Hydrophobic effect

The tendency of nonpolar substances to aggregate in water because their presence constrains water’s molecular arrangements. It helps drive the formation of membranes and the folding of many proteins.

Hydrophobic hydration: The organization of water molecules around a nonpolar solute dissolved in water. It describes the local water structures whose reorganization drives aggregation.
Protein folding: The process by which a protein adopts its functional three-dimensional structure. Burial of nonpolar residues is a major contribution to folding stability.
Gibbs free energy: A thermodynamic potential that predicts the spontaneity of processes at constant temperature and pressure. Hydrophobic association is favored when it lowers the system’s Gibbs free energy.
Hydrophilicity: The tendency of a substance to interact favorably with water. Hydrophilic groups remain compatible with water rather than clustering to reduce exposure.
Hydrophobic hydration free energy: The free-energy cost of transferring a nonpolar solute from a nonpolar environment into water. Its temperature and size dependence reveal the thermodynamics behind the effect.
Lipid bilayer: A double layer of amphiphilic lipids with hydrophilic surfaces and a nonpolar interior. The effect helps organize lipid tails away from water into a membrane interior.
Entropy: A thermodynamic quantity that measures the dispersal of energy and the number of accessible microscopic states. Changes in water’s accessible arrangements contribute to hydrophobic free-energy changes.
Van der Waals force: A family of weak intermolecular attractions arising from permanent or fluctuating electric multipoles. These direct molecular forces are distinct from the solvent-mediated hydrophobic effect.
Hydrophobic hydration shell: The layer of water molecules whose structure and dynamics differ from bulk water near a nonpolar surface. This interfacial layer is where water responds to exposed nonpolar groups.
Micelle: A roughly spherical aggregate of amphiphilic molecules, with nonpolar portions sheltered from water. Micelles form when amphiphiles reduce exposure of their nonpolar parts to water.

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