Institute for Complex Molecular Systems, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
School of Chemistry and RNA Institute, University of New South Wales, 2052 Sydney, Australia.
J Am Chem Soc. 2023 Jul 5;145(26):14379-14386. doi: 10.1021/jacs.3c03411. Epub 2023 Jun 21.
Amplification of asymmetry in complex molecular systems results from a delicate interplay of chiral supramolecular structures and their chemical reactivity. In this work, we show how the helicity of supramolecular assemblies can be controlled by performing a non-stereoselective methylation reaction on comonomers. By methylating chiral glutamic acid side chains in benzene-1,3,5-tricarboxamide (BTA) derivatives to form methyl esters, the assembly properties are modulated. As reacted comonomers, the methyl ester-BTAs induce a stronger bias in the screw-sense of helical fibers predominantly composed of stacked achiral alkyl-BTA monomers. Hence, applying the methylation in a system with the glutamic acid-BTA comonomer induces asymmetry amplification. Moreover, mixing small quantities of enantiomers of glutamic acid-BTA and glutamate methyl ester-BTA in the presence of the achiral alkyl-BTAs leads to deracemization and inversion of the helical structures in solution the reaction toward a thermodynamic equilibrium. Theoretical modeling suggests that the observed effects are caused by enhanced comonomer interactions after the chemical modification. Our presented methodology enables on-demand control over asymmetry in ordered functional supramolecular materials.
在复杂的分子体系中，不对称性的放大源于手性超分子结构及其化学反应性之间的微妙相互作用。在这项工作中，我们展示了如何通过对共聚单体进行非对映选择性甲基化反应来控制超分子组装的手性。通过在手性谷氨酸侧链上进行苯-1,3,5-三甲酰胺（BTA）衍生物的甲基化反应形成甲酯，可以调节组装性质。作为反应性共聚单体，甲酯-BTAs 在主要由堆叠的非手性烷基-BTA 单体组成的螺旋纤维中诱导螺旋手性的更强偏向。因此，在含有谷氨酸-BTA 共聚单体的体系中进行甲基化会引起不对称性放大。此外，在非手性烷基-BTAs 的存在下，混合少量的谷氨酸-BTA 和谷氨酸甲酯-BTA 的对映异构体，会导致在溶液中解旋和螺旋结构的反转——反应向热力学平衡方向进行。理论建模表明，观察到的效应是由化学修饰后增强的共聚单体相互作用引起的。我们提出的方法能够按需控制有序功能超分子材料中的不对称性。
