Singlet oxygen, formation

Figure 1. Illustration of the copper-oxygen singlet formation on the square lattice. The additional doped hole cannot go to the copper site due to strong on-site Coulomb repulsion and is distributed among four oxygen sites forming together with the copper spin a Zhang-Rice singlet.

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. 

Sera N, Tokiwa H, Miyata N (1996) Mutagenicity of the fullerene C60-generated singlet oxygen dependent formation of lipid peroxides. Carcinogenesis 17 2163-2169. 

Corey and coworkers have shown that trimethylsilyl hydrotrioxide, produced by the low-temperature (—78°C) ozonization of triethylsilane, decomposes at higher temperatures to give singlet oxygen. The formation of singlet oxygen was confirmed by the change in the IR emission at 1278 nm with time ( O2 2). ... 

The index pd corresponds to a Zhang-Rice singlet formation with one hole placed on the copper site whereas the second hole is distributed on the neighboring oxygen sites [12], Namely, T/ " " = -2= is the copper-oxygen creation operator in terms of copper (X) and oxygen... 

In contrast to triplet oxygen, singlet oxygen is very electrophilic and readily reacts with unsaturated lipids with the formation of hydroperoxides,... 

Actually, the substrates being reactive vs singlet oxygen, whose formation in the DCA-sensitized photooxidations has been already observed by Foote [119] and Santamaria [113], the author suggests a singlet oxygenation process on 64a- d... 

The peroxide radical can go to a product by abstraction and generate for example an acid and another radical. Commonly, acetic acid and also formic acid are formed in considerable amount during oxidative pyrolysis. The previous mechanism can probably explain the formation of these small molecules. The oxygen (singlet oxygen) may also react with the double bond forming a dioxetane intermediate ... 

Another important reaction expected for polymers is the direct addition or the abstraction of hydrogen atoms by singlet oxygen with formation of hydroperoxides or hydroperoxide radioals,respeotivelyt... 

New mechanistic and synthetic aspects of singlet oxygen chemistry, formation, and transformations of 1,2-dioxethanes 00T9151. 

A photosensitized process of Type II is by definition an energy transfer process [5]. The most common Type II process is oxidation via singlet oxygen ( O2) formation ... 

Oxygen, singlet. 13, 228-229 14, 247 15, 243 16, 257-258 17, 251-253 18, 269-270 Tetrakis(2,6-dichlorophenyl)porphyrin is a superior sensitizer for singlet oxygen generation. Photooxidation can be carried out in perfluorocarbons with excellent results. Oxidation of ethers. With benzil as sensitizer, the photooxidation of ethers results in the formation of esters.- This reaction may be compared with the process mediated by Cu(II). ... 

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