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Title: Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy

Abstract

In the initial steps of photosynthesis, reaction centers convert solar energy to stable charge-separated states with near-unity quantum efficiency. The reaction center from purple bacteria remains an important model system for probing the structure-function relationship and understanding mechanisms of photosynthetic charge separation. Here we perform 2D electronic spectroscopy (2DES) on bacterial reaction centers (BRCs) from two mutants of the purple bacterium Rhodobacter capsulatus, spanning the Q(y) absorption bands of the BRC. We analyze the 2DES data using a multiexcitation global-fitting approach that employs a common set of basis spectra for all excitation frequencies, incorporating inputs from the linear absorption spectrum and the BRC structure. We extract the exciton energies, resolving the previously hidden upper exciton state of the special pair. We show that the time-dependent 2DES data are well-represented by a two-step sequential reaction scheme in which charge separation proceeds from the excited state of the special pair (P*) to P+HA- via the intermediate P+BA-. When inhomogeneous broadening and Stark shifts of the B* band are taken into account we can adequately describe the 2DES data without the need to introduce a second charge-separation pathway originating from the excited state of the monomeric bacteriochlorophyll B-A*.

Authors:
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Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1479285
DOE Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 115; Journal Issue: 14; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
charge separation; global analysis; light harvesting; multidimensional spectroscopy; photosynthesis

Citation Formats

Niedringhaus, Andrew, Policht, Veronica R., Sechrist, Riley, Konar, Arkaprabha, Laible, Philip D., Bocian, David F., Holten, Dewey, Kirmaier, Christine, and Ogilvie, Jennifer P. Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy. United States: N. p., 2018. Web. doi:10.1073/pnas.1721927115.
Niedringhaus, Andrew, Policht, Veronica R., Sechrist, Riley, Konar, Arkaprabha, Laible, Philip D., Bocian, David F., Holten, Dewey, Kirmaier, Christine, & Ogilvie, Jennifer P. Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy. United States. doi:10.1073/pnas.1721927115.
Niedringhaus, Andrew, Policht, Veronica R., Sechrist, Riley, Konar, Arkaprabha, Laible, Philip D., Bocian, David F., Holten, Dewey, Kirmaier, Christine, and Ogilvie, Jennifer P. Mon . "Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy". United States. doi:10.1073/pnas.1721927115.
@article{osti_1479285,
title = {Primary processes in the bacterial reaction center probed by two-dimensional electronic spectroscopy},
author = {Niedringhaus, Andrew and Policht, Veronica R. and Sechrist, Riley and Konar, Arkaprabha and Laible, Philip D. and Bocian, David F. and Holten, Dewey and Kirmaier, Christine and Ogilvie, Jennifer P.},
abstractNote = {In the initial steps of photosynthesis, reaction centers convert solar energy to stable charge-separated states with near-unity quantum efficiency. The reaction center from purple bacteria remains an important model system for probing the structure-function relationship and understanding mechanisms of photosynthetic charge separation. Here we perform 2D electronic spectroscopy (2DES) on bacterial reaction centers (BRCs) from two mutants of the purple bacterium Rhodobacter capsulatus, spanning the Q(y) absorption bands of the BRC. We analyze the 2DES data using a multiexcitation global-fitting approach that employs a common set of basis spectra for all excitation frequencies, incorporating inputs from the linear absorption spectrum and the BRC structure. We extract the exciton energies, resolving the previously hidden upper exciton state of the special pair. We show that the time-dependent 2DES data are well-represented by a two-step sequential reaction scheme in which charge separation proceeds from the excited state of the special pair (P*) to P+HA- via the intermediate P+BA-. When inhomogeneous broadening and Stark shifts of the B* band are taken into account we can adequately describe the 2DES data without the need to introduce a second charge-separation pathway originating from the excited state of the monomeric bacteriochlorophyll B-A*.},
doi = {10.1073/pnas.1721927115},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
issn = {0027-8424},
number = 14,
volume = 115,
place = {United States},
year = {2018},
month = {3}
}