Radical (chemistry)
In chemistry, a radical, or free radical, refers to an atom, ion, or molecule that possesses an unpaired electron in its outermost shell, which makes it highly reactive and likely to form chemical bonds. Radicals can be generated through three primary processes: oxidation (loss of an electron), reduction (gain of an electron), and homolysis (breaking a covalent bond in a manner that results in two radicals). These species, while generally short-lived due to their high reactivity, can sometimes persist if steric hindrance prevents them from reacting with other substances.
Radicals are significant in biological systems, playing roles in cellular signaling and the immune response against bacteria. However, they are also implicated in various diseases and aging, as they can damage cells and DNA. Antioxidants, such as vitamins A, C, and E, are produced by the body to mitigate radical damage, and many people take these supplements with the hope of preventing diseases and slowing aging, especially before any health issues arise. While antioxidants may help prevent cellular damage, their effectiveness as a treatment after disease onset is less clear. Additionally, radicals may be formed endogenously during metabolic processes or exogenously through environmental factors like pollution and radiation. Current research aims to enhance the body’s defenses against radicals through genetic and dietary strategies.
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Radical (chemistry)
In chemistry, a “radical” or “free radical” is an atom, ion, or molecule that has an unpaired electron in its outermost, or valence, shell, making it more chemically reactive—that is, more likely to form a chemical bond. There are three main methods by which radicals are formed: oxidation, in which the atom, ion, or molecule loses an electron; reduction, in which it gains an electron; and homolysis, in which a preexisting covalent bond is broken in such a way that each resulting fragment retains one of the two electrons that formed the bond. Oxidation and reduction are reactions that happen in concert with one another; as one atom, ion, or molecule loses an electron, another one must gain that electron. The overall process is called a redox reaction. Homolysis requires a large amount of energy, the precise amount depending on the type of radical. Those requiring more energy tend to be less stable than those requiring smaller amounts of energy.
Background
The first radical was discovered in 1900 by Russian-born chemist Moses Gomberg (1866–1947). While working at the University of Michigan, Gomberg was able to synthesize the compound tetraphenylmethane, the first persistent, organic free radical. Usually radicals do not last for a long time because their high reactivity means that they easily combine with other materials. A persistent radical is an exception to this rule. Persistent radicals form when a molecule is too crowded or bulky for another atom or molecule to get close enough to react, an effect known as “steric hindrance.” Another type of radical that can remain stable for longer periods is a diradical, which possesses two unpaired electrons. An oxygen molecule is an example of a diradical.
Overview
Radicals are involved with many of the biological processes that occur in living organisms. This is especially true of the human body’s signaling systems, which transmit information from one region to another via the mechanism of chemical reactions. Radicals also play an important role in the body’s ability to destroy invasive bacteria.
At the same time, radicals are suspected of being involved in a number of diseases and degenerative processes. One theory suggests that free radicals are involved in the aging process, because part of the damage characteristic of aging may be the result of radicals reacting with an organism’s cells and destroying them. The body has several different processes for trying to limit the damage caused by radicals, including the production of antioxidants such as vitamins A, C, and E. Still, syndromes such as Parkinson’s disease and Alzheimer’s, which are thought to owe their potency to radical reactions within the body, continue to claim thousands upon thousands of lives each year.
Many people take large doses of vitamins and antioxidants in an attempt to slow the aging process and prevent cancers and other diseases. Since the theory presumes that radicals harm the body’s cells and proteins, particularly DNA, by reacting with them and causing them to either deteriorate or be destroyed, the purpose of ingesting antioxidant supplements is to have the antioxidants intercept the free radicals before they can contact the body’s cells and damage them. Antioxidants’ ability to counteract radicals in this way is known as “scavenging” because the antioxidants essentially seek out the radicals and then react with them, thus neutralizing their reactive capacity and eliminating their ability to harm the body. Research has shown that when antioxidants are taken as a preventative measure, before the onset of disease, they can in fact be effective, particularly in preventing the kind of cellular damage associated with cancer development. If taken after a cancer diagnosis in an attempt to treat cancer, however, there is little evidence that antioxidants produce any discernible benefit, and in some cases they may even have a deleterious effect.
Free radicals are produced within the body and in the environment outside the body. Those created in the body are called endogenous, while those that formed outside the body are called exogenous. Exogenous radicals can be caused by environmental pollution, radiation from the sun or from x-rays, materials made from petroleum, pesticides and other poisonous chemicals, or other caustic substances, such as paint or solvents. Endogenous radical formation can be caused by stress, as the hormones secreted by the endocrine system during stressful situations produce radicals; as a side effect of the production of energy through cellular respiration; from overconsumption of certain foods, such as those fried at high temperatures; and during the normal processes of food metabolism.
Research into free radicals tends to focus on discovering new ways to enhance the body’s ability to resist their effects. Scientists are exploring ways they may be able to manipulate human DNA to help the body produce more antioxidants. There are also efforts underway to create artificial enzymes that could behave inside the body in the same way that naturally occurring antioxidants do, neutralizing radicals before they can do any harm. Other genetic research focuses on creating new strains of edible plants that have enhanced levels of antioxidants, which people could consume to help reduce their vulnerability to radicals.
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