Redox reactions/couples/systems ligands

Redox reactions with synthetic potential have been developed by use of dialkyl phosphonate, early transition metals, and lanthanides. The Lewis acidic nature of metallic compounds is another key factor in their reactivities in addition to the redox properties. Controlling the metal-based redox systems leads to greater selectivities in their electron transfer reactions. Likewise, fine-tuning the ligands coordinated to metals results in more efficient redox systems. These approaches yield a variety of fruitful redox reactions for organic synthesis as observed in the ligand coupling and haloperoxidase-inspired reactions. 

Spectrophotometric techniques combined with flow injection analysis (FIA) and on-line preconcentration can meet the required detection limits for natural Fe concentrations in aquatic systems (Table 7.2) by also using very specific and sensitive ligands, such as ferrozine [3-(2-bipyridyl)-5,6-bis(4-phenylsulfonic acid)-l,2,4-triazine], that selectively bind Fe(II). Determining Fe(II) as well as the total Fe after on-line reduction of Fe(III) to Fe(II) with ascorbic acid allows a kind of speciation.37 A drawback is that the selective complexing agents can shift the iron redox speciation in the sample. For example, several researchers have reported a tendency for ferrozine to reduce Fe(III) to Fe(II) under certain conditions.76 Most ferrozine methods involve sample acidification, which may also promote reduction of Fe(III) in the sample. Fe(II) is a transient species in most seawater environments and is rapidly oxidized to Fe(III) therefore, unacidified samples are required in order to maintain redox integrity.8 An alternative is to couple FIA with a chemiluminescence reaction.77-78... 

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