DOPC/DPPC单层膜中分子间的相互作用及形态特征

利用Langmuir-Blodgett(LB)技术制备了不同表面压力下的1,2-二油酸-甘油-3-磷脂酰胆碱(DOPC)/1,2-二棕榈酸甘油-3-磷脂酰胆碱(DPPC)(摩尔比为1:1)和DOPC/DPPC/Chol(摩尔比为2:2:1)单层膜, 对单层膜内分子间的相互作用进行了热力学分析, 并用荧光显微镜和原子力显微镜对其形态进行了观测.热力学分析表明, DOPC与DPPC分子在单层膜结构中相互作用为排斥力, 诱导单层膜出现相变; DOPC, DPPC与胆固醇(Chol)间的相互作用均为吸引力, 当表面压力(π)大于18 mN/m时, DPPC与胆固醇的作用力大于DOPC.荧光显微镜观测表明, DOPC/DPPC单层膜出现明显相分离现象, 富含DPPC微区成“花形”结构, 且随着表面压力的升高微区逐渐增大, “花瓣”增多; 当胆固醇加入到DOPC/DPPC体系时, 单层膜相态由液相与凝胶相共存转变为液态无序相与液态有序相共存结构, 富含DPPC的微区形状从“花形”转变成“圆形”.原子力显微镜对单层膜的表征验证了荧光显微镜的观测结果, 表明胆固醇加入到DOPC/DPPC体系中对单层膜排列具有明显的影响, 压力和溶液状态等是影响脂膜结构的重要因素.

Molecular Interaction and Morphology of DOPC/DPPC Monolayer

Lipid membrane is widely used in simulation of the dynamic properties and structure characteristics of the biomembranes. We prepared the 1,2-dioleoy-sn-glycero-3-phosphocholine(DOPC)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine(DPPC)(1:1, molar ratio), DOPC/DPPC/Chol(2:2:1, molar ratio) monolayers via LB technique at different surface pressures. The interaction between molecules by the thermodynamic analysis method and the morphology were observed by fluorescence microscopy and atomic force microscopy(AFM). Thermodynamic analysis results show that the interaction between DOPC and DPPC is repulsive; it can induce phase separation in monolayers. Both DOPC and DPPC interact with cholesterol by attractive interaction. When the surface pressure is >18 mN/m, the force between DPPC and cholesterol is stronger than DOPC. There is obvious phase separation in the monolayers observation by fluorescence microscopy. The DPPC-enriched micro domains take on "flower-shaped" structure, and the size became larger and larger with increasing surface pressure. Add cholesterol to DOPC/DPPC system, the monolayer changes from gel-fluid phase to fluid-disordered and fluid-ordered phase coexistence structure. The DPPC-enriched domains shape from the "flower-shaped" into a "circular". Observations by AFM verified the results of fluorescence experiments. It can be concluded that the cholesterol has a significant impact on the arrangements of DOPC/DPPC monolayers, and pressure, state of solution are also important for forming the lipid membranes.