Study of domain shapes and orientational structure of phospholipid monolayers using Maxwell displacement current and Brewster angle microscopy

Experiments were conducted on Langmuir monolayers composed of chiral dipalmitoyl-phosphatidylcholine (D-DPPC and L-DPPC) molecules and racemic DPPC (DL-DPPC) molecules by Maxwell displacement current (MDC) measurement and Brewster angle microscopy (BAM) to examine the orientational structure and domain shapes of monolayers. The MDCs generated from chiral DPPC monolayers during monolayer compression resembled each other, indicating that the molecular chirality does not have a direct effect on the generation of MDC. The domain shapes of chiral DPPC monolayers depended on the molecular chirality. On the other hand, the MDC generated from racemic DPPC monolayers was different from that generated from chiral DPPC monolayers at the beginning of the pressure plateau, suggesting an effect of molecular chirality. Interestingly, a spanner-like domain shape of racemic DPPC monolayers was discovered. We suggest that phase separation within the domain by monolayer compression is responsible for the formation of this domain shape.