Dynamic Nuclear Polarization / solid-state NMR of membranes. Thermal effects and sample geometry

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
• Dynamic Nuclear Polarization (DNP) enhancement
• Membrane biophysics

Background:

• Dynamic Nuclear Polarization (DNP) significantly enhances NMR signal intensity.
• Previous DNP studies on membrane samples achieved lower enhancement factors compared to protein solutions.
• Factors like biradicals, reconstitution, sample geometry, and NMR probes were optimized for membrane DNP.

Purpose of the Study:

• To investigate the impact of sample preparation on DNP enhancement factors in membrane samples.
• To identify key factors beyond biradicals and reconstitution that influence DNP efficiency.
• To rationalize observed DNP effects based on sample properties and cooling dynamics.

Main Methods:

• Utilizing specially designed dinitroxide biradicals.
• Employing optimized reconstitution protocols and oriented sample geometries.
• Analyzing the effect of MAS rotor material and membrane sample distribution.
• Monitoring sample properties via T1 relaxation times and microwave ON/OFF signal intensities.

Main Results:

• MAS rotor material and sample distribution significantly affect DNP enhancement.
• Cooling efficiency and internal sample properties (T1 relaxation) correlate with DNP enhancement.
• Microwave ON/OFF signal intensities and DNP effect reveal insights into sample behavior.
• The speed of sample cooling influences membrane properties and biradical distribution.

Conclusions:

• Sample preparation, specifically rotor material and sample distribution, is critical for maximizing DNP enhancement in membrane samples.
• Cooling dynamics play a vital role in determining membrane properties and biradical distribution, thereby affecting DNP efficiency.
• Further optimization of sample preparation protocols is necessary to bridge the gap in DNP enhancement between membrane and solution samples.