Reactivity towards singlet oxygen

Trans alkenes show similar regioselectivity on their photooxygenation reactions. However, their reactivity towards singlet oxygen is much less than that of the corresponding cis aUtenes. ... 

Guanine is a preferential DNA target to several oxidants it shows the lowest ionization potential among the different purine and pyrimidine nucleobases and it is the only nucleic acid component that exhibits significant reactivity toward singlet oxygen ( O2) at neutral pH. ... 

Shetlar MD, Horn K (1987) Mixed products of thymine and cysteine produced by direct and acetone-sensitized photoreactions. Photochem Photobiol 45 703-712 Sheu C, Foote CS (1995a) Reactivity toward singlet oxygen of a 7,8-dihydro-8-oxoguanosine ( 8-hydroxyguanosine ) formed by photooxidation of a guanosine derivative. J Am Chem Soc 117 6439-6442... 

The reactivity toward singlet oxygen [238,454] should be taken into consideration if triplet states are involved (either as intermediate or as sensitizer) on irradiation of air- or oxygen-saturated solutions. Benzaldehyde, hydroperoxides, and dioxetanes have been found as products from the reaction of stilbenes with reactive oxygen species [464,465]. A rearrangement reaction has been reported for nitrostilbenes formation of a-oximinoketones, typical for / -nitrostyrenes, which may be accompanied by cleavage products [466],... 

Values for Polymer and Model Compounds. 1,4-Polyisoprene and 1,4-polybutadiene are so sufficiently reactive toward singlet oxygen that we can conveniently obtain / -values by three methods (a) from oxygen-uptake rates by photosensitized oxidation at different polymer concentrations (b) by the initial disappearance rate of rubrene on photooxygenation of solutions with and without polymer (or model olefin) and (c) for 1,4-polyisoprene, by the amount of rubrene consumed upon addition of aliquots of triphenyl phosphite ozonide in the presence and absence of olefin or polymer. The treatment of data from methods (b) and (c) was modified to give /3-values directly from the following equations ... 

The two stereoisomers A and B have been found to differ greatly in reactivity toward singlet oxygen. A is oxidized to C, but B is unreactive under similar conditions. Explain. 

Michaeli, A. Feitelson, J. (1994). Reactivity of singlet oxygen toward amino acids and peptides. Photochemistry and Photobiology, Vol.59, No.3, (March 1994), pp. 284-289, ISSN 0031-8655. 

The change of p with solvents may be due to either a change of the lifetime of singlet oxygen (1 /kB) or a change of the reactivity of the substrate toward singlet oxygen (kg), or both. Systematic studies of solvent effects are, therefore, very much needed. 

Comparison of / values obtained for various substrates under similar conditions gives some information on the relative reactivities of these substrates toward singlet oxygen (to which weshallfurther refer only as oxygen ), since ka remains unchanged and the fi values, therefore, reflect only the change of kg as a function of the nature of the substrate. 

The reactivity of alkenes towards singlet oxygen strongly depends on the electron density of the n bond, with increasing alkyl substitution bringing about increasing reactivity380 [Eq. (9.84)381] ... 

Breck at al (68) havs recently examined the reactivities of a number of saturated and unsaturated polymers towards singlet oxygen generated by microwave generator. The saturated ohain polymers as polystyrene,polyurethane and polyethylene were found to be inert within the experimental conditions with singlet oxygen,while the unsaturated polymers as poly-dienes were found to react quite readily.In this paper concentration of hydroperoxide groups has been measured. 

Saito, L, M. Imuta, and T. Matsuura. 1972. Photoinduced reactions. LIX. Reactivity of singlet oxygen toward methoxybenzenes. Tetrahedron 28 5307-5311. 

Table 3.2. Reactivity of cholesterol and fatty acid methyl esters towards singlet oxygen ( O,) =...

Doleiden, F.H., Fahrenholtz, S.R., Lamola, A.A. and Trozzolo, A.M. Reactivity of cholesterol and some fatty acids toward singlet oxygen. Photochem. Photobiol. 20, 519-521 (1974). 

Shimizu, T., Y. Nakanishi, M. Nakahara, N. Wada, Y. Moro-oka, T. Hirano, T. Konishi, and S. Matsugo. 2010. Structure effect on antioxidant activity of catecholamines toward singlet oxygen and other reactive oxygen species in vitro. Journal of Clinical Biochemistry and Nutrition 47(3) 181-190. 

The ratio of epoxide to dioxetane increased 28-fold on going from methylene chloride to benzene with tetraphenylporphin as sensitizer, such solvents as pinacolone, dioxan, and acetone occupying intermediate positions. Systematic investigation showed that epoxide more often than not accompanies the dioxetane from sensitized oxygenation of norbornene (22) and of biadamantylidene (H. J. Shapiro, quoted in (23) (26)). For each solvent-sensitizer combination, the ratio of epoxide to dioxetane increased in the order biadamantylidene < norbornene binor-bornylidene. This is also the decreasing order of reactivity of these olefins toward singlet oxygen. 

Gorman, A.A., Lovering, G. and Rodgers, M.A.J., The entropy-controlled reactivity of singlet oxygen ( Ag) towards furans and indols in toluene. A variable-temperature study by pulse radiolysis, /. Am. Chem. Soc., 101, 3050, 1979. 

Although this mechanism could explain the inertness of di-t-butyl sulphide towards oxidation due to the absence of a-hydrogen atoms, it was later ruled out by Tezuka and coworkers They found that diphenyl sulphoxide was also formed when diphenyl sulphide was photolyzed in the presence of oxygen in methylene chloride or in benzene as a solvent. This implies that a-hydrogen is not necessary for the formation of the sulphoxide. It was proposed that a possible reactive intermediate arising from the excited complex 64 would be either a singlet oxygen, a pair of superoxide anion radical and the cation radical of sulphide 68 or zwitterionic and/or biradical species such as 69 or 70 (equation 35). 

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