Through-bond electron transfer

Joachim C (1987) Ligand-length dependence of the intramolecular electron transfer through-bond coupling parameter. Chem Phys 116 339... 

Keywords Electron Tansfer m Energy Transfer m Through-Bond Coupling m Superexchange m Molecular Wires m Solvent-Mediated Electron Transfer m Electron Transfer in DNA m Charge Separation m Electron Transfer Through H-Bonds... 

Oxidative Phosphorylation Electron transfer through the cytochrome system liberating free energy which is transformed into high-energy phosphate bonds. [NIH]... 

DNA-Protein. A large number of proteins in nature perform their function by expediting electron transfer, and there is an extensive literature on electron transfer through proteins (see Refs. 122-124 for reviews). Relevant here are the observations that the excess electron has a large range (not readily trapped) [125] while the hole is relatively immobile (trapped by deprotonation at the peptide bond giving amido radicals) [126]. This raises the expectation that electrons but not holes could be transferred from protein to DNA. This has been observed by a number of groups [127-131]. 

A relationship between a reaction rate involving electron transfer through a conjugated bond system and the mobile bond (4) order has been suggested (13) and... 

When the donors and acceptors lack spherical symmetry, there will also be an orientation dependence. In cases such as those to be discussed below, where the donor and acceptor moieties are linked by covalent bonds, there is considerable evidence that in certain situations the electron transfer occurs through the linkage bonds [22]. Although such linkages are not present in photosynthetic reaction centers, it has been proposed that the accessory Bchl or other intervening material may still take part in electron transfer through a superexchange mechanism [8, 26]. The distance dependence of photoinitiated electron transfer has recently been reviewed [13]. 

Some of the first protein systems where pulse radiolysis was used to help determine mechanism were those of blue copper proteins. These are proteins that are blue in solution and contain what are known as type (I) and type (2) copper centers. Two of the most well-known and well-characterized examples of these are azurin and cytochrome c. It was the studies of these systems that opened up the field of long-distance electron transfer in proteins and, by using the protein structure as a framework for electron transfer through space and through bonds, allowed for the development of a broad theoretical basis and many fascinating experiments on long-range electron transfer. Here, I will limit the discussion to electron transfer studies in azurin as illuminated by pulse radiolysis studies. ... 

Finally, it is also important to mention that electron transfer by proteins is a process that has been studied in great detail recently. The prevailing hypothesis at present is that electron transport "through bonds" in the protein is more efficient than electron transport "through space". Regardless of the precise mechanism, however, electrons can be transported at reasonable rates over relatively long distances (up to 15 to 20 A), and thus from one protein cofactor to another. 

---