Peroxide formation, nitric oxide-metal

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.

Sulphurj in the unoxidized condition, is tested for by heating the compound with metallic sodium or with sodium carbonate, by which treatment the sulphur is converted into sodium sulphide. If the fused product is placed on a silver coin and moistened, a spot of siVoer sulphide will be produced. The fused mass may also be dissolved in water, neutralized with nitric acid, and a little lead acetate solution added. The formation of a black precipitate of lead sulphide proves the presence of sulphur. These tests are applicable only in case the sulphur is in an unoxidized form. To test for sulphur in either the oxidized or unoxidized form a little of the compound is boiled with strong nitric acid or is heated with sodium peroxide. This treatment converts the sulphur into the form of sulphuric acid or a sulphate, either of which will yield a white precipitate of barium sulphate when tested with barium nitrate in the presence of nitric acid. 

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