Define hydrophobic interactions

Hydrophobic interactions refer to the tendency of nonpolar molecules or regions of molecules to aggregate together in an aqueous environment, driven by the energetically favorable interactions between hydrophobic ("water-fearing") molecules. While the term "hydrophobic" literally means "water-fearing," it does not imply an aversion to water; rather, it describes a lack of affinity for water molecules due to the absence of polar or charged groups that can form favorable interactions with water.

In aqueous solutions, water molecules form a network of hydrogen bonds with each other, creating a highly structured environment. When nonpolar molecules or regions of molecules are introduced into this aqueous environment, they disrupt the hydrogen bonding network due to their inability to form hydrogen bonds with water. As a result, water molecules surrounding the nonpolar molecules are no longer able to form hydrogen bonds with them, leading to an increase in the entropy of the system.

To minimize the disruption to the hydrogen bonding network and maximize the entropy of the system, nonpolar molecules or regions of molecules tend to aggregate together, forming clusters or assemblies in which hydrophobic surfaces are shielded from contact with water molecules. This aggregation reduces the area of hydrophobic surface exposed to water, thereby minimizing the unfavorable interactions between water and hydrophobic molecules.

In biological systems, hydrophobic interactions play a crucial role in the folding of proteins and the assembly of lipid membranes. In proteins, hydrophobic amino acid side chains tend to cluster together in the protein core, away from the aqueous environment, contributing to the stability of the folded protein structure. In lipid membranes, hydrophobic interactions drive the self-assembly of phospholipid molecules into bilayers, with hydrophobic lipid tails facing inward and hydrophilic lipid heads facing outward, effectively excluding water from the hydrophobic interior of the membrane.

Overall, hydrophobic interactions are an important driving force in biological processes, contributing to the folding of proteins, the assembly of lipid membranes, and the formation of macromolecular complexes.