Biomedical Engineering Reference
In-Depth Information
Table 2.1. shows the results of the calculation parameter from empirical data by Eq.
2.31 (Likhtenshtein, 1993, 1995). The table of values for X, C=O, S=O, P=O and C=C,
calculated from independent experimental data, are similar. Data presented in Table 2.1
and Eq. 2.31 may be used for the analysis of alternative electron transfer pathways in
biological systems.
2.2.2. EXPERIMENTAL DATA
Remarkable progress has been made in the elucidation processes of electron transfer in
biological and model systems. This progress has been achieved through massive and
concentrated applications of the entire arsenal of modern chemical, biochemical and
physical methods. Biochemistry and biophysics provide isolated and functionally well-
characterized samples of electron transfer in biological objects. Synthetic chemistry and
genetic engineering allowed purposeful modification of biological and model molecules.
Structural methods including X-ray analysis and all kinds of spectroscopy from Gamma-
resonance to nuclear magnetic resonance reveal the detailed chemical structure of proteins
with natural and artificial donor and acceptor sites. The most advanced theories of electron
transfer have been used to analyze the experimental data.
The present section is a brief survey of experimental data on electron transfer rate and
its theoretical treatment being focused on (a) the Franc-Condon (FC) factor and (b)
electronic coupling (resonance integral) V. Role of the media molecular dynamics on ET is
discussed in Sections 3.5.1 and 4.1.7
Franc-Condon factor
According to the Marcus (Eqs. 2.9-2.10), the FC value is strongly dependent on medium
polarity. For example, for electron transfer between centers with radius about 4 A the
following values of the energy reorganization were estimated in eV: 0.052 (benzene), 0.12
(acetonitryl) and methanol (0.35). For an aqueous solution a value was estimated within
= 1.0 - 1.3 eV for the centers with radius 3 - 4 Å. Suggesting a dielectric constant of
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