Аскорбиновая кислота

Описание

Ascorbic acid, a water-soluble dietary supplement, is consumed by humans more than any other supplement. The name ascorbic means antiscurvy and denotes the ability of ascorbic to combat this disease. Vitamin C is the l-enantiomer of ascorbic acid. Ascorbic acid deficiency in humans results in the body’s inability to synthesize collagen, which is the most abundant protein in vertebrates.

Химические свойства

White crystals (plates or needles). Soluble in water; slightly soluble in alcohol; insoluble in ether, chloroform, benzene, petroleum ether, oils and fats. Stable to air when dry. One international unit is equivalent to 0.05 milligram of l-ascorbic acid.

Физические свойства

Appearance: white crystal or crystalline powder, and it is odorless and flavors sour. The color changes yellowish when exposed in the air for a long time. Its aqueous solution is acidic reaction. Solubility: vitamin C is soluble in water, slightly soluble in ethanol, and insoluble in chloroform or ether. Melting point: 190–192? °C.? It would decompose when it melts. Specific optical rotation: +20.5 to +21.5°. Ascorbic acid is two-base acid (the pKa is 4.1 and 11.8). It occurs mainly in the form of sodium salt and calcium salt, and its aqueous solution is strongly acidic reaction. Ascorbic acid is a strong reducing agent.

История

Vitamin C is a general term for compounds having ascorbic acid activity, including ascorbic acid, dehydroascorbic acid, and its isomers.
The understanding of vitamin C has gone through a long and painful process. Although the relationship between scurvy and stored food is obvious, but the treatments of this disease have been misguided. By 1601, British armed Captain James Lancaster discovered the disease on the ship of the East India Company and regarded the scurvy as “rot,” which could be made tissue alkaline.
At the early stage of the nineteenth century, the understanding and treatment of scurvy had developed to a right approach. The exposition of scurvy etiology and metabolic theory took more than a century.
By the early stage of the twentieth century, inspired by the animal model of beriberi, researchers in the Christchurch Oslo University discovered one animal that could suffer scurvy accidentally and then established a valuable scurvy animal model. This experiment demonstrated that the extract isolated from lemon had antiscurvy activity. Until 1932, many research groups obtained the anti-scurvy crystal from different plants and identified the crystal as ascorbic acid vitamin C. Next year, the chemical structure of ascorbic acid was elucidated, and then its artificial synthesis was accomplished.

Использование

antiscorbutic, antiviral

Показания

Vitamin C (ascorbic acid) is essential for the maintenance of the ground substance that binds cells together and for the formation and maintenance of collagen.The exact biochemical role it plays in these functions is not known, but it may be related to its ability to act as an oxidation–reduction system.

Определение

ChEBI: L-ascorbic acid is the L-enantiomer of ascorbic acid and conjugate acid of L-ascorbate. It has a role as a coenzyme, a flour treatment agent, a food antioxidant, a plant metabolite, a cofactor, a skin lightening agent and a geroprotector. It is an ascorbic acid and a vitamin C. It is a conjugate acid of a L-ascorbate. It is an enantiomer of a D-ascorbic acid.

Общее описание

White to very pale yellow crystalline powder with a pleasant sharp acidic taste. Almost odorless.

Реакции воздуха и воды

May be sensitive to prolonged exposure to air and light. Sensitive to moisture. Soluble in water. Aqueous solutions are oxidized by air in a reaction that is accelerated by alkalis, iron and copper. The rate depends on the pH and on oxygen concentration. Also subject to degradation under anaerobic conditions.

Профиль реактивности

L(+)-Ascorbic acid is a lactone. Reacts as a relatively strong reducing agent and decolorizes many dyes. Forms stable metal salts. Incompatible with oxidizers, dyes, alkalis, iron and copper. Also incompatible with ferric salts and salts of heavy metals, particularly copper, zinc and manganese .

Пожароопасность

Flash point data for L(+)-Ascorbic acid are not available; however, L(+)-Ascorbic acid is probably combustible.

Фармаколо?гия

Vitamin C is considered as a classical enzyme cofactor or antioxidant but also as a transition material in metal ion reaction. And all of these functions of vitamin C are related to the property of antioxidation.

Клиническое использование

Vitamin C is indicated for the treatment and prevention of known or suspect deficiency. Although scurvy occurs infrequently, it is seen in the elderly, infants, alcoholics, and drug users.Ascorbate can also be used to enhance absorption of dietary nonheme iron or iron supplements. Ascorbic acid (but not the sodium salt) was historically used to acidify the urine as a result of excretion of unchanged ascorbic acid, although this use has fallen into disfavor. Ascorbate also increases iron chelation by deferoxamine, explaining its use in the treatment of iron toxicity.

Побочные эффекты

Megavitamin intake of vitamin C may result in diarrhea due to intestinal irritation. Since ascorbic acid is partially metabolized and excreted as oxalate, renal oxalate stones may form in some patients.

Токсикология

L-Ascorbic acid, or vitamin C, is widely present in plants. The structures of ascorbic acid and dehydroascorbic acid are shown in Figure 10.5. Vitamin C is not only an important nutrient but is also used as an antioxidant in various foods. However, it is not soluble in fat and is unstable under basic conditions. Vitamin C reduces cadmium toxicity and excess doses prolong the retention time of an organic mercury compound in a biological system. Overdoses of vitamin C (106 g) induce perspiration, nervous tension, and lowered pulse rate. WHO recommends that daily intake be less than 0.15 mg/kg. Toxicity due to ascorbic acid has not been reported. Although repeated intravenous injections of 80 mg dehydroascorbic acid was reported to be diabetogenic in rats, oral consumption of 1.5 g/day of ascorbic acid for six weeks had no effect on glucose tolerance or glycosuria in 12 normal adult males and produced no change in blood glucose concentrations in 80 diabetics after five days. The same report noted that a 100-mg intravenous dose of dehydroascorbic acid given daily for prolonged periods produced no signs of diabetes. Ascorbic acid is readily oxidized to dehydroascorbic acid, which is reduced by glutathione in blood.

Профиль безопасности

Moderately toxic by ingestion and intravenous routes. Human systemic effects by intravenous route: blood, changes in tubules (including acute renal failure, acute tubular necrosis). An experimental teratogen. Other experimental reproductive effects. Mutation data reported. When heated to decomposition it emits acrid smoke and irritating fumes.

Описание

Аскорбиновая кислота — органическое соединение с формулой C6H8O6, является одним из основных веществ в человеческом рационе, которое необходимо для нормального функционирования соединительной и костной ткани. Выполняет биологические функции восстановителя и кофермента некоторых метаболических процессов, является антиоксидантом.

Химические свойства

По физическим свойствам аскорбиновая кислота представляет собой белый кристаллический порошок кислого вкуса. Легко растворим в воде, растворим в спирте. Температура плавления L-аскорбиновой кислоты — 190—192 °C (с разложением).

Из-за наличия двух асимметрических атомов существуют четыре диастереомера аскорбиновой кислоты. Две условно именуемые L- и D- формы хиральны относительно атома углерода в фурановом кольце, а изо- форма является D-изомером по атому углерода в боковой этиловой цепи.

Применение

Аскорбиновая кислота вводится при отравлении угарным газом, метгемоглобинобразователями в больших дозах — до 0,25 мл/кг 5 % раствора в сутки. Препарат является мощным антиоксидантом, нормализует окислительно-восстановительные процессы. Также применяется при гиповитаминозе C, геморрагическом диатезе, капилляротоксикозе, геморрагическом инсульте, кровотечении (в т.ч. носовом, легочном, маточном), инфекционных заболеваниях, идиопатической метгемоглобинемии, интоксикации, алкогольном и инфекционном делирии, острой лучевой болезни, посттрансфузионных осложнениях, заболеваниях печени (болезнь Боткина, хронический гепатит и цирроз), заболеваниях ЖКТ (ахилия, язвенная болезнь, особенно после кровотечения, энтерит, колит), гельминтозах, холецистите, вяло заживающих ранах, язвах, ожогах, физических и умственных перегрузках, беременности.

Производство

Синтетически получают из глюкозы с применением ферментации на некоторых этапах (бактериями Gluconobacter oxydans по методу Hoffmann-La Roche или бактериями Erwinia herbicola и Corynebacterium по методу Genentech).

Синтезируется растениями из различных гексоз (глюкозы, галактозы) и большинством животных (из галактозы), за исключением приматов и некоторых других животных (например, морских свинок), которые получают её с пищей.

Количественное определение аскорбиновой кислоты проводят методами алкалиметрии, йодатометрии либо йодометрии.

Методы очистки

Crystallise it from MeOH/Et2O/pet ether [Herbert et al. J Chem Soc 1270 1933]. [Beilstein 18/5 V 26.]