amphipathic

Amphipathic, also called amphiphilic, describes molecules that contain both hydrophilic and hydrophobic regions. The hydrophilic part is polar or charged and interacts well with water, while the hydrophobic part is nonpolar and tends to avoid water.

Common examples include phospholipids, which have a hydrophilic head group and hydrophobic fatty acid tails, and many detergents that feature a polar head and a nonpolar tail. Some proteins and peptides also display amphipathic character when certain regions are hydrophobic on one side and hydrophilic on the other.

Amphipathicity influences how molecules behave in aqueous environments. Hydrophobic regions tend to cluster away from water, while hydrophilic regions remain exposed to water, driving the formation of micelles, vesicles, or lipid bilayers. In cell membranes, phospholipids arrange into a bilayer with hydrophobic cores shielded from water.

In proteins, amphipathic alpha helices or beta sheets present segregated faces that favor interactions with membranes or other biomolecules, guiding localization and function.

This property underpins many applications, including drug delivery, emulsification, and detergency. It is characterized in part by the tendency to form micelles or bilayers and by how molecules partition between lipid and aqueous phases. Amphipathicity is a central concept in chemistry, biochemistry, and cell biology, reflecting how molecular structure governs interactions with water and with lipid environments.