Peroxidation triplet molecular oxygen

A. Peroxidation with Triplet Molecular Oxygen and Peroxy-radical... 

In some cases, the structures of oxygenation products have been crucial for assigning the structures of unusual radical cations. Eor example, the endo-peroxides (83 and 85) support the structures assigned to radical cations (24 and 84 ) derived from l,l-diaryl-2-methylenecyclopropane (23) and 2,5-diaryl-l,5-hexadiene, respectively.Time-resolved spectroscopic data suggest that 83 is generated by coupling of triplet biradical (24 ) with (triplet) molecular oxygen. 

Lipid hydroperoxides are also generated in singlet molecular oxygen mediated oxidations and by the action of enzymes such as lipoxygenases and cyclooxygenases. Chemiluminescence (CL) arising from lipid peroxidation has been used as a sensitive detector of oxidative stress both in vitro and in vivo . Several authors have attributed ultra-weak CL associated with lipid peroxidation to the radiative deactivation of O2 and to triplet-excited carbonyls (63, 72) (equations 35 and 36) " . It has been proposed that the latter emitters arise from the thermolysis of dioxetane intermediates (61, 62) (equation 35), endoperoxide (73) (equation 37) and annihilation of aUtoxyl, as well as peroxyl radicals ... 

The T)/pe I reaction often results in the formation of superoxide anion via electron transfer from the excited triplet PS to molecular oxygen. Though superoxide is not particularly damaging to the cell, it can react with itself, producing hydrogen peroxide and oxygen in the enzymatic reaction catalyzed by superoxide dismutase, or it can produce highly reactive hydroxyl radical (HO ). 

Photolysis of FL at a silica gel/air interface leads to the generation of 9-fluorenone (FLO) as the only isolable product. No dark reactions were observed and singlet molecular oxygen is not involved in the reaction. Transient spectroscopy shows that both the triplet state and the radical cation of FL are formed, thus indicating that an electron transfer mechanism is involved. Loss of a proton from the radical cation and subsequent reaction with molecular oxygen yields FL peroxide radicals, leading to the formation of 9-hydroxyfluorene. The latter readily photolyzes on the silica surface to produce FLO. 

Figure 8. Schematic of the state correlation diagram for the (diene + O2) peroxide diradical inter conversions. States of the diene-02 complex are on the left [state of molecular oxygen is specifically noted for each state. States of the peroxide are depicted in the middle. The nearly degenerate set of low lying singlet and triplet states of the diradical are shown on the right. The states are arranged in order of increasing energy, and the electronic configuration for each state is indicated...

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