Oxides potential measurements

For PPV-imine and PPV-ether the oxidation potential, measured by cyclic voltammetry using Ag/AgCl as a reference are ,M.=0.8 eV and 0.92 eV, respectively. By adopting the values 4.6 eV and 4.8 eV for the work functions of a Ag/AgCl and an 1TO electrode, respectively, one arrives at zero field injection barriers of 0.4 and 0.55 eV. These values represent lower bounds because cyclic voltammetry is carried out in polar solvents in which the stabilization cncigy of radical ions exceeds that in a polymer film, where only electronic polarization takes place. E x values for LPPP and PPPV are not available but in theory they should exceed those of PPV-imine and PPV-ether. 

The midpoint potential of a half-reaction E, is the value when the concentrations of oxidized and reduced species are equal, [Aox] = [Aredl- In biological systems the standard redox potential of a compound is the reduction/oxidation potential measured under standard conditions, defined at pH = 7.0 versus the hydrogen electrode. On this scale, the potential of 02/water is +815 mV, and the potential of water/H2 is 414 mV. A characteristic of redox reactions involving hydrogen transfer is that the redox potential changes with pH. The oxidation of hydrogen H2 = 2H + 2e is an m = 2 reaction, for which the potential is —414 mV at pH 7, changing by 59.2 mV per pH unit at 30°C. 

Oxidation potentials measure the energy required to remove an electron from a molecule. To check whether in a partial electron transfer in charge transfer complex formation, a similar correlation would hold, the equilibrium constant... 

All the oxidation potentials measured for the above solutions are around 3.5-3.85 V versus SCE. This further demonstrates the importance of the salt anion in the determination of the oxidation potentials of nonaqueous solutions of solvents with high anodic stability, such as alkyl carbonates, whereas the cations may have only a minor and secondary effect. 

The choice of solvents has considerable impact on the reduction and oxidation potentials measured. The values vary up to 400 mV depending on the solution medium. Obviously factors like donor/acceptor properties, Lewis basicity, or the ability to form hydrogen bonds have large influence on the redox potential. 

Moreover, from these expressions, the Pl values have been estimated for other ligands, by taking also into account the oxidation potentials, measured in this study, of their complexes... 

Figure 10 Correlation between oxidation potential (a) and maximum absorption wavelength (b) of thiophene oligomers [67] Oxidation potential measured in 0.5mol/L Et4NBp4 in acetonitrile versus saturated calomel electrode.

Now the next question Is, what substances are causing the different peaks Many workers have assumed that peak I Is caused by the oxidation of catecholamines such as noradrenaline. However there Is a problem In that the oxidation potentials for ascorbic acid and the catecholamines are not very different. A further problem we have found Is that oxidation potentials measured In the brain and measured In vitro can be very different. Exposing a carbon paste electrode to rats brain makes It more active. In Table 4 we give results for the... 

The low oxidation potentials measured for compounds 79 and 80 are due to the high-energy HOMO furnished by the donor benzodithiin and benzooxathiin units, respectively. The PM3 minimum-energy conformation calculated for the radical cation 79a is given in Figure 1.64. The oxidation process mainly affects the sulphur bridges because the HOMO, from which the electron is extracted, is mostly located on them. In fact 0.74 e is computed to be extracted from the sulphur atoms in 79a . As a consequence, the benzodithiin moiety becomes planar and the S-C bonds shorten to 1.70 and 1.73 A. 

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