Department of Chemistry and Biochemistry and Materials Research Laboratory, University of California, Santa Barbara, California, USA.
Phys Chem Chem Phys. 2011 May 7;13(17):7732-46. doi: 10.1039/c0cp02512g. Epub 2011 Mar 21.
The dynamics and state of lipid bilayer-internal hydration water of unilamellar lipid vesicles dispersed in solutions is characterized. This study was enabled by a recently developed technique based on Overhauser dynamic nuclear polarization (DNP)-driven amplification of (1)H nuclear magnetic resonance (NMR) signal of hydration water. This technique can, in the full presence of bulk water, selectively quantify the translational dynamics of hydration water within ∼10 Å around spin labels that are specifically introduced to the local volume of interest within the lipid bilayer. With this approach, the local apparent diffusion coefficients of internal water at different depths of the lipid bilayer were determined. The modulation of these values as a response to external stimuli, such as the addition of sodium chloride or ethanol and the lipid phase transitions, that alter the fluctuations of bilayer interfaces together with the activation energy values of water diffusivity shows that water is not individually and homogeneously solvating lipid's hydrocarbon tails in the lipid bilayer. We provide experimental evidence that instead, water and the lipid membrane comprise a heterogeneous system whose constituents include transient hydrophobic water pores or water structures traversing the lipid bilayer. We show how these transient pore structures, as key vehicles for passive water transport can better reconcile our experimental data with existing literature data on lipid bilayer hydration and dynamics.
本文对分散在溶液中的单层脂质囊泡内部的脂质双层内水合的动态和状态进行了描述。这项研究是基于最近开发的一种技术实现的，该技术基于过氧化物动核极化（DNP）驱动的水合核磁共振（NMR）信号放大。该技术可以在完全存在体相水的情况下，选择性地量化位于脂质双层中特定引入的局部感兴趣体积内自旋标记物周围 10Å范围内水的平移动力学。通过这种方法，可以确定脂质双层不同深度处内部水的局部表观扩散系数。这些值的调制可以作为对外界刺激的响应，例如添加氯化钠或乙醇以及脂质相变，这些刺激会改变双层界面的波动以及水扩散的活化能值，表明水不是单独且均匀地溶解在脂质双层中的烃尾。我们提供了实验证据表明，相反，水和脂质膜组成了一个不均匀的系统，其组成部分包括瞬时疏水性水孔或横穿脂质双层的水结构。我们展示了这些瞬时孔结构如何作为被动水传输的关键载体，可以更好地使我们的实验数据与关于脂质双层水合和动力学的现有文献数据相协调。
