Dioxygen manganese catalase

Manganese is an element that is essential for life. It is present at the active site of many en2ymes [4, 5]. Those en2ymes in which the metal center is involved in a redox process are manganese catalase [101], peroxidase [102], and SOD [103]. In addition, a cluster containing four Mn and one Ca atoms in the water-oxidizing center (WOC) of PSII is the site at which dioxygen is produced photosynthetically on Earth [3,104]. 

Manganese is used by nature to catalyze a number of important biological reactions that include the dismutation of superoxide radicals, the decomposition of hydrogen peroxide, and the oxidation of water to dioxygen. The dinuclear manganese centers that occur in Lactobacillus plantar-aum catalase and Thermus thermophilus catalase have attracted considerable attention and many model compounds have now been synthesized that attempt to mimic aspects of these biological systems.The catalases have at least four accessible oxidation states (Mn Mn , Mn°Mn , Mn" Mn", and Mn Mn ) it is believed that the Mn"Mn"/Mn"Mn" redox couple is effective in catalyzing the disproportionation of water. 

In part motivated by the desire to model biological redox processes, there have been many studies in which Robson-type macrocycles (205) (R = H) have been employed to form dinuclear manganese species.For example, a novel macrocyclic heterodinuclear catalase-like model complex of type (206) has been reported. " This complex can dismute hydrogen peroxide to dioxygen in basic aqueous solution. 

Catalases catalyze the conversion of hydrogen peroxide to dioxygen and water. Two families of catalases are known, one having a heme cofactor and the second a structurally distinct family, found in thermophilic and lactic acid bacteria. The manganese enzymes contain a binuclear active site and the functional form of the enzyme cycles between the (Mn )2 and the (Mn )2 oxidation states. When isolated, the enzyme is in a mixture of oxidation states including the Mn /Mn superoxidized state and this form of the enzyme has been extensively studied using XAS, UV-visible, EPR, and ESEEM spectroscopies. Multifrequency EPR and microwave polarization studies of the (Mn )2 catalytically active enzyme from L. plantarum have also been reported. ... 

The catalase-like function of the manganese complex was evaluated by measuring the volume of dioxygen collected in a gas burette, which evolved from the solution (total volume 4ml) containing the manganese complex (50mg) and hydrogen peroxide (1ml, 30%) in different solvents (water, dimethylformamide and methanol) at 0°C and 25 C. 

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