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Reports on the synthesis of the [[sup 18]O]-labeled endoperoxide of N,N'-di(2,3-dihydroxypropyl)-1,4-naphthalenedipropanamide. Ability of the endoperoxide to release labeled singlet oxygen; Mass spectrometry of the reaction products; Solubility in aqueous media; Mechanistic features of the reaction.

Singlet oxygen in its first excited state, denoted as O2, can be produced by type II photosensitization reaction and chemically in the reaction of hydrogen peroxide with hypochlorite or peroxynitrite, in the self-reaction of peroxyl radicals by the Russell mechanism, and through decomposition of dioxetanes and endoperoxides. It is also generated enzymatically by peroxidases and oxidases. The article focuses on the energy transfer between singlet and triplet molecular aqueous solution.

The decomposition of lipid hydroperoxides into peroxyl radicals is a potential source of singlet oxygen ((1)O(2)) in biological systems. We report herein on evidence of the generation of (1)O(2) from lipid hydroperoxides involving a cyclic mechanism from a linear tetraoxide intermediate proposed by Russell. Using (18)O-labeled linoleic acid hydroperoxide (LA(18)O(18)OH) in the presence of Ce(4+) or Fe(2+), we observed the formation of (18)O-labeled (1)O(2) ((18)[(1)O(2)]) by chemical trapping of (1)O(2) with 9,10-diphenylanthracene (DPA) and detected the corresponding (18)O-labeled DPA endoperoxide (DPA(18)O(18)O) by high-performance liquid chromatography coupled to tandem mass spectrometry. Spectroscopic evidence for the generation of (1)O(2) was obtained by measuring (i) the dimol light emission in the red spectral region (lambda > 570 nm); (ii) the monomol light emission in the near-infrared (IR) region (lambda = 1270 nm); and (iii) the quenching effect of sodium azide. Moreover, the presence of (1)O(2) was unequivocally demonstrated by the direct spectral characterization of the near-IR light emission. For the sake of comparison, (1)O(2) deriving from the H(2)O(2)/OCl(-) and H(2)O(2)/MoO(4)(2)(-) systems or from the thermolysis of the endoperoxide of 1,4-dimethylnaphthalene was also monitored. These chemical trapping and photoemission properties clearly demonstrate that the decomposition of LA(18)O(18)OH generates (18)[(1)O(2)], consistent with the Russell mechanism and pointing to the involvement of (1)O(2) in lipid hydroperoxide mediated cytotoxicity.