Isotherms of Dipalmitoylphosphatidylcholine (DPPC) Monolayers: Features Revealed and Features Obscured

Valuable as they are, isotherms may display features that Pressure–area isotherms of dipalmitoylphosphatidylcholine are difficult to interpret, or may even be featureless under (DPPC) exhibit a two-phase region wherein domains of a liquidconditions where interesting things are happening. For examcondensed (LC) phase are dispersed in the less ordered liquidple, the nonhorizontal nature of the plateau exhibited in the expanded (LE) phase. Fluorescence microscopy has been used isotherms of many lipid monolayers (corresponding to the over the past years to visualize the shapes displayed by DPPC liquid-expanded (LE)/liquid-condensed (LC) phase transidomains throughout the coexistence region; characteristic domain tion) has remained cause for debate for over 25 years. Thus shapes include those resembling dimpled beans and S-like figures. additional techniques are often called upon to resolve or In this paper we show that the types and distributions of domain further probe the state of monolayer films. One technique shapes formed throughout the coexistence region depend sensi-