Intermolecular Electronic Interactions in the Primary Charge Separation in Bacterial Photosynthesis

M. Plato, K. Möbius, M. E. Michel-Beyerle, M. Bixon, Joshua Jortner*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

190 Scopus citations

Abstract

In this paper we utilize the intermolecular overlap approximation to calculate the relative magnitudes of the electronic transfer integrals between the excited singlet state (1P*) of the bacteriochlorophyll dimer (P) and the accessory bacteriochlorophyll (B) and between B-and bacteriopheopytin (H), along the L and M subunits of the reaction center (RC) of Rps. viridis. The ratio of the electron-transfer integrals for BL-HL-BLHL-and for BM-HM-BMHM-was calculated to be 2.1 ± 0.5, which together with the value of 2.8 ±0.7 for the ratio of the transfer integrals for lP*BL-P+BL~ and for 1P*BM-P+BM' results in the electronic contribution of 33 ± 16 to the ratio kL/kmof the rate constants kLand kMfor the primary charge separation across the L and M branches of the RC, respectively. The asymmetry of the electronic coupling terms, which originates from the combination of the asymmetry in the charge distribution of 1P* and of structural asymmetry of the P-B and B-H arrangements across the L and M subunits, provides a major contribution to the unidirectionality of the charge separation in bacterial photosynthesis. A significant contribution to the transfer integrals between adjacent pigments originates from nearby methyl groups through hyperconjugation. The ratio 6 ± 2 of the transfer integrals for 1P*BL-P+BL-and for BL-HL-BLHL-was utilized to estimate the energetic parameters required to ensure the dominance of the superexchange mediated unistep electron transfer 1P*BH → P+BH-over the thermally activated 1P*B → P+B-process.

Original languageEnglish
Pages (from-to)7279-7285
Number of pages7
JournalJournal of the American Chemical Society
Volume110
Issue number22
DOIs
StatePublished - Oct 1988

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