An Anionic Ring Locked into an Anionic Axle: A Metastable Rotaxane with Chemically Activated Electrostatic Stoppers

Area of Science:

• Supramolecular Chemistry
• Nanotechnology

Background:

• Mechanically interlocked molecules (MIMs) are complex structures with unique properties.
• Controlling the assembly and disassembly of MIMs is crucial for their applications.

Purpose of the Study:

• To introduce and investigate the concept of electrostatic stoppers for MIMs.
• To demonstrate the conversion of pseudo-rotaxanes to rotaxanes using chemical stimuli.

Main Methods:

• Design and synthesis of linear guest molecules with chemically sensitive end groups (electrostatic stoppers).
• Utilizing changes in medium acidity to trigger charge alterations on the guest molecule.
• Characterization of the resulting rotaxane complexes and their stability.

Main Results:

• The electrostatic stoppers facilitate the transformation of pseudo-rotaxanes into rotaxanes upon a decrease in pH.
• The conversion involves charge inversion on the guest, leading to electrostatic repulsion between the ring and axle.
• The resulting rotaxane species exhibit enhanced stability against solvent and temperature variations.
• The system functions as a two-state degenerated molecular shuttle in solution.

Conclusions:

• Electrostatic stoppers offer a novel strategy for controlling MIMs.
• This approach enables the creation of robust, switchable molecular machines.
• The developed system holds potential for applications in molecular electronics and drug delivery.