C—Ascorbic Acid

Sources are citrus fruits and juices, melons, berries, and other fruits, peppers, broccoli, potatoes, and many other fruits and vegetables. 

The ability to synthesise ascorbic acid from glucose is absent in a small group of animal species that include man, primates, the guinea pig and the fruit-bat this is due to the absence of the gene that codes for one of the enzymes required for ascorbate synthesis. These species are therefore dependent on an external source of the vitamin in their diet and it is needed as a cofactor for several hydroxylase enzymes, notably the iron-dependent proline and lysine hydroxylases and the copper-dependent dopamine-(3-hydroxylase the function of ascorbate in these enzymes is likely to be its ability to keep the metal in the reduced form which is necessary for hydroxylation. The ability of ascorbate to reduce Fe3+ to Fe2+ is important in promoting the gastrointestinal uptake of iron and for its release from the iron store ferritin. 

Donation of one electron by ascorbate gives the semidehydroascorbate radical which on further oxidation gives dehydroascorbate, according to the scheme in Fig. 7. Dehydroascorbate is unstable and breaks down by a 

There are a number of mechanisms by which ascorbate may facilitate the removal of activated oxygen-derived molecules in vivo-, these include reaction with 0 2, HOj and OH , as well as the reduction of thiyl radicals (see section 5.1), 

The repair of organic radicals formed by ionizing radiation may also be of prime importance in radiation damage and it has been shown that ascorbate is an efficient scavenger in vitro of singlet oxygen which may be generated in vivo by the slow reaction of O2- with GSH discussed in section 5.1 [36]. 

Deficiency of ascorbate in the diet of animals that are unable to synthesise it gives rise to defects in collagen synthesis which in man results in the condition known as scurvey. No deficiency disease associated with the radical repair mechanism of action of the vitamin has been reported. 

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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... 

C Ascorbic acid Coenzyme in hydroxylation of proline and lysine in collagen synthesis antioxidant enhances absorption of iron Scurvy—impaired wound healing, loss of dental cement, subcutaneous hemorrhage... 

FIGURE 10.13 The TLC profiles of labeled peaks isolated from [U- C]ascorbic-acid-modified calf lens protein obtained from Bio-Gel P-2 chromatography. Peaks 2 to 7 were spotted on a preparative silica gel TLC plate and developed with ethanol/ammonia (7 3, v/v). The fluorescence in each lane was detected by irradiation with a Wood s lamp at 360 nm, and the pattern of radioactivity was determined by scanning the plate with AMBIS imaging system. (Reprinted with permission from Cheng, R. et al., Biochim. Biophys. Acta, 1537, 14-26, 2001. Copyright (2001) Elsevier.)... 

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. 

Reduction of dehydro-c-ascorbic acid phenylhydrazone (40) with LiAlH4 resulted in hydrogenation of the hydrazone residue and cyclization to bicyclic compound 41, which was dehydrogenated with boiling acetic anhydride during acetylation to give diacetate 43, then partly hydrolyzed to monoacetate 42 (Scheme 7) (72JOC3523). 

C Ascorbic acid Potatoes, leafy vegetables, fruits (especially rose hips, black berries, kiwi, strawberries) <1 yr 35 mg 1-19 yr 40 up to 70 mg >19 yr 70 mg pregnancy 90 mg lactating women 110 mg... 

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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