Covalent binding porphyrin

Figure 8.14 Scheme of the structure of the covalent binding porphyrin-graphene composite. Reprinted from reference [110] by permission of John Wiley Sons Ltd. 

The interaction within the active site can be either in the form of covalent binding or in the form of quasi-irreversible (tight but slowly reversible) binding, and it can involve the protein residues, the porphyrin moiety or the catalytic center (heme iron) [8]. CYP inactivation follows a stoichiometry of one substrate molecule per enzyme molecule inactivated. To measure the stoichiometry of the inactivation, it is necessary to trap all molecules that are not specifically bound to the active site, by using an appropriate scavenger, normally GSH. 

Results on catalytic activity often are only fundamental, if properties of the porphyrin are retained through covalent binding to polymers. Peroxidative activity with (20) and hydroquinone oxidation with (2i) was reported. 

Another very interesting porphyrin system based on covalently linked porphyrin grids was generated by C-C coupling through nickel-catalyzed Yamamoto reaction, instead by Pd(ll) or Pt(ll) square planar complexes as demonstrated by Drain et al. [70]. In this case, well-defined supramolecular species were obtained in contrast with the bidimensional covalent organic polymer network that can bind transition... 

Almost at the same time Nyokong et al. [125] used a similar method to covalently bind Ni(II)-2 to carboxylic acid functionalized SWCNT. More recently, Nyokong et al. [126] have reported a method of functionalization of SWCNTs, with amine groups using a previously developed diazonium approach. This makes it possible the direct attachment of the Zn(II)-10 by an amide bond to the CNT as illustrated in Fig. 4. Kim and Jeon [129] have reported on the immobilization of a cobalt porphyrin (cobalt tetrakis(o-aminophenyl)porphyrin) of several carbon nanomaterials via the diazonum strategy, but in this case, the diazotation was performed on the macrocycle, by the diazotation of aromatic amine groups of the porphyrin. 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

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