Effects of molecular flexibility and head group repulsion on aramid amphiphile self-assembly
Effects of molecular flexibility and head group repulsion on aramid amphiphile self-assembly
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DOI：
10.1039/d1me00120e
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发表时间：
2021-10-28
影响因子：
3.6
通讯作者：
Ortony, Julia H.
中科院分区：
文献类型：
--
作者：
Kaser, Samuel J.;Lew, Andrew J.;Ortony, Julia H.
两亲分子在水中的自组装导致了具有不同应用的各种纳米结构。许多纳米结构通过单体单元之间的强相互作用来稳定，例如氢键和π-π堆叠。然而，这些强大的，各向异性的相互作用的形态影响可能是难以预测的。在这项研究中，我们研究了分子的灵活性，头基排斥，和超分子几何结构之间的关系，在芳族聚酰胺两亲物纳米结构，是已知的表现出广泛的氢键和π-π堆叠的功能，使其不寻常的稳定性。我们通过电子显微镜发现，骨架柔性的增加会破坏分子堆积成高纵横比纳米带，并且在柔性最高的情况下，长程有序性就会丧失。即使当骨架刚性有利于紧密堆积时，通过pH调节增加头基电荷也会导致分子间静电排斥，这也会破坏紧密堆积。光谱测量表明，这些变化是伴随着破坏的π-π堆叠，但不是氢键。因此，骨架刚性和头基排斥是控制由π-π堆积相互作用稳定的超分子组装体中的内部稳定性和纳米结构曲率的重要设计考虑因素。
The self-assembly of amphiphilic molecules in water has led to a wide variety of nanostructures with diverse applications. Many nanostructures are stabilized by strong interactions between monomer units, such as hydrogen bonding and pi-pi stacking. However, the morphological implications of these strong, anisotropic interactions can be difficult to predict. In this study, we investigate the relationships between molecular flexibility, head group repulsion, and supramolecular geometry in an aramid amphiphile nanostructure that is known to exhibit extensive hydrogen bonding and pi-pi stacking - features that give rise to their unusual stability. We find by electron microscopy that increasing backbone flexibility disrupts molecular packing into high aspect-ratio nanoribbons, and at the highest degree of flexibility long-range ordering is lost. Even when backbone rigidity favors tight packing, increasing head group charge through pH-modulation leads to intermolecular electrostatic repulsion that also disrupts close packing. Spectroscopic measurements suggest that these changes are accompanied by disruption of pi-pi stacking but not hydrogen bonding. Backbone rigidity and head group repulsion are thus important design considerations for controlling internal stability and nanostructure curvature in supramolecular assemblies stabilized by pi-pi stacking interactions.