What are free radicals?
An atom or a group of atoms that has at least one unpaired electron and is therefore highly reactive and unstable, so such free radicals are likely to take part in chemical reactions which play an important role in atmospheric chemistry, combustion, polymerisation, plasma chemistry, biochemistry and many other chemical processes, including human physiology.
For example nitric oxide and super oxide regulate many biological processes, such as controlling vascular tone. “Radical” and “free radical” are frequently used interchangeably, however a radical may be trapped within a solvent cage or be otherwise bound. In 1900, the first organic free radical identified was triphenylmethyl radical, by Moses Gomberg at the University of Michigan.
Historically, the term radical has also been used for bound parts of the molecule, especially when they remain unchanged in reactions. For example, methyl alcohol was described as consisting of a hydroxyl ‘radical’ and methyl ‘radical’.
Neither were radicals in the usual chemical sense, as they were permanently bound to each other and had no unpaired, reactive electrons. In mass spectrometry, such radicals are seen after breaking down the substance with a hail of energetic electrons.
Free radicals play an important role in many number of biological processes, which are important for life, such as the intracellular killing of bacterias by neutrophil granulocytes.
Free radicals have also been implicated in certain cell signalling processes. The two most important oxygen-centered free radicals are super oxide and hydroxyl radical. They are derived from molecular oxygen under reducing conditions.
However, because of their reactivity, these same free radicals can participate in unwanted side reactions causing cell damage. Many kinds of cancers are thought to be the result of reactions between free radicals and DNA, resulting in mutations that can adversely affect the cell cycle and potentially lead to malignancy.
Some of the symptoms of aging such as arteriosclerosis are also attributed to free radical induced oxidation of many of the chemicals making up the body. In addition, free radicals causes alcohol-induced liver damage, perhaps more than alcohol itself. Radicals in cigarette smoke have been implicated in inactivation of alpha 1-antitrypsin in the lung. This process promotes the development of emphysema.
