Hopping multistep

In solid state materials, single-step electron transport between dopant species is well known. For example, electron-hole recombination accounts for luminescence in some materials [H]. Multistep hopping is also well known. Models for single and multistep transport are enjoying renewed interest in tlie context of DNA electron transfer [12, 13, 14 and 15]. Indeed, tliere are strong links between tire ET literature and tire literature of hopping conductivity in polymers [16]. 

The Permeation Process Barrier polymers limit movement of substances, hereafter called permeants. The movement can be through the polymer or, ia some cases, merely iato the polymer. The overall movement of permeants through a polymer is called permeation, which is a multistep process. First, the permeant molecule coUides with the polymer. Then, it must adsorb to the polymer surface and dissolve iato the polymer bulk. In the polymer, the permeant "hops" or diffuses randomly as its own thermal kinetic energy keeps it moving from vacancy to vacancy while the polymer chains move. The random diffusion yields a net movement from the side of the barrier polymer that is ia contact with a high concentration or partial pressure of the permeant to the side that is ia contact with a low concentration of permeant. After crossing the barrier polymer, the permeant moves to the polymer surface, desorbs, and moves away. 

A multistep hopping mechanism explains not only the long distance hole transfer through DNA, it can also rationalize the electron transfer through reduced DNA as T. Carell and M.D. Sevilla demonstrate in this volume. 

Long Range Charge Transport Through Multistep Hopping. 106... 

The electrochemistry of POMs is characterized by reversible multistep redox processes resulting in the formation of mixed valence species and electron self-exchange between mixed-valence metal sites (e.g.. Mo ) via electron hopping. Extensive reduction of POMs leads to the formation of heteropolybrown species in which such distinct ionic sites (e.g., W and W" ) can coexist. 

Figure 6.1 Schematic depiction of trans-biofilm electron transport by incoherent multistep electron hopping (also referred to as redox conduction) under nonturnover condition.

Pirhadian S, El-Naggar MY. Multistep hopping and extracellular charge transfer in microbial redox chains. Phys Chem Chem Phys 2012 14 13802-13808. 

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