Department of Chemistry and Institute of Nano-Bio Molecular Assemblies, Yonsei University, 50 Yonsei-ro Seodaemun-gu, Seoul 120-749, Korea.
J Phys Chem B. 2013 Jun 27;117(25):7763-70. doi: 10.1021/jp4015564. Epub 2013 Jun 13.
We introduce frustrated aggregate internal rearrangement (FAIR) mechanism for anisotropic higher-order structure formations, in which the anisotropy arose due to the structural frustration. We demonstrate the FAIR mechanism by investigating the recently observed rigid organic nanotube formations through the self-assembly of building blocks, which include rigid segments and make intermolecular H-bonds, whereas the principle of the FAIR mechanism is general and is not limited to H-bonding building blocks or nanotube formations. Initially, molecules aggregate into sheetlike structures driven by nonspecific and nondirectional intermolecular interactions such as π-π stacking or amphiphilicity. Weak intermolecular H-bonds provide additional stability to the structure. Within the aggregate, however, not all molecules have the right orientation for specific and directional H-bonds whereas collective internal rearrangement of rigid building blocks requires a large amount of energy to overcome kinetically trapped barriers. Consequently, instead of the fully H-bonded global equilibrium structure, self-assembled layers become trapped with partial and disordered H-bonding schemes at various fractions leading to an anisotropic layer that undergoes spontaneous transformation into curved structures. The FAIR mechanism can readily be extended to anisotropic higher-order structures other than nanotubes and to the assembly of diverse building blocks including hybrids such as polymer nanocomposites. Also the reversible transformation from metastable nanotubes into layered sheets is potentially useful for controlling internal cavity size of nanotubes.
我们介绍了各向异性高阶结构形成的受挫聚集内重排（FAIR）机制，其中各向异性是由于结构受挫引起的。我们通过研究最近观察到的刚性有机纳米管形成来证明 FAIR 机制，这是通过构建块的自组装实现的，其中包括刚性片段和形成分子间氢键，而 FAIR 机制的原理是普遍的，不仅限于氢键构建块或纳米管形成。最初，分子通过非特异性和无方向性的分子间相互作用（如π-π 堆积或两亲性）聚集到片状结构中。弱分子间氢键为结构提供额外的稳定性。然而，在聚集物内，并非所有分子都具有形成特定和方向性氢键的正确取向，而刚性构建块的集体内重排需要大量能量来克服动力学捕获的障碍。因此，自组装层不会形成完全氢键的全局平衡结构，而是会在各个分数处被困在具有部分和无序氢键的方案中，导致各向异性层自发转变为弯曲结构。FAIR 机制可以很容易地扩展到除纳米管以外的各向异性高阶结构，以及包括聚合物纳米复合材料等混合体在内的各种构建块的组装。此外，从亚稳纳米管到层状片的可逆转变对于控制纳米管的内部腔室尺寸可能是有用的。
