A radical (often called free radical) is a chemical species having one or more electrons not matched on its outer layer. He notes a point. The presence of a single electron gives these molecules, most of the time, a highly volatile (they do not respect the rule of the byte), which means they are able to react with many compounds in process mostly non-specific and, therefore, their life solution is very short.
The radicals are usually obtained by breaking chemical bonds. Because the chemical bonds have energies of the order of hundreds of • kJ mol-1, the conditions set Thursday to give radicals are often drastic: high temperatures, ionizing radiation, ultraviolet.
A chemical bond can be cut so homolytique (two electrons liaison AB are distributed equitably) to give two radicals
A-B \ rightarrow A \ cdot + \ cdot B
If the chemical bond is broken so hétérolytique (two electrons of the route are captured by atoms) on a ions rather than radical.
A-B \ rightarrow A ^ + + | B ^ --
The existence of free radicals was highlighted by chemists rubber in the early 1940.
The term free radical is particularly used in the context of the communication of pharmaceutical and cosmetics. The correct scientific term is "reactive oxygen species (or nitrogen)", with English abbreviations: ROS (or RONS). It also speaks of "oxygen free radicals" or "derivatives reagents oxygen."
In addition, some ROS, as hydrogen peroxide (H2O2) are not radicals in the chemical sense: indeed, this molecule, while reactive and toxic, has no character radicals.
Overall, free radicals are chemical species with high reactivity able to oxidize proteins, DNA and cell membranes (attack lipids constituent): This is one of the current theories of aging.
Involvement in physiological processes
These species, whose production physiological phenomenon is a natural association with the life aerobics, can then address the compounds vital cells.
The ROS can tackle disrupting DNA replication, leading to mutations and cancer. They can also attack the cell membranes and proteins.
The consequences are, at the cellular level, cell death by apoptosis or necrosis while Level tissue damage of ROS can lead by example, the hardening of the arteries and cardiovascular problems, the deterioration of collagen and therefore the rigidity of tissues.
Free radicals are one of the causes of ageing, it is proposed that medicines reducing the concentration in vivo of these species could extend life expectancy. However, this point is the subject of an unresolved controversy that is currently going through the scientific community.
System defence against free radicals
The organization has a number of means of defense against damage from free radicals involving enzymes like superoxide dismutases, catalases, glutathione peroxidase and glutathione reductase. When this system is overwhelmed, the organization is in a state of oxidative stress.
Other antioxidants (chemical species prevent damaging oxidation reactions caused by ROS) are small molecules such as vitamins C and E, carotenoids, some polyphenols, essential oils ... The formation of free radicals in the body is constant and inseparable from life in an atmosphere oxydante but excesses depend on external factors such as stress, fatigue and intensive exercise, consumption of tobacco, alcohol , Air pollution, or by radiation such as X-ray Some genetic diseases cause an overproduction of ROS or reduced effectiveness of the defence system. An overproduction of ROS has been observed in Alzheimer's disease and Parkinson's. The ROS can cause rejection of grafts during organ transplants.
Read also Stress oxidant