Singlet molecular oxygen generated by biological hydroperoxides

• Singlet molecular oxygen is generated from lipid hydroperoxides.
• Light emission at 1270 nm is observed from lipid hydroperoxides.
• 18-Oxygen labeled lipid hydroperoxides generates labeled singlet molecular oxygen.
• Phospholipid hydroperoxides in model membranes generates singlet molecular oxygen.

The chemistry behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chemical generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the production of excited carbonyl species and singlet molecular oxygen in the mechanism of generation of chemiluminescence in biological system. In particular, attention has been focused on the potential generation of singlet molecular oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet molecular oxygen from reactions involving the decomposition of biologically relevant hydroperoxides, especially from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chemical aspects related to the mechanism of singlet molecular oxygen generation from different biological hydroperoxides.