Tannins

Tannic compounds or tannins

Tannins are generally non-glycosylated molecules (although there are exceptions), which owe their name to the ability to precipitate proteins. From the molecular and structural point of view tannins are different compounds, but they have the same properties; an example is saponins, glucosylated molecules where aglycone can be either steroidal or triterpene.

In the case of tannins, there are: hydrolysable tannins deriving from gallic acid (C6-C1), used in cosmetics, and condensed tannins deriving from flavonoids, strong passive plant defense agents.

Hydrolyzable tannins or gallotannins are high molecular weight polymers of gallic acid, in particular they are polyphenols; they are called hydrolysable because they can be attacked and depolymerized by an enzyme, called tannase. These tannins are structurally different from condensed tannins, although both are high molecular weight polymers.

The condensed or catechinic tannins are polymers of more complex molecules, C6-C3-C6, and their monomeric unit is catechin, which has the same formula C6-C3-C6 as flavonoids.

Although the two categories present a different molecular structure, they both originate from cinnamic acid; while this derivation is more evident for the hydrolysable tannins, it is less evident for the catechinic tannins; in reality the latter derive from the stabilization of hydroxycinnamic acid, which - by presenting two hydroxyl groups - cycles to lactone or pyranic ring (C6-C3), which binds to another complex C6 variously hydroxylated, forming the catechin monomer. Monomer that also characterizes the flavonoid active principles. The policatechins are not hydrolizable by tannase, being structurally more complex molecules.

The properties ascribed to tannic compounds, whether they are gallotannins or catechinic tannins, are different:

- astringent: determined by an arrest of glandular secretion, a decrease in the permeability of membranes and capillaries, and by vasoconstriction, which reduces the metabolic work of the tissues, with an anti-inflammatory action.

-emostatic: determined by a vasoconstriction of the vessels and by the precipitation of the blood properties in favor of the formation of the thrombus. This action was used for tanning leather.

-antibiotic, antiviral and antifungal: carried out by polyphenols; in particular tea is rich in it.

- antidiarrheal: inducing a reduction in intestinal peristalsis.

- anti-inflammatory: the formation of a small clot protects the tissue from further inflammatory states.

Examples of tannin drugs are:

Witch Hazel

Arnica

Rathany

Tormentilla