Phosphatidylcholine monolayers observed with Brewster angle microscopy and π-A isotherms

Abstract

Monolayers of distearoyl phosphatidylcholine (DSPC), dimyristoyl phosphatidylcholine (DMPC), and mixtures of these phospholipids, and distearoyl phosphatidylcholine (DPPC), were observed at the air–water interface with Brewster angle microscopy. Their properties were compared to π-A isotherms. The length of the alkyl chain of phosphatidylcholine affected the morphological properties. At low surface pressure DSPC and DPPC formed the condensed domain; however, DMPC did not form a condensed domain and displayed a larger limiting area per molecule than DSPC. When DSPC and DMPC were mixed together at the same concentration, the property of the spread monolayer in a π-A isotherm was more likely to be DMPC; however, the BAM images were different from that of DMPC or DSPC at various surface pressures. The phase in π-A isotherms was not necessarily the same as the BAM images. Even when surface pressure increased with compression, a small collapse was observed in a microscopic region by BAM.