Surface Science Research Centre, Department of Chemistry, University of Liverpool, Liverpool L69 3BX, UK.
Nat Chem. 2009 Aug;1(5):409-14. doi: 10.1038/nchem.295. Epub 2009 Jul 24.
There is considerable interest in skewing the transmission of chirality, or 'handedness', from the molecular to the supramolecular level so that single-handed superstructures are created from mixed enantiomer systems. One approach is to flip the chirality of all the molecular building blocks to the same handedness. However, manipulation of molecular chirality is not possible for non-interconvertible enantiomers, and mechanisms that skew such systems are unclear. Here, we track the molecule-to-supramolecular chiral transfer in such systems at the nanoscale by probing molecular monolayers at surfaces. Scanning tunnelling microscopy and theoretical modelling show that enantiomeric imbalances lead to nonlinear symmetry breaking in organization, driven by configurational entropy effects. Thus, the majority enantiomer readily organizes into its superstructure with the minority left fragmented and disorganized, and thus impeded from realizing its superstructure. Such effects promise new strategies in chiral separations and enantioselective processes, and may have contributed to the homochiral evolution of complex matter from prebiotic environments.
人们对于手性（或“手征性”）从分子水平到超分子水平的传递进行了深入研究，希望从混合对映体体系中构建单一手性超结构。一种方法是将所有分子构建块的手性翻转到相同的手性。然而，对于不可相互转化的对映异构体，分子手性的操纵是不可能的，并且这些系统中手性扭曲的机制尚不清楚。在这里，我们通过在表面探测分子单层来跟踪此类系统中纳米尺度的分子到超分子的手性转移。扫描隧道显微镜和理论建模表明，手性不平衡导致组织中的非线性对称破缺，这是由构象熵效应驱动的。因此，多数对映体很容易组织成其超结构，而少数对映体则呈碎片化和无序状态，从而阻碍了其超结构的实现。这些效应有望为手性分离和对映选择性过程提供新的策略，并且可能有助于从前生物环境中复杂物质的同手性演化。
