hydrophobicitet

Hydrophobicitet, or hydrophobicity, is a term used in chemistry and biochemistry to describe the tendency of a molecule or a region of a molecule to avoid contact with water. Hydrophobic substances are typically nonpolar and lack charged groups; in water they tend to minimize surface exposure, leading to aggregation or separation from the aqueous phase. This behavior stems from the hydrophobic effect: water molecules form a more ordered structure around nonpolar groups, and expelling the nonpolar parts into an interior reduces the total water structure order, gaining entropy.

In biology, hydrophobicity drives the folding of proteins, where nonpolar amino acids cluster inside, and determines the association of membrane lipids with proteins. In materials science, hydrophobic surfaces repel water, influencing wettability, coating performance, and self-cleaning properties. The apparent hydrophobicity of a surface depends on context, including roughness and the surrounding liquid.

Measuring hydrophobicity can be done via contact angle on solids, partition coefficients between octanol and water, or hydrophobicity scales that assign values to functional groups or amino acids (e.g., Kyte-Doolittle, Wimley-White). Temperature, pH, ionic strength, and solvent composition can alter observed hydrophobic behavior.

Hydrophobicity contrasts with hydrophilicity, the affinity for water. Substances can be modified chemically to alter their hydrophobicity, enabling applications from drug delivery to detergent formulation. The concept is central to understanding molecular interactions, protein structure, and the behavior of colloids and biomembranes.