Electron transport intramolecular

Table 10. A comparison of rate constants for intramolecular electron transfer in Ru(NH3)j-modiiied electron transport metalloproteins, modifications at surface histidine present in native proteins, pH 7. Values of AE° by determined measurements on modified protein except as indicated...

Finally, intramolecular electron transport occurs in multicentre redox proteins, and represents a rather different situation. 

A sensitizer is of paramount importance to photovoltaic performance. The sensitizer is attached to the surface of a mesoporous wide band-gap semiconductor serving as electron transporter. While the trivial ultraviolet absorption for 375 with a molar extinction coefficient (s) of 50.0 x 103 M [ cm-1 peaks at 372 nm, the s value of its low-energy band at 525 nm (mainly stemming from the intramolecular charge transfer transition) is 44.8 x 103 IVT1 cm-1 (08JA9202). 

As shown by Nango et al. [243] for the porphyrin-quinone complex as an example, even when an electron travels via intramolecular transfer only a part of its way across the membrane, the observed overall rate of transmembrane electron transport can be notably increased as compared to transport via diffusion only. 

Now, as we have defined wire-like transport by a motion that is assisted by molecular bridges, we may proceed to the mechanistic point of view. In particular, we will contrast theoretical results with experimental data for molecular wire-like behavior in regard to the transfer of electronic charge and/or energy. Intramolecular electron-transfer (ET) rate constants characterize the charge transport in DBA conjugates and in electronic transport junction we can apply the word conductance . 

J. Frebortova, K. Matsushita, H. Arata, and O. Adachi, Intramolecular electron transport in quinoprotein alcohol dehydrogenase of Acetobacter methanolicus a redox-titration study, Biochim. Biophys. Acta 1363, 24-34 (1998). 

The unimolecular reduction of the trinuclear copper center is caused by intramolecular electron transport from the type-1 copper to the trinuclear copper species. The turnover numbers represented by the values (see Table VII) are one to two orders of magnitudes greater than the observed intramolecular electron transfer rate constants. They should be at least as large as the turnover numbers. The low rates seem to imply that the enzymes are in an inactive form under the conditions of the anaerobic reduction experiments. It will be shown later that there is experimental evidence for this assumption. 

Mechanism. The electron-transport pathway of nitrite reductase begins with the type 1 copper center of pseudoazurin, continues to the type 1 copper center of nitrite reductase, and from there to its type 2 copper center. This last electron transfer is not conducted directly from copper to copper, but via an intramolecular Cysl36-Hisl35 bridge, similar to the one proposed for ascorbate oxidase [26,208] (Fig. 35). 

Investigations of intramolecular ET In heme proteins have focused on cytochrome c (104 amino acids in the horse protein 12.5 kDa ii° = 0.26 V vs. NHE) see Iron Heme Proteins Electron Transport) (Figure 2). Early... 

The intramolecular Ei mechanism is most commonly accepted to account for these pyrolytic processes. Considering the usual electronegativity of the atoms, the cyclic transition states as designated (128-131) simulate the last step of the base-induced ylid mechanism. Of course, for a completely concerted cyclic process a distinction between heterolytic and homolytic reactions is not possible and the direction of electron transport as either single or paired electrons is uncertain . However, if considerable charge separation occurs in the transition state, due to a departure from a completely synchronous process, then specific experiments can be designed to determine the direction of electron transport. For example, the variation in the value of the isotope effect... 

---