Overview
1 g of ascorbic acid is dissolved in 5 ml of water, 25 ml of ethyl alcohol or 100 ml of glycerol. Ascorbic acid is insoluble in benzene, chloroform, ether, petroleum ether and fats. Ascorbic acid reacts with metal cations, health ascorbates with the general formula C6H7O6M. Ascorbic acid is easily oxidized by atmospheric oxygen. Oxidation of ascorbic acid is accelerated in neutral and alkaline solutions. It is catalyzed by light, ions of copper, iron, silver and plant enzymes: ascorbin oxidase and polyphenol oxidase. During oxidation, ascorbic acid is converted to dehydroascorbic acid, which has the same high C-vitamin effect as ascorbic acid. Dehydroascorbic acid is rapidly restored in tissues. It does not contain a conjugated system and does not detect absorption in ultraviolet light. Along with ascorbic acid and dehydroascorbic acid, a protein-associated form of ascorbic acid, ascorbigen, which is resistant to oxidation, is found in plant products. In the case of irreversible oxidation, dehydroascorbic acid, after opening the lactone ring at a pH of more than 4, passes into 2,3-diketogulonic acid, and then into oxalic and omgreonic acid. The oxidation of ascorbic acid is delayed by thiosulfate, thiourea, thioacetates, flavonoids, o-diphenols, metaphosphoric acid, acid polysaccharides, etc. Most proteins and amino acids also inhibit the oxidation of ascorbic acid by forming complexes either with ascorbic acid itself Macu-Vision with copper. Ascorbic acid easily reduces silver nitrate, solutions of bromine, iodine and 2,6-dichlorophenolin-dophenol. Ascorbic acid is so effective as a reducing agent that it has found wide application in analytical chemistry in determining a number of mineral elements and in polarographic studies of a large number of substances, in particular uranium and other compounds. Ascorbic acid is widespread in nature (see table). It is found in plants, mainly in reduced form. Of the organs of animals, the adrenal glands, the pituitary gland, the lens, and the liver are rich in ascorbic acid. During cooking, up to 50% of ascorbic acid is lost on average. Even more is lost when standing ready meals. A number of stabilizers found in egg protein, meat, liver, cereals, cottage cheese, starch, salt, helps to preserve ascorbic acid during cooking. The long-term preservation of ascorbic acid is facilitated by: pickling, freezing, dehydration, canning, cooking berries and fruits with sugar (see also Vitaminization of food products).
Ascorbic open page is synthetically obtained from D-glucose, which is reduced to D-sorbitol, which is then converted by bacterial synthesis to D-sorbose, 2-oxo-L-gulonic acid and L-ascorbic acid. A good stabilizer of ascorbic acid is sodium sulfite, used in the preparation of ampoule solutions. The only antagonist of ascorbic acid is glucoascorbic acid.
All plants and many animals synthesize ascorbic acid, with the exception of humans, monkeys, guinea pigs, Indian fruit bats (Pteropus medius), and red-headed bulbs (Pycnonotus cafer Linn.) - birds from the Passeriformes order, due to the lack of D-glucuronoreductase and L-gulono-gamma-lactone-O2-oxidoreductase, possibly due to a congenital genetic defect.
Ascorbic acid received in the human body is absorbed in the small intestine. The total amount of ascorbic acid in the body of a healthy person is Blackmores g. The plasma contains 0.7–1.2 mg%, and in leukocytes 20–30 mg%. A number of oxidases (ascorbin oxidase, cytochrome oxidase, peroxidase, lactase, etc.) directly or indirectly catalyze the oxidation of ascorbic acid. The synthesis of ascorbic acid in an animal organism occurs from D-glucuronolactone. The mechanism of action of ascorbic acid is not yet fully deciphered. It plays an important role in the hydroxylation of proline to collagen oxyproline, participates in the oxidation of aromatic amino acids (tyrosine and phenylalanine), and also in the hydroxylation of tryptophan to 5-hydroxytryptophan in the presence Macu-Vision copper ions. Ascorbic acid is involved in the biogenesis of corticosteroids, has a protective effect on pantothenic and nicotinic acid and promotes the enzymatic conversion of folic acid to folic acid. In species that do not synthesize ascorbic acid (humans, guinea pigs), as well as those capable of biosynthesis, ascorbic acid has a saving effect on vitamins B1, B2, A, E, folic acid, pantothenic acid, reducing consumption, that is, it reduces need for them. This effect is apparently associated with the reducing and antioxidant properties of ascorbic acid.
The daily human need for ascorbic acid - see Vitamins.
Ascorbic acid preparations used for the prevention and treatment of C-vitamin deficiency, as well as for increased physiological needs of the body in ascorbic acid (during pregnancy and lactation, with increased physical activity, increased mental and emotional stress).
For therapeutic purposes, ascorbic acid is used in the complex treatment of infectious diseases and various types of intoxications, for liver diseases, pregnant nephropathy, for Addison’s disease, for sluggishly healing wounds and bone fractures, for diseases of the gastrointestinal tract Blackmores, peptic ulcer disease, etc.) with atherosclerosis. Ascorbic acid is prescribed for the prevention of bleeding in the treatment high doses anticoagulants.
Ascorbic acid is prescribed orally (after eating), intramuscularly and intravenously. Therapeutic doses for adults when taken orally 0.05-0.1 g 3-5 times a day; parenteral ascorbic acid is administered as a 5% solution from 1 to 5 ml. Children are prescribed orally at 0.05-0.1 g 2-3 times a day; parenterally 1-2 ml of 5% solution. The timing of treatment depends on the nature and course of the disease.
With prolonged use of high doses of ascorbic acid, pancreatic function, kidney function, and blood pressure should be monitored, as there are some observations indicating that prolonged use of significant amounts of ascorbic acid causes inhibition of the pancreatic insular apparatus, contributes to the development of renal diabetes and can increase blood pressure.
Caution must be exercised when prescribing maximum doses of ascorbic acid when administered intravenously in cases of increased blood coagulation, with thrombophlebitis and a tendency to thrombosis.
Method of release: powder, pills 0.05 g, tablets 0.025 g with glucose, tablets 0.05 g and 0.1 g; ampoules containing 1 and 5 ml of a 5% solution. In addition, ascorbic acid is part of various multivitamin preparations.
Store in a well-sealed container that protects from the effects of light and air.
Methods for the determination of ascorbic acid depend on the object of study, the concentration of ascorbic acid in the object, the presence in the object of substances that interfere with the determination, etc. The objects of research can be animal organs and tissues, biological fluids (blood, urine, etc.), plant products (vegetables, fruits, etc. .), prepared food, ascorbic acid medicines. In the listed objects, ascorbic acid is found both in reduced and in oxidized form (dehydroascorbic acid), which can form, for example, during processing and storage of food products. Therefore, it must also be determined.
The main steps for determining ascorbic acid are as follows:
1) receipt of material;
2) storage of the received material;
3) extraction of ascorbic acid from the sample;
4) the release of the obtained extract from impurities that Blackmores with the determination of ascorbic acid;
5) determination of the amount of ascorbic acid.
Ascorbic acid is easily destroyed, and therefore ensuring its safety is very essential for any research method. The destruction of ascorbic acid is enhanced by the influence of sunlight, aeration, temperature increase and increase in pH. Macu-Vision lower the content of ascorbic acid in the analyzed object, the greater the difficulty in determining it. Some of the methods, for example, the determination of ascorbic acid in blood and urine, are valuable for recognizing the degree to which the human body is provided with ascorbic acid. When taking material from the studied object, it is necessary to create conditions for the maximum preservation of ascorbic acid in the obtained sample.
For example, when examining blood, you need to take it without hemolysis. If necessary, it is necessary to create such material storage conditions that reduce or eliminate the inactivation of ascorbic acid (cold, the prescription of preservatives, etc.). Extraction is carried out at a pH of at least 4, preliminary binding of metal ions catalyzing the oxidation of ascorbic acid, and inactivation of enzymes that oxidize ascorbic acid. A solution of acetic, trichloroacetic, oxalic and metaphosphoric acids is used for extraction. Most preferred 5-6% metaphosphoric acid, well stabilizing
Ascobic acid, which precipitates proteins and inactivates the ascorbinase enzyme in raw plant objects. Exemption from impurities that interfere with determination is carried out by means of deposition of the latter, as well as using various chromatography methods (on thin-layer, ion-exchange paper).
A number of methods have been proposed for the quantitative determination of the content of ascorbic acid in biological materials. So, the determination of ascorbic acid in urine is carried out by the Tillmans method, which is based on the ability of ascorbic acid to restore certain substances, in particular 2,6-dichlorophenolindophenol. For this, the analyzed sample is titrated with 0.001 N. a solution of sodium salt of 2,6-dichlorophenolindophenol until the discoloration of the solution ceases. The same principle underlies the determination of ascorbic acid in blood plasma (see Farmer-Abt method). When quantifying leukocytes, the Bessey method is used (see Bessey methods). The method is quite accurate and requires an extremely small amount of biological material for analysis (0.2 ml of whole blood).
In the study of products containing the so-called reductons that come into contact with 2,6-dichlorophenol indophenol (syrups, compotes, dried vegetables, fruits, ingredient, it is best to use formaldehyde treatment of the extract [Schillinger (A. Schillinger), 1966 ]. When analyzing objects containing natural pigments (dyes), titration with 2,6-dichlorophenolindophenol in the presence of an organic solvent (chloroform, xylene, isoamyl acetate, etc.) that extract excess dye is most often used. When determining ascorbic acid in colored fruit and berry juices, amperometric titration is used. The endpoint of titration of ascorbic acid with 2,6-dichlorophenolindophenol is determined by a change in potential — potentiometrically [Harris, Marson (LJ Harris, LW Marson) et al., 1947] or by the appearance of a polarizing current — amperometrically [Kharlampovich, Wozniak (Z. Charlampowicz, W. Woznjak) and others, 1969]. This method is quite accurate.
To determine dehydroascorbic acid, it is reduced to ascorbic acid, followed by titration of 2,6-dichlorophenol with indophenol. To restore the use of hydrogen sulfide [Tillmans (J. Tillmans) and others, 1932]. However, hydrogen sulfide does not completely restore dehydroascorbic acid. The best results are obtained when it is reduced by sulfhydryl compounds (homocysteine, cysteine, 2,3-dimercaptopropanol).
In addition to biological and redox methods for the determination of ascorbic acid, methods are used that are based on color reactions with ascorbic acid or its oxidation products.
These methods determine ascorbic acid, dehydroascorbic and diketogulonic acids. The most common method proposed in 1948 by Rowe (J. N. Roe) and others using 2,4-dinitrophenyl hydrazine. Diketogulonic acid obtained during the analysis during the oxidation of dehydroascorbic acid forms ozones with an orange color. Ozones are dissolved in acids (sulfuric, acetic and mixtures of hydrochloric and phosphoric acids) and the optical density of the solutions is measured using photocolorimetry. The best conditions: solution temperature 37 °, reaction time - 6 hours.
Determination of ascorbic acid is also carried out using labeled isotopes, fluorimetric method, etc.
