Redox metalloproteins and oxygen

Oxygen can be bound to metal ions with several geometries side-on (to form a triangle), end-on linear and end-on bent. The electronic possibiUties include a simple electron-pair donation from oxygen, 1-electron acceptance by oxygen so that there is effectively a coordinated superoxide ion and the charge on the metal is increased one unit (M O2 M 02 ) and 2-electron acceptance to give effectively coordinated peroxide with the oxidation state of the metal increased by two (M Oj M - 0 ) 

One of the effects of ligation to metal ions on the properties of superoxide ion is to stabilise it with respect to reduction to oxygen (the reduction potential of O2 is made more positive). 

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