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Ascorbic Acid

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GENERAL FEATURES

Name: Ascorbic Acid
Generic Names:
Trade Names: Redoxon®[32]
IUPAC name:
Molecular Formula:
Molecular
Weight:
Structure: [1],[33],[34],[40]
Functional Group/chemical constitution:: It has dienol structure which imparts it powerful reducing ability[2]
Chemical
Nature:
A reductant[3]
electron donor[35] Water-soluble[4]
Pro-oxidant[5]
At physiological pH the predominant form of ascorbate is ascorbate monoion, which is a poor electron donor and oxidizes to the energetically unfavourable neutral free radical.

ascorbic acid is a water soluble ketolactone wthtwo ionizable hydroxyl groups. Ascorbate monoion is predominant fprm at physiological pH. Ascorbate readily undergoes two consecutive, one-electron oxidation to form ascorbate radical and dehydroascorbic acid. The ascorbic radical is relatively inreactive due to resonance stabilization of the upaired electron. it readily converts into ascorbate and dehydroascorbate.[35]
ascorbic acid is white crystallinepowder, extremely water soluble[35] The ascorbate dianion forms a relatively stable semihydroascorbate radical anion and is powerful electron donor; however present in insufficient concentration at neutral pH[3].
In neutral and basic solutions, the ascorbic acid anion is readily oxidized to form a trioxo radical anion. Most phenoxyl radicals oxidize ascorbic anion by electron transfer process; however radicals such as .CH2OH, phenyl and benzene para-semiquinone, meta-hydroxyphenyl do not oxidize ascorbic anion.[6]
easily gets oxidized, soluble in water , has two ionizable groups, is a good reducing agent[7]
mono-anion of ascorbate is the predominant form in all body compartments except the gastric juice[7]
semidehydroascorbate radical derived from it. by donating one electron, has low reactivity; loss of second electron converts this radical into unstable dehydroascorbate[7]
Its a alpha-ketolactone. At physiological pH, ascorbate exists as the monovalent hydroxyl anion[1]
Also, at physiological pH, ascorbic acid (pKa, 4.2) is largely found in the anion form[8]
ascorbic acid is unstable in water and is readily oxidized under atmosphere[36]
Source: Paprika(Capsicum annuum) contains ascorbic acid in relatively large quantities and its isolation from it is fairly simple[9].
Ascorbic acid is synthesized in rodent liver, circulates in blood and is concentrated in the brain[10]
Lemon juice[11].
citrus fruits and dark-green leafy vegetables are the richest source[1]
Cellular Functions: Ascorbate keeps prosthetic metal ions and certain enzymes in their reduced form by acting as a reductant. Ascorbate protects tissues from oxidative damage by acting as free radical scavenger[12]
Ascorbic acid is suggested to have a role in lowering body’s exposure to endogenously produced mutagens[13]
Ascorbic acid participated in the detoxification of compounds by hydroxylation and maintains the cytochrome P 450 levels in liver.
Ascorbic acid is necessary for absorption and accumulation of iron and efficient functioning of immune system[14].
Ingestion of 2 and 3 g ascorbate daily enhanced neutrophil motility to a chemotactic stimulus of endotoxin-activated serum in normal volunteers[15]
Acts as a enzyme cofactor, generally for enzymes like monooxygenase or dioxygenase[1]
Ascorbic acid reported to be appeared important for normal attachment of polyribosomes to the endoplasmic reticulum[8]
vitamin C is required as a co-factor in some oxidation reactions requiring molecular Oxygen[37]
Actions & Indications: Pharmcological Action-
Free radical scavenger[12], [16] Chain-breaking antioxidant[4], [17]. Pro-oxidant activity[17].
exhibits Oxygen-detoxifying nature[38] Therapeutic benefits:
Vitamin C containing food is found to have associated with lower risk for particulary gastric and esophageal cancer[18].
beneficial effects of vitamin C supplementation for wound healing, cancer and catarect prevention, atherosclerosis prevention and enhances immune mechanism is observed[1]
Preclinical Data:
In radiotherapy of human abdominal cancers, prophylactic use of ascorbic acid is suggetsed to reduce the damage to GI tract [36] Ascorbic acid 3 gm daily regressed rectal polyp in a patient with familial polyposis[19] .
ascorbic acid, in forebrain mitochondria isolated from rats, protected from ischemia/reperfusion injury when administered prior to onset of ischemia[20].
supplemental ascorbate, 10g/day, when given to terminal cancer patients, mean survival time of patients increased significantly[21]
1g vitamin C daily for 28 days, in patients with benign peptic ulcer, exhibited protective effect against development of gastric cancer, due to its effect on DNA adduction[39] Ascorbic acid prophylaxis in coal-tar workers reduced frequency of chromosome aberrations exposed to benzene in peripheral blood lymphocytes[22]
ascorbic acid supplements has been shown to lower the incidence and severity of common cold[23]; however controveries exist to this observation[24].
ascorbic acid anion form is believed to provide protection against hepatotoxicity induced by dimethylnitrosamine[8]
Ascorbic acid has been in use as a urinary acidifying agent[25]
It is advised to a rescue team members to promptly take ascorbic acid orally whhile rescuing victims from a radiation-contaminated area just after a radiation accident or terrorism[36]
Notes: Ascorbic acid from adrenal glands retained its activity even after five times recrystallization [9]
Ascorbic acid readily found to disappear from the adrenal gands of Guinea pigs when kept on a vitamin-C free diet[9]
In a study with two species of spiny mice(Acomys russatus), high concentration of ascorbic acid in eye lens is suggested to be an adaptation that permits eye to wistand increase solar radiation[26].
6-Bromo- and 6-chloro-6-deoxy derivatives of ascorbate anion are able to transfer an electron to the oxidizing radicals .OH, Br2.- and RS[27]
vitamin C has very short life in tissue culture media[28]
Some female guinea-pigs were observed to be able to readjust their ascorbic acid metabolism in times of deficiency[29]
derivatives: The palmitoyl derivative of ascorbic acid 2-glucoside, 6-palmitoyl ascorbic acid-2-glucoside, acts as a radioprotector under in vitro, ex vivo and in vivo models. Protected cellular DNA in spleen, bone marrow, blood from gamma radiation(6 Gy)[30]
High concentration of vitamin C is shown in vitro to participate in production of hydroxyl free radicals through a Fenton reaction[31]
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