Redox potential aggregates

In conclusion, the order of reduction of metal ions is controlled by their redox potential. This is also true in other pairs of precious metals such as Pd/Pt, Au/Pd, etc. (53). In addition, poly(jV-vinyl-2-pyrrolidone) (PVP) plays an important role for the formation of the core/shell structure. In the case of the Au/Pt system, the aggregation starts from Au but not Pt. This is probably due to the coordinating ability of metals to PVP. The Pt atoms or microclusters coordinating to PVP are more stable than the Au atoms or microclusters, since Au cannot coordinate to PVP. Thus, Au atoms or microcluster aggregate at first after the reduction, and then Pt atoms or microclusters deposit on the Au nuclei. In summary, the core/shell structure is controlled by (1) the redox potential of metal ions, and (2) the coordination ability of metals to PVP, stabilizing polymer. 

The difference of these redox potentials is too big to be explained by a complexation with the surfactant aggregate (23). A detailed study of the dependence of the redox potential of MPT from the nature and the concentration of the surfactant leads to the conclusion that MPT+ is interacting with the anionic surfactant system, interaction most pronounced with the monomeric surfactant entities (24). 

Since the redox potentials of dye aggregates adsorbed onto platinum electrode exhibit a broad distribution centred at the formal oxidation potential Eox, the direct information on the ionization energy of the aggregated cyanines can be obtained, even in case of irreversibly oxidizing dyes, from the potential dependence of the fractional degree of dye oxidation, 0, derived from the potential-step electrochemical measurements [52, 53]. The analogue of Nemst equation describing the oxidation process can be written as ... 

The reactive site of the cysteinyl residue is the thiol group, which is deprotonated at alkaline pH (pXa around 8.5). The residue under oxidizing conditions (and neutral to alkaline pH) is able to react with a similar residue under formation of a disulfide bond. Many proteins are stabilized by intramolecular disulfide bonds (e.g., insulin, growth hormone, lGF-1), but intermolecular bonds may also result from the reaction under formation of aggregates. In order to avoid unintended disulfide bond formation/cleavage, the redox potential of the solution must be monitored and controlled. In practice, aqueous buffers contain micromolar amounts of dissolved oxygen assuring a redox potential of 200-600 mV, which is sufficient to maintain the intramolecular disulfide bonds. Proteins with free cysteines may... 

The O2—H2O couple is the redox pair controlling reactions in aerated solutions, so that reaeration of anoxic soils drives reduced species (e.g., Fe " ) toward the oxidized state. The range of redox potentials over which Fe ", and NH4 have been found to oxidize and disappear on aeration of a reduced soil are denoted by the open boxes in Figure 7.5. Nitrate reappearance on aeration is also depicted by an open box. The measured redox potentials that follow re-aeration do not directly reflect the 02—H20 equilibrium state but rather the status of redox couples having faster electron exchange rates. Furthermore, while each redox couple would be expected (in theory) to undergo complete conversion to the reduced form (in flooded soils) or to the oxidized form (in re-aerated soils) before the adjacent redox couple on the Eh scale became active, actual behavior in soils is much less ideal. Several redox reactions are typically active simultaneously. This may reflect spatial variability in the aeration (and redox potential) of soil aggregates, caused by slow diffusion processes in micropores. 

The normal redox potential of the system [Ru(bipy>3]3+/[Ru(bipy)3]2+ is + 1,26 V99) which is far from the potential of the system H20/0H( m 7 = 2,33 V, see Ref.100)). Lately, surface active derivatives of [Ru(bipy)3l2+ aggregated to monolayers have been discussed as to be suitable catalysts for in vitro models of photolytic water cleavage1003). 

---