Tristram-Nagle S, Petrache H I, Nagle J F
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 USA. stn+@andrew.cmu.edu
Biophys J. 1998 Aug;75(2):917-25. doi: 10.1016/S0006-3495(98)77580-0.
This study focuses on dioleoylphosphatidylcholine (DOPC) bilayers near full hydration. Volumetric data and high-resolution synchrotron x-ray data are used in a method that compares DOPC with well determined gel phase dipalmitoylphosphatidylcholine (DPPC). The key structural quantity obtained is fully hydrated area/lipid A0 = 72.2 +/- 1.1 A2 at 30 degrees C, from which other quantities such as thickness of the bilayer are obtained. Data for samples over osmotic pressures from 0 to 56 atmospheres give an estimate for the area compressibility of KA = 188 dyn/cm. Obtaining the continuous scattering transform and electron density profiles requires correction for liquid crystal fluctuations. Quantitation of these fluctuations opens an experimental window on the fluctuation pressure, the primary repulsive interaction near full hydration. The fluctuation pressure decays exponentially with water spacing, in agreement with analytical results for soft confinement. However, the ratio of decay length lambda(fl) = 5.8 A to hydration pressure decay length lambda = 2.2 A is significantly larger than the value of 2 predicted by analytical theory and close to the ratio obtained in recent simulations. We also obtain the traditional osmotic pressure versus water spacing data. Our analysis of these data shows that estimates of the Hamaker parameter H and the bending modulus Kc are strongly coupled.
本研究聚焦于接近完全水合的二油酰磷脂酰胆碱（DOPC）双层膜。在一种将DOPC与已明确的凝胶相二棕榈酰磷脂酰胆碱（DPPC）进行比较的方法中，使用了体积数据和高分辨率同步加速器X射线数据。得到的关键结构量是在30℃时完全水合的面积/脂质A0 = 72.2±1.1 Ų，由此可得出双层膜厚度等其他量。0至56个大气压渗透压下样品的数据给出了面积压缩性KA = 188 dyn/cm的估计值。获得连续散射变换和电子密度分布需要对液晶涨落进行校正。对这些涨落的定量开启了一个关于涨落压力的实验窗口，涨落压力是接近完全水合时的主要排斥相互作用。涨落压力随水间距呈指数衰减，这与软约束的分析结果一致。然而，衰减长度λ(fl) = 5.8 Å与水合压力衰减长度λ = 2.2 Å的比值明显大于分析理论预测的2值，且接近近期模拟得到的比值。我们还获得了传统的渗透压与水间距数据。我们对这些数据的分析表明，哈梅克参数H和弯曲模量Kc的估计值紧密相关。
