Low-temperature dynamic nuclear polarization with helium-cooled samples and nitrogen-driven magic-angle spinning.

Area of Science:

• Physical Chemistry
• Biophysics
• Spectroscopy

Background:

• Solid-state Nuclear Magnetic Resonance (NMR) is a powerful technique for molecular structure determination.
• Dynamic Nuclear Polarization (DNP) enhances NMR signal sensitivity, but requires specialized instrumentation for low-temperature applications.
• Previous publications have not detailed specific aspects of low-temperature DNP-NMR instrumentation.

Purpose of the Study:

• To describe novel instrumentation for low-temperature solid-state NMR with DNP and magic-angle spinning (MAS).
• To characterize the performance of key components, including a 264 GHz extended interaction oscillator (EIO) microwave source.
• To demonstrate the utility of this instrumentation for structural studies of biochemical systems.

Main Methods:

• Utilized a novel MAS NMR probe with liquid helium for cooling and nitrogen gas for spinning.
• Employed a quasi-optical microwave polarizing system coupled with an EIO microwave source.
• Conducted Dynamic Nuclear Polarization (DNP) experiments at cryogenic temperatures (25K).

Main Results:

• Achieved significant enhancement factors for cross-polarized (13)C NMR signals (100-200 range).
• Demonstrated sample temperatures below 30K with low helium consumption rates (<1.3 l/h).
• Presented detailed dependences of signal amplitudes on temperature, microwave power, polarization, and frequency.

Conclusions:

• The novel instrumentation enables efficient low-temperature DNP-NMR experiments.
• The system is suitable for structural studies of biochemical systems, as shown with a calmodulin-binding peptide.
• Detailed characterization provides valuable insights for optimizing DNP-NMR experiments.