Ascorbic acid: Vitamin C

The fat-soluble vitamins are still generally referred to by their alphabetical names. On the other hand, the water-soluble vitamins are now for the most part usually given chemical names which have no relation to the alphabet. This became necessary when what was originally the B vitamin became a whole assortment of heterogeneous substances, distinguished by somewhat variable and uncertain subscripts of the letter B. At present the water-soluble vitamins include the clearly defined ascorbic acid (vitamin C) plus the vitamins of the B complex. Because of the fact that vitamin C is one substance, clearly defined and understood, we shall consider it first rather than in its alphabetical order.

Ascorbic acid is now well understood chemically and it can indeed be synthesized. The structural formula of the L-form is:

The L-form is much more potent than the D-form. Ascorbic acid is really an acid hexose sugar. Its acidity is due to the dissociation of an enolic hydrogen rather than to opening of the lactone ring.

Ascorbic acid is a strongly reducing substance, and because of this, it is easy to demonstrate its presence in cells and tissues. A standard method involves the reduction of silver nitrate. Because of its reducing power, there is doubtless a relation of ascorbic acid to the oxidative processes in cells, but there is still no clear understanding as to the exact function or functions of the vitamin in metabolism. In animals suffering from scurvy there is lack of intercellular material; presumably the cells enclosing the blood vessels are not held together as firmly as they should be and this is doubtless the cause of hemorrhage. Mucopolysaccharides are known to be important constituents of the cementing substances which hold cells together. In view of the fact that mucopolysaccharides are polymers of acid sugars, it is possible that ascorbic acid is involved in the synthesis of such substances. There is some indirect evidence for this. Normally in wound healing mucopolysaccharides are detectable in the healing tissues and may have considerable importance for the process. However, when the store of ascorbic acid is depleted, these substances do not appear.