Local analyses redox potential

BChl a in solution ( 660 + 10 mV).66 ENDOR/TRIPLE further showed that the spin is completely localized on one BChl half (Fig. 3). The pigment analysis showed that the RC contains 3 BChl and 3 BPh, whereas 4 BChl and two BPh are found in wild type. On the basis of earlier work5467 it is therefore assumed that in these mutants, a BChl-BPh heterodimer is the primary donor. Since BPh has a higher redox potential than BChl,66 only the BChl half is oxidized and carries the spin and positive charge. This situation is energetically less favorable than delocalization in a dimeric species, which leads to the observed increase of P 865. For the heterodimer mutants, a lower quantum yield and reduced ET rates have been observed. The experiments clearly show that dimer formation alone significantly lowers and, thereby, adjusts the donor s oxidation potential.68... 

A few years ago Bard and his group developed the technique called scanning electrochemical microscopy (SECM) which makes possible a spatial analysi,s of charge transfer processes [9]. In this method an additional tip electrode of a diameter of about 2 pm is used as well as the three other electrodes (semiconductor, counter and reference electrode). Assuming that a redox system is reduced at the semiconductor, then the reduced species can be re-oxidized at the tip electrode, the latter being polarized positively with respect to the redox potential. The corresponding tip current / [ is proportional to the local concentration of the product formed at the semiconductor surface and therefore also to the corresponding local semiconductor current, provided... 

In most cases, the interpretation of these kinetic data assumes (usually without a detailed analysis) that the reaction is localized at the film solution interface. For qualitative considerations, films with sufficiently high electronic conductivities are identified with the metal electrode, which means that the whole potential drop, i.e., its varying part, is attributed to the film solution interface. Quite the opposite view (i.e., that the latter interfacial potential is practically constant [72,355]) means a close analogy to the case of redox polymer films [306,356]. 

---