Metal Actuated Ring Translocation Switches in Water

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Nanotechnology

Background:

• Cucurbiturils (CBs) are macrocyclic hosts with potential applications in molecular machines.
• Controlling the movement of CBs on molecular threads is crucial for developing advanced functional materials.
• Existing methods for controlling CB movement often lack specificity or are sensitive to environmental factors like pH.

Purpose of the Study:

• To investigate the selective and reversible control of cucurbit[7]uril (CB[7]) movement on a molecular thread using metal ions.
• To explore the potential of silver ions (Ag+) as a specific stimulus for controlling CB[7] translocation and uptake.
• To demonstrate a metal-actuated molecular system that avoids pH-dependent side reactions.

Main Methods:

• Synthesis of a rigid, linear three-station viologen-phenylene-imidazole (V-P-I) derivative as the molecular thread.
• Utilizing a series of metal ions in aqueous solution to probe interactions with the CB[7]-V-P-I system.
• Employing complementary techniques including 1H NMR, UV-vis spectroscopy, mass spectrometry, and Isothermal Titration Calorimetry (ITC).
• Computational modeling to elucidate the mechanism of metal ion interaction and CB[7] movement.

Main Results:

• Silver ions (Ag+) were identified as the sole metal ion capable of remotely and reversibly inducing CB[7] movement (translocation or uptake) along the V-P-I molecular thread.
• The Ag+-induced movement was specific and occurred without undesired pH actuation, unlike other metal ions tested.
• Spectroscopic and calorimetric data, supported by modeling, confirmed the translocation or uptake of CB[7] along the molecular thread in water.

Conclusions:

• Ag+ ions provide a unique and effective stimulus for precise control over cucurbituril movement on molecular architectures in aqueous media.
• This metal-actuated system represents a significant advancement in the design of responsive supramolecular systems and molecular machines.
• The findings open avenues for developing novel sensors, actuators, and targeted delivery systems based on metal-ion-controlled molecular shuttles.