Design tetraphenylporphyrins

Dloxygen reduction electrocatalysis by metal macrocycles adsorbed on or bound to electrodes has been an Important area of Investigation (23 ) and has achieved a substantial molecular sophistication in terms of structured design of the macrocyclic catalysts (2A). Since there have been few other electrochemical studies of polymeric porphyrin films, we elected to inspect the dloxygen electrocatalytic efficacy of films of electropolymerized cobalt tetraphenylporphyrins. All the films exhibited some activity, to differing extents, with films of the cobalt tetra(o-aminophenylporphyrin) being the most active (2-4). Curiously, this compound, both as a monomer In solution and as an electropolymerized film, also exhibited two electrochemical waves... 

Callot and co-workers established in 1982 that iodorhodium(III) porphyrin complexes could be used as cyclopropanation catalysts with diazo esters and alkenes with c/.s-disubstituted alkenes these catalysts provide preferential production of cis(syn) disubsdtutcd cyclopropancs (syn/anti up to 3.3 with 1,4-cyclohexadiene) [72], More recently, chiral porphyrins have been designed and prepared by Kodadek and co-workers [73], and their iodorhodium(lll) complexes have been examined for asymmetric induction in catalytic cyclopropanation reactions [74,751. The intent here has been to affix chiral attachments onto the four porphyrin positions that are occupied in tetraphenylporphyrin by a phenyl group. Iodorhodium(III) catalysts with chiral binaphthyl (27, called chiral wall porphyrin [74]) and the structurally analogous chiral pyrenyl-naphthyl (28,... 

Design and Synthesis of Tetraphenylporphyrin-based Protein Surface... 

Different substitution patterns will be labeled with additional lowercase letters, e.g., la, lb, lc. To save space, structures available in several substitution patterns will often be drawn with no substituents. Instead, the substituents will be listed after corresponding structure symbols. For instance, la 5,10,15,20-Ph" corresponds to 5,10,15,20-tetraphenylporphyrin (la). Letter designations will be omitted when (i) there is just one substitution pattern and it is shown explicitly in the scheme, (ii) no reference to any specific substitution is made. 

For designing the enzyme model, it is important to consider the functional and structural similarity between the model and the active site of enzyme. With this in mind, we chose the iron(II) complexes of octaethylporphyrin and tetraphenylporphyrin, (OEP Fe(II) py2 and TPP Fe(II) py2), respectively, as models of the heme and benzene as the hydrophobic environment surrounding the heme. 

Figure 3 Chemical structures of porphyrins used inmetallopeptide design, (a) protoporphyrin IX (b) deuteroporphyrin IX (c) mesoporphyrin IX (d) mesoporphyrin II (e) coproporphyrin (f) meio-tetraphenylporphyrin ...

The capped porphyrins prepared by Baldwin et al. [56, 57] are other model systems designed to test the consequences of steric hindrance on CO binding (Scheme 4). These compounds were reported to discriminate against dioxygen in favor of carbon monoxide [62, 119-121]. The CO affinity of the capped porphyrins differs by less than a factor of three from that of unprotected iron(II) tetraphenylporphyrin, while the dioxygen affinity is more than a factor of 100 lower. Kinetic studies of CO binding show that the CO dissociation rate constants are very similar to those of unprotected hemes. Recently, the X-ray crystal structure of a carbonylated complex of the smallest capped porphyrin was obtained [122]. The CO ligand is reported to deviate 7° and 4° from the heme normal, respectively, for each independent molecule present in the unit cell. 

Reaction of [Rh(CO)2Cl]2 with tetraphenylporphyrin (TPP) in glacial acetic acid generates a material identified as [Rh(TPP)] and the authors state that they found no evidence. .. for the formation of oxygen complexes. . This was questioned by Wayland and Newman who found that octaethylporphyrin (OEP) formed a monomeric Rh " superoxo complex [Rh(0EP)(02)]. Its spectral and chemical properties strongly support the superoxo designation reexamination of the TPP complex implied that the previously identified Rh" complex [Rh(TPP)] is actually the Rh" superoxo complex [Rh(TPP)(02)]. Dioxygen (in air) reacts with the (presumably) Rh" dimers... 

The heat-treated M/N/C composite materials, such as CoPPy/C, can also be considered as multifunctional catalysts, featuring Co nanoparticles coated with Co oxides and Co " species associated with N-C moieties that originate from the polypyrrole structures [82]. An illustration of the CoPPy/C catalyst surface and the ORR processes is shown in Fig. 15.30. The Co-N type site (shown as a C0-N4 complex) supports the initial adsorption of the O2 molecule and conversion of O2 to the intermediate reaction prcxluct, H02, by a 2e reduction reacticm. The H02 species can further react at a decorating Cof)y/Co nanopaiticle phase. Chu et al. [126] found that the mixture of the heat-treated Co- and Fe-tetraphenylporphyrins (CoTPP/FeTPP) had better catalytic performance for ORRs in acid media than that of the respective heat-treated single components. All of the above cited research results point to the fact that carefully designed bifuncticmal or multifunctional catalysts can be much more active for ORR than their single components. 

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... 

For understanding the photochemistry of porphyrin compounds, characteristics of absorption spectrum, fluorescence quantum yield, lifetime of singlet excited state, phosphorescence quantum yield, and excited triplet state lifetime are most crucial. These data are actually helpful for a more sophisticated design of a photo-responsive molecular system. In this section, comprehensive data on excited states of porphyrins, mainly on tetraphenylporphyrin (TPP), octaethylporphyrin (OEP), and fiieir metal complexes, are presented. Some empirical rules for estimating those data will also be described. 

The design of a system for photoswitching on and off coordination sites in a self-assembled mono-layer (SAM) containing an azopyridine unit has recently been reported by Cook and co-workers. The required SAM was prepared by depositing an unsymmetrical disulfide 28 having 4-(arylazo)pyridine and phenoxy moieties onto an 8-nm-thick film of gold supported on a quartz glass slide. Scheme 64 outlines the system for the evanescent field-driven SAM photoswitch. Zinc tetraphenylporphyrin (ZnTPP) was... 

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