LIPID PEROXIDATION-DEPENDENT CHEMILUMINESCENCE FROM THE CYCLIZATION OF ALKYLPEROXYL RADICALS TO BIOXETANE RADICAL INTERMEDIATES

This work reveals a novel mechanism for triplet carbonyl formation (an d hence chemiluminescence) during lipid peroxidation, whose chemilumin escence has been attributed to both triplet carbonyls and singlet oxyg en. As a model for polyunsaturated fatty acid hydroperoxides, we have synthesized 3-hydroperoxy-2,3-dimethyl-1-butene by photooxygenation of tetramethylethylene. One-electron oxidation of-this hydroperoxide wit h heme proteins and peroxynitrite to the corresponding alkylperoxyl ra dical results in chemiluminescence, both direct and 9,10-dibromoanthra cene-2-sulfonate-sensitized, the latter attributed to the formation of triplet acetone. It; is postulated that triplet acetone results from the cyclization of the alkylperoxyl radical to a dioxetane radical int ermediate followed by its thermolysis. This is supported by EPR spin-t rapping experiments in which discrimination between carbon-centered ra dicals derived from the alkyloxyl and alkylperoxyl radicals is achieve d through the use of one-electron oxidants and reductants, e.g., Fe-II and Ti-III.