Rhodium complexes redox potential

Covalent attachment has also been exploited for protein incorporation of non-native redox active cofactors. A photosensitive rhodium complex has been covalently attached to a cysteine near the heme of cytochrome c (67). The heme of these cytochrome c bioconjugates was photoreducible, which makes it possible for these artificial proteins to be potentially useful in electronic devices. The covalent anchoring, via a disulfide bond, of a redox active ferrocene cofactor has been demonstrated in the protein azurin (68). Not only did conjugation to the protein provide the cofactor with increased water stability and solubility, but it also provided, by means of mutagenesis, a means of tuning the reduction potential of the cofactor. The protein-aided transition of organometallic species into aqueous solution via increased solubility, stability and tuning are important benefits to the construction of artificial metalloproteins. 

Like the corresponding rhodium complexes, the present iridium species undergo two successive one-electron oxidations. As illustrated in Fig. 7-44 for [Fe(f -C5H4S)2]Ir(f -C5Me5)(PMe3), in these complexes loss of the second electron is also generally reversible [136]. The redox potentials of these steps are reported in Table 7-27. 

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