eicos

Eicos is a combining form derived from the Greek eikosi, meaning twenty. In scientific nomenclature, the prefix eicos- (also rendered as eicosa- or icosa- in some contexts) indicates twenty carbon atoms or a twenty-carbon backbone. It is used across chemistry and biochemistry to name molecules with twenty-carbon chains or rings.

In biochemistry, the term eicos- appears in the word eicosanoids, a family of bioactive lipids derived from twenty-carbon fatty acids such as arachidonic acid (C20:4). Eicosanoids include prostaglandins, thromboxanes, leukotrienes, and lipoxins. They function as local signaling mediators involved in inflammation, immunity, vascular tone, and hemostasis. Their synthesis typically involves enzymes such as cyclooxygenases, lipoxygenases, and cytochrome P450 pathways, and their effects are usually rapid and short-lived.

Chemical examples illustrating the use of the prefix include eicosane, a saturated alkane with 20 carbon atoms (C20H42); eicosanoic acid (arachidic acid), a twenty-carbon saturated fatty acid (C20:0); and eicosapentaenoic acid (EPA), a twenty-carbon polyunsaturated fatty acid (C20:5). The prefix eicos- is common in systematic chemical names to denote twenty-carbon structures and is not tied to a single substance.

Etymology and usage: The root comes from Greek, reflecting molecular size rather than a specific function. In practice, eicos- appears in naming conventions for a wide range of twenty-carbon compounds, including lipids, hydrocarbons, and related metabolites.