Porphyrin metal induced oxidation

Fig. 4. Mechanisms of trace metal-induced porphyria and cell injury i, metals promote increased reactive oxidant formation 2, metals complex with GSH, compromising antioxidant and thiol status 3, metals impair SH-dependent enzymes and other proteins via mercaptide bond formation and/or exchange reactions 4, metal-induced oxidant stress causes oxidation of reduced porphyrins (porphyrinuria) and other biomolecules (cell injury)...

HO-1 is controlled at the level of transcription by oxidative stress and several inducers such as porphyrins, metals, and progesterone (8). The absence of HO-1 is associated with severe growth retardation, anemia, and enhanced endothelial cell injury 156, 157). In addition, HO-1 has been implicated in protection against transplant rejection 158, 159). HO-2 is constitutively expressed, and its presence in brain and the noted similar effects of CO and NO has led to the proposal that CO-generated by HO-2 is involved in signaling processes 8, 160-162). 

Phenanthroline, on the other hand, stimulates the activity of some enzymes, perhaps by removing a metal that is inhibitory to the enzyme.523 524 It can induce porphyrin synthesis525 and improve the rate of ascorbate oxidation.526 It induces lysis of sensitized sheep erythrocytes.527 It is reported to reverse the resistance of microorganisms to penicillins.528 It binds to an immunoglobulin.529 It also protects rat liver from injury induced by dimethylnitrosamine530 and ethionine.531... 

Other metal-centered catalysts that have been studied include (te)strapped chiral porphyrins derived from L-proline, which can induce modest (< 30%) enantioselectivity <02EJIOC1666>. Supported amidate-bridged platinum blue complexes, which have not yet been applied to chiral epoxidation, but which show promise of utilizing molecular oxygen as the terminal oxidant, have... 

An interesting example of sullur-bridged systems is shown in equation (27). The disulftir-bridged dianion does not contain a metal bond. Chemical or electrochemical oxidation generates the neutral species that does have a metal metal bond. This process of electrochemically induced changes in bond order will be discussed below for porphyrin complexes as well. 

Usually the chemical oxidation of porphyrins and their deprotonated anions and protonated cations is not reversible. Poor reductants and oxidants do not induce any reaction, whereas the action of powerful reagents usually leads to irreversible decomposition. There are, however, some reports on unresolved, low-percentage radical esr signals in solutions of free-base porphyrins and phthalocyanines [George (81), Gibson (52)], and there are reports of polarographic redox potentials of some non-metallic porphyrin derivatives, which correspond to reversible reactions (Tables 2 and 3). 

Hydrophobic or anionic porphyrin derivatives do not exhibit any intrinsic affinity for DNA and so the only ways to induce DNA oxidative damage are to force them to stay close to DNA, either by linking to DNA vectors, by using dicationic metal salts in order to favor ternary associations of porph nin/metallic cation/DNA, or by working at high concentrations with derivatives able to generate diffiising active species. 

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