Porphyrins oxidation

Porphyrin oxidation Porphyrin reduction Cobaltocenium reduction... 

It has been observed that PI14PHSO5 alone does not transfer its oxygen to manganese porphyrin. It is necessary to add either imidazole or pyridine derivatives, i.e. species which act as axial ligands in metalloporphyrins and are known to accelerate also the catalytic oxidation of organic substances . The kinetics and mechanism of manganese porphyrins oxidation by PI14PHSO5 were well studied . ... 

A second reaction involves the chlorin-to-porphyrin conversion. Any chlorin which has hydrogen atoms at the sp -hybridized centers of the reduced ring can be oxidized to the respective porphyrin. Oxidation may be achieved by various oxidants including oxygen . Likewise, rednctions to hydroporphyrins and other reactions of the macrocycle are possible. However, most of these are of interest only for the specialist. Under... 

In addition to the above-mentioned reactions, metal complexes catalyze decarboxylation of keto acids, hydrolysis of esters of amino acids, hydrolysis of peptides, hydrolysis of Schiff bases, formation of porphyrins, oxidation of thiols, and so on. However, polymer-metal complexes have not yet been applied to these reactions. 

The chromium(II) complex of mesoporphyrin IX dimethyl ester (276) can be prepared by metal insertion with an excess of chromium hexacarbonyl under nitrogen.1242 After removal of solvent and extinction with toluene, Crn(MPDME) is crystallized by the addition of n-pentane. Presumably the weakly acidic NH protons of the porphyrin oxidize Cr° to Cr11 and form H2. 

Autoreduction of Fe(III) Porphyrins. Oxidation of Piperidine. The autoreduction of TPPFeCl with neat piperidine is rapid, however the reaction rate can be decreased by dilution with CDC13 or DMSO. The NMR spectrum of TPPFeCl in CDC13, on addition of piperidine, shows resonances consistent with the presence of high spin Fe(III) and low spin TPPFen(Pip)2. A low spin TPPFem(Pip)2 species was not observed. It is likely that the latter complex rapidly reduces at room temperature. 

N-substituted porphyrins are formed during the metabolism of xeno-biotics that include terminal alkenes and alkynes, as well as activated organic molecules such as halocarbons, diazo compounds, and hydrazines. In the synthetic laboratory, N-substituted porphyrins are prepared easily via alkylation of a pyrrole nitrogen atom of the porphyrin, followed by metallation. Biomimetic reactions between iron porphyrins, oxidants, and alkenes (or activated carbon sources) may also be used to alkylate the pyrrole nitrogen. 

Protoporphyrinogen oxidase converts protoporphyrinogen IX to the fully desaturated porphyrin in a reaction that uses O2 as the terminal electron acceptor (Fig. 3). The crystal structure of the homodimeric enzyme shows it has one FAD per monomer, which presumably mediates the porphyrin oxidation reaction (19). Like the decarboxylation mediated by coproporphyrinogen oxidase, this reaction also occurs in the mitochondrion. Mutations in the protoporphyrinogen oxidase gene are responsible for variegate porphyria (21). Acute attacks of this disease can be effectively treated by intravenous administration of hematin. 

The catalytic carboxylation and reduction of an organic halide by Co TPP showed that the initially formed RCoin(TPP) is reduced by one electron to the anion which dissociates by homolytic cleavage to reform Co TPP-. Decomposition of the complex was thought to proceed as a result of attack of the cleaved organic radical on the porphyrin ring, at the pyrrole nitrogen.170 Porphyrin oxidation-state marker bands have been used to monitor the [U(OEP)2]+/2+ redox process.72... 

Figure 3. Mechanisms of Ruthenium Porphyrin Oxidation Catalysis...

Raman and resonance Raman R, RR Vibrational modes involving a change in polarizability. For RR enhancement of modes coupled with electronic transition excited by laser light source. Complementary to IR. v(P—0) and KM—O) espiecially in metallo-proteins. In porphyrins, oxidation and spin state. 

Scheme 1.16. Mechanisms of ruthenium porphyrin oxidation catalysis.

A = 430, 440 nm) with HS04. Electrochemical studies displayed cathodic shifts in the [Cp2Co]/[Cp2Co] redox couple of 35-75 mV on addition of Gl or HS04, and 225 mV for H2P04. Smaller shifts were seen in the porphyrin oxidation wave. It should be noted that these anion-sensing effects are specific to the m-a,a,a,a-atropisomer. 

Smaller shifts were observed for the porphyrin oxidation redox couple. 

Bruice, T.C. and G. He (1991). Nature of the epoxidizing species generated by reaction of aUcyl hydroperoxides with iron(III) porphyrins. Oxidations of cis-stilbene and (Z)-l,2-bis(trans-2, trans-3-diphenylcyclopropyl)ethene by tert-BuOOH in the presence of [meso-tetrakis(2,4,6-trimethylphenyl)porphinato]-, [meso-tetrakis(2,6-dichlorophenyl)-porphinato]-, and [meso-tetrakis(2,6-dibromophenyl)porphinato]rron(III) chloride. J. Am. Chem. Soc. 113, 2747-2753. 

Artificial porphyrins oxidized forms of porphyrinogen other than porphyrins... 

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