statement
Country of Publication:
United States
Language:
English

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