Reversible Formation and Dispersion of Chiral Assemblies Responding to Electron Transfer

摘要

Supramolecular chiral assemblies are widespread and play a crucial role in a variety of biological systems such as the DNA double helix, heme proteins, and the photosynthetic architecture. Those chiral assemblies are achieved by noncovalent interactions between chiral building blocks (e.g., amino acid, nucleic acids, sugars, lipids, etc.), and its chirality is transferred to quaternary structure through noncovalent interactions. The strength of noncovalent interactions in natural systems is often associated with redox reactions, being related to conformational changes of biological macromolecules. Effective redox control on building affinity of the chiral supramolecules [e.g., hydrogen bonds and metal— ligand interactions] would ultimately afford reversible formation and dispersion of chiral assemblies in response to a simple external signal such as an electron, giving achiral—chiral switchability.rnWe report herein reversible formation of a chiral π-dimer complex between p-benzosemiquinone radical anions, which are one of the most important biological redox molecules, and a chiral scandium complex of 2,6-bis-(oxazolinyl)pyridine, [Sc-pybox]-(OTf)_3 [OTf = OSO_2CF_3] in response to a change in the redox state of p-benzoquinones. Stereochemistry of novel chiral π-dimer complexes assigned by ~1H NMR, COSY NMR, and NOE experiments provides valuable insight into how the chirality is transferred from chiral Sc~(3+)-pybox to p-benzoquinones with high symmetry through noncovalent interactions.