Path integral simulation of charge transfer dynamics in photosynthetic reaction centers

Eun Ji Sim, Nancy Makri

Research output: Contribution to journalArticle

84 Citations (Scopus)

Abstract

We present accurate path integral simulations of the primary charge separation in bacterial photosynthesis. The process is modeled in terms of the three coupled electronic states corresponding to the photoexcited special pair (the electron donor), the reduced accessory bacteriochlorophyll (the bridge), and the reduced bacteriopheophytin (the primary electron acceptor) of the L branch which interact with a dissipative medium of protein and solvent degrees of freedom. The electronic state populations are followed over 17 ps via an iterative procedure that employs a propagator functional [Comput. Phys. Commun. 1997, 99, 335]. In a previous article [Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 3926] the free energy of the reduced accessory bacteriochlorophyll state and its coupling to the excited special pair were estimated by comparing the simulation results against available experimental observations on wild-type and modified reaction centers. The determined optimal parameters correspond to a simple two-step electron transfer mechanism. Additional simulations presented in this article demonstrate that the obtained parameters and the inferred mechanism are in accord with the temperature dependence of the primary charge separation and other kinetic effects observed in wild-type and modified reaction centers. We point out that the superexchange mechanism implies a large temperature effect in modified reaction centers which should be directly amenable to experimental testing. We also investigate the sensitivity of the calculated dynamics to various assumptions of the model. The results are found to be rather stable with respect to reasonable changes of the medium spectral density and the specifics of the nonequilibrium configuration o the photoexcited donor state, implying that the picture emerging from our simulations is robust and the conclusions are reliable.

Original languageEnglish
Pages (from-to)5446-5458
Number of pages13
JournalJournal of Physical Chemistry B
Volume101
Issue number27
Publication statusPublished - 1997 Jul 3

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Photosynthetic Reaction Center Complex Proteins
Bacteriochlorophylls
Charge transfer
charge transfer
Accessories
Electronic states
Electrons
accessories
polarization (charge separation)
Photosynthesis
simulation
Spectral density
Thermal effects
Free energy
photosynthesis
electronics
Proteins
temperature effects
emerging
electron transfer

All Science Journal Classification (ASJC) codes

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

Cite this

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title = "Path integral simulation of charge transfer dynamics in photosynthetic reaction centers",
abstract = "We present accurate path integral simulations of the primary charge separation in bacterial photosynthesis. The process is modeled in terms of the three coupled electronic states corresponding to the photoexcited special pair (the electron donor), the reduced accessory bacteriochlorophyll (the bridge), and the reduced bacteriopheophytin (the primary electron acceptor) of the L branch which interact with a dissipative medium of protein and solvent degrees of freedom. The electronic state populations are followed over 17 ps via an iterative procedure that employs a propagator functional [Comput. Phys. Commun. 1997, 99, 335]. In a previous article [Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 3926] the free energy of the reduced accessory bacteriochlorophyll state and its coupling to the excited special pair were estimated by comparing the simulation results against available experimental observations on wild-type and modified reaction centers. The determined optimal parameters correspond to a simple two-step electron transfer mechanism. Additional simulations presented in this article demonstrate that the obtained parameters and the inferred mechanism are in accord with the temperature dependence of the primary charge separation and other kinetic effects observed in wild-type and modified reaction centers. We point out that the superexchange mechanism implies a large temperature effect in modified reaction centers which should be directly amenable to experimental testing. We also investigate the sensitivity of the calculated dynamics to various assumptions of the model. The results are found to be rather stable with respect to reasonable changes of the medium spectral density and the specifics of the nonequilibrium configuration o the photoexcited donor state, implying that the picture emerging from our simulations is robust and the conclusions are reliable.",
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Path integral simulation of charge transfer dynamics in photosynthetic reaction centers. / Sim, Eun Ji; Makri, Nancy.

In: Journal of Physical Chemistry B, Vol. 101, No. 27, 03.07.1997, p. 5446-5458.

Research output: Contribution to journalArticle

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AB - We present accurate path integral simulations of the primary charge separation in bacterial photosynthesis. The process is modeled in terms of the three coupled electronic states corresponding to the photoexcited special pair (the electron donor), the reduced accessory bacteriochlorophyll (the bridge), and the reduced bacteriopheophytin (the primary electron acceptor) of the L branch which interact with a dissipative medium of protein and solvent degrees of freedom. The electronic state populations are followed over 17 ps via an iterative procedure that employs a propagator functional [Comput. Phys. Commun. 1997, 99, 335]. In a previous article [Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 3926] the free energy of the reduced accessory bacteriochlorophyll state and its coupling to the excited special pair were estimated by comparing the simulation results against available experimental observations on wild-type and modified reaction centers. The determined optimal parameters correspond to a simple two-step electron transfer mechanism. Additional simulations presented in this article demonstrate that the obtained parameters and the inferred mechanism are in accord with the temperature dependence of the primary charge separation and other kinetic effects observed in wild-type and modified reaction centers. We point out that the superexchange mechanism implies a large temperature effect in modified reaction centers which should be directly amenable to experimental testing. We also investigate the sensitivity of the calculated dynamics to various assumptions of the model. The results are found to be rather stable with respect to reasonable changes of the medium spectral density and the specifics of the nonequilibrium configuration o the photoexcited donor state, implying that the picture emerging from our simulations is robust and the conclusions are reliable.

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