Department of Chemical Engineering and Materials Science, ‡Department of Integrative Biology and Physiology, and §Department of Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States.
Langmuir. 2017 Nov 7;33(44):12624-12634. doi: 10.1021/acs.langmuir.7b02279. Epub 2017 Oct 25.
Block copolymers composed of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) have been widely used in cell membrane stabilization and permeabilization. To explore the mechanism of interaction between PPO-PEO block copolymers and lipid membranes, we have investigated how polymer structure influences the polymer-lipid bilayer association by varying the overall molecular weight, the hydrophobic and hydrophilic block lengths, and the end-group structure systematically, using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) unilamellar liposomes as model membranes. Pulsed-field-gradient NMR (PFG-NMR) was employed to probe polymer diffusion in the absence and presence of liposomes. The echo decay curves of free polymers in the absence of liposomes are single exponentials, indicative of simple translational diffusion, while in the presence of liposomes, the decays are biexponential, with the slower decay corresponding to polymers bound to liposomes. The binding percentage of polymer to the liposome was quantified by fitting the echo decay curves to a biexponential model. The NMR experiments show that increasing the total molecular weight and hydrophobicity of the polymer can significantly enhance the polymer-lipid bilayer association, as the binding percentage and liposome surface coverage both increase. We hypothesize that the hydrophobic PPO block inserts into the lipid bilayer due to the fact that little molecular exchange between bound and free polymers occurs on the time scale of the diffusion experiments. Additionally, as polymer concentration increases, the liposome surface coverage increases and approaches a limit. These results demonstrate that PFG-NMR is a simple yet powerful method to quantify interactions between polymers and lipid bilayers.
由聚环氧乙烷（PEO）和聚环氧丙烷（PPO）组成的嵌段共聚物已被广泛应用于细胞膜的稳定和渗透化。为了探究PPO-PEO 嵌段共聚物与脂膜相互作用的机制，我们通过系统地改变聚合物的总分子量、疏水性和亲水性嵌段长度以及端基结构，研究了聚合物结构如何影响聚合物-脂双层的结合。采用 1-棕榈酰基-2-油酰基-sn-甘油-3-磷酸胆碱（POPC）单层脂质体作为模型膜。使用脉冲梯度 NMR（PFG-NMR）来探测聚合物在没有和存在脂质体时的扩散。在没有脂质体的情况下，自由聚合物的回波衰减曲线是单指数的，表明是简单的平移扩散，而在存在脂质体的情况下，衰减是双指数的，较慢的衰减对应于与脂质体结合的聚合物。通过将回波衰减曲线拟合到双指数模型来定量聚合物与脂质体的结合百分比。NMR 实验表明，增加聚合物的总分子量和疏水性可以显著增强聚合物-脂双层的结合，因为结合百分比和脂质体表面覆盖率都增加。我们假设由于在扩散实验的时间尺度上结合和游离聚合物之间几乎没有分子交换，疏水性的 PPO 嵌段插入到脂质双层中。此外，随着聚合物浓度的增加，脂质体表面覆盖率增加并趋于极限。这些结果表明，PFG-NMR 是一种简单而强大的方法，可以定量聚合物与脂双层之间的相互作用。
