Biomaterial Database

The pecking order of free radicals and antioxidants: lipid peroxidation, alpha-tocopherol, and ascorbate. 1993

G R Buettner

ESR Center/EMRB 68, College of medicine, University of Iowa, Iowa City 52242.

Free radicals vary widely in their thermodynamic properties, ranging from very oxidizing to very reducing. These thermodynamic properties can be used to predict a pecking order, or hierarchy, for free radical reactions. Using one-electron reduction potentials, the predicted pecking order is in agreement with experimentally observed free radical electron (hydrogen atom) transfer reactions. These potentials are also in agreement with experimental data that suggest that vitamin E, the primary lipid soluble small molecule antioxidant, and vitamin C, the terminal water soluble small molecule antioxidant, cooperate to protect lipids and lipid structures against peroxidation. Although vitamin E is located in membranes and vitamin C is located in aqueous phases, vitamin C is able to recycle vitamin E; i.e., vitamin C repairs the tocopheroxyl (chromanoxyl) radical of vitamin E, thereby permitting vitamin E to function again as a free radical chain-breaking antioxidant. This review discusses: (i) the thermodynamics of free radical reactions that are of interest to the health sciences; (ii) the fundamental thermodynamic and kinetic properties that are associated with chain-breaking antioxidants; (iii) the unique interfacial nature of the apparent reaction of the tocopherol free radical (vitamin E radical) and vitamin C; and (iv) presents a hierarchy, or pecking order, for free radical electron (hydrogen atom) transfer reactions.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008563	Membrane Lipids	Lipids, predominantly phospholipids, cholesterol and small amounts of glycolipids found in membranes including cellular and intracellular membranes. These lipids may be arranged in bilayers in the membranes with integral proteins between the layers and peripheral proteins attached to the outside. Membrane lipids are required for active transport, several enzymatic activities and membrane formation.	Cell Membrane Lipid,Cell Membrane Lipids,Membrane Lipid,Lipid, Cell Membrane,Lipid, Membrane,Lipids, Cell Membrane,Lipids, Membrane,Membrane Lipid, Cell,Membrane Lipids, Cell
D010084	Oxidation-Reduction	A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).	Redox,Oxidation Reduction
D005231	Fatty Acids, Unsaturated	FATTY ACIDS in which the carbon chain contains one or more double or triple carbon-carbon bonds.	Fatty Acids, Polyunsaturated,Polyunsaturated Fatty Acid,Unsaturated Fatty Acid,Polyunsaturated Fatty Acids,Acid, Polyunsaturated Fatty,Acid, Unsaturated Fatty,Acids, Polyunsaturated Fatty,Acids, Unsaturated Fatty,Fatty Acid, Polyunsaturated,Fatty Acid, Unsaturated,Unsaturated Fatty Acids
D005609	Free Radicals	Highly reactive molecules with an unsatisfied electron valence pair. Free radicals are produced in both normal and pathological processes. Free radicals include reactive oxygen and nitrogen species (RONS). They are proven or suspected agents of tissue damage in a wide variety of circumstances including radiation, damage from environment chemicals, and aging. Natural and pharmacological prevention of free radical damage is being actively investigated.	Free Radical
D000975	Antioxidants	Naturally occurring or synthetic substances that inhibit or retard oxidation reactions. They counteract the damaging effects of oxidation in animal tissues.	Anti-Oxidant,Antioxidant,Antioxidant Activity,Endogenous Antioxidant,Endogenous Antioxidants,Anti-Oxidant Effect,Anti-Oxidant Effects,Anti-Oxidants,Antioxidant Effect,Antioxidant Effects,Activity, Antioxidant,Anti Oxidant,Anti Oxidant Effect,Anti Oxidant Effects,Anti Oxidants,Antioxidant, Endogenous,Antioxidants, Endogenous
D001205	Ascorbic Acid	A six carbon compound related to glucose. It is found naturally in citrus fruits and many vegetables. Ascorbic acid is an essential nutrient in human diets, and necessary to maintain connective tissue and bone. Its biologically active form, vitamin C, functions as a reducing agent and coenzyme in several metabolic pathways. Vitamin C is considered an antioxidant.	Vitamin C,Ascorbic Acid, Monosodium Salt,Ferrous Ascorbate,Hybrin,L-Ascorbic Acid,Magnesium Ascorbate,Magnesium Ascorbicum,Magnesium di-L-Ascorbate,Magnorbin,Sodium Ascorbate,Acid, Ascorbic,Acid, L-Ascorbic,Ascorbate, Ferrous,Ascorbate, Magnesium,Ascorbate, Sodium,L Ascorbic Acid,Magnesium di L Ascorbate,di-L-Ascorbate, Magnesium
D013816	Thermodynamics	A rigorously mathematical analysis of energy relationships (heat, work, temperature, and equilibrium). It describes systems whose states are determined by thermal parameters, such as temperature, in addition to mechanical and electromagnetic parameters. (From Hawley's Condensed Chemical Dictionary, 12th ed)	Thermodynamic
D014810	Vitamin E	A generic descriptor for all TOCOPHEROLS and TOCOTRIENOLS that exhibit ALPHA-TOCOPHEROL activity. By virtue of the phenolic hydrogen on the 2H-1-benzopyran-6-ol nucleus, these compounds exhibit varying degree of antioxidant activity, depending on the site and number of methyl groups and the type of ISOPRENOIDS.
D015227	Lipid Peroxidation	Peroxidase catalyzed oxidation of lipids using hydrogen peroxide as an electron acceptor.	Lipid Peroxidations,Peroxidation, Lipid,Peroxidations, Lipid