Oxygen radical-nitric oxide reactions

Oxygen Radical-Nitric Oxide Reactions in Vascular Diseases... 

Reaction with other radicals is characteristic of the triarylmethyls and the chain reaction with oxygen has already been discussed. The absorption of the radical nitric oxide is also used as an analytical tnethod for triphenylmethyl. 

The theoretical treatment of reaction (1), when catalyzed by paramagnetic centres, was developed by Wigner, 3>, and the reaction was shown to occur, using oxygen or nitric oxide in the gas phase, or oxygen, paramagnetic ions or free radicals in solution 14 1S>. 

Fig. 3. Production of reactive species. (A) ROS can be produced from the weak radical oxygen in the mitochondria and endoplasmic reticulum, by various enzymatic reactions, and from oxyhemoglobin. Normally, nontoxic hydrogen peroxide can give rise to the powerful hydroxyl radical in the presence of transition metals (R5). Oxygen can also be induced to react with biomolecules by transition metals and enzymes. RNS can be produced by reaction of superoxide anion radical with the weak radical nitric oxide. These can react to form the powerful oxidant peroxynitrite/peroxynitrous acid, which can cause formation of other radicals, some with longer lives. See the text for details. SOD, superoxide dismutase. (B) Myeloperoxidase in leukocytes can produce the reactive species hypochlorous acid and tyrosyl radical. Unpaired electrons are indicated by the dense dots and paired electrons by the light ones.

Hunter R, Hutchings GJ, Pickl W. Methanol conversion to hydrocarbons over the zeolite catalyst H-ZSM-5 in the presence of oxygen and nitric-oxide—further evidence against a radical reaction-mechanism. J Chem Soc Chem Commun 1987 1369. 

Reaction rates in the presence of oxygen and nitric oxides [82], in the presence of hydroxyl radicals [89] or in the presence of mixtures of nitric oxides of varying composition [90] have been compared for various aromatics, m-xylene and trimethyl benzenes react substantially faster than the other xylenes, toluene, and in particular benzene. In the presence of nitric oxides, the following products are formed from aromatics with side chains particularly from toluene methyl glyoxal, dimethyl glyoxal, and biacetyl [83,84], larger quantities of m-nitrotoluene, 2-methyl-4-nitro-phenol, 2-methyl-4,6-dinitrophenol, benzaldehyde, benzyl nitrate, o-cresol, and p-nitrophenol [91-93]. 

An important side reaction in all free-radical nitrations is reaction 10, in which unstable alkyl nitrites are formed (eq. 10). They decompose to form nitric oxide and alkoxy radicals (eq. 11) which form oxygenated compounds and low molecular weight alkyl radicals which can form low molecular weight nitroparaffins by reactions 7 or 9. The oxygenated hydrocarbons often react further to produce even lighter oxygenated products, carbon oxides, and water. 

Their rates are decreased or the reactions are suppressed entirely by substances that scavenge free radicals (e.g., nitric oxide, molecular oxygen, or benzo-... 

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