ABSTRACT

Stable lipid bilayers are formed in water only from amphiphilic molecules, i.e., those lipid molecules which have a hydrophilic polar headgroup in addition to hydrophobic hydrocarbon chains. Such amphipathic lipids can be classified according to their interaction with water:

1. Insoluble, nonhydrated lipids. This class does not disperse in water and exists as microcrystals or a coagel. The microcrystals are almost certainly of a bilayer form. Of the biologically relevant lipids considered here, this class includes certain phosphatidylethanolamines and glycolipids below their chain-melting temperatures. Often in these cases a metastable, hydrated gel phase will form on cooling below the chain-melting temperature, which reverts spontaneously on incubation to the less hydrated, crystalline form.