Promoted electron transfer

Fig. 1.16 Schematic representation of the nanofibrous poly (acrylonitrile-co-acrylic acid) membrane containing MWCNTs, as well as the promoted electron transfer from hydrogen peroxide to the immobilized catalase through the PANCAA/MWCNTs nanofiber. Reprinted from [209] (reproduced by permission ofWiley-VCH).

The protocol demonstrated for the development of Cu, Zn-SOD-based third-generation 02 - biosensors is also sutiable for other kinds of SODs, such as Fe-SOD and Mn-SOD in the SOD family [138], In those cases, MPA was used as promoter for the SODs instead of cysteine because cysteine was unable to promote electron transfer of Fe-SOD and Mn-SOD. Figure 6.10 compares the CVs obtained at the Cu, Zn-SOD- (a), Fe-SOD- (b), and Mn-SOD- (c) based electrodes in the absence and presence of 02". As shown, the presence of 02 - in solution obviously increases both anodic and cathodic peak currents of the SODs confined on the electrodes, suggesting the good bifunctional catalytic activity for the reduction and oxidation of 02 - at the SODs, which is similar to the results obtained with the Cu,Zn-SOD/cysteine-modified Au electrode. It should be mentioned that the same response was observed neither at the MPA-modified Au electrode nor at the bare Au electrode under the same conditions. Such a bidirectional electromediation of the SOD-based biosensors is essentially based on the inherent specificity... 

J.H.T. Luong, S. Hrapovic, D. Wang, F. Bensebaa, and B. Simard, Solubilization of multiwall carbon nanotubes by 3-aminopropyltriethoxysilane towards the fabrication of electrochemical biosensors with promoted electron transfer. Electroanalysis 16, 132-139 (2004). 

These charge-transfer structures have been studied [4] in terms a very limited number of END trajectories to model vibrational induced electron transfer. An electronic 3-21G+ basis for Li [53] and 3-21G for H [54] was used. The equilibrium structure has the geometry with a long Li(2)—H bond (3.45561 a.u.) and a short Li(l)—H bond (3.09017 a.u.). It was first established that only the Li—H bond stretching modes will promote electron transfer, and then initial conditions were chosen such that the long bond was stretched and the short bond compressed by the same (%) amount. The small ensemble of six trajectories with 5.6, 10, 13, 15, 18, and 20% initial change in equilibrium bond lengths are sufficient to illustrate the approach. 

There are several molecular interfaces for redox enzymes to promote electron transfer at the electrode surface (Fig.6). 

Clays may also promote electron transfer between adsorbed organic reactants. This process is termed redox disproportionation if the electron transfer occurs between two identical species. The formation of p-cymene and p-menthene from p-menthene is an example (56). In the presence of polymers were the main products. 

One of the most popular photo-promoted electron transfer systems is the trisbipyridylruthenium(II)-methyl viologen (MV++) system which, on excitation, produces Ru and reduced methyl viologen (MV+) ... 

It seems reasonable to note that the micro-jet stream generated by the ultrasonic cavitation promotes mass transport. Such an effect was discussed for proton transport in aqueous solutions (Atobe et al. 1999). Understandably, a proton moves in the solution as a hydrated particle. Nevertheless, we should pay attention on the similarity between proton and electron, in the sense that both are essentially quantum particles. A solvated electron, therefore, can be considered as a species that is similar to a hydrated proton. Hence, the micro-jet stream can promote electron transfer. 

SrY < CaY) as observed in the uninitiated cyclohexane auto-oxidation. These workers believe that in both the gas- and liquid-phase photo-oxidations that electrostatically promoted electron transfer to generate a cyclohexane radical cation-superoxide ion pair occurs. However, only under liquid-phase conditions is there a continuous medium in which radical reactions can propagate themselves. 

Reductive dissolution may be more complex than the two previous mechanisms in that it involves electron transfer processes. Formation of Fe" via reductive dissolution can be effected by adsorption of an electron donor, cathodic polarization of an electrode supporting the iron oxide and by transfer of an electron from within a ternary surface complex to a surface Fe ". Addition of Fe" to a system containing a ligand such as EDTA or oxalate promotes electron transfer via a surface complex and markedly accelerates dissolution. 

Although a large number of different possible ways of using micelles to promote electron transfer reactions has been discussed,329 we consider only those in which hydrogen, or a hydrogen precursor, is generated using a metal complex as sensitizer. 

Finally, the effect of reaction conditions and solvents on chemoselectivity should also be considered.18 Empirically, polar, more basic solvents, e.g. HMPA, DMF, serve to minimize counterion effects by formation of solvent-separated ion pairs and promote electron-transfer processes which are conducive for... 

Since silicon stabilizes an a-carbanion by d jr-p jr interaction, silicon should promote electron transfer to a carbon-halogen bond which generates the a-carbanion. In fact,... 

Ly D, Kan Y, Armitage B, Schuster GB (1996) Cleavage of DNA by irradiation of substituted anthraqui-nones intercalation promotes electron transfer and efficient reaction at GG steps. J Am Chem Soc 118 8747-8748... 

Finally, as discussed before in Section 2.1, suitable orbital overlap must exist between the donor and acceptor, which will promote electron transfer and preferably prevent wasteful back reactions. 

The most active catalysts were obtained by preexchange with Cu2 + followed by postexchange with Pd2 +. This would seem to indicate the importance of cation siting in promoting electron transfer which was assumed to occur via adsorbed water molecules which bridge Pd° and Cu2 + through a hydrogen bond. 

A special case of conjugate addition involves diaryl ketones. As noted in Section 4.2, conjugate addition of organomagnesium compounds may lead to products formally derived from addition to a ring. Such reactions are favoured by conditions promoting electron transfer, particularly when polar addition to the carbonyl group is sterically hindered [3]. 

Among CT band promoted electron transfers, some cases are known for anionic donors as for example when mixtures of methyl viologen (as its tetrafluoroborate) and dithiophosphate anions are irradiated by visible light in acetonitrile [202]. In this system, the dark back electron transfer is prevented by the dimerization of the obtained thio radicals. 

The advantages of earbon nanotubes for promoting electron transfer reaetions -with special emphasis in those involving biomolecules-, the different methodologies for incorporating carbon nanotubes in sensors (either suspended in solutions, in polymeric films or in composite matrices), the analytieal performanee of the resulting biosensors as well as future prospects are diseussed in this book. 

The rate constants of M" promoted electron transfer (/tet) were determined from the slopes of the linear plots of k jversus [M"" "]. There is a striking linear correlation between log /tet and the AE values of O2 derived from the gzz... 

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