Abstract: The egg yolk phosphatidylcholine(PC) liposomes loaded with bufalin(BF) were prepared so as to improve BF's therapeutic effect. The effects of BF on PC model membrane have been examined using the ³¹P NMR spectroscopy. The results show that the incorporation of BF into PC liposome can stabilize the lipid bilayer structure of PC, with the basal linewidth of the ³¹P spectrum increasing with increasing the content of BF in liposome. This may be related to the formation of hydrogen bonding between BF and polar headgroup of PC, or insertion of BF into PC by hydrophobic interaction. On the other hand, it was found for the first time that after exposure to ultrasonic waves, pure PC shows an additional narrow peak at the isotropic chemical shift (i.e., about 0.23ppm) in its ³¹P spectrum which corresponds to the mobile lipidic particles, e.g., micelles or small resicles, and furthermore, the addition of BF can significantly trigger such a transition from the phospholipid bilaryer to the micellar phase. This could be explained by the insertion of BF into the micellar phase or the formation of mobile BF-PC complexes. These studies demonstrate that the presence of BF has two-sided effect on the membrane structure of PC, depending on the preparation conditions of the liposome. Therefore, on preparing the BF-loaded liposome, partial attention should be paid to the potential influence of the preparation conditions on the structure and then physiochemical properties of the liposome, in addition to the effects of the medicine itself.

Key words: Bufaln, Phosphatidylcholine, Liposome, Ultrasonic dispersion, ³¹P NMR