Oxygen singlet molecular

Hartman, P. E., Hartman, Z., and Ault, K. T. (1990). Scavenging of singlet molecular oxygen by imidazole compounds high and sustained... 

Suzuki, N., et al. (1991). Chemiluminescent detection of active oxygen species, singlet molecular oxygen and superoxide, using Cypridina luciferin analogs. Nippon Suisan Gakkaishi 57 1711-1715. 

Singlet molecular oxygen ( A is an electron acceptor powerful enough to react with olefins in the pseudoexcitation band. The [2h-2] cycloaddition and ene reactions and the stereoselectivities are reviewed in this subsection. 

After 28 years the perepoxide quasi-intermediate was supported by a two-step no intermediate mechanism [71, 72]. The minimum energy path on the potential energy surface of the reaction between singlet molecular oxygen ( A and dg-teramethylethylene reaches a vaUey-ridge inflection point and then bifurcates leading to the two final products [73]. 

The concept, quasi-intennediate [70], was introduced in 1975 to symbolize a boundary between concerted and stepwise mechanisms. Recent advances in computer chemistry are allowing us to investigate subtle problems more clearly in the years since 2000. Concerted/stepwise boundary mechanisms were proposed for other diverse reactions than those of singlet molecular oxygen ( A. ... 

Following the discovery of the ene reaction of singlet molecular oxygen ( Ap (Scheme 15) in 1953 by Schenck [88], this fascinating reaction continues to receive considerable mechanistic attention today. The importance of a path via the perepoxide intermediate or a perepoxide-Iike transition state [13] or the perepoxide quasi-intermediate [70] was proposed for the ene reactions of singlet oxygen with alkenes affording allylic hydroperoxides. 

On the other hand. Type II process competes efficiently with the electron-transfer pathway in aerobic environments where the concentration of ground triplet state molecular oxygen is relatively high ( 0.27 mM), and singlet molecular oxygen (1O2) is the most abimdant ROS generated under these conditions, with a quantum yield 0.48 (Valle et al., 2011), eqn. 8. It is also possible an electron-transfer reaction from 3RF to 02 to form anion superoxide, but this reaction occurs with very low efficiency <0.1% (Lu et al., 2000). 

Criado, S. Escalada, J. P. Pajares, A. Garcia, N. A. (2008). Singlet molecular oxygen [02(lAg)]-mediated photodegradation of tyrosine derivatives in the presence of cationic and neutral micellar systems. Amino Acids, Vol. 35, No. 1, (June 2008), 201-208, ISSN 0939-4451... 

The protective effects of carotenoids against chronic diseases appear to be correlated to their antioxidant capacities. Indeed, oxidative stress and reactive oxygen species (ROS) formation are at the basis of oxidative processes occurring in cardiovascular incidents, cancers, and ocular diseases. Carotenoids are then able to scavenge free radicals such as singlet molecular oxygen ( O2) and peroxyl radicals particularly, and protect cellular systems from oxidation. 

DiMascio, P. et al., Carotenoids, tocopherols and thiols as biological singlet molecular oxygen quenchers, Biochem. Soc. Trans., 18, 1054, 1990. 

Devasagayam, T.P.A., Werner, T., Ippendorf, H., Martin H.-D., and Sies, H. 1992. Synthetic carotenoids, novel polyene polyketones and new capsorubin isomers as efficient quenchers of singlet molecular oxygen. 

Wilkinson, F. and Ho, W.-T. 1978. Electronic energy transfer from singlet molecular oxygen to carotenoids. Spectrosc. Lett. 11 455-463. 

Cadenas, F. and Sies, H. (1984). Low-level chemiluminescence as an indicator of singlet molecular oxygen in biological systems. Methods in Enzymology 105 221 231. 

A. P. Schaap Singlet Molecular Oxygen, Dowden, Hutchinson and Ross, 1976... 

J. Photochemistry 1984, 25, 99-553 (Proc. of COSMO 84 Conf. on Singlet Molecular Oxygen, Clearwater Beach, FL, 1984)... 

The basic structure of carotenoids is a conjugated polyprenoid chain. Carotenoids exert a positive impact on human welfare. They show marked singlet molecular oxygen quenching capacity [11] and they protect against photosensitized peroxidation of lipids [12],... 

M. Montenegro, M. Nazareno, E. Durantini and C. Borsarelli, Singlet molecular oxygen quenching ability of carotenoids in a reverse-micelle membrane mimetic system. Photochem. Photobiol. 75 (2002) 353-361. 

A. P. Schapp (ed.), Singlet Molecular Oxygen, Benchmark Papers in Organic Chemistry, Vol. 5, Dowden, Hutchinson, and Ross, New York (1976). 

J. G. Parker and W. D. Stanbro, Optical determination of the collisional lifetime of singlet molecular oxygen in acetone and deuterated acetone, J. Am. Chem. Soc. 104, 2067-2069 (1982). 

OXYGEN, OXIDES 0X0 ANIONS SINGLET MOLECULAR OXYGEN... 

Singlet Molecular Oxygen, Bimolecular Reactivity of (Gorman). 17 217... 

Singlet Molecular Oxygen, Physical Quenchers of (Bellus). 11 105... 

SCHEME 1. [4 + 2], [2 + 2] and ene addition reactions of singlet molecular oxygen to alkenes... 

Type 1 intrazeolite photooxygenation of alkenes has been also reported to give mainly allylic hydroperoxides (Scheme 42). In this process, the charge transfer band of the alkene—O2 complex within Na-Y was irradiated to form the alkene radical cation and superoxide ion. The radical ion pair in turn gives the allylic hydroperoxides via an allylic radical intermediate. On the other hand, for the Type II pathway, singlet molecular oxygen ( O2) is produced by energy transfer from the triplet excited state of a photosensitizer to 02. 

Lipid hydroperoxides are also generated in singlet molecular oxygen mediated oxidations and by the action of enzymes such as lipoxygenases and cyclooxygenases. Chemiluminescence (CL) arising from lipid peroxidation has been used as a sensitive detector of oxidative stress both in vitro and in vivo . Several authors have attributed ultra-weak CL associated with lipid peroxidation to the radiative deactivation of O2 and to triplet-excited carbonyls (63, 72) (equations 35 and 36) " . It has been proposed that the latter emitters arise from the thermolysis of dioxetane intermediates (61, 62) (equation 35), endoperoxide (73) (equation 37) and annihilation of aUtoxyl, as well as peroxyl radicals ... 

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