School of Chemistry, University of Manchester, Manchester M13 9PL, UK.
Science. 2017 Jan 13;355(6321):159-162. doi: 10.1126/science.aal1619.
Knots may ultimately prove just as versatile and useful at the nanoscale as at the macroscale. However, the lack of synthetic routes to all but the simplest molecular knots currently prevents systematic investigation of the influence of knotting at the molecular level. We found that it is possible to assemble four building blocks into three braided ligand strands. Octahedral iron(II) ions control the relative positions of the three strands at each crossing point in a circular triple helicate, while structural constraints on the ligands determine the braiding connections. This approach enables two-step assembly of a molecular 8 knot featuring eight nonalternating crossings in a 192-atom closed loop ~20 nanometers in length. The resolved metal-free 8 knot enantiomers have pronounced features in their circular dichroism spectra resulting solely from topological chirality.
结可能最终证明在纳米尺度上和在宏观尺度上一样具有多功能性和实用性。然而，目前除了最简单的分子结之外，缺乏合成途径来阻止对分子水平上结的影响的系统研究。我们发现，有可能将四个构建块组装成三个编织配体链。八面体铁(II)离子控制三个链在每个交叉点的相对位置，在一个圆形的三螺旋中，而配体的结构约束决定了编织连接。这种方法可以两步组装一个分子 8 结，该结在一个 192 个原子的闭环中具有八个非交替交叉，闭环长度约为 20 纳米。解析的无金属 8 结对映异构体在圆二色光谱中具有显著特征，这些特征仅来自拓扑手性。
