Heterochiral Domain Formation in Homochiral α-Dipalmitoylphosphatidylcholine (DPPC) Langmuir Monolayers at the Air/Water Interface

alpha-Dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers at the air/water interface are an important biomimetic system. Previous studies using optical imaging have shown that enantiomerically pure DPPC molecules form periodical homochiral domains with close packing. However, it is unclear whether the chirality of these domains is stable or dynamic. Recently, we investigated the chirality of L-DPPC Langmuir monolayers using second-harmonic-generation linear dichroism (SHG-LD). The change in the degree of chiral excess (DCE) and its sign with time indicated that the chirality transformed from homochiral to heterochiral domains, with an associated change in handedness. Here we propose that hydrolysis of L-DPPC is responsible for the formation of the opposite chiral state. On the basis of quantum chemistry calculations and effective pair potential (EPP) theory, we give a molecular explanation for this transformation. These results provide an insight into the lipid monolayers that the chiral state of domains composed of chiral lipids is dynamic.