Securing a Supramolecular Architecture by Tying a Stopper Knot.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Nanotechnology

Background:

• Rotaxanes are mechanically interlocked molecules with a ring threaded on an axle.
• Controlling the position of the ring on the axle is crucial for their function.
• Existing methods for controlling ring movement often involve complex synthesis or harsh conditions.

Purpose of the Study:

• To develop a novel method for controlling the threading and dethreading of a macrocycle on a molecular axle.
• To utilize in-situ knot tying as a mechanism for locking and unlocking a rotaxane-like architecture.
• To demonstrate reversible control over molecular assembly using lanthanide ion complexation.

Main Methods:

• Synthesis of a tris(2,6-pyridyldicarboxamide) axle.
• In-situ complexation with lutetium ions (Lu3+) to form an overhand knot.
• Demonstration of macrocycle locking and unlocking by manipulating the knot.
• Controlled threading and dethreading of a crown ether onto the axle.

Main Results:

• A rotaxane-like architecture was successfully constructed and stabilized by an in-situ formed overhand knot.
• The knot formation, induced by Lu3+ complexation, sterically locks the crown ether onto the axle.
• Removal of Lu3+ unties the knot, allowing for spontaneous dethreading when the axle binding site is deactivated.
• Re-threading of the crown ether was achieved by reactivating the binding site, demonstrating reversible control.

Conclusions:

• In-situ knot tying provides an effective strategy for controlling the mechanical bond in rotaxane-like systems.
• Lanthanide ion complexation offers a reversible switch for manipulating molecular architecture.
• This work presents a new approach for designing switchable molecular machines with potential applications in nanotechnology.