Reactive species hydroperoxyl radical

In formulas such as that of superoxide, the dot represents an unpaired electron. Species that have unpaired electrons are very reactive free radicals. Addition of H+ ion to superoxide produces reactive hydroperoxyl radical, H02. ... 

Nitric oxide has recently been shown to react very rapidly with organic hydroperoxyl radicals (Padmaja and Huie, 1993). This rapid radical-radical addition could account for the ability of nitric oxide to inhibit lipid peroxidation (Rubbo et al., 1995). Given the relatively high lipid solubility of nitric oxide, it could readily partition into membranes, where it would be sequestered from reactive species such as superoxide and remain for longer periods to act as a chain terminator of radical-mediated lipid peroxidation. Virtually any radical species formed in or near the lipid bilayer could react with nitric oxide (e.g., tocopheryl or ascorbyl radicals) to give nitrosated intermediates or products which could in turn act as nitric oxide reservoirs. 

Dehydroascorbic acid exists in a variety of forms with the hemiketal being favored in aqueous solution. The delocalized nature of the unpaired electron in the ascorbyl radical makes it relatively unreactive, and thus it may disproportionate as shown in Fig. 4. Under aerobic conditions a variety of reactive species derived from oxygen may potentially be involved with ascorbic acid. However, the reactions of the hydroperoxyl radical (HO2) and the superoxide anion radical (02 0 with ascorbic acid have been studied using pulse radiolysis and photolysis and are probably the two most likely to be found under normal physiological conditions (Fridovich, 1976). 

Most of our previous studies have been devoted to reactive oxygen species (ROS) at the air-water interface because such species are ubiquitous and play a crucial role in atmospheric chemistry, in environmental processes, water treatment technologies and biochemical reactions. The complex chemistries associated to these species, and their interconnection across different reaction media, have recently been reviewed [53]. The stability of ozone, molecular oxygen, hydrogen peroxide, hydroxyl and hydroperoxyl radicals, and other related compounds at the air-water interface had been established through classical molecular dynamics simulations [54—56]. Those studies, in particular, suggested that many of the compounds could accumulate at the surface of cloud water droplets, influencing in this way the overall chemistry of the troposphere. Recenfly, combined QM/MM MD simulations have confirmed the marked aflSnity of ROS species such as HO2 [27] and ozone [30] for the air-water interface. 

The high energy electrons are emitted by the chromophore and then are free to imdergo reactions with molecules such as O2, thereby generating highly reactive and imstable species, such as the free radicals O2 (superoxide), H02 (hydroperoxyl), OH... 

Also, reactive oxygen species such as hydroxyl radicals ( OH), organoperoxyl radicals (R02 ), hydroperoxyl-superoxide radicals, and singlet molecular oxygen ( 02) can oxidize halocarbons. Dehalogenation often is not a major pathway in indirect photooxidations, however. 

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