Metalloporphyrins, applications porphyrins

Binding of organic nitroso compounds to metalloporphyrins 99ACR529. Design and applications of chiral porphyrins 98YGK201. 

Bis(cyclopentadienyl) complexes are central to the organometallic chemistry of the early transition metals and feature in applications such as alkene polymerization chemistry. Parallels can be drawn between a porphyrin ligand and two cyclopentadienyl ligands, in that they both contribute a 2— formal charge and exert a considerable steric influence on other ligands in the same molecule. Several of the metalloporphyrin complexes discussed below have bis(cyclopentadienyl) counterparts, and authors in some ca.ses have drawn quite detailed comparisons, although these discussions will not be repeated here. 

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. 

A decade ago, almost every metal had been inserted into a porphyrin, i.e., the periodic table of metalloporphyrins was nearly completed [8, 29], A review article devoted to the porphyrin complexes of individual metals gave examples for metal insertions according to following reactions (1) to (8) [8] for abbreviations see Table 1. Recent applications and improvements are noted below the respective equations. 

The second example of the application of TDDFT to the electronic spectroscopy of metalloporphyrins concerns a CO-ligated iron porphyrin, a system that models the active centers of hemoproteins, recently investigated by Head-Gordon et al [146, 147] in the context of a theoretical study of the initial step of the photodissociation pathway of CO-ligated heme. 

As shown in Fig. 1-33, metalloporphyrins exhibit a number of porphyrin core vibrations in which local modes such as v(C=C) and v(C=N) are strongly coupled (Section 1.21) due to its planar 7r-conjugated structure. Several groups of workers (5-8) have carried out normal coordinate analysis on metalloporphyrins. If we consider the simplest metalloporphyrin in which all the peripheral groups are the hydrogen atoms, it should have 105 (3 x 37 - 6) normal vibrations, which can be classified under D4h symmetry as shown in Table 4-4. Table 4-5 shows major local coordinates that describe general characters of 35 Raman-active in-plane vibrations (8) together with observed frequencies for Ni(OEP) (Fig. 1-32). These normal mode descriptions are applicable to other metalloporphyrins with minor modifications. 

The last decade has greatly increased our knowledge on how metallo-porphyrins are able to interact with hydrogen peroxide without producing the unspecific hydroxyl radical. It would therefore appear likely that in the near future, industrial applications of such metalloporphyrins with hydrogen peroxide will be started in earnest. 

Radiative and Nonradiative Decay Processes - Due to the potential application of these compounds as photosensitizers for photodynamic therapy" the photophysical properties of porphyrins and phthalocyanines, and their corresponding metal complexes, have been investigated extensively over the past decade. The photophysical properties of water-soluble metalloporphyrins, and especially the tetraphenylsulfonates," have been re-examined but nothing new has been found. The disulfonated metallophthalocyanines (MPcS2, where M = Al ", Ga" , or Zn") form complexes with fluoride ions for which the fluorescence yields and lifetimes are decreased with respect to the parent dyes while there are... 

Within the large number of multiredox arrays containing metalloporphyrins/covalently bound (conjugate) fullerene-metalloporphyrin dyads have gained enormous interest in the last ten years, mainly due to their potential application as artificial antennae Due to the multiredox behaviour of the fullerenes (up to six reversible one-electron reductions and at least one reversible one-electron oxidation), the porphyrin ligands and the incorporated metals, the assignment of electron-transfer steps in such systems is difficult. Recently, spectroelectrochemical characterisation has been carried out on a number of fullerene-[(TPP)Co] dyads shown in Scheme 4.3, which exhibit rather complex redox behaviour (Figure 4.19). 

An example of application of Fe(III) porphyrins is the hydroxylation of the anticancer drug cyclophosphamide to active metabolite 4-hydroxycyclophosphamide in yields similar or higher than those typically obtained by the action of liver enzymes in vivo [198]. This allows the development of novel anticancer drugs for the treatment of tumors with less toxic side effects to the patient. There are many other examples of metalloporphyrin-based systems for the synthesis of drugs or agrochemicals that mimic P450 catalyzed processes. 

Several murine models support a role for oxidative stress in neuronal degeneration. For example, overexpression of SOD isoenzymes reduces both global and focal ischemic injury in models of traumatic brain injury (58-60). Conversely, targeted deletion of Cu, Zn-SOD and extracellular (EC)-SOD worsens the outcome of focal ischemia (61,62). Recently, an especially intriguing protective effect has been observed in a model of cerebral ischemia using middle cerebral artery occlusion (63-65). Application of the EC-SOD mimic, AEOL10113 (a metalloporphyrin catalytic antioxidant) [manganese(III) maso-tetrakis (A-ethylpyridinium-2-yl) porphyrin],... 

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