The absorption of paclitaxel through cell membrane and the preparation of paclitaxel liposome are closely related with interactions between paclitaxel and lipids. The interactions between paclitaxel and dipalmitoyl phosphatidylcholine (DPPC) in mixed monolayers at the air/water interface have been studied by langmuir technique and atomic force microscopy (AFM). The surface pressure-area (π-A) curves have been measured. The miscibility analysis, thermodynamic stability analysis and compressibility analysis have been carried out based on π-A curves. The results indicate that paclitaxel and DPPC are miscible, repulsion exists between different molecules, and phase separation appears in mixed monolayers. Except for x_pac (paclitaxel mole fraction x_pac＝0.4, all these states increase with the compression of monolayers to a certain extent and then start to decrease. For x_pac＝0.4, the miscibility, repulsion and phase separation always increase with the compression of monolayer, and are much greater than those for all the other mixed monolayers with different x_pac. For x_pac＝0.4, the influence of the interactions between different molecules on these states is much greater than the effect of the extent of the compression of monolayer. For x_pac≤0.4, paclitaxel has a little influence on the structure of DPPC monolayer|for x_pac＞0.4, the structure of DPPC monolayer is destroyed seriously. The morphology of paclitaxel/DPPC monolayers has been observed by AFM and is consistent with the conclusion obtained by langmuir study.

Key words: paclitaxel, langmuir monolayer, thermodynamic stability, compressibility, AFM observation