| Ascorbic acid is a sugar acid with antioxidant | | | | calcium salts are commonly used as antioxidant food |
| properties. Its appearance is white to light-yellow | | | | additives. These compounds are water-soluble and |
| crystals or powder. It is water-soluble. The | | | | thus cannot protect fats from oxidation: For this |
| L-enantiomer of ascorbic acid is commonly known as | | | | purpose, the fat-soluble esters of ascorbic acid with |
| vitamin C. The name is derived from the alpha | | | | long-chain fatty acids (ascorbyl palmitate or ascorbyl |
| privative a- (meaning no) and scorbuticus (scurvy), the | | | | stearate) can be used as food antioxidants. Eighty |
| disease caused by a deficiency of vitamin C. In 1937 | | | | percent of the world's supply of ascorbic acid is |
| the Nobel Prize for chemistry was awarded to Walter | | | | produced in China. The relevant European food |
| Haworth for his work in determining the structure of | | | | additive E numbers are: E300 ascorbic acid, E301 |
| ascorbic acid (shared with Paul Karrer, who received | | | | sodium ascorbate, E302 calcium ascorbate, E303 |
| his award for work on vitamins), and the prize for | | | | potassium ascorbate, and E304 fatty acid esters of |
| Physiology or Medicine that year went to Albert | | | | ascorbic acid (i) ascorbyl palmitate (ii) ascorbyl |
| Szent-Györgyi for his studies of the biological | | | | stearate. It can be added to water that has been |
| functions of L-ascorbic acid. At the time of its | | | | treated with iodine to make it potable, neutralizing the |
| discovery in the 1920s, it was called hexuronic acid by | | | | unpleasant iodine taste, and increasing the health |
| some researchers. Ascorbic acid, formula C6H8O6, | | | | benefits of drinking water, although increasing the |
| behaves as a vinylogous carboxylic acid, wherein the | | | | chance of tooth decay. In plastic manufacturing, |
| double bond ("vinyl") transmits electron pairs between | | | | ascorbic acid can be used to assemble molecular |
| the hydroxyl and the carbonyl. There are two | | | | chains more quickly and with less waste than |
| resonance structures for the deprotonated form, | | | | traditional synthesis methods. Ascorbate acts as an |
| differing in the position of the double bond. Another | | | | antioxidant by being available for energetically |
| way to look at ascorbic acid is to consider it as an | | | | favorable oxidation. Many oxidants (typically, reactive |
| enol. The deprotonated form is an enolate, which is | | | | oxygen species) such as the hydroxyl radical (formed |
| usually strongly basic. However, the adjacent double | | | | from hydrogen peroxide), contain an unpaired electron, |
| bond stabilizes the deprotonated form. Ascorbic acid | | | | and, thus, are highly reactive and damaging to humans |
| also rapidly interconverts into two unstable diketone | | | | and plants at the molecular level. This is due to their |
| tautomers by proton transfer, although it is the most | | | | interaction with nucleic acid, proteins, and lipids. |
| stable in the enol form. The proton of the enol is lost, | | | | Reactive oxygen species oxidize (take electrons |
| and reacquired by electrons from the double bond, to | | | | from) ascorbate first to monodehydroascorbate and |
| produce a diketone. This is an enol reaction. There are | | | | then dehydroascorbate. The reactive oxygen species |
| two possible forms: 1,2-diketone and 1,3-diketone. The | | | | are reduced to water, while the oxidized forms of |
| concentration of a solution of ascorbic acid can be | | | | ascorbate are relatively stable and unreactive, and do |
| determined in many ways, the most common ways | | | | not cause cellular damage. Ascorbic acid is found in |
| involving titration with an oxidizing agent. A | | | | plants, animals, and single-cell organisms. All living |
| commonly-used oxidizing agent is the dye | | | | animals make it, eat it, or die from scurvy due to lack |
| 2,6-dichlorophenol-indophenol, or DCPIP for short. The | | | | of it. Reptiles and older orders of birds make ascorbic |
| blue dye is run into the ascorbic acid solution until a | | | | acid in their kidneys. Recent orders of birds and most |
| faint pink colour persists for 15 seconds. Another | | | | mammals make ascorbic acid in their livers where the |
| method involves using iodine and a starch indicator, | | | | enzyme L-gulonolactone oxidase is required to convert |
| wherein iodine reacts with ascorbic acid, and, when all | | | | glucose to ascorbic acid. Humans, guinea pigs, and |
| the ascorbic acid has reacted, the iodine is then in | | | | some other primates are not able to make |
| excess, forming a blue-black complex with the starch | | | | L-gulonolactone oxidase because of a genetic defect |
| indicator. This indicates the end-point of the titration. As | | | | and are therefore unable to make ascorbic acid in their |
| an alternative, ascorbic acid can be reacted with iodine | | | | livers. This genetic mutation occurred about 63 million |
| in excess, followed by back titration with sodium | | | | years ago This would have had lethal consequences |
| thiosulfate while using starch as an indicator. The | | | | for the mutated primate were it not for the fact that it |
| above method involving iodine requires making up and | | | | occurred to an arboreal animal living in a tropical |
| standardizing the iodine solution. One way around this is | | | | environment where plenty of foodstuffs containing |
| to generate the iodine in the presence of the ascorbic | | | | ascorbic acid were available throughout the year. |
| acid by the reaction of iodate and iodide ion in acid | | | | Although ascorbic acid is a vital food nutrient for |
| solution. A much-less-common oxidizing agent is | | | | humans and is therefore termed a vitamin, it is a |
| N-bromosuccinimide, (NBS). In this titration, the NBS | | | | natural liver metabolite in most other animals. Vitamin C |
| oxidizes the ascorbic acid (in the presence of | | | | or Ascorbic acid is the enolic form of |
| potassium iodide and starch). When the NBS is in | | | | 3-oxo-L-gulofuranolactone. It can be prepared by |
| excess (i.e., the reaction is complete), the NBS liberates | | | | synthesis from glucose, or extracted from plant |
| the iodine from the potassium iodide, which then forms | | | | sources such as rose hips, blackcurrants or citrus fruits. |
| the blue/black complex with starch, indicating the | | | | It is easily oxidized in air. It is essential for the formation |
| end-point of the titration. Ascorbic acid is easily | | | | of collagen and intercellular material, bone and teeth |
| oxidized and so is used as a reductant in photographic | | | | and for the healing of wounds. It helps maintain |
| developer solutions (among others) and as a | | | | elasticity of the skin aids the absorption of iron and |
| preservative. Exposure to oxygen, metals, light, and | | | | improves resistance to infection. It is used in the |
| heat destroys ascorbic acid, so it must be stored in a | | | | treatment of scurvy. It may prevent the occurrence |
| dark, cold, and non-metallic container. The L-enantiomer | | | | and development of cancer. Man is one of the few |
| of ascorbic acid is also known as vitamin C. The name | | | | mammals unable to manufacture ascorbic acid in his |
| "ascorbic" comes from its property of preventing and | | | | liver. Good sources of Vitamin C are Broccoli, Brussels |
| curing scurvy. Primates, including humans, and a few | | | | sprouts, cauliflower, cabbage, mangetout, green leafy |
| other species in all divisions of the animal kingdom, | | | | vegetables, red peppers, chilies, watercress, parsley, |
| notably the guinea pig, have lost the ability to | | | | blackcurrants, strawberries, kiwi fruit, guavas, and citrus |
| synthesize ascorbic acid, and must obtain it in their | | | | fruit. |
| food. Ascorbic acid and its sodium, potassium, and | | | | |