A Switchable Open/closed Polyaromatic Macrocycle that Shows Reversible Binding of Long Hydrophilic Molecules

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Materials Science

Background:

• Synthetic macrocycles are crucial in supramolecular chemistry.
• Controlling the dynamic behavior of macrocycles, particularly their open-close functions, remains a significant challenge.
• Developing stimuli-responsive macrocyclic frameworks is essential for advanced applications.

Purpose of the Study:

• To design and synthesize a novel polyaromatic macrocycle with pH-responsive open-close switching capabilities.
• To investigate the structural and functional properties of the new macrocycle in aqueous media.
• To demonstrate the controlled binding and release of hydrophilic guests within the macrocycle's cavity.

Main Methods:

• Three-step synthesis of the polyaromatic macrocycle.
• Single-crystal X-ray diffraction for structural confirmation of open and closed states.
• Binding and release studies of hydrophilic molecules in neutral water and upon pH change.

Main Results:

• A new macrocycle with a 1 nm hydrophobic cavity and four pH-responsive acridinium panels was successfully synthesized.
• The macrocycle exhibits reversible switching between open and closed forms triggered by acid and base stimuli.
• The cavity demonstrated the ability to bind hydrophilic molecules up to 2.7 nm in length in neutral water.
• Guest release was achieved via a reversible structural change upon addition of base.

Conclusions:

• The developed macrocycle offers a controllable platform for molecular encapsulation and release.
• Its pH-responsive nature and ability to bind long hydrophilic guests open avenues for applications in sensing and drug delivery.
• This work addresses the challenge of incorporating dynamic open-close functions into synthetic macrocyclic frameworks.