Ferricenium half-reactions

The data for the ferricenium half-reaction deserve several comments. The Michaelis-Menten kinetics obtained in the UV-vis experiment supports the formation of the GO-ferricenium intermediates postulated in Scheme 5. The ratio k2i)/K which corresponds to the bimolecular interaction of GO(red) with the ferricenium ion, equals ca. 1 x 105 M-1 s 1 (79) and this must be compared with the observed rate constants of 1.4 x 105 M-1 s 1 found for ferrocene using the electrochemical technique under similar conditions (87). 

The pH-dependence of the ferrocene half-reaction has been convincingly demonstrated by using a more illustrative spectrophoto-metric technique (79). The rate of reaction (29) increases sharply in the pH range 3-7 (Fig. 4). The maximal rate is around pH 7.5-8. The pH profile in Fig. 4 classifies ferricenium salts as Group II electron... 

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