Gemini表面活性剂18-3-18与磷脂DPPC在气液界面的混合性质

Interaction between Dipalmitoylphosphatidylcholine and Gemini Surfactant(18-3-18)in Mixed Monolayers at Air-Water Interface

摘要:Gemini表面活性剂作为基因转染的非病毒载体受到国内外学者的广泛关注,其传递过程与细胞膜密切相关。通过Langmuir膜天平测得Gemini表面活性剂18-3-18与磷脂类表面活性剂DPPC混合膜的表面压力与平均分子面积(π-A)等温线,定量分析了平均分子面积(A_m)、混合单分子膜的过剩面积(A_(ex))、过剩吉布斯自由能(△G_(ex))、混合表面自由能(△G_(mix))及相互作用参数等,确定了单层膜的混合性质,并在此基础上研究了18-3-18与DPPC相互作用。用原子力显微镜(AFM)观察了相应LB膜的表面形貌。结果表明:18-3-18与DPPC的物质的量之比及膜压对单层膜的稳定性、热力学特性及它们之间的相互作用有显著影响。特别地,在X_(DPPC)为0.20和0.67时,18-3-18与DPPC混合膜的△G_(ex)和△G_(mix)出现了两个极值点,这表明在X_(DPPC)为0.20～0.67之间时,混合膜会出现相分离,与AFM结果一致。

As a non-viral vector in the gene transfection, of which the transfer process is closely associated with cell membrane, Gemini surfactant has become a major focus of research. In this work, the surface pressure-area per molecule （π-A） isotherms of the mixed monolayers of Gemini surfactant （18-3- 18） and dipalmitoylphosphatidylcholine （DPPC） were measured by Langmuir balance, and then the mean molecular area（Am）, excess area of mixed monolayers （△ex）, the excess Gibbs free energy （△Gex）, the Gibbs free energy of mixing （△Gmix） and the interaction parameter a were quantitatively examined. The mixed nature was determined, and the interaction between 18-3-18 and DPPC was further investigated. In addition, the morphologies of the corresponding LB films were observed by AFM. The results indicate that the stability and themodynamics of mixed monolayer of 18 3-18 and DPPC as well as their interactions were affected significantly by the molar ratio of 18-3-18 and DPPC and the surface pressure. In particular, two minima of △G, x and △Gmix for the mixed monolayer of 18-3-18 and DPPC appeared at XDPPC =0. 20 and 0.67, which indicated that the phase separation would occur in the range of 0.20-0.67. This is consistent with the observation by AFM.