Interaction of dipalmitoyl phosphatidylcholine with n-hexadecanol in monolayer and liposome

The monolayer collapse behavior of n-hexadecanol/dipalmitoyl phosphatidylcholine (DPPC) was investigated in this study at the air/water interface at 37 °C. Surface pressure variations with time for the mixed monolayers of DPPC with 20 mol% and 50 mol% n-hexadecanol at corresponding collapse points were recorded by a Langmuir trough system. In addition, the interaction of n-hexadecanol with a pure DPPC monolayer was identified by fluorescence microscopy (FM). The results demonstrated distinct differences between these systems; according to our observation, the higher the ratio of n-hexadecanol to DPPC, the more nucleation domains can be induced. The FM images demonstrated that pronounced domain formation was associated with a longer relaxation time of the collapsed DPPC and DPPC/nhexadecanol monolayers, and the presence of n-hexadecanol appeared to enhance the relaxation processes. The liposome was prepared by the thin-film hydration method. The average diameter of DPPC and DPPC/n-hexadecanol liposomes was investigated by dynamic light scattering. It is shown that the diameter of DPPC liposome with n-hexadecanol is smaller than pure DPPC liposome at the initial state. After 24 hours, DPPC/n-hexadecanol liposome became larger than pure DPPC liposome and lasted for the next four days. The effects of a greater ratio of n-hexadecanol did not play an important role in DPPC liposome formation based on our dynamic light scattering analysis. Our result demonstrated that n-hexadecanol might affect the DPPC liposome stability. The increased ratio of n-hexadecanol in DPPC liposomes could only a play a minor role in DPPC liposome fusion.