Redox contrasts boundaries

In addition to plate boundary and plume-related hydrothermal systems, the chemistry of the prebiotic world would have had strong redox contrasts in the restricted areas that had tidal coasts, and perhaps within the oceans where differing water masses interacted, or under ice. These redox contrasts were ultimately driven by photolysis in the atmosphere/ocean (presumably... 

Estuaries exhibit physical and chemical characteristics that are distinct from oceans or lakes. In estuaries, water renewal times are rapid (10 to 10 years compared to 1 to 10 years for lakes and 10 years for oceans), redox and salinity gradients are often transient, and diurnal variations in nutrient concentrations can be significant. The biological productivity of estuaries is high and this, coupled with accumulation of organic debris within estuary boundaries, often produces anoxic conditions at the sediment-water interface. Thus, in contrast to the relatively constant chemical composition of the... 

In contrast, the conversion of Fe3+ into Fe2+ (Fig. 15, number 6), is a pure redox reaction, independent of the pH-value (horizontal boundary). It is calculated after Eq. 58 ... 

Electrodes of the first kind consist of a metal wire, which is in contact with a solution containing the cations of this metal. In contrast to redox electrodes, ions as charged particles are exchanged across the phase boundary, i.e. the electrode reaction can be regarded as an ion-transfer reaction. An example of this electrode is the silver electrode, a silver wire in a silver-ion-containing solution (Fig. II.9.3a). With this electrode all reactions can be monitored, which are accompanied by a change of the activity of silver ions ... 

These evaluations suggest that Ceo and related fullerenes should be more reactive than benzene. However, it is difficult to directly compare the reactivities of these typical representatives of two- and three-dimensional aromatics. In contrast to benzene and other planar aromatics, the jt systems of the fullerenes have no boundaries. In other words, the fullerenes contain no hydrogens that can be replaced via substitution reactions. As a consequence, a chemical transformation of fullerenes is always accompanied with a change of the structure, whereas retention of the structural type is characteristic for reactions of benzene-like aromatics. Two main types of primaiy chemical transformations are possible addition reactions and redox reactions. 

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