Types of Free Radicals

A free radical is any atom with one or more unpaired electrons in the outermost shell. Free radicals are formed when a covalent bond is broken, leaving constituent atoms with one electron each. Due to the presence of an unpaired electron, free radicals are extremely reactive. In human biology, free radicals (oxygen-centered free radicals) perform a variety of necessary cellular functions, but when they are over-abundant they can cause damage to those same cells.

Superoxide

• Superoxide is produced within the cell at the membrane level of specialized cells as oxygen atoms take on an additional electron. Usually these cells are phagocytic (attacking and destroying unwanted materials within the body) and use superoxide to destroy unwanted bacteria. Superoxide can be neutralized by superoxide dismutase.

Hydroxyl Radical

• Hydroxyl radicals are the most unstable form of free radicals found within the body. Their instability means they have a short life; however, they are also the most damaging to living tissue. Hydroxyl radicals can be formed either from the Herber-Weiss reaction (between O2 and H2O2) or by combining copper or iron and H202. Unlike superoxide, hydroxyl cannot be neutralized via enzymatic reaction; they essentially must destabilize themselves.

Singlet Oxygen

• Singlet oxygen is not a free radical in the true sense of the word, but is formed during many reactions between free radicals and can catalyze others. Singlet oxygen is capable of transferring energy between molecules, which can result in the jumping of electrons to new orbital shells, creating unpaired electrons. Therefore, singlet oxygen can catalyze the formation of free radicals.

Hydrogen Peroxide

• Hydrogen peroxide can be produced in the body through a variety of reactions. Hydrogen peroxide can either be converted into hydroxyl radicals or excreted as harmless water. Glutathione peroxidase is necessary for converting hydrogen peroxide to water instead of damaging hydroxyl radicals.