Singlet oxygen mechanism

Type II involves electron transfer from the excited triplet state of the sensitiser to triplet oxygen producing the highly oxidative singlet oxygen. This mechanism has already been discussed (see Figure 4.14). 

Several research groups have focused their attention on the photooxidation of 2 -deoxyguanosine that is used as a model compound for DNA. The major photooxidation products of this nucleoside were identified and classified according to their formation through a radical mechanism (type I) or a singlet oxygen-mediated mechanism (type II). The major type I product was identified as 2,2-diamino-[(2-deoxy-p-D-e/7f/zro-pentofuranosyl)-4-amino]-5(27/)-oxazolone 98 (Fig. 7.16). ... 

Bowen145 has pointed out that the decrease in rate is due to a change in kBjkg. He concluded that neither the energy-transfer (singlet oxygen formation) mechanism nor the complex-formation mechanism... 

This product suggests a singlet oxygen mediated mechanism for quinone formation (Lee-Ruff et al., 1986). 

PAHs photooxidized by the type II singlet oxygen mediated mechanism include acenaphthylene, whose oxidized products and yields are shown in Fig. 10.29B (Barbas et al., 1994), phenanthrene (Barbas et al., 1996), anthracene (Dabestini et al., 1995), and tetracene (Dabestini et al., 1996). An additional photochemical process, the formation of photodimers, is also observed for acenaphthylene, anthracene, and tetracene. 

This hypothesis assumes the intermediate formation of singlet oxygen ( 0,), mechanism first proposed by Kautsky.u The energy levels of singlet oxygens areO,(1S,)=37.8 kcal mol-1, Oa(,A,)=22.5 kcal mol-1. 0, state is likely to be formed in an energy transfer step. 

Manring, L.E. and Foote, C.S. (1983) Chemistry of singlet oxygen. 44. Mechanism of photooxidation of 2,5-dimethyl-2,4-diene and 2-methyl-2-pentene. Journal of the American Chemical Society, 105, 4710-4717. 

Another form of reactive oxygen that can be formed on Ti02 irradiation is singlet oxygen. The mechanisms of 02 formation that are usually discussed are ... 

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 ... 

Singlet Oxygen Quenching Mechanisms of Dithiolene Nickel Complexes in Solution... 

Finally, one unusual case of 3-Q2 quenching should be mentioned. In some studies It was shown that molecular oxygen can enhance the fluorescence of aromatic hydrocarbons In polymer matrices (63, 306-307). Bolton et al. (63) proposed a singlet oxygen feedback mechanism to account for this phenomenon In systems under conditions of steady-state excitation. In this mechanism the enhanced fluorescence Is attributed to a singlet oxygen-triplet organic molecule annihilation fluorescence ... 

Li B, Ahmed F, Bernstein PS (2010) Studies rat the singlet oxygen scavenging mechanism of human macular pigment. Arch Biochem Biophys 504 56-60. doi 10.1016/j.abb.2010.07.024... 

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