Hydrogen peroxide reaction with iron porphyrins

Luminol chemiluminescence has also been recommended for measuring bacteria populations (304,305). The luminol—hydrogen peroxide reaction is catalyzed by the iron porphyrins contained in bacteria, and the light intensity is proportional to the bacterial concentration. The method is rapid, especially compared to the two-day period required by the microbiological plate-count method, and it correlates weU with the latter when used to determine bacteria... 

The results from the publications mentioned are of interest because they can help in the creation of effective catalytic systems containing porphyrins, which combine functions typical of multienzyme systems. The task in hand is the possible synthesis of bifunctional catalysts based on metalloporphyrin systems, when with the help of manganese porphyrins, for example, or SOD mimic, hydrogen peroxide is accumulated in the system. Afterwards, the accumulated hydrogen peroxide is used in oxidation reactions of various substrates with iron porphyrin components of the catalyst. 

This behavior, as well as complementary observations, can be explained on the basis of the reaction mechanism depicted in Scheme 5.3. The main catalytic cycle involves three successive forms of the enzyme in which the iron porphyrin prosthetic group undergoes changes in the iron oxidation state and the coordination sphere. E is a simple iron(III) complex. Upon reaction with hydrogen peroxide, it is converted into a cation radical oxo complex in which iron has a formal oxidation number of 5. This is then reduced by the reduced form of the cosubstrate, here an osmium(II) complex, to give an oxo complex in which iron has a formal oxidation number of 4. 

Epoxidation of cyclooctene with hydrogen peroxide, catalysed by the methoxide-ligated form of iron(III) tetrakispentafluorophenyl [F20TPPFe(III)] porphyrin, is proposed to involve a reaction of F20TPPFe(in) with hydrogen peroxide to form an iron(III) hydroperoxide species, which then undergoes both heterolytic and homolytic cleavage to form iron(IV) n -radical cations and iron(IV) oxo species, respectively. 

Traylor TG, Ciccone JP (1989) Mechanism of reactions of hydrogen peroxide and hydroperoxides with iron(III) porphyrins. Effects of hydroperoxide structure on kinetics. J Am Chem Soc 111 8413-8420... 

Traylor TG, Xu F (1990) Mechanisms of reactions of iron(III) porphyrins with hydrogen peroxide and hydroperoxides solvent and solvent isotope effects. J Am Chem Soc 112 178-186... 

As already mentioned above, iron(I) porphyrins can undergo various reactions. They are of synthetic value for preparation of a-alkyl iron porphyrins, which can be obtained by direct alkylation of the corresponding electrochemically generated iron(I) porphyrins with alkyl halides. The highly reduced species can also be oxidized by molecular oxygen or hydrogen peroxide to yield the iron oxyporphyrin (oxophlorin), which is further oxidized to verdoheme by molecular oxygen, " as discussed in Section 6.1.5. 

Haem peroxidases are globular proteins with an iron-porphyrin complex as a prosthetic group. These enzymes are widespread among prokaryotes and eukaryotes. They catalyze the oxidation of substrates by organic peroxides or hydrogen peroxide. During the past decades, considerable scientific effort has been put into elucidation ofthe mechanisms of reactions catalyzed by these enzymes. Pulse radiolysis technique has made an important contribution by providing information on the redox states of the enzymes and their interconversion, as well as on the properties ofthe free radical intermediates involved [23]. 

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