Neutron reflectivity and atomic force microscopy studies of a lipid bilayer in water adsorbed to the surface of a silicon single crystal
Neutron reflectivity and atomic force microscopy studies of a lipid bilayer in water adsorbed to the surface of a silicon single crystal
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DOI：
10.1021/la950580r
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发表时间：
1996-03-06
期刊：
影响因子：
3.9
通讯作者：
Gawrisch, K
中科院分区：
文献类型：
--
作者：
Koenig, BW;Kruger, S;Gawrisch, K
用中子的镜面反射表征了从水溶液中吸附在平面硅表面的单脂双层膜的结构。我们使用了一种新的实验装置，它显著减少了非相干背景散射，并允许我们测量低至5×10(-7)的中子反射率。厚度和中子散射长度密度是通过使用(I)由参数B-样条表示的随机生成的光滑函数和(Ii)基于理论脂组成的阶跃函数的拟合过程来确定的。用原子力显微镜测定其表面脂结构域的大小和表面复盖度。在(H2O)-H-2和(H2O)-H-2和H2O的混合物中，研究了与硅的散射密度相匹配的链质子化和氚代双棕榈酰磷脂酰胆碱(DPPC)双层膜。此外，还对具有较长酰基链的双硬脂酰磷脂酰胆碱双层进行了一次测量以供比较。脂质以连续层的形式吸附在硅表面，中间有大小为100-500埃的不规则形状的未复盖区域。表面覆盖率估计为70+/-20%。DPPC在60℃时的反射率测量表明，氧化硅层的厚度约为4埃，氧化硅和脂类之间的粗糙氧化硅/水层厚度在2到8埃之间，以及单一的脂类双层。拟合解析出一层厚度为28+/-2埃的中心膜层，它代表脂族碳氢链。这一层夹在脂头基团的界面膜层和厚度为11.5+/-1埃的水之间。随着脂类的相态和碳氢链长度的变化，很容易检测到中央膜层的埃尺度厚度变化。
Specular reflection of neutrons has been used to characterize the structure of single lipid bilayers adsorbed to a planar silicon surface from aqueous solution. We used a novel experimental setup which significantly decreased the incoherent background scattering and allowed us to measure neutron reflectivities as low as 5 x 10(-7). Thicknesses and neutron scattering length densities were determined by a fitting procedure using (i) randomly generated smooth functions represented by parametric B-splines and (ii) stepped functions based on the theoretical lipid composition. The size of lipid domains at the surface and the degree of surface coverage were determined by atomic force microscopy. Chain-protonated and -deuterated dipalmitoylphosphatidylcholine (DPPC) bilayers were investigated in (H2O)-H-2 and a mixture of (H2O)-H-2 and H2O which matches the scattering density of silicon. Also, one measurement on a distearoylphosphatidylcholine bilayer which has longer acyl chains was performed for comparison. The lipid adsorbs to the silicon surface as a continuous layer interrupted by irregularly shaped uncovered areas which are 100-500 Angstrom in size. The surface coverage was estimated to be 70 +/- 20%. The reflectivity measurements on DPPC at 60 degrees C show a silicon oxide layer with a thickness of the order of 4 Angstrom, a rough silicon oxide/water layer between silicon oxide and lipid with a thickness between 2 and 8 Angstrom, and a single lipid bilayer. Fitting resolved a central membrane layer with a thickness of 28 +/- 2 Angstrom which represents the lipid hydrocarbon chains. This layer is sandwiched between interface membrane layers of lipid head groups and water which are 11.5 +/- 1 Angstrom in thickness. The angstrom-scale thickness changes of the central membrane layer as a function of the phase state of the lipid and of the length of the hydrocarbon chains are easily detected.