Mechanism of Triplet Energy Transfer in Photosynthetic Bacterial Reaction Centers

Sarthak Mandal, Anne Marie Carey, Joshua Locsin, Bing Rong Gao, Joann C. Williams, James Paul Allen, Su Lin, Neal W. Woodbury

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

In purple bacterial reaction centers, triplet excitation energy transfer occurs from the primary donor P, a bacteriochlorophyll dimer, to a neighboring carotenoid to prevent photodamage from the generation of reactive oxygen species. The BB bacteriochlorophyll molecule that lies between P and the carotenoid on the inactive electron transfer branch is involved in triplet energy transfer between P and the carotenoid. To expand the high-resolution spectral and kinetic information available for describing the mechanism, we investigated the triplet excited state formation and energy transfer pathways in the reaction center of Rhodobacter sphaeroides using pump-probe transient absorption spectroscopy over a broad spectral region on the nanosecond to microsecond time scale at both room temperature and at 77 K. Wild-type reaction centers were compared with a reaction center mutant (M182HL) in which BB is replaced by a bacteriopheophytin (Φ), as well as to reaction centers that lack the carotenoid. In wild-type reaction centers, the triplet energy transfer efficiency from P to the carotenoid was essentially unity at room temperature and at 77 K. However, in the M182HL mutant reaction centers, both the rate and efficiency of triplet energy transfer were decreased at room temperature, and at 77 K, no triplet energy transfer was observed, attributable to a higher triplet state energy of the bacteriopheophytin that replaces bacteriochlorophyll in this mutant. Finally, detailed time-resolved spectral analysis of P, carotenoid, and BB (Φ in the M182HL mutant) reveals that the triplet state of the carotenoid is coupled fairly strongly to the bridging intermediate BB in wild-type and Φ in the M182HL mutant, a fact that is probably responsible for the lack of any obvious intermediate 3BB/3Φ transient formation during triplet energy transfer.

Original languageEnglish
Pages (from-to)6499-6510
Number of pages12
JournalJournal of Physical Chemistry B
Volume121
Issue number27
DOIs
Publication statusPublished - Jul 13 2017

Fingerprint

carotenoids
Carotenoids
Energy transfer
energy transfer
Bacteriochlorophylls
atomic energy levels
room temperature
Excitation energy
Spectral resolution
Absorption spectroscopy
Excited states
Dimers
Spectrum analysis
Temperature
Electron energy levels
spectrum analysis
unity
Reactive Oxygen Species
electron transfer
absorption spectroscopy

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

Mandal, S., Carey, A. M., Locsin, J., Gao, B. R., Williams, J. C., Allen, J. P., ... Woodbury, N. W. (2017). Mechanism of Triplet Energy Transfer in Photosynthetic Bacterial Reaction Centers. Journal of Physical Chemistry B, 121(27), 6499-6510. https://doi.org/10.1021/acs.jpcb.7b03373

Mechanism of Triplet Energy Transfer in Photosynthetic Bacterial Reaction Centers. / Mandal, Sarthak; Carey, Anne Marie; Locsin, Joshua; Gao, Bing Rong; Williams, Joann C.; Allen, James Paul; Lin, Su; Woodbury, Neal W.

In: Journal of Physical Chemistry B, Vol. 121, No. 27, 13.07.2017, p. 6499-6510.

Research output: Contribution to journalArticle

Mandal, S, Carey, AM, Locsin, J, Gao, BR, Williams, JC, Allen, JP, Lin, S & Woodbury, NW 2017, 'Mechanism of Triplet Energy Transfer in Photosynthetic Bacterial Reaction Centers', Journal of Physical Chemistry B, vol. 121, no. 27, pp. 6499-6510. https://doi.org/10.1021/acs.jpcb.7b03373
Mandal, Sarthak ; Carey, Anne Marie ; Locsin, Joshua ; Gao, Bing Rong ; Williams, Joann C. ; Allen, James Paul ; Lin, Su ; Woodbury, Neal W. / Mechanism of Triplet Energy Transfer in Photosynthetic Bacterial Reaction Centers. In: Journal of Physical Chemistry B. 2017 ; Vol. 121, No. 27. pp. 6499-6510.
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