Defining a Free Radical
A free radical is an atom, molecule, or ion that has one or more unpaired valence electrons. This unpaired electron makes the radical highly reactive, as it seeks to gain or lose an electron to achieve a more stable, paired electron configuration. Free radicals can exist independently and are typically short-lived due to their high reactivity.
Formation and Types of Free Radicals
Free radicals typically form through homolytic cleavage of a chemical bond, where each atom retains one of the shared electrons, or through redox reactions. They can also form in biological systems during normal metabolic processes or due to external factors like radiation and pollution. Common examples include hydroxyl radicals (•OH), superoxide radicals (O₂⁻•), and nitric oxide (NO•).
Role in Chemical Reactions
Due to their unstable electron configuration, free radicals readily participate in chemical reactions, particularly radical chain reactions. These reactions involve initiation, propagation, and termination steps, where the radical 'propagates' its unpaired electron to other molecules, leading to a cascade of reactions. They are important in combustion, polymer synthesis, and atmospheric chemistry.
Impact on Biological Systems
In biological systems, free radicals play crucial roles in cellular signaling and defense mechanisms. However, an imbalance where too many free radicals are produced, or too few antioxidants are present, can lead to 'oxidative stress.' Oxidative stress can damage cells, proteins, and DNA, contributing to aging, various diseases, and cell death. Antioxidants like vitamins C and E help neutralize free radicals.