Chapter 32: [¹⁸O]-Labeled Singlet Molecular Oxygen: Chemical Generation and Trapping as a Tool for Mechanistic Studies

The present chapter focuses on how the use of [¹⁸O]-labeled endoperoxides and hydroperoxides can be applied to study mechanistic aspects related to singlet molecular oxygen (¹O₂) generation and reactions in biological system. Identification of ¹O₂, which was achieved using different approaches: [¹⁸O]-labeled molecular oxygen, a clean naphthalene derivative [¹⁸O]-labeled thermolabile endoperoxide as a source of [¹⁸O]-labeled ¹O₂, chemical trapping of [¹⁸O]-¹O₂ with anthracene derivatives and liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The peroxidation reactions of the main cellular targets including nucleic acids, proteins and unsaturated lipids have received major attention during the last two decades. We highlighted some key mechanistic aspects related to [¹⁸O]-peroxides decomposition to alkoxyl or peroxyl radicals. As a biochemical application this chapter focused on the recombination reactions involving lipid-derived [¹⁸O]-labeled peroxyl radicals that can be formed on different lipid species giving rise to [¹⁸O]-labeled ¹O₂ through the mechanism proposed by Russell. A relevant major topic deals with the search for the molecular signature of the ¹O₂ formation in targeted biomolecules within cells. It may be anticipated that labeled peroxides and [¹⁸O]-labeled ¹O₂ in association with a sensitive mass spectrometric method such as LC-ESI-MS/MS should constitute powerful tools for this purpose.