Electronic coupling superexchange

Curtiss, L.A., Naleway, C.A., Miller, J.R. Superexchange pathway calculation of long-distance electronic coupling in H2C(CH2)m 2CH2 chains. Chem. Phys. 1993,176, 387. 

Electronic states of DNA fragments where the electron hole is located on a pyrimidine base are of high energy because cytosine and thymine are relatively weak hole acceptors [7, 51]. Nevertheless, the electronic coupling between nucleobases within (GC) and (AT) pairs may be of interest when one compares different CT paths in DNA using the superexchange model [14]. In Table 5, we present results of the electronic coupling within the base pairs (GC) and (AT) [41]. 

The third, and possibly the most important conclusion is that the distance dependence of TB-mediated electronic coupling in 15(h) is much weaker than that predicted by the simple McConnell model. In that model, a /3el value of about 2.3 bond-1 is estimated, whereas the average /3el value of ca. 1.0 bond-1 for 15(/t) is 2.3 times smaller Thus, the attenuation in the ET rate, mediated by superexchange through a saturated hydrocarbon bridge, could be as small as ca. 2.5 bond-1, as opposed to ca. 10 bond-1, predicted from the simple McConnell model. 

In direct LRET the direct electronic coupling between D and A is negligible and this mechanism is not practically realized in condensed media being non-competitive with the consecutive and superexchange processes. In theoretical consideration of the consecutive LRET a relevant theory ofET in two-term systems can be applied. 

The artificial intelligence-superexchange method in which the details of the electronic structure of the protein medium are taken into account was used for estimating the electronic coupling in the metalloproteins (Siddarth and Marcus, 1993a,b,c). Fig.2.11 demonstrates a correlation of experimental and calculated ET rate constants for cytochrome c derivatives, modified by Ru complexes. The influence of the special mutual orientation of the donor and acceptor orbitals in Ru(bpy)2im HisX-cytochrome c on the rate of electron transfer was analyzed by the transition amplitude methods (Stuchebrukhov and Marcus, 1995). In this reaction the transferring electron in the initial and the final states occupies the 3d shell of the Fe atom and the 4d shell of Ru, respectively. It was shown that the electron is localized on t2g subshells of the metal ions. Due to the near-... 

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