Hydrogen peroxide-ionic iron system

Another difference between the reactions of the enzymes and ionic ion, where the mechanism is generally accepted to involve free radicals, appears when the products of hydrogen peroxide oxidation obtained using peroxidase are compared with those obtained using ferrous iron. Mann and Saunders (109), Saunders and Mann (110), and Chapman and Saunders (111) investigated the oxidation of aniline, p-toluidine, and mesidine by these two systems and found very different reaction products in the two cases. 

There are some further aspects of the ionic iron-hydrogen peroxide system which have a possible bearing on hemoprotein reactions. Apart from the reactions of the HO radical listed above (1 and 2) and reactions with oxidizable or polymerizable substrates, there is some experimental evidence that two additional types of reaction may occur. The first... 

It is possible to extend the free radical mechanism so that the derived rate equation has the required first order dependence by assuming that there is an auxiliary electron accepting group in hemoglobin and myoglobin that can act as cupric ions do in the ionic iron-hydrogen peroxide system catalyzing the reaction between Fe3+ and 02. ... 

It is the reaction of the ferric forms of these hemoproteins with hydrogen peroxide that provides the sharpest contrast to ionic iron. Complexes are formed in both systems. Although ferric ion only gives an ion pair complex Fe02H2+, whereas peroxidase can give three com-... 

Electrocatalytic ORR carries out in three pathways the 1-electron transfer pathway, producing superoxide ion the 2-electron transfer pathway, producing hydrogen peroxide and the 4-electron transfer pathway, producing water. In a non-aqueous aprotic solvent system, a room-temperature ionic liquid system, and on specific transition-metal, macrocyclic-compounds-coated graphite electrodes in alkaline solutions, 1-electron reduction can be observed. Carbon materials, quinone and derivatives, mono-nuclear cobalt macrocyclic compounds, and some chalcogenides can only catalyze 2-electron ORR. Noble metal, noble metal alloy materials, iron-macrocyclic complexes, di-nuclear cobalt macrocyclic complexes, some chalcogenides, and transition-metal carbide-promoted Pt catalysts can catalyze 4-electron reduction. 

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