What Are the Characteristics of Alkaloids?

Ⅰ. Understanding alkaloids

Alkaloids are a class of nitrogen-containing alkaline organic compounds present in living organisms (mainly plants). Most of them have a complex ring structure, nitrogen is mostly contained in the ring, and has significant biological activity. It is one of the important active ingredients in Chinese herbal medicine. Such as berberine (berberine) in Coptis chinensis, ephedrine in ephedra, reserpine in Raufwort, camptothecin in camptotheca, vincristine in periwinkle, etc.

Ⅱ. What are the characteristics of alkaloids?

1. Most alkaloids are crystalline substances with a bitter taste, and a few are liquids (such as nicotine and arecoline).

2. The general alkaloids are colorless and optically active (most of them are left-active). But there are a few exceptions, such as berberine is yellow, piperine has no optical activity, individual alkaloids are volatile, such as ephedrine.

3. Most alkaloids show alkaline reaction: Pharmasources collects and sorts out the alkalinity of alkaloids, which is closely related to the state of nitrogen atoms in their molecules. Generally, quaternary ammonium base > secondary amine base > tertiary amine base. If the nitrogen atom is in the amide state, the alkalinity is very weak or disappears; some alkaloid molecules have phenolic hydroxyl or carboxyl groups, so they have acid-base amphoteric; although the alkalinity of alkaloids is strong or weak, it is generally compatible with inorganic alkaloids. Acids (hydrochloric acid, sulfuric acid) or organic acids (tartaric acid) combine to form salts.

4. Most of the alkaloids are insoluble or insoluble in water, but soluble in organic solvents such as ethanol, chloroform, ether, and benzene. In addition to being soluble in ethanol, alkaloid salts have the opposite solubility to alkaloids. Due to this property, alkaloids can be dissolved in an acidic solution (alkaloids and acids are combined into salts and dissolved in water). If an alkali is added to this acidic solution to make it alkaline, the alkaloid salts will become free organisms. The base is precipitated from the aqueous solution. The solubility of alkaloids is often used for extraction, separation and purification when preparing Chinese herbal medicines containing alkaloids. Another few types of alkaloids are soluble in water but their salts are insoluble, such as berberine, ephedrine soluble in water and organic solvents, and quaternary ammonium alkaloids are easily soluble in water.

5. General alkaloids can be combined with some special reagents (called alkaloid reagents, often heavy metal salts or double salts with larger molecular weight) and special inorganic acids (such as silicotungstic acid, phosphotungstic acid, or organic acids such as bitterness) acid solution), resulting in the formation of water-insoluble salts and precipitation. This property can be used to check whether Chinese herbal medicines contain alkaloids and to isolate alkaloids.