Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands.
Nature. 2012 Jan 18;481(7382):492-6. doi: 10.1038/nature10720.
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. 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 that go beyond traditional concepts of homogeneous and secondary nucleation events. The self-assembly of synthetic supramolecular polymers has also been studied and even modulated, but our quantitative understanding of the processes involved remains limited. Here we report time-resolved observations of the formation of supramolecular polymers from π-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. 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.
自组装为功能性有机材料提供了一条有吸引力的途径，其性能和因此的性能取决于分子构建块的组织方式。分子组织是超分子组装过程中所涉及途径的直接结果，当使用一维系统时，更便于对其进行详细研究。在蛋白质原纤维的情况下，其形成和生长归因于超出传统均相和二级成核事件概念的复杂聚集途径。合成超分子聚合物的自组装也已经被研究甚至被调控，但我们对所涉及过程的定量理解仍然有限。在这里，我们报告了从π共轭寡聚物形成超分子聚合物的时间分辨观察。我们的动力学实验表明存在一种动力学上有利的亚稳组装，它可以快速形成，但随后会转化为热力学上有利的形式。从动力学模型计算中获得了对动力学实验的定量见解，该计算揭示了两种平行且竞争的途径，它们导致具有相反螺旋的组装体。这些见解促使我们使用手性酒石酸作为辅助剂来改变组装过程的热力学偏好。我们发现，我们可以将聚合完全沿着动力学有利的途径进行，因此，在去除辅助剂后，我们只能得到亚稳组装体。
