Engineering Helical Chirality in Metal-Coordinated Cyclodextrin Nanochannels

Abstract

Helicates are a defining element of DNAs and proteins, with functions that are critical to a variety of biological processes. Cyclodextrins are promising candidates for forging multiple-stranded helicates with well-defined helicity, but a lack of available tools has precluded the construction of artificial helical nanochannels with a controllable geometry and helicity from these widely available chiral building blocks. Herein, we disclose a family of Ag₆L₂ helical nanochannels that can be readily assembled from α-cyclodextrin-derived ligands through coordination between pyridinyl groups and Ag⁺ cations. We discovered that the nanochannels exhibit either an M or a P helicity when the Ag⁺ cations adopt a tetrahedral coordination geometry while losing most of their helicity when the Ag⁺ cations are linearly coordinated. Both the geometry and helicity of the nanochannels can be precisely controlled by simply changing the number of methyl groups at the ortho positions of the pyridinyl ligands. The tetracoordinated Ag⁺ cations interconnect the helical nanochannels into an infinite two-dimensional coordinative network characterized by hexagonal tessellation. Theoretical calculations, which reveal lower energies of the helical conformations observed in crystals compared with those of their inverted counterparts, support the experimental results.