Structural Changes of a Doubly Spin-Labeled Chemically Driven Molecular Shuttle Probed by PELDOR Spectroscopy.

Area of Science:

• Supramolecular Chemistry
• Chemical Physics
• Nanotechnology

Background:

• Understanding molecular machines requires detailed knowledge of their structural dynamics.
• Stimuli-induced movements are fundamental to molecular machine operation.
• Rotaxanes are a class of molecular machines with potential applications in nanotechnology.

Purpose of the Study:

• To investigate the structural rearrangements of an acid-base-controlled molecular shuttle ([2]rotaxane).
• To monitor geometrical changes upon chemical switching using advanced spectroscopic techniques.
• To elucidate the relationship between molecular movement and structural conformation.

Main Methods:

• Utilized Pulsed Electron-Electron Double Resonance (PELDOR) spectroscopy.
• Incorporated stable nitroxide radical units into both the ring and axle components of the rotaxane.
• Combined PELDOR data with molecular dynamics (MD) calculations.

Main Results:

• Observed that base-induced ring displacement along the axle did not significantly alter the distance between nitroxide labels.
• Detected a profound change in the macrocycle's geometry accompanying the ring movement.
• PELDOR and MD calculations provided complementary insights into the structural dynamics.

Conclusions:

• The study demonstrates that chemical switching in this [2]rotaxane induces significant conformational changes in the macrocycle.
• These findings contribute to a deeper understanding of stimuli-responsive molecular machines.
• The methodology provides a powerful approach for characterizing molecular movements in complex systems.