Ferrocenes oxidation into ferricenium cations

Horseradish peroxidase catalyzes the oxidation of ferrocenes into ferricenium cations by hydrogen peroxide according the stoichiometric Eq. (37) (113). 

The simplest kinetic scheme of the alkane oxygenation based on the kinetic data was proposed. In the first stage, ferrocene FeCp2 is oxidized to ferricenium cation (FeCp2)" ", which is in turn transformed into species Fe that is a fragment containing one iron ion. 

Photochemical studies of iron-group metallocene substrates have received much attention, e.g. quenching of excited uranyl ion luminescence, formation of charge-transfer complexes with TCNE, redox reactions of octamethyl-ferrocene and of carboxylate anions of the types FcCOj and Fc(X)COr (X = saturated or unsaturated alkyl chain). Enzyme-catalysed one-electron oxidation of ferrocene derivatives has also been studied. Ferrocene-ferricenium cation redox systems have been incorporated into electrochemical and photo-electrochemical cells, and have found use for catalysis of photo-addition of MeOH to Bu NCO. Inter-valence electron-transfer properties of partially oxidized Fc(C C)nFc ( = 0—2), meso-tetraferrocenylporphyrin, and poly(vinylferrocene) have been assessed. 

Irrespective of the actual mechanism imderlying the tumoristatic action, the prevailing conclusion to be drawn from the collected experimental data must be that any ferrocene compoimd qualifying for candidacy as an antitumor drug should be water-soluble and either exist directly in a cationic (i.e., oxidized ferricenium-type) dosis form or else possess the capacity for smooth in vivo transformation into that oxidized state on parenteral administration. 

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