Structural Charges Induced by Electronic Transfer

A theoretical analysis of charge distribution within supercomplexes (or clusters in which the movement of diffusible carriers is restricted) has been developed by Lavergne et al [4]. This theory predicts the evolution of the redox state of the carriers under continuous illumination or flash excitation for any cluster stoichiometry. The predictive power of this treatment is illustrated by the analysis of the light-induced oxidation of primary and secondary donors in isolated centers of Rhodopseudomonas viridis (Fig. 3). In this case, it is definitely established that the secondary donors (cytochromes) are irreversibly bound to the reaction center. In the absence of mediators, no electron exchange is expected to occur between photocenters. In the presence of 200yM ascorbate, only two of the four cytochromes (cyt 556 and cyt 559) are in their reduced state prior to the illumination. As expected, the apparent equilibrium constant between P and the cytochromes measured during the course of illumination is much lower than that computed from the value of the redox potentials (K = 50 for cyt 559 and K 1500 for cyt 556). The fit between the experimental data and the theoretical simulation (dashed lines) is excellent and clearly demonstrates that the measurement of electron transfer reactions under weak illumination is a powerful tool to characterize the degree of structuration of a photosynthetic electron transfer chain. 

R. Lazzaroni, M. Logdiund, S. Stafstrom, W. R. Salaneck, and J. L. Bredas. The poly-3-hexylthio-phene/NOPF6 system a photoelectron spectroscopy study of electronic structural changes induced by the charge transfer in the solid state, J. Chem. Pins. 93 4433 (1990). 

These charge-transfer structures have been studied [4] in terms a very limited number of END trajectories to model vibrational induced electron transfer. An electronic 3-21G+ basis for Li [53] and 3-21G for H [54] was used. The equilibrium structure has the geometry with a long Li(2)—H bond (3.45561 a.u.) and a short Li(l)—H bond (3.09017 a.u.). It was first established that only the Li—H bond stretching modes will promote electron transfer, and then initial conditions were chosen such that the long bond was stretched and the short bond compressed by the same (%) amount. The small ensemble of six trajectories with 5.6, 10, 13, 15, 18, and 20% initial change in equilibrium bond lengths are sufficient to illustrate the approach. 

Fe3+X6...Fe2+X6, which is the reactant of the outer-sphere electron transfer reaction mentioned above when X = Y. Clearly the ground state involves a symmetric linear combination of a state with the electron on the right (as written) and one with the electron on the left. Thus we could create the localized states by using the SCRF method to calculate the symmetric and antisymmetric stationary states and taking plus and minus linear combinations. This is reasonable but does not take account of the fact that the orbitals for non-transferred electrons should be optimized for the case where the transferred electron is localized (in contrast to which, the SCRF orbitals are all optimized for the delocalized adiabatic structure). The role of solvent-induced charge localization has also been studied for ionic dissociation reactions [109],... 

However, electron transfer-induced photoreactions in the presence of nucleophiles have attracted by far the greatest attention a rich variety of cyclopropane systems have been subjected to these reaction conditions. We will consider several factors that may affect the structure of the radical cations as well as the stereo- and regiochemistry of their nucleophilic capture. Factors to be considCTcd include (1) the spin and charge density distribution in the cyclopropane radical cation (the educt) (2) the spin density distribution in the free-radical product (3) the extent of... 

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