Laboratory of Quantum and Computational Chemistry, Department of Physical Chemistry, Faculty of Chemistry, University of Sofia, 1 James Bourchier Avenue, 1164 Sofia, Bulgaria.
Langmuir. 2010 Jun 1;26(11):8093-105. doi: 10.1021/la9047352.
Atomistic modeling of insoluble monolayers is currently used to inspect their organization and electric characteristics, providing a link between theory and experiment. Extensive molecular dynamics simulations at 300 K were carried out for model films of the lipids dipalmitoylphosphatidylcholine (DPPC) and dicaprin (DC) at the air/water interface. Surface concentrations corresponding to a set of points along the surface pressure/area isotherms of the surfactants were considered. The models contained 25 or 81 lipid molecules in hexagonal arrangement and explicit aqueous media (TIP3P) treated in periodic boundary conditions. Molecular dynamics simulations based on a classical force field (CHARMM27) were carried out and key characteristics of the studied films were estimated. The dielectric properties of the films in normal and tangential direction were quantified by means of dipole moment magnitude and orientation analysis and by monolayer dielectric permittivity. The contributions of lipids and interfacial water to each component of the considered characteristics were assessed and their variations upon film compression were discussed and compared for the two monolayers and to earlier results. The dielectric permittivity tensors were analyzed. Electrostatic potential profiles across the layers and surface pressure values were used for more detailed clarification of experimental measurements. The results show dissimilar behavior of the two lipids at the air-water interface. While the average electric and dielectric properties of DPPC monolayers result from opposite surfactant and water contributions, the two subsystems are synergetic in the DC films. The anisotropy of the monolayer dipole moment and dielectric permittivity is explained by domination of a different subsystem in the various components. Tangential characteristics turn out to be more sensitive to the size of the model and to the degree of film compression.
目前，人们使用非溶性单层的原子模型来检查它们的组织和电特性，从而在理论和实验之间建立联系。在 300 K 下，对在空气/水界面处的二棕榈酰磷脂酰胆碱（DPPC）和二辛酸酯（DC）模型膜进行了广泛的分子动力学模拟。考虑了表面压力/面积等温线上一系列点对应的表面浓度。这些模型包含了 25 或 81 个以六方排列的脂质分子和以周期性边界条件处理的明确水介质（TIP3P）。基于经典力场（CHARMM27）的分子动力学模拟得以进行，并且对所研究的膜的关键特性进行了估算。通过偶极矩大小和取向分析以及单层介电常数，定量地量化了膜在正常和切向方向上的介电特性。评估了膜中脂质和界面水对所考虑特性各个分量的贡献，并讨论了它们在两个单层上以及与早期结果相比在膜压缩时的变化。分析了介电常数张量。通过跨层的静电势分布和表面压力值，对实验测量结果进行了更详细的澄清。结果表明，这两种脂质在空气-水界面上的行为不同。虽然 DPPC 单层的平均电和介电特性来自相反的表面活性剂和水的贡献，但在 DC 膜中，这两个子系统是协同作用的。单层偶极矩和介电常数的各向异性可由不同子系统在各分量中占主导地位来解释。切向特性被证明对模型的大小和膜压缩的程度更为敏感。
