The Chemical Structure Of Vitamin C Chemistry

Vitamin C

Chemistry

L-ascorbic acid with empirical formula of (C6H8O6) is the trivial name of Vitamin C.

It is described chemically as 2-oxo-L-threo-hexono-1,4-lactone-2,3-enediol (Naidu , 2003).

L-ascorbic is a water soluble 6-carbon α-ketolactone with two enolic hydrogen atoms (Packer, 2002), while Ascorbyl palmitate which is the synthetic form is lipid soluble. Ascorbic acid is sensitive to air, light, heat and easily destroyed by prolonged storage and over processing of food (Naidu, 2003).

Chemical structure

Chemical structure of vitamin C

Biochemistry

Vitamin C is a six-carbon lactone that is synthesized from glucose in the liver of most mammalian species, but not by humans,

Therefore, it takes part as a co-factor in many enzymatic reactions, and also acts as a plasma localized anti-oxidant molecules (Farbstein, 2010).

The two major properties of vitamin C which make it an ideal antioxidant: First is the low one-electron reduction potentials of both ascorbate (282 mV) and its one-electron oxidation product, the ascorbyl radical (2174 mV) which is derived from the ene-diol functional group in the molecule. These low reduction potentials enable ascorbate and the ascorbyl radical to react with and reduce basically all physiologically relevant radicals and oxidants. For this reason, vitamin C has been said to be “at the bottom of the pecking order” (Carr and Frei, 1999). The second major property that makes vitamin C such an effective antioxidant is the stability of semidehydro-ascorbic acid or ascorbyl free radical(ASF) ,the species formed after the loss of one electron, with a half-life of 10−5 seconds and low reactivity of them (Carr and Frei, 1999;Packer, 2002; Padayatty et al., 2003).Once oxidized, ascorbate is turned into ascorbate free radical (AFR) a molecule that is relatively stable due to electron delocalization. Although AFR can donate another electron, it does not undergo further oxidation. Rather, it is reduced back to ascorbate via NADH-dependent

Most of it (80–90%) will be absorbed when the intake is up to 100 mg/day.

Eventhough ascorbic acid is a water soluble compound, easily absorbed, it is not stored in the body. The average half life of ascorbic acid in adult human is about 10–20 days, with a turn over of 1.0 mg/kg body and a body pool of 22 mg/kg at plasma ascorbate concentration of 50 μmol/ L. The major metabolites of ascorbic acid in human are dehydroascorbic acid, 2,3-diketogulonic acid and oxalic acid (Naidu, 2003 and Nantel, 2004). The main route of elimination of ascorbic acid and its metabolites is through urine. It is excreted unchanged when high doses of ascorbic acid are consumed (Naidu, 2003).

Figure 4: Catabolism of ascorbic acid (Naidu, 2003)

Dietary sources and recommendation of vitamin