- In biological systems, oxygen is an electron acceptor.
- Molecular oxygen accepts one electron and becomes a radical anion called
superoxide (
O 2 −).
- Superoxide is involved in both positive and negative physiological roles:
i) The immune system uses superoxide in its defense against pathogens.
ii) Superoxide is suspected of being involved in degenerative disease processes
associated with aging and oxidative damage to healthy cells.
- The enzyme superoxide dismutase regulates the level of superoxide by
catalyzing conversion of superoxide to hydrogen peroxide and molecular
oxygen.
i) Hydrogen peroxide is also harmful because it can produce hydroxyl (HO•)
radicals.
ii) The enzyme catalase helps to prevent release of hydroxyl radicals by
converting hydrogen peroxide to water and oxygen.
2 superoxidedismutase H 2
2 catalase 2
+ 2 +
+
H+
H 2 H 2
O 2 O 2
O 2
O 2 −
O 2 O
10.11B COMBUSTION OF ALKANES
- When alkanes react with oxygen a complex series of reactions takes place,
ultimately converting the alkane to CO 2 and H 2 O.
R
R
OO
OO
OO
R H R OOH
Initiating
Propagating
+ R + H
+
++
O 2
R O 2
R
R H
- The O–O bond of an alkyl hydroperoxide is quite weak, and it can break and
produce radicals that can initiate other chains:
RO–OH RO• + •OH
