Efficient cross-effect dynamic nuclear polarization without depolarization in high-resolution MAS NMR.

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Solid-State Chemistry
• Biophysics

Background:

• Dynamic nuclear polarization (DNP) significantly enhances NMR sensitivity for structural analysis.
• The cross-effect (CE) mechanism using biradicals is common but limited by nuclear depolarization at high magnetic fields (≥5 T).
• Existing biradicals induce reverse CE, reducing proton polarization by over 50%.

Purpose of the Study:

• To develop a novel polarizing agent that overcomes depolarization losses in DNP-MAS NMR.
• To investigate a new trityl-nitroxide biradical for enhanced NMR sensitivity at high fields.
• To demonstrate the potential of the new agent for atomic resolution structural studies.

Main Methods:

• Design and synthesis of a novel trityl-nitroxide biradical (TEMTriPol-1).
• Utilizing numerical simulations to understand depolarization mechanisms.
• Experimental validation of sensitivity enhancement using magic-angle spinning (MAS) NMR at high magnetic fields (≥10 T).

Main Results:

• TEMTriPol-1 effectively prevents depolarization losses observed with conventional biradicals.
• This biocompatible agent achieves the highest MAS NMR sensitivity at ≥10 T.
• The relative efficiency of TEMTriPol-1 increases with magnetic field strength.
• The first solid-state 2D 13C-13C correlation spectrum at natural abundance was recorded at 18.8 T.

Conclusions:

• TEMTriPol-1 represents a next-generation polarizing agent for DNP-MAS NMR.
• It overcomes limitations of previous agents, enabling higher sensitivity and efficiency.
• This advancement facilitates atomic resolution structural analysis of complex systems, including biological ones.