Manganese complexes with peroxides

Apart from the catalytic properties of the Mn-porphyrin and Mn-phthalo-cyanine complexes, there is a rich catalytic chemistry of Mn with other ligands. This chemistry is largely bioinspired, and it involves mononuclear as well as bi- or oligonuclear complexes. For instance, in Photosystem II, a nonheme coordinated multinuclear Mn redox center oxidizes water the active center of catalase is a dinuclear manganese complex (75, 76). Models for these biological redox centers include ligands such as 2,2 -bipyridine (BPY), triaza- and tetraazacycloalkanes, and Schiff bases. Many Mn complexes are capable of heterolytically activating peroxides, with oxidations such as Mn(II) -> Mn(IV) or Mn(III) -> Mn(V). This chemistry opens some perspectives for alkene epoxidation. 

Human serum transferrin and chicken ovotransferrin have been reported to bind cobalt, iron, copper, zinc, and manganese. The iron complex is red with an absorption maximum at 465 mp.. Complexes of copper and manganese are yellow. Ulmer and Vallee (128) formed a complex with Mn3+ by standing for 12 hours while Inman (68) formed a complex by addition of hydrogen peroxide to a mixture of Mn2+ and the transferrins. Absorption spectra for three of the colored complexes of human serum transferrin are given in Fig. 5. Extinction coefficients are listed in Table 9. 

Another class of Mn( III) complexes involves the polyaminocarboxylic acid ligands. The earliest study appeared in 1962 ( 44) and was followed shortly by studies of the cyclohexane analog of EDTA as well as other derivatives of EDTA (45). A recent paper discusses the reactivity of the manganese (III )-diaminocyclohexanetetraacetate complex with hydrogen peroxide (46). A mechanism is proposed which involves complexation by the peroxide anion followed by subsequent electron transfer to produce the Mn(II) complex and the H02 radical. The results are interesting and indicate the potential for selective catalysis by the higher oxidation state manganese complexes. 

The reactions of the several manganese gluconate complexes with molecular oxygen and hydrogen peroxide have been studied in terms of stoichiometry and reaction kinetics. Reaction mechanisms are proposed on the basis of the kinetic data. In addition, the thermodynamic and mechanistic characteristics of an ideal model system for photosystem-II are analyzed and evaluated. 

On the basis of these prior electrochemical (62, 63) and kinetic (64) studies and the present results, the reaction stoichiometries for the manganese gluconate complexes with molecular oxygen and hydrogen peroxide can be expressed by a series of reactions. The primary reaction between the Mn(II) complex and molecular oxygen is rapid (Reaction... 

Inman first showed that trivalent manganese formed a complex with transferrins by adding hydrogen peroxide to a mixture of Mn2+ and the apoenzyme (118). Displacement studies revealed that the order of binding for both the human serum enzyme and ovotransferrin was Fe3+ > Mn3+ > Cu2+. The Mn complex displayed a distinctive visible band maximum at 429 nm. Further studies of the Mn-containing protein by... 

Catalysis of the decomposition by several metal ions has been reported . The order in peroxomonosulphate was found to be one, except for reaction with cobalt(II) and cerium(IV) (both second-order in the sulphate) and manga-nese(II) (half-order). Formation of a complex with cerium(IV) and peroxomonosulphate has been both asserted and denied . Catalysis by copper(II) is not significant unless manganese is also added, at least in the presence of some hydrogen peroxide ... 

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