Morphology of Three Lyotropic Liquid Crystalline Biological NMR Media Studied by Translational Diffusion Anisotropy
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- 作者：Sander Gaemers and Ad Bax
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：December 12, 2001
- 年：2001
- 卷：123
- 期：49
- 页码：12343 - 12352
- 全文大小：118K
- 年卷期：v.123,no.49(December 12, 2001)
- ISSN：1520-5126
文摘
The morphologies of three dilute liquid crystalline phases, which are widely used for biologicalNMR spectroscopy, are investigated by the study of tracer self-diffusion. The aqueous liquid crystalline mediainvestigated include the common phospholipid bicelle medium, a phase consisting of a mixture ofpentaethyleneglycol mono dodecyl ether and hexanol, and a medium containing cetylpyridinium bromide andhexanol. Threonine and water were used as tracer molecules for probing the aqueous environment, andtetramethylsilane (TMS) was for probing the lipophilic environment. Pulsed field gradient NMR was used tomeasure tracer self-diffusion rates in three orthogonal directions. Although results for the water-soluble tracersin bicelle media do not contradict the widely accepted disk-shaped bicelle model, the high TMS diffusion rateobserved in the bilayer plane requires extensive transient edge-to-edge contacts of such disks. This morphologyis essentially that of a heavily perforated lamellar bilayer phase and explains why this medium remains liquidcrystalline well below the Onsager limit for disk-shaped nematogens. Below 25 
C, a bicelle mixture consistingof dimyristoyl phosphatidyl choline and dihexanoyl phosphatidyl choline remains isotropic, but tracer diffusionobstruction indicates that the particles are significantly oblate. The diffusion anisotropy in the penta(ethyleneglycol) mono dodecyl ether liquid crystals confirms the previously proposed 
-lamellar phase. However,weak inhibition of aqueous-phase self-diffusion in the z direction points to the presence of bridge- or caplikeobstructions, and the bilayers appear slightly permeable to water. If the previously proposed concentric cylindersuperstructure of bilayers applies, the diffusion data indicate that the most outer cylinder must have a diametergreater than 50 
m. The tracer self-diffusion data for the cetylpyridinium bromide/hexanol medium is onlycompatible with a planar -lamellar phase, with its local director orthogonal to the magnetic field, and a verylarge domain size over which the director remains parallel.
C, a bicelle mixture consistingof dimyristoyl phosphatidyl choline and dihexanoyl phosphatidyl choline remains isotropic, but tracer diffusionobstruction indicates that the particles are significantly oblate. The diffusion anisotropy in the penta(ethyleneglycol) mono dodecyl ether liquid crystals confirms the previously proposed -lamellar phase. However,weak inhibition of aqueous-phase self-diffusion in the z direction points to the presence of bridge- or caplikeobstructions, and the bilayers appear slightly permeable to water. If the previously proposed concentric cylindersuperstructure of bilayers applies, the diffusion data indicate that the most outer cylinder must have a diametergreater than 50 m. The tracer self-diffusion data for the cetylpyridinium bromide/hexanol medium is onlycompatible with a planar -lamellar phase, with its local director orthogonal to the magnetic field, and a verylarge domain size over which the director remains parallel.