Pathway complexity in supramolecular polymerization
Pathway complexity in supramolecular polymerization
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DOI：
10.1038/nature10720
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发表时间：
2012-01-26
期刊：
影响因子：
64.8
通讯作者：
Meijer, E. W.
中科院分区：
文献类型：
--
作者：
Korevaar, Peter A.;George, Subi J.;Meijer, E. W.
自组装为功能性有机材料提供了一种有吸引力的途径，其性质以及因此产生的性能敏感地取决于分子构建模块的组织形式（1 - 5）。分子组织是超分子组装过程所涉及途径的直接结果，当使用一维体系时，更便于进行详细研究。就蛋白质纤维而言，其形成和生长归因于复杂的聚集途径（6 - 8），这些途径超越了均相（9 - 11）和二次（12 - 14）成核事件的传统概念。合成超分子聚合物的自组装也已得到研究，甚至受到调控（15 - 18），但我们对相关过程的定量理解仍然有限。在此，我们报道了对由π-共轭低聚物形成超分子聚合物的时间分辨观察结果。我们的动力学实验表明存在一种动力学上有利的亚稳态组装体，它快速形成，然后转变为热力学上有利的形式。通过动力学模型计算获得了对动力学实验的定量认识，结果显示存在两条平行且相互竞争的途径，导致形成具有相反螺旋性的组装体。这些见解促使我们使用手性酒石酸作为助剂来改变组装过程的热力学偏好（19）。我们发现我们可以完全迫使聚集沿着动力学上有利的途径进行，这样在去除助剂后，我们只能得到亚稳态组装体。
Self-assembly provides an attractive route to functional organic materials, with properties and hence performance depending sensitively on the organization of the molecular building blocks(1-5). Molecular organization is a direct consequence of the pathways involved in the supramolecular assembly process, which is more amenable to detailed study when using one-dimensional systems. In the case of protein fibrils, formation and growth have been attributed to complex aggregation pathways(6-8) that go beyond traditional concepts of homogeneous(9-11) and secondary (12-14) nucleation events. The self-assembly of synthetic supramolecular polymers has also been studied and even modulated(15-18), but our quantitative understanding of the processes involved remains limited. Here we report time-resolved observations of the formation of supramolecular polymers from pi-conjugated oligomers. Our kinetic experiments show the presence of a kinetically favoured metastable assembly that forms quickly but then transforms into the thermodynamically favoured form. Quantitative insight into the kinetic experiments was obtained from kinetic model calculations, which revealed two parallel and competing pathways leading to assemblies with opposite helicity. These insights prompt us to use a chiral tartaric acid as an auxiliary to change the thermodynamic preference of the assembly process(19). We find that we can force aggregation completely down the kinetically favoured pathway so that, on removal of the auxiliary, we obtain only metastable assemblies.