Ascorbic acid, constitution

The action of ascorbic acid on many enzymes appears to be conditioned by other substances, notably metallic ions, present in reaction mixtures certainly where its action has been critically examined, this has been found to be so. Whether ascorbic acid in vivio has any regulatory influence on these enzymes is uncertain. Still more improbable is the view that this action of ascorbic acid constitutes one of its essential roles in the living cell, since it has been shown both for j3-amylase and urease that other dienols (reductone, dehydroxymaleic acid, reductic acid, hydroxy-tetronic acid) which are biologically inactive react similarly (Hanes, 1935 Mapson, 1946). 

In order to use any of the results obtained by objective methods as the basis for the acceptance or rejection of a product, there must be available reliable information as to the relationship between the values obtained and organoleptic quality in terms of consumer acceptance and utility. Where standards are based upon measurement of such labile constituents as ascorbic acid or sugar, a knowledge of the normal values for good commercial practice is necessary. Such values have not yet been adequately established. This should constitute a useful field for research of inestimable value to the industry. 

Due to its electronic conductivity, polypyrrole can be grown to considerable thickness. It also constitutes, by itself, as a film on platinum or gold, a new type of electrode surface that exhibits catalytic activity in the electrochemical oxidation of ascorbic acid and dopamine in the reversible redox reactions of hydroquinones and the reduction of molecular oxygen iV-substituted pyrroles are excellent... 

Ascorbic acid, which is closely related to the sugars and is no doubt derived from them in the metabolism of the cells of plants, has been shown to be identical with vitamin- C (Szent-Gyorgyi). It has the constitution of a lactone of a-keto-i-gulonic acid (W. N. Haworth, T. Reichstein) ... 

It is interesting that, when Reichstein and coworkers published the first synthesis of L-ascorbic acid, the correct structure was not yet known, and they considered their synthesis to constitute support of structure 35, earlier proposed by Micheel and Kraft. ... 

Ascorbic acids reduce Fehling solution in the cold, and react with ferric chloride to produce the violet color typical of enolic compounds. They are readily oxidized reversibly to their primary oxidation products, 2,3-glycodiulosono-1,4-lactones (commonly known as dehydroascorbic acids 148, Scheme 16), by such mild oxidizing agents as aqueous iodine. Titration with such oxidants constitutes a quantitative method for distinguishing ascorbic acids from 2-glyculosonic acids. 

The structure of 138 was elucidated, shortly after its isolation, in extensive contributions by many groups. Several important discoveries relating to its constitution were reported in 1933, the same year in which the first successful synthesis was described (see Refs. 274, 324). Thus, the group at the University of Birmingham335 found that the primary oxidation product of 138, the 2,3-diulosono-lactone 148 (dehydroascorbic acid), could be quantitatively oxidized by sodium hypoiodite to generate oxalic acid and L-threonic acid (Scheme 16), which was identified as the crystalline tri-O-methyl-L-threonamide. These results established the stereochemical relationship between 138 and L-gulonic (and L-idonic) acid. The work that provided support for the structure of L-ascorbic acid has been summarized in several reviews.274,336... 

Chelation, in osazone formation, III, 43 Chemical constitution, physiological activity and, of ascorbic acid analogs,... 

The Constitution of Ascorbic Acid. Action of Sodium Hypochlorite on a-Methoxy-acid Amides, R. G. Ault, W. N. Haworth, and E, L. Hirst,/. Chem. Soc., 1722 (1934). 

In partnership with ascorbic acid, GSH constitutes the body s major antioxidant defence system [31]. The liver is a main source of circulating GSH. It has been estimated that approximately 45 mmol (or 14 g) of GSH are released into the circulatory system of humans during a 24 h period [32]. 

Ascorbic acid 3 g/day for 6 days causes a significant loss of high altitude resistance, persisting for 2 weeks after withdrawal of treatment. High doses may therefore constitute a risk in people who take them under conditions in which the oxygen supply suddenly becomes impaired, and is also undesirable in people with pathological hypoxia, for example due to respiratory diseases (12). 

Patients with idiopathic (genetic) hemochromatosis constitute a risk group with regard to ingestion of large doses of ascorbic acid, which can lead to deterioration in cardiac function (36). 

Crystal structures of L-ascorbic acid varying from coarse to ultrafine powder constitute the major commercial product forms of the compound, followed by special coated and granulated forms. Sodium L-ascorbate is also produced in granular and powder forms. Limited production of other forms such as calcium ascorbate and ascorbyl palmitate depend on demand of these products in specialty use applications. 

Under GRAS conditions, the quantity added does not exceed the amount reasonably required to accomplish its intended physical, nutritional, or other technical effect on food, and the quantity of ascorbic acid becomes a component of food as a result of its use in the manufacturing, processing, or packaging of food, and which is not intended to accomplish any physical or other technical effect on the food itself, shall be reduced to the extent reasonably possible and the ascorbic acid is of appropriate food grade and is prepared and handled as a food ingredient and the inclusion of ascorbic acid in the list of nutrients does not constitute a finding on the part of the Department that ascorbic acid is useful as a supplement to the diet for humans. ... 

A detectable rise in plasma nickel concentration after the oral administration of 22.4 mg of nickel sulfate was reported (69). In collaborative studies, we have examined the interaction of nickel and ascorbic acid in the human intestine. Healthy volunteers received 5 mg of elemental nickel as 22.4 mg of nickel sulfate, as in the previous report. The total volume was 100 mL. This was ingested either alone or with 1 g of ascorbic acid. This constituted a Ni AA molar ratio of 0.015. A significant depression in the rise of plasma nickel was observed when ascorbic acid was present as compared with the situation of aqueous nickel alone see Table V). Our Ni AA ratio of 0.015 compares with a molar ratio... 

In 1933 he synthesized vitamin C (ascorbic acid) and worked on plant glycosides. From 1953 to 1954 he worked with several other scientists and was the first to isolate and explain the constitution of aldosterone, a hormone of the adrenal cortex. He also collaborated with E. C. Kendall and P. S. Hench in their work on the hormones of the adrenal cortex. For this work, Reichstein, Kendall, and Hench were jointly awarded the Nobel Prize for physiology or medicine in 1950. 

Aerobic organisms evolved a complex system of antioxidant defenses to minimize the oxidative damage resulting from the presence of oxygen. Antioxidant enzymes and low molecular weight antioxidants, such as reduced glutathione (GSH), comprise the biochemical constitutive antioxidant defense. In addition, mammals in general complement the antioxidant defenses with nutritional antioxidants, such as ascorbic acid, a-tocopherol, and -carotene, and for such... 

The amino acid composition of collagen is distinctive. Glycine constitutes approximately one-third of the amino acid residues. Proline and 4-hydroxyproline may account for as much as 30% of a collagen molecule s amino acid composition. Small amounts of 3-hydroxyproline and 5-hydroxylysine also occur. (Specific proline and lysine residues in collagen s primary sequence are hydroxylated within the rough ER after the polypeptides have been synthesized. These reactions, which are discussed in Chapter 19, require the antioxidant ascorbic acid.)... 

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