Free Radicals, Types, Sources and Damaging Reactions

Submitted by Dr. Tamer Fouad, M.D.

	Free radicals are a chemical species that possess an unpaired electron in the outer shell of the molecule.
	send to a friend   printer friendly version
	Related   Antioxidants Oxidative mechanisms in carcinogenesis

Types of free radicals in the body

The most important free radicals in the body are the radical derivatives of oxygen better known as reactive oxygen species (Cheeseman and Slater, 1993). These include oxygen in its triplet state (3O₂) or singlet state (¹O₂), superoxide anion (O₂^·⁻), hydroxyl radical (·OH), nitric oxide (NO·), peroxynitrite (ONOO⁻), hypochlorous acid (HOCl), hydrogen peroxide (H₂O₂) alkoxyl radical (LO·), and the peroxyl radical (LO·₂). Others are carbon-centered free radical (CCI₃·) that arises from the attack of an oxidizing radical on an organic molecule. Hydrogen centered radicals result from attack of the H atom (H·). Another form is the sulfur-centered radical produced in the oxidation of glutathione resulting in the thiyl radical (R-S·). A nitrogen-centered radical also exists for example the phenyl diazine radical.

Table 1: Biologically significant free radicals.

Fig. 2: Molecular orbital configuration of oxygen. Ground-state oxygen O₂ has two unpaired electrons in the outer (p·2p) orbitals and is therefore a free radical. Singlet oxygen has two paired electrons in this orbit and is not a free radical. The superoxide ion (O₂^·⁻) has an unpaired electron and so is a free radical, but the peroxide ion (O₂²) has paired electrons and so is not a free radical (Ward and Peters 1995).

		Are you a doctor or a nurse? Do you want to join the Doctors Lounge online medical community? Participate in editorial activities (publish, peer review, edit) and give a helping hand to the largest online community of patients. Click on the link below to see the requirements: Doctors Lounge Membership Application

send to a friend printer friendly version

Click here for The Main Discussion Board     Chest Diseases Forums       Dermatology Forums       Endocrinology & Diabetes Forums Click here for Internal Medicine Articles