Influence of the Electrochemical Properties of the Bacteriochlorophyll Dimer on Triplet Energy-Transfer Dynamics in Bacterial Reaction Centers

Sarthak Mandal, Eduardo Espiritu, Natalie Akram, Su Lin, Joann C. Williams, James Paul Allen, Neal W. Woodbury

Research output: Contribution to journalArticle

Abstract

Energetics, protein dynamics, and electronic coupling are the key factors in controlling both electron and energy transfer in photosynthetic bacterial reaction centers (RCs). Here, we examine the rates and mechanistic pathways of the P+HA - radical-pair charge recombination, triplet state formation, and subsequent triplet energy transfer from the triplet state of the bacteriochlorophyll dimer (P) to the carotenoid in a series of mutant RCs (L131LH + M160LH (D1), L131LH + M197FH (D2), and L131LH + M160LH + M197FH (T1)) of Rhodobacter sphaeroides. In these mutants, the electronic structure of P is perturbed and the P/P+ midpoint potential is systematically increased due to addition of hydrogen bonds between P and the introduced residues. High-resolution, broad-band, transient absorption spectroscopy on the femtosecond to microsecond timescale shows that the charge recombination rate increases and the triplet energy transfer rate decreases in these mutants relative to the wild type (WT). The increase of the charge recombination rate is correlated to the increase in the energy level of P+HA - and the increase in the P/P+ midpoint potential. On the other hand, the decrease in rate of triplet energy transfer in the mutants can be explained in terms of a lower energy of 3P and a shift in the electron spin density distribution in the bacteriochlorophylls of P. The triplet energy-transfer rate follows the order of WT > L131LH + M197FH > L131LH + M160LH > L131LH + M160LH + M197FH, both at room temperature and at 77 K. A pronounced temperature dependence of the rate is observed for all of the RC samples. The activation energy associated to this process is increased in the mutants relative to WT, consistent with a lower 3P energy due to the addition of hydrogen bonds between P and the introduced residues.

Original languageEnglish
Pages (from-to)10097-10107
Number of pages11
JournalJournal of Physical Chemistry B
Volume122
Issue number44
DOIs
Publication statusPublished - Nov 8 2018

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Bacteriochlorophylls
Electrochemical properties
Dimers
Energy transfer
energy transfer
dimers
Hydrogen bonds
atomic energy levels
Electrons
Carotenoids
Absorption spectroscopy
hydrogen bonds
Electron energy levels
Electronic structure
carotenoids
Activation energy
electron spin
Proteins
density distribution
Temperature

ASJC Scopus subject areas

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

Cite this

Influence of the Electrochemical Properties of the Bacteriochlorophyll Dimer on Triplet Energy-Transfer Dynamics in Bacterial Reaction Centers. / Mandal, Sarthak; Espiritu, Eduardo; Akram, Natalie; Lin, Su; Williams, Joann C.; Allen, James Paul; Woodbury, Neal W.

In: Journal of Physical Chemistry B, Vol. 122, No. 44, 08.11.2018, p. 10097-10107.

Research output: Contribution to journalArticle

Mandal, Sarthak ; Espiritu, Eduardo ; Akram, Natalie ; Lin, Su ; Williams, Joann C. ; Allen, James Paul ; Woodbury, Neal W. / Influence of the Electrochemical Properties of the Bacteriochlorophyll Dimer on Triplet Energy-Transfer Dynamics in Bacterial Reaction Centers. In: Journal of Physical Chemistry B. 2018 ; Vol. 122, No. 44. pp. 10097-10107.
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