Scherer J R
Western Regional Research Center, U.S. Department of Agriculture, Albany, CA 94710.
Proc Natl Acad Sci U S A. 1987 Nov;84(22):7938-42. doi: 10.1073/pnas.84.22.7938.
A new algorithm is presented for interpreting the hydration dependence of x-ray diffraction measurements. The method assumes that the volume of the hydrocarbon phase of the lipid bilayer is not affected by hydration and that the volume expansion between bilayers at maximum hydration is caused by incorporation of water molecules whose partial molar volume is that of pure bulk water. These simple assumptions lead to a determination of the area expansion (and hence change in hydrocarbon-phase thickness) as a function of hydration. An analysis is made of x-ray data of the L alpha and L beta' phases of dimyristoyl phosphatidylcholine and the L alpha phase of egg phosphatidylcholine. The partial molar volume of water depends critically on the degree of lipid hydration and the presence of voids between the head groups of adjacent lipids. The calculated head-group spacings at minimum hydration are consistent with those obtained from neutron diffraction and indicate that the methyl groups of the choline are almost in contact with corresponding groups in the opposing bilayer. This calls into question the origin of the repulsive forces observed in dehydration experiments.
提出了一种新算法，用于解释X射线衍射测量的水合依赖性。该方法假定脂质双层烃相的体积不受水合作用影响，且最大水合时双层之间的体积膨胀是由水分子的掺入引起的，这些水分子的偏摩尔体积与纯体相水的偏摩尔体积相同。这些简单假设可确定面积膨胀（进而确定烃相厚度的变化）与水合作用的函数关系。对二肉豆蔻酰磷脂酰胆碱的Lα相和Lβ'相以及卵磷脂的Lα相的X射线数据进行了分析。水的偏摩尔体积严重依赖于脂质的水合程度以及相邻脂质头部基团之间空隙的存在。计算得出的最小水合时的头部基团间距与中子衍射得到的结果一致，表明胆碱的甲基几乎与相对双层中的相应基团接触。这对脱水实验中观察到的排斥力的起源提出了质疑。
