鞘氨醇与DPPC,DPPE单层膜的热力学特性及形态观察

A Monolayer Study on Thermodynamic Behavior and Morphology of D-Sphingosine with DPPC and DPPE

鞘氨醇(sphingosine)是生物体内合成鞘脂的母体化合物,是生物膜中的重要组分之一.通过分析表面压力和平均分子面积(π-A)等温线数据分别研究了鞘氨醇与二棕榈酰基磷脂酰胆碱(DPPC)和二棕榈酰基磷脂酰乙醇胺(DPPE)二元组分单层膜的热力学特性,并在恒定膜压下制备不同摩尔比例的混合脂膜用原子力显微镜进行观测.实验结果表明:(1)鞘氨醇与DPPC组成的系统中,XD-Sph=0.2,0.4,0.6时,过量分子面积与过量吉布斯自由能在所研究的表面压力下表现为负值,而当XD-Sph=0.8时,表现为正值;(2)鞘氨醇与DPPE组成的系统中,当表面压力π<25mN?m-1时,过量分子面积与过量吉布斯自由能在所研究的组分比例下表现为负值,当π≥25mN?m-1时为正值.混合单层膜的分子面积与表面吉布斯自由能决定了分子间的相互作用,当为负值时分子间相互作用表现为吸引力,出现凝聚现象;为正值时分子间相互作用表现为排斥力,促使单层膜出现相分离现象.过量吉布斯自由能值越小,单层膜的热稳定性越高.弹性系数曲线分析和AFM图片观测进一步验证了理论分析的结果.

As the precursor of sphingolipids, sphingosine is one of important constituents of cell mem- branes. In this work, the thermodynamic behavior,of mixed systems of D-sphingosine with 1,2-dipalmitoyl- sn-glycero-3-phosphocholine （DPPC） and 1,2-dipatmitoyl-sn-glycero-3-phosphoethanolamine （DPPE） has been investigated by analyzing the data of surface pressure-mean molecular area isotherms. The deposited Langmuir-Blodgett （LB） monolayers of different ratios were investigated with atomic force microscopy （AFM） under certain surface pressure. The results show that： （1） in D-sphingosine/DPPC system, the excess molecular area and excess Gibbs energy took on negative deviations from the ideal behavior at D-sphingo- sine ratios of XD_Sph=0.2, 0.4, 0.6 and positive values at Xo.Sph=0.8; and （2） as for D-sphingosine/DPPE systems, the excess molecular area and excess Gibbs energy displayed negative values at the surface pres- sure of ~r〈25 mN.m-1, and positive at zr〉~25 mN.m-I. The interaction of mixtures was determined by mo- lecular area and Gibbs energy. The negative deviations from ideality suggest attractive interaction between molecules, with aggregating phenomenon. Furthermore, positive deviation from linearity indicates repelling interaction between the two compounds, inducing phase separation. Moreover, the mixed monolayer is more stable if the value of excess Gibbs energy is lower. The compression and AFM experiments support the above findings effectively as well as interpretation.