Electron transfer free-energy dependence

Sekiguchi S, Kobori Y, Akiyama K and Tero-Kubota S 1998 Marcus free energy dependence of the sign of exchange interactions in radical ion pairs generated by photoinduced electron transfer reactions J. Am. Chem. Soc. 120 1325-6... 

Figure 4 Free energy dependence of electron transfer reaction rate for case A where —X is approximately equal to AGS (or AGp) and case B where —X is closer in energy to AGq.

The reverse transfer affects each quantity in Eq. (3.382) but mainly in the region of resonance (AG,- 0). This is the favorable interval for reverse transfer which manifests itself by the high but narrow peak in the free energy dependence of Q [solid line in Fig. 3.49(a)]. There Q > Kg because it accounts not only for primary, but all subsequent ionization acts as well. These acts follow reverse electron transfer, which occurs much more often within than outside resonant interval. However, for the same reasons the quantum yield of irrevocable electron transfer dashed line in Figure 3.49(c). 

Fig. 9. (A) Free-energy dependence of the second- the formation product (/

Gunner, M. R., Robertson, D. E., and Dutton, P. L., 1986, Kinetic Studies on the Reaction Center Protein form Rps. Sphaeroides Temperature and Free Energy Dependence of Electron Transfer between various Quinones in the QA site and Oxidized Bacteri-ochlorophyll Dimer J. Phys. Chem. 90 378333795. 

Brooks, H. B., and Davidson, V. L., 1994b, Free energy dependence of the electron transfer reaction between methylamine dehydrogenase and amicyanin. J. Am. Chem. Soc. 116 11201911202. 

Figure 18.8. Free-Energy Dependence of Electron-Transfer Rate. The rate of an electron-transfer reaction at first increases as the driving force for the reaction increases. The rate reaches a maximum and then decreases at very large driving forces.

Figure 5. Free-energy dependence of triplet energy transfer from a biacetyl donor trapped within a hemicarcerand cage to several rigid aromatic acceptors in solution. Note that the curve is much narrower, and that the inverted region is reached at a much lower value of AG° than is typically observed in electron-transfer systems. The oscillations in the calculated line are artifacts of the single high frequency mode approximation (from the work of Deshayes, Piotrowiak, et al. [52]).

Figure 4. Free-energy dependence of return electron transfer for contact ion pairs (A D ) and solvent-separated ion pairs (A SD+) for recombination of dicyanonaphthalene anions with al-kylbenzene cation radicals. Solid lines represent fits to the data with values for V and Aj given. From Gould, I. R. Farid, S. Acc. Chem. Res., 1996, 29, 522, with permission from the American Chemical Society.

The question of the free-energy dependence of heterogeneous electron-transfer reactions at liquid-liquid interfaces was addressed by Bard and coworkers. They ex-... 

A quasi-linear correlation of log/c or AG with the ionization potentials of the electron donors as observed in the FeL3 - + reactions is predicted by Marcus theory for outer-sphere electron transfers. Accordingly, the free-energy dependence of AG can be satisfactorily simulated with the Marcus equation (Eq. 90), taking a (constant) value of A = 41 kcal mol as reorganization energy for all tetraalkyltin compounds (see Figure 19A) [32]. 

There are a number of ways to describe this FC term. An early way of describing the nuclear position and free energy-dependent FC term was proposed in Nobel prize-winning work by Marcus [9, 10]. Marcus approximated the reactant and product, before and after electron transfer, as simple harmonic oscillators with intersecting parabolic potential surfaces. As the driving force of the reaction increases and the product potential surface drops further down in energy, the barrier that must be crossed in going from the bottom of the reactant parabola to the bottom of... 

Progress in the understanding of ES reactions now allows ESs to be so well characterized that quencher exchange rates and potentials are being determined from the free-energy dependence of [ RuL3] + quenching rate constants . Study of ES electron transfer permits a detailed examination of very exothermic reactions and provides a probe of the intimate details of electron transfer. 

Fajardo A. M. and Lewis N. S. (1997), Free-energy dependence of electron-transfer rate constants at Si/liquid interfaces , J. Phys. Chem. B 101, 11136-11151. 

Free-Energy Dependence of Electron Transfer in Cytochrome c Labeled with Ruthenium(II)-Polypyridine Complexes... 

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