Ascorbic acid is a natural organic compound with antioxidant properties. It is a solid white sample, but not pure can look yellowish. It dissolves well in water to provide a mild acid solution. Ascorbic acid is one of the forms ("vitamins") of vitamin C. It was originally called L -hexuronic acid, but, when it was found to have vitamin C activity in animals ("vitamin C" certain substances), suggestions made to change his name. The new name, ascorbic acid, comes from a - (meaning "no") and scorbutus (scurvy), a disease caused by a deficiency of vitamin C. Because it comes from glucose , almost all animals are capable of producing it, but humans need it as part of their nutrients. Other vertebrates that do not have the ability to produce ascorbic acid include other primates, guinea pigs, teleost fish, bats, and some birds, all of which require it as dietary micronutrients (ie in the form of vitamins). Ascorbic acid has two forms of enantiomers. Only L -sorbidic acid is found in nature, whereas D -cascorbic acid can be made by chemical synthesis.
Video Chemistry of ascorbic acid
Histori
From the mid-18th century, it was noted that lemon juice and lime juice can help prevent sailors from scurvy. Initially, it was suspected that the acidic nature was responsible for these benefits; However, it soon became clear that other dietary acids, such as vinegar, did not have such benefits. In 1907, two Norwegian doctors reported an important disease-preventing compound in different foods from preventing beriberi. These doctors are investigating the diseases of food shortage using new guinea pig model animals, which are susceptible to scurvy. The newly discovered food factor is finally called vitamin C.
From 1928 to 1932, the Hungarian research team led by Albert Szent-GyÃÆ'¶rgyi, as well as American researcher Charles Glen King, identified the antiscorbutic factor as a single chemical. Szent-GyÃÆ'¶rgyi isolates the first chemical hexuronic acids from the plant and then from the animal's adrenal glands. He suspects it to be an antiscorbutic factor but can not prove it without a biological test. The exam was finally performed at the University of Pittsburgh in the King's laboratory, which has been working on issues for years, using guinea pigs. At the end of 1931, King's laboratory acquired indirect adrenal hexuronic acid from Szent-GyÃÆ'¶rgyi and, using their animal model, proved that it was vitamin C, as early as 1932.
This is the last compound from animal sources, but, by the end of the year, the Szent-GyÃÆ'¶rgyi group found that the chili pepper, a common spice in Hungarian food, was the source of rich hexuronic acids. He sent some chemicals that are now more available to Walter Norman Haworth, an English sugar chemist. In 1933, working with Assistant Director of Research (later Sir) Edmund Hirst and their research team, Haworth summed up the true structure and properties of optical isomers of vitamin C, and in 1934 reported the first synthesis of vitamins. In honor of the antiscorbutic properties of the compound, Haworth and Szent-GyÃÆ'¶rgyi now propose the new name "a-scorbic acid" for the compound. It was named L -sorborbic acid by Haworth and Szent-GyÃÆ'¶rgyi when its structure was finally proven by synthesis.
In 1937, the Nobel Prize for chemistry was awarded to Haworth for his work in determining the structure of ascorbic acid - along with Paul Karrer, who received the award for work on vitamins - and a prize for Physiology or Medicine that year went to Albert Szent-GyÃÆ'¶rgyi for his studies about the biological function of L -Asorborbic acid.
American Doctor Fred R. Klenner, M.D. promoting vitamin C as a cure for many diseases in the 1950s by increasing the dose very much up to tens of grams of vitamin C every day orally and by injection. From 1967, Nobel Prize winner Linus Pauling recommended a high dose of ascorbic acid as a precaution against colds and cancers. However, modern evidence does not support the role of high doses of vitamin C in the treatment of cancer or prevention of common cold in the general population.
Maps Chemistry of ascorbic acid
Acidity
Ascorbic acid is classified as reductton. An ascorbic anion is stabilized by the delocalization of electrons, as shown above in terms of resonance between two canonical forms. For this reason, ascorbic acid is much more acidic than would be expected if the compound contains only isolated hydroxyl groups.
Antioxidant Mechanism
Ionic ascorbate is the dominant species at a typical biological pH value. It is a mild reduction agent and an antioxidant. It is oxidized by losing an electron to form a radical cation and then by the loss of a second electron to form dehydroascorbic acid. It usually reacts with oxidants of reactive oxygen species, such as hydroxyl radicals. Such radicals damage animals and plants at the molecular level because of their possible interactions with nucleic acids, proteins, and lipids. Sometimes these radicals start a chain reaction. Ascorbate can stop this chain's radical reaction by electron transfer. Ascorbic acid is special because it can transfer a single electron, due to its own radical ion-resonance properties, called semidehydroascorbate. The net reaction is:
- RO o C
6 H
7 O -
6 -> RO - C 6 H 7 O < span> o
Reaction
Food chemistry
Ascorbic acid and sodium, potassium, and calcium salts are commonly used as antioxidant food additives. These compounds are soluble in water and, therefore, can not protect fat from oxidation: For this purpose, fat-soluble esters of ascorbic acid with long chain fatty acids (ascorbyl palmitate or ascorbyl stearate) may be used as food antioxidants. Eighty percent of the world's supply of ascorbic acid is produced in China.
The relevant E numbers of European food additives are:
- E300 ascorbic acid (approved for use as food additives in EU US and Australia and New Zealand)
- E301 sodium ascorbate (approved for use as food additives in EU US and Australia and New Zealand)
- E302 calcium ascorbate (approved for use as food additives in EU US and Australia and New Zealand)
- E303 potassium askorbat
- E304 fatty acid ester of ascorbic acid (i) ascorbyl palmitate (ii) ascorbyl stearate.
It creates volatile compounds when mixed with glucose and amino acids in 90 Ã, Â ° C.
This is a cofactor in the oxidation of tyrosine.
Niche, non-food uses
Biosynthesis
Ascorbic acid is found in plants and animals in which it is produced from glucose. Animals should either produce or digest them, otherwise no vitamin C deficiency can cause scabies, which can eventually lead to death. Reptiles and older bird orders make ascorbic acid in their kidneys. Recent orders of birds and most mammals make ascorbic acid in their livers where the enzyme L -gulonolactone oxidase is needed to convert glucose into ascorbic acid. Humans, other higher primates, guinea pigs and bats most in need of dietary ascorbic acid because the enzyme L -gulonolactone oxidase catalyze the last step in highly mutated and non-functioning biosynthesis, therefore, can not make ascorbate. AC ID. The nature of synthesis and signals is still under investigation.
Animal ascorbic acid biosynthesis path
Ascorbic acid biosynthesis begins with the formation of UDP-glucuronic acid. UDP-glucuronic acid is formed when UDP-glucose undergoes two oxidations catalyzed by UDP-glucose 6-dehydrogenase enzyme. UDP-glucose 6-dehydrogenase uses co-factor NAD as an electron acceptor. The transferase UDP-glucuronate pyrophosphorylase removes UMP and glucuronokinase, with cofactor ADP, removing the final phosphate leading to D -glucuronic acid. The group's aldehyde is reduced to primary alcohol using the enzyme glucuronate reductase and the NADPH cofactor, yielding L -gulonic acid. This is followed by the formation of lactones with the hydrolysis of gluconolactonase between carbonyls in C 1 and hydroxyl groups in C 4. L -Gulonolactone then reacts with oxygen, catalyzed by the enzyme L -gulonolactone oxidase (which does not work in humans and other Haplorrhini primates) and the FAD cofactor. This reaction produces 2-oxogulonolactone, which spontaneously enzymes to form ascorbic acid.
Pathways ascorbic acid biosynthesis
There are many different biosynthetic pathways for ascorbic acid in plants. Much of this pathway comes from products found in glycolysis and other pathways. For example, one path passes through the plant cell wall polymer. The most important ascorbic acid biosynthesis pathway seems to be L -galactose. L -Galactose reacts with the enzyme L -galactose dehydrogenase, where the lactone ring is open and re-formed but with between carbonyl in C 1 and hydroxyl groups at C4, yields -galactonolactone. L -Galactonolactone then reacts with mitochondrial flavoenzyme L -galactonolactone dehydrogenase. to produce ascorbic acid. L - Ascorbic acid has negative feedback on L -galactose dehydrogenase in spinach. The removal of ascorbic acid by embryo from dikotyl plants is an established mechanism of iron reduction, and is a mandatory step for iron absorption.
Yeast does not make lactic acid L but its stereoisomer, eritorbat acid.
Industry Preparation
Ascorbic acid is prepared in the industry of glucose in a method based on the historical Reichstein process. In the first process of the five steps, glucose is catalytically hydrogenated into sorbitol, which is then oxidized by the microorganisms Acetobacter suboxydans into sorbose. Only one of the six hydroxy groups is oxidized by this enzymatic reaction. From this point, two routes are available. The treatment of the product with acetone in the presence of an acid catalyst converts the remaining four hydroxyl groups to acetals. The unprotected hydroxyl group is oxidized to carboxylic acid by reaction with TEMPO oxide catalyst (regenerated by sodium hypochlorite bleach solution). Historically, industrial preparations through the Reichstein process use potassium permanganate as a bleaching solution. The acid-catalyst hydrolysis of this product performs a dual function of removing the two acetal groups and the closure of the lactoneization ring. This step produces ascorbic acid. Each of the five steps has a result greater than 90%.
The more biotechnological processes, first developed in China in the 1960s, but developed further in the 1990s, bypass the use of groups that protect acetone. Genetically modified microbial species, such as the Erwinia mutant, among others, oxidize the sorbose into 2-ketogluconic acid (2-KGA), which can then undergo lactone closure of the ring through dehydration. This method is used in the dominant process used by the ascorbic acid industry in China, which supplies 80% of the world's ascorbic acid. American and Chinese researchers compete to engineer mutants that can ferment one pot directly from 2-KGA glucose, passing the need for a second fermentation and the need to reduce glucose to sorbitol.
There is <Î ±> D acid-a small drug, which does not occur in nature but can be artificially synthesized. To be specific, L -ascorbate is known to participate in many specific enzyme reactions requiring the correct enantiomers ( L -ascorbate instead of D - ascorbate ). L -Ascorbic acid has a specific rotation of <20> br> D Ã, = Ã, 23Ã, Â °.
Determination
The traditional way to analyze ascorbic acid content is the titration process with the oxidizing agent, and several procedures have been developed, primarily relying on iodometry. Iodine is used in the presence of starch indicator. Iodine is reduced by ascorbic acid, and, when all ascorbic acid has reacted, iodine then overreacts, forming a blue-black complex with a kanji indicator. This shows the end point of the titration. Alternatively, ascorbic acid may be over-treated with iodine, followed by back titration with sodium thiosulfate using starch as an indicator. Previous iodometric methods have been revised to exploit ascorbic acid reactions with iodate and iodide in acidic solutions. Electrolysis of potassium iodide solution produces iodine, which reacts with ascorbic acid. The end of the process is determined by potentiometric titration in a manner similar to Karl Fischer's titration. The amount of ascorbic acid can be calculated by Faraday's law.
An unusual oxidizing agent is N -bromosuccinimide (NBS). In this titration, NBS oxidizes ascorbic acid in the presence of potassium iodide and starch. When NBS is excessive (ie, the reaction is completed), NBS releases iodine from potassium iodide, which then forms a blue-black complex with starch, indicating the endpoint of the titration.
Compendium status
- English Pharmacopoeia
- Japanese Pharmacopoeia
See also
- Color retention agent
- Eritorbat acid: ascorbic acid diastereomers.
- Mineral content: ascorbic acid salt
- Acid in wine
Notes and references
Further reading
- Clayden; Greeves; Warren; Wothers (2001), Organic Chemistry , Oxford University Press, ISBNÃ, 0-19-850346-6 Ã, .
- Davies, Michael B.; Austin, John; Partridge, David A., Vitamin C: Chemistry and Biochemistry , Royal Society of Chemistry, ISBN 0-85186-333-7 .
- Coultate, TP, Food: Chemical Components (3rd ed.), Royal Society of Chemistry, ISBN 0-854-4- 513-9 .
- Gruenwald, J.; Brendler, T.; Jaenicke, C., eds. (2004), PDR for Herbal Medicines, Montvale, New Jersey: Thomson PDR . McMurry, John (2008), Organic Chemistry (7e ed.), Thomson Learning, ISBNÃ, 978-0-495-11628 - 8 .
External links
- International Chemical Safety Card 0379
- SIDS Preliminary Assessment Report for L -Aric acid from Organization for Economic Cooperation and Development (OECD)
- IPO Poisons Information Monograph (PIM) 046
- An interactive 3D structure of vitamin C with details about the x-ray structure
Source of the article : Wikipedia
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