Electron-hopping mechanism

Tran E, Cohen A, Murray R, Rampi MA, Whitesides GM (2009) Redox site-mediated charge transport in a Hg-SAM//Ru(NH3)63+/2+//SAM-Hg junction with a dynamic interelectrode separation compatibility with redox cycling and electron hopping mechanisms. J Am Chem Soc 131 2141-2150... 

The temperature dependence of the conductivity behavior of the nanoparticle films predicted that electronic conduction occurred via an electron hopping mechanism. 

Berg et al. 711 proposed that the adenine and cytosine residues in native DNA are reduced by a so-called electron hopping mechanism, the only condition for this being adsorption of protonated DNA at the electrode surface at the reduction potential of these bases. It was also assumed that the DNA is adsorbed in its A-form, exhibiting semi-conducting properties. There is consequently no surface denaturation of the DNA. 

Fig. 9 Electron-hopping mechanism from wired enzymes in a redox polymer.

In the case of conducting polymers, the motion of delocalized electrons occurs through conjugated systems however, the electron hopping mechanism is likely to be operative, especially between chains (interchain conduction) and defects. Electrochemical transformation usually leads to a reorganization of the bonds of the polymers prepared by oxidative or less frequently reductive polymerization of ben-zoid or nonbenzoid (mostly amines) and heterocyclic compounds. 

Fig. 5.5 Schematic representation of the cysteine oxidation mediated by modified LbL electrode containing 3-bilayers of the insulator PAH and Co TsPc species. These supramolecular layers are electrically connected working through an electron hopping mechanism promoted by the redox sites of the Co TsPc species right after oxidation of cysteine to cystine. Reproduced with permission from [5]...

Although metal hexacyanoferrates (HCFs) cannot be considered RPs, from both a structural and a compositional viewpoint, charge percolation occurs through electron-hopping mechanisms quite similar to those just described. For this reason, these pure inorganic materials are dealt with in the frame of this chapter. 

Figure 8.16 Illustration of four electron-transfer modes in polymer modified electrodes. Polymers containing redox molecules (where A + e = D) can mediate electrons to a solution-based analyte (where O + e = R) through an electron hopping mechanism (la), or by diffusion of free redox molecules within the film (lb). Permeable polymer layers, on the other hand, provide a suitable chemical environment for diffusion of O through the layer (2a) or contain channel/pinholes where electron-transfer occurs (2b). This material is adapted with permission from A. J. Bard, Integrated Chemical Systems A Chemical Approach to Nanotechnology, John Wiley Sons, Inc. New York, 1994. Copyright 1994 John Wiley Sons, Inc.

In Chapter 21, we described the chemistry of the first row c(-block metal(II) oxides, but said little about their electrical conductivity properties. The oxides TiO, VO, MnO, FeO, CoO and NiO adopt NaCl-type stmctures, but are non-stoichiometric, being metal-deficient as exemplified for TiO and FeO in Section 6.17. In TiO and VO, there is overlap of the metal 2g orbitals giving rise to a partially occupied band (Fig. 28.5) and, as a result, TiO and VO are electrically conducting. In contrast, MnO is an insulator at 298 K but is semiconducting (see Section 6.9) at higher temperatures. FeO, CoO and NiO behave similarly, their conductivities (which are low at 298 K) increasing with temperature. The conductivity is explained in terms of an electron-hopping mechanism, in which an electron moves from an... 

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