Dendrimer dendritic iron porphyrin

Porphyrin-based self-assembled molecular squares 389 can form mesoporous thin films in which the edge of a square, thus the size of the cavity, can be adjusted by appropriate choice of substituents [8]. Fibers that form coil-coiled aggregates with distinct, tunable helicity are built from crown ethers bearing porphyrins 390 [9]. In addition to the porphyrin applications discussed in Sections 6.3.2.2 and 6.4, dendrimer metalloporphyrins 391 to be applied in catalysis [10] and the water-soluble dendritic iron porphyrin 319 modelling globular heme proteins [11] can be mentioned. 

Modification of the electrochemical properties of a redox centre surrounded by dendritic fragments [93] can lead to two different dendritic effects. The first one is manifested in a shift of the redox potentials, the extent and direction depending upon the dendritic architecture and the solvent. Such behaviour was observed in dendritic iron-porphyrins [94]. The second effect is apparent in a delay of redox transfer kinetics and is characterised by a stepwise increase in the distance between the peaks in a cyclovoltammogram with increasing dendrimer generation number. 

D.L. Jiang, T. Aida, A Dendritic Iron Porphyrin as a Novel Haemoprotein Mimic Effects of the Dendrimer Cage on Dioxygen-Binding Activity , Chem. Commun., 1523-1524 (1996)... 

Jiang, D.-L. and Aida, T. (1996) A dendritic iron porphyrin as a novel haemoprotein mimic Effects of the dendrimer cage on dioxygen binding affinity, Chem. Commun. 1523-1524. 

In other work, Dandliker et al. have reported the inclusion of iron porphyrins within dendrimers to serve as functional mimics of redox-based proteins (Dandliker et al., 1994, 1995, 1997). These redox-switchable porphyrins show that the Fe3+/Fe2+ redox couple can be altered by the polarity of the surrounding environment. By changing the polarity imposed by the tightly packed branches of the dendritic core, the authors have illustrated that electrochemical behavior can be controlled by slight and subtle through-space environmental factors. These mimics may potentially model a wide variety of redox-driven enzymes and possibly provide mechanistic insights into their function. 

Zingg. A. Felber, B. Gramlich. V. Fu. L. Collman. J.P. Diederich. F. Dendritic iron(II) porphyrins as models for hemoglobin and myoglobin Specific stabilization of O2 complexes in dendrimers with H-bond-donor centers. Hell. Chim. Acta 2002. 85 (1). 333-351. 

In an attempt to create biomimetic systems, there has been much research on designing dendritic molecules with porphyrins and similar molecules at their cores. Diederich etal. have synthesized dendrimers with iron and zinc-porphyrin cores in an effort to model heme and cytochrome c systems [46-49]. In these cases, the redox reactions occurring at the center of the molecule were found to be affected by the nature of the dendritic foliage. The porphyrin-centered (the Zn(II) is not electroactive) first oxidation in the zinczinc-tetraphenylporphyrin to 4-0.65 V for the largest zinc-porphyrin dendrimer (compare to the results of Kaifer [35] above). However, for the iron porphyrin dendrimers, the Fe(II/III) redox couple shifts from —0.23 V versus SCE for the smaller dendrimer to 4-0.19 V for the larger one [48]. In a different set of experiments, Diederich and coworkers demonstrated that increasing the amount... 

Diederich et al. had postulated that the highly reactive iron-oxo species, arising from oxygen transfer from the oxidant to the Fem site [87], should be greatly stabilised by enclosure within a dendritic superstructure. The catalytic potential of the dendrimers 6 a-c was determined in the epoxidation of alkenes [83 a, 88] (1-octene and cyclooctene) and the oxidation of sulphides [83 a] ((methylsulphanyl)benzene and diphenyl sulphide) to sulphoxides - in dichloro-methane with iodosylbenzene as oxidising agent. Compared to the known metal-porphyrin catalysts, 6a-c exhibit only low TON (7 and 28, respectively, for... 

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