MacDonald R C, Simon S A
Proc Natl Acad Sci U S A. 1987 Jun;84(12):4089-93. doi: 10.1073/pnas.84.12.4089.
Uncommon methods of formation and analysis of lipid monolayers have enabled the recognition of several monolayer states and the identification of that in which molecular organization corresponds closely to that of the bilayer. Monolayers were formed by continuously adding a solution of phospholipid [dimyristoyl phosphatidylcholine in hexane/ethanol, 9:1 (vol/vol)] to the air/water interface of a constant-area trough. This procedure generates unconventional surface pressure (pi)-surface concentration (gamma) isotherms, which for liquid-crystalline monolayers consist of straight lines with three prominent intersections, two of which are not apparent in conventional pi-A isotherms. The regions of linear change of pi are explicable in terms of the area dependence of alkyl chain entropy. The two breaks at lower pi delimit states in which both chains lie parallel to the surface. The third occurs at collapse, which corresponds to a true equilibrium for unstressed liposomes. Mechanical and thermodynamic properties of bilayers, particularly phase-transition parameters, correspond closely to those of monolayers with which they are in equilibrium.
脂质单分子层形成与分析的非常规方法，使得人们能够识别出几种单分子层状态，并确定其中分子组织与双分子层紧密对应的状态。通过将磷脂溶液[己烷/乙醇（体积比9:1）中的二肉豆蔻酰磷脂酰胆碱]连续添加到恒定面积水槽的空气/水界面来形成单分子层。此过程产生非常规的表面压力（π）-表面浓度（γ）等温线，对于液晶单分子层，其由具有三个显著交点的直线组成，其中两个交点在传统的π-A等温线中并不明显。π的线性变化区域可以根据烷基链熵的面积依赖性来解释。在较低π处的两个断点界定了两条链均与表面平行的状态。第三个断点出现在塌陷时，这对应于无应力脂质体的真正平衡。双分子层的力学和热力学性质，特别是相变参数，与处于平衡状态的单分子层的性质密切对应。
