Vitamin C Ascorbic Acid

Vitamin C is a vitamin for only a limited number of vertebrate species humans and the other primates, the guinea pig, bats, the passeriform birds, and most fishes. Most insects and invertehrates are also incapahle of ascorbate synthesis. Ascorbate is synthesized as an intermediate in the gulonolactone pathway of glucose metabolism in those vertebrate species for which ascorbate is a vitamin, one enzyme of the pathway, gulonolactone oxidase, is absent. 

Ascorbic acid was isolated from cabbage, lemon juice, and adrenal glands by Szent-Gyorgy in 1928, and identified as the antiscorbutic factor by Waugh and King in 1932. Its structure was established by Haworth and coworkers in 1933, and the same year Haworth, in Birmingham, and Reichstein, in Switzerland, succeeded in synthesizing the vitamin. 

Ascorbate is a reducing sugar in addition to its specific role as cofactor for a variety of redox reactions, it also functions as a relatively nonspecific reducing agent. Some of these nonspecific reactions are physiologically important  

Ascorbate is synthesized in large amounts in plants, it can reach 20 to 300 mmol per L in chloroplasts, where its function is mainly to remove hydrogen peroxide formed during photosynthesis. Ascorbate-deficient mutant plants are especially sensitive to ozone- and ultraviolet-induced stress (Smirnoff, 2000). 

Organic acids usually contain a carboxylic acid group, -CO2H. L-Ascorbic acid, commonly known as Vitamin C, is an obvious exception. 

Electrostatic potential map for ascorbic acid shows positively-charged regions (in blue) as likely acidic sites. 

Examine atomic charges as well as the electrostatic potential map of ascorbic acid. Which hydrogen(s) is likely to be most acidic  

Obtain the energies of the various conjugate bases of ascorbic acid. Which one is the most stable Is it the base which results from deprotonation of the hydrogen you previously assigned as the most acidic  

Examine the structures and atomic charges for the various conjugate bases. How do they differ What distinctive features, if any, characterize the most stable conjugate base Draw all of the resonance contributors needed to account for the electron distribution and geometry of the most stable conjugate base. 

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Water treated with iodine can have any objectionable taste removed by treating the water with vitamin C (ascorbic acid), but it must be added after the water has stood for the correct treatment time. Flavored beverages containing vitamin C will... 

Figure 12.3 Effects of 6 weeks vitamin C (ascorbic acid) supplementation In both patients and controls (from Sinclair et al., 1991). Controls "O", no complications group - a complications group. P < 0.001 compared with 0 weeks in all groups. P < 0.05 compared with 3 weeks. P < 0.01 compared with 3 weeks.

Vitamin C (ascorbic acid) is present in green tea but only traces are found in black tea.112 Five cups of Japanese green tea provide 25 to 30% of the RDA. 

Well-characterized transition metal complexes of vitamin C (ascorbic acid) are rare, and a select number of these exhibit anticancer properties. Hollis et al. have described the first examples to be fully characterized by X-ray crystallography.316 Treatment of [Pt(H20)2L2]2+ (L = NH3, MeNH2 L2 = en, 1,2-chxn) with ascorbic acid gives either the mono- or bisascorbate species of the type cis-[PtL2(C2,Os-ascorbate)] (e.g., (125)) or m-[PtL2(C2-ascorbate)(03-ascorbate)], respectively. Interestingly, in both types of complexes, platinum(II) forms a bond with the C-2 atom of ascorbic... 

Antioxidants Reducing agents, such as vitamins C (ascorbic acid) and E (a-tocopherol), which scavenge toxic free radicals generated by oxidative reactions in the cell. 

Vitamin C (ascorbic acid) is probably the most known vitamin in the world. Its legendary fame is based on the two events its exceptionally important role in the treatment of scurvy and Linus Pauling s proposal to use the huge doses of ascorbic acid for the prevention of common cold. The latter proposal, based obviously on the antioxidant properties of ascorbic acid, generated numerous studies and was frequently disputed, but many people (me including) successfully apply ascorbic acid for the treatment of starting stage of common cold. 

Group-transfer reactions often involve vitamins3, which humans need to have in then-diet, since we are incapable of realizing their synthesis. These include nicotinamide (derived from the vitamin nicotinic acid) and riboflavin (vitamin B2) derivatives, required for electron transfer reactions, biotin for the transfer of C02, pantothenate for acyl group transfer, thiamine (vitamin as thiamine pyrophosphate) for transfer of aldehyde groups and folic acid (as tetrahydrofolate) for exchange of one-carbon fragments. Lipoic acid (not a vitamin) is both an acyl and an electron carrier. In addition, vitamins such as pyridoxine (vitamin B6, as pyridoxal phosphate), vitamin B12 and vitamin C (ascorbic acid) participate as cofactors in an important number of metabolic reactions. 

Choy et al. [193] reported that vitamin A (retinoic acid), vitamin C (ascorbic acid) and vitamin E (tocopherol) could be intercalated into Zn/Al LDHs by the coprecipitation method. In solutions, these vitamins are normally all sensitive to light, heat and oxygen, and it was proposed that incorporating the molecules into a layered inorganic lattice may lead to their stabilization, resulting in a wider range of potential apphcations. 

Vitamin C, ascorbic acid, is a coenzyme for the enzyme prolyl hydroxylase. The action of this enzyme is critical for the formation of normal collagen, a key component of structural and connective tissues. 

Vitamin C (ascorbic acid) is also a well-known antioxidant. It can readily lose a hydrogen atom from one of its enolic hydroxyls, leading to a resonance-stabilized radical. Vitamin C is acidic (hence ascorbic acid) because loss of a proton from the same hydroxyl leads to a resonance-stabilized anion (see Box 12.8). However, it appears that vitamin C does not act as an antioxidant in quite the same way as the other compounds mentioned above. 

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. 

Not all acids are dangerous and corrosive. Many acids, such as Vitamin C (ascorbic acid), are essential to health, Even our own bodies produce acids, particularly to help break down food in our digestive systems. 

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