Li zhanting and Zhang Danwei of Fudan University have made important progress in the construction of supramolecular helix driven by hydrogen and halogen bonds

Recently, Li zhanting and Zhang Danwei, Department of chemistry, Fudan University, used the intermolecular n · · I halogen bond to "bond" the short aromatic amide folding body into a super molecular helix structure It is found that the new self-assembled helix can form a more complex bimolecular double helix or even four helix structure Liu Chuanzhi, Ph.D., and Satish koppireddi, Ph.D., were the co first authors Their research results were published in German Applied Chemistry (angelw Chem Int ed 2019, 58, 226-230) The research team designed a kind of aromatic amide oligomers, and selected - CF 2I group as halogen bond donor and pyridine group as halogen bond acceptor to introduce them to both ends of the aromatic amide oligomers The crystal structure shows that the molecular conformation is controlled by intramolecular n ‒ h ·· o hydrogen bond, and the intermolecular n ·· I halogen bond induces these molecules to form two kinds of chiral supramolecular helical structures, P and m Fig 1 The four strand spiral stacking mode of compound 1 (source: angel Chem Int ed.) is shown in Fig 1 For compound 1 with halogen donor and acceptor at both ends of the same molecule, X-ray single crystal diffraction analysis shows that it is formed by the end-to-end connection of strong n ·· I halogen bond (n ·· I distance 2.87 Å, rxb = 0.81) between molecules Supramolecular polymer The halogenated bond induces the formation of supramolecular P and M helices, which are mirror symmetric in form The twist in the molecule makes the angle between the two aromatic ring planes of the end position reach 51.5 °, and the pitch of the adjacent helix is 17.5 μ Despite such a large pitch, the two helices still produce a cavity, which does not capture any solvent molecules The neighboring P and M helices stack their component molecules on the inner side in an antiparallel manner, forming a super molecular double helix structure The double helix structure further accumulates to form a super molecular four helix structure similar to the G-quadruplex As shown in Fig 2, the two end groups of compound 2 are all halogen receptor pyridine, which is eutectic with 1,2-diisoperfluoroethane (3) The results of crystal structure analysis show that the two-component permutation of P and M supramolecular spirochetes is induced by n ·· I halogen bond, and a round of spirochetes consists of four molecules (2 + 2) Two p-helices and two m-helices are stacked alternately to form another four helix structure This four helix structure is further stacked in two-dimensional space to form a plane array structure This work proves that the halogen bond is an effective noncovalent bond, which has a high degree of orthogonality with the hydrogen bond, and can drive the short aromatic amide folding body to grow into a supramolecular spiral structure In addition, the construction units of spirochetes can also be extensively modified, and it is possible to obtain stable cavities for the study of new object recognition or transport.