Diffusion NMR for Measuring Dynamic Ligand Exchange on Colloidal Nanocrystals

Area of Science:

• Nanotechnology
• Surface Chemistry
• Analytical Chemistry

Background:

• Ligand exchange is critical for nanoparticle synthesis and solution processing.
• Understanding ligand dynamics requires real-time quantification of bound and free ligands.
• Current methods for ligand exchange analysis have limitations in applicability and detection.

Purpose of the Study:

• To develop and validate diffusion-based solution-state Nuclear Magnetic Resonance (NMR) as a general strategy for probing ligand exchange dynamics.
• To establish a method for in situ and real-time quantification of bound and free ligands.
• To overcome limitations of existing analytical techniques for ligand exchange studies.

Main Methods:

• Utilized diffusion-based methods of solution-state Nuclear Magnetic Resonance (NMR).
• Employed comprehensive numerical simulations to optimize diffusion NMR sequences.
• Experimentally validated the method on colloidal Cadmium Selenide (CdSe) nanocrystal systems.

Main Results:

• Diffusion NMR effectively distinguishes bound and free ligands.
• Successfully measured ligand exchange rate constants ranging from 0.5 to 200 s^-1.
• Obtained kinetic rate constants, activation energies, and thermodynamic parameters for ligand exchange on CdSe nanocrystals.

Conclusions:

• Diffusion NMR provides a general and effective strategy for calibrating ligand exchange dynamics.
• The developed method overcomes limitations of previous techniques, enabling previously undetectable exchange rate measurements.
• This approach is expected to be broadly applicable to various nanoparticle systems and organic ligands.