In -1... chemistry, free radicals are uncharged Properties An atom ( Greek The ). Only the electrons in the outermost orbital (the ), or it can remove electrons from other atoms (an While Democrituss theory has been widely disproven, the recent string theory is based on a similar idea of shape and vibration governing a subatomic particles properties... atomic or In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. A molecule consists of multiple atoms joined by shared pairs of electrons in a is usually confined to chemical compounds, of multiple atoms. A substance that consists of molecules... molecular species with unpaired Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. In an atom the electrons surround the nucleus of protons and neutrons in an electron configuration. The word , which he called . Philosophical Magazine. Series 5, Volume 38, p. 418-420 October 1894. Eric Weissteins... electrons or an otherwise In the context of atomic orbitals, an open shell is a valence shell which is not completely filled with electrons or which has not given all of its valence electrons through chemical bonds with other atoms or molecules during a chemical reaction. The valence shell of most common elements must... open shell configuration. These unpaired electrons are highly This article is in need of attention. Please improve it in any way you see fit. A chemical reaction or is a reaction of two or more chemicals ( reagents), yielding a chemical change and a product(s). A chemical change is defined as molecules attaching to each other to form... reactive, so free radicals are likely to take part in chemical reactions. Free radicals play an important role in Combustion or burning is an exothermic reaction between a substance (the fuel) and a gas (the oxidizer) to release heat. Combustion normally occurs in oxygen (often in the form of gaseous O2) to form oxides. However, combustion can also take place in other gases like chlorine. Since the fuel is... combustion, Atmospheric chemistry is a multidisciplinary field of research in which the chemistry of the atmosphere is studied. It also involves physics, meteorology, computer modeling, oceanography, geology and volcanology and other disciplines. The composition and chemistry of the atmosphere is of interest to scientists for several reasons, but primarily because of... atmospheric chemistry, Polymerization is the formation of long, repeating organic polymer chains. There are many forms of polymerization, and different systems exist to categorize them. Categorizations include the (the identical molecules which make up the polymers) have extra, internal, bonds which are able to break and link up with other monomers to... polymerization, plasma chemistry, Biochemistry is the chemistry of life. Biochemists study the elements, compounds and chemical reactions that are controlled by enzymes and take place in all living organisms. Biochemistry is focused on the structure and function of cellular components, such as proteins, carbohydrates, lipids, nucleic acids, and other biomolecules. Recently biochemistry has... biochemistry, and many other chemical processes.

In written chemical equations, free radicals are frequently denoted by a dot placed immediately to the right of the atomic symbol or molecular formula as follows:

H₂ + hν → 2 H·

This is derived from Lewis Dot notation is a way of describing the outer shell (also called the valence shell) of an atoms electrons. Dots are drawn around the elements symbol to represent the electrons in the valence shell of the atom. This is where the chemical reactions take place. External links... Lewis dot notation.

Reactions involving free radicals are usually divided into three categories: initiation, propagation, and termination.

• Initiation reactions are those which result in a net increase in the number of free radicals. They may involve the formation of free radicals from stable species as in Reaction 1 above or they may involve reactions of free radicals with stable species to form more free radicals.
• Propagation reactions are those reactions involving free radicals in which the total number of free radicals remains the same.
• Termination reactions are those reactions resulting in a net decrease in the number of free radicals. Typically two free radicals combine to form a more stable species, for example: 2H· → H₂

The formation of radicals requires covalent bonds to be broken homolytically, a process that requires significant amounts of energy. For example, splitting H₂ into 2H· has a ΔH° of +435 kJ/mol, and Cl₂ into 2Cl· has a ΔH° of +243 kJ/mol. This is known as the homolytic In chemistry, bond dissociation is a process in which a specific bond is cleaved to give two new species. If a neutral molecule causes bond dissociation, it gives two free radicals. That is, two electrons that are involved in the bond are distributed one by one to the two species... bond dissociation energy, and is usually abbreviated as the symbol DH°. The bond energy between two covalently bonded atoms is affected by the structure of the molecule as a whole, not just the identity of the two atoms, and radicals requiring more energy to form are less stable than those requiring less energy. This shows that free radicals are difficult to form.

However, the extreme reactivity of the radical comes from their very low The activation energy in chemistry is the energy needed by a system to initiate a particular process. Activation energy is often used to denote the minimum energy needed for a specific chemical reaction to occur. For a reaction to occur between two colliding molecules they must collide in the correct... activation energy; when a free radical reacts with something, it will produce another free radical, e.g., H· + 1/2O₂ → OH· ( Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. Organic molecules containing a hydroxyl group are known as alcohols (CnH2n... hydroxyl). Note that all species are electrically neutral; 1 electron to 1 proton for hydrogen, 6 electrons to 6 protons for oxygen, and 7 electrons for 7 protons for the hydroxyl radical. Very little force is required to get the atoms close enough to react → low activation energy → extremely fast reaction rate and This article is in need of attention. Please see its listing on A + and is the activation energy, the energy per mole it is necessary for the molecules to have to react. Since at temperature has to do with stuff like the probability that molecules are in the right orientation... kinetics. The hydroxyl radical is free to undergo another reaction, and the lone electron may be swapped around many times before it joins with another radical in termination (see Polymerization is the formation of long, repeating organic polymer chains. There are many forms of polymerization, and different systems exist to categorize them. Categorizations include the (the identical molecules which make up the polymers) have extra, internal, bonds which are able to break and link up with other monomers to... polymerization).

Probably the most familiar free-radical reaction for most people is combustion. In order for combustion to occur the relatively strong O=O Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. Atoms tend to share electrons in such a way that their outer electron shells are filled... double bond must be broken to form oxygen free radicals. It is noteworthy that oxygen is actually a diradical with two unpaired electrons in the outer orbitals. Reactivity is limited because these electrons have parallel spins. However, this barrier is overcome by enzymes in the body (respiration) and by energy (heat). The flammability of a given material is strongly dependent on the concentration of free radicals that must be obtained before initiation and propagation reactions dominate leading to combustion of the material. Once the combustible material has been consumed, termination reactions again dominate and the flame dies out.

In addition to combustion, many Polymerization is the formation of long, repeating organic polymer chains. There are many forms of polymerization, and different systems exist to categorize them. Categorizations include the (the identical molecules which make up the polymers) have extra, internal, bonds which are able to break and link up with other monomers to... polymerization reactions involve free radicals. As a result many plastics, enamels, and other polymers are formed through free-radical reactions.

In the upper atmosphere free radicals are produced through dissociation of the source molecules, particularly the normally unreactive CFC molecules CFCs (chlorofluorocarbons) are a family of artificial chemical compounds containing chlorine, fluorine and carbon. They were formerly used widely in industry, for example as refrigerants, propellants and cleaning solvents. Their use has been generally prohibited by the Montreal Protocol, because of fears of their possible destructive effects on... chlorofluorocarbons by solar Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength shorter than that of the visible region, but longer than that of soft X-rays. It can be subdivided into near UV (380–200 nm wavelength) and extreme or vacuum UV (200–10 nm). When considering the effects of... ultraviolet radiation or by reactions with other stratospheric constituents. These free radicals then react with Ozone (O3) is an allotrope of oxygen, the molecule consisting of three oxygen atoms instead of the more stable diatomic O2. At standard temperature and pressure ozone is a blue gas. Ozone forms a dark blue liquid, below -112 °C, and a dark blue solid, below -193 °C... ozone in a catalytic A Chain reaction is any process which is self catalyzing, meaning that the process creates the conditions for its own continuation. An example is the nuclear fission process that takes place in nuclear reactors and atomic weapons. Chain Reaction is the title of a film starring Keanu Reeves and Morgan... chain reaction which destroys the ozone, but regenerates the free radical, allowing it to participate in additional reactions. Such reactions are believed to be the primary cause of depletion of the The ozone layer is that part of the Earths stratosphere which contains relatively high concentrations of ozone. The total quantity of ozone in the ozone layer is not very large; if just the ozone were compressed to the pressure of the air at sea level, it would be only... ozone layer and this is why the use of chlorofluorocarbons as refridgerants has been restricted.

Relatively stable, persistent free radical compounds include Fremys salt (Potassium nitrosodisulfonate, (KSO₃)₂NO·)and nitroxides, (general formula R₂NO·).

A widely-used technique for studying free radicals, and other paramagnetic species, is Overview Electron Paramagnetic Resonance (EPR) or Electron Spin Resonance (ESR) is a spectroscopic technique which detects species that have unpaired electrons, generally meaning that it must be a free radical, if it is an organic molecule, or that it has transition metal ions if it is a inorganic complex. Because... electron spin resonance Spectroscopy is the study of spectra, ie. the dependence of a physical measure to frequency. Spectroscopy is often used in physical and analytical chemistry for the identification of substances, through the spectrum emitted or absorbed. A device for recording a spectrum is a spectrometer. Spectroscopy can be classified according to... spectroscopy (ESR). This is alternately referred to as "electron paramagnetic resonance" (EPR) spectroscopy. It is conceptually related to Pacific Northwest National Laboratorys 800 MHz NMR spectrometer being loaded with sample. Nuclear magnetic resonance (NMR) is a physical phenomenon involving the interaction of atomic nuclei placed in an external magnetic field with an applied electromagnetic field oscillating at a particular frequency. Magnetic conditions within the material are measured... nuclear magnetic resonance, though electrons resonate with higher-frequency fields at a given fixed In physics, a magnetic field is an entity produced by moving electric charges (electric currents) that exerts a force on other moving charges. (The quantum-mechanical spin of a particle produces magnetic fields and is acted on by them as though it were a current; this accounts for the fields... magnetic field than do most nuclei.

Free Radicals in Biology

Free radicals play an important role in a number of biological processes, some of which are necessary for life, such as the intracellular killing of bacteria by Neutrophil granulocytes (commonly referred to as neutrophils) are a class of white blood cells and are part of the immune system. Role in blood Neutrophil granulocytes have an average volume of 330 femtoliters (fl) and a diameter of 12-15 micrometers (µm) in peripheral blood smears. They are the most... neutrophil granulocytes. Free radicals have also been implicated in certain In biology, signal transduction is any process by which a cell converts one kind of signal or stimulus into another. Processes referred to as signal transduction often involve a sequence of biochemical reactions inside the cell, which are carried out by enzymes and linked through second messengers. Such processes take... cell signalling processes. The two most important oxygen-centered free radicals are Superoxide is a reactive anion and free radical, formally O2-. It is produced most easily by burning rubidium or caesium in oxygen. It has an unpaired electron, is not particularly stable, and spontaneously decomposes into peroxide and oxygen over time. In phagocytes, superoxide is produced in large quantities by the... superoxide and Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. Organic molecules containing a hydroxyl group are known as alcohols (CnH2n... 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 resulting in cell damage. Many forms of When normal cells are damaged or old they undergo apoptosis; cancer cells, however, avoid apoptosis. Cancer is a group of diseases characterized by uncontrolled cell division leading to growth of abnormal tissue. It is believed that cancers arise from both genetic and environmental factors that lead to aberrant growth regulation... cancer are thought to be the result of reactions between free radicals and DNA replication Deoxyribonucleic acid (DNA) is a nucleic acid which is capable of carrying genetic instructions for the biological development of all cellular forms of life and many viruses. DNA is sometimes referred to as the molecule of heredity as it is inherited and used to propagate traits. During reproduction... DNA, resulting in Mutations are permanent, transmissible changes to the genetic material (usually DNA or RNA) of a cell. Mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses, or can occur deliberately under cellular control during the processes such as... mutations that can adversely affect the The cell cycle is the cycle of events in a eukaryotic cell from one cell division to the next. It consists of interphase, mitosis, and usually cell division. The cell cycle is regulated by cyclins and cyclin-dependent kinases. Leland H. Hartwell, R. Timothy Hunt, and Paul M. Nurse won... cell cycle and potentially lead to malignancy. Some of the symptoms of In biology, senescence is the state or process of aging. For the social, cultural, and economic aspects see ageing. The word is a phenomenon where isolated cells demonstrate a limited ability to divide in culture. to worms such as , a NAD+-dependent histone deacetylase. In yeast, Sir2 is required for... aging such as Atherosclerosis is a disease of arterial blood vessels. Venous vessels are not involved unless surgically moved to function as an artery. Atherosclerosis is commonly referred to as a hardening of blood vessels, but this is an over_simplification. Vascular lesions known as atheromatous plaques or atheromata (singular: atheroma) are formed in... atherosclerosis are also attributed to free-radical induced oxidation of many of the chemicals making up the body. In addition free radicals contribute to In general usage, alcohol (from Arabic or by the suffix ) is bound to a carbon atom, which in turn is bound to other hydrogen and/or carbon atoms. The general formula for a simple alcohol containing no rings is CnH2n+1OH. Structure The functional group of an alcohol is a... alcohol-induced The liver is an organ in vertebrates including humans. It plays a major role in metabolism and has a number of functions in the body including detoxification, glycogen storage and plasma protein synthesis. It also produces bile which is important for digestion. Medical terms related to the liver often start... liver damage, perhaps more than alcohol itself. Radicals in A cigarette will burn to ash on one end. A cigarette is a small paper-wrapped cylinder (generally less than 10cm in length and 10mm in diameter) of cured and shredded or cut tobacco leaves which is ignited at one end and allowed to smoulder for the purpose of allowing... cigarette Smoke is a suspension in air of small particles resulting from incomplete combustion of a fuel. It is commonly an unwanted by-product of fires (including in stoves and lamp), but may also be used for pest control, communication (smoke signals) or inhalation. Smoke sometimes also is a component of... smoke have been implicated in inactivation of Alpha 1-antitrypsin or α1-antitrypsin (A1AT) is a serine protease inhibitor (serpin). It protects tissue from enzymes from inflammatory cells, especially elastase. It is present in human blood at 1.5 - 3.5 gram/liter. Function A1AT is a 52 kDa serine protease inhibitor, and in medicine it... alpha 1-antitrypsin in the The heart and lungs (from an older edition of Grays Anatomy) The lung is an organ belonging to the respiratory system and interfacing to the circulatory system of air-breathing vertebrates. Its function is to exchange oxygen from air with carbon dioxide from blood. The process in which this... lung. This process promotes the development of Emphysema is a chronic lung disease. It is often caused by exposure to toxic chemicals or long-term exposure to tobacco smoke. Signs and symptoms Emphysema is characterised by loss of elasticity of the lung tissue; destruction of structures supporting the alveoli; and destruction of capillaries feeding the alveoli. The... emphysema.

Because free radicals are necessary for life, the body has a number of mechanisms to minimize free radical induced damage and to repair damage which does occur, such as the Neuraminidase ribbon diagram An enzyme (in Greek with the enzyme, they run in the same direction as they would without the enzyme, just more quickly; the concept is similar to the likelihood of a ball rolling down a hill versus the likelihood of it rolling up the hill. This is... enzymes Superoxide dismutase The enzyme superoxide dismutase , or SOD (EC 1.15.1.1), catalyzes the dismutation of superoxide into oxygen and hydrogen peroxide. As such it is an important antioxidant defense in nearly all cells exposed to oxygen. One of the exceedingly rare exceptions is Lactobacillus plantarum and related lactobacilli... superoxide dismutase, Catalase Catalase (human erythrocyte catalase: PDB 1DGF, EC 1.11.1.6) is a common enzyme found in living organisms. Its functions include catalyzing the decomposition of hydrogen peroxide to water and oxygen. Hydrogen peroxide is formed as a waste product of metabolism in many living organisms. It is toxic... catalase, Categories: Biochemistry stubs | EC 1.11.1 ... glutathione peroxidase and glutathione reductase. In addition, An antioxidant is a chemical that prevents the oxidation of other chemicals. In biological systems, the normal processes of oxidation (plus a minor contribution from ionizing radiation) produce highly reactive free radicals. These can readily react with and damage other molecules: in some cases the body uses this to fight... antioxidants play a key role in these In psychoanalytic theory, a defence mechanism is an unconscious way to protect ones personality from unpleasant thoughts which may otherwise cause anxiety. This can work well in small doses. However, a defence mechanism can also lead to a neurosis if it causes a person to adopt ineffectual or inappropriate... defense mechanisms. These are often the three vitamins, Retinol, the dietary form of vitamin A, is a fat-soluble, antioxidant vitamin important in vision and bone growth. It belongs to the family of chemical compounds known as retinoids. Retinol is ingested in a precursor form; animal sources (milk and eggs) contain retinyl esters, whereas plants (carrots, spinach) contain... vitamin A, Vitamin C is a water-soluble vitamin used by the body for several purposes. Most animals can synthesize their own vitamin C, but some animals, including guinea pigs, humans, and other primates, cannot. Vitamin C was first isolated in 1928, and in 1932 it was proved to be the agent... vitamin C and Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. Vitamin E is often used in skin creams and lotions because it is believed to play a role in encouraging skin healing and reducing scarring after injuries such as burns. Natural vitamin E... vitamin E. Further, there is good evidence Bilirubin is a yellow breakdown product of haem (heme in American English). Haem is a special ring shaped molecule that is found in haemoglobin. The haem ring holds the iron atoms of haem and is essential to the oxygen carrying capacity of blood. Physiology Bilirubin is essentially a waste product... bilirubin and Uric Acid Uric acid is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula C5H4N4O3 It is a minor end-product of nitrogen metabolism in the human body (the main product being urea), and is found in small amounts in urine. In some other animals, such as... uric acid can act as antioxidants to help neutralize certain free radicals. Bilirubin comes from the breakdown of Human red blood cells Red blood cells are the most common type of blood cell and are the vertebrate bodys principal means of delivering oxygen to body tissues via the blood. Red blood cells are also known as RBCs or erythrocytes (from Greek erythros for red and kytos for... red blood cells' contents, while uric acid is a breakdown product of Purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring that is fused with an imidazole ring. The general term purines refers to substituted purines and their tautomers. Two of the bases in nucleic acids, adenine and guanine, are purines. In DNA, these bases form hydrogen bonds with... purines. Too much bilirubin, though, can lead to Jaundice, technically known as icterus, is yellowing of the skin, sclera (eyes) and mucous membranes caused by increased levels of bilirubin in the system. Usually the concentration of bilirubin in the blood must exceed 2-3mg/dL for the coloration to be easily visible. Jaundice comes from the French word... jaundice which could eventually damage the central nervous system, while too much uric acid causes Gout (old name: podagra) is a form of arthritis caused by the accumulation of uric acid crystals (due to hyperuricemia) in joints. It is an immensely painful disease, which in most cases affects only one joint, most commonly the big toe. The patient usually suffers from two sources of pain... gout.

See also

• Free-radical theory. The theory that people age because inside their cells unstable oxygen molecules known as free radicals are produced. These ricochet around the cells damaging the DNA and other cellular structures. As free radicals bounce around inside of cells, their damage can lead to a range of disorders... Free-radical theory
• Free radical addition occurs when a peroxide is present in an alkene. The basic steps are: 1. Initiation: H-O-O-H -> H-O* H-O* + Br-Br -> H-O-Br Br* 2. Propagation: Br* + H2CCH2 -> H-Br + *CHCH2. H3C* + Br-Br -> Br* + BrCH3. ... Free radical addition

External link

• Free Radicals, Types, Sources and Damaging Reactions (http://www.thedoctorslounge.net/medlounge/articles/freeradicals/index.htm)