Iron-porphyrin polymer-attached

In the example of Figure 20, the heme of cytochrome 562 of Escherichia coli is bound within a protein bundle by coordination of the heme s iron to a methionine and a histidine." Attachment of a modified heme (iron porphyrin derivative) to the protein s surface is performed via mutation of the histidine 63 to introduce a cysteine residue opposite to the heme pocket. The subsequent removal of the native heme leaves a protein receptor that can self-assemble by ligation of the pendant external heme in a neighboring heme pocket. The assemblies have some flexibility, as shown by the bends observed in AFM images of the polymers. The right amount of flexibility was important in obtaining a 100-mer that was approximately 350 nm long. 

In recent years, much attention has been focused on electrochemical studies of metalloporphyrins, not only as mimetic compounds of the iron porphyrin unit in heme proteins but also as potential electrocatalysts . Metalloporphyrins have been found to be applicable in both homogeneous and heterogeneous catalysis - and, because oxygen can be reduced directly through a 4-electron pathway on some transition metal porphyrins, catalysis in the heterogeneous electrochemical oxygen reduction reaction has received particular attention The application of metalloporphyrins to heterogeneous electrocatalysis requires their attachment to solid electrodes which can be realized based on chemisorption, chemical reactions with previously functionalized electrodes, chemical reactions with a functionalized polymer, incorporation of the porphyrin with the polymer film and electrochemical polymerization. 

C. Polymer-Attached Iron-Porphyrins in Aqueous Solution... 

Porphyrin-based complexes pass their redox sensitivity on to the corresponding polymers. Advanced conjugated main-chain structures with attached dendrons have been introduced [220]. Grafting of porphyrin-zinc main-chain polymers onto carbon nanotubes was reported [221]. An interesting example dealing with a nonelectrochemically switched polymer was recently given. Here, polymers with porphyrin-iron end groups could be switched between linear and cyclic polymers by a dimerization procedure (Fig. 14) [222, 223],... 

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