Van Gorp Judith J, Vekemans Jef A J M, Meijer E W
Contribution from the Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.
J Am Chem Soc. 2002 Dec 11;124(49):14759-69. doi: 10.1021/ja020984n.
Hydrogen bonded C(3)-symmetrical molecules that associate into supramolecular stacks are described. Structural mutation on these molecules has been performed to elucidate the contribution of the different secondary interactions (hydrogen bonding, pi-pi stacking) to the self-assembly of the disks into chiral stacks. Twelve C(3)-symmetrical molecules have been investigated, six of which contain three central amide functionalities (1a-f) and six of which contain three central urea groups (2a-f). Peripheral groups of the disks are "small", "medium", or "large", half of them being achiral and the other half being chiral, to enable investigation of the supramolecular architectures with CD spectroscopy. In all of the cases, elongated, helical stacks are formed in apolar solution, except for the "medium" amide disks 1c/d. The elongated stacks of the C(3)-symmetrical disks form gels, which are visualized by AFM and SANS, and this confirms the directionality of the interactions. For the "large" urea disk, 2f, fibers with a length of up to 2 microm are observed. Temperature dependent and "sergeants-and-soldiers" CD measurements reveal that the urea stacks are much more rigid than the corresponding amide ones. In case of the "medium" urea disks, 2c/d, a true rigid rod, is formed. Where amide disks immediately reach their thermodynamic equilibrium, kinetic factors seem to govern urea aggregation. In a number of experiments aimed at reversibility with the urea stacks, hysteresis is observed, implying that these urea disks initially form a poorly defined stack, which subsequently transforms slowly into a well-defined, chiral architecture.
本文描述了通过氢键作用形成超分子堆叠的C(3)对称分子。对这些分子进行了结构突变，以阐明不同二级相互作用（氢键、π-π堆积）对盘状分子自组装成手性堆叠的贡献。研究了12个C(3)对称分子，其中6个含有三个中心酰胺官能团（1a-f），另外6个含有三个中心脲基（2a-f）。盘状分子的外围基团为“小”、“中”或“大”，其中一半为非手性，另一半为手性，以便通过圆二色光谱研究超分子结构。在所有情况下，除了“中”酰胺盘1c/d外，在非极性溶液中都会形成细长的螺旋堆叠。C(3)对称盘状分子的细长堆叠形成凝胶，通过原子力显微镜（AFM）和小角中子散射（SANS）可以观察到，这证实了相互作用的方向性。对于“大”脲盘2f，观察到长度可达2微米的纤维。温度依赖性和“军士-士兵”圆二色测量表明，脲堆叠比相应的酰胺堆叠更刚性。对于“中”脲盘2c/d，形成了真正的刚性棒。酰胺盘立即达到其热力学平衡，而动力学因素似乎控制着脲的聚集。在一些旨在使脲堆叠具有可逆性的实验中，观察到滞后现象，这意味着这些脲盘最初形成定义不明确的堆叠，随后缓慢转变为定义明确的手性结构。
