Ottiger M, Bax A
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
J Biomol NMR. 1998 Oct;12(3):361-72. doi: 10.1023/a:1008366116644.
Weak alignment of solute molecules with the magnetic field can be achieved in a dilute liquid crystalline medium, consisting of an aqueous mixture of dimyristoyl-phosphatidylcholine (DMPC) and dihexanoyl-phosphatidylcholine (DHPC). For a certain range of molar ratios, DMPC and DHPC can form large, disc-shaped particles, commonly referred to as bicelles (Sanders and Schwonek, 1992), which cooperatively align in the magnetic field and induce a small degree of alignment on asymmetrically shaped solute molecules. As a result, dipolar couplings between pairs of 1H, 13C or 15N nuclei are no longer averaged to zero by rotational diffusion and they can be readily measured, providing valuable structural information. The stability of these liquid crystals and the degree of alignment of the solute molecules depend strongly on experimental variables such as the DMPC:DHPC ratio and concentration, the preparation protocol of the DMPC/DHPC mixtures, as well as salt, temperature, and pH. The lower temperature limit for which the liquid crystalline phase is stable can be reduced to 20 degrees C by using a ternary mixture of DHPC, DMPC, and 1-myristoyl-2-myristoleoyl-sn-glycero-3-phosphocholine, or a binary mixture of DHPC and ditridecanoyl-phosphatidylcholine. These issues are discussed, with an emphasis on the use of the medium for obtaining weak alignment of biological macromolecules.
在由二肉豆蔻酰磷脂酰胆碱（DMPC）和二己酰磷脂酰胆碱（DHPC）的水性混合物组成的稀液晶介质中，可以实现溶质分子与磁场的弱排列。在一定的摩尔比范围内，DMPC和DHPC可以形成大的盘状颗粒，通常称为双分子层（Sanders和Schwonek，1992），它们在磁场中协同排列，并在不对称形状的溶质分子上诱导一定程度的排列。结果，1H、13C或15N核之间的偶极耦合不再通过旋转扩散平均为零，并且可以很容易地测量，从而提供有价值的结构信息。这些液晶的稳定性和溶质分子的排列程度在很大程度上取决于实验变量，如DMPC:DHPC的比例和浓度、DMPC/DHPC混合物的制备方案，以及盐、温度和pH值。通过使用DHPC、DMPC和1-肉豆蔻酰-2-肉豆蔻烯酰-sn-甘油-3-磷酸胆碱的三元混合物，或DHPC和二月桂酰磷脂酰胆碱的二元混合物，可以将液晶相稳定的下限温度降低到20摄氏度。本文将讨论这些问题，重点是使用该介质获得生物大分子的弱排列。
