Arnold Alexandre, Labrot Thomas, Oda Reiko, Dufourc Erick J
Institut Européen de Chimie et Biologie, Ecole Polytechnique, 16 Avenue Pey Berland, 33607 Bordeaux-Pessac cedex, France.
Biophys J. 2002 Nov;83(5):2667-80. doi: 10.1016/S0006-3495(02)75276-4.
The influence of salts (KCl, NaCl, CaCl(2), and MgCl(2)) on bicelles (bilayered micelles) made of dimyristoylphosphatidylcholine (DMPC, molar fraction X = 78%) and dicaproylphosphatidylcholine (DCPC) was investigated by solid-state (31)P- and (2)H NMR as well as by freeze-fracture electron microscopy. Sizes were determined from (2)H- and (31)P NMR on the basis of a model that incorporated a planar bilayer and a (half-torus) curved rim representing the DMPC and DCPC regions of the bicelle, respectively. Good agreement was shown with sizes determined independently from freeze-fracture electron microscopy images. In the presence of K(+) and Na(+), bicelles have diameters of approximately 300 A while in the presence of Ca(2+) and Mg(2+); their diameter increases to approximately 500 A. Bicelle magnetic alignment is considerably improved by the presence of salts. The optimum salt concentration for such an effect ranges from 50 to 200 mM. Bicelles are magnetically aligned for temperatures roughly ranging from 30 degrees C to 40 degrees C with monovalent cations; this range is slightly extended in the presence of divalent salts. In this temperature range, the dynamics of the long-chain hydrocarbon region of the bicelle (leading to a bicelle thickness of 38 A) and of water is about the same independently of cation nature and concentration. However, at higher temperatures, considerable differences in water dynamics are observed between systems with monovalent and divalent cations. In these conditions, the system consists of a mixture of micelles and extended bilayers, which show residual macroscopic alignment in the magnetic field.
通过固态³¹P和²H核磁共振以及冷冻断裂电子显微镜研究了盐（KCl、NaCl、CaCl₂和MgCl₂）对由二肉豆蔻酰磷脂酰胆碱（DMPC，摩尔分数X = 78%）和二己酰磷脂酰胆碱（DCPC）制成的双分子层微囊（双层微囊）的影响。基于一个模型，从²H和³¹P核磁共振确定尺寸，该模型分别包含一个平面双层和一个代表双分子层微囊DMPC和DCPC区域的（半圆环）弯曲边缘。与从冷冻断裂电子显微镜图像独立确定的尺寸显示出良好的一致性。在K⁺和Na⁺存在的情况下，双分子层微囊的直径约为300 Å，而在Ca²⁺和Mg²⁺存在的情况下，其直径增加到约500 Å。盐的存在显著改善了双分子层微囊的磁取向。这种效果的最佳盐浓度范围为50至200 mM。对于单价阳离子，双分子层微囊在大约30℃至40℃的温度范围内进行磁取向；在二价盐存在的情况下，这个范围略有扩大。在这个温度范围内，双分子层微囊长链烃区域（导致双分子层微囊厚度为38 Å）和水的动力学与阳离子性质和浓度无关，大致相同。然而，在较高温度下，观察到单价和二价阳离子系统之间水动力学存在显著差异。在这些条件下，系统由微囊和延伸双层的混合物组成，它们在磁场中显示出残余的宏观取向。
