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Interpretation of the Electric Field Sensitivity of the Primary Charge Separation in Photosynthetic Reaction Centers
Author(s) -
Moser Christopher C.,
Alegria Guillermo,
Gunner M.R.,
Leslie Dutton P.
Publication year - 1988
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198800023
Subject(s) - chemistry , bacteriochlorophyll , superexchange , photosynthetic reaction centre , excited state , electron transfer , picosecond , electric field , photochemistry , molecular physics , atomic physics , chemical physics , photosynthesis , physics , ion , optics , laser , biochemistry , organic chemistry , quantum mechanics
Popovic et al. ( Biochim. Biophys. Acta , 1986, 851 : 38–48) have shown that the efficiency of light‐induced charge separation in a monolayer of oriented photosynthetic reaction center (RC) is sensitive to the electric field. With the data provisionally interpreted as indicating a sensitivity of the picosecond electron transfer to field‐induced free‐energy change of the charge‐separated states, current models for the light‐induced picosecond electron transfer in the RC from bacteriochlorophyll dimer (BChl 2 ) to bacteriopheophytin, assisted by an interposed bacteriochlorophyll monomer (BChl), are challenged to fit the results. A model presuming a simple field‐sensitive Franck‐Condon overlap between BChl 2 and BChl, based on single classical vibration coupled to electron transfer, can only fit the data if the free‐energy change does not match the reorganization energy. An even simpler model presuming a rapid field‐sensitive thermal equilibrium between BChl 2 and the nearby BChl fits equally well. However, a model involving a superexchange electronic coupling between the excited BChl 2 and BChl, with or without similar field‐dependent Franck‐ Condon overlap factors, provides the best fits to the data and suggests that the relevant dielectric constant of the RC may be about 1 with a BChl 2 ‐BChl energy gap of about 100 meV.