S: NCBI – https://pubmed.ncbi.nlm.nih.gov/?term=alkaloid (last access: 15 July 2020); SDir – https://www.sciencedirect.com/topics/chemical-engineering/alkaloid (last access: 15 July 2020).
N: 1. 1831, from “alkali” (q.v.) + “-oid”. “A general term applied to basic compounds of vegetable origin, bitter in taste, and having powerful effects on the animal system” [Flood], including morphine and nicotine. As an adjective by 1859.
Frequent use in plural: alkaloids.
2. Alkaloid, any of a class of naturally occurring organic nitrogen-containing bases. Alkaloids have diverse and important physiological effects on humans and other animals. Well-known alkaloids include morphine, strychnine, quinine, ephedrine, and nicotine.
3. Alkaloids are found primarily in plants and are especially common in certain families of flowering plants. In fact, as many as one-quarter of higher plants are estimated to contain alkaloids, of which several thousand different types have been identified. In general, a given species contains only a few kinds of alkaloids, though both the opium poppy (Papaver somniferum) and the ergot fungus (Claviceps) each contain about 30 different types. Certain plant families are particularly rich in alkaloids; all plants of the poppy family (Papaveraceae) are thought to contain them, for example. The Ranunculaceae (buttercups), Solanaceae (nightshades), and Amaryllidaceae (amaryllis) are other prominent alkaloid-containing families. A few alkaloids have been found in animal species, such as the New World beaver (Castor canadensis) and poison-dart frogs (Phyllobates). Ergot and a few other fungi also produce them.
4. The function of alkaloids in plants is not yet understood. It has been suggested that they are simply waste products of plants’ metabolic processes, but evidence suggests that they may serve specific biological functions. In some plants, the concentration of alkaloids increases just prior to seed formation and then drops off when the seed is ripe, suggesting that alkaloids may play a role in this process. Alkaloids may also protect some plants from destruction by certain insect species.
5. The chemical structures of alkaloids are extremely variable. Generally, an alkaloid contains at least one nitrogen atom in an amine-type structure—i.e., one derived from ammonia by replacing hydrogen atoms with hydrogen-carbon groups called hydrocarbons. This or another nitrogen atom can be active as a base in acid-base reactions. The name alkaloid (“alkali-like”) was originally applied to the substances because, like the inorganic alkalis, they react with acids to form salts. Most alkaloids have one or more of their nitrogen atoms as part of a ring of atoms, frequently called a cyclic system. Alkaloid names generally end in the suffix -ine, a reference to their chemical classification as amines. In their pure form most alkaloids are colourless, nonvolatile, crystalline solids. They also tend to have a bitter taste.
S: 1. OED – https://www.etymonline.com/search?q=alkaloid (last access: 15 July 2020); SDir – https://www.sciencedirect.com/topics/food-science/alkaloid (last access: 15 July 2020). 2 to 5. EncBrit – https://www.britannica.com/science/alkaloid (last access: 15 July 2020).