Amphiphilicity

Definition

Amphiphilicity refers to the property of some molecules to have an affinity to two phases and most notably in biochemical systems the affinity to both a polar solvent phase (in this case water) and hydrophobic phase (such as the interior of cell membranes or proteins). Amphiphilic molecules usually contain both hydrophobic (e.g., benzyl or alkyl) and hydrophilic groups (e.g., -OH, -NH₂ and -COOH). Amphiphilic molecules are often useful as surfactants. Sodium dodecylbenzene sulfonate is a typical amphiphilic molecule used as a laundry detergent or shampoo and complexes hydrophobic substances such as dirt and oil with its hydrophobic dodecylbenzene moiety (C₁₂H₂₅-C₆H₄-) and is dispersed by affinity of the sulfonate moiety (-SO₃H⁻) to water.

Amphiphilic molecules can assemble in various solvents. Phospholipids are typical amphiphilic biomolecules, having hydrophilic heads including phosphate ions or charged tertiary or quaternary amines and hydrophobic tails including fatty...