Metalloporphyrins, applications porphyrin complex

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 oxidation of OH by [Fe(CN)6] in solution has been examined. Application of an electrical potential drives the reaction electrochemically, rather than merely generating a local concentration of OH at the anode, as has been suggested previously, to produce both O and [Fe(CN)6] in the vicinity of the same electrode. With high [OH ] or [Fe(CN)6] /[Fe(CN)6] ratio, the reaction proceeds spontaneously with a second-order rate constant of 2.2 x 10 M s at 25 °C. Under anaerobic conditions, iron(III) porphyrin complexes in dimethyl sulfoxide solution are reduced to the iron(II) state by addition of hydroxide ion or alkoxide ions. Excess hydroxide ion serves to generate the hydroxoiron(II) complex. The oxidation of hydroxide and phenoxide ions in acetonitrile has been characterized electrochemically " in the presence of transition metal complexes [Mn(II)L] [M = Fe,Mn,Co,Ni L = (OPPh2)4,(bipy)3] and metalloporphyrins, M(por) [M = Mn(III), Fe(III), Co(II) por = 5,10,15,20-tetraphenylpor-phinato(2-), 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphinato(2-)]. Shifts to less positive potentials for OH and PhO are suggested to be due to the stabilization of the oxy radical products (OH and PhO ) via a covalent bond. Oxidation is facilitated by an ECE mechanism when OH is in excess. 

A behavior envisaging possible application in electroanalysis is found in Ref. [88] the shift of the potential exhibited by the redox system due to the Fe-porphyrin complex in a metalloporphyrin functionalized PTh is shown to depend on the concentration of 2,4,5-trichlorophenol in solution. Interactirai of the chlorinated phenol with the Fe centre is hypothesized to cause the modification of the electron... 

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. 

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). 

Metalloporphyrins consist of porphyrin ring structures complexed to a central atom. Among them, hemin structures with central iron atoms at different oxidation states and chlorophyll pigments containing magnesium are most abundant The interest in their spectroelectrochemical studies is multiple. Thus, their adsorption and electrochemical behaviour at the electrode surface can be used not only to model their functions in a biological matrix but also to improve the practical application of porphyrin coated electrodes as catalysts or sensitizers in photoelectrochemical cells... 

Stemming from their multifarious roles in natural processes, [metallo] porphyrins have found numerous applications in artificial systems aimed at mimicking important biological functions. Many different metalloporphyrins have been designed in order to accomplish specific tasks and, in particular, novel approaches have been used to assemble several porphyrins into a cluster. This ability to concentrate metalloporphyrins into a supramolecular assembly is of special relevance in that it takes us one step closer to constructing practical devices. This chapter will attempt to review the progress made in the assembly of porphyrin derivatives into supramolecular systems and will describe the aptitude of such assemblies to photosensitize particular reactions. The work described here is primarily concerned with trying to reproduce, under controlled conditions, some of the important features of photosynthetic reaction center complexes. 

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