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Porphyrins redox properties

The consequences of polychlorination of porphyrins on redox properties of complexes has been investigated.1404 The highly chlorinated porphyrin 3-octachloro-/ /c.vo-tetrakis(3,5-dichloro-2,6-dimethoxyphenyl)porphyrin exhibits a substantial anodic shift for reduction of over 0.5 V and a smaller shift for oxidation versus the unchlorinated precursor. Contrastingly, small potential shifts for the octabromo-substituted 5,10,15,20-tetraphenylporphyrinate arise from the dominance of macrocycle ruffling over electronic effects. In the polychloro complex, distortion does not compensate fully for electron-withdrawing effects of the Cl substituents. [Pg.119]

Functionalization can be used to alter the redox properties of the zinc metalloporphyrin the zinc heptanitroporphyrin shows facile reduction to the air-stable 7r-anion radical.768 Modification of the zinc porphyrin at the, 8 position with chlorine or bromine to induce saddling of the... [Pg.1216]

Why, we may ask, does nature use Mg2+ as the metal to capture solar energy Perhaps, as has been suggested by Frausto da Silva and Williams (2001), the reasons are that Mg2+ does not have the redox properties of other metal ions such as Mn, Co, Fe, Ni and Cu when inserted into a porphyrin, and that it does not enhance fluorescence as much as the corresponding Zn porphyrin would. [Pg.179]

Dendritic derivatives of these macrocycles can be placed in the wider context of studies on metalloporphyrins with sterically hindered faces which have been designed in attempts to mimic the properties of heme proteins and chlorophylls, and there are suggestions that steric isolation of the metalloporphyrin nucleus is important in certain biological functions, The redox properties of metalloporphyrins are well-documented they are dominated by two, reversible one-electron transfers involving both the metal and the ligand. The first dendritic porphyrins of general structure 47 and their Zn complexes were reported by Inoue et al. who... [Pg.137]

The simplest covalently linked systems consist of porphyrin linked to electron acceptor or donor moiety with appropriate redox properties as outlined in Figure 1. Most of these studies have employed free base, zinc and magnesium tetrapyrroles because the first excited singlet state is relatively long-lived (typically 1-10 ns), so that electron transfer can compete with other decay pathways. Additionally, these pigments have relatively high fluorescence quantum yields. These tetrapyrroles are typically linked to electron acceptors such as quinones, perylenes , fullerenes , acetylenic fragments (14, 15) and aromatic spacers and other tetrapyrroles (e.g. boxes and arrays). [Pg.196]

It is noteworthy that siroheme is present in the enzymes responsible for catalyzing two out of only three known six-electron processes, and accordingly it is of great interest to try and identify any feature in siroheme that makes it particularly suitable for the mediation of multielectron transfer. A comparison of octaethylporphyrin, octaethylchlorin and octaethylisobacteriochlorin complexes of iron shows that redox potentials and vco of Fe(P)L(CO) and Fe(P)L(CO)2 were nearly independent of the porphyrin. The property that was most dependent upon the macrocycle structure was the potential for ring-based oxidation which increased in the order OEiBC < OEC < OEP.734... [Pg.625]

L Her, M, Pondaven A (2003) Redox properties and electrochemistry of phthalocyanines In Kadish KM, Smith KM, Guilard R (eds) Porphyrin handbook, phthalocyanine properties and materials, vol 16, Chap 104. Academic Press, New York... [Pg.85]

Therefore, it appears that the redox properties of the metallo-porphyrin are required only for the initiation step in these free-radical autoxidations and that the porphyrin is not a stoichiometrically significant catalyst (21, 22, 23). The failure of these simple approaches to a reaction iron-porphine oxide or its equivalent could indicate that the ligation state of iron in the protein, presumably including an axial thiolate, is crucial to the oxygen-transfer properties of P 450. Support... [Pg.283]

Felton RH. Primary redox properties of metalloporphyrins. In Dolphin D, ed. The Porphyrins. New York Academic Press, 1978 53-125. [Pg.328]

Porphyrins and metalloporphyrins exhibit planar, relatively rigid structures suitable for the preparation of materials displaying cavities or that can self-assemble by electrostatic and n-n interactions. They also provide very interesting functional building blocks because of their rich coordination, catalytic, electro-catalytic, photochemical, and redox properties, as described in many papers (100-102) and review articles by Toma and co-workers (31,38,39), Latos-Grazynski et al. (103), Imamura and Fukushima (104), Sanders (105), Chambron et al. (106), Baldini and Hunter (107), and Prodi et al. (108). [Pg.387]

The preparation and characterization of novel man-ganese(III) complexes of various porphyrin and porphyrin-likes macrocycles have continued to attract strong attention especially because of their importance in catalytical oxidation processes through the formation of a Mn(V)0 intermediate (see Section 6) and as model for metalloenzymes. In this line, an artificial enzyme formed through a directed assembly of a molecular square that encapsulated a Mn porphyrin has been prepared and investigated as a catalyst. In contrast to symmetrical binuclear bis(phenoxo) bridged macrocyclic Mn(III)Mn(III) complexes, unsymmetrical ones are rare. A new series of these kinds of carboxylate-free complexes has been described and their redox properties investigated. ... [Pg.2514]


See other pages where Porphyrins redox properties is mentioned: [Pg.177]    [Pg.184]    [Pg.665]    [Pg.213]    [Pg.219]    [Pg.268]    [Pg.487]    [Pg.487]    [Pg.178]    [Pg.71]    [Pg.236]    [Pg.465]    [Pg.579]    [Pg.117]    [Pg.116]    [Pg.139]    [Pg.145]    [Pg.172]    [Pg.63]    [Pg.232]    [Pg.96]    [Pg.980]    [Pg.177]    [Pg.105]    [Pg.143]    [Pg.303]    [Pg.39]    [Pg.147]    [Pg.159]    [Pg.308]    [Pg.180]    [Pg.2102]    [Pg.2154]    [Pg.2163]    [Pg.197]    [Pg.277]    [Pg.189]    [Pg.28]    [Pg.673]   
See also in sourсe #XX -- [ Pg.217 , Pg.245 , Pg.246 , Pg.247 , Pg.248 , Pg.249 , Pg.250 , Pg.251 , Pg.252 ]




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