Organizational consequences of the hydrophobic interaction

If otherwise hydrophobic molecules also contain hydrophilic groups, they become known as “amphiphilic” and they are then subject to a potent organizational effect, which orients each molecule so as to satisfy as far as possible the thermodynamic requirements of both parts of the molecule. One consequence is the formation of monolayers of oil on water, which has been of great historical importance in physics and chemistry, leading to the first determinations of molecular size, symmetry and flexibility. The most important role of this kind of organizational force, however, is in biology. Here amphiphilic phospholipid molecules are organized into bilayers that are essential to the very existence of a living cell, defining the boundary between the inside of a cell and its environment. The formation of specific structures of proteins, too, is dominated by the hydrophobic interaction: in this case the need to fold the protein in such a way (intricately, with many twists and turns) as to minimize contact between hydrophobic groups and the surrounding aqueous medium. It is not an exaggeration to say that hydrophobic interactions are essential for all aspects of the chemistry of life as we know it.