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Title: Magnitude and direction of the change in dipole moment associated with excitation of the primary electron donor in Rhodopseudomonas sphaeroides reaction centers

Abstract

The magnitude and direction of the change in dipole moment, ..delta mu.., associated with the Q/sub y/ transition of the dimeric primary electron donor (special pair or P870) in Rhodopseudomonas sphaeroides reaction centers have been measured by Stark spectroscopy at 20 /sup 0/C. The magnitude of ..delta mu.. is found to be f/sup -1/ (10.3 +/- 0.7) D, where f is a correction factor for the local dielectric properties of the protein matrix. With the spherical cavity approximation and an effective local dielectric constant of 2, f = 1.2, and absolute value of ..delta mu.. is 8.6 +/- 0.6 D. Absolute value of ..delta mu.. for the Q/sub y/ transition of the special pair is approximately a factor of 3.4 and 2 greater than for the monomeric bacteriochlorophylls and bacteriopheophytins, respectively, in the reaction center. The angle between ..delta mu.. and the transition dipole moment for excitation of the first singlet electron state of the special pair was found to be 24 +/- 2/sup 0/. The measured values are combined to suggest a physical model in which the lowest excited singlet state of the special pair has substantial charge-transfer character and where charge is separated between the two monomers comprisingmore » the dimeric special pair. This leads to the hypothesis that the first charge-separated state in bacterial photosynthesis is formed directly upon photoexcitation. These data provide stringent values for comparison with theoretical calculations of the electronic structure of the chromophores in the reaction center.« less

Authors:
;
Publication Date:
Research Org.:
Stanford Univ., CA
OSTI Identifier:
6802541
Resource Type:
Journal Article
Journal Name:
Biochemistry; (United States)
Additional Journal Information:
Journal Volume: 26:3
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; PHOTOSYNTHETIC REACTION CENTERS; ABSORPTION SPECTROSCOPY; DIPOLE MOMENTS; RHODOPSEUDOMONAS; BIOCHEMISTRY; EXCITATION; STARK EFFECT; VALENCE; BACTERIA; CHEMISTRY; ENERGY-LEVEL TRANSITIONS; MICROORGANISMS; SPECTROSCOPY; 140505* - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-)

Citation Formats

Lockhart, D J, and Boxer, S G. Magnitude and direction of the change in dipole moment associated with excitation of the primary electron donor in Rhodopseudomonas sphaeroides reaction centers. United States: N. p., 1987. Web. doi:10.1021/bi00377a001.
Lockhart, D J, & Boxer, S G. Magnitude and direction of the change in dipole moment associated with excitation of the primary electron donor in Rhodopseudomonas sphaeroides reaction centers. United States. https://doi.org/10.1021/bi00377a001
Lockhart, D J, and Boxer, S G. 1987. "Magnitude and direction of the change in dipole moment associated with excitation of the primary electron donor in Rhodopseudomonas sphaeroides reaction centers". United States. https://doi.org/10.1021/bi00377a001.
@article{osti_6802541,
title = {Magnitude and direction of the change in dipole moment associated with excitation of the primary electron donor in Rhodopseudomonas sphaeroides reaction centers},
author = {Lockhart, D J and Boxer, S G},
abstractNote = {The magnitude and direction of the change in dipole moment, ..delta mu.., associated with the Q/sub y/ transition of the dimeric primary electron donor (special pair or P870) in Rhodopseudomonas sphaeroides reaction centers have been measured by Stark spectroscopy at 20 /sup 0/C. The magnitude of ..delta mu.. is found to be f/sup -1/ (10.3 +/- 0.7) D, where f is a correction factor for the local dielectric properties of the protein matrix. With the spherical cavity approximation and an effective local dielectric constant of 2, f = 1.2, and absolute value of ..delta mu.. is 8.6 +/- 0.6 D. Absolute value of ..delta mu.. for the Q/sub y/ transition of the special pair is approximately a factor of 3.4 and 2 greater than for the monomeric bacteriochlorophylls and bacteriopheophytins, respectively, in the reaction center. The angle between ..delta mu.. and the transition dipole moment for excitation of the first singlet electron state of the special pair was found to be 24 +/- 2/sup 0/. The measured values are combined to suggest a physical model in which the lowest excited singlet state of the special pair has substantial charge-transfer character and where charge is separated between the two monomers comprising the dimeric special pair. This leads to the hypothesis that the first charge-separated state in bacterial photosynthesis is formed directly upon photoexcitation. These data provide stringent values for comparison with theoretical calculations of the electronic structure of the chromophores in the reaction center.},
doi = {10.1021/bi00377a001},
url = {https://www.osti.gov/biblio/6802541}, journal = {Biochemistry; (United States)},
number = ,
volume = 26:3,
place = {United States},
year = {Tue Feb 10 00:00:00 EST 1987},
month = {Tue Feb 10 00:00:00 EST 1987}
}