ROO Scavenging activity

The regeneration of NO via reactivity of NOR with ROO was explained by either a -hydrogen abstraction (Scheme 17, pathway e, for 128, R = H) or by a somewhat slower radical substitution (Scheme 17, pathway /, for 128, R = alkyl) [189]. The process explains the ROO" scavenging activity of HAS, which cannot be ascribed directly to NH or the derived NO. ... 

NADPH might be considered as an indirect antioxidant due to its function as the reductant of various oxidized substrates, for example in the re-reduction of GSSG into GSH. However, it has recently been shown [1] that NADPH possesses the free radical scavenging activity reacting with such free radicals as CO/, N02 ROO and R0 . It should be noted that the efficiency of NADPH may increase under in vivo conditions due to its regeneration by numerous enzymes. 

The high efficiency of aromatic amines in rubbers, and R /ROO scavenging capacities due to some amine transformation products, encouraged an extended use of amines in stabilization of PO [47,88] and, moreover, in stabilization of vinylic monomers [89]. For example, combinations of PD with the respective BQDI, i.e. the ROO /R scavenging system, are effective stabilizers against premature polymerization [90]. A similar activity is performed by 11 in vinylic... 

Consequently, the antioxidant activity of GA in biological systems is still an unresolved issue, and therefore it requires a more direct knowledge of the antioxidant capacity of GA that can be obtained by in vitro experiments against different types of oxidant species. The total antioxidant activity of a compound or substance is associated with several processes that include the scavenging of free radical species (eg. HO, ROO ), ability to quench reactive excited states (triplet excited states and/ or oxygen singlet molecular 1O2), and/or sequester of metal ions (Fe2+, Cu2+) to avoid the formation of HO by Fenton type reactions. In the following sections, we will discuss the in vitro antioxidant capacity of GA for some of these processes. 

Reactivity with ROO was also used for explanation of the nitroxide regeneration from 65 and, consequently, of the high stoichiometric factor of DPA in autoxida-tion of hydrocarbons [66]. Thermolysis of NOR 65 at temperatures exceeding 100 °C was proposed as another process regenerating the antioxidant activity [65]. Hydroxylamines 66, strong CB AO, are formed. NOH 66 are reoxidized to 56 either by scavenging ROO (Scheme 7) or by oxidation with ROOH via CTC pN +OH, HO, RO ]. 

Cellular systems have evolved a powerful and complex antioxidant defence system to limit inappropriate exposure to these stressors. a-Tocopherol is quantitatively the most important chain-breaking antioxidant in plasma and biological membranes. The antioxidant activities of chain-breaking antioxidants are determined primarily by how rapidly they scavenge peroxyl radicals, thereby preventing the propagation of free radical reactions. When the chromanol phenolic group of a-tocopherol (TOH) encounters a ROO it forms hydroperoxide (ROOH), and in the process a tocopheroxyl radical (TO ) is formed ... 

---