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Chemical and Biological Properties of Vitamin C
L-ascorbic acid, or vitamin C
(CAS #: [50-81-7]; MW=176.1; mp=193°C [dec]), is a natural
compound, whose peculiar antioxidant properties are used in
biological systems and for the conservation of several different
manufacts (1).
The ascorbic acid molecule (see Fig. 1) contains four hydroxyl
groups in positions 2, 3, 5 and 6; the -OH group in position 3 is
acidic (pKa,3=4.2), the hydroxyl in position 2 has pKa,2=11.6,
while those in position 5 and 6 behave as a secondary and primary
alcoholic residue respectively (2).
Vitamin C is very sensitive to even slight heating, to the
light, and to the action of oxidizing agents and metal
ions.Vitamin C is readily oxidized, especially in aqueous
solutions, by reacting with atmospheric oxygen, and behaves as a
two-electron donor:
Ascorbic acid is active in many biological processes; it
maintains prolyl hydroxylase in an active form by preserving its
iron atom in the reduced Fe2+ state, and it keeps
collagen in a sufficiently hydroxylated form preventing skin
lesions and blood-vessel fragility that are so prominent in
scurvy (3).
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