An antioxidant is a molecule that inhibits the oxidation of other molecules. Oxidation is a chemical reaction that can produce free radicals, leading to chain reactions that may damage cells. Antioxidants such as thiols or ascorbic acid (vitamin C) terminate these chain reactions. The term "antioxidant" is mainly used for two different groups of substances: industrial chemicals which are added to products to prevent oxidation, and natural chemicals found in foods and body tissue which are said to have beneficial health effects.
To balance the oxidative state, plants and animals maintain complex systems of overlapping antioxidants, such as glutathione and enzymes (e.g., catalase and superoxide dismutase) produced internally or the dietary antioxidants, vitamin A, vitamin C, and vitamin E.
Antioxidant dietary supplements do not improve health nor are they effective in preventing diseases. Randomized clinical trials including supplements of beta-carotene, vitamin A, and vitamin E singly or in different combinations found no effect on mortality rate and cancer risk, or may even increase cancer risk. Supplementation with selenium or vitamin E does not reduce the risk of cardiovascular disease. Oxidative stress can be considered as either a cause or consequence of some diseases, an area of research stimulating drug development for antioxidant compounds for use as potential therapies.
| Antioxidant metabolite |
Solubility |
Concentration in human serum (μM) |
Concentration in liver tissue (μmol/kg) |
| Ascorbic acid (vitamin C) |
Water |
50 – 60 |
260 (human) |
| Glutathione |
Water |
4 |
6,400 (human) |
| Lipoic acid |
Water |
0.1 – 0.7 |
4 – 5 (rat) |
| Uric acid |
Water |
200 – 400 |
1,600 (human) |
| Carotenes |
Lipid |
β-carotene: 0.5 – 1
retinol (vitamin A): 1 – 3 |
5 (human, total carotenoids) |
| (vitamin E) |
Lipid |
10 – 40 |
50 (human) |
| Ubiquinol (coenzyme Q) |
Lipid |
5 |
200 (human) |
| Fuel additive |
Components |
Applications |
| AO-22 |
N,N'-di-2-butyl-1,4-phenylenediamine |
Turbine oils, transformer oils, hydraulic fluids, waxes, and greases |
| AO-24 |
N,N'-di-2-butyl-1,4-phenylenediamine |
Low-temperature oils |
| AO-29 |
2,6-di-tert-butyl-4-methylphenol |
Turbine oils, transformer oils, hydraulic fluids, waxes, greases, and gasolines |
| AO-30 |
2,4-dimethyl-6-tert-butylphenol |
Jet fuels and gasolines, including aviation gasolines |
| AO-31 |
2,4-dimethyl-6-tert-butylphenol |
Jet fuels and gasolines, including aviation gasolines |
| AO-32 |
2,4-dimethyl-6-tert-butylphenol and 2,6-di-tert-butyl-4-methylphenol |
Jet fuels and gasolines, including aviation gasolines |
| AO-37 |
2,6-di-tert-butylphenol |
Jet fuels and gasolines, widely approved for aviation fuels |
2 Fe3+ + Ascorbate → 2 Fe2+ + Dehydroascorbate
2 Fe2+ + 2 H2O2 → 2 Fe3+ + 2 OH· + 2 OH−
2 Fe2+ + 2 H2O2 → 2 Fe3+ + 2 OH· + 2 OH−
- Nick Lane Oxygen: The Molecule That Made the World (Oxford University Press, 2003)
- Barry Halliwell and John M.C. Gutteridge Free Radicals in Biology and Medicine (Oxford University Press, 2007)
- Jan Pokorny, Nelly Yanishlieva and Michael H. Gordon Antioxidants in Food: Practical Applications (CRC Press Inc, 2001)
...
Wikipedia
