Singlet oxygen media

Af.fV-Dimethylhydrazones are photolyzed in the presence of oxygen, under conditions that are assumed to generate singlet oxygen (medium-pressure mercury lamp with Methylene Blue as a sensitizer) in 48-88% yields (see Scheme 23). 

Burke M, Edge R, Land EJ, McGarvey DJ, and Truscott TG. 2001. One-electron reduction potentials of dietary carotenoid radical cations in aqueous micellar environments. FEBS Letters 500(3) 132-136. Bystritskaya EV and Karpukhin ON. 1975. Effect of the aggregate state of a medium on the quenching of singlet oxygen. Doklady Akademii Nauk SSSR 221 1100-1103. 

The elementary reaction step, which involves the formation of singlet oxygen, is a reaction of superoxide anion radicals CO ), which are the reaction intermediates of the above oxidation when performed in an alkaline medium. In the presence of water they may be converted to hydrogen peroxyl radicals HOO as follows ... 

So, fullerenes C60 and their derivatives may be potential damaging agents of biologic systems upon PDT, because upon irradiation C60 molecule is able to generate singlet oxygen, selectively penetrate tumor cells, and be accumulated there and could be easily removed from biologic medium. 

Substituent effects in the dye-sensitized (Rose Bengal or methylene blue) singlet oxygen photooxidation of a wide variety of furans have been investigated.287 Solvents effects on the value of p, which became less negative as polarity of the medium was increased was indicative of... 

Toluene, durene, hexamethylbenzene, 1- and 2-methylnaphthalenes are oxidized to the corresponding benzaldehydes by irradiation in oxygen-equilibrated acetonitrile sensitized by 1,4-dicyanonaphthalene, 9-cyano-, 9,10-dicyano-, and 3,7,9,10-tetracyanoanthracene. The reaction involves proton transfer from the radical cation of the donor to the sensitizer radical anion or the superoxide anion, to yield the benzyl radical which is trapped by oxygen. In the case of durene, some tetramethylphthalide is also formed with this hydrocarbon it is noteworthy that the same photosensitization, when carried out in an nonpolar medium, yields the well-known singlet oxygen adduct, not the aldehyde [227,228] (Sch. 20). 

While the correlation of in vitro photosensitization and singlet oxygen yield was good, exceptions were noted for compounds with low pKa values (near 5.0). Thus, at pH 7.4 (cell culture medium), these compounds exist primarily in the unprotonated imine form. It was shown that this form of the dyes is taken up poorly by the cells. However, it should be noted also that the neutral forms of these compounds absorb near 500 nm, with about half the extinction coefficient of the protonated forms absorbing near the mid-600nm range. 

The medium used to perform DSO plays a key role in the efficiency of the singlet oxygenation process. It involves both thermodynamic and kinetic aspects as it must take into account (i) the ability of the peroxo intermediates to form and to decompose readily into 02 [58] (ii) the lifetime of 02 in this medium (fii) the solubility of the organic substrate, which is most often hydrophobic while the catalyst and the oxidant, that is, H2O2, are hydrophilic (iv) the reactivity of the substrate toward and finally (v) the accessibility ofthe substrate by the excited... 

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