Chain porphyrins, supramolecular assembly

A chromophore such as the quinone, ruthenium complex, C(,o. or viologen is covalently introduced at the terminal of the heme-propionate side chain(s) (94-97). For example, Hamachi et al. (98) appended Ru2+(bpy)3 (bpy = 2,2 -bipyridine) at one of the terminals of the heme-propionate (Fig. 26) and monitored the photoinduced electron transfer from the photoexcited ruthenium complex to the heme-iron in the protein. The reduction of the heme-iron was monitored by the formation of oxyferrous species under aerobic conditions, while the Ru(III) complex was reductively quenched by EDTA as a sacrificial reagent. In addition, when [Co(NH3)5Cl]2+ was added to the system instead of EDTA, the photoexcited ruthenium complex was oxidatively quenched by the cobalt complex, and then one electron is abstracted from the heme-iron(III) to reduce the ruthenium complex (99). As a result, the oxoferryl species was detected due to the deprotonation of the hydroxyiron(III)-porphyrin cation radical species. An extension of this work was the assembly of the Ru2+(bpy)3 complex with a catenane moiety including the cyclic bis(viologen)(100). In the supramolecular system, vectorial electron transfer was achieved with a long-lived charge separation species (f > 2 ms). 

In the former case, polymers were assembled by complexation of a pyridyl-substituted porphyrin with the hexacoordinate metal ion, cobalt(II). The resulting supramolecular polymers, (60) (Figure 37), were characterized by UV/vis spectroscopy, NMR diffusion studies, and SEC. Polymers with concentration-dependent molecular weights up to 136 kDa (DP 100) formed, as indicated by SEC data. The dynamic nature of polymer formation was implied in the concentration dependence of the molecular weights as well as in capping studies with a porphyrin chain stopper [122],... 

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