Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA.
Soft Matter. 2020 Apr 1;16(13):3245-3256. doi: 10.1039/c9sm02111f.
We present the derivation of a new model to describe neutron spin echo spectroscopy and quasi-elastic neutron scattering data on liposomes. We compare the new model with existing approaches and benchmark it with experimental data. The analysis indicates the importance of including all major contributions in the modeling of the intermediate scattering function. Simultaneous analysis of the experimental data on lipids with full contrast and tail contrast matched samples reveals highly confined lipid tail motion. A comparison of their dynamics demonstrates the statistical independence of tail-motion and height-height correlation of the membrane. A more detailed analysis indicates that the lipid tail relaxation is confined to a potential with cylindrical symmetry, in addition to the undulation and diffusive motion of the liposome. Despite substantial differences in the chemistry of the fatty acid tails, the observation indicates a universal behavior. The analysis of partially deuterated systems confirms the strong contribution of the lipid tail to the intermediate scattering function. Within the time range from 5 to 100 ns, the intermediate scattering function can be described by the height-height correlation function. The existence of the fast-localized tail motion and the contribution of slow translational diffusion of liposomes determine the intermediate scattering function for t < 5 ns and t > 100 ns, respectively. Taking into account the limited time window lowers the bending moduli by a factor of 1.3 (DOPC) to 2 (DMPC) compared to the full range.
我们提出了一个新模型来描述脂质体的中子自旋回波谱学和准弹性中子散射数据。我们将新模型与现有方法进行了比较，并与实验数据进行了基准测试。分析表明，在建模中间散射函数时，必须包括所有主要贡献。对具有全对比和尾部对比匹配样品的脂质的实验数据进行同时分析，揭示了高度受限的脂质尾部运动。它们的动力学比较表明，尾部运动和膜的高度相关高度之间具有统计独立性。更详细的分析表明，除了脂质体的波动和扩散运动之外，脂质尾部的松弛被限制在具有圆柱对称性的势中。尽管脂肪酸尾部的化学性质有很大差异，但观察到的结果表明存在普遍行为。部分氘化系统的分析证实了脂质尾部对中间散射函数的强烈贡献。在 5 到 100 纳秒的时间范围内，中间散射函数可以用高度相关函数来描述。快速局部化尾部运动的存在和脂质体的缓慢平移扩散的贡献分别决定了 t < 5 ns 和 t > 100 ns 的中间散射函数。考虑到有限的时间窗口，与全范围相比，弯曲模量降低了 1.3 倍（DOPC）至 2 倍（DMPC）。
