Energetics and kinetics of primary charge separation in bacterial photosynthesis

David N. LeBard, Vitaliy Kapko, Dmitry Matyushov

Research output: Contribution to journalArticle

42 Citations (Scopus)

Abstract

We report the results of molecular dynamics (MD) simulations and formal modeling of the free-energy surfaces and reaction rates of primary charge separation in the reaction center of Rhodobacter sphaeroides. Two simulation protocols were used to produce MD trajectories. Standard force-field potentials were employed in the first protocol. In the second protocol, the special pair was made polarizable to reproduce a high polarizability of its photoexcited state observed by Stark spectroscopy. The charge distribution between covalent and chargetransfer states of the special pair was dynamically adjusted during the simulation run. We found from both protocols that the breadth of electrostatic fluctuations of the protein/water environment far exceeds previous estimates, resulting in about 1.6 eV reorganization energy of electron transfer in the first protocol and 2.5 eV in the second protocol. Most of these electrostatic fluctuations become dynamically frozen on the time scale of primary charge separation, resulting in much smaller solvation contributions to the activation barrier. While water dominates solvation thermodynamics on long observation times, protein emerges as the major thermal bath coupled to electron transfer on the picosecond time of the reaction. Marcus parabolas were obtained for the free-energy surfaces of electron transfer by using the first protocol, while a highly asymmetric surface was obtained in the second protocol. A nonergodic formulation of the diffusion-reaction electron-transfer kinetics has allowed us to reproduce the experimental results for both the temperature dependence of the rate and the nonexponential decay of the population of the photoexcited special pair.

Original languageEnglish (US)
Pages (from-to)10322-10342
Number of pages21
JournalJournal of Physical Chemistry B
Volume112
Issue number33
DOIs
StatePublished - Aug 21 2008

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photosynthesis
Photosynthesis
polarization (charge separation)
electron transfer
Kinetics
Electrons
Solvation
kinetics
Free energy
solvation
Molecular dynamics
Electrostatics
free energy
electrostatics
molecular dynamics
proteins
Proteins
parabolas
Water
simulation

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Energetics and kinetics of primary charge separation in bacterial photosynthesis. / LeBard, David N.; Kapko, Vitaliy; Matyushov, Dmitry.

In: Journal of Physical Chemistry B, Vol. 112, No. 33, 21.08.2008, p. 10322-10342.

Research output: Contribution to journalArticle

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