QUANTUM-CHEMICAL AND STATISTICAL CALCULATIONS ON PHOSPHOLIPIDS
QUANTUM-CHEMICAL AND STATISTICAL CALCULATIONS ON PHOSPHOLIPIDS
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DOI：
10.1016/0009-3084(82)90049-4
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发表时间：
1982-01-01
影响因子：
3.4
通讯作者：
PEINEL, G
中科院分区：
文献类型：
--
作者：
FRISCHLEDER, H;PEINEL, G
使用经验势函数对磷脂酰乙醇胺（PE）和磷脂酰胆碱（PC）头基进行准统计构象计算。对于这两个系统，偶极矩的主要分量（约20D[德拜]）位于单层平面内，而法向分量（约-5D）较小并反映所产生的正表面电荷。头基静态排列上的分子静电势的模型计算表明，只有通过距离相关的介电常数来模拟水的屏蔽效应才能解释模型膜与离子的立体特异性相互作用。除了静态特性之外，磷脂还是高度流动的系统，可以通过模拟方法进行研究：蒙特卡罗（MC）和分子动力学（MD）。通过 MC 方法研究了层内 C16 烃链的协同重新取向。大多数扭转角位于反围平面区域，平均值为 1.4 个高斯缺陷/链。扭结形成的概率仅为 0.15，不能用来描述链条的柔韧性。 MD方法用于以简化的方式研究磷脂作为整体的动力学，近似为双圆柱体。对于密集液晶的特性，链的最近邻计数为 ncc = 5.46。动力学行为反映了平移扩散系数 DT = 3.6 .cntdot。 10-2 m2s-1，旋转扩散系数 DR = 1.2 .cntdot。分别为 109 rad2s-1。研究了由 1 个两性离子基团和 16 个水分子组成的系统（在二维上具有周期性边界条件）的 PE 头基层上方的水结构。发现了两个高度结构化的区域，其中含有多达 10 个水分子/脂质，可补偿头部基团的偶极子。
Using empirical potential functions quasi-statistical conformational calculations were performed on phosphatidylethanolamine (PE) and phosphatidylcholine (PC) head groups. For both systems the main component of the dipole moment (.apprx. 20 D [Debye]) lies within the plane of the monolayer, while the normal component (.apprx. -5 D) is smaller and reflects a resulting positive surface charge. Model calculations of the molecular electrostatic potential on a static arrangement of head groups show that only the inclusion of a simulated screening effect of water by a distance dependent dielectric constant gives an explanation of stereospecific interaction of model membranes with ions. Besides the static properties phospholipids are highly fluid systems, which can be studied by simulation methods: Monte Carlo (MC) and molecular dynamics (MD). The cooperative reorientation of a C16 hydrocarbon chain within a layer was investigated by the MC method. Most of the torsion angles are in the antiperiplanar region, with a mean value of 1.4 gauche defects/chain. Kink formation occurs with a probability of 0.15 only, which cannot be used to describe chain flexibility. The MD method was used to study the dynamics of phospholipids as a whole in a simplified manner, approximated by double cylinders. Characteristic for a densely packed liquid crystal, the nearest neighbor count of chains is ncc = 5.46. The dynamical behavior reflects the translational diffusion coefficient DT = 3.6 .cntdot. 10-2 m2s-1, and the rotational diffusion coefficient DR = 1.2 .cntdot. 109 rad2s-1, respectively. The water structure above a PE head group layer was studied for a system of 1 zwitterionic group and 16 water molecules with periodic boundary conditions in 2 dimensions. Two highly structured regions were found of up to 10 water molecules/lipid, which compensate the dipoles of the head groups.