Redox-Driven Reactions

TABLE 5A. Soil and Sediment Processes Causing pH Changes 

Oxidative metabolism (enzymatically available organic matter + 02 — C02 + H20) 

Therefore, oxidation-reduction processes in nature control the behavior of elements or substances. During oxidation-reduction, the potential for reactions to take effect changes because the redox status of elements changes. A summary of soil-water mineral-ion properties known to be affected by redox chemistry is listed below  

Soil-water pH (reducing conditions increase pH, oxidizing conditions decrease pH Table 5A) 

Mineral surface chemistry [PZC of 5-Mn02 = 2.8 or PZC of fi-Mn02 = 7.2 vs. Mn(II)(OH)2 a very soluble mineral under natural pH with very high PZC] 

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Two important variants in this process replace the organometallic partner with an alkyne oralkene nucleophile. These reactions are also catalysed by Pd(0) in a redox-driven reaction cycle but differ in some of the key details of the reaction cycle. 

In the most general situation, a redox-active metal ion is translocated from a given site to another site of the same molecular system, following a chemical (a redox reaction) or an electrochemical input. The redox-driven reversible translocation of a metal ion in a two-component molecular system is schematically sketched in Fig. 2.2. 

Early life most likely depended on exploiting the transient redox contrasts available from two sources within the inorganic geological system— especially at hydrothermal vents (Reysenbach and Shock, 2002) and secondly from inorganic light-driven reactions, such as the formation of transient oxidizing and reducing species in the atmosphere by incident radiation. 

Electrochemical reactions have many practical applications. Some are spontaneous, and others are driven uphill by applying an external potential. In this section, we present practical examples of spontaneous redox processes. We describe externally driven redox reactions in Section 19-1. 

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