Dioxygen reactions

T. VanngaRD (ed.), Biophysical Chemistry of Dioxygen Reactions in Respiration and Photosynthesis, Cambridge Univ. Press, New York, 1988, 131 pp. 

For the values of the rate constants of dioxygen reaction with monomers, see Table 4.4. 

The first term on the right-hand side denotes the rate of dioxygen reaction with styrene (see Chapter 4) and the second term is the rate of catalytic free radical generation via the reaction of styrene with dioxygen catalyzed by cobaltous stearate or cobaltous acetylacetonate. The rate constants were found to be ki = 7.45 x 10-6 L mol-1 s-1, k2 = 6.30 x 10 2 L2 mol 2 s 1 (cobaltous acetylacetonate), and k2 = 0.31L2 mol-2 s 2 (cobaltous stearate) (T = 388 K, solvent = PhCl [169]). The mechanism with intermediate complex formation was proposed. 

The formation of hydroxyl or hydroxyl-like radicals in the reaction of ferrous ions with hydrogen peroxide (the Fenton reaction) is usually considered as a main mechanism of free radical damage. However, Qian and Buettner [172] have recently proposed that at high [02]/ [H202] ratios the formation of reactive oxygen species such as perferryl ion at the oxidation of ferrous ions by dioxygen (Reaction 46) may compete with the Fenton reaction (2) ... 

In accord with this mechanism, free peroxyl radical of the reaction product hydroperoxide activates the inactive ferrous form of enzyme (Reaction (1)). Then, active ferric enzyme oxidizes substrate to form a bound substrate radical, which reacts with dioxygen (Reaction (4)). The bound peroxyl radical may again oxidize ferrous enzyme, completing redox cycling, or dissociate and abstract a hydrogen atom from substrate (Reaction (6)). 

These authors supposed that the repairing function of antioxidants may be even more important compared to scavenging reactive free radicals. However, although Reactions (3) and (4) may occur in biological systems, it is very difficult to estimate their importance. First of all, there is always a competition between the repairing Reaction (4) and the reaction of the biomolecule free radical R with dioxygen (Reaction (5)) ... 

According to a recent study with iron(III) complexes of tripodal ligands, systematic variation of one ligand arm strongly affects the steric shielding of the iron(III) center and the bonding of catechol substrates (61). It was shown that the dioxygenation reactions of catechols... 

Nitric Oxide Dioxygenation Reactions and Their Mechanistic Insights... 

Factors That Control the Reactivity of Cobalt(III)-Nitrosyl Complexes in Nitric Oxide Transfer and Dioxygenation Reactions... 

Mechanistic Insight into the Nitric Oxide Dioxygenation Reaction of Nonheme Fe(III)-Superoxo and Mn(IV)-Peroxo Complexes... 

In this paper, author reported the reactivity of newly synthesized Fem-superoxo and MnIV-peroxo complexes with nitric Oxide (NO) to follow nitric oxide dioxygenation reactions. Reactions of nonheme Fem—superoxo and Mnlv—pcroxo complexes bearing a common tetraamido macrocyclic igand (TAML), namely [(TAML)Fem(02)]2" and [(TAML)MnIV(02)]2% with NO afford the Fem-N03 complex [(TAML)Fem(N03)]2- and the Mnv-oxo complex [(TAML)Mnv(0)]" plus N02, respectively. 

There are photocalorimetric enthalpy data for two other ozonides, both coming from sensitized photochemical dioxygenation reactions in non-polar solvents . This study reports the enthalpies of the reactions of 2,5-dimethylfuran and 1,3-diphenylisobenzofuran to their corresponding endoperoxides to be exothermic by —45 20 and —92 25 kJmoU (the latter value is an average of the values given for different solvents). From... 

Lehmann, W.D. 1994. Regio- and stereochemistry of the dioxygenation reaction catalyzed by (S)-type lipoxygenases or by the cyclooxygenase activity of prostaglandin H synthases. Free Radical Biol. Med. 16 241-253. 

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