Toxicity of hydroperoxides and their radical by-products

The first metastable molecules which accumulate as a consequence of oxidative stress are hydroperoxides. Hydroperoxide-producing enzymes will also result in oxidative stress if they are stimulated over a prolonged period of time. 

As for iron, there is ample evidence that OH is generated in the Fenton reaction when the latter is carried out at acidic pH, but direct OH generation is often questionable at neutral or basic pH [4,24]. As above mentioned, other hydroxylation mechanisms have been proposed, based on the formation of hyper-valent iron species [100] such as perferryl (Fe=03+) or ferryl (Fe=02+), whose oxidizing powers are smaller than that of OH, for example  

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