Dioxygen singlet

According to the quantum-chemical law of conservation of orbital symmetry in products and reactants of the elementary reaction, all products of tetroxide decomposition should have the singlet orbits including dioxygen [4], The singlet dioxygen is formed as a result of R02 disproportionation, however, in a yield sufficiently less than unity [15]. 

The CL that accompanied the disproportionation of secondary and primary peroxyl radicals (see later 2.5.4). The R1 R2C 000 biradical formed in the cage is a predecessor of exited carbonyl compound and singlet dioxygen. 

SINGLE-STEP REACTION Single-stranded RNA and DNA substrates, NUCLEASE SI Singlet dioxygen,... 

Fig. I. Tig orbital occupancy and energies (6) of triplet and singlet dioxygen.

The riboflavin triplet reacts with dGMP acid by ET (k = 6.6 x 109 dm3 mol-1 s 1), and evidence for the formation of the (deprotonated) Gua radical cation has been obtained by laser flash photolysis (Lu et al. 2000). The photosensitized reactions of dGuo by TRP is thought to follow two pathways, the formation of Z has been attributed to an ET reaction (Type I), and the reaction of singlet dioxygen [ChCAg) Type II] leads to 4-OH-8-oxo-G and 8-oxo-G (Ravanat et al. 1998). The effect of D20 and azide on the 4-OH-8-oxo-G yields shows that this... 

Given that the myeloperoxidase enzyme see Peroxidases) within the neutrophils produces hypochlorous acid, an intriguing possibility is that it may combine with another hydrogen peroxide molecule. Such a reaction in the laboratory produces a stoichiometric quantity of singlet dioxygen ( O2), which is selectively reactive with conjugated polyenes. 

The [ROOOOR] intermediate decomposes to dialkyl peroxide and singlet dioxygen, but also reacts more vigorously than O2 with O2 substrates (1,4-CHD, 1,3-diphenylisobenzofuran, rubrene). 

The most direct means to activate 2 is by reduction with electrons or hydrogen atoms to give 2 % H -, H H, and H . Ground-state dioxygen ( 2) also can be activated by photochemical energy transfer to yield singlet dioxygen ( 2) (equation 107). ... 

Ground-state dioxygen ( 2) can be activated by photolytic energy transfer to the singlet state ( 2) (eqnation 129) and this may be dnplicated at the snrface of biomembranes by solar radiation. In the laboratory, singlet dioxygen is conveniently prodnced by the stoichiometric oxidation of hydrogen peroxide by hypochlorous acid (eqnation 130). 

Singlet dioxygen in biological systems is highly selective 2 is umeactive with most organic functional groups (e.g. saturated a bonds, simple alkenes, and carbonyl groups). In part, this is due to its limited lifetime (2 ts in H2 , 58 ps in H2 , 16 ps in DMF, 65 ps in MeCN, and 610 ps in d -MeCN), to its paired valence-electton shell, and to its... 

A likely example of HOOH-nucleophilicity is the formation of singlet dioxygen (IO2) via the combination of hypochlorous acid [HOCl, pKa(.li2O) 7.1] and HOOH. 

Ground-state dioxygen ( 02) also can be activated by photochemical energy transfer to yield singlet dioxygen 102-7... 

---