Biozentrum, Division of Biophysical Chemistry, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland.
Langmuir. 2011 Aug 16;27(16):10041-9. doi: 10.1021/la201027p. Epub 2011 Jul 20.
The synthetic lipid 1,2-dimyristoyl-sn-3-phosphoglycerol (DMPG), when dispersed in water/NaCl exhibits a complex phase behavior caused by its almost unlimited swelling in excess water. Using deuterium ((2)H)- and phosphorus ((31)P)-NMR we have studied the molecular properties of DMPG/water/NaCl dispersions as a function of lipid and NaCl concentration. We have measured the order profile of the hydrophobic part of the lipid bilayer with deuterated DMPG while the orientation of the phosphoglycerol headgroup was deduced from the (31)P NMR chemical shielding anisotropy. At temperatures >30 °C we observe well-resolved (2)H- and (31)P NMR spectra not much different from other liquid crystalline bilayers. From the order profiles it is possible to deduce the average length of the flexible fatty acyl chain. Unusual spectra are obtained in the temperature interval of 20-25 °C, indicating one or several phase transitions. The most dramatic changes are seen at low lipid concentration and low ionic strength. Under these conditions and at 25 °C, the phosphoglycerol headgroup rotates into the hydrocarbon layer and the hydrocarbon chains show larger flexing motions than at higher temperatures. The orientation of the phosphoglycerol headgroup depends on the bilayer surface charge and correlates with the degree of dissociation of DMPG-Na(+). The larger the negative surface charge, the more the headgroup rotates toward the nonpolar region.
合成脂质 1,2-二肉豆蔻酰-sn-3-磷酸甘油（DMPG）在水/NaCl 中分散时，由于其在过量水中几乎无限膨胀，表现出复杂的相行为。使用氘（(2)H）-和磷（(31)P）-NMR，我们研究了 DMPG/水/NaCl 分散体的分子特性，作为脂质和 NaCl 浓度的函数。我们用氘化 DMPG 测量了脂质双层疏水区的有序轮廓，而磷酸甘油头部基团的取向则是从(31)P NMR 化学屏蔽各向异性推断出来的。在温度 >30°C 时，我们观察到分辨率很高的(2)H-和(31)P NMR 谱，与其他液晶双层没有太大区别。从有序轮廓可以推断出柔性脂肪酸链的平均长度。在 20-25°C 的温度范围内，会得到异常的光谱，表明存在一个或多个相转变。在低脂质浓度和低离子强度下，变化最为显著。在这些条件下，在 25°C 时，磷酸甘油头部基团旋转进入烃层，烃链的弯曲运动比在较高温度下更大。磷酸甘油头部基团的取向取决于双层表面电荷，并与 DMPG-Na(+)的离解程度相关。表面负电荷越大，头部基团越向非极性区域旋转。
